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

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 degrees 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 degrees 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 OsO, in dioxane. The RuO4 oxidation of cholesteryl acetate at room temperature also furnishes two ruthenium(vr) diesters (9 and 10) structurally analogous to compounds 2 and 5. NMR evidence is reported that the Ru=O and Os=O 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.