Highly Enantioselective Aza‐Baylis–Hillman Reactions Catalyzed by Chiral Thiourea Derivatives

Abstract
We report the discovery of asymmetric aza‐Baylis–Hillman (ABH) reactions of N‐p‐nitrobenzenesulfonylimines with methyl acrylate catalyzed by chiral thiourea derivatives. A series of aromatic imines was found to undergo coupling with methyl acrylate with unprecedented levels of enantioselectivity (87–99% ee), albeit only in modest (25–49%) yields. A DABCO‐acrylate‐imine adduct was isolated as a key intermediate in the ABH reaction. We provide a mechanistic analysis based on the identity of this intermediate as well as kinetic investigations and isotope studies, and propose a rationale for the observed limitations in yield. Synthetic applications of the ABH products are also described.