Diisopropylethylamine → 3-Diethylcarbamoyl-pyrrolidine-1-carboxylic acid 2,2,2-trichloro-ethyl ester

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A solution of 1-benzyl-pyrrolidine-3-carboxylic acid methyl ester (109.6 mg, 0.5 mmol) in 2N hydrochloric acid (3 mL) and dioxane (1 mL) was heated to 80-90° C. for 1 h. The solvent was evaporated under vacuum and the residue redissolved in dioxane/methanol/toluene and evaporated under vacuum. The residue was then heated under reflux in chloroform containing an excess of thionyl chloride for 1 h and then the solvent was evaporated under vacuum. The residue was dissolved in anhydrous dichloromethane (5 mL) and diethylamine (300 μL) was added. After 20 minutes the solvent was evaporated and the residue dissolved in dichloromethane, washed with dilute sodium hydroxide, dried over anhydrous sodium sulfate and evaporated under vacuum. This material was dissolved in anhydrous acetonitrile (2 mL) and 2,2,2-trichloroethyl chloroformate (1.1 eq, 76 μL) was added at room temperature. After 1.5 h a further aliquot of the chloroformate (0.52 eq., 36 μL) was added. After 30 minutes thin layer chromatography (5% methanol-dichloromethane) indicated that the reaction was still incomplete so a further aliquot of the chloroformate (0.52 eq., 36 μL) and N,N-diisopropylethylamine (0.2 eq., 20 μL) was added. After 1 h the reaction was diluted with dichloromethane, washed with dilute sodium hydroxide, dried over anhydrous sodium sulfate and evaporated under vacuum. The residue was purified by chromatography on silica gel eluting with 40:1 dichloromethane-methanol to give 3-diethylcarbamoyl-pyrrolidine-1-carboxylic acid 2,2,2-trichloro-ethyl ester (102.2 mg, 60%)

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