PROCESS FOR PREPARING FUNCTIONALIZED 1,2,4,5-TETRAZINE COMPOUNDS

Abstract

The present invention relates to a process for the synthesis of 3,6 functionalized 1,2,4,5-tetrazine compounds.

Claims

1. A process for producing a compound of formula (I), ##STR00092## wherein A is ##STR00093## B is ##STR00094## A and B being the same; R.sub.1, R.sub.1, R.sub.2 and R.sub.2 may be the same or different and represent each a hydrogen atom, a halogen atom, a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, alkyloxycarbonyl, aryloxy, alkylamino, cycloalkylamino, arylamino, provided that at least one of R.sub.1, R.sub.1, R.sub.2 and R.sub.2 is a halogen atom or acetate group; R.sub.3, R.sub.3, R.sub.4, R.sub.4, R.sub.5, R.sub.5 may be the same or different and represent each a hydrogen atom, a halogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, arylamino; R.sub.8, R.sub.8, R.sub.9, R.sub.9 may be the same or different and represent each a hydrogen atom, a halogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, and arylamino; R.sub.10, R.sub.10 may be the same or different and represent each a hydrogen atom or a halogen atom, provided that at least one of R.sub.10 and R.sub.10 is a halogen atom or acetate group; and E is an oxygen atom, a sulfur atom or NR.sub.11, wherein R.sub.11 is selected from hydrogen, alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; said process comprising: reacting a compound of formula (II) ##STR00095## wherein A is ##STR00096## B is ##STR00097## A and B being the same; R.sub.6, R.sub.6, R.sub.7 and R.sub.7 may be the same or different and represent each a hydrogen atom, a halogen atom, a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, and arylamino, provided that at least one of R.sub.6, R.sub.6, R.sub.7 and R.sub.7 is a hydrogen atom; R.sub.3, R.sub.3, R.sub.4, R.sub.4, R.sub.5, R.sub.5 may be the same or different and represent each a hydrogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, and arylamino; R.sub.8, R.sub.8, R.sub.9, R.sub.9 may be the same or different and represent each a hydrogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; and E is an oxygen atom, a sulfur atom or NR.sub.11, wherein R.sub.11 is selected from hydrogen, alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; with an oxidative reagent in presence of a catalyst.

2. The process according to claim 1 for producing a compound of formula (Ia), corresponding to a compound of formula (I) wherein A is ##STR00098## and B is ##STR00099## R.sub.1, R.sub.1, R.sub.2 and R.sub.2 may be the same or different and represent each a hydrogen atom, a halogen atom, a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, alkyloxycarbonyle, aryloxy, alkylamino, cycloalkylamino, arylamino, provided that at least one of R.sub.1, R.sub.1, R.sub.2 and R.sub.2 is a halogen atom or acetate group; and R.sub.3, R.sub.3, R.sub.4, R.sub.4, R.sub.5, R.sub.5 may be the same or different and represent each a hydrogen atom, a halogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, arylamino; said process comprising: reacting a compound of formula (IIa) wherein A is ##STR00100## and B is ##STR00101## R.sub.6, R.sub.6, R.sub.7 and R.sub.7 may be the same or different and represent each a hydrogen atom, a halogen atom, a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, arylamino, provided that at least one of R.sub.6, R.sub.6, R.sub.7 and R.sub.7 is a hydrogen atom; and R.sub.3, R.sub.3, R.sub.4, R.sub.4, R.sub.5 and R.sub.5 may be the same or different and represent each a hydrogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, arylamino; with an oxidant in presence of a catalyst.

3. The process according to claim 1 for producing a compound of formula (Ib), corresponding to a compound of formula (I) wherein A is ##STR00102## and B is ##STR00103## R.sub.8, R.sub.8, R.sub.9, R.sub.9 may be the same or different and represent each a hydrogen atom, a halogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, and arylamino; R.sub.10, R.sub.10 may be the same or different and represent each a hydrogen atom or a halogen atom, provided that at least one of R.sub.10 and R.sub.10 is a halogen atom or acetate group; and E is an oxygen atom, a sulfur atom or NR.sub.11, wherein R.sub.11 is selected from hydrogen, alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; said process comprising: reacting a compound of formula (IIb) wherein A is ##STR00104## and B is ##STR00105## R.sub.8, R.sub.8, R.sub.9, R.sub.9 may be the same or different and represent each a hydrogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; and E is an oxygen atom, a sulfur atom or NR.sub.11, wherein R.sub.11 is selected from hydrogen, alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino and arylamino; with an oxidative reagent in presence of a catalyst.

4. The process according to claim 1, wherein the oxidative reagent is selected from the group comprising N-chlorosuccinimide, N-bromosuccinimide, N-iodosuccinimide, N-fluorobenzenesulfonimide and (diacetoxyiodo)benzene.

5. The process according to claim 1, wherein the catalyst is a palladium catalyst.

6. The process according to claim 1, wherein the catalyst is selected from the group comprising palladium(II) catalyst and palladium(0) catalyst.

7. The process according to claim 1, wherein the catalyst is selected from the group comprising palladium acetate, tris(dibenzylideneacetone)dipalladium, bis(dibenzylideneacetone)palladium, allylpalladium(II) chloride dimer and palladium chloride.

8. The process according to claim 1, wherein the process is carried out in presence of a polar solvent.

9. The process according to claim 8, wherein the polar solvent is selected from the group comprising dichloroethane, trifluoromethylbenzene, nitromethane, acetic acid, pivalic acid and propionic acid.

10. The process according to claim 1, wherein the amount of oxidative reagent is ranging from 1 equivalent to 12 equivalent of compound (II).

11. process according to claim 1, wherein the amount of catalyst is ranging from 0.1% to 50%, more preferably 0.1% to 30%, more preferably 0.1% to 20%, more preferably 1% to 50%, more preferably 5% to 20%, more preferably 8% to 15% and more preferably 1% to 15%, in mole to compound (II).

12. The process according to claim 1, wherein the process is performed at a temperature ranging from 80 C. to 150 C., preferably from 90 C. to 130 C., more preferably from 100 C. to 120 C.

13. Compounds of formula (Ia) ##STR00106## wherein R.sub.1, R.sub.1, R.sub.2 and R.sub.2 may be the same or different and represent each a halogen atom, the halogen atom being the same or different, provided that at least one of R.sub.1, R.sub.1, R.sub.2 and R.sub.2 is a different halogen atom compared to the others; and R.sub.3, R.sub.3, R.sub.4, R.sub.4, R.sub.5, R.sub.5 may be the same or different and represent each a hydrogen atom, an halogen atom or a substituted or unsubstituted group selected from alkyl, cycloalkyl, aryl, alkyloxy, cycloalkyloxy, aryloxy, alkylamino, cycloalkylamino, arylamino.

Description

EXAMPLE 1: SYNTHESIS OF COMPOUNDS OF FORMULA (I)

Material

[0082] 3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine is synthesized under the conditions developed by Clavier et al (G. Clavier, P. Audebert, Chem. Rev. 2010, 110, 3299-3314). All others reagents were purchased from commercial suppliers and used without purifications. All reactions were performed in Schlenk tubes or in a microwave reaction vessel under argon. Microwave heating was carried out using a CEM Discover microwave reactor. The microwave reactions were run in closed reaction vessels with magnetic stirring and with the temperature controlled via IR detection. .sup.1H (300 MHz), .sup.13C (75 or 125 MHz), .sup.19F (282 MHz) spectra were recorded on Brucker AVANCE III instrument in CDCl.sub.3 solutions. Chemical shifts are reported in ppm relative to CDCl.sub.3 (.sup.1H: 7.26 and .sup.13C: 77.16) and coupling constants J are given in Hz. High resolution mass spectra (HRMS) were obtained on a Thermo LTQ-Orbitrap XL with ESI source. Flash chromatography was performed on silica gel (230-400 mesh). Elemental analysis experiments were performed Thermo Electron Flash EA 1112 Series. Absorption spectra (in solution or liposome suspension) were measured on a Shimadzu UV-2550 spectrophotometer. Spectra were recorded in DCM in glass cuvettes 113 cm (1 cm path).

Results:

A. Optimisation of the Synthesis of Compound of Formula (Ia)

A.1 Optimisation of CH Monofunctionalization of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] or [b]

[0083] ##STR00014##

TABLE-US-00001 Oxidant Conv. 2a-5a Entry [Pd] (equiv) Solvent (%) (%) 1 NBS (1.0) DCE 0 0 2 Pd(OAc).sub.2 NBS (1.0) DCE 75 55 (48) 3 PdCl.sub.2 NBS (1.0) DCE 26 26 4 Pd(dba).sub.2 NBS (1.0) DCE 67 54 (45) 5 Pd(dba).sub.2 NBS (1.7) DCE 87 57 6 Pd(dba).sub.2 NBS (2.2) DCE 96 41 7 Pd(dba).sub.2 NIS (1.0) DCE 55 49(33) .sup.8[b] PdCl.sub.2 NCS (1.0) HOAc 48 44(32) 9 Pd(OAc).sub.2 PhI(OAc).sub.2 HOAc 84 64(51) (1.0) [a] Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), X source (1.0 to 2.2 equiv), solvent (0.125M), 100 C., under argon, 17 h. .sup.1H NMR yield and isolated yield under bracket. DCE: dichloroethane, HOAc: Acetic acid. [b]same as [a] except 120 C.

[0084] In the absence of palladium no reaction occurred (entry 1). The reaction of equimolar amounts of tetrazine (1) and NBS in the presence of 10 mol % of [Pd(OAc).sub.2] in dichloroethane (DCE) at 100 C. for 17 h converted (1) in 75%, and afforded the expected monobrominated product (2a) with two dibrominated side-products (2b) and (2c), in a [73:17:10] ratio, respectively (entry 2). Compound (2a) can be easily purified and isolated in about 50% yield. Other palladium catalysts, such as [PdCl.sub.2] and [Pd(dba).sub.2] provided to lower conversions (entries 3, 4). Increasing amounts of NBS allowed greater conversions but was detrimental to the selectivity in (2a) (entries 5, 6).

[0085] Iodination of (1) was achieved using N-iodosuccinimide in the presence of 10% [Pd(dba).sub.2] in DCE, to afford 55% conversion yield and a [89:11] ratio of the monoiodinated product (3a) and the symmetrical diiodinated analogue (3b) (entry 7). Chlorination of (1) was achieved using N-chlorosuccinimide and 10% [PdCl.sub.2] in HOAc at 120 C. (entry 8, conversion 48%) to afford the monochlorinated tetrazine (4a) with 92% selectivity. The scope of such an unprecedented CH functionalization of s-tetrazine was extended to acetoxylation reactions using PhI(OAc).sub.2 and 10 mol % [Pd(OAc).sub.2] in HOAc to afford pure (5a) in 51% yield ((1) converted in 84%, entry 9).

A.2 Optimisation of Tetra-Functionalization of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a]

[0086] ##STR00015##

TABLE-US-00002 Oxidant Entry [Pd] (equiv) Solvent T C. 2e-4e 1 Pd(dba).sub.2 NBS (8.0) HOAc 100 2e: 99 (98) 2 Pd(OAc).sub.2 NBS (6.0) HOAc 120 2e: 99 (89) 3 Pd(OAc).sub.2 NIS (12.0) HOAc 120 3e: 71 (64) 4 Pd(OAc).sub.2 NCS (10.0) HOAc 120 4e: 80 (34) [a] Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NXS (6 to 12 equiv), solvent (0.125M), under argon, 17 h. .sup.1H NMR yield and isolated yield under bracket.

[0087] Tetrahalogenation of 3,6-diphenyl-1,2,4,5-tetrazine was achieved upon adjusting the amounts of halogenation reagent. 8 equiv of NBS and 10 mol % of Pd catalyst were necessary to achieve full conversion of (1) affording tetrabrominated tetrazine (2e) in 98% isolated yield (entry 1). Di- and trihalogenated species (2b), (2d) were also isolated when lower amounts of NBS were used. The reaction was even faster using lower amounts of NBS (6 equiv, entry 2) in the presence of 10 mol % of [Pd(OAc).sub.2] in HOAc at 120 C.

