Preparation of 2-chlorobuta-1,3-dienes by dichlorocyclopropanation of allylsilanes followed by desilylation

Abstract

Allylsilanes react with dichlorocarbene to form dichlorocyclopropanes which, in turn, afford 2-chlorobuta-1,3-dienes when treated with cesium fluoride in DMF under reflux. The Z stereochemistry of the products differs from that of the starting allylsilanes. Lengthy reaction times were necessary to induce desilylation because of the lack of steric congestion in the intermediate silylmethyl-substituted cyclopropanes. 5-Methyl-7-trimethylsilylhepta-1,5-diene was cyclopropanated regioselectively at the inner ene function in spite of unfavourable steric congestion, possibly as a result of the electron-donating effect of the allylic silyl group induced by the σ-π conjugation.