Catalytic C(sp2) homologation of alkylboranes

Abstract

Organoboron compounds are important intermediates in organic synthesis, commonly used in metal-catalysed cross-coupling reactions. Their unique reactivity also allows modifications of their carbon framework with preservation of the valuable boryl group. Traditionally, these homologation reactions have been confined to the formation of alkyl boron compounds via C(sp³) insertion into a C–B bond. However, recent advancements in C(sp²)-insertive homologation highlight the potential of these reactions in synthesizing complex alkenes, despite current limitations in scope and control of the alkene geometry. Here we demonstrate a catalytic C(sp²)-insertive homologation for the regio- and diastereoselective synthesis of complex trisubstituted diborylalkenes from simple alkylboranes and alkynyl boronic esters. Our work demonstrates a broad reaction scope and application of the resulting products in modular and stereoselective synthesis of highly substituted alkenes. Furthermore, we provide evidence supporting a unique mechanism responsible for the excellent stereoselectivity observed in the reaction.