- Phenyl Silicates with Substituted Catecholate Ligands: Synthesis, Structural Studies and Reactivity
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While the generation of aryl radicals by photoredox catalysis under reductive conditions is well documented, it has remained challenging under an oxidative pathway. Because of the easy photo-oxidation of alkyl bis-catecholato silicates, a general study of phenyl silicates bearing substituted catecholate ligands has been achieved. The newly synthesized phenyl silicates have been fully characterized, and their reactivity has been explored. It was found that, thanks to the substitution of the catecholate moiety, notably with the 4-cyanocatecholato ligand, the phenyl radical could be generated and trapped. Computational studies provided a rationale for these findings.
- Levernier, Etienne,Jaouadi, Khaoula,Zhang, Heng-Rui,Corcé, Vincent,Bernard, Aurélie,Gontard, Geoffrey,Troufflard, Claire,Grimaud, Laurence,Derat, Etienne,Ollivier, Cyril,Fensterbank, Louis
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- Photo-CIDNP and Nanosecond Laser Flash Photolysis Studies on the Photodecomposition of Triarylsulfonium Salts
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The direct and sensitized photodecomposition of triarylsulfonium salts have been investigated by nanosecond laser flash photolysis and steady-state photo-CIDNP.The direct photoreaction of triphenylsulfonium salts was shown to proceed via a singlet diphenylsulfinyl radical cation-phenyl radical pair which is produced by internal electron transfer from the initially formed phenyl cation-diphenyl sulfide pair.Recombination of both sets of intermediates gives protonated (phenylthio)biphenyls, identified as a broad transient absorption centered at 465 nm, which lose H+ to give 2-, 3-, and 4-(phenylthio)biphenyl.The acetone-sensitized photoreaction gave a triplet excited state of the salt, which then dissociated to give the triplet diphenylsulfinyl radical cation (λ max 750, 340 nm)-phenyl radical pair and subsequently underwent escape reactions with the solvent.Anthracene-, 9,10-diphenylanthracene-, naphthalene-, and perylene-sensitized photoreactions of triphenylsulfonium salts proceeded by electron transfer from the singlet excited state of the aromatic hydrocarbon to give the singlet aromatic hydrocarbon radical cation-triphenylsulfur radical pair, which dissociates to the in-cage triad of diphenyl sulfide, phenyl radical and the aromatic hydrocarbon radical cation.In the solvent cage naphthalene radical cation can oxidize diphenyl sulfide to diphenylsulfinyl radical cation, identified by transient absorptions at 750 and 340 nm, whereas the other hydrocarbon radical cations cannot.In contrast to the triphenylsulfonium salts, the diphenylsulfonium salt decomposed via the triplet excited state upon both direct and triplet-sensitized photolysis.Photo-CIDNP gave a strong enhanced absorption which was quenched upon the addition of oxygen and also gave transients, identified as diphenylsulfinyl radical cation (λ max 750, 340 nm), upon both direct and triplet-sensitized photolysis.
- Welsh, Kevin M.,Dektar, John L.,Garcia-Garibaya, Miguel A.,Hacker, Nigel P.,Turro, Nicholas J.
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- Stereochemistry of Dehydrogenation of 1,4-cyclohexadiene with 2,3-dichloro-5,6-dicyano-p-benzoquinone
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cis- and trans-(3,6-D2)-1,4-cyclohexadienes 1a and 1b have been synthesized from cis-3,4-dichlorocyclobutene (5).Aromatization to benzene with DDQ is cis-stereospecific with an uncertainty of 5percent.This results is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4-dihydroaromatics with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ).
- Mueller, Paul,Joly, Daniel,Mermoud, Francois
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- Simulation of vibrational spectra of isotopic benzenes by an extended molecular mechanics method
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Vibrational spectra of benzene and benzene-d6 in the gas and liquid phase have been simulated by a molecular mechanics method including the calculation of equilibrium structures, thermodynamic quantities, normal frequencies and vibrational transition probabilities.The potential parameters have been estimated by referring to the observed frequencies of benzene, benzene-d6 and 1,3,5-benzene-d3 and also to results of ab initio, calculations.Four and ten independent parameters are required, respectively, for elucidating the infrared absorption and Raman intensities of these compounds in the gas and liquid phase.The infrared absorption spectrum of benzene-d1 is reproduced well by using the potential and the intensity parameters estimated for benzene and benzene-d6.The change of relative band intensities on the phase change has been elucidated in terms of the change of various intensity parameters.
- Miwa, Yoshihisa,Mimura, Norio,Machida, Katsunosuke,Nakagawa, Tetsuo,Umemura, Junzo,Hayashi, Soichi
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- C-C bond Activation: Cycloheptatriene Reaction on W(100), W(100)-(5X1)-C,and W(100)-(2X1)-O
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The adsorption and reaction of cycloheptatriene (c-C7H8) was investigated on W(100), W(100)-(5X1)-C, and W(100)-(2X1)-O surfaces under ultra-high-vacuum conditions with use of thermal desorption spectroscopy and isotope exchange reactions.Irreversible dehydrogenation yielding gaseous H2 was the only reaction observed on clean W(100).Cycloheptatriene dehydrogenation was suppressed on W(100)-(5X1)-C, allowing reactions involving C-C bond activation to produced.Benzene formation was uniquely observed on the -(5X1)-C surface.Reaction of cycloheptatriene-7d1 on W(100)-(5X1)-C demonstrated that the 7-position was initially dehydrogenated, yielding a coordinated C7H7 adsorption intermediate which subsequently eliminated one carbon to yield benzene.
