Method for the preparation of diazoalkanes

Abstract

The present invention relates to a method of forming diazoalkanes. One aspect of the present invention provides a method for the production of a N-alkyl-N-nitroso compound from a starting material, comprising the use of a tribasic acid to acidify an amine. A second aspect of the present invention provides a method for the production of a diazoalkane, comprising reacting a N-alkyl-N-nitroso compound with a base and a phase transfer catalyst, wherein no organic solvent is used.

Claims

1. A method for the production of a diazoalkane, comprising reacting an N-alkyl-N-nitroso compound with a base and a phase transfer catalyst in a reaction mixture, wherein no organic solvent is used; the phase transfer catalyst is selected from the group consisting of quaternary ammonium salts and phosphonium salts; the N-alkyl-N- nitroso compound has the general formula: ##STR00011## wherein RI, R2, R3 and R4 are hydrogen, alkyl, alkenyl, alkoxy, alkoxylate, alkyloxy, alkenyloxy or alkoxyalkyl groups, R6 is an alkyl group and R.sup.5 is hydrogen or an alkyl group; and an organic by-product which is formed during diazoalkane production separates from the reaction mixture as a discrete phase, and wherein said base is present in aqueous solution at a concentration of between 10% and 50%.

2. The method according to claim 1, wherein the phase transfer catalyst is tetrabutyl ammonium bromide (TBAB).

3. The method according to claim 2, wherein the TBAB is used at a loading of between 0.1 mol % and 2 mol %.

4. The method according to claim 3, wherein the TBAB is used at a loading of 1 mol %.

5. The method according to claim 1, wherein the reaction occurs at a temperature of between 0 and 20 C.

6. The method according to claim 1, wherein the reaction occurs at a temperature of less than 10 C.

7. The method according to claim 5, wherein the reaction occurs at a temperature of 10 C.

8. The method according to claim 1, wherein the base is present at a concentration of 50% w/w.

9. The method according to claim 1, wherein the yield of the diazoalkane is above 75%.

10. The method according to claim 9, wherein the yield of the diazoalkane is approximately 90%.

11. The method according to claim 1, wherein the diazoalkane is diazomethane.

12. The method according to claim 1, wherein the N-alkyl-N-nitroso compound is a N-methyl-N-nitroso compound.

13. The method according to claim 1, wherein the by-product does not require purification after it has been recovered from the reaction mixture.

14. The method according to claim 1, wherein the organic by-product is used to produce a further N-alkyl-N-nitroso compound.

15. The method according to claim 1, wherein the organic by-product has the general formula: ##STR00012## wherein RI, R2, R3 and R4 are hydrogen, alkyl, alkenyl, alkoxy, alkoxylate, alkyloxy, alkenyloxy or alkoxyalkyl groups and R.sup.5 is hydrogen or an alkyl group.

16. The method according to claim 1, wherein the N-alkyl-N-nitroso compound is N-nitroso--methylaminoisobutyl methyl ketone (Liquizald) and wherein the organic by-product is mesityl oxide.

17. The method according to claim 1, wherein the reaction occurs in the presence of water.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) Preparation of a Diazoalkane from a N-alkyl-N-nitroso Compound

(2) ##STR00005##

(3) The preparation of a diazoalkane from a N-alkyl-N-nitroso compound using a base is well known in the prior art. An exemplary method for the preparation of a diazoalkane according to the present invention is outlined in Scheme 1 above. In the above embodiment, the diazoalkane is diazomethane, the N-alkyl-N-nitroso compound is Liquizald and the organic by-product of the reaction is mesityl oxide. The above method can be done continuously or in batches.

(4) The present invention includes the use of a phase transfer catalyst. The phase transfer catalyst is preferably present at a catalytic amount. Any known phase transfer catalyst can be used, such as quaternary ammonium, phosphonium salts, crown ethers and glycol ethers. Preferably, this phase transfer catalyst is TBAB. In one embodiment, TBAB is present at a loading of 1 mol %, though any loading of more than 0.1 mol %, preferably between 0.1 mol % and 2 mol % and even more preferably between 0.1 mol % and 1 mol % may be used. The phase transfer catalyst has been shown to advantageously affect the yield, significantly increasing the yield when compared to the yield of reactions without the catalyst.

