Reaction of RuO4 with carbon–carbon double bonds. Part 8.1 Reaction of 7,8-didehydrocholesteryl acetate and cholesteryl acetate with RuO4 and OsO4. A comparative view

Abstract

The title reactions have been studied. The first formed compound from the oxidation of 7,8-didehydrocholesteryl acetate with RuO₄ performed in acetone–water (5∶1), both at room temperature and –70 °C, is the ruthenium(VI) diester 5. In mild acidic conditions compound 5 converts into the isomeric compound 6 that in turn is in equilibrium in the same conditions with a third isomeric ruthenium(VI) diester, 2, a compound previously isolated from the same oxidative process conducted at –70 °C. The structural relationship between the isomeric compounds 2, 5 and 6 has been established by careful spectral analyses and comparison of their NMR properties with those exhibited by the osmium-containing analogues (7 and 8) of the ruthenate esters 2 and 5, synthesized by reaction of 7,8-didehydrocholesteryl acetate with OsO₄ in dioxane. The RuO₄ oxidation of cholesteryl acetate at room temperature also furnishes two ruthenium(VI) diesters (9 and 10) structurally analogous to compounds 2 and 5. NMR evidence is reported that the RuO and OsO groups possess similar magnetic anisotropy. The isomerization process involving the ruthenate esters of 7,8-didehydrocholesteryl acetate has also been studied by ¹H NMR spectroscopy and is briefly discussed.