- Pearlstine, K. A.,Friend, C. M.
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- Nucleophilic Aromatic Substitution at Benzene with Powerful Strontium Hydride and Alkyl Complexes
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Key to the isolation of the first alkyl strontium complex was the synthesis of a strontium hydride complex that is stable towards ligand exchange reactions. This goal was achieved by using the super bulky β-diketiminate ligand DIPePBDI (CH[C(Me)N-DIPeP]2, DIPeP=2,6-diisopentylphenyl). Reaction of DIPePBDI-H with Sr[N(SiMe3)2]2 gave (DIPePBDI)SrN(SiMe3)2, which was converted with PhSiH3 into [(DIPePBDI)SrH]2. Dissolved in C6D6, the strontium hydride complex is stable up to 70 °C. At 60 °C, H–D isotope exchange gave full conversion into [(DIPePBDI)SrD]2 and C6D5H. Since H–D exchange with D2 is facile, the strontium hydride complex served as a catalyst for the deuteration of C6H6 by D2. Reaction of [(DIPePBDI)SrH]2 with ethylene gave [(DIPePBDI)SrEt]2. The high reactivity of this alkyl strontium complex is demonstrated by facile ethylene polymerization and nucleophilic aromatic substitution with C6D6, giving alkylated aromatic products and [(DIPePBDI)SrD]2.
- R?sch, Bastian,Gentner, Thomas Xaver,Elsen, Holger,Fischer, Christian A.,Langer, Jens,Wiesinger, Michael,Harder, Sjoerd
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- Formation of α-[KSiH3] by hydrogenolysis of potassium triphenylsilyl
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Hydrogenation of easily accessible potassium triphenylsilyl [K(Me6TREN)SiPh3] gave the hydrogen storage material α-[KSiH3] in high yields by an unusual hydrogenolytic cleavage of silicon-phenyl bonds.
- Leich,Spaniol,Okuda
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- Ag-Mediated Radical Cyclization of 2-Alkynylthio(seleno)anisoles: Direct Synthesis of 3-Phosphinoylbenzothio(seleno)phenes
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A new method for the direct synthesis of 3-phosphinoylbenzothio(seleno)phenes has been achieved through an Ag-mediated radical addition-cyclization of 2-alkynylthio(seleno)anisoles with secondary phosphine oxides in good yields under mild conditions. In this single reaction, benzenethiophene or benzeneselenophene skeleton, C(sp2)-P and C(sp2)-S bonds can be constructed with the cleavage of the C(sp3)-S bond, highlighting the efficiency and step-economics of this protocol.
- Cai, Tao,Liu, Jian,Zhang, Huimiao,Wang, Xiaolong,Feng, Jing,Shen, Runpu,Gao, Yuzhen
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- Temperature Effect on Gas Phase Alkylbenzene Dealkylation
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Dealkylation of ethylbenzene, propylbenzene, and isopropylbenzene by radiolytically formed 2H+3 ions has been studied in the gaseous phase as a function of the irradiation temperature.The extent of the reaction, which increases with the temperature follows the order ethylbenzene-1 between the activation energies for dealkylation of ethylbenzene and isopropylbenzene, and of ethylbenzene and propylbenzene, respectively.
- Perez, Giorgio
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- Rates and Mechanisms of Gas-Phase Desubstitution of Hexadeuteriobenzene and Benzene Derivatives C6H5X, X = CH3, CF3, OH, Cl, and F, by H Atoms between 898 and 1039 K
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Mixtures of C6D6 and C6H5X, X = CH3, CF3, OH, Cl, and F, have been thermolyzed in H2 in a tubular flow system at atmospheric pressure between 898 and 1039 K.Removal of D or X occurs via hydrogen atom attack and lower deuterated benzenes and C6H6 are formed.Mass spectral analyses for (deuterio)benzenes have been used to determine the rates of desubstitution C6H5X + H --> C6H6 relative to H + C6D6 --> C6D5H (9).For X = D, CH3, CF3, and OH, desubstitution occurs by addition of a H atom to the ring followed by loss of X. from the substituted cyclohexadienyl intermediate.For X = Cl direct abstraction also takes place and for X = F abstraction is the only operative mechanism.No evidence for hydrogen migration around the ring in cyclohexadienyl intermediates was found.On a per-site basis, the dedeuteration rates of C6D6, C6D5H, C6D4H2, ..., C6DH5 were found to be equal.On the basis of log k9/L mol-1 s-1 = 10.69 - 2350/2.3T, we have found the following log k(benzene)/L mol-1 s-1 for C6H5X + H --> C6H6: X = CH3, 10.19 - 2914/2.3T; CF3, 9.79 - 2832/2.3T; OH, 9.93 - 2945/2.3T; Cl, 10.48 - 4148/2,3T; F, 10.31 - 5066/2.3T.Results are compared with relevant literature data.
