Bismuth(III) salt-catalyzed Westphalen and “backbone” rearrangements of 5β,6β-epoxysteroids

A new process using the “ecofriendly” bismuth(III) salts as catalysts for the Westphalen and “backbone” rearrangements of 5β,6β-epoxysteroids is reported. This method is particularly sensitive to changes on solvent, temperature, stereochemistry of starting epoxysteroid, and its substituent at C17. Depending on the reaction conditions, either Westphalen-type or “backbone” rearranged products were obtained, all being 3β-acetoxy-6β-hydroxy-substituted. Several new olefinic 19-nor and 18,19-dinorsteroids were obtained and their structural elucidation was fully accomplished using 2D NMR and X-ray crystallography techniques.