[0088] Using the same catalytic system, further multiple CH halogenation reactions were successfully achieved with other N-halosuccinimides (10 equiv) albeit in lower yields (entries 3, 4): tetraiodotetrazine (3e) and tetrachlorotetrazine (4e) were obtained from NIS in 71% yield and from NCS in 80% yield, respectively.

A.3 Optimisation of Fluorination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Toward Fast-Time Good Selectivity in Monofluorinated Product (6a) Under Conditions [a] to [d]

[0089] ##STR00016##

TABLE-US-00003 NFSI Entry [Pd] (equiv) Solvent Time 6a 1 PdCl2 1.0 CH.sub.3NO.sub.2 17 h 34[b] 2 [PdCl(allyl)].sub.2 1.0 CH.sub.3NO.sub.2 17 h 45[b] 3 Pd(dba).sub.2 1.0 CH.sub.3NO.sub.2 17 h 41(30) 4 Pd2(dba).sub.3 1.0 CH.sub.3NO.sub.2 17 h 35 5 Pd2(dba).sub.3 1.0 CH.sub.3NO.sub.2 17 h 46 6 Pd2(dba).sub.3 1.5 CH.sub.3NO.sub.2 17 h 57 7 Pd2(dba).sub.3 1.0 PhCF.sub.3 17 h 47 8 Pd(dba).sub.2 1.5 PhCF.sub.3 30 min 62 9 Pd(dba).sub.2 2.0 PhCF.sub.3 10 min 71(44) 10 Pd(dba).sub.2 2.2 PhCF.sub.3 10 min 70(50) 11 Pd(dba).sub.2 2.5 PhCF.sub.3 10 min 63(47) [a] Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NFSI (1-2.5 equiv), solvent (0.125M), 110 C., under argon. .sup.1H and .sup.19F NMR yield and isolated yield under bracket. [b]Chlorination product was detected. [c] Pd.sub.2(dba).sub.3 (20 mol %). [d] Pd.sub.2(dba).sub.3 (20 mol %), microwave 200 W, under air.

[0090] The first reaction between 3,6-diphenyl-1,2,4,5-tetrazine (1), and 1 equiv of N-fluorobenzenesulfonimide (NFSI) was conducted in nitromethane at 110 C., using 10 mol % of [Pd(dba).sub.2]. The monofluorinated compound (6a) was isolated in 30% yield, with a corresponding conversion in (1) around 41% over 17 h (entries 1-7). The reaction time may be dropped to 30 min, upon using microwave irradiation (entries 8-11), 20 mol % of [Pd(dba).sub.2], trifluoromethylbenzene (PhCF.sub.3) as a solvent at 110 C. in the presence of air (entry 8). The amount of NFSI was crucial to achieve full conversion of (1). [9] Using 2.5 equiv of NFSI, (1) was fully converted into mono and difluorinated species (6a), (6b), (6c) in a [63:27:9] ratio (entry 11). A [77:18:5] ratio with a 91% conversion yield in (1) and 50% yield in isolated (6a) could be achieved using 2.2 equiv of NFSI (entry 10).

A.4 Tetrafluorination of 3,6-diphenyl-1,2,4,5-tetrazine (1) or 3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine (6b)

[0091] ##STR00017##

[0092] The synthesis of species (6e) may be of interest for future radiolabeled products incorporating four times more isotopes than (6a). This was achieved starting from either aryltetrazine (1) or its difluorinated derivative (6b).

BGeneral Synthesis of Diphenyltetrazine

3,6-diphenyl-1,2,4,5-tetrazine (1): CAS 6830-78-0

[0093] ##STR00018##

[0094] To a mixture of benzonitrile (1 mL, 9.70 mmol) and hydrazine monohydrate (2.4 mL, 48.50 mmol) in absolute ethanol (10 mL) was added Sulfur (311 mg, 9.70 mmol). The resulting suspension was placed under nitrogen atmosphere, magnetically stirred and heated at 60 C. for 3 h. Upon cooling, the solvent was removed under reduced pressure to afford a yellowish solid. The crude mixture was dissolved in dichloromethane (2.9 mL), a solution of was NaNO.sub.2 added (195, mL, 0.3 mM in distilled water), followed by addition of acetic acid (2.8 mL) at 0 C. A pink color develops that is characteristic of the tetrazine (I.sub.abs=550 nm). The solvent was removed in vacuo and the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (1) (purple solid) in 30% (348.4 mg) yield.

[0095] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.68-8.66 (m, 4H), 7.67-7.61 (m, 6H).

3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine (6b): CAS 108350-48-7

[0096] ##STR00019##

[0097] To a mixture of 2-fluorobenzonitrile (0.88 mL, 8.26 mmol) and hydrazine monohydrate (2 mL, 41.30 mmol) in absolute ethanol (10 mL) was added sulfur (265 mg, 8.26 mmol). The resulting suspension was placed under nitrogen atmosphere, magnetically stirred and heated at 60 C. for 4 h. Upon cooling, the solvent was removed under reduced pressure to afford a yellowish solid. The crude mixture was dissolved in dichloromethane (2.5 mL), a solution of was NaNO.sub.2 added (166 mL, 0.3 mM in distilled water), followed by addition of acetic acid (2.4 mL) at 0 C. A pink color develops that is characteristic of the tetrazine (I.sub.abs=540 nm). The solvent was removed in vacuo and the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (1) (purple solid) in 10% (107.8 mg) yield.

[0098] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.38 (td, J=7.64, 1.77 Hz, 2H), 7.67-7.60 (m, 2H), 7.41 (td, J=7.74, 1.06 Hz, 2H), 7.34 (ddd, J=10.85, 8.34, 0.94 Hz, 2H); .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.6; .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.4 (d, J=260.1 Hz), 163.2 (d, J=5.6 Hz), 134.3 (d, J=8.8 Hz), 131.5 (d, J=0.8 Hz), 124.9 (d, J=3.9 Hz), 120.6 (d, J=9.8 Hz), 117.6 (d, J=21.5 Hz); Elemental analysis: Calcd (%) for C.sub.14H.sub.8F.sub.2N.sub.4: C, 62.22, H, 2.98, N, 20.73. Found: C, 61.10, H, 2.84, N, 20.77; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8F.sub.2N.sub.4: 293.061. Found: m/z=293.060.

CGeneral Procedure of Functionalization of Tetrazine

3-(2-bromophenyl)-6-phenyl-1,2,4,5-tetrazine (2a)

[0099] ##STR00020##

[0100] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NBS (44.4 mg, 0.25 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. 1,2-dichloroethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the brominated product. Then, the crude product was purified by silica gel column chromatography

[0101] (Dichloromethane-Heptane=1:1) to afford (2a) (purple solid) in 45% (34.9 mg) yield.

[0102] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.73-8.69 (m, 2H), 8.02 (ddd, J=7.49, 1.93, 0.23 Hz, 1H), 7.82 (ddd, J=7.94, 0.99, 0.30 Hz, 1H), 7.70-7.60 (m, 3H), 7.57 (td, J=8.06, 0.52 Hz, 1H), 7.47 (ddd, J=7.96, 7.54, 1.80 Hz, 1H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.6, 163.3, 134.5, 133.9, 133.2, 132.5, 132.2, 131.7, 129.5, 128.6, 128.0, 122.5; Elemental analysis: Calcd (%) for C.sub.14H.sub.9BrN.sub.4: C, 53.70, H, 2.90, N, 17.89. Found: C, 53.86, H, 2.73, N, 17.87; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.9BrN.sub.4: 313.008. Found: m/z=313.008.

3,6-bis(2-bromophenyl)-1,2,4,5-tetrazine (2b): CAS 108350-48-7

[0103] ##STR00021##

[0104] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NBS (177.9 mg, 1.00 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. 1,2-dichloroethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the brominated product.

[0105] Then, the crude product was filtered through a plug of silica (Dichloromethane-Heptane=1:1) to afford (2b) (purple solid) in 19% (18.6 mg) yield.

[0106] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.07 (dd, J=7.68, 1.76 Hz, 2H), 7.84 (dd, J=7.96, 1.13 Hz, 2H), 7.58 (td, J=7.52, 1.23 Hz, 2H), 7.49 (td, J=7.90, 1.81 Hz, 2H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.7, 134.6, 133.6, 132.8, 132.5, 128.1, 122.7; Elemental analysis: Calcd (%) for C.sub.14H.sub.8Br.sub.2N.sub.4: C, 42.89, H, 2.06, N, 14.29. Found: C, 44.92, H, 2.66, N, 13.55; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.8Br.sub.2N.sub.4: 390.918. Found: m/z=390.919.

3-(2,6-dibromophenyl)-6-phenyl-1,2,4,5-tetrazine (2c)

[0107] ##STR00022##

[0108] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NBS (133.5 mg, 0.75 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. 1,2-dichloroethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the brominated product. Then, the crude product was filtered through a plug of silica (Dichloromethane-Heptane=1:1) to afford (2c) (purple solid) in 14% (14.1 mg) yield.

[0109] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.77-8.73 (m, 2H), 7.76 (d, J=8.10 Hz, 2H), 7.69-7.62 (m, 3H), 7.33 (t, J=7.94 Hz, 1H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=167.9, 163.9, 136.0, 133.4, 132.8, 132.3, 131.6, 129.6, 128.8, 124.1.

3-(2,6-dibromophenyl)-6-(2-bromophenyl)-1,2,4,5-tetrazine (2d)

[0110] ##STR00023##

[0111] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NBS (177.9 mg, 1.00 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. 1,2-dichloroethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the brominated product. Then, the crude product was filtered through a plug of silica (Dichloromethane-Heptane=1:1) to afford (2d) (red solid) in 57% (66.8 mg) yield.

[0112] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.09 (ddd, J=7.72, 1.68, 0.11 Hz, 1H), 7.85 (ddd, J=7.92, 1.27, 0.28 Hz, 1H), 7.77 (d, J=8.10 Hz, 2H), 7.60 (td, J=7.52, 1.24 Hz, 1H), 7.53-7.47 (m, 1H), 7.35 (dd, J=8.33, 7.89 Hz, 1H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.9, 166.4, 135.8, 134.5, 133.7, 133.0, 132.9, 132.4, 132.2, 128.1, 123.9, 122.7; Elemental analysis: Calcd (%) for C.sub.14H.sub.7Br.sub.3N.sub.4: C, 35.70, H, 1.50, N, 11.90. Found: C, 35.38, H, 1.16, N, 11.53; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7Br.sub.3N.sub.4: 469.837. Found: m/z=469.837.

3,6-bis(2,6-dibromophenyl)-1,2,4,5-tetrazine (2e)

[0113] ##STR00024##

[0114] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NBS (266.9 mg, 1.50 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the brominated product. Then, the crude product was filtered through a plug of silica (Dichloromethane-Heptane=1:1) to afford (2e) (pink solid) in 89% (122.8 mg) yield.

[0115] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.77 (d, J=8.10 Hz, 4H), 7.36 (t, J=8.20 Hz, 2H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=167.6, 135.9, 133.1, 132.2, 123.7; Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.4N.sub.4: C, 30.58, H, 1.10, N, 10.19. Found: C, 29.96, H, 1.38, N, 9.30; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.6Br.sub.4N.sub.4: 568.721. Found: m/z=568.720.

3-(2-iodophenyl)-6-phenyl-1,2,4,5-tetrazine (3a)

[0116] ##STR00025##

[0117] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NIS (56.4 mg, 0.25 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. 1,2-dichloroethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the iodinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (3a) (purple solid) in 33% (29.8 mg) yield.

