- SITE OF PROTONATION AND CONFORMATIONAL EFFECTS ON GAS-PHASE BASICITY IN beta -AMINO ALCOHOLS. THE NATURE OF INTERNAL H BONDING IN beta -HYDROXY AMMONIUM IONS.
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The influence of interfunctional distance on the gas-phase basicity of beta -amino alcohols is investigated by the method of equilibrium proton-transfer reactions in an ion cyclotron resonance (ICR) spectrometer. It is found that in the protonated species, interaction between the most basic center (amino group) with the hydroxy group results in stabilization of the system. The stabilization energy increases as the interfunctional distance decreases to reach a maximum value of about 7 kcal/mol for coplanar systems. Comparison with the values determined by ab initio calculations indicates that internal H bonding can be described in terms of the ion-dipole potential energy between the ammonium ion and the hydroxy group. External vs. internal ion solvation effects are also discussed.
- Houriet,Reufenacht,Carrupt,Vogel,Tichy
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- Synthesis, spectral, thermal and kinetic studies on the adducts with pyridines of tungsten(V) binuclear thiocomplexes with di-isopropyl-dithiocarbamate
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We report the synthesis and the thermal and kinetic behaviour of di-μ-sulfido-bis-(sulfido N,N,di-i-propyldithiocarbamate)di-tungsten(V) adducts with pyridine or substituted pyridines, the formula of which is [W2S4(di-i-propyldtc)2B2], where dtc = dithiocarbamate and B = pyridine (Py), 3-methylpyridine (3-MP), 4-methylpyridine (4-MP), 3,5-dimethylpyridine (3,5-DMP), 3-aminopyridine (3-AP) and 4-aminopyridine (4-AP). The synthesized complexes have been identified by IR and electronic spectra, magnetic susceptibility measurements and analytical data. We have also inferred the thermal behaviour and kinetic parameters by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the thermal decomposition of these adducts in the solid state. From the DSC curves, the activation energies and pre-exponential Arrhenius factors for the endothermic process corresponding to the loss of two moles of coordinated base were calculated. We have also deduced the reaction mechanism using a new non-isothermal kinetic method. Steric hindrance and inductive effects prompted by amino and methyl pyridine functional groups in the adducts formation are discussed. A relationship between the pyridines basicity, infrared and electronic spectral data and activation energies has also been explored.
- Lozano,de Jesús,Lozano
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- Two-State Reactivity in Iron-Catalyzed Alkene Isomerization Confers σ-Base Resistance
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A low-coordinate, high spin (S = 3/2) organometallic iron(I) complex is a catalyst for the isomerization of alkenes. A combination of experimental and computational mechanistic studies supports a mechanism in which alkene isomerization occurs by the allyl mechanism. Importantly, while substrate binding occurs on the S = 3/2 surface, oxidative addition to an η1-allyl intermediate only occurs on the S = 1/2 surface. Since this spin state change is only possible when the alkene substrate is bound, the catalyst has high immunity to typical σ-base poisons due to the antibonding interactions of the high spin state.
- Lutz, Sean A.,Hickey, Anne K.,Gao, Yafei,Chen, Chun-Hsing,Smith, Jeremy M.