- Manion, Jeffrey A.,Louw, Robert
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- Selective C-O Bond Reduction and Borylation of Aryl Ethers Catalyzed by a Rhodium-Aluminum Heterobimetallic Complex
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We report the catalytic reduction of a C-O bond and the borylation by a rhodium complex bearing an X-Type PAlP pincer ligand. We have revealed the reaction mechanism based on the characterization of the reaction intermediate and deuterium-labeling experiments. Notably, this novel catalytic system shows steric-hindrance-dependent chemoselectivity that is distinct from conventional Ni-based catalysts and suggests a new strategy for selective C-O bond activation by heterobimetallic catalysis.
- Hara, Naofumi,Nakao, Yoshiaki,Saito, Teruhiko,Seki, Rin
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supporting information
p. 6388 - 6394
(2021/05/31)
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- ZnMe2-Mediated, Direct Alkylation of Electron-Deficient N-Heteroarenes with 1,1-Diborylalkanes: Scope and Mechanism
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The regioselective, direct alkylation of electron-deficient N-heteroarenes is, in principle, a powerful and efficient way of accessing alkylated N-heteroarenes that are important core structures of many biologically active compounds and pharmaceutical agents. Herein, we report a ZnMe2-promoted, direct C2- or C4-selective primary and secondary alkylation of pyridines and quinolines using 1,1-diborylalkanes as alkylation sources. While substituted pyridines and quinolines exclusively afford C2-alkylated products, simple pyridine delivers C4-alkylated pyridine with excellent regioselectivity. The reaction scope is remarkably broad, and a range of C2- or C4-alkylated electron-deficient N-heteroarenes are obtained in good yields. Experimental and computational mechanistic studies imply that ZnMe2 serves not only as an activator of 1,1-diborylalkanes to generate (α-borylalkyl)methylalkoxy zincate, which acts as a Lewis acid to bind to the nitrogen atom of the heterocycles and controls the regioselectivity, but also as an oxidant for rearomatizing the dihydro-N-heteroarene intermediates to release the product.
- Jo, Woohyun,Baek, Seung-Yeol,Hwang, Chiwon,Heo, Joon,Baik, Mu-Hyun,Cho, Seung Hwan
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supporting information
p. 13235 - 13245
(2020/09/01)
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- Electrocatalytic Deuteration of Halides with D2O as the Deuterium Source over a Copper Nanowire Arrays Cathode
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Precise deuterium incorporation with controllable deuterated sites is extremely desirable. Here, a facile and efficient electrocatalytic deuterodehalogenation of halides using D2O as the deuteration reagent and copper nanowire arrays (Cu NWAs) electrochemically formed in situ as the cathode was demonstrated. A cross-coupling of carbon and deuterium free radicals might be involved for this ipso-selective deuteration. This method exhibited excellent chemoselectivity and high compatibility with the easily reducible functional groups (C=C, C≡C, C=O, C=N, C≡N). The C?H to C?D transformations were achieved with high yields and deuterium ratios through a one-pot halogenation–deuterodehalogenation process. Efficient deuteration of less-active bromide substrates, specific deuterium incorporation into top-selling pharmaceuticals, and oxidant-free paired anodic synthesis of high-value chemicals with low energy input highlighted the potential practicality.
- Chong, Xiaodan,Han, Shuyan,Li, Mengyang,Liu, Cuibo,Zhang, Bin
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supporting information
p. 18527 - 18531
(2020/08/21)
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- Lanthanide Ions Coupled with Photoinduced Electron Transfer Generate Strong Reduction Potentials from Visible Light
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Metal ions can have beneficial effects on photoinduced electron transfer. Merging such metal-ion-coupled electron transfer (MCET) with consecutive photoinduced electron transfer (conPET) enables the one-electron reduction of chlorobenzene with blue light in the presence of diisopropylethylamine as an electron donor. The presence of the metal ions extends the substrate scope of the photoredox catalysis to extreme reduction potentials (beyond ?3 V vs. SCE).
- Meyer, Andreas Uwe,Slanina, Tomá?,Heckel, Alexander,K?nig, Burkhard
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supporting information
p. 7900 - 7904
(2017/06/19)
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- Sodium Diisopropylamide in Tetrahydrofuran: Selectivities, Rates, and Mechanisms of Arene Metalations
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Sodium diisopropylamide (NaDA)-mediated metalations of arenes in tetrahydrofuran (THF)/hexane or THF/Me2NEt solutions are described. A survey of >40 benzenoid- and pyridine-based arenes with a range of substituents demonstrates the efficacy and regioselectivity of metalation. Metalations of activated disubstituted arenes and selected monosubstituted arenes are rapid at -78 °C. Rate studies of 1,3-dimethoxybenzene and related methoxylated arenes show exclusively monomer-based orthometalations with two or three coordinated THF ligands. Rate studies of the isotopic exchange of benzene and monosubstituted arenes with weakly activating groups reveal analogous di- and trisolvated monomer-based metalations. Cooperative inductive, mesomeric, steric, and chelate effects are discussed.
- Algera, Russell F.,Ma, Yun,Collum, David B.
