合成路线1

3) An alterantive synthesis of the intermediate 26,26,26,27,27,27-hexafluorocholest-5-en-1alpha,3beta,25-triol (VIII) is as follows: The oxidative dehydrogenation of 3beta-hydroxy-5-cholene-24-oic acid methyl ester (XII) with dichlorodicyanobenzoquinone (DDQ) in refluxing dioxane gives 3-oxochola-1,4,6-triene-24-oic acid methyl ester (XIII), which is selectively epoxidized with 30% H2O2 and NaOH in methanol yielding the 1alpha,2alpha-epoxide (XIV). The reductive cleavage of (XIV) with lithium in liquid NH3, followed by hydrolysis with water affords the unsaturated triol (XV), which by selective protection with trityl chloride in pyridine, followed by acetylation with acetic anhydride and dimethylaminopyridine (DMAP) and elimination of the trityl group with p-toluenesulfonic acid, gives 1alpha,3beta-diacetoxy-5-cholen-24-ol (XVI). The reaction of (XVI) with tosyl chloride-pyridine and then with LiBr in DMF yields the 24-bromo derivative (XVII), which is treated with sodium phenylsulfinate in hot DMF affording the sulfone (XVIII). Hydrolysis of the acetoxy groups of (XVIII) with KOH in methanol, followed by silylation of the resulting diol with trimethylsilyl chloride and triethylamine in pyridine gives the silylated sulfone (XIX), which is then condensed with hexafluoroacetone by means of lithium diisopropylamide in THF yielding the sulfonated adduct (XX). Finally, this compound is desilylated to the previously reported triol (VIII) with HCl in methanol.