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- Pd0-mediated rapid coupling between methyl iodide and heteroarylstannanes: an efficient and general method for the incorporation of a positron-emitting11C radionuclide into heteroaromatic frameworks
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The Pd0-mediated rapid trapping of methyl iodide with an excess amount of a heteroaryl-substituted tributylstannane has been investigated with the aim of incorporating a shortlived 11C-labelled methyl group into the heteroaromatic carbon frameworks of important organic compounds, such as drugs with various heteroaromatic structures, in order to execute a positron emission tomography (PET) study of vital systems. The reaction was first performed by using our previously developed CH3I/stannane/[Pd 2(dba)3]/ P(o-CH3C6H 4)3/CuCl/K2CO3 (1:40:0.5:2:2:2) system in DMF at 60°C for 5 min (conditions A), however, the reaction gave low yields for various heteroaromatic compounds. Increasing the amount of phosphine ligand (condi tions B) led to a significant improvement in the yield, but the conditions were still not suitable for a range of basic heteroaromatic structures. Use of the CuBr/CsF system (conditions C) also provided a result similar to that obtained under conditions B with an increased amount of the phosphine. Thus, pyridine and related heteroaromatic compounds remained less reactive substrates. The problem was overcome by replacing the DMF solvent with N-methyl-2-pyrolidinone (NMP). The reaction in NMP at 60-100°C for 5 min using a CH3I/stannane/[Pd2-(dba)3]/P(o-CH 3C6H4)3/CuBr/CsF (1:40:0.5:16:2:5) combination (conditions D) gave the methylated products in yields of more than 80% (based on the reaction of CH3I) for all of the heteroaromatic compounds listed in this study. Thus, the combined use of NMP and an increased amount of phosphine is important for promoting the reaction efficiently. The use of this general approach to rapid methylation has been well demonstrated by the synthesis of the PET tracers 2- and 3-[11C]methylpyridines by using [Pd2(dba)3]/P(o-CH3C6H 4)3/CuBr/CsF (1:16:2:5) in NMP at 60°C for 5 min, which gives the desired products in HPLC analytical yields of 88 and 91%, respectively.
- Suzuki, Masaaki,Sumi, Kengo,Koyama, Hiroko,Siqin,Hosoya, Takamitsu,Takashima-Hirano, Misato,Doi, Hisashi
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- Oxygenation of hydrocarbons mediated by mixed-valent basic iron trifluoroacetate and valence-separated component species under Gif-type conditions involves carbon- and oxygen-centered radicals
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Hydrogen-atom abstraction by hydroxyl radicals takes place to generate both tert- and sec-adamantyl radicals in Gif-type oxygenation of adamantane by H2O2 in pyridine/trifluoroacetic acid when the reaction is mediated by [Fe(O2CCF3)2(py)4] or [Fe2O(O2CCF3)4(py)6], which are formed by dissociation of [Fe3O(O2CCF3)6- (L)3] in pyridine (L = H2O, DMSO; see scheme).
- Tapper, Amy E.,Long, Jeffrey R.,Staples, Richard J.,Stavropoulos, Pericles
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- Unsaturated aldehydes: a novel route for the synthesis of pyridine and 3-picoline
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A novel reaction pathway was developed for the synthesis of pyridine and 3-picoline from the condensation of gas-phase acrolein dimethyl acetal or acrolein diethyl acetal and ammonia over various catalysts in a fixed-bed reactor. ZnO loaded on alkaline-acid sequentially-treated HZSM-5, namely ZnO/HZSM-5-At-acid, was prepared and employed in these reactions for the first time. 3-Picoline, without the generation of 4-picoline, was obtained from the condensation of acrolein dimethyl acetal and ammonia. The ZnO/HZSM-5-At-acid catalyst was proven to be the most promising catalyst relative to other catalysts in this study. The stability of the ZnO/HZSM-5-At-acid catalyst was remarkably higher than that of the ZnO/HZSM-5 catalyst. The catalysts were characterized using XRD, 27Al MAS NMR, XPS, UV-vis DRS, N2-physisorption, NH3-TPD and TG technologies and the results revealed that the pore structure, acidity and location of ZnO had great influence on the total yield of pyridine and 3-picoline, and the catalyst stability.
- Luo, Cai-Wu,Chao, Zi-Sheng
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- A computational, X-ray crystallographic and thermal stability analysis of TETROL and its pyridine and methylpyridine inclusion complexes
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The identification and application of (+)-(2R,3R)-1,1,4,4- tetraphenylbutane-1,2,3,4-tetrol (TETROL) as an efficient and selective host compound is described. Computational and single crystal X-ray diffraction analyses revealed that the butane backbone of TETROL adopts a relatively rigid anti-conformation, with the hydroxy groups oriented syn and connected through a cyclic, homodromic arrangement of their O-H bonds. This structure is stabilised through a pair of 1,3-hydrogen bonding interactions. TETROL forms inclusion complexes with pyridine and 3- and 4-methylpyridine, and does so selectively from mixtures of the pyridines. X-ray diffraction (single crystal and powder) and thermal analyses of the inclusion compounds are described.
