Catalytic Asymmetric Direct Vinylogous Aldol Reaction of Isatins with β,γ-Unsaturated Butenolides.

A direct asymmetric vinylogous aldol reaction of nonactivated natural α-angelica lactone to isatins has been developed. With a N,N'-dioxide-Sc(OTf)3 complex as catalyst, a variety of δ-hydroxy butenolides bearing congested adjacent tetrasubstituted stereocenters were obtained in good yields with high diastereoselectivities and excellent enantioselectivities. Besides, a possible transition state was proposed to explain the origin of the asymmetric induction.