[0118] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.74-8.70 (m, 2H), 8.12 (dd, J=7.97, 0.95 Hz, 1H), 7.99 (dd, J=7.74, 1.60 Hz, 1H), 7.70-7.58 (m, 4H), 7.31-7.26 (m, 1H); .sup.13C NMR (125 MHz, CDCl.sub.3): (ppm)=167.5, 163.4, 141.2, 137.2, 133.2, 132.4, 131.7, 131.6, 129.5, 128.8, 128.6, 95.7; Elemental analysis: Calcd (%) for C.sub.14H.sub.9IN.sub.4: C, 46.69, H, 2.52, N, 15.56. Found: C, 46.78, H, 2.22, N, 14.72; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.9IN.sub.4: 382.976. Found: m/z=382.975.

3,6-bis(2-iodophenyl)-1,2,4,5-tetrazine (3b)

[0119] ##STR00026##

[0120] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NIS (140.6 mg, 0.63 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the iodinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (3b) (purple solid) in 24% (29.5 mg) yield.

[0121] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.12 (dd, J=7.99, 0.93 Hz, 2H), 8.07 (dd, J=7.75, 1.61 Hz, 2H), 7.62 (td, J=7.58, 1.15 Hz, 2H), 7.33-7.28 (m, 2H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.5, 141.2, 136.9, 132.6, 131.7, 128.8, 95.9; Elemental analysis: Calcd (%) for C.sub.14H.sub.8I.sub.2N.sub.4: C, 34.60, H, 1.66, N, 11.53. Found: C, 35.03, H, 1.22, N, 11.17; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8I.sub.2N.sub.4: 508.873. Found: m/z=508.872.

3-(2,6-diiodophenyl)-6-phenyl-1,2,4,5-tetrazine (3c)

[0122] ##STR00027##

[0123] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NIS (140.6 mg, 0.63 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the iodinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (3c) (purple solid) in 17% (21 mg) yield.

[0124] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.78-8.75 (m, 2H), 8.04 (d, J=7.97 Hz, 2H), 7.68-7.62 (m, 3H), 6.96 (t, J=7.96 Hz, 1H); .sup.13C NMR (125 MHz, CDCl.sub.3): (ppm)=171.4, 163.7, 142.7, 139.3, 133.4, 133.2, 131.6, 129.6, 129.5, 128.8, 128.2, 96.6; Elemental analysis: Calcd (%) for C.sub.14H.sub.9I.sub.2N.sub.4: C, 34.60, H, 1.66, N, 11.53. Found: C, 34.95, H, 2.52, N, 10.46; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.9I.sub.2N.sub.4: 508.873. Found: m/z=508.872.

3-(2,6-diiodophenyl)-6-(2-iodophenyl)-1,2,4,5-tetrazine (3d)

[0125] ##STR00028##

[0126] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NIS (281.2 mg, 1.25 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the iodinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (3d) (purple solid) in 20% (30.1 mg) yield.

[0127] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.14 (dd, J=7.88, 0.96 Hz, 1H), 8.13 (dd, J=7.75, 1.71 Hz, 1H), 8.05 (d, J=7.97 Hz, 2H), 7.64 (td, J=7.58, 1.14 Hz, 1H), 7.32 (td, J=7.63, 1.66 Hz, 1H), 6.98 (t, J=7.96 Hz, 1H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=170.2, 166.9, 142.6, 141.2, 139.3, 137.0, 133.3, 132.8, 131.8, 128.9, 96.3, 96.0; Elemental analysis: Calcd (%) for C.sub.14H.sub.7I.sub.3N.sub.4: C, 27.48, H, 1.15, N, 9.16. Found: C, 28.14, H, 1.26, N, 8.72; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.7I.sub.3N.sub.4: 634.769. Found: m/z=634.770.

3,6-bis(2,6-diiodophenyl)-1,2,4,5-tetrazine (3e)

[0128] ##STR00029##

[0129] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NIS (674.9 mg, 3.00 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the iodinated product. Then, the crude product was purified by silica gel column chromatography (Ethyl acetate-Heptane=1:4, and then Dichloromethane=100%) to afford (3e) (pink solid) in 64% (118.1 mg) yield.

[0130] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.06 (d, J=7.97 Hz, 4H), 6.99 (t, J=7.96 Hz, 2H); .sup.13C NMR (125 MHz, (CD.sub.3).sub.2SO): (ppm)=170.7, 141.8, 138.8, 134.2, 97.2; Elemental analysis: Calcd (%) for C.sub.14H.sub.6I.sub.4N.sub.4: C, 22.79, H, 0.82, N, 7.59. Found: C, 23.26, H, 0.73, N, 7.27; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6I.sub.4N.sub.4: 738.684. Found: m/z=738.684.

3-(2-chlorophenyl)-6-phenyl-1,2,4,5-tetrazine (4a): CAS74115-26-7

[0131] ##STR00030##

[0132] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NCS (44.4 mg, 0.25 mmol), and PdCl.sub.2 (4.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the chlorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (4a) (purple solid) in 32% (21.3 mg) yield.

[0133] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.72-8.69 (m, 2H), 8.08-8.05 (m, 1H), 7.70-7.60 (m, 4H), 7.56-7.49 (m, 2H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.9, 163.3, 133.9, 133.2, 132.5, 132.2, 131.9, 131.7, 131.3, 129.5, 128.5, 127.5; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.9ClN.sub.4: 269.058. Found: m/z=269.058.

3,6-bis(2-chlorophenyl)-1,2,4,5-tetrazine (4b): CAS 74115-24-5

[0134] ##STR00031##

[0135] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NCS (166.9 mg, 1.25 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the chlorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (4b) (purple solid) in 35% (29.4 mg) yield.

[0136] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.13-8.10 (m, 2H), 7.66-7.63 (m, 2H), 7.60-7.50 (m, 4H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.1, 134.0, 132.8, 132.5, 131.7, 131.4, 127.75; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.8C.sub.12N.sub.4: 303.019. Found: m/z=303.019.

3-(2,6-dichlorophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (4d)

[0137] ##STR00032##

[0138] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NCS (200.3 mg, 1.50 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the chlorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (4d) (purple solid) in 8% (6.8 mg) yield.

[0139] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.15-8.11 (m, 1H), 7.67-7.61 (m, 1H), 7.59-7.49 (m, 5H); .sup.13C NMR (125 MHz, CDCl.sub.3): (ppm)=165.8, 164.9, 135.4, 134.1, 132.9, 132.5, 132.4, 132.3, 131.7, 131.4, 128.6, 127.5.

3,6-bis(2,6-dichlorophenyl)-1,2,4,5-tetrazine (4e): CAS 162320-76-5

[0140] ##STR00033##

[0141] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NCS (333.8 mg, 2.50 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the chlorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (4e) (pink solid) in 34% (31.7 mg) yield.

[0142] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.58-7.48 (m, 6H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.5, 135.2, 132.5, 132.3, 128.6; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6C.sub.14N.sub.4: 370.941. Found: m/z=370.943.

3-(2-bromophenyl)-6-phenyl-1,2,4,5-tetrazine (5a)

[0143] ##STR00034##

[0144] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), PhI(OAc).sub.2 (80.5 mg, 0.25 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the acetylated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane=100%) to afford (5a) (purple solid) in 43% (31.4 mg) yield.

[0145] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.68-8.64 (m, 2H), 8.49 (dd, J=7.87, 1.70 Hz, 1H), 7.69-7.58 (m, 4H), 7.51 (td, J=7.77, 1.24 Hz, 1H), 7.30 (dd, J=8.09, 1.15 Hz, 1H), 2.40 (s, 3H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=170.1, 164.1, 163.3, 149.9, 133.4, 132.9, 131.8, 131.2, 129.4, 128.3, 126.9, 125.2, 124.7, 21.2; Elemental analysis: Calcd (%) for C.sub.16H.sub.12N.sub.4O.sub.2: C, 65.75, H, 4.14, N, 19.17. Found: C, 65.04, H, 4.32, N, 18.78.

[0146] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.16H.sub.12N.sub.4O.sub.2: 315.085. Found: m/z=315.084.

3,6-bis(2-acetoxyphenyl)-1,2,4,5-tetrazine (5b)

[0147] ##STR00035##

[0148] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), PhI(OAc).sub.2 (241.6 mg, 0.75 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the acetylated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane=100%) to afford (5b) (red solid) in 29% (25.4 mg) yield.

[0149] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.50 (dd, J=7.88, 1.66 Hz, 2H), 7.67 (ddd, J=9.19, 7.49, 1.72 Hz, 2H), 7.52 (td, J=7.79, 1.24 Hz, 2H), 7.30 (dd, J=8.10, 1.10 Hz, 2H), 2.37 (s, 6H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=170.0, 163.2, 150.0, 133.7, 131.4, 126.9, 125.0, 124.8, 21.2; Elemental analysis: Calcd (%) for C.sub.18H.sub.14N.sub.4O.sub.4: C, 61.71, H, 4.03, N, 15.99. Found: C 61.19.11, H, 4.32, N, 15.34; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.16H.sub.12N.sub.4O.sub.2: 373.090. Found: m/z=373.089.

3-(2,6-diacetoxyphenyl)-6-phenyl-1,2,4,5-tetrazine (5c)

[0150] ##STR00036##

[0151] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), PhI(OAc).sub.2 (241.6 mg, 0.75 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 100 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the acetylated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane=100%) to afford (5c) (red solid) in 11% (9.6 mg) yield.

[0152] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.69-8.66 (m, 2H), 7.68-7.60 (m, 4H), 7.27 (d, J=8.26 Hz, 2H), 2.22 (s, 6H); .sup.13C NMR (125 MHz, CDCl.sub.3): (ppm)=169.2, 163.3, 163.0, 150.2, 133.2, 132.3, 131.8, 129.5, 128.6, 121.9, 120.0, 20.9; Elemental analysis: Calcd (%) for C.sub.18H.sub.14N.sub.4O.sub.4: C, 61.71, H, 4.03, N, 15.99. Found: C, 61.15, H, 4.26, N, 15.37.

[0153] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.16H.sub.12N.sub.4O.sub.2: 373.090. Found: m/z=373.089.

3-(2,6-diacetoxyphenyl)-6-(2-acetoxyphenyl)-1,2,4,5-tetrazine (5d)

[0154] ##STR00037##

[0155] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), PhI(OAc).sub.2 (805.3 mg, 2.50 mmol), and Pd(OAc).sub.2 (5.6 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Acetic acid (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 120 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the acetylated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane=100%) to afford (5d) (red solid) in 21% (21.4 mg) yield.

[0156] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.54 (dd, J=7.89, 1.67 Hz, 1H), 7.71-7.65 (m, 1H), 7.27 (t, J=8.26 Hz, 1H), 7.55-7.50 (m, 1H), 7.30 (dd, J=8.10, 1.10 Hz, 1H), 7.27 (d, J=8.26 Hz, 2H), 2.35 (s, 3H), 2.20 (s, 6H); .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=170.0, 169.1, 163.1, 162.2, 150.2, 133.9, 132.4, 131.6, 127.0, 124.8, 121.9, 119.8, 21.1, 20.8; Elemental analysis: Calcd (%) for C.sub.20H.sub.16N.sub.4O.sub.6: C, 58.82, H, 3.95, N, 13.72. Found: C, 57.98, H, 3.66, N, 13.13; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.20H.sub.16N.sub.4O.sub.6: 409.114. Found: m/z=409.114.

3-(2-fluorophenyl)-6-phenyl-1,2,4,5-tetrazine (6a)

[0157] ##STR00038##

[0158] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NFSI (78.8 mg, 0.25 mmol), and Pd(dba).sub.2 (14.4 mg, 0.025 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Nitromethane (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 110 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the fluorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (6a) (purple solid) in 30% (18.7 mg) yield.

[0159] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.70-8.66 (m, 2H), 8.34 (td, J=7.63, 1.77 Hz, 1H), 7.68-7.58 (m, 4H), 7.40 (td, J=7.70, 1.14 Hz, 1H), 7.33 (ddd, J=10.87, 8.31, 0.96 Hz, 1H); .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=112.0;

[0160] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=164.0 (d, J=5.9 Hz), 163.4 (d, J=5.6 Hz), 159.9, 134.1 (d, J=8.7 Hz), 133.0, 131.7, 131.4 (d, J=0.9 Hz), 129.5, 128.4, 124.9 (d, J=3.9 Hz), 120.9 (d, J=9.9 Hz), 117.7 (d, J=21.8 Hz); Elemental analysis: Calcd (%) for C.sub.14H.sub.9FN.sub.4: C, 66.66, H, 3.60, N, 22.21. Found: C, 65.49, H, 3.53, N, 21.16; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.9FN.sub.4: 253.088. Found: m/z=253.088.

