Mechanism of the reaction of dihalogeno-oxirans with ketones catalysed by some Lewis acids

Abstract

Kinetic studies of the reaction of substituted dihalogenoepoxybutanes with ketones catalysed by Lewis acids reveal its multicentre character. Interaction of an oxiran with a Lewis acid already complexed with a ketone (or other ligand) probably results in the formation of a donor–acceptor Lewis acid–oxiran complex. The transformation of this complex into the activated form involves attack by a ketone molecule from the salvation shell of the complex according to a ‘push–pull’ mechanism. This step can lead to isomerisation of the oxiran as well as to the formation of a dioxolan. The formation of the Lewis acid–oxiran complex can in some cases be the rate-limiting process.