Conversion of nor-ketones into prochiral terminal methylene groups: synthesis of (24E)- and (24Z)-[28-2H]ergosta-5,24(28)-dien-3β-ols

Abstract

The synthesis of 24-prochiral methylene steroids from nor-ketones, illustrated by the preparation of (24E)- and (24Z)-[28-²H]ergosta-5,24(28)-dien-3β-ols starting from 6β-methoxy-3α,5-cyclo-5α-cholestan-24-one (3), is described.

The ketone (3) was transformed into (24E)- and (24Z)-6β-methoxy-3α,5-cyclo-5α-stigmast-24(28)-en-29-als labelled with deuterium at C-28 or at C-29 by using labelled reagents in the different steps of the reaction sequence. Stereospecific decarbonylation of the aldehyde groups then affords the prochiral methylenes.