(5) The above reaction occurs without the presence of organic solvents, which were previously thought to be necessary. Further, there is no need for the use of organic solvents to separate the reaction products after the reaction and no purification steps are necessary. The elimination of the need for organic solvents not only reduces the cost of the method of the present invention compared to those of the prior art, but also has advantageous environmental and waste disposal implications.

(6) In other embodiments, when R.sup.5 is R.sup.7, the organic by-product of the diazoalkane formation separates from the reaction mixture as a less dense upper phase, after the production of the diazoalkane. In a further preferred embodiment, the organic by-product can be easily removed from the reaction mixture by simple liquid-liquid separation. This is possible as there are no other organic compounds within the reaction mixture. In a further preferred embodiment, the organic by-product recovered in this manner is identical to the fresh material, as analysed by .sup.1H NMR, and so can be recycled.

(7) The base used in the above reaction can be any inorganic alkali metal base. Preferably, the base is sodium or potassium hydroxide. The base can be present at a concentration of between 10% and 50% w/w, preferably 50% w/w. Most preferably, the base is 50% aqueous potassium hydroxide.

(8) In one embodiment, the reaction occurs at a temperature of between 0 C. and 40 C., preferably between 0 C. and 20 C. and most preferably between 0 C. and 10 C. In a further embodiment, the reaction occurs at a temperature of 10 C.

(9) The yield of the diazoalkane from the above method is high. Preferably, the yield is above 75%. More preferably, the yield is around 90%.

(10) The diazoalkane product is preferably produced as a gas, so as to allow for convenient separation of the diazoalkane product and the reaction mixture. In a further embodiment, the diazoalkane may be collected in combination with nitrogen, due to nitrogen sparging.

(11) In one embodiment of the present invention, the above reaction is carried out with continual sparging with nitrogen gas sub-surface. Such sparging aids the mixing of the reaction mixture and helps displace the diazoalkane gas from the reaction mixture. Preferably, the flow rates of the sparge diluent gas are such that the concentration of the diazoalkane gas is maintained below an explosive level, especially when the diazoalkane is diazomethane. When the sparge diluent gas is nitrogen, the concentration of diazomethane in nitrogen is preferably below the explosive limit of 14.7%.

(12) In further embodiments, the above method is carried out at atmospheric pressure. In still further embodiments, the above method is carried out at a sub-atmospheric pressure.

(13) In one embodiment of the present invention, as shown in Scheme 1, Liquizald is treated with 50% aqueous potassium hydroxide and 1 mol % TBAB at a temperature of less than 10 C., to form diazomethane and mesityl oxide. Gas sparging with nitrogen gas sub-surface occurs continuously throughout the method.

(14) Preparation of a N-alkyl-N-nitroso Compound

(15) ##STR00006##

(16) The general method of adding an aliphatic amine to a starting material to form an intermediate amine, followed by the addition of an acid and an alkali metal nitrite to prepare a N-alkyl-N-nitroso compound is well known in the art. An exemplary method for the preparation of a N-alkyl-N-nitroso compound according to the present invention is outlined in Scheme 2 above. In the above embodiment, the N-alkyl-N-nitroso compound is Liquizald and the starting material is mesityl oxide. The above method can be done continuously or in batches.

(17) One aspect of the present invention involves the use of a tribasic acid to acidify an amine. Any tribasic acid may be used, such as phosphoric acid or citric acid. In a further embodiment, the tribasic acid is phosphoric acid. Preferably, the phosphoric acid is between 60% and 80% aqueous phosphoric acid, most preferably 75% aqueous phosphoric acid. It has been found that the use of a tribasic acid surprisingly reduces the acid contamination of the N-alkyl-N-nitroso product, as sub-stoichiometric quantities of acid can be used. Preferably, the acid contamination of the product is eliminated.

