Copper-Catalyzed Asymmetric Hydroboration of Alkynes to C-N Axially Chiral Azaborines via Dynamic Kinetic Resolution

Despite the substantial application potential of C-N axially chiral motifs across diverse fields, and the growing interest in azaborine frameworks owing to their distinctive physicochemical properties, the direct catalytic synthesis of C-N axially chiral azaborines has remained elusive, significantly impeding the practical deployment of these promising molecular scaffolds. Herein, we disclose a copper-catalyzed asymmetric hydroboration reaction of alkynes with N-arylazaborines under mild reaction conditions, which enables the efficient access to C-N axially chiral azaborine products in high yields, accompanied by excellent regioselectivity, Z-stereoselectivity, and enantioselectivity. Mechanistic experiments and density functional theory calculations reveal that a dynamic kinetic resolution process is involved in this reaction. Specifically, the two enantiomers of racemic N-arylazaborines can undergo racemization via a dearomative tetracoordinate boron intermediate under the action of NaO^tBu.