Efficient routes to epimerically-pure side-chain derivatives of lanosterol.

A technically simple route is described to individual epimers of side-chain derivatives of lanosterol (3beta-hydroxy-5alpha-lanosta-8,24-diene). Epimerically pure 24,25-epoxy-, 24,25-dihydroxy- and 24-bromo-25-hydroxy-lanosterol have been prepared in good yield from commercial (50-60%) lanosterol. Hypophosphorous acid was used as a catalyst for the cohalogenation of the Delta24(25) bond and also for the efficient conversion of 24,25-epoxy- and 24-bromo-25-hydroxylanosterol to epimerically pure 24(R) or 24(S)-24,25-dihydroxylanosterols.