Steroids. Part X. Acid-catalysed rearrangement of cholesta-1,3,5-trien-7-one

Abstract

Treatment of cholesta-1,3,5-trien-7-one with toluene-p-sulphonic acid in acetic anhydride affords 7-acetoxy-1-methyl-19-norcholesta-1,3,5(10),6-tetraene (IV) in high yield. Mild hydrolysis of this enol acetate gives 1-methyl-19-norcholesta-1,3,5(10)-trien-7-one (II) which is rapidly and completely isomerised at C-8 under more vigorous conditions. Dehydration of the alcohols derived from (II) and its 8-epimer (III) with phosphorus pentoxide yields 1-methyl-19-norcholesta-1,3,5(10),8(14)-tetraene as the major product while (XVII) and its 8-epimer (XVIII) predominate with phosphoryl chloride in pyridine as the reagent.

1α-Cholorocholesta-3,5-dien-7-one is formed when cholesta-1,3,5-trien-7-one is treated with hydrogen chloride in chloroform.