β-Boron Effect Enables Regioselective Baeyer–Villiger Oxidation for Selective C–C Bond Cleavage

Abstract The Baeyer–Villiger oxidation is a fundamental transformation for converting ketones into esters, yet achieving high regioselectivity among structurally similar alkyl groups remains a longstanding challenge. Herein, we report a β-boron-directed strategy to control migratory selectivity in Baeyer–Villiger oxidations of alkyl ketones. This approach exploits the β-boron effect, wherein hyperconjugative interaction between the σ(C–B) bond and the adjacent σ*(C–C) orbital weakens the C–C bond and enhances its migratory aptitude. As a result, β-boryl ketones undergo highly regioselective rearrangement, overriding the classical migratory order. A broad range of β-MIDA boronate substrates are compatible with this protocol, enabling the efficient synthesis of diverse 1,2-amphiphilic building blocks. Mechanistic studies support the critical role of the β-boron effect in the migration step. Furthermore, preliminary results demonstrate that this effect can be extended to the Beckmann rearrangement, revealing boron as a versatile and previously underexplored directing group for controlling regioselectivity in rearrangement reactions.