- Mechanistic Insights into Rhenium-Catalyzed Regioselective C-Alkenylation of Phenols with Internal Alkynes
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A (μ-aryloxo)rhenium complex was isolated and confirmed as a key precatalyst for rhenium-catalyzed ortho-alkenylation (C-alkenylation) of unprotected phenols with alkynes. The reaction exclusively provided ortho-alkenylphenols; the formation of para or multiply alkenylated phenols and hydrophenoxylation (O-alkenylation) products was not observed. Several mechanistic experiments excluded a classical Friedel–Crafts-type mechanism, leading to the proposed phenolic hydroxyl group assisted electrophilic alkenylation as the most plausible reaction mechanism. For this purpose, the use of rhenium, a metal between the early and late transition metals in the periodic table, was key for the activation of both the soft carbon–carbon triple bond of the alkyne and the hard oxygen atom of the phenol, at the same time. ortho-Selective alkenylation with allenes also provided the corresponding adducts with a substitution pattern different from that obtained by the addition reaction with alkynes.
- Murai, Masahito,Yamamoto, Masaki,Takai, Kazuhiko
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supporting information
p. 15189 - 15197
(2019/11/16)
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- Photocatalytic Hydrogen-Evolution Cross-Couplings: Benzene C-H Amination and Hydroxylation
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We present a blueprint for aromatic C-H functionalization via a combination of photocatalysis and cobalt catalysis and describe the utility of this strategy for benzene amination and hydroxylation. Without any sacrificial oxidant, we could use the dual catalyst system to produce aniline directly from benzene and ammonia, and phenol from benzene and water, both with evolution of hydrogen gas under unusually mild conditions in excellent yields and selectivities.
- Zheng, Yi-Wen,Chen, Bin,Ye, Pan,Feng, Ke,Wang, Wenguang,Meng, Qing-Yuan,Wu, Li-Zhu,Tung, Chen-Ho
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supporting information
p. 10080 - 10083
(2016/09/04)
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- Platinum catalyzed H-D exchange reaction of various aromatic compounds under hydrothermal condition
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Various aromatic compounds were treated with deuterium oxide under hydrothermal conditions in the presence of a catalytic amount of platinum (IV) oxide. An efficient H-D exchange reaction was observed, which gave various deterium labeled aromatic compounds.
- Yamamoto, Mitsuru,Oshima, Koichiro,Matsubara, Seijiro
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p. 353 - 359
(2007/10/03)
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- Stoichiometric and catalytic H/D incorporation by cationic iridium complexes: A common monohydrido-iridium intermediate
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A mechanistic study of the Stoichiometric and catalytic H/D exchange reactions involving cationic iridium complexes is presented. Strong evidence suggests that both Stoichiometric and catalytic reactions proceed via a monohydrido-iridium species. Stoichiometric deuterium incorporation reactions introduce multiple deuterium atoms into the organic products when aryliridium compounds Cp*PMe3Ir(C6H4X)(OTf) (X = H, o-CH3, m-CH3, p-CH3) react with D2. Multiple deuteration occurs at the unhindered positions (para and meta) of toluene, when X = CH3. The multiple-deuteration pathway is suppressed in the presence of an excess of the coordinating ligand, CH3CN. The compound Cp*PMe3IrH(OTf) (1-OTf) is observed in low-temperature, Stoichiometric experiments to support a monohydrido-iridium intermediate that is responsible for catalyzing multiple deuteration in the stoichiometric system. When paired with acetone-d6, [Cp*PMe3IrH3][OTf] (4) catalytically deuterates a wide range of substrates with a variety of functional groups. Catalyst 4 decomposes to [Cp*PMe3Ir(η3-CH 2C(OH)CH2)][OTf] (19) in acetone and to [Cp*PMe 3IrH(CO)]-[OTf] (1-CO) in CH3OH. The catalytic H/D exchange reaction is not catalyzed by simple H+ transfer, but instead proceeds by a reversible C-H bond activation mechanism.
- Yung, Cathleen M.,Skaddan, Marc B.,Bergman, Robert G.
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p. 13033 - 13043
(2007/10/03)
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- Efficient H-D exchange of aromatic compounds in near-critical D2O catalysed by a polymer-supported sulphonic acid
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Hydrogen atom exchange of aromatic compounds in neutral near-critical D2O has been improved by using a polymer-supported sulphonic acid catalyst. Phenol, aniline, quinoline, and substituted aromatic hydrocarbons are selectively ring-perdeuterated in high yields with insignificant by-product formation at 325 °C for 24 h in D2O/Deloxan.
