The dehydrogenation of 3beta-hydroxycholest-5-en-24-one with dichlorodicyanobenzoquinone in refluxing dioxane, or of cholest-4-ene-3,24-dione (II) with chloranil in refluxing tert-butyl alcohol gives cholesta-1,4,6-triene-3,24-dione (III), which is epoxidized with 30% H2O2 and NaOH in methanol-dioxane-THF yielding 1 alpha,2alpha-epoxycholesta-4,6-diene-3,24-dione (IV). The reduction of (IV) with Li in liquid NH3 affords 1alpha,3beta,24-trihydroxycholest-5-ene (V), which is benzoylated with benzoyl chloride in pyridine and submitted to column chromatography on silica gel to give 1alpha,3beta,24R-tribenzoyloxycholest-5-ene (VI). The dehydrogenation of (VI) with dibromodimethylhydantoin of N-bromosuccinimide yields lalpha,3beta,24R-trihydroxy-cholesta-5,7-diene (VII), which is finally submitted to irradiation with a medium-pressure Hg lamp in ether.