Steroidal sulphur compounds. Part XII. Regiospecific formation of steroidal olefins by thermolysis of sulphoxides

Abstract

The first examples of the regiospecific generation of isomeric olefins from two sulphoxides diastereoisomeric at sulphur are reported. Thermolysis of (R)- and (S)-3α-(1-adamantylsulphinyl)-5α-cholestane at 110 °C gave respectively 5α-cholest-3-ene and 5α-cholest-2-ene; (S)-3β-(1-adamantylsulphinyl)-5β-cholestane gave 5β-cholest-3-ene at a rate much greater than that at which the diastereoisomeric (R)-sulphoxide decomposed to 5β-cholest-2-ene, so providing a convenient preparation of these erstwhile rather inaccessible olefins. In contrast, thermolysis of 3α-(1-naphthyl)- and 3α-(anthracen-9-yl)-5α-cholestanes was not highly regioselective, and the corresponding steroidal diphenyl sulphoxides underwent stereomutation at sulphur more readily than elimination to give olefins.