(18) Further, the yield of the above method has been shown to be high compared to the methods of the prior art. Preferably, the yield of the N-alkyl-N-nitroso compound is around 80%, without the need for an extraction step.

(19) Another aspect of the invention relates to the above method that does not include a purification step or an extraction step in order to obtain the end product. Instead, the N-alkyl-N-nitroso compound separates out from the reaction mixture after ageing as an upper organic phase. This is optimised by the fact that the sodium phosphate salts produced as a by-product of the reaction are close to saturation in the aqueous phase. The high level of salt saturation reduces the solubility of the N-alkyl-N-nitroso compound in the aqueous phase, ensuring high yields and clean separation of the product. The product can then be easily removed from the reaction mixture, without the use of further methods that may involve an additional organic solvent or a distillation reaction. Preferably, the reaction occurs at a temperature of between 15 C. and 25 C. during the stir out and separation stages.

(20) In one embodiment of the present invention, as shown in Scheme 2, mesityl oxide is reacted with 40% aqueous methylamine to form an intermediate amine. The intermediate amine is acidified with 75% aqueous phosphoric acid and then reacted with 30% aqueous sodium nitrite. Liquizald separates out from the reaction mixture after aging as an upper organic phase.

(21) Reagents suitable for use in the above method, such as alternative aliphatic amines, are well-known in the art. The preferred reagents for use in the above reaction are outlined in Table 1.

(22) TABLE-US-00001 TABLE 1 Source/Lot Strength Chemical MW number Wt (g) (%) Moles Equiv Mesityl 98.14 Acros 300 g 89.9%* 2.75 1.00 oxide 271933 Methylamine 31.06 Sigma 230 g 39.7% 2.94 1.07 (39.7%) S57254-448 aq solution Phosphoric 98.00 Aldrich 310.2 g 75% 2.37 0.86 acid (75%) S67971-039 Sodium 69.00 Sigma 771.3 g 30% 3.35 1.22 nitrite (30%) 26430JB *Ratio of / isomers by .sup.1H NMR

(23) Preparation of a Diazoalkane from a Starting Material with a N-Alkyl-N-Nitroso Compound Intermediate

(24) In a further aspect of the present invention, there is provided a method for the preparation of a diazoalkane from a starting material, with a N-alkyl-N-nitroso compound as an intermediate, comprising the reactions of the previous two aspects. In one embodiment, the starting material is mesityl oxide, an intermediate is Liquizald and the diazoalkane is diazomethane, as shown in Schemes 1 and 2.

(25) One embodiment of the present invention provides that, when R.sup.5 is R.sup.7, the starting material separates from the reaction mixture as a less dense upper phase, after the production of the diazoalkane. In a further preferred embodiment, the starting material can be easily removed from the reaction mixture by simple liquid-liquid separation. In a further preferred embodiment, the starting material recovered in this manner is identical to fresh material, as analysed by .sup.1H NMR. This starting material can then be used in subsequent reactions, without the need for purification.

(26) In further embodiments, the above method is carried out at atmospheric pressure. In still further embodiments, the above method is carried out at a sub-atmospheric pressure.

(27) The method of the present invention is cheaper than those disclosed in the prior art. For example, the method disclosed in WO01/47869 produces diazomethane at a cost of around 4.15 per mol. In contrast, the present invention produces diazomethane at a cost of around 0.62 per mol without mesityl oxide recycling and 0.28 per mol with mesityl oxide recycling.

Method for producing tert-butyl (S)-4-chloro-3-oxo-1-phenylbutan-2-ylcarbamate (Boc-CK) using diazomethane

(28) ##STR00007##

(29) In a final aspect of the present invention, there is provided a method of producing tert-butyl (S)-4-chloro-3-oxo-1-phenylbutan-2-ylcarbamate (Boc-CK), using diazomethane produced from the methods of the previous examples. Boc-CK is an intermediate used for the production of HIV protease inhibitors, such as Atazanavir and Fosamprenavir.

(30) In one embodiment, the diazomethane is produced from Liquizald, as shown in Scheme 3 above. The diazomethane produced from the reactions of the present invention is in the gas phase and so the above reactions can occur with substrates in different solvents if desired. This further demonstrates the versatility and the utility of the reaction of the present invention.

