Modular Assembly of <i>E</i>-Selective Trisubstituted Alkenylborons via Nickel-Catalyzed Reductive Dicarbofunctionalization of Ethynylboron

While alkenylborons have emerged as powerful precursors for the stereospecific construction of substituted alkenes, efficient synthetic methods toward stereodefined trisubstituted alkenylborons remain limited. Herein, we report a modular and practical approach for the stereoselective synthesis of E-trisubstituted alkenylborons through the nickel-catalyzed three-component reductive coupling of two readily available carbon electrophiles with an ethynyl-Bdan reagent. The protocol exhibits a broad substrate scope and good functional group tolerance, providing expedient access to a variety of trisubstituted alkenylborons with exclusive E-selectivity. The work demonstrates the possibility of applying ethynyl-Bdan as a type of boron reagent in organic synthesis.