A mixture of 90.5 parts of ethyl cis-4-[(4-chloro-2-methoxy-5-nitrobenzoyl)amino]-3-methoxy-1-piperidinecarboxylate, 3 parts of a solution of thiophene in methanol 4% and 400 parts of methanol was hydrogenated at normal pressure and at 50° C. with 5 parts of platinum-on-charcoal catalyst 5%. After the calculated amount of hydrogen was taken up, the catalyst was filtered off and the filtrate was evaporated. The residue was crystallized from 2-propanol. The product was filtered off and dried, yielding 80 parts (94%) of ethyl cis-4-[(5-amino-4-chloro-2-methoxybenzoyl)amino]-3-methoxy-1-piperidinecarboxylate: mp. 142.5° C. (interm. 14).
