Enantioselective Cyanoborylation of Allenes by N-Heterocyclic Carbene-Copper Catalysts

The simultaneous incorporation of both a cyano group and a boryl unit into the C=C double bonds of allenes in a regio- and stereoselective fashion is of much interest and importance but remains a significant challenge. We report herein a copper-catalyzed chemo-, regio-, and enantioselective cyanoborylation of allenes, which afforded a family of valuable enantiopure beta-boryl allyl nitriles. The high enantioselectivity was achieved by installing of appropriate substituents at the C2 and C6 positions of the naphthyl groups in our newly synthesized N-heterocyclic carbene (NHC) ligands. The reaction mechanism has been clarified by some stoichiometric reactions and computational studies. This work provides an inspiring example of the development of selective catalytic reactions for the synthesis of functional molecules through fine-tuning the ligands in catalysis.