Lewis Acid Catalyzed Ene Reactions: Comment on the “Cycloaddition of Olefins to Methyl Acrylate”

Abstract

Recently we became aware of a communication describing a very simple synthesis of cyclobutanes. Sands¹⁾ claimed to have obtained substituted methyl cyclobutanecarboxy-lates by aluminium chloride catalyzed reaction of methyl aerylate with olefins, such as isobutylene, 2-methyl-2-butene, tetramethylethylene, 4-methyl-2-butene (?) and 2,3-dimethyl-1-butene. This synthesis of cyclobutanes seemed amazingly simple, but questionable in view of the fact that certain olefins had been reported to undergo ene reactions with methyl acrylate under very similar reaction conditions^2),3). These conflicting reports provoked our effort to establish irrevocably the nature of the products obtained by Sands' method.