- Barton, Benita,Caira, Mino R.,Hosten, Eric C.,McCleland, Cedric W.
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- Thermal study of [Pd(2-Phpy)Cl(L)] complexes (L=pyridines and amines)
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The complex [Pd(2-Phpy)(μ-Cl)]2 reacts with pyridines (L=pyridine, α-picoline and γ-picoline), amines (L=isopropylamine, tert-butylamine) and ammonia to form the corresponding ortho-palladated derivatives [Pd(2-Phpy)CIL]. The compounds have bee
- Perez,Sanchez,Garcia,Serrano,Lopez
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- Nitrogen kinetic isotope effects on the decarboxylation of 4-pyridylacetic acid
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Nitrogen kinetic isotope effects on the decarboxylation of 4-pyridylacetic acid have been measured in solvents of different polarity and have been found to vary from the inverse value of 0.994 to the normal value of 1.002 upon increase of water content of
- Sicinska,Lewandowicz,Vokal,Paneth
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- Kinetics and mechanistic study on deoxygenation of pyridine oxide catalyzed by {MeReVO(pdt)} 2 dimer
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The oxorhenium(V) dimer {MeReO(pdt)}2 (where pdt?=?1,2-propanedithiolate) catalyze the oxygen atom transfer (OAT) reaction from the pyridine oxide to triphenylarsine (Ph3As). The rate law is given by ν?=?k[Re-dimer][PyNO] and zero order dependence on Ph3As. The value of k at 25?°C in CHCl3 is 139?±?3?L?mol?1?s?1. The activation parameters are ΔH??=?12.2?±?1.0?kcal?mol?1 and ΔS??=??7.9?±?3.24?cal?K?1?mol?1. According to the proposed mechanism, the rate determining step is the oxidation of ReVO to ReVIIO2 and the pyridine release. The triphenylarsine enters the catalytic cycle after the rate determining step. The reaction constant ρ?=??1.4 obtained from Hammett correlation with σ for different substituted pyridine N-oxide. The computational study indicates that the oxidation of ReV to ReVII and release of the pyridine step is insensitive to the nature of the substituent on the pyridine with the average estimated activation barrier ≈11.5?kcal/mol from six different substituted pyridine oxide. It is proposed that electron donor substituent enrich the equilibrium of the first step of the proposed mechanism which is the coordination of the pyridine oxide with one rhenium atom to form I1 (Scheme 2). The electron donor substituent on the pyridine increase the concentration of I1 which will increase the rate of the reaction as the ν?=?k2[I1].
- Ibdah, Abdellatif,Alduwikat, Salwa
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- Properties of mixed polyfunctional fluoride catalysts for synthesis of pyridine bases from acetylene and ammonia (methanol)
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New catalysts based on cadmium, zinc, chromium, iron, and aluminum compounds were synthesized and their properties were studied. A pilot catalyst batch was obtained and tested on a pilot installation.
- Khamidullaev,Yusupov
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- SYNTHESIS OF METHYLPYRIDINES IN THE PRESENCE OF Pd COMPLEXES CONTAINING S
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Synthesis of methylpyridines from acetaldehyde and ammonia in the presence of heterogeneous Pd complexes containing S is studied by a pulsed microcatalytic method.The process occurs with selective formation of 4-methylpyridine.The difference in the catalytic activity of the studied complexes is explained on the basis of 13C NMR spectra.
- Chekurovskaya, E. D.,Akimov, A. N.,Vaistub, T. G.,Tarasova, T. M.
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- NMR Studies of Picolyl-type Carbanions. VIII. Anions Produced by Reactions of Alkyl-substituted Pyridines with Butyllithium
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The 1H and 13C NMR spectra have been observed for the anions, produced from methyl-, ethyl-, and isopropylpyridines, in tetrahydrofuran (THF).Two kinds of anions are formed concomitantly by lithium-proton exchange and addition of butyllithium from 2-ethyl, 2-isopropyl, 4-methyl, and 4-ethylpyridines.The former reaction tends to occur at the substituent bonded to the position adjacent to nitrogen, and the latter one occurs at the position adjacent to nitrogen without substituent.In the anions formed by the exchange from 2- and 4-ethylpyridines, a specific ring protonis coupled to the α-carbon, and, further, the ortho- or meta-protons (or -carbons) in the latter anion are nonequivalent respectively at room temperature.The α-carbons in these anions are virtually sp2-hybridized.
