Enantioselective B-H Insertion of Branched α-Alkyl Carbenes.

The intermolecular asymmetric carbene transfer reaction of branched α-alkyl Fischer carbenes remains inaccessible due to their high susceptibility to rearrangement side reactions. This study overcomes these limitations by achieving copper-catalyzed, highly enantioselective insertion reactions of branched α-alkyl carbenes into B-H bonds. A variety of important chiral pharmaceuticals starting from readily available ketones has been effectively achieved based on this reaction platform. The precise modulation of carbene electronic properties and transfer reaction kinetics enables sterically demanding and unstable branched α-alkyl carbenes to undergo intermolecular transfer reactions with excellent efficiency and selectivity. The realization of versatile transformations of structurally diverse branched α-alkyl carbenes substantially promotes the development of carbene chemistry from both experimental and theoretical perspectives.