4,5-Seco-4,6-cyclosteroids. II. Synthesis of 4,5-Seco-4,6-cyclo-6β-cholestan-5α-ol

Abstract

5-oxo-4,5-secocholestan-4-oic acid methyl ester (XIIIb) was converted into the corresponding cyclic ethylene acetal (XIVb) which, upon successive reduction with lithium aluminium hydride and acid hydrolysis, gave 4-hydroxy-4,5-secochol-estan-5-one (XVa), converted into the tosyl ester (XVb). Base-catalysed intra-molecular alkylation of the latter gave mainly A-homo-4a-oxacholest-5-ene (XVII), together with 4,5-seco-4,6-cyclo-6β-cholestan-5-one (IIIc), reduced with lithium aluminium hydride to 4,5-seco--1,6-cyclo-6β-cholestan-5α-ol (IIb). This was identical with material previously prepared by transformation of 4,5-seco-4,6-cyclo-6β-cholestane-3β,5α-diol (IIa), obtained from reductive rearrangement of 6β-bromo-4β,5-epoxy-5,β-cholestan-3β-ol (I).     Some other approaches to the synthesis of 4,5-seco-4,6-cyolo-6β- cholestane derivatives are described.