Catalytic Asymmetric Conjugate Addition of a Borylalkyl Copper Complex for Chiral Organoboronate Synthesis

We report the catalytic enantioselective conjugate addition of a borylalkyl copper nucleophile generated in situ from a 1,1‐diborylmethane derivative to α,β‐unsaturated diesters. In the presence of a chiral N‐heterocyclic carbene (NHC)–copper catalyst, this method facilitated the enantioselective incorporation of a CH₂Bpin moiety at the β‐position of the diesters to yield β‐chiral alkyl boronates in up to 86 % yield with high enantioselectivity. The alkylboron moiety in the resulting chiral diester products was converted into various functional groups by organic transformation of the C?B bond.