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supporting information
p. 15197 - 15204
(2017/10/31)
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- A substituted heteroaryl compounds and compositions containing such compounds and use thereof (by machine translation)
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The present invention provides a substituted heteroaryl compounds and compositions containing such compounds and its use, the invention discloses a formula (I) indicated by the heteroaryl compound, or its crystalline form, a pharmaceutically acceptable salt, prodrug, stereoisomer, hydrate or compound solvent. The invention of monocyclic the base states compounds and compositions containing such compounds may be used to modulate hypoxia inducible factor (HIF) and/or endogenous erythropoietin (EPO), but also has good pharmacokinetic parameter characteristic, can improve the compound in animal drug concentration, in order to improve the effect of drugs and safety. (by machine translation)
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Paragraph 0137; 0138-0139
(2017/04/19)
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- Metal-Free sp2-C-H Borylation as a Common Reactivity Pattern of Frustrated 2-Aminophenylboranes
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C-H borylation is a powerful and atom-efficient method for converting affordable and abundant chemicals into versatile organic reagents used in the production of fine chemicals and functional materials. Herein we report a facile C-H borylation of aromatic and olefinic C-H bonds with 2-aminophenylboranes. Computational and experimental studies reveal that the metal-free C-H insertion proceeds via a frustrated Lewis pair mechanism involving heterolytic splitting of the C-H bond by cooperative action of the amine and boryl groups. The adapted geometry of the reactive B and N centers results in an unprecedentently low kinetic barrier for both insertion into the sp2-C-H bond and intramolecular protonation of the sp2-C-B bond in 2-ammoniophenyl(aryl)- or -(alkenyl)borates. This common reactivity pattern serves as a platform for various catalytic reactions such as C-H borylation and hydrogenation of alkynes. In particular, we demonstrate that simple 2-aminopyridinium salts efficiently catalyze the C-H borylation of hetarenes with catecholborane. This reaction is presumably mediated by a borenium species isoelectronic to 2-aminophenylboranes.
- Chernichenko, Konstantin,Lindqvist, Markus,Kótai, Bianka,Nieger, Martin,Sorochkina, Kristina,Pápai, Imre,Repo, Timo
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p. 4860 - 4868
(2016/05/10)
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- Electrochemical hydrodefluorination of fluoroaromatic compounds
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The BH4-- promoted electrochemical hydrodefluorination of fluoroaromatic compounds was reported. Using platinum as electrodes in an undivided cell, the electrolysis was carried out at constant current at room temperature under air without the need of pretreatment of the solvent. This reaction could proceed smoothly on both nonactivated monofluoroarenes and perfluoroarenes with high yields and good selectivities.
- Wu, Wen-Bin,Li, Mei-Li,Huang, Jing-Mei
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p. 1520 - 1523
(2015/03/14)
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- Iridium(iii) catalyzed trifluoroacetoxylation of aromatic hydrocarbons
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A tridentate, NNC-tb (where NNC-tb = 2-(pyridin-2-yl)benzo[h]quinoline) ligated IrIII complex (NNC-tb)Ir(Ph)(4-MePy)(TFA), 11 along with analogues are very active for CH activation as evidenced by rapid catalytic H/D exchange between benzene and trifluoroacetic acid-d1 (DTFA). The complexes were examined with a variety of oxidants for the catalytic conversion of benzene to phenyltrifluoroacetate. Herein, the synthesis and characterization of (NNC-tb)Ir complexes is described along with the reactivity of these complexes towards arenes and alkanes.
- Bischof, Steven M.,Hashiguchi, Brian G.,Lokare, Kapil S.,Gunsalus, Niles,Yousufuddin, Mohammed,Periana, Roy A.
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p. 35639 - 35648
(2014/12/10)
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- PtII-catalyzed ethylene hydrophenylation: Influence of dipyridyl chelate ring size on catalyst activity and longevity
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Expansion of the dipyridyl ligand from a five- to six-membered chelate for PtII-catalyzed ethylene hydrophenylation provides an enhancement of catalyst activity and longevity. Mechanistic studies of [(dpm)Pt(Ph)(THF)] [BAr′4] [dpm = 2,2′-dipyridylmethane, and Ar′ = 3,5-(CF3)2C6H3] attribute the improved catalytic performance at elevated temperatures to a favorable change in entropy of activation with an increase in chelate ring size. The Pt II catalyst precursor [(dpm)Pt(Ph)(THF)][BAr′4] is among the most active catalysts for ethylene hydrophenylation by a non-acid-catalyzed mechanism.
- McKeown, Bradley A.,Gonzalez, Hector Emanuel,Gunnoe, T. Brent,Cundari, Thomas R.,Sabat, Michal
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p. 1165 - 1171
(2013/07/26)
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- Efficient indium-mediated dehalogenation of aromatics in ionic liquid media
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An efficient indium-mediated dehalogenation reaction of haloaromatics and haloheteroaromatics in ionic liquids has been studied. This method is simple and effective in the presence of [bmim]Br. Furthermore, this methodology is environmentally friendly compared with conventional ones.
- Canete, Alvaro F.,Salas, Cristian O.,Zacconi, Flavia C.
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p. 398 - 407
(2013/03/13)
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- Catalytic arylation of a C-H bond in pyridine and related six-membered N-heteroarenes using organozinc reagents
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Despite significant advances in the catalytic direct arylation of heteroarenes, the application of this reaction to pyridines has been met with limited success. An oxidative nucleophilic arylation strategy has been developed to overcome this problem. Pyridine, pyrazine, quinolone, and related electron-deficient N-heteroarenes can be arylated at the most electrophilic site using the developed nickel-catalyzed reaction. This protocol serves as a complementary method to catalytic direct arylation reactions. Less is more: Pyridine, pyrazine, quinoline and related electron-deficient N-heteroarenes can be arylated at the most electrophilic site using organozinc reagents through nickel catalysis. This protocol serves as a complementary method to catalytic direct arylation reactions. Copyright
- Hyodo, Isao,Tobisu, Mamoru,Chatani, Naoto
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supporting information; experimental part
p. 1357 - 1365
(2012/08/08)
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- Synthesis, structure and reactivity of organogold compounds of relevance to homogeneous gold catalysis
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Organogold(I) phosphane complexes were prepared, their structure was investigated and their reactivity in reactions with Michael acceptors, sources of electrophilic halogens and protons were investigated.
