Preparative Method for the Quantitative Separation of Methylenic Sterols from Unsaturated Sterol Mixtures by Chemoselective Hydroxymercuration-Deoxymercuration

Abstract

An unprecedented selective and quantitative method allowing the separation of the methylenic sterols from unsaturated sterol mixtures is reported. We have extended the hydroxymercuration reaction under modified Brown’s conditions to a systematic study on thirty unsaturated sterols as various sterol mixtures. A high-yielding directed chemoselective hydroxymercuration was achieved on methylenic side chain of sterols. The resulting organomercurial intermediates were easily purified by flash chromatography on silica gel column and the reactive alkenes were regenerated by deoxymercuration in a biphasic system (ethyl acetate/1 M HCl, 2:1 ratio). These conditions leave the ring double bonds of steroids intact. No isomerization of methylene double bonds was observed.

Key words

alkenes - chemoselectivity - steroids - hydroxymercuration - deoxymercuration

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