Reactivity of steroidal dienes towards the methyltrioxorhenium/H2O2-urea oxidation system: Isolation and characterization of new oxygenated steroids

To examine the reactivity of conjugated diene steroids towards methyltrioxo rhenium (MTO)-catalysed oxidation with the urea-hydrogen peroxide adduct (U HP) and its possible use in functionalization of the rings of the steroid n ucleus, the reactions of the MTO/UHP system with cholesta-3,5-diene (4) and 5a-cholesta-7,9(11)-dien-3 beta -yl acetate (13) in aprotic solvents were investigated. These oxidations were performed both at 0 degreesC and at 25 degreesC, in either CHCl3 or diethyl ether as solvents, and in the presence of pyridine as ligand. Three new 4,5-epoxy-3,6-dihydroxyl compounds 10, 11 , and 12 were isolated from the treatment of diene 4 in CHCl3 at 0 C, while oxidations of the Delta (7,9(11))-diene steroid 13 allowed us to isolate t he new monoepoxy and diepoxy steroids 14 and 15 and the new triol 19. The s tructures of all new steroids were verified on the basis of chemical eviden ce and interpretation of spectroscopic data including H-H COSY, HMBC, and H MQC experiments.