- Distribution of Spin Density on Phenoxyl Radicals Affects the Selectivity of Aerobic Oxygenation of Phenols
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Phenoxyl radical was generally suggested as the intermediate during copper-catalyzed aerobic oxygenation of phenols. However, the substrate-dependent selectivity has not been well interpreted, due to insufficient characterization of the radical intermediate under reaction conditions. When studying the CuCl-LiCl-catalyzed aerobic phenol oxidation, we obtained EPR spectra of phenoxyl radicals generated by oxidizing phenols with the preactivated catalyst. Upon correlation to the selectivity of benzoquinone, the hyperfine coupling constant of para-site proton (aH, para) was found to be better than the Hammett constant. The catalysis mechanism was studied based on EPR detection and the reaction results of phenoxyl radicals under N2 or O2 atmosphere. It appeared that the chemoselectivity depended on the attack of activated dioxygen on phenoxyl radicals, and the activation of dioxygen by [CunCln+1]- (n = 1, 2, 3) was suggested as the rate-determining step. Understanding of the substrate-dependent selectivity contributed to predicting the chemoselectivity in the aerobic oxidation of phenols.
- Chen, Kaizhou,Du, Renfeng,Fan, Mengtian,Guan, Jun,Jiang, Zheng,Li, Haoran,Lu, Rui,Mei, Bingbao,Wang, Yongtao,Yao, Jia
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- Dimethyl carbonate: an environmentally friendly solvent for hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic oxidations
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Environmentally friendly oxidations of various organic compounds with the hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3, MTO) catalytic system have been described in dimethyl carbonate (DMC), a cheap commercially available and benign chemical having interesting solvating properties, low toxicity and high biodegradability. Oxidations proceeded with good conversions and in good yields. Spectrophotometric analysis demonstrated that the [CH3ReO(O-O)2] complex was formed in DMC and that it was stable for several days at room temperature.
- Bernini, Roberta,Mincione, Enrico,Barontini, Maurizio,Crisante, Fernanda,Fabrizi, Giancarlo,Gambacorta, Augusto
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p. 6895 - 6900
(2008/02/10)
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- Convenient oxidation of alkylated phenols and methoxytoluenes to antifungal 1,4-benzoquinones with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) catalytic system in neutral ionic liquid
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Alkylated phenol and methoxytoluene derivatives were catalytically and selectively oxidized to the corresponding 1,4-benzoquinones in good conversions and yields. Reactions were performed with hydrogen peroxide (H2O2)/methyltrioxorhenium (CH3ReO3) in 1-butyl-3-methylimidazolium tetrafluoroborate [bmim]BF4, a neutral ionic liquid. Compounds were tested in vitro for their antifungal activity against the growth of several widespread soil fungi. Some of them were proved to be potent inhibitors of Fusarium sp. than ketoconazole, a commercially available and expensive antifungal agent.
- Bernini, Roberta,Mincione, Enrico,Barontini, Maurizio,Fabrizi, Giancarlo,Pasqualetti, Marcella,Tempesta, Sabrina
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p. 7733 - 7737
(2007/10/03)
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- Selective oxidation of phenols to hydroxybenzaldehydes and benzoquinones with dioxygen catalyzed by polymer-supported copper
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Oxidation of 2,6-disubstituted 4-methylphenols with dioxygen by using a CuCl2-poly(4-methyl-4′-vinyl-2,2′-bipyridine) catalyst gave the corresponding 4-hydroxybenzaldehydes in high yields. The activity of the catalyst and the selectivity of the products significantly depended on the reaction conditions and the composition of the catalyst. When the molar ratio of the bipyridine unit of the polymer ligand to Cu was unity, i.e., N/Cu = 2, the best results were obtained. Moreover, the reaction is likely to be promoted by coordination of the products to the catalyst. Similarly, 2,3,6-trimethylphenol and related compounds were converted to p-benzoquinones selectively with a CuCl2-poly(4-vinylpyridine) catalyst. These polymer-supported catalysts were readily recovered and are reusable without noticeable decrease of their activity.
- Takaki, Ken,Shimasaki, Yohei,Shishido, Tetsuya,Takehira, Katsuomi
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p. 311 - 317
(2007/10/03)
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- Oxidative coupling of some 2,6-disubstituted phenol derivatives in perchloric acid mediated by cerium(IV) ions
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2,6-Disubstituted phenol derivatives have been oxidized by cerium(IV) perchlorate in aqueous or aqueous-acetonitrile solutions of perchloric acid as well as in two-phase systems to the corresponding 1,4-benzoquinones, 4,4′-diphenoquinones, and oligomeric
- Domagala, Slawomir,Steglinska, Violetta,Dziegiec, Jozef
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p. 761 - 768
(2007/10/03)
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- 4-Hydroxytetrahydropyran-2-one derivatives
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4-hydroxytetrahydropyran-2-one derivatives with general formula (I) are useful as cholesterol reducing agents as well as lipid reducing agents, serving as inhibitors of HMG-CoA reductase, and capable of inhibiting the biosynthesis of peroxidized lipids, and therefore effective for curing arteriosclerosis: STR1 wherein R1 represent hydrogen or a 2-tetrahydropyranyl group; R2 and R3 each represent hydrogen or an alkyl group having 1 to 6 carbon atoms; R4 represents hydrogen, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an aryl group, an aralkyl group, an acyl group, an aroyl group or a substituted sulfonyl group; A represents --CH2 CH2 --, or --CH=CH--; and n is an integer of 1 or 2, and intermediates for synthesizing the 4-hydroxytetrahydropyran-2-one derivatives are disclosed.
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- The Oxidation of p-Substituted Phenols Using a t-Butyl Hydroperoxide-Heteropolyacid System
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The oxidation of p-substituted phenols with t-BuOOH in the presence of heteropolyacids was carried out. 4-t-Butylperoxy-2,5-cyclohexadien-1-ones were obtained in good yields by the oxidation of 2,4,6-trialkylsubstituted phenols in this oxidation system.
- Shimizu, Masao,Orita, Hideo,Hayakawa, Takashi,Watanabe, Yoshihito,Takehira, Katsuomi
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p. 2583 - 2584
(2007/10/02)
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- Electrochemical Oxidation, VII. Synthesis and Structure of 7-tert-Butyl-2-methylbenzoxazoles
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Anodic oxidation of 15 tert-butylphenols 1a - o in absolute acetonitrile or acetonitrile/perchloric acid leads to the corresponding 7-tert-butyl-2-methylbenzoxazoles 3a - o.The proof of the structure was achieved by independent synthesis of 3k, and by 13C NMR spectroscopy as well as by X-ray analysis of 7-tert-butyl-2-methyl-5-benzoxazolecarbaldehyde (3j).The influence of the supporting electrolyte on the formation of the oxidation products is discussed.
- Dreher, Eberhard-Ludwig,Bracht, Juergen,El-Mobayed, Medhat,Huetter, Peter,Winter, Werner,Rieker, Anton
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p. 288 - 308
(2007/10/02)
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