Enantioselective Asymmetric Michael Addition of Cyclic Diketones to β,γ-Unsaturated α-Keto Esters

An efficient, organocatalytic enantioselective addition of cyclic diketones with beta,gamma-unsaturated a-keto esters has been developed that affords products in high yields (up to 95 %) and excellent enantioselectivity (up to >99?% ee) under mild conditions with a low catalyst loading (2.5 mol-%). The unsaturated a-keto esters are effectively coordinated and activated through hydrogen bonds with the squaramides and proved to be excellent hydrogen-bond acceptors in this asymmetric organocatalytic reaction. This reaction provides valuable and easy access to chiral Michael adducts, which are important moieties in the skeletons of biological and pharmaceutical molecules.