Synthesis of Naphthyridine and Azepine Backbones through Formal [4+3] and [4+2] Annulation via Cascade Ring-Opening/Cyclization Reaction of 2H-Azirines

A zinc-mediated cascade ring-opening cyclization of 2H-azirines and enolized-o-alkenylquinoline carbaldehydes for the synthesis of naphthyridine and azepine skeletons has been disclosed. The regioselectivity of the reaction can be switched from a seven- to a six-membered ring by shifting from two- to monosubstituted 2H-azirine. This transformation involves the construction of two C=C and C=N double bonds. This report describes 2H-azirine-dependent cascade annulation in formal [4+3], and [4+2] cyclization reactions.