Directed, Palladium(II)-Catalyzed Enantioselective anti-Carboboration of Alkenyl Carbonyl Compounds

A substrate-directed enantioselective anti-carboboration reaction of alkenes has been developed, wherein a carbon based nucleophile and a boron moiety are installed across the C=C bond through a 5- or 6-membered palladacycle intermediate. The reaction is promoted by a palladium(II) catalyst and a mondentate oxzazoline ligand. A range of enantioenriched secondary alkylboronate products were obtained with moderate to high enantioselectivity that could be further upgraded by recrystallization. This work represents a new method to synthesize versatile and valuable alkylboronate building blocks. Building on an earlier mechanistic proposal by Peng, He, and Chen, a revised model is proposed to account for the stereoconvergent nature of this transformation.