N,N′-Dioxide–nickel(II) complex catalyzed asymmetric Michael addition of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-ketoesters

A direct asymmetric Michael addition of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-ketoesters could be efficiently catalyzed by an N,N′-dioxide–nickel(II) complex. A series of chiral warfarin derivatives were obtained in excellent yields (up to 99%) with high enantioselectivities (up to 90% ee) under mild conditions within shorter reaction time.