Superelectrophilic aluminium(iii)–ion pairs promote a distinct reaction path for carbonyl–olefin ring-closing metathesis

Abstract

Catalytic carbonyl–olefin metathesis reactions represent powerful synthetic strategies for alkene formation. Successful approaches for carbonyl–olefin ring-closing, ring-opening and cross metathesis have been developed in recent years, but current limitations hamper the generality of these transformations. Stronger, more efficient catalytic systems are needed to further broaden the scope of these transformations while they prevent undesired reaction pathways. Here we report the development of an aluminium-based heterobimetallic ion pair as a superior catalyst that promotes carbonyl–olefin ring-closing metathesis via a distinct reaction mechanism and allows access to six- and seven-membered rings, which suffer from low yields and poor conversion under previously reported conditions. Mechanistic investigations support a distinct reaction profile in which two productive reaction pathways competitively form metathesis products. These insights are expected to have important implications in the catalyst design and development for carbonyl–olefin metathesis and enable future advances to ultimately expand the synthetic utility of these transformations. Carbonyl–olefin metathesis reactions are a valuable tool in synthetic chemistry, but there are still some limitations in scope. Now, a catalyst system allows the activation of previously unreactive substrates for such a reaction by aluminium(iii)–ion pairs acting as Lewis acidic superelectrophiles.