Novel epimerization of steroidal allylic alcohols.

Epimerization of 4-pregnene-3 beta,20 alpha-diol into 4-pregnene-3 alpha,20 alpha-diol was achieved under the mild condition of an acidic medium at room temperature. This reaction was favorable for synthesis of 4-pregnene-3 alpha,20 alpha-diol in better yield, after chemical reduction of 20 alpha-hydroxy-4-pregnen-3-one with metal hydrides, which resulted in predominant production of 4-pregnene-3 beta,20 alpha-diol. The by-product which was formed more by raising the temperature was identified as 3,5-pregnadien-20 alpha-ol. This method was also applicable for epimerization of other delta 4-3 beta-hydroxysteroids.