Synthesis of (3S)-Hydroxyandrosta-5,7-diene-17-ones via Intramolecular Cobalt-Mediated [2+2+2] Cycloaddition

A new method for the synthesis of lumisterin-type steroids following the D(right arrow)ABCD approach is reported. A key step is the cobalt-induced cyclization of a cyclopentanoid enediyne, which was prepared via thioalkylation of the zinc enolate of a 2,3-substituted cyclopentanone with (alpha)-chlorosulfides.