Westphalen-Lettré rearrangement

The Westphalen-Lettré rearrangement is a classic organic reaction in organic chemistry describing a rearrangement reaction of cholestane-3β,5α,6β-triol diacetate with acetic anhydride and sulfuric acid. In this reaction one equivalent of water is lost, a double bond is formed at C10-C11 and importantly the methyl group at the C10 position migrates to the C5 position.^{[1][2] [3]}

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The reaction is first order in steroid with access of sulfuric acid^[4] and the first reaction step in the reaction mechanism is likely the formation of an sulfate ester followed by that of a carbocation at C5 after which the actual rearrangement takes place.

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