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

The CpRu+ 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 [CpRu(eta6-aryl steroid)]+ products. Reacti on of 1 with testosterone, progesterone, cholesterol, dehydroisoandros terone, or androsterone at 90-120-degrees-C leads to selective and (ex cept for androsterone) near-quantitative aromatization of the A-ring o f the steroid substrates via C-O, C-H and C-C bond activation, affordi ng eta6-aryl derivatives as above and CH4 ,H-2, and/or H2O as byproduc ts. 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 lat ter case, the triene has been trapped by reaction with NaOMe, which le ads to addition of a methoxo group to the carbon C6 of the steroid; th e single crystal X-ray structure of the resultant metal complex is pre sented. CpRu+ forms a 1:1 adduct with prednisolone; reaction of 2 equ iv of 1 with prednisolone causes fragmentation of the steroid.