Photo‐promoted Skeletal Rearrangement of Phosphine–Borane Frustrated Lewis Pairs Involving Cleavage of Unstrained C−C σ‐Bonds

An unprecedented photo‐promoted skeletal rearrangement reaction of phosphine–borane frustrated Lewis pairs, o‐(borylaryl)phosphines, involving cleavage of an unstrained sp²C–sp³C σ‐bond is reported. The reaction realizes an efficient synthesis of cyclic phosphonium borate compounds. The reaction mechanism via a boranorcaradiene intermediate is proposed based on theoretical calculations. This work sheds light on the new photoreactivity of phosphine–borane FLPs.