Synthesis of a triangulene ring system and derivatives thereof

Abstract

A three step synthesis of the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation (triangulenium cation) is effected by cascade cyclization of a tetra-benzyl alcohol precursor in triflic acid solution. This cation is easily observed by NMR and optical spectroscopy. Quenching of the cation into basic solutions or by hydride transfer from triethylsilane provides access to stable dihydro and tetrahydro[3]triangulenes. This route makes several [3]triangulene precursors more readily available for development of new applications in the field of molecular electronics.

Claims

1. A method for the preparation of 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation comprising: reacting an allyl-protected benzyl alcohol having the following structure: ##STR00007## with diethyl carbonate to form tris(2-((allyloxy)methyl)phenyl)methanol having the following structure: ##STR00008## deprotecting said tris(2-((allyloxy)methyl)phenyl)methanol in the presence of a palladium catalyst to produce ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol having the following structure: ##STR00009## converting by cyclization said ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol in the presence of triflic acid to produce the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation having the following structure: ##STR00010##

2. The method of claim 1 wherein said 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation is converted by contacting with Et.sub.3SiH/DCM at 0° C. to produce 3a.sup.2,4,8,12-tetrahydrodibenzo[cd,mn]pyrene having the following structure: ##STR00011##

3. The method of claim 1 wherein said 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation is converted by contacting with Et.sub.3SiH/DCM or NaHCO.sub.3 at 0° C. to produce 1,2,3,8-tetrahydrodibenzo[cd,mn]pyrene having the following structure: ##STR00012##

4. The method of claim 1 wherein said 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation is converted by contacting with Et.sub.3SiH/DCM or NaHCO.sub.3 or Et.sub.3NDCM at 0° C. to produce 1,8-dihydrodibenzo[cd,mn]pyrene having the following structure: ##STR00013##

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Triangular-shaped aromatic hydrocarbons where 1 is the phenalenyl radical and 2 and 3 are higher homologs.

(2) FIG. 2. Route for the preparation of the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation.

(3) FIG. 3. Preparation of di- and trihydrotriangulenes from the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) FIG. 2 summarizes the preferred route herein for the preparation of the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation. Taking advantage of the 3-fold symmetry of this structure, condensation of three equivalents of allyl protected benzyl alcohol 4 using n-butyl lithium followed by diethyl carbonate afforded tris(2-((allyloxy)methyl)phenyl)methanol 5 in a single synthetic step and relatively high yield 90%). Palladium catalyzed deprotection yielded the crystalline tetraol 6. Attempts at cyclization of 6 with catalysts and acidic media known to promote benzyl cation chemistry afforded incomplete cyclization or mixtures of the desired products and oligomers, with mass balances in the 20-50% range. As one example, exposure of 5 to polyphosphoric acid at 100° C. gave nearly quantitative conversion to 7. This result supports initial ionization at the central hydroxyl group.

(5) When tetraol 6 was added to an NMR tube containing 1 M TfOD (deuterated triflic acid) in DCE-d.sub.4 (deuterated dichloroethane), the fluorescent green solution exhibited very simple .sup.1H and .sup.13C NMR spectra, displaying three unique hydrogens and six carbon signals for the major species in solution. These data support formation of the symmetrical 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation (8). Density functional theory (DFT) computations on 8 support a D.sub.3b symmetrical structure, with predicted NMR chemical shifts in good agreement with experiment. The optical spectrum of 8 also supports this structure. NMR samples of cation 8 were stable for >24 h. As expected, exposure of the partly cyclized structure 7 to the same acidic reaction conditions led cleanly to 8.

Preparation of Dihydro And Tetrahydro[3]triangulenes

(6) After preparation of cation 8 by the method described above, neutralization by hydride transfer during slow addition to triethylsilane in DCM produced a mixture of hydrocarbons 9-11 in 96% isolated yield. See FIG. 3 Neutralization of 8 by addition to saturated aqueous NaHCO.sub.3 afforded a mixture of compounds 10 and 11, while slow addition to Et.sub.3N gave a 66% isolated yield of pure compound 11.

(7) See Table 1 below.

