Formation of N-acyl-N,N'-dicyclohexylureas from DCC and arenecarboxylic acids in the presence of hydroxybenzotriazole in CH_2Cl_2 at room temperature

摘要

The syntheses of N-acyl-N,N'-dicyclohexylureas from 1,3-dicyclohexylcarbodiimide and arenecarboxylic acids [p-XC_6H_4CO_2H (X = H or NO_2), 2-, 3- or 4-pyridinecarboxylic acid and pyrazinecarboxylic acid] in the presence of hydroxybenzotriazole in CH_2Cl_2 at room temperature are reported. The reactions proceed via the intermediacy of O-acyl-N,N'-dicyclohexylurea derivatives which undergo rapid O-acyl to N-acyl rearrangements. No acid anhydrides were detected. Under the same reaction conditions, the O-acyl derivative from the alkanecarboxylic acid, N-(benzyloxycarbonyl)-DL-pipecolic acid does not undergo rearrangement, as shown by the subsequent reaction with MeOH to give methyl N-(benzyloxycarbonyl)-DL-pipecolate. Characterisations were generally achieved by spectroscopic means, and specifically for N-(p-nitrobenzenecarbonyl)-N,N'-dicyclohexylurea by X-ray crystallography.