Examples

(31) Preparation of Liquizald

(32) A 2 L glass reactor was equipped with a 500 mL addition funnel, agitator, thermometer and cooling bath. 1. The reactor was charged with 39.7% aqueous methylamine solution (230 g) and cooled to 10 C. 2. When the temperature reached 7 C., addition of mesityl oxide (300 g) was started. The temperature was controlled at between 10 C. and 15 C. Total addition time was 57 minutes. 3. The clear pale orange solution was warmed to 22 C. over 5 minutes and then stirred at this temperature for 60 minutes. 4. The solution was cooled to 10 C. over 5 minutes. 75% Phosphoric acid (310.2 g) was added over 60 minutes. The temperature was maintained between 15 C. and 20 C. During the addition the mixture became more viscous. The pH at the end of the addition was 6.65. 5. 30% aqueous sodium nitrite (771.3 g) was added over 8 minutes at between 10 C. and 15 C. 6. The mixture was stirred at between 20 C. and 25 C. for 18.3 hours and then settled for 1 hour. 7. The lower aqueous phase (1122 g, pH=5.76) was separated from the upper product Liquizald phase (466.6 g, 73.4% active, 79% yield from mesityl oxide). The Liquizald phase was analysed by .sup.1H NMR in d6-DMSO, the results of which are shown in Table 2.

(33) TABLE-US-00002 TABLE 2 Compound % w/w by NMR Mesityl oxide 8.6% Liquizald 73.4% Water 18.3%

(34) This process is both robust and reproducible, as demonstrated in Table 3 below. This table shows the results of four additional repeats of the above method.

(35) TABLE-US-00003 TABLE 3 Active Crude Molar Assay (% w/w NMR) Yield Yield Liquizald Mesityl Oxide Water Experiment (g) (%) (%) (%) (%) 1 483.5 g 86.7% 78.1% 9.3% 12.6% 2 480.0 g 89.7% 81.3% 11.8% 6.9% 3 469.8 g 80.3% 74.3% 11.9% 13.7% 4 466.6 g 79.0% 73.4% 8.6% 18.0%

(36) This is in contrast to when a mono- or a di-basic acid is used. For example, when the above method was carried out with acetic acid instead of phosphoric acid, the Liquizald produced had the composition by .sup.1H NMR as shown in Table 4 below. The use of the Liquizald phase of Table 2 resulted in a 39% higher yield of diazomethane than when using the phase as outlined in Table 4.

(37) TABLE-US-00004 TABLE 4 Component Assay (% w/w by NMR) Mesityl oxide 13.1% Liquizald 79.5% Water 1.0% Acetic acid 6.4%

(38) The Liquizald phase produced by the above method can be used in the preparation of diazomethane from Liquizald, as discussed below, without any further purification steps.

(39) Preparation of Diazomethane from Liquizald

(40) A 100 mL reaction vessel was charged with 50% aqueous potassium hydroxide solution (10.0 g) and tetrabutyl ammonium bromide (TBAB) phase transfer catalyst. The solution was cooled to 10 C. whilst stirring. Liquizald (10.0 g) was added to the solution over 60 minutes and the reaction temperature was maintained at 10 C. whilst continually sparging with nitrogen gas sub-surface. The vent gases were sparged into 100 mL of 1 M benzoic acid in dimethoxyethane (DME). Once addition of Liquizald was complete, nitrogen sparging was continued for an additional 30 minutes. The concentration of residual benzoic acid was determined by titrating the DME solution with 0.5 M sodium hydroxide using phenolphthalein indicator. The yield of diazomethane was determined from the consumption of benzoic acid.

(41) Runs 1 to 4, as shown below in Table 5, used 1.0, 0.5, 0.1 and 0.0 mol % TBAB respectively. Run 5 used 1.0 mol % TBAB but achieved mass transfer of diazomethane by application of a vacuum (200 mbar) and a reduced nitrogen flow rate of 0.05 L/min. The resulting yields are shown in Table 5.

