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 hexahydropyrrolo3,2-c]quinolin-2-ones and hexahydropyridino3,2-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 BF₃·OEt₂-promoted dehydration in dichloromethane at room temperature. The hexahydropyrrolo3,2-c]quinolin-2-ones were formed as a single exo-stereoisomer in most cases and hexahydropyridino3,2-c]quinolin-2-ones were formed as a mixture of exo- and endo-isomers favoring the endo-diastereomer.