Asymmetric [3 + 2] cycloaddition of donor–acceptor cyclopropanes with azadienes enabled by Brønsted base catalysis

Abstract

A chiral bifunctional Brønsted base-catalyzed enantioselective [3 + 2] cycloaddition of D–A cyclopropanes and azadienes is reported. A wide range of spiro-cyclopentane benzofurans bearing three contiguous stereogenic centers are obtained in excellent yields (up to 97%), moderate to excellent enantioselectivities (up to 95%) and moderate diastereoselectivities. The protocol features broad substrate scope, mild reaction conditions and high functional group tolerance.