3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine (6b): CAS 108350-48-7

[0161] ##STR00039##

[0162] The 3,6-diphenyl-1,2,4,5-tetrazine (58.0 mg, 0.25 mmol), NFSI (275.9 mg, 0.88 mmol), and Pd(dba).sub.2 (28.8 mg, 0.05 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Dry trifluoromethylbenzene (2 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 110 C. and reactants were allowed to stir for 17 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the fluorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1) to afford (6b) (purple solid) in 30% (20.3 mg) yield.

[0163] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.38 (td, J=7.64, 1.77 Hz, 2H), 7.67-7.60 (m, 2H), 7.41 (td, J=7.74, 1.06 Hz, 2H), 7.34 (ddd, J=10.85, 8.34, 0.94 Hz, 2H); .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.6; .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.4 (d, J=260.1 Hz), 163.2 (d, J=5.6 Hz), 134.3 (d, J=8.8 Hz), 131.5 (d, J=0.8 Hz), 124.9 (d, J=3.9 Hz), 120.6 (d, J=9.8 Hz), 117.6 (d, J=21.5 Hz); Elemental analysis: Calcd (%) for C.sub.14H.sub.8F.sub.2N.sub.4: C, 62.22, H, 2.98, N, 20.73. Found: C, 61.10, H, 2.84, N, 20.77; HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8F.sub.2N.sub.4: 293.061. Found: m/z=293.060.

3,6-bis(2,6-difluorophenyl)-1,2,4,5-tetrazine (6e)

[0164] ##STR00040##

[0165] The 3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine (67.5 mg, 0.25 mmol), NFSI (630.7 mg, 2 mmol), and Pd(dba).sub.2 (28.8 mg, 0.05 mmol) were introduced in a 10 mL microwave reaction vessel, equipped with a magnetic stirring bar. Dry trifluoromethylbenzene (2 mL) was added, and the reaction mixture was heated in the microwave at 110 C. for 30 min (200 W, 2 min ramp). After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analyzed by NMR to determine the conversion of the fluorinated product. Then, the crude product was purified by silica gel column chromatography (Dichloromethane-Heptane=1:1, then dichloromethane=100%) to afford (6e) (red solid) in 46% (35.2 mg) yield.

[0166] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.66-7.57 (m, 2H), 7.22-7.14 (m, 4H); .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=112.4; .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.0 (dd, J=5.5, 257.3 Hz), 161.5 (m), 134.0 (t, J=10.5 Hz), 112.7 (AAX, N=12.5 Hz), 111.9 (t, J=16.8 Hz); Elemental analysis: Calcd (%) for C.sub.14H.sub.6F.sub.4N.sub.4: C, 54.91, H, 1.97, N, 18.30. Found: C, 54.61, H, 1.72, N, 18.34; HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6F.sub.4N.sub.4: 307.060. Found: m/z=307.060.

DTypical Procedure of Inverse Electron-Demand Diels-Alder Reaction

[0167] ##STR00041##

[0168] Strained-promoted [4+2] cycloaddition of 1,2,4,5-tetrazine ((1) or (6b)) with bicyclononyne was monitored by UV/Vis spectroscopy upon careful examination of the decay of the absorption band at 540 nm (6b) and 550 nm (1). The reaction went to completion in less than an hour with (6b), and was slightly longer with (1). Such a result shows that the presence of the F atoms did not prevent the cycloaddition, but it affects the electron-density of the dieneophile increasing the rate of the reaction.

[0169] The reaction was also done on the following compounds:

##STR00042##

Synthesis

[0170] A solution of 3,6-diphenyl-1,2,4,5-tetrazine with a concentration of 1 mM (2.3 mg into 10 mL of THF) and a solution of cyclooctyne with a concentration of 46 mM (2 mg into 150 L of THF) were prepared. The 1 mM solution of 3,6-diphenyl-1,2,4,5-tetrazine (2 mL) and the 46 mM solution of cyclooctyne (50 L) were mixed into a glass cuvette and the reaction was followed by UV/Vis spectrophotometer.

[0171] The procedure was the same with a solution of 3,6-bis(2-fluorophenyl)-1,2,4,5-tetrazine with a concentration of 1 mM (2.5 mg into 10 mL of THF) instead of 3,6-diphenyl-1,2,4,5-tetrazine.

EXAMPLE 2: OPTIMIZATION OF THE SYNTHESIS OF UNEQUALLY HALOGENATED COMPOUNDS OF FORMULA (IA)

Material

[0172] All reagents were purchased from commercial suppliers and used without purifications. All reactions were performed in Schlenk tubes or in a microwave reaction vessel. Microwave heating was carried out using a CEM Discover microwave reactor. The microwave reactions were run in closed reaction vessels with magnetic stirring and with the temperature controlled via IR detection. .sup.1H (300 MHz), 13C (75 or 125 MHz), .sup.19F (282 MHz) spectra were recorded on Brucker AVANCE III instrument in CDCl.sub.3 solutions. Chemical shifts are reported in ppm relative to CDCl3 (.sup.1H: 7.26 and .sup.13C: 77.16) and coupling constants J are given in Hz. High resolution mass spectra (HRMS) were obtained on a Thermo LTQ-Orbitrap XL with ESI source. Flash chromatography was performed on silica gel (230-400 mesh). Elemental analysis experiments were performed Thermo Electron Flash EA 1112 Series.

Results:

[0173] ##STR00043##

[0174] Fast synthetic access to halogenated s-aryltetrazines has been extended towards a wider set of functionalized compounds, including polyhalogenated molecules, including the symmetrical ortho-difunctionalized previously described 2b-6b.

A.1 Optimisation of CH Mono-Bromination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] to [f]

[0175] ##STR00044##

TABLE-US-00004 Oxidant Conv. 2a 2b 2c 2d Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) 1 X NBS (1.0) CH.sub.3NO.sub.2 0 0 0 0 0 2.sup.[b] Pd(dba).sub.2 NBS (1.0) CH.sub.3NO.sub.2 44 41 3 0 0 (25) 3 Pd(dba).sub.2 NBS (1.0) CH.sub.3NO.sub.2 53 47 7 0 0 (47) 4 Pd.sub.2(dba).sub.3 NBS (1.0) CH.sub.3NO.sub.2 51 46 5 0 0 (38) 5 Pd(OAc).sub.2 NBS (1.0) CH.sub.3NO.sub.2 76 61 9 6 0 (52) (6) 6.sup.[c] Pd(dba).sub.2 NBS (1.0) CH.sub.3NO.sub.2 53 49 4 0 0 (30) 7 Pd(dba).sub.2 TBATB (1.0) CH.sub.3NO.sub.2 0 0 0 0 0 8 Pd(dba).sub.2 PTB (1.0) CH.sub.3NO.sub.2 0 0 0 0 0 9 Pd(dba).sub.2 NBS (2.0) CH.sub.3NO.sub.2 69 53 9 7 0 (46) 10 Pd(dba).sub.2 NBS (3.0) CH.sub.3NO.sub.2 87 54 22 8 3 (46) (20) 11 Pd(dba).sub.2 NBS (1.0) PhCF.sub.3 47 42 5 0 0 12.sup.[d] Pd(dba).sub.2 NBS (1.0) HOAc 55 48 6 1 0 13.sup.[e] Pd(dba).sub.2 NBS (1.0) DCE 26 25 1 0 0 14.sup.[f] Pd(dba).sub.2 NBS (1.0) CH.sub.3NO.sub.2 28 27 1 0 0 15.sup.[g] Pd(dba).sub.2 NBS (1.0) CH.sub.3NO.sub.2 60 49 8 3 0 16.sup.[d] Pd(OAc).sub.2 NBS (1.0) HOAc 81 61 15 5 0 (53) (13) 17.sup.[d] Pd(OAc).sub.2 NBS (2.0) HOAc 100 28 51 11 10 (45) (5) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), [X] (1-3.0 equiv), solvent (0.125 M), 100 C., microwave 200 W, under air, 10 min. .sup.1H NMR yield and isolated yield under bracket. dba: dibenzylidene acetone. TBATB = tetrabutylammonium tribromide. PTB = pyridinium tribromide. DCE: dichloroethane. .sup.[b]Under argon. .sup.[c][Pd] (20 mol %). .sup.[d]110 C. instead of 100 C. .sup.[e]90 C. instead of 100 C. .sup.[f]80 C. instead of 100 C. .sup.[g]30 mn instead of 10 min.

[0176] In the absence of palladium no reaction occurred. For practical reasons catalytic conditions screening was achieved under air. It was successfully established that inert gas conditions are unnecessary for CH activation/bromination. The reaction using 10 mol % of zerovalent palladium precursors Pd.sub.2(dba).sub.3, and Pd(dba).sub.2, in nitromethane at 100 C., afforded the expected 3-(2-bromophenyl)-6-(phenyl)-1,2,4,5-tetrazine (2a) with only traces of dibrominated 3,6-bis(2-bromophenyl)-1,2,4,5-tetrazine (2b) (<5%). The palladium (II) precursor Pd(OAc).sub.2, known for its efficiency in sp.sup.2CH activation, furnished a better conversion albeit with a slightly lower selectivity. Then compound (2a) can be easily purified and isolated in 52% yield. Other solvents, such as trifluoromethylbenzene, acetic acid or 1,2-dichlorethane led to lower conversions. In comparison, under thermal heating condition, the best catalytic system we determined for the production of (2a) furnished 45% isolated yield after 17 h under argon.

A.2 Optimisation of Mono-Iodination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] or [b]

[0177] ##STR00045##

TABLE-US-00005 Oxidant Conv. 3a 3b 3c 3d Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) 1 Pd(dba).sub.2 NIS (1.0) CH.sub.3NO.sub.2 10 10 0 0 0 2 Pd(dba).sub.2 NIS (1.0) AcOH 66 54 9 3 0 (47) (4) 3.sup.[b] Pd(OAc).sub.2 NIS (1.0) AcOH 82 56 19 7 0 (34) (11) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NIS (1 equiv), solvent (0.125 M), 100 C., microwave 200 W, under air, 10 min. .sup.1H NMR yield and isolated yield under bracket. .sup.[b]110 C. instead of 100 C.

[0178] With the microwave assisted protocol for monobromination, a fast and facile access to monoiodinated s-aryltetrazines using N-iodosuccinimide was achieved. The monoiodinated product (3a) was obtained in 47% isolated yield. The diiodinated aryltetrazine (3b) was obtained using 2 equiv of NIS with [Pd(OAc).sub.2] as the catalyst in AcOH in 10 min at 120 C. with 45% isolated yield. Side products of 3-(2,6-diiodophenyl)-6-phenyl-1,2,4,5-tetrazine (3c) (22%) and (3d) (27%).

A.3 Optimisation of Mono-Chlorination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] to [d]

[0179] ##STR00046##

TABLE-US-00006 Oxidant Conv. 4a 4b 4c 4d Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) 1 Pd(dba).sub.2 NCS (1.0) CH.sub.3NO.sub.2 0 0 0 0 0 2.sup.[b] Pd(dba).sub.2 NCS (1.0) AcOH 47 43 4 0 0 (33) 3.sup.[b] Pd(OAc).sub.2 NCS (1.0) AcOH 45 41 4 0 45 (37) 4.sup.[b] Pd(dba).sub.2 NCS (3.0) AcOH 79 56 15 8 0 (54) (9) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NCS (1-2.5 equiv), solvent (0.125 M), 100 C., microwave 200 W, under air, 45 min. .sup.1H NMR yield and isolated yield under bracket. .sup.[b]110 C. instead of 100 C. .sup.[d]PivOH (30% mol).