(8) TABLE-US-00001 TABLE 1 Synthesis of Dihydro and Tetrahydro[3]triangulenes Total Yield Et.sub.3SiH/DCM 0° C. 38  9 49 96% sat. NaHCO.sub.3 0° C. — 27 53 80% Et.sub.3N/DCM 0° C. — — 66 66%

(9) The three compounds 9, 10 and 11 were separable by chromatography, providing pure samples of each hydrocarbon. Dihydrotriangulene 11 has been described previously as a precursor to compound 2.sup.26 and its dianion.sup.13 but was prepared according to the earlier synthetic route of Clar. The spectral data match those reported. 1,2,3,8-Tetrahydrotriangulene 10, is believed to be a new derivative of olympicene,.sup.27 but with one additional saturated ring. Isomeric tetrahydrotriangulene 9 is also believed to be a new substance, characterized by its NMR spectra. The central methine hydrogen in 9 appears as a quartet (J=5.5 Hz) in the NMR because of long range coupling to the pseudoaxial methylene hydrogens. .sup.5J Homoallylic coupling has been described previously in 1,4-cyclohexadienes..sup.28

EXPERIMENTAL

1-((allyloxy)methyl)-2-bromobenzene (4

(10) To an oven-dried 500 mL flask purged with nitrogen and cooled to 0° C. was added NaH (60% w/w, 7.04 g, 176 mmol) and anhydrous THF (50 mL) to give a grey suspension. A solution of 2-bromobenzyl alcohol (16.4 g, 88 mmol) in anhydrous THF (126 mL) was added dropwise via addition funnel and sonicated at 0° C. for 1 hr. Allyl bromide (15.2 mL, 176 mmol) was added dropwise then the mixture was sonicated at room temperature overnight to give a chalky white suspension. This was cooled to 0° C., quenched with water, extracted with DCM, washed with brine, dried with MgSO.sub.4, gravity filtered, and condensed to give an orange oil. This oil was purified via vacuum distillation to give the desired product as a colorless oil (19.4 g, 97% yield, bp 58° C. at 0.17 torr). .sup.1H NMR (500 MHz, CDCl.sub.3): δ 7.56-7.51 (m, 2H), 7.32 (td, J=7.53, 1.18 Hz, 1H), 7.17-7.12 (m, 1H), 6.00 (ddt, J=17.21, 10.43, 5.55 Hz, 1H), 5.37 (dq, J=17.24, 1.65 Hz, 1H) 5.27-5.23 (m, 1H), 4.60 (s, 2H), 4.13 (dt, J=5.56, 1.44 Hz, 2H); .sup.13C NMR (500 MHz, CDCl.sub.3): δ 137.8, 134.6, 132.6, 129.1, 128.9, 127.5, 122.7, 117.3, 71.8, 71.48.

tris(2-((allyloxy)methyl)phenyl)methanol (5

(11) To an oven-dried 500 mL flask purged with nitrogen was added a solution of 1-((allyloxy)methyl)-2-bromobenzene (4) (18.3 g, 81 mmol) in anhydrous THF (208 mL) and the mixture was cooled to −78° C. n-BuLi (2.5 M, 35.6 mL, 89 mmol) was added dropwise over 30 min and the mixture was stirred at −78° C. for 1 hour to give a pale yellow solution. Freshly distilled diethyl carbonate (3.28 mL, 27 mmol) was added dropwise followed by stirring at −78° C. for 1 hour to give a bright orange solution. This was heated to 50° C. and stirred over night to give a yellow suspension. The crude product was cooled to 0° C., quenched with sat. aqueous NH.sub.4Cl, extracted with DCM, dried with MgSO.sub.4, gravity filtered, and condensed to give an orange oil. The impurities were removed by vacuum distillation to give the desired product as a viscous orange oil (12.05 g, 95% yield). .sup.1H NMR (500 MHz, CDCl.sub.3): δ 7.65 (d, J=6.70 Hz, 3H), 7.33 (td, J=7.49, 1.23 Hz, 3H), 7.09 (td, J=7.69, 1.33 Hz, 3H), 6.68 (d, J=7.67 Hz, 3H), 6.33 (s, 1H), 5.79 (ddt, J=17.16, 10.56, 5.31 Hz, 3H), 5.17 (dq, J=17.24, 1.62 Hz, 3H), 5.10 (dq, J=10.40, 1.33 Hz, 3H), 4.64 (d, J=13.21, 3H), 4.39 (d, J=13.23, 3H), 3.81 (dddt, J=41.37, 12.70, 5.58, 1.37 Hz, 6H); .sup.13C NMR (126 MHz, CDCl.sub.3): δ 144.6, 138.2, 134.4, 129.9, 129.0, 127.8, 126.8, 117.0, 85.5, 71.3, 71.0; HRMS (ESI/Q-TOF) m/z: [M+Na]+ Calcd for C.sub.31H.sub.34O.sub.4Na 493.2355; Found 493.2351.

