Organocatalytic regio- and enantioselective formal [4+2]-annulation of chiral nitrogen-containing dipoles

Abstract

Quinidine-catalyzed regio- and enantioselective formal [4 + 2]-cycloadditions of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with N-tosyl-2-methylenebut-3-enoates and 2-methylene-3-oxoalkanoates have been developed for the first time. The reaction features the in situ formation of chiral nitrogen-containing dipolar intermediates, a ring-opening/Michael addition/annulation cascade reaction and works well over a broad substrate scope to furnish the tetrahydroquinolines in high yields with high asymmetric induction under mild conditions.