4,5-Epoxycholestane-3,6-diols: Templates for generating the full set of eight cholestane-3,5,6-triol stereoisomers in multigram scales, but not for a cholestane-3,4,6-triol

Cholestane-3β,5α,6β-triol is an extensively studied biologically important oxysterol. The full set of eight cholestane-3,5,6-triol stereoisomers was synthesised in diastereomerically pure forms by the stereoselective cleavage of eight diastereomerically pure 4,5-epoxycholestane-3,6-diols with LiAlH4, in high yields on multigram scales and without chromatography for most of them. However, applying various reportedly successful combinations of a hydride donor and a Lewis acid to the same substrates under a variety of conditions failed to generate a single unsubstituted cholestane-3,4,6-triol. The products of the eight cholestane-3,5,6-triol stereoisomers will serve as a good probe in the study of biological functions of oxysterols in a biological process.