- Catalytic hydrogenation of aromatic rings catalyzed by Pd/NiO
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A simple and efficient heterogeneous palladium catalyst was prepared for aromatic ring hydrogenation. The catalyst was prepared by a reduction-deposition method and exhibited high activity and selectivity for the hydrogenation of a variety of substituted aromatic compounds to the corresponding cyclohexane and cyclohexanol derivatives with up to 99% yields. The catalyst was characterized by BET, TEM, XRD, XPS and ICP. Meanwhile the reusability of the catalyst was investigated, and it can be reused for several runs without significant deactivation.
- Wang, Yanan,Cui, Xinjiang,Deng, Youquan,Shi, Feng
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p. 2729 - 2732
(2014/01/06)
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- Chemoselective Pd-catalyzed oxidation of polyols: Synthetic scope and mechanistic studies
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The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate α-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that β-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.
- Chung, Kevin,Banik, Steven M.,De Crisci, Antonio G.,Pearson, David M.,Blake, Timothy R.,Olsson, Johan V.,Ingram, Andrew J.,Zare, Richard N.,Waymouth, Robert M.
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supporting information
p. 7593 - 7602
(2013/07/05)
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- Efficient oxidation of 1,2-diols into a-hydroxyketones catalyzed by organotin compounds
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Electrochemical oxidation of 1,2-diols with a catalytic amount of an organotin compound and a bromide ion as mediators has been developed. Various cyclic and acyclic 1,2-diols were oxidized into the corresponding α-hydroxyketones in good to excellent yields without C-C bond cleavage. Also, oxidation with the use of chemical oxidants was accomplished in the presence of a catalytic amount of an organotin compound. These reactions could discriminate 1,2-diols from isolated hydoxyl groups or 1,3-diols. In the case of a conformationally restricted cyclic 1,2-diol, the axial hydroxyl group was oxidized exclusively. Mono-, di-, and trialkylated tin compounds were examined as mediators and dialkylated tin compounds showed higher catalytic activity than mono- and trisubstituted ones. Me2SnCl2 was found to be the most suitable mediator for the selective oxidation..
- Maki, Toshihide,Iikawa, Shinya,Mogami, Gen,Harasawa, Hitomi,Matsumura, Yoshihiro,Onomura, Osamu
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experimental part
p. 5364 - 5370
(2009/12/22)
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- Diastereoselective inter- and intramolecular pinacol coupling of aldehydes promoted by monomeric titanocene(III) complex Cp2TiPh
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A monomeric titanocene(III) derivative, Cp2TiPh, effectively promoted the pinacol coupling of both an aromatic aldehyde, benzaldehyde, and an aliphatic aldehyde, 3-phenylpropionaldehyde. The same reactive complex was successfully generated by a catalytic amount of a precursor, Cp2Ti(Ph)Cl, and its stoichiometric amount of Zn. The Cp2TiPh-catalyzed pinacol coupling of benzaldehyde derivatives and aliphatic aldehydes afforded the corresponding 1,2-diols in high yields with moderate to good threo-selectivity. On the other hand, Cp2TiPh-catalyzed pinacol-cyclization of dials gave cyclic 1,2-diols with excellent diastereoselectivity. The extension of this protocol to chiral dials demonstrated that the phenyltitanium complex catalytically transmitted an axial chirality or a central, chirality of the starting dials to the central chirality of the resultant 1,2-diols.
- Yamamoto,Hattori,Miwa,Nakagai,Kubota,Yamamoto,Okamoto,Itoh
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p. 3865 - 3870
(2007/10/03)
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- Highly trans-selective intramolecular pinacol coupling of dials catalyzed by bulky Cp2TiPh
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Cp2Ti(Ph)Cl in the presence of Me3SiCl and Zn provides an effective pinacol coupling catalyst for aromatic and aliphatic aldehydes.
- Yamamoto, Yoshihiko,Hattori, Reiko,Itoh, Kenji
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p. 825 - 826
(2007/10/03)
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- The Use of Bismuth(III) Acetate in 'Wet' and 'Dry' Prevost Reactions
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cis-Diol and trans-diol derivatives can be prepared from alkenes by reaction with iodine and bismuth(III) acetate in 'wet' and 'dry' acetic acid, respectively.Reactions using lesser amounts of bismuth(III) acetate under 'dry' conditions give iodo acetates and under 'wet' conditions a mixture of iodohydrins and iodo ethers.Comparison of these reactions with those promoted by silver, copper, mercury and thallium salts is included.
- Trainor, Robert W.,Deacon, Glen B.,Jackson, W. Roy,Giunta, Nunzio
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p. 1265 - 1280
(2007/10/02)
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