- Boix, Carmen,Poliakoff, Martyn
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p. 4433 - 4436
(2007/10/03)
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- Semi-empirical and vibrational studies of flavone and some deuterated analogues
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The infrared solid state, Raman solid state and tetrachloride solution spectra of flavone have been obtained.Assignments of most of the vibrational data have been performed by comparison between the spectra of flavone and three isotopic species, deuterated on the A, B and C rings, respectively.The vibrational frequencies for all the investigated compounds have been calculated from the conformational analysis of flavone using the semi-empirical AM1 method and compared with experimental values.The correlation is more or less satisfactory; however, for some vibrational modes, the calculated isotopic shifts agree better with experiment than do the frequencies themselves.Specific vibrational modes which retain a benzene ring mono-substituted and ortho-distributed character have been recognized in the spectra, according to literature data, isotopic frequency shifts and graphic representation of the atomic displacements.
- Vrielynck, L.,Cornard, J. P.,Merlin, J. C.,Lautie, M. F.
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p. 2177 - 2188
(2007/10/02)
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- Gas-phase oxygenation of benzene derivatives around 300 K with O(3P) atoms produced by microwave discharge of N2O. Part 2. Kinetic H/D isotope effects.
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The possible pathways for the formation of (chloro)phenol, following the addition of O(3P) to (chloro)benzene, have been examined using deuterated substrates: C6D6 (also in admixture with C6H6) and p-deuterochlorobenzene.Whereas with O-C6H6 adduct biradicals, loss of H* to give phenoxy radicals predominates, only one-third of the O-C5D6 intermediates undergo the corresponding reaction.Phenoxy radicals lead to phenol by transfer of an H(D) atom from cyclohexadienyl-type radicals, formed from H* (D*) and substrate.Analogously, in reactions of p-deuterochlorobenzene, loss of H is a major reaction after addition of an oxygen atom to a meta position, whereas loss of D (to give p-chlorophenol) occurs only with 35percent of the corresponding O(3P) adduct biradicals.The isotopic composition of phenol formed from p-DC6H4Cl (via p-DC6H4O*; generated by ipso substitution) revealed that H transfer to phenoxy radicals primarily gives the keto tautomers as major products.Isomerization of (chloro)benzene-O(3P) adduct biradicals to the corresponding phenols also appears to involve mainly, keto tautomers.The reaction of O(3P) with p-deuterochlorobenzene showed a slight change in the o/m/p distribution; this can be explained by the absence of a net secondary H/D isotope effect for O(3P) addition to the para site and a normal secondary isotope effect for meta addition.
- Sol, Veronica M.,Louw, Robert,Mulder, Peter
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p. 346 - 352
(2007/10/02)
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- Palladium catalyzed direct oxidation of benzene with molecular oxygen to phenol
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Direct phenol synthesis from benzene is currently one of the most important problems in modern chemistry. We have reported new phenol synthesis from benzene and O2 via direct activation of a C-H aromatic bond by the Pd(OAc)2/phenanthroline catalyst system. The evidence for direct oxidation of benzene by O2 was obtained using 18O and 2H isotopes. The mechanism was proposed on the basis of these results and the reactions of Ph-Pd σ complex intermediates.
- Jintoku,Takaki,Fujiwara,Fuchita,Hiraki
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p. 438 - 441
(2007/10/02)
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- Relaxation in an A2 coupled spin system dissolved in a perdeuterated liquid crystal: The intermolecular dipolar random field cross relaxation term
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A perdeuterated nematic liquid crystal N-(p-ethoxybenzylidene)-p-n-butylaniline (EBBA-d23, 98percent deuterium) was synthesized to study relaxation of small molecules dissolved in anisotropic solvents.Proton spin-lattice relaxation in the coupled A2 spin system of methylene chloride (CH2Cl2) was studied using both perhydro and perdeutero EBBA as the solvent.The relaxation was modeled as intramolecular dipole-dipole interactions plus other mechanisms that were treated collectively as fluctuating external random magnetic fields.Comparison of relaxation in EBBA and EBBA-d23 allowed the first experimental measurement of the correlation coefficient between external random fields at the two protons due to dipolar interactions of the methylene protons with the protons or deuterons of the solvent (78percent correlated).The selective nuclear Overhauser effect was also studied.
- Courtieu, J.,Jullien, J.,Lai, Nguyen Thoi,Guillois, A.,Gonord, P.,et al.
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p. 953 - 959
(2007/10/02)
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