- Hashmi, A. Stephen K.,Ramamurthi, Tanuja Dondeti,Rominger, Frank
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experimental part
p. 592 - 597
(2009/06/05)
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- Nickel-catalyzed reaction of arylzinc reagents with N-aromatic heterocycles: A straightforward approach to C-H bond arylation of electron-deficient heteroaromatic compounds
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(Chemical Equation Presented) The reaction of electron-deficient N-heteroaromatic compounds, such as pyridines and quinolines, with arylzinc reagents in the presence of a catalytic amount of a nickel complex affords the arylated products. The reaction is likely to proceed through a formal nucleophilic 1,2-addition, thus exhibiting a reactivity complementary to conventional direct arylation through electrophilic substitution.
- Tobisu, Mamoru,Hyodo, Isao,Chatani, Naoto
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supporting information; experimental part
p. 12070 - 12071
(2009/12/27)
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- TRIDENTATE (NNC) CATALYSTS FOR THE SELECTIVE OXIDATION OF HYDROCARBONS
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The synthesis of discrete, air, protic, and thermally stable transition metal NNC complexes that catalyze the CH activation and functionalization of alkanes and arenes is disclosed. Methods for the selective conversion of methane to methanol or methyl esters in acidic and neutral media are disclosed.
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Page/Page column 12
(2009/09/28)
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- Factors controlling photochemical cleavage of the energetically unfavorable Ph-Se bond of alkyl phenyl selenides
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(Chemical Equation Presented) Primary photochemical paths of alkyl phenyl selenides (1) were investigated, and an origin of large deviations in the chemical yields of products obtained by carbon radical reactions induced by photolysis of phenyl selenides was clarified. KrF excimer laser photolyses of n-pentyl phenyl selenide (1a) yielded 1-pentene (2a), n-pentane (3a), n-decane (4a), dipentyl selenide (5a), benzene (6), dipentyl diselenide (7a), and diphenyl diselenide (7) as major photoproducts, with compounds 2a, 3a, 4a, 5a, and 7 formed by pentyl-Se bond cleavage, and 5a, 6, and 7a by Ph-Se bond cleavage. The selectivity of the photoproducts revealed the occurrence of an unexpected amount of Ph-Se bond cleavage (35% in n-hexane at 248 nm) during photolysis. Solvent viscosity, wavelength of light, and the structure of alkyl substituents were the major factors that controlled Ph-Se bond cleavage. The ratio of Ph-Se bond cleavage decreased with increasing solvent viscosity and laser wavelength. The effect of alkyl substituents on the ratio of bond cleavages, Ph-Se/total C-Se, was investigated for five alkyl phenyl selenides; the ratio decreased in the order pentyl > 2-methylallyl > allyl > 1-ethylpropyl > tert-butyl groups. The contribution of Ph-Se bond cleavage is most probably the origin of the large deviations in the yields of radical reactions induced by photolyses of 1, which can be minimized by selecting appropriate solvents and wavelength of light.
- Ouchi, Akihiko,Liu, Suyou,Li, Zhong,Kumar, S. Ajaya,Suzuki, Toshiaki,Hyugano, Takeshi,Kitahara, Haruo
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p. 8700 - 8706
(2008/03/12)
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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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- Rhodium-catalyzed addition of arylstannanes to carbon-heteroatom double bond
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The addition of arylstannanes to the carbon-heteroatom double bond in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) was examined. The reactions of aldehydes, α-dicarbonyl compounds, and N-substituted aldimines with the arylstannanes gave corresponding alcohols, α-hydroxy carbonyl compounds, and amines, respectively. An arylrhodium complex generated by the transmetalation with the arylstannane was probably the active catalytic species.
- Oi, Shuichi,Moro, Mitsutoshi,Fukuhara, Hiroe,Kawanishi, Takanori,Inoue, Yoshio
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p. 4351 - 4361
(2007/10/03)
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- Solid-solid palladium-catalysed water reduction with zinc: Mechanisms of hydrogen generation and direct hydrogen transfer reactions
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Facile generation of hydrogen gas from water takes place under moderate conditions in the presence of zinc powder and catalytic palladium on carbon; 82% conversion of zinc is obtained. An unusually large kinetic isotope effect is observed using D2O (k(H)/k(D) = 14), which may reflect the cleavage of both O-H bonds in the rate-determining step. Experiments using D2O-H2O mixtures evidence that water molecules adsorbed on the catalyst surface undergo H-D exchange reactions (with molecules from the solvent bulk) that are approximately 100 times faster than the hydrogen generation reaction. The primary factors in this system appear to be palladium-hydrogen and zinc- oxygen interactions. Conversely, in the presence of an organic hydrogen acceptor, such as benzaldehyde, a different course is realised, consisting of direct hydrogen transfer from 'zinc-activated' water to the substrate, without the participation of Pd-H intermediates. Quantitative hydrogenation of benzaldehyde to benzyl alcohol, and of aromatic nitro compounds to the corresponding amines, is obtained. Another application of the above system is the specific deutero-dehalogenation of aromatic halides. Possible mechanisms and the implications of a chemical reaction involving two macroscopic solid particles are discussed.
