- 1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones
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Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.
- Baschieri, Andrea,Amorati, Riccardo,Valgimigli, Luca,Sambri, Letizia
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p. 13655 - 13664
(2019/10/28)
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- Diels-Alder trapping of in situ generated dienes from 3,4-dihydro-2H-pyran with p-quinone catalysed by p-toluenesulfonic acid
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This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids. The products were accomplished by the Diels-Alder cycloaddition reaction and their mechanistic pathways have been formulated. The impact of C2 and C2,5 substituents of the p-quinones on the cycloaddition reaction has been explored. Remarkably, it is the first report to explore this kind of in situ generated diene for the Diels-Alder cycloaddition reaction.
- Mohan Raj, Radhakrishnan,Balasubramanian, Kalpattu K.,Easwaramoorthy, Deivanayagam
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p. 1115 - 1121
(2017/02/10)
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- Catalytic defluorination of perfluorinated aromatics under oxidative conditions using N-bridged diiron phthalocyanine
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Carbon-fluorine bonds are the strongest single bonds in organic chemistry, making activation and cleavage usually associated with organometallic and reductive approaches particularly difficult. We describe here an efficient defluorination of poly- and perfluorinated aromatics under oxidative conditions catalyzed by the μ-nitrido diiron phthalocyanine complex [(Pc)Fe III(μ-N)FeIV(Pc)] under mild conditions (hydrogen peroxide as the oxidant, near-ambient temperatures). The reaction proceeds via the formation of a high-valent diiron phthalocyanine radical cation complex with fluoride axial ligands, [(Pc)(F)FeIV(μ-N)FeIV(F) (Pc+?)], which was isolated and characterized by UV-vis, EPR, 19F NMR, Fe K-edge EXAFS, XANES, and Kβ X-ray emission spectroscopy, ESI-MS, and electrochemical techniques. A wide range of per- and polyfluorinated aromatics (21 examples), including C6F6, C6F5CF3, C6F5CN, and C6F5NO2, were defluorinated with high conversions and high turnover numbers. [(Pc)FeIII(μ-N)Fe IV(Pc)] immobilized on a carbon support showed increased catalytic activity in heterogeneous defluorination in water, providing up to 4825 C-F cleavages per catalyst molecule. The μ-nitrido diiron structure is essential for the oxidative defluorination. Intramolecular competitive reactions using C6F3Cl3 and C6F3H 3 probes indicated preferential transformation of C-F bonds with respect to C-Cl and C-H bonds. On the basis of the available data, mechanistic issues of this unusual reactivity are discussed and a tentative mechanism of defluorination under oxidative conditions is proposed.
- Colomban, Cédric,Kudrik, Evgenij V.,Afanasiev, Pavel,Sorokin, Alexander B.
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supporting information
p. 11321 - 11330
(2014/11/07)
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- Mechanism of ruthenium-catalyzed hydrogen transfer reactions. Concerted transfer of OH and CH hydrogens from an alcohol to a (cyclopentadienone) ruthenium complex
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Kinetic studies of the ruthenium-catalyzed dehydrogenation of 1-(4-fluorophenyl)ethanol (4) by tetrafluorobenzoquinone (7) using the Shvo catalyst 1 at 70 °C show that the dehydrogenation by catalytic intermediate 2 is rate-determining with the rate = k [4][1]1/2 and with ΔH? = 17.7 kcal mol-1 and ΔS? = -13.0 eu. The use of specifically deuterated derivative 4-CHOD and 4-CDOH gave individual isotope effects of kCHOH/kCHOD = 1.87 ± 0.17 and kCHOH/kCDOH = 2.57 ± 0.26, respectively. Dideuterated derivative 4-CDOD gave a combined isotope effect of k CHOH/kCDOD = 4.61 ± 0.37. These isotope effects are consistent with a concerted transfer of both hydrogens of the alcohol to ruthenium species 2.
- Johnson, Jeffrey B.,Baeckvall, Jan-E.
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p. 7681 - 7684
(2007/10/03)
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- Steric effects in photoinduced electron transfer reaction of halogenated 1,4-benzoquinones with donor olefins
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(Equation presented) The photoinduced electron transfer reaction of halogenated 1,4-benzoquinones with 2,3-dimethyl-2-butene or 3,4-dimethyl-2-pentene gave the primary, secondary, and tertiary monoallyl ethers of hydroquinones, with the product distributi
- Kokubo, Ken,Masaki, Takayoshi,Oshima, Takumi
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p. 1979 - 1981
(2007/10/03)
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