Photocatalytic α-Selective σ-Bond Hydroboration of Bicyclo[1.1.0]butanes

Cyclobutylboranes are important synthetic precursors for introducing strained cyclobutyl groups, yet their efficient synthesis remains a significant challenge. The recent development in photochemistry concerning bicyclo[1.1.0]butanes (BCBs, which are highly reactive radical acceptors) offers a direct route to access these motifs using boryl radicals. Herein, we report an effective and mild photomediated borylation of BCBs with high regioselectivity, enabling the synthesis of a series of cyclobutylborane compounds bearing diverse substituents. Comprehensive mechanistic studies provide strong evidence of a radical process involving hydrogen atom transfer (HAT).