((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol (6

(12) To an oven-dried 250 mL flask purged with nitrogen was added Pd(PPh.sub.3).sub.4 (0.049 g, 0.04 mmol) and MeOH (50 mL). A solution of tris(2-((allyloxy)methyl)phenyl)methanol (5) (2.0 g, 4.2 mmol) in MeOH (67 mL) was added followed by stirring at room temperature for 15 min. K.sub.2CO.sub.3 (10.5 g, 75.6 mmol) was added and the yellow suspension was heated to reflux. After 1 hour, a second equivalent of Pd(PPh.sub.3).sub.4 was added and this process was repeated twice more for a total of four equivalents (0.196 g, 0.17 mmol, 4 mol %). The mixture was stirred at reflux overnight to give a yellow suspension. This was cooled to room temperature, condensed to remove MeOH, washed with sat. aqueous NH.sub.4Cl, extracted with DCM, and flushed through a silica plug with ethyl acetate. The filtrate was condensed to give an orange slurry, which was dissolved in a minimum volume of DCM, then hexane was added to give a white precipitate. This was vacuum filtered and rinsed with cold hexane to give the desired product as a white solid (1.02 g, 69% yield, mp 182-184° C.). .sup.1H NMR (400 MHz, DMSO-d.sub.6): δ 7.69-7.62 (m, 3H), 7.33 (td, J=7.50, 1.18 Hz, 3H), 7.16 (s, 1H), 7.09 (td, J=7.74, 1.30 Hz, 3H), 6.56 (d, J=7.73 Hz, 3H), 5.31 (t, J=5.26 Hz, 3H), 4.34 (ddd, J=52.82, 14.18, 4.90 Hz, 6H); .sup.13C NMR (101 MHz, DMSO-d.sub.6): δ 143.48, 141.71, 128.03, 128.03, 127.44, 126.04, 84.99, 62.11; HRMS (ESI/Q-TOF) m/z: [M+Na]+ Calcd for C.sub.22H.sub.22O.sub.4Na 373.1400; Found 373.1404.

((1,3-dihydroisobenzofuran-1,1-diyl)bis(2,1-phenylene))dimethanol (7

(13) To a 50 mL flask was added water (2.8 mL), PPA (0.28 mL) and DCE (20 mL). The colorless solution was heated to reflux and a solution of ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol (6) (0.100 g, 0.28 mmol) in DCE (8 mL) was added carefully followed by refluxing overnight (18 hours). The resultant opaque solution was cooled to room temperature, diluted with water, extracted with DCM, dried with MgSO.sub.4, gravity filtered, and condensed to give pure the spirocycle 7 as an off-white solid (0.093 g, 97% yield, mp 126-130° C.). NMR (400 MHz, CDCl.sub.3): δ 7.51 (d, J=7.12 Hz, 2H), 7.40-7.27 (m, 5H), 7.14 (td, J=7.66 1.42 Hz), 6.89 (d, J=7.52 Hz, 1H), 6.83 (d, J=7.63 Hz, 2H) 5.10 (s, 2H), 4.38 (s, 4H), 2.96 (s, 2H) .sup.13C NMR (101 MHz, CDCl.sub.3): δ 142.67, 141.46, 140.27, 138.84, 131.63, 128.84, 128.38, 128.06, 127.65, 127.22, 124.96, 121.39, 96.26, 70.64, 63.84; HRMS (ESI/Q-TOF) m/z: [M+Na]+ Calcd for C.sub.22H.sub.20O.sub.3Na 355.1310; Found 355.1311

8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.SUP.2.-ylium cation (8

(14) To a nitrogen-flushed NMR tube was added a solution of ((hydroxymethanetriyl)tris(benzene-2, 1-diyl))trimethanol (6) (0.018 g, 0.05 mmol) in 1,2-dichloroethane-d.sub.4 (1.0 mL) and triflic acid-d (0.09 mL, 1.0 mmol) to give a dark green solution. This was identified as the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a.sup.2-ylium cation. The same results were observed when using these reaction conditions on internally cyclized product (7) and tetrahydrotriangulene (9). .sup.1H NMR (400 MHz, 1,2-dichloromethane-d.sub.4): δ 8.11 (t, J=7.65 Hz, 3H), 7.89 (d, 7.71 Hz, 6H), 5.03 (s, 6H); NMR (101 MHz, 1,2-dichloromethane-d.sub.4): δ 147.03, 139.25, 128.96, 123.32, 120.16, 116.99, 113.83, 36.93. UV-VIS λ.sub.max 404.5, 463, 5 (sh) nm.

