Direct Catalytic Enantioselective Vinylogous Aldol Reaction of α-Branched Enals with Isatins

The direct vinylogous aldol reaction of alpha-substituted alpha,beta-unsaturated aldehydes with isatins is described. The chemistry provides easy access to valuable 3-substituted 3-hydroxyoxindole derivatives with high stereocontrol and perfect gamma-site selectivity. Preliminary mechanistic studies suggest that, depending on the nature of the a-branched enal substituents, two divergent reaction mechanisms can be operating, leading to different products and stereochemical outcomes.