Regiocontrolled hydrobromination of unactivated alkenes via direct and chain-walking pathways.

Abstract

The development of regioselective methods for C(sp³)─Br bond formation in unactivated alkenes remains a fundamental challenge in organic synthesis. Herein, we report a nickel hydride-catalyzed method that enables regiocontrolled hydrobromination of both terminal and internal alkenes through strategic deployment of an <i>N</i>-fluoropyridinium oxidant. The method features two complementary approaches: direct hydrobromination of alkenes with high proximal selectivity and a chain-walking strategy that enables switchable site-selective functionalization in extended alkyl chains. Notably, temperature-controlled reaction parameters enable regiodivergent access to β- or γ-brominated products from identical alkenes with excellent selectivity. The protocol demonstrates broad functional group tolerance and enables late-stage functionalization of pharmaceuticals. Mechanistic studies, including deuterium labeling, radical clock experiments, and density functional theory calculations, revealed a radical-mediated pathway featuring temperature-dependent regioselectivity in the chain-walking process. This unified method provides a versatile platform to access diverse alkyl bromides and offers fundamental insights into selective C─Br bond construction through direct and chain-walking pathways.