Enantioselective Vinylogous Mannich Reaction of Acyclic Vinylketene Silyl Acetals with Ketimines Using Chiral Bis(imidazoline)–Cu(II) Catalysts

The enantioselective vinylogous Mannich reaction of ketimines derived from isatins with acyclic vinylketene silyl acetals has been developed using a chiral bis­(imidazoline)–Cu­(II) catalyst. A series of chiral 3-aminooxindole derivatives bearing tetra-substituted stereogenic centers with an α,β-unsaturated ester moiety were obtained in excellent yields (up to 99%) with high enantioselectivities (up to 98% ee). Enantioselective bisvinylogous Mannich reaction to ketimines derived from isatins also afforded product with high enantioselectivity. Based on the experimental investigations, a possible transition state has been proposed to explain the origin of the asymmetric induction.