Diastereo- and Enantioselective Allylation of α-Hydroxy Ketones Enabled by Palladium/Borinic Acid Dual Catalysis

Asymmetric allylation reactions between unsymmetrical allyl carbonates and α-hydroxy ketones synergistically catalyzed by a palladium/borinic acid catalytic platform have been developed. The reaction proceeds through nucleophilic activation of α-hydroxy ketone by an achiral borinic acid to form a tetracoordinated enediol boronate complex and its subsequent interception of an electrophilic π-allyl palladium complex generated from a chiral Pd catalyst and an allyl component. A broad scope of substrates was suitable in this reaction, providing a series of allyl-substituted α-hydroxy ketones bearing vicinal stereocenters with high enantioselectivities (up to 99% ee) and diastereoselectivities (up to 24:1 dr). The methodology also achieved effective kinetic resolution of 1,3-disubstituted allylic carbonates, with the unreacted substrates being recovered with high ee values. A plausible mechanism and model for chiral induction in this reaction are proposed. The diastereo- and enantioselectivites observed in this reaction were rationalized by density functional theory studies. The utility of this method was demonstrated by a gram-scale reaction and subsequent elaboration of the allylation products.