Abstract
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 HC1 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-disuhstituted > 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 /3-keto esters and substituted dimethyl
glutarates, respectively.