O.[OH-].[Na+].[NH2:4][CH:5]1[CH2:9][CH2:8][N:7]([C:10]([O:12][CH2:13][CH3:14])=[O:11])[CH2:6]1.C(Cl)(=O)OCC.[C:21](=S)=[S:22]>>[N:4]([CH:5]1[CH2:9][CH2:8][N:7]([C:10]([O:12][CH2:13][CH3:14])=[O:11])[CH2:6]1)=[C:21]=[S:22](a-2) To 192 parts of cooled water were added portionwise 12.8 parts of sodium hydroxide. Upon complete addition, 25.3 parts of carbon disulfide were added and stirring was continued for 30 minutes at 10° C. 55 Parts of ethyl 3-aminopyrrolidinecarboxylate were added and the whole was stirred for 30 minutes at 10° C. 34.8 Parts of ethyl carbonochloridate were added dropwise (exothermic reaction) and stirring was continued for 4 hours at 60° C. After cooling, the product was extracted with methylbenzene. The extract was washed twice with water, dried, filtered and evaporated. The residue was purified by column chromatography over silica gel using a mixture of dichloromethane and ethanol (99:1 and 100:0.5 by volume) as eluents. The pure fractions were collected and the eluent was evaporated at a warm water bath at 30° C., yielding 25 parts (39.0%) of ethyl 3-isothiocyanato-1-pyrrolidinecarboxylate as a residue (interm. 6).
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