To a stirred and cooled (5° C.) suspension of 81 parts of 4-chloro-2-methoxy-5-nitrobenzoic acid in 1350 parts of trichloromethane were added first 35.4 parts of N,N-diethylethanamine and then 38 parts of ethyl carbonochloridate at a temperature below 5° C. The whole was stirred for 2 hours in an ice bath. A solution of 65 parts of ethyl cis-4-amino-3-methoxy-1-piperidinecarboxylate in 1125 parts of trichloromethane was added while the temperature was kept below 10° C. Stirring was continued first for 1 hour in an ice bath and then overnight at room temperature. The mixture was washed successively once with water, twice with a sodium hydroxide solution 5% and three times with water, dried, filtered and evaporated. The residue was crystallized from acetonitrile. The product was filtered off and dried, yielding 100 parts (75%) of ethyl cis-4-[(4-chloro-2-methoxy-5-nitro-benzoyl)amino]-3-methoxy-1-piperidinecarboxylate; mp. 181.3° C. (interm. 13).
