Steroids dehydrogenation, selenium dioxide

Selenium dioxide was first employed in steroid dehydrogenation for the direct formation of 12-ketones in corticoid synthesis. This dehydroge-... 

Selenium dioxide was first employed in steroid dehydrogenation for the direct formation of A9( 11 12-ketones in corticoid synthesis.172 This dehydrogenation reaction was developed by Mattox and co-workers173 to give yields of 80-85% and it remains the most satisfactory application of selenium dioxide in steroid synthesis. 

In a further study of routes to steroids with an aromatic ring C, 18-norandrost-13-enes (273) were found to give 7a-hydroxy-18-norandrosta-8,l 1,13-trienes (274) on reaction with selenium dioxide, while the 18-norandrosta-7,13-dienes reacted with mercury(n) acetate to give the 7a-acetate (276), as well as its 7j8-epimer. Mechanisms, including stepwise dehydrogenations, are discussed.226... 

Selenium dioxide (SeOa) in tert-alcohols has been widely used for the dehydrogenation of 3-0x0 steroids, and particularly in the conversion of A -3-ketones into A dienones [240]. Other steroidal ketones suffer similar a,jS -dehydrogena-tion e.g. i2-ketones [241] and a 4,4-dimethyl-7-ketone [242]), but the same reagent in different solvents will also effect oxidation of certain steroidal ketones with adjacent methylene groups ( C0-CH2 ) into a -diketones (-CO CO-), a reaction which is common outside the steroid field. In ethanolic solution, for example, 5a-cholestan-3 one was oxidised by SeOa to give 5a-cholestane-2,3-dione [243], isolated in its enoHc forms. 

Selenium dioxide dehydrogenated the 3)8-fluoro-oestra-5(10)-ene (155) to give the 5(10),9(ll)-diene (156). Allylic oxidation of a 3) -fluoro-A -steroid (157) with selenium dioxide gives the 4)5-hydroxy-derivative (160). A similar oxidation is well known in 3) -hydroxy-A -steroids, where the 3/i-hydroxy-group... 

Benzeneseleninic acid and anhydride appear to be attractive alternatives to selenium dioxide as dehydrogenation agents of steroidal ketones (31) and amides (32). Potassium fencholate as the base, and fenchone as hydride acceptor, is an effective mixture for deprotonation-elimination of acidic C—H bonds, e.g. (33) to (34) in 90% yield." ... 

Of all the methods currently used for the dehydrogenation of carbonyl and similar compounds, those utilizing selenium-based reagents have possibly received the greatest attention. Historically, selenium first found utility as its dioxide for the dehydrogenation of steroidal ketones (equation but the re-... 

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