- Konishi, Kazuyori,Matsumoto, Hiroshi,Saito, Katsuhiro,Takahashi, Kensuke
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- Nucleophilicities and carbon basicities of pyridines
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Rate and equilibrium constants for the reactions of pyridines with donor-substituted benzhydrylium ions have been determined spectrophotometrically. The correlation equation log k(20°C) = s(N+E). in which s and N are nucleophile-specific parameters and E is an electrophile-specific parameter, has been used to determine the nucleophilicity parameters of various pyridines in CH2Cl2 and aqueous solution and to compare them with N of other nucleophiles. It is found that the nucleophilic organocatalyst 4-(dimethylamino)pyridine (DMAP) and tertiary phosphanes have comparable nucleophilicities and carbon basicities despite widely differing Bronsted basicities. For that reason, these reactivity parameters are suggested as guidelines for the development of novel organocatalysts. The Marcus equation is employed for the determination of the intrinsic barriers of these reactions.
- Brotzel, Frank,Kempf, Bernhard,Singer, Thomas,Zipse, Hendrik,Mayr, Herbert
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- Kinetic and Computational Studies of Rhenium Catalysis for Oxygen Atom Transfer Reactions
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The rhenium(v)oxo dimer {MeReO(edt)}2 (edt≤1,2-ethanedithiolate) is an effective catalyst for the oxygen atom transfer (OAT) reaction from pyridine oxide and picoline oxide to triphenylarsine (Ph3As) as oxygen acceptor. Kinetics measurements were carried
- Ibdah, Abdellatif,Bakar, Heba Bani,Alduwikat, Salwa
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- Expansion of Azulenes as Nonbenzenoid Aromatic Compounds for C-H Activation: Rhodium- And Iridium-Catalyzed Oxidative Cyclization of Azulene Carboxylic Acids with Alkynes for the Synthesis of Azulenolactones and Benzoazulenes
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Rhodium-catalyzed oxidative [4 + 2] cyclization reactions through the C-H activation of azulene carboxylic acids as nonbenzenoid aromatic compounds with symmetrical and unsymmetrical alkynes were developed under aerobic conditions, which produced azulenolactone derivatives with a wide substrate scope and excellent functional group tolerance. Interestingly, azulenic acids in reaction with alkynes underwent iridium-catalyzed [2 + 2 + 2] cyclization accompanied by decarboxylation to afford tetra(aryl)-substituted benzoazulene derivatives. The reactivity order for C-H activation reaction is greater toward azulene-6-carboxylic acid, azulene-1-carboxylic acid, and azulene-2-carboxylic acid. For the first time, the expansion of azulenes having directing group as nonbenzenoid aromatic compounds for C-H activation was successful, indicating that nonbenzenoid aromatic compounds can be used as good substrates for the C-H activation reaction. Therefore, the research area of C-H activation will certainly expand to nonbenzenoid aromatic compounds in future.
- Maeng, Chanyoung,Son, Jeong-Yu,Lee, Seung Cheol,Baek, Yonghyeon,Um, Kyusik,Han, Sang Hoon,Ko, Gi Hoon,Han, Gi Uk,Lee, Kyungsup,Lee, Kooyeon,Lee, Phil Ho
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- Can Heteroarenes/Arenes Be Hydrogenated Over Catalytic Pd/C Under Ambient Conditions?
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Hydrogenation of over a dozen aromatic compounds, including both heteroarenes and arenes, over palladium on carbon (Pd/C, 1–100 molpercent) with H2-balloon pressure at room temperature is reported. Analyses using pyridine as a model substrate revealed that acetic acid was the best solvent, as using only 1 molpercent Pd/C provided piperidine quantitatively. Substrate scope analysis and density functional theory calculations indicated that reaction rates are highly dependent on frontier molecular orbital characteristics and the steric bulkiness of substituents. Moreover, the established method was used for the concise synthesis of the anti-Alzheimer drug donepezil (Aricept?).
