Asymmetric β-Boration of α,β-Unsaturated Esters with Chiral (NHC)Cu Catalysts

Copper complexes containing chiral N-heterocyclic carbene ligands catalyze the regioselective nucleophilic boryl attack at the beta-carbon of alpha,beta-unsaturated esters with enantioselectivities up to 74% ee, depending on the nature of the ester group.