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.
alkenes - chemoselectivity - steroids - hydroxymercuration - deoxymercuration
