[OH-].[Na+].O.[NH2:4][CH:5]1[CH2:10][CH2:9][N:8]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:7][CH2:6]1.C(Cl)(=O)OCC.[C:22](=S)=[S:23]>>[N:4]([CH:5]1[CH2:6][CH2:7][N:8]([C:11]([O:13][CH2:14][CH3:15])=[O:12])[CH2:9][CH2:10]1)=[C:22]=[S:23]To a stirred and cooled mixture of 4 parts of sodium hydroxide in 60 parts of water were added successively 7.9 parts of carbon disulfide and 17.2 parts of ethyl 4-amino-1-piperidinecarboxylate at a temperature below 10° C. Stirring was continued for 30 minutes at this temperature. Then there were added dropwise 10.9 parts of ethyl carbonochloridate (exothermic reaction: temp. rises to about 35° C.). Upon completion, stirring was continued for 2 hours at 60° C. The reaction mixture was cooled and the product was extracted with methylbenzene. The extract was dried, filtered and evaporated, yielding 22 parts (100%) of ethyl 4-isothiocyanato-1-piperidinecarboxylate as a residue (intermediate 26).
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