N-Acyl imine and enamide intermediates in the palladium-catalyzed amidocarbonylation reaction

N-Acyl imines and enamides have been synthesized and subjected to the reaction conditions for palladium-catalyzed amidocarbonylation of aldehydes. These compounds were competent substrates resulting in the formation of N-acyl amino acids; however, the presence of water was found to be necessary. Direct study of the same amidocarbonylation reaction revealed that enamides could be detected during the course of the reaction. A slight enhancement in the yield of the amidocarbonylation is observed in the presence of radical inhibitors ruling out a meaningful radical pathway. The results are most consistent with a mechanism involving complex equilibration of the starting materials to a number of intermediates which can converge to a haloamidal that subsequently undergoes a palladium insertion.