- Tanaka, Nao,Usuki, Toyonobu
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- Nonclassical oxygen atom transfer reactions of oxomolybdenum(vi) bis(catecholate)
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Mechanistic studies indicate that the oxomolybdenum(vi) bis(3,5-di-tert-butylcatecholate) fragment deoxygenates pyridine-N-oxides in a reaction where the oxygen is delivered to molybdenum but the electrons for substrate reduction are drawn from the bound catecholate ligands, forming 3,5-di-tert-butyl-1,2-benzoquinone.
- Marshall-Roth, Travis,Liebscher, Sean C.,Rickert, Karl,Seewald, Nicholas J.,Oliver, Allen G.,Brown, Seth N.
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- Synthesis of picolines over metal modified HZSM-5 catalyst
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A series of metal (i.e. Pb, Cd, Zn, Co, Cr) modified H-ZSM-5 catalysts were prepared by an ion-exchange method and were characterized by XRD, FT-IR, NH3-TPD and N2 adsorption techniques. There catalytic activity was evaluated in the Chichibabin condensation of acetaldehyde and ammonia giving 2-picoline, 4-picoline and a small amount of pyridine as the product. The catalyst coking behaviour was also characterized by TG measurement. The characterization results showed that the crystal structure of H-ZSM-5 was well reserved and the active metal ions were evenly spread in the ZSM-5 framework. The surface acidity was enhanced a lot after the metal modification. Catalytic results showed that metal incorporated catalysts greatly increased the total yield of pyridine bases, especially which of 2-picoline and 4-picoline, meanwhile the ratio of 2-picoline/4-picoline was also enhanced.
- Jiang,Huang,Xiao,Xiao,Li
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- Synthesis of Pyridine Bases over Ion-exchanged Pentasil Zeolite
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The catalytic activity of pentasil zeolite for the synthesis of pyridine bases from aldehydes and ammonia was found to depend upon the Si/Al ratio and the metal cation.The best choices are 30 to 120 of Si/Al ratios and metal cations Such as Tl(I), Pb(II), Co(II) and Zn(II).
- Sato, Hiroshi,Shimizu, Shinkichi,Abe, Nobuyuki,Hirose, Ken-ichi
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- Probing the nature of the Co(III) ion in corrins: Comparison of reactions of aquacyanocobyrinic acid heptamethyl ester and aquacyano-stable yellow cobyrinic acid hexamethyl ester with neutral N-donor ligands
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Equilibrium constants (log K) for substitution of coordinated H 2O in aquacyanocobyrinic acid heptamethyl ester (aquacyanocobester, ACCbs) and aquacyano-stable yellow cobyrinic acid hexamethyl ester (aquacyano-stable yellow cobester, ACSYCbs), in which oxidation of the C5 carbon of the corrin interrupts the normal delocalized system of corrins, by neutral N-donor ligands (ammonia, ethanolamine, 2-methoxyethylamine, N-methylimidazole, and 4-methylpyridine) have been determined spectrophotometrically as a function of temperature. Log K values increase with the basicity of the ligand, but a strong compensation effect between ΔH and ΔS values causes a leveling effect. The aliphatic amines with a harder donor atom produce ΔH values that are more negative in their reactions with ACSYCbs than with ACCbs, while the softer, aromatic N donors produce more negative ΔH values with ACCbs than with ACSYCbs. Molecular modeling (DFT, M06L/SVP, and a quantum theory of atoms in molecules analysis of the electron density) shows that complexes of the aliphatic amines with SYCbs produce shorter and stronger Co-N bonds with less ionic character than the Co-N bonds of these ligands with the cobester. Conversely, the Co-N bond to the aromatic N donors is shorter, stronger, and somewhat less ionic in the complexes of the cobester than in those of the SYCbs. Therefore, the distinction between the harder Co(III) in ACSYCbs and softer Co(III) in ACCbs, reported previously for anionic ligands, is maintained for neutral N-donor ligands.
