- Allylic Oxidations Catalyzed by Dirhodium Catalysts under Aqueous Conditions
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The present invention relates to compositions and methods for achieving the efficient allylic oxidation of organic molecules, especially olefins and steroids, under aqueous conditions. The invention concerns the use of dirhodium (II,II) “paddlewheel complexes, and in particular, dirhodium carboximate and tert-butyl hydroperoxide as catalysts for the reaction. The use of aqueous conditions is particularly advantageous in the allylic oxidation of 7-keto steroids, which could not be effectively oxidized using anhydrous methods, and in extending allylic oxidation to enamides and enol ethers.
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Page/Page column 18-19
(2009/04/24)
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- Allylic oxidations catalyzed by dirhodium caprolactamate via aqueous tert-butyl hydroperoxide: The role of the tert-butylperoxy radical
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Dirhodium(II) caprolactamate exhibits optimal efficiency for the production of the tert-butylperoxy radical, which is a selective reagent for hydrogen atom abstraction. These oxidation reactions occur with aqueous tert-butyl hydroperoxide (TBHP) without rapid hydrolysis of the caprolactamate ligands on dirhodium. Allylic oxidations of enones yield the corresponding enedione in moderate to high yields, and applications include allylic oxidations of steroidal enones. Although methylene oxidation to a ketone is more effective, methyl oxidation to a carboxylic acid can also be achieved. The superior efficiency of dirhodium(II) caprolactamate as a catalyst for allylic oxidations by TBHP (mol % of catalyst, % conversion) is described in comparative studies with other metal catalysts that are also reported to be effective for allylic oxidations. That different catalysts produce essentially the same mixture of products with the same relative yields suggests that the catalyst is not involved in product-forming steps. Mechanistic implications arising from studies of allylic oxidation with enones provide new insights into factors that control product formation. A previously undisclosed disproportionation pathway, catalyzed by the tert-butoxy radical, of mixed peroxides for the formation of ketone products via allylic oxidation has been uncovered.
- McLaughlin, Emily C.,Choi, Hojae,Wang, Kan,Chiou, Grace,Doyle, Michael P.
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supporting information; experimental part
p. 730 - 738
(2009/07/04)
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- THE BIOTRANSFORMATION OF SOME STEROIDS BY CEPHALOSPORIUM APHIDICOLA
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Hydroxylation of 5α-androstane-3-one and 3,6-dione by C. aphidicla takes place at C-17β and, in the case of the latter, at C-5α.The fungus reduces 5α-androstan-17-one and the 3,17-dione to the 17β-alcohols. Key Word Index - Cephalosporium aphidicola; fungus; microbiological hydroxylation; steroids.
- Hanson, James R.,Nasir, Habib
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p. 831 - 834
(2007/10/02)
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- OXIDATIONS OF ENONE SYSTEMS IN STEROIDS BY OXIDIZERS WITH REVERSIBLE REDOX POTENTIAL
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The oxidation of steroid enones by oxidizers with reversible redox potentials (mostly tetrazolium salts) is described.Products containing an oxo or hydroxy group at the position γ with respect to the oxo of the enone group were isolated in relatively high yields.The results of kinetic studies on the redox processes are reported and a reaction mechanism is proposed.
- Jasiczak, Jan
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p. 2687 - 2692
(2007/10/02)
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