(42) TABLE-US-00005 TABLE 5 TBAB Loading Temperature Nitrogen Flow Diazomethane Run (mol %) ( C.) (L/min) Yield (%) 1 1.0 mol % 10 C. 0.5 L/min 90.6% 2 0.5 mol % 10 C. 0.5 L/min 86.8% 3 0.1 mol % 10 C. 0.5 L/min 79.8% 4 0.0 mol % 10 C. 0.5 L/min 2.2% 5 1.0 mol % 10 C. 0.05 L/min 92.7% and 200 mbar vacuum

(43) As shown in Table 5, the concentration of TBAB has a significant effect on the diazomethane yield, with the maximum yield being obtained at a TBAB loading of 1.0 mol %.

(44) Preparation of Diazomethane from Liquizald at Different Reaction TemperaturesKinetic Analysis

(45) All kinetic experiments were conducted using a 50 mL 3-neck round vessel equipped with a 15 mm10 mm magnetic stirrer bar. The vessel was charged with 50% KOH (20 g) and TBAB (0.3 g). The mixture was equilibrated to the desired reaction temperature over 10 to 15 minutes whilst being agitated at around 1000 rpm and sparged sub-surface with nitrogen at a rate of 0.55 L/min. The nitrogen residence time in the headspace was calculated to be 2.9 seconds.

(46) Liquizald (10 g crude, 7.34 g active) was added in one portion. The exiting diazomethane/nitrogen gas stream was bubbled into a solution of benzoic acid (6.0 g) in dichloromethane (150 mL) cooled to around 5 C. in a 500 mL vessel. The conversion of benzoic acid to methyl benzoate was continually monitored using a Mettler Toledo SiComp attenuated total reflectance ReactIR probe with a sampling interval of 60 seconds.

(47) Each reaction showed an induction period of between 1 and 6 minutes, which were entirely consistent with other hydroxide ion initiated reactions under phase transfer catalysed conditions (for example Org. Chem. 1983, 48, 1022-1025). The induction arises from the need for the [Q.sup.+OH.sup.] ion pair to reach an equilibrium concentration in the organic phase. The reactions followed pseudo first order kinetics after the initial induction period, with an activation energy (Ea) of 69.5 kJ mol.sup.31 1 (16.6 kcal mol.sup.1) and the pre-exponential factor (A) of 9.1810.sup.9 mol.sup.1s.sup.1. The half-lives across the temperature range investigated are shown in Table 6 below, along with the induction periods:

(48) TABLE-US-00006 TABLE 6 Temperature C. Half-life (mins) Induction Period (mins) 0 30.8 ~5.5 10 8.0 ~3.5 20 2.1 ~2.5 30 1.2 ~1.5 40 0.6 ~1.5

(49) Preparation of Diazomethane from Liquizald at Scale

(50) An appropriate glass-lined reaction vessel was charged with 50% KOH solution (1296 kg). TBAB catalyst (26.4 kg, 2 mol %) was then charged. The vessel contents were cooled to 10 C. and well agitated. Nitrogen gas was added sub-surface at a rate of 8 kg/hr and into the headspace of the vessel at a rate of 34 kg/hr. Liquizald (as 100% active) was added at a rate of 27 kg/hr. The exiting diazomethane/nitrogen gas stream was at a concentration of 10% v/v. The gas stream was passed through a gas-liquid separator and a packed scrubber tower attached to the vessel. A solution of substrate (for example Boc-mixed anhydride) flowed on a continuous recycle loop through the scrubber tower from a second vessel. At 10 C., the half-life of Liquizald is 8 minutes and with a Liquizald feed rate of 27 kg/hr there was no accumulation of Liquizald in the vessel.

(51) Diazomethane generated by this process is capable of converting 542 kg of Boc-mixed anhydride (as 100% active) in a 24 hour period.