Synthesis of 3a.SUP.2.,4,8,12-tetrahydrodibenzo[cd,mn]pyrene (9

(15) To an oven-dried 100 mL flask purged with nitrogen was added ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol (6) (0.058 g, 0.16 mmol) and DCM (33 mL) to give a colorless solution. Triflic acid (2.9 mL, 32.8 mmol) was added turning the solution dark green. This was transferred to an addition funnel and slowly added to a solution of triethylsilane (10.0 mL, 62.6 mmol) in DCM (28 mL) over 30 min at 0° C. to give a yellow solution. Water was added (100 mL) to give a bright yellow-green solution. The mixture was extracted with DCM, dried over MgSO.sub.4, gravity filtered, and condensed to give a yellow oil. The crude product was purified by CombiFlash (100% hexanes) to afford 1,2,3,8-tetrahydrodibenzo[cd,mn]pyrene (10) (0.004 g, 9% yield), 1,8-dihydrodibenzo[cd,mn]pyrene (11) (0.022 g, 49% yield), and tetrahydrotriangulene (9) as an orange solid (0.017 g, 38% yield). 3a.sup.2,4,8,12-tetrahydrodibenzo[cd,mn]pyrene .sup.1H NMR (400 MHz, CDCl.sub.3): δ 7.25-7.23 (m, 9H), 7.21-7.63 (m, 1H), 4.18 (dd, J=18.08, 4.69 Hz, 3H), 4.06 (d, J=17.92); .sup.13C NMR (101 MHz, CDCl.sub.3): δ 135.61, 133.95, 126.75, 125.61, 36.43, 35.99; HRMS (EI.sup.+/Q-TOF) m/z: [M]+ Calcd for C.sub.22H.sub.16 280.1252; Found 280.1255.

Synthesis of 1,2,3,8-tetrahydrodibenzo[cd,mn]pyrene (10

(16) To an oven-dried 50 mL flask was added a solution of ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol (6) (0.100 g, 0.28 mmol) in DCM (28 mL). TfOH (1.0 mL, 11.3 mmol) was carefully added and the resultant dark green solution was stirred at room temperature for 5 minutes. This was transferred to an addition funnel and slowly added to a solution of sat. NaHCO.sub.3 (100 mL) at 0° C. over the course of 30 min to give a dark green solution. This was extracted with DCM, dried with MgSO.sub.4, gravity filtered and condensed to give a dark green solid. The crude product was purified by CombiFlash (100% hexanes) to afford tetrahydrotriangulene 10 as a bright yellow solid (0.021 g, 27% yield) and 1,8-dihydrodibenzo[cd,mn]pyrene (11) as a bright yellow solid (0.041 g 53% yield). 1,2,3,8-tetrahydrodibenzo[cd,mn]pyrene (10).sup.1H NMR (500 MHz, CDCl.sub.3): δ 7.66-7.63 (m, 2H), 7.57 (s, 2H), 7.49-7.45 (m, 2H), 7.39 (dq, J=7.15, 1.45 Hz, 2H), 4.94 (s, 2H), 3.24-3.18 (m, 4H), 2.16-2.11 (m, 2H); .sup.13C NMR (101 MHz, CDCl.sub.3): δ 133.96, 133.25, 130.90, 126.48, 125.56, 125.34, 124.92, 123.90, 123.53, 123.44, 33.44, 31.06, 22.47; HRMS (ESI/FTMS) m/z: [M-H]+ Calcd for C.sub.22H.sub.15 279.1170; Found 279.1172.

Synthesis of 1,8-dihydrodibenzo[cd,mn]pyrene (11

(17) To an oven-dried 250 mL flask was added a solution of ((hydroxymethanetriyl)tris(benzene-2,1-diyl))trimethanol (6) (0.500 g, 1.4 mmol) in DCM (140 mL). TfOH (6.2 mL, 70 mmol) was carefully added over 20 minutes and the resultant dark green solution was stirred at room temperature for 5 minutes. This was transferred to an addition funnel and slowly added to a solution of triethylamine (19.5 mL, 140 mmol) in DCM (280 mL) at 0° C. over the course of 2 hours to give a brown-yellow solution. The reaction mixture was diluted with water (200 mL), extracted with DCM, dried with MgSO.sub.4, gravity filtered, and condensed to give a brown solid. The crude product was purified by CombiFlash (100% hexane) to afford 1,8-dihydrodibenzo[cd,mn]pyrene as a bright yellow solid (0.256 g, 66% yield) estimated to be >95% pure by NMR. .sup.1H NMR (400 MHz, CDCl.sub.3): δ 7.64-7.58 (m, 3H), 7.45 (dt, J=13.16, 7.53 Hz, 2H), 7.40-7.33 (m, 3H), 6.74-6.69 (m, 111), 6.15 (dt, J=10.07, 4.01 Hz), 4.90 (s, 2H), 4.11 (s, 2H); .sup.13C NMR (101 MHz, CDCl.sub.3): δ 134.20, 134.13, 132.55, 132.14, 132.05, 130.47, 128.07, 127.91, 127.75, 126.98, 126.81, 126.63, 125.99, 125.47, 125.23, 125.03, 124.79, 124.52, 124.45, 123.25, 34.25, 31.91; HRMS (EI.sup.+/Q-TOF) m/z: [M]+ Calcd for C.sub.22H.sub.14 278.1096; Found 278.1100.

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