[0180] With the microwave assisted protocol for monobromination, a fast and facile access to monochlorinated s-aryltetrazines using the appropriate N-halosuccinimide was achieved. The monochlorinated product (4a) was obtained in 54% isolated yield.

[0181] The dichlorinated s-aryltetrazine (4b) was synthesized using of NCS with [Pd(OAc).sub.2] as the catalyst in AcOH 120 C. in only a few minutes and was isolated in 37% yield.

A.4 Tetrabromination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] to [f]

[0182] ##STR00047##

TABLE-US-00007 Oxidant Conv. 2a 2b 2c 2d 2e Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) (%) 1 Pd(OAc).sub.2 NBS (3.0) AcOH 100 0 43 6 48 3 (37) (41) 2 Pd(OAc).sub.2 NBS (5.0) AcOH 100 0 0 0 62 38 (60) (32) 3 Pd(OAc).sub.2 NBS (8.0) AcOH 100 0 0 0 40 60 (35) (44) 4.sup.[c] Pd(OAc).sub.2 NBS (8.0) AcOH 100 0 0 0 44 56 5.sup.[d] Pd(OAc).sub.2 NBS (8.0) AcOH 100 0 0 0 59 41 6 Pd(OAc).sub.2 NBS (8.0) PivOH 52 45 7 0 0 0 (36) 7.sup.[e] Pd(OAc).sub.2 NBS (8.0) AcOH 100 0 0 0 10 90 (6) (79) 8.sup.[f] Pd(OAc).sub.2 NBS (8.0) AcOH 100 0 0 0 0 99 (89) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NBS (3-8 equiv), solvent (0.125 M), 110 C., microwave 200 W, under air, 10 min. .sup.1H NMR yield and isolated yield under bracket. .sup.[b]TFA = trifluoroacetic acid (30% mol.). .sup.[c]PivOH (30% mol). .sup.[d]30 min instead of 10 min. .sup.[f]45 min instead of 10 min.

A.5 Tetra-Iodination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] to [e]

[0183] ##STR00048##

TABLE-US-00008 Oxidant Conv. 3a 3b 3c 3d 3e Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) (%) 1.sup.[b] Pd(OAc).sub.2 NIS (2.0) AcOH 100 13 38 22 27 0 (17) (13) 2 Pd(OAc).sub.2 NIS (8.0) AcOH 100 0 0 0 67 33 (7) (31) 3 Pd(OAc).sub.2 NIS (10.0) AcOH 100 0 0 0 52 .sup.38.sup.[c] 4 Pd(OAc).sub.2 NIS (12.0) AcOH 100 0 0 0 0 .sup.26.sup.[c] 5.sup.[d] Pd(OAc).sub.2 NIS (12.0) CH.sub.3NO.sub.2 100 0 0 0 58 42 (9) (42) 6.sup.[d, e] Pd(OAc).sub.2 NIS (12.0) CH.sub.3NO.sub.2 100 0 0 0 78 22 (15) (20) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NIS (8-12 equiv), solvent (0.125 M), 110 C., microwave 200 W, under air, 10 min. .sup.1H NMR yield and isolated yield under bracket. .sup.[b]120 C. instead of 110 C. .sup.[c]3-(2-acetoxy-6-iodophenyl)-6-(2,6-diiodophenyl)-1,2,4,5-tetrazine was detected by .sup.1H NMR et GC-MS. .sup.[d]100 C. instead of 110 C. .sup.[e]PivOH (30% mol).

A.6 Tetra-Chlorination of 3,6-diphenyl-1,2,4,5-tetrazine (1) Under Conditions [a] to [e]

[0184] ##STR00049##

TABLE-US-00009 Oxidant Conv. 4a 4b 4c 4d 4e Entry [Pd] (equiv) Solvent (%) (%) (%) (%) (%) (%) 1.sup.[b] Pd(OAc).sub.2 NIS (2.0) AcOH 100 13 38 22 27 0 (17) (13) 2 Pd(OAc).sub.2 NIS (8.0) AcOH 100 0 0 0 67 33 (7) (31) 3 Pd(OAc).sub.2 NIS (10.0) AcOH 100 0 0 0 52 .sup.38.sup.[c] 4 Pd(OAc).sub.2 NIS (12.0) AcOH 100 0 0 0 0 .sup.26.sup.[c] 5.sup.[d] Pd(OAc).sub.2 NIS (12.0) CH.sub.3NO.sub.2 100 0 0 0 58 42 (9) (42) 6.sup.[d, e] Pd(OAc).sub.2 NIS (12.0) CH.sub.3NO.sub.2 100 0 0 0 78 22 (15) (20) .sup.[a]Conditions: 3,6-diphenyl-1,2,4,5-tetrazine (1) (1 equiv), [Pd] (10 mol %), NCS (4-12 equiv), solvent (0.125 M), 110 C., microwave 200 W, under air, 45 min. .sup.1H NMR yield and isolated yield under bracket. .sup.[c]10 min instead of 45 min. .sup.[d]120 C. instead of 110 C. .sup.[e]PivOH (30% mol).

A.7 Di- and Tri-Halogenation of 3,6-diphenyl-1,2,4,5-tetrazine (1)

[0185] ##STR00050##

[0186] This is a fast synthetic access to halogenated s-aryltetrazines towards a wider set of polyhalogenated compounds including the symmetrical ortho-dihalogenated (2b-4b) and the dissymmetrical ortho-trihalogenated (2d-4d). These latter being already pertinent candidates for further construction of dissymmetrized s-tetrazines. The dibrominated aryltetrazine (2b), which is a useful precursor for the synthesis of benzo[a]acecorannulene bowl-shaped fullerene materials, was obtained using 2 equiv of NBS with [Pd(OAc).sub.2] as the catalyst in AcOH in 10 min at 110 C. with 45% isolated yield. Its iodinated analogue (3b) was synthesized under similar conditions using a slightly higher temperature of 120 C. Side products 3-(2,6-diiodophenyl)-6-phenyl-1,2,4,5-tetrazine (3c) (22%) and (3d) (27%) makes workup more difficult. The dichlorinated s-aryltetrazine (4b) was synthesized again in only a few minutes using 4 equiv of NCS at 120 C., and was isolated in 37% yield.

[0187] One-step tri halogenation of (1) was efficiently achieved from larger amounts of electrophilic halide sources and longer reaction periods under microwave heating (still lesser than one hour reaction time). Tris-brominated s-aryltetrazine 3-(2,6-dibromophenyl)-6-(2-bromophenyl)-1,2,4,5-tetrazine (2d) was isolated in 60% yield under pure form. The access to tris-iodinated s-aryltetrazine (3d) was found troublesome since from a satisfactory 67% conversion of (1) pure (3d) was isolated in only low 7% yield due to its sensitiveness to column chromatography. Tris-chlorinated (4d) was isolated in pure form in 35% yield from a 48% yield conversion.

BGeneral Procedure of Functionalization of Tetrazine

[0188] ##STR00051##

[0189] As a typical experiment, the tetrazine (1.0 eq., 0.25 mmol), halogenated source (X eq.), and palladium source (10 mol %) were introduced in a 10 mL microwave reaction vessel, equipped with a magnetic stirring bar. The solvent (mL, 0.125 M) was added, and the reaction mixture was heated in the microwave at T C. for corresponding reaction time (200 W, 2 min ramp). After cooling down to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water+3% of TEA (or Na.sub.2S.sub.2O.sub.3 when NIS was involved). The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the residue was analysed by NMR to determine the conversion of the halogenated product. Then, the crude product was purified by silica gel column chromatography using an appropriate ratio of the eluent. For elemental analysis, the product was recrystallized with a slow diffusion of dichloromethane into heptane (RPE quality).

[0190] According to the above-described process, the following compounds are obtained: [0191] 3-(2-bromophenyl)-6-phenyl-1,2,4,5-tetrazine (2a), [0192] 3,6-bis(2-bromophenyl)-1,2,4,5-tetrazine (2b), [0193] 3-(2,6-dibromophenyl)-6-(2-bromophenyl)-1,2,4,5-tetrazine (2d), [0194] 3,6-bis(2,6-dibromophenyl)-1,2,4,5-tetrazine (2e), [0195] 3-(2-iodophenyl)-6-phenyl-1,2,4,5-tetrazine (3a), [0196] 3,6-bis(2-iodophenyl)-1,2,4,5-tetrazine (3b), [0197] 3-(2,6-diiodophenyl)-6-(2-iodophenyl)-1,2,4,5-tetrazine (3d), [0198] 3,6-bis(2,6-diiodophenyl)-1,2,4,5-tetrazine (3e), [0199] 3-(2-chlorophenyl)-6-phenyl-1,2,4,5-tetrazine (4a), [0200] 3,6-bis(2-chlorophenyl)-1,2,4,5-tetrazine (4b), [0201] 3-(2,6-dichlorophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (4d), and [0202] 3,6-bis(2,6-dichlorophenyl)-1,2,4,5-tetrazine (4e).

CSynthesis of Unequally Polyhalogenated Compounds of Formula (Ia)

[0203] From the difluorinated s-aryltetrazine (6b), monobromination and monoiodination proceeded selectively in only ten minutes with precisely 2 equiv of N-halosuccinimide. Products (12a) and (12b) were then isolated pure in 33% and 54% yield, respectively. For the more demanding selective monochlorination of (6b) the reaction time was not extended but instead 4 equiv of NCS was used to isolate (12c) in 50% yield. Monobromination and monoiodination of the dichlorinated s-aryltetrazine (4b) were found easier and the trihalogenated products (13a) and (13b) were converted in 71% and 75%. A more challenging two-steps access to tri halogenated species is the reverse process where di halogenation follows mono halogenation of s-aryltetrazine. This was done for dibromination and dichlorination of (6a) to reach targets (14a) and (14b).

##STR00052## ##STR00053## ##STR00054##

[0204] [a] Conditions: 3,6-diaryl-1,2,4,5-tetrazine derivative (1 equiv), Pd(OAc).sub.2 (10 mol %), [NYS]: NBS or NIS or NCS (2.0 to 4.0 equiv), solvent (0.125 M), 120 C., microwave 200 W, under air, 10 min. .sup.1H NMR yield and isolated yield under bracket.

[0205] Combining the above-described one-step mono-, di-, and tri halogenation reactions, successively, allows forming the polyhalogenated compounds described below, that can be unequally functionalized with up to three different functions in the four positions.

3-(2-bromo-6-fluorophenyl)-6-(2,6-dibromophenyl)-1,2,4,5-tetrazine (15)

[0206] ##STR00055##

[0207] Rf=0.59 (Dichloromethane-Heptane=1:1 (v/v)).

[0208] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.78 (d, J=8.10 Hz, 2H), 7.63 (dt, J=8.10, 0.92 Hz, 1H), 7.54-7.47 (m, 1H), 7.39-7.30 (m, 2H).

[0209] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=109.9.

[0210] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=167.4, 163.9 (d, J=1.3 Hz), 162.6 (d, J=256.3 Hz), 135.6, 133.4 (d, J=9.0 Hz), 133.0, 132.0, 129.0 (d, J=3.6 Hz), 123.7 (d, J=17.8 Hz), 123.6, 123.5 (d, J=2.6 Hz), 115.6 (d, J=21.3 Hz).

[0211] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.3FN.sub.4: C, 34.39, H, 1.24, N, 11.46. Found: C, 34.62, H, 1.47, N, 11.15.

[0212] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.3FN.sub.4: 486.820. Found: m/z=486.821.

3-(2-iodo-6-fluorophenyl)-6-(2,6-diiodophenyl)-1,2,4,5-tetrazine (16)

[0213] ##STR00056##

[0214] Rf=047 (Dichloromethane-Heptane=1:1 (v/v)).

[0215] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.05 (d, J=8.00 Hz, 2H), 7.91-7.85 (m, 1H), 7.37-7.33 (m, 2H), 6.99 (t, J=8.00 Hz, 2H).

[0216] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=108.6.