- Mukhopadhyay, Sudip,Rothenberg, Gadi,Wiener, Harold,Sasson, Yoel
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p. 305 - 308
(2007/10/03)
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- Chromium(ii)-mediated reactions of iodonium tetrafluoroborates with aldehydes: Umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates
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The method described herein allows us, for the first time, to perform umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates. The method involves generation of organochromium(III) species via reaction of iodonium salts with anhydrous chromium dichloride, followed by their nucleophilic addition to aldehydes to yield alcohols. In contrast to the reaction of aryl and alkenyl halides with chromium dichloride, these iodonium salts are so active that organochromium(III) could be generated without using a nickel catalyst. Substituent effects of unsymmetrically substituted diaryliodonium salts on the product profiles are in good agreement with the reported mode of decomposition of the intermediate unsymmetrical diaryliodanyl radicals. Alkenyl(mesityl)iodonium tetrafluoroborates undergo exclusive alkenylation of aldehydes with no signs of the formation of an arylation product.
- Chen, Da-Wei,Ochiai, Masahito
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p. 6804 - 6814
(2007/10/03)
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- Gas-phase hydrogenolysis mediated by activated carbon: Deuterated benzenes
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Hydrogenolyses of hexadeuterobenzene C6D6 and pentadeuterochlorobenzene C6D5Cl have been studied in flow reactors packed with activated carbon (AC) between 300° and 600°C, with void residence times of 4-5 s. At 579°C overall dedeuteration - proceeding in a near statistical manner - was close to 40% in both cases, whereas C6D5Cl is almost completely dechlorinated to deuterated benzenes at 505°C. On a per-site basis, replacement of Cl by H is ca. 20 times faster than that of D. These results clearly demonstrate a catalytic activity of AC in both cases of desubstitution. In the absence of AC, temperatures of 700-900°C are necessary to obtain the same result. Then, replacement of Cl and D have almost equal rates, both reactions occurring via addition of free H atoms. In the AC-mediated reactions, the yields of (D) benzenes are quantitative from C6D6, but around 50% with C6D5Cl. Apparently the latter compound reacts with bonding of its phenyl group to the AC surface, whereas D → H substitutions involve H transfer to a physisorbed (D) benzene.
- Arends, Isabel W.C.E.,Louw, Robert,Mulder, Peter
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p. 271 - 274
(2007/10/03)
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- Interaction of D(H) atoms with physisorbed benzene and (1,4)-dimethylcyclohexane: Hydrogenation and H abstraction
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Benzene and (1,4)-dimethyl-cyclohexane monolayers were physisorbed on graphite covered Pt(111) surfaces. Exposure of benzene monolayers at 125 K to D atoms (1700 K) initially hydrogenates sp2 hybridized C atoms with a cross section of ca. 8 A2 producing C6H6D intermediates. Additional D atom reactions either transform this intermediate via a second hydrogenation reaction to cyclohexadiene-d2, C6H6D2, or restore benzene, C6H5D, via H abstraction. Once the aromaticity is broken, successive hydrogenation of the diene occurs rapidly generating the saturated cyclohexane-d6, C6H6D6. The C6H5D reaction product can undergo further H/D exchange reactions and, at any level of deuteration, the benzene species might get hydrogenated. Monolayers of the saturated hydrocarbon (1,4)-dimethyl-cyclohexane (DMCH) that are exposed to D atoms produce deuterated DMCH via successive abstraction/hydrogenation reactions. Thermal desorption mass spectra revealed that H atoms at the ring were exchanged with an apparent cross section of 1.7 A2. Methyl groups H atoms were exchanged much more slowly than ring H atoms. It was also observed that D exposed molecules/radicals exhibit a tendency to desorb from the surface, which is ascribed to the exothermicity of the reactions which lead to these species.
- Lutterloh,Biener,Schenk,Kueppers
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p. 2392 - 2400
(2007/10/03)
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- Thermal rearrangement, XXV: The automerization of benzene as a radical-initiated reaction
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The thermal isomerization of [1,4-D2]-(3a) and [1,2-13C2]benzene (1a) has been studied in excess hydrogen at 750-850°C with contact time less than 1.2 s and very low partial pressure in a quartz flow system. In both cases, the main isomerization products are the corresponding meta isomers. The data suggest a radical intramolecular interchange of the benzene carbon atoms by 1,2-C shifts. The multistep reaction cascade is initiated by H addition to the benzene ring followed by transannular homoallyl rearrangements involving the intermediate formation of bicyclo[3.1.0]hexenyl and cyclopentadienylmethyl radicals. This pathway constitutes a side reaction competing with the direct stabilization of the cyclohexadienyl radicals formed preferentially at high temperature. VCH Verlagsgesellschaft mbH, 1996.
