- Synthesis of 2-substituted quinones, vitamin K3, and vitamin K1 from p-cresol. BF3·OEt2-catalyzed methyl migration of 4-tert-butyldioxycyclohexadienones
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BF3·OEt2-catalyzed methyl group migration of 4-methyl-4-tert-butyldioxycyclohexadienone, which is obtained by ruthenium-catalyzed oxidation of p-cresol with tert-butyl hydroperoxide, in hexafluoro-2-propanol/toluene gave toluquinone efficiently. The reaction can be applied to the regio-selective short-step syntheses of vitamin K3 and vitamin K1 from p-cresol.
- Murahashi, Shun-Ichi,Fujii, Akiko,Inubushi, Yasutaka,Komiya, Naruyoshi
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- Ruthenium-catalyzed oxidative dearomatization of phenols to 4-(tert-butylperoxy)cyclohexadienones: Synthesis of 2-substituted quinones from p-substituted phenols
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The ruthenium-catalyzed oxidation of phenols with tert-butylhydroperoxide efficiently gives the corresponding 4-(tert-butylperoxy)cyclohexadienones. The oxidation proceeds selectively because of ruthenium's ability for rapid single-electron transfer. This biomimetic oxidation reaction is highly useful to obtain the metabolic compounds desired for confirming the safety of medicines and related compounds. Typically, the first metabolic compound of the female hormone estrone is readily obtained by this biomimetic oxidation reaction. The resulting 4-(tert-butylperoxy)cyclohexadienones are versatile synthetic intermediates, which can be transformed into 2-substituted 1,4-benzoquinones by treatment with acid catalysts. Acid-promoted rearrangement followed by a Diels-Alder reaction provides a new strategy for the synthesis of fused cyclic compounds, such as naphthoquinone and anthraquinone derivatives, from readily available phenols. The nonnatural 1,4-diacetoxy steroidal skeleton is obtained by the oxidation of estrone followed by zinc-mediated migration. Vitamin K 3 is synthesized selectively from p-cresol in an overall 79 % yield in 4 steps, and the synthesis includes the ruthenium-catalyzed oxidation.
- Murahashi, Shun-Ichi,Miyaguchi, Noriko,Noda, Shinji,Naota, Takeshi,Fujii, Akiko,Inubushi, Yasutaka,Komiya, Naruyoshi
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- Ingold-Fischer "Persistent Radical Effect", Solvent Effect, and Metal Salt Oxidation of Carbon-Centered Radicals in the Synthesis of Mixed Peroxides from tert-Butyl Hydroperoxide
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Mixed peroxides are formed from tert-butyl hydroperoxide (TBH), tert-butyl peroxalate (TBP), and a variety of substrates (p-cresol, cyclohexene, styrene, α-methylstyrene, acrylonitrile, 2-methylcyclohexanone). Also, the oxidation of THF in the presence of acrylonitrile under the same conditions gives the mixed peroxide, generated by addition of the tetrahydrofuranyl radical to the double bond and the cross-coupling of the radical adduct with the tert-butylperoxyl radical. Similarly, benzoyl peroxide, TBH, and acrylonitrile give the mixed peroxide by oxidative arylation of the double bond. Paradoxically, TBH acts as effective inhibitor of the polymerization of vinyl monomers (acrylonitrile, styrene). An overall kinetic evaluation suggests that the conditions for the Ingold-Fischer "persistent radical effect", characterized by the simultaneous formation of a persistent and a transient radical, are fulfilled in all cases. The reactions are strongly affected by solvents, which form hydrogen bonds with TBH. Catalytic amounts of Cu(II) and Fe(III) salts influence the selectivity; the possibility that the mixed peroxides can also be generated by metal salt oxidation of carbon-centered radicals is discussed.
- Bravo, Anna,Bjorsvik, Hans-Rene,Fontana, Francesca,Liguori, Lucia,Minisci, Francesco
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- Dirhodium-catalyzed phenol and aniline oxidations with T-HYDRO. Substrate scope and mechanism of oxidation
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Dirhodium caprolactamate, Rh2(cap)4, is a very efficient catalyst for the generation of the tert-butylperoxy radical from tert-butyl hydroperoxide, and the tert-butylperoxy radical is a highly effective oxidant for phenols and anilines. These reactions are performed with 70% aqueous tert-butyl hydroperoxide using dirhodium caprolactamate in amounts as low as 0.01 mol % to oxidize para-substituted phenols to 4-(tert-butyldioxy) cyclohexadienones. Although these transformations have normally been performed in halocarbon solvents, there is a significant rate enhancement when Rh 2(cap)4-catalyzed phenol oxidations are performed in toluene or chlorobenzene. Electron-rich and electron-poor phenolic substrates undergo selective oxidation in good to excellent yields, but steric influences from bulky para substituents force oxidation onto the ortho position resulting in ortho-quinones. Comparative results with RuCl2(PPh 3)3 and CuI are provided, and mechanistic comparisons are made between these catalysts that are based on diastereoselectivity (reactions with estrone), regioselectivity (reactions with p-tert-butylphenol), and chemoselectivity in the formation of 4-(tert-butyldioxy)cyclohexadienones. The data obtained are consistent with hydrogen atom abstraction by the tert-butylperoxy radical followed by radical combination between the phenoxy radical and the tert-butylperoxy radical. Under similar reaction conditions, para-substituted anilines are oxidized to nitroarenes in good yield, presumably through the corresponding nitrosoarene, and primary amines are oxidized to carbonyl compounds by TBHP in the presence of catalytic amounts of Rh 2(cap)4.
- Ratnikov, Maxim O.,Farkas, Linda E.,McLaughlin, Emily C.,Chiou, Grace,Choi, Hojae,El-Khalafy, Sahar H.,Doyle, Michael P.
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scheme or table
p. 2585 - 2593
(2011/06/19)
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- 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 29
(2009/04/24)
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- Free-radical oxidation of para-substituted phenols by hypervalent tert-butylperoxiodane and tert-butyl hydroperoxide: Synthesis of 4-(tert-butylperoxy)-2,5-cyclohexadien-1-ones
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Oxidation of 4-alkylphenols 1 by 1-(tert-butylperoxy)-1,2-benziodoxol-3(1H)-one (2) in the presence of tert-butyl hydroperoxide affords selectively 4-(tert-butylperoxy)-2,5-cyclohexadien-1-ones 3 in good yields. Evidence for the involvement of free-radicals is reported.
- Ochiai, Masahito,Nakanishi, Akinobu,Yamada, Akiko
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p. 3927 - 3930
(2007/10/03)
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- A free-radical mechanism in a novel metalloporphyrin-catalyzed oxidation of phenols by t-BuOOH
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Metalloporphyrins, a chemical model of cytochrome P450, catalyze the oxidation of phenols with the para-position free to the corresponding p-quinones. Evidences of a free-radical mechanism are reported, including the results obtained with p-cresol.
- Brovo, Anna,Fontana, Francesca,Minisci, Francesco
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p. 401 - 402
(2007/10/03)
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- AN IMPROVED PROCEDURE FOR THE CONVERSION OF 3,3-DISUBSTITUTED-1,4-CYCLOHEXADIENES TO 2,5-CYCLOHEXADIEN-1-ONES
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The bis-allylic oxidations of 1,4-cyclohexadienes with tert-butyl hydroperoxide and pyridinium dichromate give 2,5-cyclohexadien-1-ones in good to excellent yields.
- Schultz, Arthur G.,Taveras, Arthur G.,Harrington, Roger E.
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p. 3907 - 3910
(2007/10/02)
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