[0217] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=170.7, 165.3 (d, J=1.4 Hz), 162.0 (d, J=256.9 Hz), 142.3, 139.1, 135.4 (d, J=3.6 Hz), 133.8 (d, J=9.0 Hz), 133.2, 127.11 (d, J=17.3 Hz), 116.4 (d, J=21.3 Hz), 97.1 (d, J=0.9 Hz), 96.0.

[0218] Elemental analysis: Calcd (%) for C.sub.14H.sub.6FI.sub.3N.sub.4: C, 26.69, H, 0.96, N, 8.89. Found: C, 26.86, H, 1.09, N, 8.43.

[0219] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.6FI.sub.3N.sub.4: 652.760. Found: m/z=652.760.

3-(2-bromo-6-fluorophenyl)-6-(2,6-dichlorophenyl)-1,2,4,5-tetrazine (17)

[0220] ##STR00057##

[0221] Rf=0.57 (Dichloromethane-Heptane=1:1 (v/v)).

[0222] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.54-7.42 (m, 4H), 7.39 (td, J=8.10, 0.92 Hz, 1H), 7.22 (dt, J=8.10, 0.92 Hz, 1H).

[0223] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.0.

[0224] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.3, 163.2 (d, J=1.4 Hz), 162.8 (d, J=256.9 Hz), 135.1, 134.8 (d, J=3.6 Hz), 133.1 (d, J=9.0 Hz), 132.4, 132.0, 128.4, 126.0 (d, J=3.6 Hz), 121.8 (d, J=17.3 Hz), 115.0 (d, J=21.3 Hz).

[0225] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Cl.sub.3FN.sub.4: C, 47.29, H, 1.70, N, 15.76. Found: C, 47.58, H, 1.32, N, 15.45.

[0226] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Cl.sub.3FN.sub.4: 354.971. Found: m/z=354.970.

3-(2-bromo-6-chlorophenyl)-6-(2,6-dibromophenyl)-1,2,4,5-tetrazine (18)

[0227] ##STR00058##

[0228] Rf=0.68 (Dichloromethane-Heptane=2:1 (v/v)).

[0229] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.78 (d, J=8.10 Hz, 2H), 7.73 (dd, J=8.10, 0.90 Hz, 1H), 7.61 (dd, J=8.10, 0.90 Hz, 1H), 7.44 (t, J=8.10 Hz, 1H), 7.39 (t, J=8.10 Hz, 1H).

[0230] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=167.4, 166.3, 135.6, 134.8, 133.9, 132.9, 132.7, 132.0, 131.5, 128.9, 123.7, 123.5.

[0231] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.3ClN.sub.4: C, 33.27, H, 1.20, N, 11.09. Found: C, 33.78, H, 1.54, N, 10.69.

[0232] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.3ClN.sub.4: 502.790. Found: m/z=502.792.

3,6-bis(2-bromo-6-fluorophenyl)-1,2,4,5-tetrazine (19)

[0233] ##STR00059##

[0234] Rf=0.61 (dichloromethane-heptane=7:3 (v/v)).

[0235] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.62 (dt, J=8.10, 0.92 Hz, 2H), 7.51 (t, J=8.31 Hz, 2H), 7.48 (t, J=8.33 Hz, 2H), 7.35-7.29 (m, 2H).

[0236] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=109.9.

[0237] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=164.2 (d, J=1.3 Hz), 162.9 (d, J=256.3 Hz), 133.6 (d, J=9.1 Hz), 129.3 (d, J=3.6 Hz), 123.8 (d, J=17.3 Hz), 123.7 (d, J=2.6 Hz), 115.8 (d, J=21.3 Hz).

[0238] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.2F.sub.2N.sub.4: C, 39.29, H, 1.41, N, 13.09. Found: C, 39.24, H, 1.75, N, 11.95.

[0239] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.2F.sub.2N.sub.4: 426.900. Found: m/z=426.900.

3,6-bis(2-iodo-6-fluorophenyl)-1,2,4,5-tetrazine (20)

[0240] ##STR00060##

[0241] Rf=0.58 (dichloromethane-heptane=7:3 (v/v)).

[0242] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.90-7.84 (m, 2H), 7.38-7.32 (m, 4H).

[0243] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=108.6.

[0244] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.5 (d, J=1.4 Hz), 162.2 (d, J=256.9 Hz), 135.6 (d, J=3.7 Hz), 133.9 (d, J=8.7 Hz), 127.2 (d, J=16.6 Hz), 116.6 (d, J=21.3 Hz), 97.2 (d, J=0.9 Hz).

[0245] Elemental analysis: Calcd (%) for C.sub.14H.sub.6I.sub.2F.sub.2N.sub.4: C, 32.21, H, 1.16, N, 10.73. Found: C, 33.79, H, 1.58, N, 10.38.

[0246] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6F.sub.2I.sub.2N.sub.4: 522.872. Found: m/z=522.871.

3,6-bis(2-chloro-6-fluorophenyl)-1,2,4,5-tetrazine (21)

[0247] ##STR00061##

[0248] Rf=0.59 (dichloromethane-heptane=7:3 (v/v)).

[0249] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.58 (t, J=8.27 Hz, 1H), 7.56 (t, J=8.23 Hz, 1H), 7.45 (dt, J=8.17, 1.03 Hz, 2H), 7.31-7.25 (m, 2H).

[0250] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.0.

[0251] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.3 (d, J=1.3 Hz), 163.0 (d, J=255.7 Hz), 135.1 (d, J=3.5 Hz), 133.3 (d, J=9.5 Hz), 126.2 (d, J=3.6 Hz), 121.9 (d, J=17.3 Hz), 115.2 (d, J=21.3 Hz).

[0252] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Cl.sub.2F.sub.2N.sub.4: C, 49.58, H, 1.78, N, 16.52. Found: C, 46.64, H, 2.08, N, 14.68.

[0253] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.6Cl.sub.2F.sub.2N.sub.4: 360.982. Found: m/z=360.982.

3,6-bis(2-bromo-6-chlorophenyl)-1,2,4,5-tetrazine (22)

[0254] ##STR00062##

[0255] Rf=0.49 (dichloromethane-heptane=1:1 (v/v)).

[0256] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.75 (dd, J=8.08, 1.03 Hz, 2H), 7.60 (dd, J=8.16, 1.03 Hz, 2H), 7.44 (t, J=8.11 Hz, 2H).

[0257] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.5, 135.1, 134.1, 132.8, 131.6, 129.1, 123.9.

[0258] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.2Cl.sub.2N.sub.4: C, 36.48, H, 1.31, N, 12.16. Found: C, 35.61, H, 1.71, N, 10.90.

[0259] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.2Cl.sub.2N.sub.4: 458.840. Found: m/z=458.840.

3,6-bis(2-chloro-6-iodophenyl)-1,2,4,5-tetrazine (23)

[0260] ##STR00063##

[0261] Rf=0.37 (dichloromethane-heptane=1:1 (v/v)).

[0262] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.77 (dd, J=8.00, 0.98 Hz, 2H), 7.64 (dd, J=8.14, 0.97 Hz, 2H), 7.27 (t, J=8.06 Hz, 2H). .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=168.2, 137.9, 137.6, 134.1, 133.0, 129.9, 97.4.

[0263] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Cl.sub.2I.sub.2N.sub.4: C, 30.30, H, 1.09, N, 10.10. Found: C, 30.09, H, 1.06, N, 10.05.

[0264] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Cl.sub.2I.sub.2N.sub.4: 554.813. Found: m/z=554.812.

3-(2-bromophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (24)

[0265] ##STR00064##

[0266] Rf=0.33 (Dichloromethane-Heptane=1:1 (v/v)).

[0267] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.40 (td, J=7.9, 1.8 Hz, 1H), 8.05 (dd, J=7.7, 1.7 Hz, 1H), 7.83 (dd, J=7.9, 1.8 Hz, 1H), 7.69-7.61 (m, 1H), 7.58 (td, J=7.6, 1.2 Hz, 1H), 7.49 (dd, J=7.9, 1.8 Hz, 1H), 7.43 (dd, J=8.0, 1.1 Hz, 1H), 7.40-7.32 (m, 1H).

[0268] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.5.

[0269] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.7, 163.4 (d, J=260.0 Hz), 163.1 (d, J=5.8 Hz), 134.4, 134.4 (d, J=8.8 Hz), 133.5, 132.6, 132.3, 131.6 (d, J=0.9 Hz), 127.9, 124.9 (d, J=3.9 Hz), 122.4, 120.4 (d, J=9.8 Hz), 117.6 (d, J=21.6 Hz).

[0270] Elemental analysis: Calcd (%) for C.sub.14H.sub.8BrFN.sub.4: C, 50.78, H, 2.44, N, 16.92. Found: C, 50.56, H, 3.04, N, 16.51.

[0271] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8BrFN.sub.4: 352.980. Found: m/z=352.980.

3-(2-bromo-6-fluorophenyl)-6-phenyl-1,2,4,5-tetrazine (25)

[0272] ##STR00065##

[0273] Rf=0.46 (Dichloromethane-Heptane=1:1 (v/v)).

[0274] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.75-8.72 (m, 2H), 7.69-7.60 (m, 4H), 7.51-7.44 (m, 1H), 7.30 (td, J=8.10, 0.90 Hz).

[0275] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=110.1.

[0276] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=164.3 (d, J=1.5 Hz), 163.9, 163.0 (d, J=256.0 Hz), 133.4, 133.3 (d, J=9.1 Hz), 131.5, 129.6, 129.2 (d, J=3.6 Hz), 128.7, 124.1 (d, J=18.0 Hz), 123.8 (d, J=2.6 Hz), 115.7 (d, J=21.5 Hz).

[0277] Elemental analysis: Calcd (%) for C.sub.14H.sub.8BrFN.sub.4: C, 50.78, H, 2.44, N, 16.92.

[0278] Found: C, 50.56, H, 3.04, N, 16.51.

[0279] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8BrFN.sub.4: 352.980. Found: m/z=352.980.

3-(2-fluorophenyl)-6-(2-iodophenyl)-1,2,4,5-tetrazine (26)

[0280] ##STR00066##

[0281] Rf=0.36 (Dichloromethane-Heptane=1:1 (v/v)).

[0282] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.41 (td, J=1.80, 7.63.Hz, 1H), 8.13 (dd, J=1.01, 8.00 Hz, 1H), 8.03 (dd, J=1.63, 7.75 Hz, 1H), 7.69-7.58 (m, 2H), 7.42 (td, J=1.13, 7.72 Hz, 1H), 7.36-7.27 (m, 2H).

[0283] .sup.9F NMR (282 MHz, CDCl.sub.3): (ppm)=111.5.

[0284] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.4, 163.4 (d, J=260.1 Hz), 163.2 (d, J=5.9 Hz), 141.2, 136.8, 134.4 (d, J=8.8 Hz), 132.4, 131.7, 131.6 (d, J=1.0 Hz), 128.7, 124.9 (d, J=3.9 Hz), 120.5 (d, J=9.8 Hz), 117.6 (d, J=21.6 Hz), 95.6.

[0285] Elemental analysis: Calcd (%) for C.sub.14H.sub.8FIN.sub.4: C, 44.47, H, 2.13, N, 14.82. Found: C, 44.74, H, 2.84, N, 14.23.

[0286] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.8FIN.sub.4: 378.985. Found: m/z=378.985.

3-(2-fluoro-6-iodophenyl)-6-phenyl-1,2,4,5-tetrazine (27)

[0287] ##STR00067##

[0288] Rf=0.42 (Dichloromethane-Heptane=1:1 (v/v)).

[0289] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.76-8.72 (m, 2H), 7.90-7.84 (m, 1H), 7.70-7.61 (m, 3H), 7.34-7.30 (m, 2H).

[0290] .sup.9F NMR (282 MHz, CDCl.sub.3): (ppm)=108.9.

3-(2-chlorophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (28)

[0291] ##STR00068##

[0292] Rf=0.35 (Dichloromethane-Heptane=1:1 (v/v)).

