A ruthenium catalyzed oxidation of steroidal alkenes to enones (original) (raw)
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A variety of 5 -steroids were converted into ␣, -unsaturated 7-ketones using a modification of the already known method of t-butyl hydroperoxide in the presence of copper iodide in acetonitrile. The same alteration was applied to another oxidative procedure, which had never been used before on steroidal substrates. The same oxidative agent was used in the presence of copper iodide, and tetra-n-butylammonium bromide was used as a phase-transfer catalyst in a two-phase system of water/methylene chloride. It was found that the allylic oxidation proceeded more efficiently when t-butyl hydroperoxide was added to the reaction mixture in portions. The initial addition of the total amount of oxidant or its dropwise addition afforded low yields. This observation contributes to the investigation of the reaction mechanism, and high-yield conversions of steroidal 5,6-enes into the corresponding conjugated 7-ones in short reaction times are reported.
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Steroids and their oxidation products are widely distributed in living organisms and are important intermediates for the synthesis of many biologically active molecules. Due to their pharmacological and synthetic relevance, several oxidative chemical processes for the functionalization of the steroid nucleus have been developed. Green chemistry principles have been incorporated in some oxidative transformations of steroids, allowing significant advances in synthetic chemistry applied to these compounds. This chapter presents a selection of relevant applications of pharmaceutical green chemistry to steroid's oxidative processes. Special emphasis is given to catalytic processes encompassing heterogeneous nanocatalysts, whose application in this context is increasing over the past years. This chapter is organized according to the reaction type that includes alcohol oxidation, epoxidation of alkenes, and allylic oxidation of alkenes to enones, among other relevant oxidative transformations. Biocatalytic oxidative methods applied to steroid synthesis are not included in this review.
Steroids, 2006
We have investigated the oxidative behavior of sterols such as cholesteryl acetate (1), 7-dehydrocholesteryl acetate (2), ergosteryl acetate (3), cholecalciferol acetate (Vitamin D3 acetate) (4) and ergocalciferol acetate (Vitamin D2 acetate) (5) with the oxidant system methyltrioxorhenium/H2O2/pyridine in order to check potential parameters controlling the selectivity. The reactions, performed in CH2Cl2/H2O at 25°C, have shown good regio- and stereoselectivity. All
The oxidation of Δ2, Δ2,4 and Δ4,6 steroids with RuO4
Steroids, 2004
In order to find new ways for the functionalization of the A and B rings of the steroid nucleus, the reaction of 5alpha-androst-2-en-17beta-ol 17-acetate (1), cholesta-2,4-diene (4) and cholesta-4,6-dien-3beta-ol 3-acetate (7) was examined using stoichiometric amounts of ruthenium tetraoxide to yield 1,2-cis diols and/or alpha-hydroxy ketones. The reaction of 5alpha-cholest-2-en-3-ol 3-acetate (9) with ruthenium tetraoxide was also carried out and afforded, apart from an alpha-hydroxy ketone, also a diketone and a seco-dicarboxylic acid. The structures of all new steroids, including stereochemical details, were deduced by analysis of spectral data.