Journal of the American Chemical Society, Vol.132, No.31, 10650-10651, 2010
Chiral Bisguanidine-Catalyzed Inverse-Electron-Demand Hetero-Diels-Alder Reaction of Chalcones with Azlactones
A new type of C-2-symmetric chiral bisguanidine was designed as a highly efficient catalyst in the inverse-electron-demand hetero-Diels-Alder reaction of chalcones with azlactones for the first time. A wide variety of gamma,delta-unsaturated delta-lactone derivatives with alpha-quaternary-beta-tertiary stereocenters were obtained in high yields (up to 88%) with excellent enantioselectivities (up to 99% ee). Hydrogen bonds were considered to be crucial for the activation and stereoinduction of the reaction. In all cases, the major was HDA adducts, which were obtained as a single diastereomer along with little amount of Michael addition products.