The photocycloaddition of an 5α-androst-1-en-3-one to olefins

Abstract

The triplet photocycloaddition of 17β-acetoxy-5α-androst-1-en-3-one to the olefins cyclopentene, a ketene acetal, and isobutylene is described. The addition to cyclopentene forms cis- and trans-fused cyclobutanes. The trans-adduct is remarkably stable to both strong acid and base at room temperature, requiring extended heating in alcoholic base for epimerization to occur. This stability is ascribed to steric shielding of the enolizable proton. Addition to the ketene acetal, followed by careful hydrolysis, yields the novel trans-fused cyclobutanone. Epimerization and deuteriation demonstrated the stereochemistry as being 1β,2α. Isobutylene, in addition to the cis- and trans-fused cyclobutanes, also yielded an ene-type product.