Synthesis of 3β-fluoro derivatives of 7-dehydrocholesterol and of ergosterol

It has been established that the fluorination of 3-hydroxy-^5,7-steroids, unlike that of 3-hydroxy-⁵-steroids, does not lead to the formation of 3-fluoro derivatives. The reaction products are 3,5-cyclo-^6,8(14) compounds. Consequently, to obtain the 3-fluoro derivatives of provitamins D — 7-dehydrocholesterol and ergosterol — the 5,7-diene system was first protected by the formation of a cyclo-adduct with 4-phenyl-1,2,4-triazoline-3,5-dione after which the adduct was fluorinated with morpholinosulfur trifluoride to the 3-fluoro adduct, and then the 5,7-double bonds were regenerated by treating the adduct with a solution of sodium methanolate in methanol.A. V. Palladin Institute of Biochemistry, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 102–107, January–February, 1985.