Aromatization steroid rings

The hydrogenation of ring A aromatic steroids over ruthenium occurs, almost invariably, from the a side and all substituents on the original aromatic ring are cis in the resulting cyclohexane. Estrone (62) is hydrogenated over ruthenium to 5a,10a-estrane-3/3,17j6-diol (63) in 85-90% yield. 

Hydrogenation of monoenes, 123 Hydrogenation of ring A aromatic steroids, 138... 

The structurally simplest steroids, the aromatic A ring estrogens, have ironically proven most difficultly accessible because this aromatic ring is not found in any of the plant sterols available in commercial quantities. The main task of partial synthesis from naturally occurring material thus becomes... 

The female of mammalian species secretes a series of steroid hormones characterized by an aromatic A ring and the lack of a side chain at the 17 position. These compounds serve as regulators in the reproductive processes of the species. The name (estrogens) comes from the fact that in some lower animals the elaboration of this type of compound is directly involved with the phe-... 

Steroids that bear hydroxyl groups at the 3 position of an aromatic A ring or at the 17 position can be linked covalently to a polyphos-phazene chain by the use of the sodium salt of the hydroxyl unit (29). Example polymers are shown in structures 1 and 20. 

In view of our results obtained in reactions of the tetrahalogeno-benzynes with aromatic compounds we carried out a reaction of tetra-fluorobenzyne with the A-ring aromatic steroid 3,l7,fl-dimethoxy-oestra-l(10),2,4-triene (119) 154>. As we expected the initially formed enol-ethers were very rapidly hydrolysed and the adducts were isolated as the ketones (120) and (121). The mass spectra of the compounds (120) and (121) did not show molecular ion peaks and as anticipated the ketones were rapidly converted into the naphthalenes (122) and (123) photo-chemically. 

Removable cation-stabilizing auxiliaries have been investigated for polyene cyclizations. For example, a silyl-assisted carbocation cyclization has been used in an efficient total synthesis of lanosterol. Other conditions for the cyclization of polyenes and of ene-ynes to steroids have been investigated. Oxidative free-radical cyclizations of polyenes produce steroid nuclei with exquisite stereocontrol Besides the aforementioned A-ring aromatic steroids and contraceptive agents, partial synthesis from steroid raw materials has also accounted for the vast majority of industrial-scale steroid synthesis. 

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