合成路线1

This compound has been obtained by several related ways: 1. The selective reduction of 6alpha,9alpha-difluoro-16alpha-prednisolone (I) with H2 over tris(triphenylphosphine)rhodium chloride catalyst in ethanol gives 6alpha,9alpha-difluoro-11beta,16alpha,17alpha,21-tetrahydroxypregn-4-ene-3,20-dione (II), which is cyclized with butanal (III) catalyzed by HClO4 in dioxane to yield the butylidenedioxy derivative (IV) as a diastereomeric mixture. Finally, the desired (R)-diastereomer is separated by column chromatography over Sephadex LH-20. 2. By selective reduction of 16alpha,17alpha-((R)-butylidenedioxy)-6alpha,9alpha-difluoro-11beta,21-dihydroxypregna-1,4-diene-3,20-dione (V) with H2 over tris(triphenylphosphine)rhodium chloride catalyst in ethanol. 3. The selective reduction of fluocinolone acetonide (VI) with H2 over tris(triphenylphosphine)rhodium chloride catalyst in ethanol gives 6alpha,9alpha-difluoro-11beta,21-dihydroxy-16alpha,17alpha-(isopropylidenedioxy)pregen-4-ene-3,20-dione (VII), which is then treated with butanal (III) and HClO4 over SiO2 in heptane.