- Zimmermann, Gerhard,Nuechter, Matthias,Hopf, Henning,Ibrom, Kerstin,Ernst, Ludger
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p. 1407 - 1411
(2007/10/03)
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- Solvent Dependence of Electron-Transfer Sensitized Photolysis of Onium Salts
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The photoreactions of 9, 10-diphenylanthracene with two iodonium salts and a suifonium salt in different solvents were investigated by fluorescence quenching, flash photolysis with UV/vis detection, measurements of the quantum yields of sensiiizer decomposition, and photo-CIDNP spectroscopy. Energy-transfer sensitization is precluded by thermodynamics in these systems. In a solvent of lower polarity such as dimethoxyetnane, the quenching rate constant is still about a third of the value in acetonitrile; ihe quantum yields of formation of radical cations and the quantum yields of sensitizer decomposition are decreased by about the same factor. In contrast, dramatic effects occur in the CIDNP spectra of the iodonium salts, which derive from two consecutive radicals pairs, the first containing the radical caiion DPA·+ of the sensitizer and the radical On of the onium salt, the second comprising DPA·+ and a phenyl radical produced by fragmentation of On: In less polar solvents, the polarizations from the first pair are strongly reduced, and the polarizations from the second pair are larger by an order of magnitude. From a kinetic analysis, this effect was attributed to a higher rate of transformation of the first radical pair into the second in the !ess polar solvent. For the suifonium salt, this transformation is faster than in the case of iodonium salts, so even in acetonitrile all polarizations stem from the second radical pair. S-T±1-type CIDNP, which had been proposed in the literature for analogous chemical systems, could be excluded unambiguously, and all CIDNP effects could be explained by radical pair theory (S-T0-type CIDNP). VCH Verlagsgesellschaft mbH, 1996.
- Eekert, Gerd,Goez, Martin,Maiwaid, Beate,Mueller, Uwe
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p. 1191 - 1198
(2007/10/03)
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- Reaction of 1,2-Diphenylethane with D2
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The reaction of 1,2-diphenylethane (DPE) with D2 (2000 psi) was studied at 450 deg C.The results of GC/MS and NMR analysis of reaction products and of products from reactions of 1,2-diphenylethane-1,1-d2, 1,2-di(phenyl-d5)ethane, and 1,2,3,4-tetraphenylbutane confirm a mechanistic scheme in which the main process for introduction of D is the reaction of 1,2-diphenylethyl radical with D2.This reaction, though energetically uphill, competes with termination processes because of the high concentration of D2 relative to that of radical species.The reaction generates D atoms which attack aromatic ring positions to give substitution for both H and alkyl substituents.Evidence is provided for D and H atom transfer between aliphatic positions in DPE in the presence of either N2 or H2 and between aromatic positions only when provoked by H2 or D2.Only a small amount of exchange between aromatic and aliphatic positions is observed under any conditions.The attack of D atoms at H-carrying aromatic positions makes H atoms available for transfer to other aromatic positions.The process results in a D2-provoked generation of benzene-d0.Mechanistic alternatives for these and other processes are discussed.
- Guthrie, Robert D.,Shi, Buchang,Rajagopal, Venkatsubramanian,Ramakrishnan, Sreekumar,Davis, Burtron H.
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p. 7426 - 7432
(2007/10/02)
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- Electrophilic substitution with allylic rearrangement (SE′) stereochemistry of trifluoroacetolysis of some cyclohex-2-enylmetal compounds
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A range of (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)silanes, (4-alkylcyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)germanes, and (4-alkyl-cyclohex-2-enyl)-, (5-alkylcyclohex-2-enyl)-, and (6-alkylcyclohex-2-enyl)stannanes were cleaved to the cycloalkene (and R3MX) with trifluoroacetic acid-d in various solvents. Complete allylic rearrangement (γ-attack) was observed, and the preferred direction of delivery of the electrophile (formally D+) to the γ-carbon of the allylic triad was determined by detailed 1H, 13C, and 2H NMR analyses of the derived dibromides of the various alkyl-substituted cyclohexenes or by direct 2H NMR analysis and comparisons with 2H-substituted alkylcyclohexenes of established relative configurations. A highly preferred γ-anti mode of acidolysis is established for all systems, except for the trans-4-tert-butylcyclohex-2-enyl derivatives, such exception being ascribed to steric impedance of electrophile approach, promoting syn attack. Thus, overall, highly γ-regioselective and anti-stereoselective substitutions (SE′) are observed.
- Wickham, Geoffrey,Young, David,Kitching, William
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p. 1187 - 1195
(2008/10/08)
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- MOLECULAR MECHANISMS IN THE CYCLOTRIMERIZATION OF ACETYLENE TO BENZENE ON PALLADIUM(III).
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Multiplexed temperature programmed reaction measurements have been used to examine mechanistic details of the acetylene yields benzene reaction on Pd(111). Results obtained from (C//2H//2 plus C//2D//2) experiments are in quantitative accord with a nondissociative reaction pathway; H/D scrambling in the reactants is not of significance, but at higher temperatures some H/D scrambling is observed between product molecules. The effects of surface crowding by unreacted acetylene on the binding and conformation of the benzene product are investigated, and it is shown that all benzene desorption is the result of the same initial reactive events. (C//2D//2 plus C//6H//6) data demonstrate that benzene desorption is not reaction-rate limited, consistent with the above conclusion.