Production of tert-butyl (S)-4-chloro-3-oxo-1-phenylbutan-2-ylcarbamate (Boc-CK), an Intermediate Used for the Production of HIV Protease Inhibitors Such as Atazanavir and Fosamprenavir, Using Diazomethane Generated from Liquizald

(52) Preparation of Boc-Mixed Anhydride

(53) ##STR00008##

(54) A 250 mL glass reactor was equipped with a 250 mL addition funnel, agitator, thermometer and cooling bath. 1. Boc-Phe (20.93 g) was dissolved in dichloromethane (100 mL) in a conical flask. N-methylmorpholine (8.78 g) was added in one portion with stirring. The clear colourless solution was transferred to the addition funnel. 2. The reactor was charged with a solution of ethyl chloroformate (10.27 g) in dichloromethane (42 mL) and cooled to between 5 C. and 10 C. 3. Boc-Phe/NMM/dichloromethane was added over 2 minutes at 5 C. to 10 C. Once addition was complete the mixture was stirred for 5 minutes. 4. The reaction mixture which contained white solids of precipitated N-methylmorpholine hydrochloride was transferred into a 500 mL separating funnel. The mixture was washed with water (50 g) and then brine (50 g). The lower clear colourless mixed anhydride solution was transferred into a 500 mL reaction vessel and used as described below. 5. A sample was analysed by HPLC which indicated an area % response of 98.3% for Boc-MA.

(55) Preparation of Diazomethane and Boc-Diazoketone

(56) ##STR00009## 1. A 250 mL 3-neck vessel was equipped with a magnetic stirrer, nitrogen sparge tube, Liquizald addition syringe pump and diazomethane vent sparge pipe. The vessel was charged with 50% KOH solution (50 g) and TBAB (0.75 g) and the mixture cooled to 10 C. 2. Nitrogen gas was sparged into the solution using a porosity 2 sinter at a flow rate of 0.4 L/min (controlled by a VA meter). 3. Liquizald (50 g) was added using a syringe pump over 120 minutes (flow rate=0.42 g/min). 4. The diazomethane/nitrogen gas produced in the reactor was vented via a porosity 2 sinter into a 500 mL 3-neck vessel charged with the mixed anhydride solution prepared above. The reaction temperature was maintained at 5 C. The vessel was equipped with a magnetic stirrer and dry-ice condenser. Note: the condenser vent gases were analysed using a type 1301 photoacoustic FT-IR gas analyser for residual diazomethane.

(57) Once addition of Liquizald was complete the sparging of nitrogen was continued for 25 minutes. The clear pale yellow diazoketone solution was stirred at 5 C. for a further 2 hours. HPLC analysis indicated an area % response of 96.9% for Boc-DAK. The DAK was used directly in the next stage.

(58) Preparation of Boc-Chloroketone from Boc-Diazoketone

(59) ##STR00010## 1. The Boc-DAK solution from the previous method was cooled to 5 C. Concentrated (37%) hydrochloric acid was added in small aliquots. After 14.0 g of acid had been added, all the Boc-DAK had been consumed. Note nitrogen gas was evolved during HCl addition. 2. The clear pale yellow solution was transferred into a 500 mL separating flask. The lower product solution was separated from the upper orange aqueous phase (8.3 g, pH<1). 3. The product phase was washed with water (50 mL). The aqueous wash had a pH of around 7. 4. The product solution was washed with brine (50 mL). 5. The clear pale yellow Boc-CK solution (237.7 g) was concentrated to afford a thick yellow slurry (61.7 g). 6. The slurry was mixed with heptanes (158 g) and warmed to 65 C. to dissolve all solids. The clear pale yellow solution was cooled initially to ambient temperature and then further cooled for one hour at 0 C. to 5 C. 7. A very thick white crystalline mass had formed which was filtered through a 54 micron paper using a Buchner filter. The cake was washed with pre-chilled heptanes (225 g) and then sucked dry on the filter for 21 hours. 8. Boc-CK (19.6 g) was obtained as a white solid with an area % response by HPLC of 97.2%. Molar yield from Boc-Phe=81.1% (based on the area % assay).

