合成路线1

Ketalization of 17alpha-methyltestosterone (I) by means of ethylene glycol and p-toluenesulfonic acid provided the DELTA5(6)-ketal (II), and subsequent allylic oxidation of (II) with CrO3-3,5-dimethylpyrazole complex gave enone (III). Hydrogenation of the olefinic double bond of (III) afforded the saturated ketone (IV), which was reduced employing NaBH4 and CeCl3 to furnish an unseparable mixture of epimeric alcohols (Va-b). After removal of the ethylene ketal of (Va-b) with p-toluenesulfonic acid/acetone, the major 7beta-alcohol (VI) was isolated by flash chromatography. The 7beta-tosylate (VII) was then prepared by reaction of (VI) with p-tosyl chloride in pyridine. Finally, exchange of the tosylate group of (VII) with tetrabutylammonium fluoride yielded the desired 7alpha-fluoride.