- Chemaly, Susan M.,Kendall, Louise,Nowakowska, Monika,Pon, Dale,Perry, Christopher B.,Marques, Helder M.
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- Basicity of pyridine and some substituted pyridines in ionic liquids
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Figure presented The equilibrium constants for ion pair formation of some pyridines have been evaluated by spectrophotometric titration with trifluoroacetic acid in different ionic liquids. The basicity order is the same in ionic liquids and in water. The substituent effect on the equilibrium constant has been discussed in terms of the Hammett equation. Pyridine basicity appears to be less sensitive to the substituent effect in ionic liquids than in water.
- Angelini, Guido,De Maria, Paolo,Chiappe, Cinzia,Fontana, Antonella,Pierini, Marco,Siani, Gabriella
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- Ionic Liquids as “Masking” Solvents of the Relative Strength of Bases in Proton Transfer Reactions
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Equilibrium constants for the proton transfer reaction between pyridines and trifluoroacetic acid were measured in room-temperature ionic liquids (ILs) of different cation–anion compositions. The experimental equilibrium constants for ion-pair formation were corrected according to the Fuoss equation. The calculated equilibrium constants for the formation of free ions were taken as a quantitative measure of the base strength in IL solutions and compared with the relative constants in water. The effect of IL composition is discussed for a series of fixed IL anions and fixed IL cations. Finally, the sensitivity of the proton transfer reaction to the electronic effects of the substituent groups on the pyridine ring was quantified by applying the Hammett equation. A more marked levelling effect on the base strength was observed in ILs than in water. The Hammett reaction constants ρ were then correlated with solvent parameters according to a multi-parametric analysis, which showed that both specific hydrogen-bond donor/acceptor and non-specific interactions play an important role, with α and permittivity being the main parameters affecting the ability of the IL to differentiate the strength of the base.
- Zappacosta, Romina,Di Crescenzo, Antonello,Ettorre, Valeria,Fontana, Antonella,Pierini, Marco,Siani, Gabriella
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- Solvent dependence of oxygen isotope effects on the decarboxylation of 4-pyridylacetic acid
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Oxygen isotope effects on the decarboxylation of 4-pyridylacetic acid have been measured by the remote-label technique. The isotope effect varies from k16/k18 = 0.995 per oxygen in 25% dioxane to 1.003 in 75% dioxane. The isotope effect reflects three contributions: An inverse isotope effect of 0.98-0.99 due to the change in carbon-oxygen bond order on going from ground state to transition state, an effect of 1.01-1.02 due to desolvation of the carboxyl group, and an effect of approximately 1.01 due to the acid-base equilibrium of the carboxyl group. Thus, oxygen isotope effects on decarboxylation should be a useful probe for carboxyl desolvation in enzymatic decarboxylations.
- Headley, George W.,O'Leary, Marion H.
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- Catalytic Deoxygenation of Amine and Pyridine N-Oxides Using Rhodium PCcarbeneP Pincer Complexes
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Rhodium PCcarbeneP pincer complexes 1-L (L = PPh3, PPh2(C6F5), PCy3) readily facilitate deoxygenation of amine and pyridine N-oxides. The resulting complexes exhibit δ2-C= O coordination of the resulting keto POP pincer ligand. These δ2-Ca? O linkages in the metalloepoxide complexes are readily reduced by isopropyl alcohol and various benzylic alcohols. Thus, efficient catalytic deoxygenation of amine and pyridine N-oxides is possible using complexes 1-L and isopropyl alcohol. This represents a pioneering example of PCcarbeneP pincer complexes being used as catalysts for catalytic deoxygenation.
- Tinnermann, Hendrik,Sung, Simon,Cala, Beatrice A.,Gill, Hashir J.,Young, Rowan D.
