One-pot synthesis of pyrrolidino- and piperidinoquinolinones by three-component aza-Diels–Alder reactions of in situ generated N-arylimines and cyclic enamides

An efficient synthesis of hexahydropyrrolo[3,2- c ]quinolin-2-ones and hexahydropyridino[3,2- c ]quinolin-2-ones has been developed in moderate to high yields by one-pot two-step aza-Diels–Alder reactions of N -arylimines, formed in situ from anilines and benzaldehydes, with cyclic enamides, formed in situ from 5-hydroxypyrrolidin-2-ones and 6-hydroxypiperidin-2-ones by BF 3 ·OEt 2 -promoted dehydration in dichloromethane at room temperature. The hexahydropyrrolo[3,2- c ]quinolin-2-ones were formed as a single exo -stereoisomer in most cases and hexahydropyridino[3,2- c ]quinolin-2-ones were formed as a mixture of exo - and endo -isomers favoring the endo -diastereomer.