Imidazo[1,5-a]pyridin-3-ylidene-Catalyzed Oxidative Esterification of Aldehydes: Remarkable Electronic Effect Regarding π-Accepting Character of Ring-Fused N-Heterocyclic Carbene

Abstract Imidazo[1,5-a]pyrid-3-ylidene (IPC)-catalyzed oxidative esterification of aldehydes was investigated. A series of IPCs showed good catalytic activity, in particular, sterically hindered ones. Substituents on the 3-position of imidazo[1,5-a]pyridine ring significantly influenced its catalytic activity, and electron-withdrawing substituent accelerated the reaction.