Studies towards the synthesis of polyoxygenated steroids. Reaction of 7,9(11)-diene steroids with RuO4

In order to find an entry to C-ring oxygenated steroids, the reaction of ruthenium tetroxide with some Δ7,9(11)-sterols has been explored. The reaction has been performed both at −70°C and room temperature using an equimolecular amount of the oxidant and acetone-water as solvent system in the absence of a cooxidant. The change in the temperature conditions moderately affect the yields of the reaction products. When 3β,6α- and 3β,6β-diacetoxy-Δ7,9(11)-sterols were used the diene system was predominantly attacked at the 9(11)-double bond from the α-face of the molecule giving Δ7-9α-hydroxy-11-keto- and Δ7-9α-11α-dihydroxy-sterols. RuO4 oxidation of cholesta-7,9(11)-dien-3β-yl acetate, yielded, in addition to the above oxidation products, minor amounts of three related C-7,C-11 oxigenated 8α,9α-epoxysterols, arising from the oxidation of both double bonds of the diene system. These results, that in part parallel those we recently found on RuO4 oxidation of trisubstituted [Δ4, Δ5 and Δ7] steroidal alkenes, shed further light on the reactivity of this oxidizing agent which, neverthless, seems far from being completely understood. In addition, our procedure furnishes a reliable route to Δ7-9α,11β-dihydroxysterols via LiAlH4 reduction of the 11-keto group.