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- Activation of rhenium(I) toward substitution in fac -[Re(N,O′ -Bid)(CO)3(HOCH3)] by Schiff-base bidentate ligands (N,O′ -Bid)
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A series of fac-[Re(N,O′-Bid)(CO)3(L)] (N,O′-Bid = monoanionic bidentate Schiff-base ligands with N,O donor atoms; L = neutral monodentate ligand) has been synthesized, and the methanol substitution reactions have been investigated. The complexes were characterized by NMR, IR, and UV-vis spectroscopy. X-ray crystal structures of the compounds fac-[Re(Sal-mTol)(CO)3(HOCH3)], fac-[Re(Sal-pTol)(CO) 3(HOCH3)], fac-[Re(Sal-Ph)(CO)3(HOCH 3)], and fac-[Re(Sal-Ph)(CO)3(Py)] (Sal-mTol = 2-(m-tolyliminomethyl)phenolato; Sal-pTol = 2-(p-tolyliminomethyl)phenolato; Sal-Ph = 2-(phenyliminomethyl)phenolato; Py = pyridine) are reported. Significant activation for the methanol substitution is induced by the use of the N,O bidentate ligand as manifested by the second order rate constants, with limiting kinetics being observed for the first time. Rate constants (25 C) (k1 or k3) and activation parameters (ΔH ka, kJ mol-1; ΔS ka, J K-1 mol-1) from Eyring plots for entering nucleophiles as indicated are as follows: fac-[Re(Sal-mTol)(CO)3(HOCH3)] 3-chloropyridine: (k 1) 2.33 ± 0.01 M-1 s-1; 85.1 ± 0.6, 48 ± 2; fac-[Re(Sal-mTol)(CO)3(HOCH3)] pyridine: (k1) 1.29 ± 0.02 M-1 s-1; 92 ± 2, 66 ± 7; fac-[Re(Sal-mTol)(CO)3(HOCH3)] 4-picoline: (k1) 1.27 ± 0.05 M-1 s-1; 88 ± 2, 53 ± 6; (k3) 3.9 ± 0.03 s-1; 78 ± 8, 30 ± 27; (kf) 1.7 ± 0.02 M-1 s-1; 86 ± 2, 49 ± 6; fac-[Re(Sal-mTol)(CO) 3(HOCH3)] DMAP (k3) 1.15 ± 0.02 s -1; 88 ± 2, 52 ± 7. An interchange dissociative mechanism is proposed.
- Brink, Alice,Visser, Hendrik G.,Roodt, Andreas
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- 1,4-dioxobenzene compounds of gallium: Reversible binding of pyridines to [{(tBu)2Ga}2(μ-OC6H 4O)]n in the solid state
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The gallium aryloxide polymer, [{(tBu)2Ga} 2(μ-OC6H4O)]n (1) is synthesized by the addition of Ga(tBu)3 with hydroquinone in a noncoordinating solvent, and reacts with pyridines to yield the yellow compound [(tBu)2Ga(L)]2(μ-OC6H 4O) [L = py (2), 4-Mepy (3), and 3,5-Me2py (4)] via cleavage of the Ga2O2 dimeric core. The analogous formation of Ga(tBu)2(OPh)(py) (5) occurs by dissolution of [(tBu)2Ga(μ-OPh)]2 in pyridine. In solution, 2-4 undergo dissociation of one of the pyridine ligands to yield [(tBu)2Ga(L)(μ-OC6H4O)Ga( tBu)2]2, for which the ΔH and ΔS have been determined. Thermolysis of compounds 2-4 in the solid-state results in the loss of the Lewis base and the formation of 1. The reaction of 1 or [(tBu)2Ga-(μ-OPh)]2 with the vapor of the appropriate ligand results in the solid state formation of 2-4 or 5, respectively. The ΔH? and ΔS? for both ligand dissociation and association for the solid-vapor reactions have been determined. The interconversion of 1 into 2-4, as well as [(tBu) 2Ga(μ-OPh)]2 into 5, and their reverse reactions, have been followed by 13C CPMAS NMR spectroscopy, TG/DTA, SEM, EDX, and powder XRD. Insight into this solid-state polycondensation polymerization reaction may be gained from the single-crystal X-ray crystallographic packing diagrams of 2-5. The crystal packing for compounds 2, 3, and 5 involve a head-to-head arrangement that is maintained through repeated ligand dissociation and association cycles. In contrast, when compound 4 is crystallized from solution a head-to-tail packing arrangement is formed, but during reintroduction of 3,5-Me2py in the solid state-vapor reaction of compound 1, a head-to-head polymorph is postulated to account for the alteration in the ΔH? of subsequent ligand dissociation reactions. Thus, the ΔH? for the condensation polymerization reaction is dependent on the crystal packing; however, the subsequent reversibility of the reaction is dependent on the polymorph.
