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 Delta(7,9(11))-sterols gas been explored. The reaction has been performed both at -70 degrees 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 affects the yields of the reaction products. When 3 beta,6 alpha- and 3 beta,6 beta-diacetoxy-Delta(7,9(11))-sterols were used the diene system was predominantly attacked at the 9(11)-double bond from the alpha-face of the molecule giving Delta(7)-9 alpha-hydroxy-11-keto- and Delta(7)-9 alpha,11 alpha-dihydroxy-sterols. RuO4 oxidation of cholesta-7,9(11)-dien-3 beta-yl acetate, yielded, in addition to the above oxidation products, minor amounts of three related C-7,C-11 oxigenated 8 alpha,9 alpha-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 [Delta(4), Delta(5) and Delta(7)] 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 Delta(7)-9 alpha,11 beta-dihydroxysterols via LiAlH4 reduction of the 11-keto group.