[1,3]-Hydride Shift in α-Boryl Cations: Strategic Design of Fluorine-Triggered Cyclopropanation.

Abstract

Hydride shift represents an important process in carbocation chemistry, yet controlled access to the [1,3]-hydride shift has remained elusive despite its potential synthetic utility. Here, we report direct observation and synthetic demonstration of the [1,3]-hydride shift using α-fluoro-diborylalkanes. Initial [1,2]-fluoride migration generates an α-boryl cation that selectively undergoes a [1,3]-hydride shift via a three-center two-electron interaction, enabling efficient synthesis of cyclopropyl boronic esters. Deuterium labeling experiments and computational studies reveal the key electronic factors governing this unusual selectivity. The methodology provides both mechanistic insights into longer-range hydride shifts and a practical platform for accessing diverse molecular architectures through versatile transformations of the resulting cyclopropyl boronic esters.