Equatorial Preference in the GaCl₃-Promoted Ethenylation of Cyclic Ketones

Abstract

Silyl enol ethers derived from substituted cyclohexanones are ethenylated with trimethylsilylethyne in the presence of GaCl3. Carbon-carbon bond formation was completed in less than 5 min at room temperature and protodegallation of the organogallium intermediate formed with 6 M sulfuric acid gave β-enones. The reactions exhibit a bias for the equatorial C-C bond formation, which contrasts the axial stereochemistry of enolate alkylation. The origin of this stereoselectivity is discussed.