Asymmetric [3 + 2] Cycloaddition of Methyleneindolinones with N,N′-Cyclic Azomethine Imines Catalyzed by a N,N′-Dioxide–Mg(OTf)2 Complex

A highly efficient chiral N,N'-dioxide-Mg(OTf)2 catalyst system has been developed for the asymmetric 1,3-dipolar cycloaddition between methyleneindolinones and N,N'-cyclic azomethine imines. The desired pyrazolidine products with contiguous quaternary-tertiary stereocenters were obtained in up to 99% yields with up to 99% ee and >19:1 dr under mild reaction conditions.