Lewis Acid Catalyzed Reactions of Acetylenic Esters with Alkenes. Stereochemistry and Regiochemistry

Article abstract of DOI:10.1021/jo01302a007

The Lewis acid catalyzed reaction of methyl chloropropiolate or dimethyl acetylenedicarboxylate with alkenes leads to ene reactions and/or stereospecific <2+2> cycloaddition.Ethylaluminum dichloride was found to be a very effective catalyst since it is a strong Lewis acid and an HCl scavenger.With trisubstituted alkenes the ene reaction is regiospecific.A hydrogen is transferred from the alkyl group trans to the alkenyl hydrogen.The regio- and stereoselectivity of the ene reactions of methyl chloropropiolate, methyl propiolate, and dimethyl acetylenedicarboxylate are described.From cyclohexenes, pseudoaxial hydrogens are transferred exclusively.The relative reactivity of alkenes was found to be 1,1-disubstituted > trisubstituted >> monosubstituted and 1,2-disubstituted.The ene adducts and cyclobutenecarboxylates derived from methyl chloropropiolate undergo substitution reactions with organocuprates and can be hydrolyzed to β-keto esters and substituted dimethyl glutarates, respectively.