Copper(I)-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides with bicyclic alkenes.

A variety of tetrahydroquinoline-fused bicycles bearing multiple stereocenters are prepared in good yields with high diastereoselectivity through Cu2O-catalyzed [4 + 2] cycloaddition of aza-ortho-quinone methides (ao-QMs) with bicyclic alkenes. Mechanistic studies reveal that the Cu(i) catalyst not only promotes the formation of ao-QMs through a radical process by single electron transfer but also accelerates [4 + 2] cycloaddition. The reaction was easily performed on gram scale and the obtained tetrahydroquinoline-fused bicycles can be converted to diverse tetrahydroquinoline scaffolds.