Synthesis of some unsaturated 19a-homocholestane derivatives

Abstract

A synthesis of unsaturated alcohols I, IV-VI is described. The 3,4-unsaturated derivative I was prepared in three steps from the mesylate VIII which by elimination of methanesulfonic acid afforded a mixture of olefins IX yielding two bromo epoxides XII and XIII on treatment with hypobromous acid. Zinc reduction of the compound XIII gave the hydroxy olefin I. In the synthesis of the derivative IV inversion of configuration at C(3) (formally II → IV) was performed in the following manner: reaction of the hypobromous acid with III gave the cyclic ether XV which after saponification and oxidation was converted into the ketone XVIII and the latter was reduced with lithium aluminum hydride to yield a mixture with prepondering equatorial alcohol XX. This compound was acetylated and reduced with zinc to give IV. The 3-epimeric 10β-vinylalcohols V and VI were obtained by reduction of the ketone XXVII.