Westphalen Rearrangement

Abstract

This rearrangement is an acid‐promoted Wagner–Meerwein rearrangement of 5‐hydroxycholesterol derivatives with a substituent at C‐6 in β‐configuration, from which the 5‐hydroxy is removed by acidic dehydration accompanying the migration of the angular methyl group at C‐10 to C‐5 and the formation of double bond between C‐9 and C‐10 and this transformation is generally referred to as the Westphalen rearrangement. It has been reported that the rearranged compound by means of the treatment of cholestane‐3β,5α,6β‐triol 3,6‐diacetate with sulfuric acid and acetic anhydride is referred to as the Westphalen's diol diacetate and is quite general among the steroids. The study finds that depending on the substituents around C‐5 and C‐6, the Westphalen rearrangement can be initiated by different reagents. However, it has been noticed that only those steroids having a substituent at C‐6 with a β‐configuration can undergo the Westphalen rearrangement. The initial protocol used by Westphalen has been improved by the use of potassium bisulfate. This rearrangement is quite often for steroids with 6β‐groups and 5α‐OH, or a 5α,6α‐ epoxide ring, which has been used for the structural transformation among the steroids.