[0293] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.40 (td, J=7.65, 1.80 Hz, 1H), 8.10 (td, J=7.00, 1.80 Hz, 1H), 7.69-7.50 (m, 4H), 7.43 (td, J=7.65, 1.80 Hz, 1H), 7.36 (ddd, J=10.8, 7.65, 1.10 Hz, 1H).

[0294] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.5.

[0295] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.0, 163.4 (d, J=260.0 Hz), 163.1 (d, J=5.8 Hz), 134.4 (d, J=9.9 Hz), 133.8, 132.6, 132.2, 131.6 (d, J=0.9 Hz), 131.2, 127.4, 124.9 (d, J=3.9 Hz), 120.5 (d, J=9.8 Hz), 117.6 (d, J=21.6 Hz).

[0296] Elemental analysis: Calcd (%) for C.sub.14H.sub.8ClFN.sub.4: C, 58.65, H, 2.81, N, 19.54. Found: C, 58.41, H, 2.68, N, 19.32.

[0297] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8ClFN.sub.4: 309.031. Found: m/z=309.031.

3-(2-chloro-6-fluorophenyl)-6-phenyl-1,2,4,5-tetrazine (29)

[0298] ##STR00069##

[0299] Rf=0.48 (Dichloromethane-Heptane=1:1 (v/v)).

[0300] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.74-8.71 (m, 2H), 7.69-7.61 (m, 3H), 7.58-7.50 (m, 1H), 7.44 (td, J=7.00, 1.80 Hz, 1H), 7.26 (td, J=7.00, 1.80 Hz, 1H).

[0301] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.2.

[0302] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.9, 163.3 (d, J=1.5 Hz), 163.0 (d, J=255.0 Hz), 135.1 (d, J=3.5 Hz), 133.4, 132.9 (d, J=9.5 Hz), 131.5, 129.5, 128.7, 126.2 (d, J=3.6 Hz), 122.2 (d, J=17.4 Hz), 115.7 (d, J=21.5 Hz).

[0303] Elemental analysis: Calcd (%) for C.sub.14H.sub.8ClFN.sub.4: C, 58.65, H, 2.81, N, 19.54. Found: C, 58.41, H, 2.68, N, 19.32.

[0304] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8ClFN.sub.4: 309.031. Found: m/z=309.031.

3-(2-bromophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (30)

[0305] ##STR00070##

[0306] Rf=0.33 (Dichloromethane-Heptane=2:3 (v/v)).

[0307] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.13-8.05 (m, 2H), 7.84 (dd, J=7.00, 1.80 Hz, 1H), 7.67-7.46 (m, 5H).

[0308] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.6, 164.9, 134.4, 133.9, 133.4, 132.7, 132.6, 132.3, 132.3, 131.5, 131.2, 127.9, 127.4, 122.5.

[0309] Elemental analysis: Calcd (%) for C.sub.14H.sub.8BrClN.sub.4: C, 48.38, H, 2.32, N, 16.12. Found: C, 48.59, H, 2.53, N, 15.88.

[0310] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.8BrClN.sub.4: 346.969. Found: m/z=346.970.

3-(2-bromo-6-chlorophenyl)-6-phenyl-1,2,4,5-tetrazine (31)

[0311] ##STR00071##

[0312] Rf=0.28 (Dichloromethane-Heptane=2:3 (v/v)).

[0313] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.76-8.73 (m, 2H), 7.71 (dd, J=8.10, 1.00 Hz, 1H), 7.70-7.62 (m, 3H), 7.59 (dd, J=8.10, 1.00 Hz, 1H), 7.41 (t, J=8.12 Hz, 1H).

3-(2-chlorophenyl)-6-(2-iodophenyl)-1,2,4,5-tetrazine (32)

[0314] ##STR00072##

[0315] Rf=0.36 (Dichloromethane-Heptane=1:1 (v/v)).

[0316] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.15-8.11 (m, 2H), 8.06 (dd, J=7.75, 1.60 Hz, 1H), 7.67-7.51 (m, 4H), 7.30 (td, J=7.75, 1.60 Hz, 1H).

[0317] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.3, 164.9, 141.2, 136.7, 133.9, 132.7, 132.5, 132.3, 131.7, 131.5, 131.2, 128.7, 127.36, 95.7.

[0318] Elemental analysis: Calcd (%) for C.sub.14H.sub.8ClIN.sub.4: C, 42.61, H, 2.04, N, 14.20. Found: C, 42.98, H, 2.57, N, 11.86.

[0319] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.8ClIN.sub.4: 394.955. Found: m/z=394.955.

3-(2-chloro-6-iodophenyl)-6-phenyl-1,2,4,5-tetrazine (33)

[0320] ##STR00073##

[0321] Rf=0.47 (Dichloromethane-Heptane=1:1 (v/v)).

[0322] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.77-8.74 (m, 2H); 7.96 (dd, J=8.00, 1.00 Hz, 1H), 7.70-7.63 (m, 3H), 7.61 (dd, J=8.00, 1.00 Hz, 1H), 7.24 (t, J=8.00 Hz, 1H).

3-(2-bromophenyl)-6-(2-iodophenyl)-1,2,4,5-tetrazine (34)

[0323] ##STR00074##

[0324] Rf=0.36 (Dichloromethane-Heptane=1:1 (v/v)).

[0325] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.13 (dd, J=7.98, 1.04 Hz, 1H), 8.10-8.05 (m, 2H), 7.84 (dd, J=7.95, 1.16 Hz, 1H), 7.65-7.56 (m, 2H), 7.49 (td, J=7.54, 1.77 Hz, 1H) 7.30 (dd, J=7.58, 1.70 Hz, 1H).

[0326] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.3, 165.5, 141.0, 136.7, 134.4, 133.4, 123.6, 132.5, 132.3, 131.6, 128.7, 127.9, 122.5, 95.7.

[0327] Elemental analysis: Calcd (%) for C.sub.14H.sub.8BrIN.sub.4: C, 38.30, H, 1.84, N, 12.76. Found: C, 38.86, H, 2.42, N, 12.14.

[0328] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for C.sub.14H.sub.8BrIN.sub.4: 460.887. Found: m/z=460.887.

3-(2-bromo-6-iodophenyl)-6-phenyl-1,2,4,5-tetrazine (35)

[0329] ##STR00075##

[0330] Rf=0.47 (Dichloromethane-Heptane=1:1 (v/v)).

[0331] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.77-8.74 (m, 2H), 7.01 (dd, J=8.00, 1.00 Hz, 1H), 7.79 (dd, J=8.10, 1.00 Hz, 1H), 7.70-7.62 (m, 3H), 7.16 (t, J=8.04 Hz, 1H).

3-(2-bromo-6-fluorophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (12a)

[0332] ##STR00076##

[0333] Rf=0.52 (dichloromethane-heptane=7:3 (v/v)).

[0334] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.42 (td, J=7.53, 1.69 Hz, 1H), 7.70-7.64 (m, 1H), 7.62 (dt, J=8.14, 0.98 Hz, 1H), 7.52-7.27 (m, 4H).

[0335] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=110.1, 111.1.

[0336] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=164.0 (d, J=5.9 Hz), 163.5 (d, J=260.6 Hz), 163.5 (d, J=1.3 Hz), 163.0 (d, J=256.0 Hz), 134.6 (d, J=8.8 Hz), 133.3 (d, J=9.2 Hz), 131.8 (d, J=0.8 Hz), 129.1 (d, J=3.6 Hz), 124.9 (d, J=3.9 Hz), 124.0 (d, J=17.2 Hz), 123.8 (d, J=2.6 Hz), 120.4 (d, J=9.7 Hz), 117.7 (d, J=21.6 Hz), 115.6 (d, J=21.4 Hz).

[0337] Elemental analysis: Calcd (%) for C.sub.14H.sub.7BrF.sub.2N.sub.4: C, 48.16, H, 2.02, N, 16.05. Found: C, 50.53, H, 3.34, N, 13.56.

[0338] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7BrF.sub.2N.sub.4: 348.989. Found: m/z=348.988.

3-(2-fluoro-6-iodophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (12b)

[0339] ##STR00077##

[0340] Rf=0.51 (dichloromethane-heptane=7:3 (v/v)).

[0341] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.46-8.40 (m, 1H), 7.88-7.84 (m, 1H), 7.71-7.63 (m, 1H), 7.46-7.30 (m, 4H).

[0342] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=108.8, 111.0.

[0343] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.1 (bs), 163.9 (d, J=5.9 Hz), 163.6 (d, J=260.7 Hz), 162.3 (d, J=256.6 Hz), 135.7 (d, J=3.7 Hz), 134.8 (d, J=8.8 Hz), 133.8 (d, J=8.8 Hz), 131.9 (d, J=0.8 Hz), 127.3 (d, J=16.4 Hz), 125.1 (d, J=3.9 Hz), 120.5 (d, J=9.8 Hz), 117.8 (d, J=21.6 Hz), 116.6 (d, J=21.5 Hz), 97.4 (d, J=0.9 Hz).

[0344] Elemental analysis: Calcd (%) for C.sub.14H.sub.7F.sub.2IN.sub.4: C, 42.45, H, 1.78, N, 14.14. Found: C, 42.23, H, 2.29, N, 13.38.

[0345] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7F.sub.2IN.sub.4: 396.975. Found: m/z=396.974.

3-(2-chloro-6-fluorophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (12c)

[0346] ##STR00078##

[0347] Rf=0.55 (dichloromethane-heptane=7:3 (v/v)).

[0348] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.42 (td, J=7.62, 1.78 Hz, 1H), 7.70-7.63 (m, 1H), 7.59-7.51 (m, 1H), 7.46-7.43 (m, 2H), 7.41-7.23 (m, 2H).

[0349] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.1, 111.1.

[0350] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=163.9 (d, J=5.9 Hz), 163.6 (d, J=260.6 Hz), 163.1 (d, J=255.3 Hz), 162.7 (bs), 135.1 (d, J=3.5 Hz), 134.8 (d, J=8.8 Hz), 133.1 (d, J=9.5 Hz), 131.9 (d, J=0.8 Hz), 126.2 (d, J=3.6 Hz), 125.0 (d, J=3.9 Hz), 122.1 (d, J=17.3 Hz), 120.5 (d, J=9.7 Hz), 117.8 (d, J=21.6 Hz), 115.2 (d, J=21.4 Hz).

[0351] Elemental analysis: Calcd (%) for C.sub.14H.sub.7ClF.sub.2N.sub.4: C, 55.19, H, 2.32, N, 18.39. Found: C, 55.59, H, 3.20, N, 16.61.

[0352] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7ClF.sub.2N.sub.4: 305.040. Found: m/z=305.039.

3-(2-bromo-6-chlorophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (13a)

[0353] ##STR00079##

[0354] Rf=0.41 (dichloromethane-heptane=1:1 (v/v)).

[0355] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.15-8.12 (m, 1H), 7.72 (dd, J=8.08, 1.05 Hz, 1H), 7.67-7.52 (m, 4H), 7.43 (t, J=8.11 Hz, 1H).

[0356] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.9, 165.7, 135.2, 134.1, 134.0, 132.9, 132.7, 132.5, 131.7, 131.6, 131.3, 129.2, 127.5, 124.1.

[0357] Elemental analysis: Calcd (%) for C.sub.14H.sub.6BrCl.sub.2N.sub.4: C, 44.01, H, 1.85, N, 14.67. Found: C, 44.62, H, 1.98, N, 14.45.

[0358] HRMS+p ESI (m/z) [M+Na.sup.+] Calcd for Cl.sub.4H.sub.6BrCl.sub.2N.sub.4: 402.912. Found: m/z=402.913.

3-(2-chloro-6-iodophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (13b)

[0359] ##STR00080##

[0360] Rf=0.31 (dichloromethane-heptane=1:1 (v/v)).

[0361] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.16-8.13 (m, 1H), 7.76 (dd, J=7.99, 0.97 Hz, 2H), 7.67-7.52 (m, 4H), 7.25 (t, J=8.06 Hz, 1H).

