Metal-Free Asymmetric 1,3-Dipolar Cycloaddition of N-Arylmaleimides to Azomethine Ylides Catalyzed by Chiral Tertiary Amine Thiourea

The first metal-free asymmetric 1,3-dipolar cycloaddition of N-arylmaleimides to azomethine ylides catalyzed by chiral tertiary amine thiourea to form multiply substituted pyrrolidines in excellent yields (up to 89%) and enantioselectivities (up to 96% ee) is presented. This procedure allows a rapid diversity-oriented synthesis of chiral pyrrolidine derivatives with high optical purity.