Synthesis of Bridged N,O-Heterocyclic 1,6-Epoxybenzo[c]azocines via Migration-Annulation Cascade Reaction of -Imino Rhodium Carbenes

A rhodium-catalyzed cascade migration-annulation reaction of 1-sulfonyl-1,2,3-triazole has been developed. As the key step, the 1,3-sulfinate migration of & alpha;-imino rhodium carbene yielded an extended zwitterion, which was intramolecularly trapped by aldehyde group furnishing bridged N,O-heterocyclic 1,6-epoxybenzo[c]azocine as the [5+2] cyclization product. This migration-annulation strategy provides more flexibility for heterocycle synthesis and medium-sized ring construction, especially for the construction of polycycles with complex skeletons.