(60) Preparation of Boc-Mixed Anhydride in Toluene

(61) A 1500 mL glass reactor was equipped with a 500 mL addition funnel, agitator, thermometer and cooling bath. 1. Boc-Phe (63 g) was dissolved/suspended in toluene (354 mL) in a conical flask. N-methylmorpholine (26.4 g) was added in one portion with stirring. The clear colourless solution was transferred to the addition funnel. 2. The reactor was charged with a solution of ethyl chloroformate (30.9 g) in toluene (300 mL) and cooled to between 5 and 10 C. 3. The Boc-Phe/NMM/toluene solution was then added over 2 minutes at 50 to 10 C. Once addition was complete, the mixture was stirred for 5 minutes. 4. The reaction mixture which contained white solids of precipitated N-methylmorpholine hydrochloride was transferred into a 2000 mL separating funnel. The mixture was washed with water (250 mL) and then brine (250 mL). The upper slightly cloudy colourless mixed anhydride phase was dried using around 3 g of anhydrous magnesium sulphate to give a clear colourless solution of Boc-mixed anhydride, which was transferred to a 1000 mL reaction vessel and used as described below.

(62) Preparation of Diazomethane and Boc-Diazoketone in Toluene 1. A 500 mL 3-neck vessel was equipped with a magnetic stirrer, nitrogen sparge tube, Liquizald addition syringe pump and diazomethane vent sparge pipe. The vessel was charged with 50% KOH solution (216 g) and TBAB (4.4 g). The TBAB did not dissolve. The mixture was cooled using an ice/water bath to 10 C. 2. Nitrogen gas was sparged into the solution sub-surface using a porosity 2 sinter at a flow rate of 600 mL/min (controlled by a VA meter). 3. Liquizald (146.6 g) was added using a syringe pump over 4 hours (with a flow rate of 36.3 g/hr). 4. The diazomethane/nitrogen gas produced in the reactor was vented via a 3 mm id glass pipe into a 1000 mL 3-neck vessel charged with the Boc-mixed anhydride solution prepared above. The reaction temperature was maintained at 5 C. The vessel was equipped with a magnetic stirrer, dry-ice condenser and SiComp ReactIR probe. On-line FTIR spectra were collected at 1 minute intervals. The condenser vent gases were analysed using a type 1301 photoacoustic FT-IR gas analyser for residual diazomethane. 5. Samples of the MA/DAK reaction solution were taken for HPLC analysis at regular intervals throughout the four hour Liquizald addition. 6. Once Liquizald addition was complete, sparging of nitrogen was continued until the ReactIR profile remained level. Both on-line ReactIR data and off-line HPLC data indicated smooth conversion. The ReactIR profiles flattened approximately 3 hours after the Liquizald feed had stopped. No diazomethane was observed in solution by ReactIR. The vent gases were analysed using a 1301 photoacoustic gas analyser. This indicated a low parts per million concentration of diazomethane in the vent to scrubber.

(63) Preparation of Diazomethane and Boc-Chloroketone from Boc-Diazoketone in Toluene 1. The Boc-DAK solution prepared above was cooled to 5 C. Concentrated (37%) hydrochloric acid was added in 4.68 g aliquots and after each addition the reaction mixture was sampled for HPLC analysis. After 24.4 g of acid had been added, all of the Boc-DAK had been consumed. Nitrogen gas was evolved after each aliquot of HCl was added. 2. The clear pale yellow solution was transferred into a 2000 mL separating flask. The lower aqueous phase was separated (17 g, pH<1). 3. The product phase was washed sequentially with water (100 mL):

(64) TABLE-US-00007 Wash Volume (mL) pH 1 100 mL 1.5 2 100 mL 2.7 3 100 mL 5.3 4 100 mL 6.4 4. The clear pale yellow Boc-CK toluene solution (620.8 g) was concentrated to 200 g using a RFE at a bath temperature of 43 C. under vacuum. The straw yellow solution was initially cooled to 20 C. and held for three hours after which time a solid crystalline mass had formed. The mixture was cooled to 10 C. for two hours and then filtered and the cake sucked dry overnight. Boc-CK (61 g) was obtained as a white solid with an area % response by HPLC of 89%. The molar yield from Boc-Phe was 76% (based on the area % assay).