[0362] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=167.5, 165.6, 137.9, 137.5, 134.3, 134.1, 133.0, 132.9, 132.5, 131.7, 131.3, 129.9, 127.5, 97.6.

[0363] Elemental analysis: Calcd (%) for C.sub.14H.sub.7Cl.sub.2IN.sub.4: C, 39.19, H, 1.64, N, 13.06. Found: C, 38.80, H, 1.73, N, 12.78.

[0364] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Cl.sub.2IN.sub.4: 428.916. Found: m/z=428.916.

3-(2-bromo-6-fluorophenyl)-6-(2-bromophenyl)-1,2,4,5-tetrazine (14a)

[0365] ##STR00081##

[0366] Rf=0.50 (dichloromethane-heptane=1:1 (v/v)).

[0367] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=110.0.

3-(2,6-dibromophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (36)

[0368] ##STR00082##

[0369] Rf=0.50 (dichloromethane-heptane=1:1 (v/v)).

[0370] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=110.9.

3-(2-chloro-6-fluorophenyl)-6-(2-chlorophenyl)-1,2,4,5-tetrazine (37)

[0371] ##STR00083##

[0372] Rf=0.39 (dichloromethane-heptane=1:1 (v/v)).

[0373] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.14-8.10 (m, 1H), 7.67-7.64 (m, 1H), 7.62-7.52 (m, 3H), 7.45 (dt, J=8.1, 1.0 Hz, 1H), 7.27 (td, J=8.1, 1.0 Hz, 1H).

[0374] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.1.

[0375] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=165.7, 163.1 (d, J=255.5 Hz), 162.7 (d, J=1.56 Hz), 135.1 (d, J=3.5 Hz), 134.1, 133.2 (d, J=9.6 Hz), 133.0, 132.6, 131.5, 131.4, 127.5, 126.2 (d, J=3.6 Hz), 122.0 (d, J=7.3 Hz), 115.2 (d, J=21.4 Hz).

[0376] Elemental analysis: Calcd (%) for C.sub.14H.sub.7Cl.sub.2FN.sub.4: C, 52.36, H, 2.20, N, 17.45. Found: C, 53.13, H, 2.74, N, 16.97.

[0377] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7Cl.sub.2FN.sub.4: 321.010. Found: m/z=321.010.

3-(2,6-dichlorophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (38)

[0378] ##STR00084##

[0379] Rf=0.39 (dichloromethane-heptane=1:1 (v/v)).

[0380] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.0.

3-(2-bromo-6-fluorophenyl)-6-(2-chloro-6-fluorophenyl)-1,2,4,5-tetrazine (39)

[0381] ##STR00085##

[0382] Rf=0.59 (dichloromethane-heptane=3:2 (v/v)).

[0383] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.64-7.44 (m, 4H), 7.35-7.26 (m, 2H).

[0384] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=109.9, 111.0.

[0385] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=164.2 (d, J=1.3 Hz), 163.2 (d, J=1.3 Hz), 163.0 (d, J=255.6 Hz), 162.9 (d, J=256.3 Hz), 135.1 (d, J=3.5 Hz), 133.6 (d, J=9.2 Hz), 133.3 (d, J=9.5 Hz), 129.3 (d, J=3.6 Hz), 126.2 (d, J=3.6 Hz), 123.7 (sb), 123.7 (d, J=13.7 Hz), 121.9 (d, J=17.3 Hz), 115.8 (d, J=21.2 Hz), 115.2 (d, J=21.2 Hz).

[0386] Elemental analysis: Calcd (%) for C.sub.14H.sub.6BrClF.sub.2N.sub.4: C, 43.84, H, 1.58, N, 14.61. Found: C, 44.51, H, 2.02, N, 14.25.

[0387] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6BrClF.sub.2N.sub.4: 382.951. Found: m/z=382.951.

3-(2-chloro-6-fluorophenyl)-6-(2-fluoro-6-iodophenyl)-1,2,4,5-tetrazine (40)

[0388] ##STR00086##

[0389] Rf=0.54 (dichloromethane-heptane=1:1 (v/v)).

[0390] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.73 (dd, J=8.08, 1.05 Hz, 1H), 7.64-7.59 (m, 2H), 7.54-7.41 (m, 2H), 7.33 (td, J=8.80, 1.05 Hz, 1H).

[0391] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=109.9.

[0392] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.5, 164.2 (d, J=1.3 Hz), 162.8 (d, J=256.2 Hz), 135.1, 134.0, 133.6 (d, J=9.1 Hz), 132.8, 131.7, 129.2 (d, J=3.7 Hz), 129.1, 123.9, 123.8 (d, J=17.4 Hz), 123.7 (d, J=2.7 Hz), 115.8 (d, J=21.2 Hz).

[0393] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.2ClFN.sub.4: C, 37.83, H, 1.36, N, 12.61. Found: C, 38.57, H, 1.86, N, 11.98.

[0394] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.2ClFN.sub.4: 442.870. Found: m/z=442.871.

3-(2-bromo-6-chlorophenyl)-6-(2-bromo-6-fluorophenyl)-1,2,4,5-tetrazine (41)

[0395] ##STR00087##

[0396] Rf=0.54 (dichloromethane-heptane=1:1 (v/v)).

[0397] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.73 (dd, J=8.08, 1.05 Hz, 1H), 7.64-7.59 (m, 2H), 7.54-7.41 (m, 2H), 7.33 (td, J=8.80, 1.05 Hz, 1H).

[0398] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=109.9.

[0399] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.5, 164.2 (d, J=1.3 Hz), 162.8 (d, J=256.2 Hz), 135.1, 134.0, 133.6 (d, J=9.1 Hz), 132.8, 131.7, 129.2 (d, J=3.7 Hz), 129.1, 123.9, 123.8 (d, J=17.4 Hz), 123.7 (d, J=2.7 Hz), 115.8 (d, J=21.2 Hz).

[0400] Elemental analysis: Calcd (%) for C.sub.14H.sub.6Br.sub.2ClFN.sub.4: C, 37.83, H, 1.36, N, 12.61. Found: C, 38.57, H, 1.86, N, 11.98.

[0401] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6Br.sub.2ClFN.sub.4: 442.870. Found: m/z=442.871.

3-(2-chloro-6-iodophenyl)-6-(2-fluoro-6-iodophenyl)-1,2,4,5-tetrazine (42)

[0402] ##STR00088##

[0403] Rf=0.57 (dichloromethane-heptane=1:1 (v/v)).

[0404] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=7.97 (dd, J=8.0, 1.0 Hz, 1H), 7.89-7.86 (m, 1H), 7.63 (dd, J=8.0, 1.0 Hz, 1H), 7.37-7.33 (m, 2H), 7.27 (t, J=8.10 Hz, 1H).

[0405] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=108.62.

[0406] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=168.1, 165.6 (d, J=1.4 Hz), 158.8 (d, J=256.9 Hz), 137.9, 137.4, 135.6 (d, J=3.7 Hz), 134.2, 134.0 (d, J=9.7 Hz), 133.1, 129.9, 127.2 (d, J=16.7 Hz), 116.6 (d, J=21.2 Hz), 97.4, 97.3 (d, J=0.9 Hz).

[0407] Elemental analysis: Calcd (%) for C.sub.14H.sub.6ClFI.sub.2N.sub.4: C, 31.23, H, 1.12, N, 10.40. Found: C, 31.76, H, 1.78, N, 9.63.

[0408] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.6ClFI.sub.2N.sub.4: 538.843. Found: m/z=538.844.

3-(2-chlorophenyl)-6-(2-bromo-6-fluorophenyl)-1,2,4,5-tetrazine (43)

[0409] ##STR00089##

[0410] Rf=0.38 (dichloromethane-heptane=1:1 (v/v)).

[0411] .sup.1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.08 (dd, J=8.0, 1.0 Hz, 1H), 7.85 (dd, J=8.0, 1.0 Hz, 1H), 7.62-7.43 (m, 4H), 7.27 (td, J=8.10, 1H Hz, 1H).

[0412] .sup.19F NMR (282 MHz, CDCl.sub.3): (ppm)=111.1.

[0413] .sup.13C NMR (75 MHz, CDCl.sub.3): (ppm)=166.4, 163.0 (d, J=255.5 Hz), 162.6 (d, J=1.4 Hz), 135.1 (d, J=3.5 Hz), 135.0, 133.5, 133.2 (d, J=9.7 Hz), 132.9, 132.5, 128.1, 126.2 (d, J=3.6 Hz), 122.7, 122.0 (d, J=7.3 Hz), 115.2 (d, J=21.3 Hz).

[0414] Elemental analysis: Calcd (%) for C.sub.14H.sub.7BrClFN.sub.4: C, 46.00, H, 1.93, N, 15.33. Found: C, 46.50, H, 2.05, N, 14.51.

[0415] HRMS+p ESI (m/z) [M+H.sup.+] Calcd for C.sub.14H.sub.7BrClFN.sub.4: 364.960. Found: m/z=364.960.

[0416] The halogenated and acetylated mono and polyfunctionalized compounds above-described are useful precursors for further organic and organometallic reactions as exemplified below with Suzuki-Miyaura cross-coupling towards ortho-arylated tetrazines 44-45. The exemplification with 44a-e and 45a-b validate a determining interest of the halogenated precursors.

EXAMPLE 3: FUNCTIONALIZATION OF COMPOUNDS OF FORMULA (I) WITH SUZUKI-MIYAURA CROSS-COUPLING REACTION

[0417] ##STR00090##

[0418] As a typical experiment, 3-(2-bromophenyl)-6-(2-fluorophenyl)-1,2,4,5-tetrazine (23.0 mg, 0.07 mmol), phenylboronic acid (17.1 mg, 0.14 mmol), Pd(dba).sub.2 (4.0 mg, 0.007 mmol) and K.sub.2CO.sub.3 (19.3 mg, 0.14 mmol) were introduced in a Schlenk tube, equipped with a magnetic stirring bar. Dry toluene (0.7 mL) was added, and the Schlenk tube purged several times with argon. The Schlenk tube was placed in a pre-heated oil bath at 110 C. and reactants were allowed to stir for 5 h. After cooling to room temperature, the reaction mixture was diluted with dichloromethane, and was washed three times with water. The combined organic layer was washed with water and dried over MgSO.sub.4. The solvent was removed in vacuo and the crude product was purified by silica gel column chromatography to afford 20 in 59% (13.6 mg) yield.

3-(2-fluorophenyl)-6-[(1,1-biphenyl)-2-yl]-1,2,4,5-tetrazine (44a)

[0419] ##STR00091##

[0420] Rf=0.50 (dichloromethane-heptane=7:3 (v/v)).

[0421] 1H NMR (300 MHz, CDCl.sub.3): (ppm)=8.24 (td, J=7.65, 1.78 Hz, 1H), 8.13-8.10 (m, 1H), 7.72-7.56 (m, 4H), 7.35 (td, J=7.65, 1.78 Hz, 1H), 7.30-7.26 (m, 4H), 7.16-7.13 (m, 2H).

[0422] 19F NMR (282 MHz, CDCl.sub.3): (ppm)=112.0.

[0423] 13C NMR (300 MHz, CDCl.sub.3): (ppm)=167.0 (d, J=0.8 Hz), 163.3 (d, J=259.6 Hz), 162.6 (d, J=5.8 Hz), 143.0, 140.5, 134.2 (d, J=8.7 Hz), 131.8, 131.6, 131.4, 131.3, 129.5, 128.6, 128.1, 127.4, 124.9 (d, J=3.9 Hz), 120.8 (d, J=9.9 Hz), 117.6 (d, J=21.6 Hz).

[0424] Elemental analysis: Calcd (%) for C20H13FN4: C, 73.16, H, 3.99, N, 17.06. Found: C, 72.64, H, 4.39, N, 16.83.

[0425] HRMS+p ESI (m/z) [M+H+] Calcd for C20H13FN.sub.4: 329.120. Found: m/z=329.120.