SELECTIVE AROMATIZATION OF THE A-RING OF STEROIDS THROUGH C-C, C-H, AND C-O BOND ACTIVATION BY AN ELECTROPHILIC RUTHENIUM COMPLEX

The Cp*Ru+ fragment (1) generated by the protonation of [Cp*Ru(OMe)]2 by CF3SO3H reacts with oestradiol and oestrone in THF or CH2Cl2 at 293 K to form mixed sandwich [Cp*Ru(eta6-aryl steroid)]+ products. Reaction of 1 with testosterone, progesterone, cholesterol, dehydroisoandrosterone, or androsterone at 90-120-degrees-C leads to selective and (except for androsterone) near-quantitative aromatization of the A-ring of the steroid substrates via C-O, C-H and C-C bond activation, affording eta6-aryl derivatives as above and CH4 ,H-2, and/or H2O as byproducts. The reactions with testosterone and progesterone proceed through a hydrido cyclohexadienyl intermediate, whereas those with cholesterol and dehydroisoandrosterone occur via a triene intermediate. In the latter case, the triene has been trapped by reaction with NaOMe, which leads to addition of a methoxo group to the carbon C6 of the steroid; the single crystal X-ray structure of the resultant metal complex is presented. Cp*Ru+ forms a 1:1 adduct with prednisolone; reaction of 2 equiv of 1 with prednisolone causes fragmentation of the steroid.