5α,6α-Epoxy-3β-methanesulfonyloxyandrostan-17-one undergoes a Westphalen backbone rearrangement rather than an aromatisation in acetic acid: acetic anhydride containing sulfuric acid catalyst, suggesting that under these conditions the formation of a 5α-sulfate from the epoxide and its ionisation takes precedence over the elimination of the 3β-methanesulfonate.