- Patterson,Lambert
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p. 1266 - 1270
(2007/10/02)
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- Mechanistic Studies of Gas-Phase Negative Ion Unimolecular Decompositions. Alkoxide Anions
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The unimolecular decompositions of 15 gas-phase alkoxide negative ions have been studied by infrared multiple photon photochemical activation in an ion cyclotron resonance spectrometer.Upon pulsed CO2 laser irradiation, alkoxide anions undergo elimination of neutral molecules (e.g., alkanes RH) to yield enolate anions.The observed reactivity patterns and kinetic isotope effects further establish a stepwise decomposition mechanism involving initial heterolytic cleavage to an intermediate anion-ketone complex followed by proton transfer to give the ultimate products.A relative order of leaving group propensities CF3 > Ph > H > t-Bu > Me > i-Pr > Et was observed.The apparent anomalous reactivity order for the alkyl groups can be rationalized by invoking a change in mechanism to one involving an intermediate in which an electron is not bound specifically by the eliminated alkyl group for R + t-Bu, i-Pr, and Et: either a radical-ketone radical anion complex produced by homolytic cleavage or an anionic cluster.This order also leads to the conclusion that methane elimination from alkoxide anions proceeds via the pathway involving heterolytic cleavage.The results of this study have implications for bimolecular ion-molecule reaction dynamics, since the photochemically generated intermediates are also intermediates in bimolecular proton transfer reactions.
- Tumas, William,Foster, Robert F.,Brauman, John I.
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p. 2714 - 2722
(2007/10/02)
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- Hydrogen Transfer Reactions, 10. The cis-Selective Two-Step Mechanism in Hydrogen Transfer from 1,4-Dihydroarenes to o- and p-Quinones
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Deuterium labeling experiments prove a high cis selectivity for hydrogen transfer reactions between 1,4-dihydroarenes and o- and p-quinones.Solvent effects and the size of primary isotope effects exclude a symmetry-allowed synchronous transfer of both hydrogens.They are consistent with a primary hydride abstraction to form a sterically fixed ion pair.The cis selectivity is raised by the larger ? system of 2 and reduced in the case of polar solvents.Tunneling of hydrogen is indicated by large primary isotope effects.
- Brock, Martin,Hintze, Horst,Heesing, Albert
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p. 3727 - 3736
(2007/10/02)
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- An Increment System for Deuterium Isotope Effects on 13C Chemical Shifts of Methylated Benzenes
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The complete series of all possible benzenes bearing one deuterium atom and one to five methyl groups was synthesized.The deuterium isotope effects on the carbon chemical shifts of the aromatic and aliphatic carbon atoms were measured and shown to obey an empirical increment system.The isotope effects over one bond correlate with the C,H spin coupling constants. KEY WORDS 13C NMR, deuterium isotope effects, methylbenzenes
- Berger, Stefan,Diehl, Bernd W. K.
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p. 1073 - 1076
(2007/10/02)
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- Electrochemical Initiation of Aromatic SRN1 Reactions Using Redox Catalysts
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Electrochemical reduction of benzonitrile in the presence of bromobenzene and tetra-N-butylammonium benzenethiolate in dimethyl sulfoxide (Me2SO) forms diphenyl sulfide (67percent) and benzene (38percent).The reaction consumes 0.37 faraday per mol of bromobenzene, indicating that an SRN1 chain reaction is occuring.Reaction in Me2SO-d6 gives a decreased yield of benzene (17percent), 57percent of which was monodeuterated, which along with coulometric data indicates that a major termination pathway is abstraction of hydrogen atoms from Me2SO by phenyl radicals.Photoinitiated reactions in the presence and absence of tetra-N-butylammonium ions indicate that they are also a significant source of hydrogen atoms in termination.Evidence from reactions of 4-bromotoluene with benzenethiolate ion indicates that fragmentation of the diaryl sulfide radical anion intermediate is an important reaction in these systems.The presence of benzonitrile suppresses that cleavage.
- Swartz, James E.,Stenzel, Timothy T.
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p. 2520 - 2524
(2007/10/02)
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- Coordination Chemistry of Benzene, Toluene, Cyclohexadienes, Cyclohexene, and Cyclohexane on Pt100)
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The surface chemistry of benzene, toluene, cyclohexane, cyclohexene, and cyclohexadienes on Pt(100) is described.Benzene chemisorption was largely molecular although H-D exchange between chemisorbed C6H6 and C6D6 was observed at temperatures of 100 deg C and above.Toluene chemisorbed with bond breaking to give Pt-(100)-benzyl.This benzyl species (C6D5CD2) underwent H-D exchange with chemisorbed hydrogen.Exchange was more facile at the CH2 site than at aromatic C-H sites.Cyclohexane, cyclohexene, and cyclohexadienes chemisorbed on Pt(100) to form benzene with expected relative ease of dehydrogenation of cyclohexadienes >/= cyclohexene > cyclohexane.
- Tsai, Min-Chi,Muetterties, E. L.
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p. 5067 - 5071
(2007/10/02)
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- PHOTOCHEMICAL TRANSFORMATION OF TETRACYCLO2,4.03,6>OCT-7-ENE
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Cyclooctatetraene is a common product of photolysis of the title compound 1a.Depending on reaction conditions it is accompanied by benzene solvent: cyclohexane, λ = 253.7 nm), benzene plus semibullvalene (acetone, 300 nm), and an oxetane (cyclohexane, 350 nm, presence of equimolar amount of benzophenone).
- Stapersma, J.,Klumpp, G. W.
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p. 274 - 275
(2007/10/02)
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