- Van Poppel, Laura H.,Bott, Simon G.,Barron, Andrew R.
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- HETEROGENIZED TRANSITION METAL COMPLEXES AS CATALYSTS FOR SYNTHESIZING METHYLPYRIDINES FROM ACETALDEHYDE AND AMMONIA
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The synthesis of methylpyridines from acetaldehyde and ammonia in the presence of N- and F-containing heterogenized transition metal complexes is studied by a pulse microcatalytic method.A correlation between the donor-acceptor properties of the ligand, of the complexed metal, and of the catalytically active complex is found using 31P NMR.The reaction direction depends on the properties of the solvent used to heterogenize the complex on the carrier.
- Chekurovskaya, E. D.,Akimov, A. N.,Tarasova, T. M.
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- Bifunctional Mechanism of Pyridine Hydrodenitrogenation
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The role of Mo coordinatively unsaturated sites (CUS) and Broensted acidic sites in the hydrodenitrogenation of pyridine was investigated in an atmospheric-pressure microreactor.The test catalysts consisted of nonsulfided Mo oxide supported on Al2O3, SiO2, and silica-aluminas, containing different concentrations of Mo CUS and Broensted acidic sites.The kinetic study revealed that Mo loading and support composition affect the specific activity of Mo and selectivity of the catalysts.For the range of conditions used in this study (360-420 deg C, 1 atm H2, 0.2 molpercent pyridine concentration, differential conversion), the most abundant reaction intermediate was trans-2-pentene, and the rate-limiting step was the hydrogenation of the ring.Thus, the overall activity was correlated with the concentration of Mo CUS, which are the hydrogenation sites.The yield of denitrogenated product was also correlated with concentration of CUS.The Broensted acidic sites determined the selectivity towards the observed cracking, isomerization, and alkylation products.
- Marzari, J. A.,Rajagopal, S.,Miranda, R.
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- Clean protocol for deoxygenation of epoxides to alkenes: Via catalytic hydrogenation using gold
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The epoxidation of olefin as a strategy to protect carbon-carbon double bonds is a well-known procedure in organic synthesis, however the reverse reaction, deprotection/deoxygenation of epoxides is much less developed, despite its potential utility for the synthesis of substituted olefins. Here, we disclose a clean protocol for the selective deprotection of epoxides, by combining commercially available organophosphorus ligands and gold nanoparticles (Au NP). Besides being successfully applied in the deoxygenation of epoxides, the discovered catalytic system also enables the selective reduction N-oxides and sulfoxides using molecular hydrogen as reductant. The Au NP catalyst combined with triethylphosphite P(OEt)3 is remarkably more reactive than solely Au NPs. The method is not only a complementary Au-catalyzed reductive reaction under mild conditions, but also an effective procedure for selective reductions of a wide range of valuable molecules that would be either synthetically inconvenient or even difficult to access by alternative synthetic protocols or by using classical transition metal catalysts. This journal is
- Fiorio, Jhonatan L.,Rossi, Liane M.
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p. 312 - 318
(2021/01/29)
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- Metal-Free Deoxygenation of Amine N-Oxides: Synthetic and Mechanistic Studies
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We report herein an unprecedented combination of light and P(III)/P(V) redox cycling for the efficient deoxygenation of aromatic amine N-oxides. Moreover, we discovered that a large variety of aliphatic amine N-oxides can easily be deoxygenated by using only phenylsilane. These practically simple approaches proceed well under metal-free conditions, tolerate many functionalities and are highly chemoselective. Combined experimental and computational studies enabled a deep understanding of factors controlling the reactivity of both aromatic and aliphatic amine N-oxides.
- Lecroq, William,Schleinitz, Jules,Billoue, Mallaury,Perfetto, Anna,Gaumont, Annie-Claude,Lalevée, Jacques,Ciofini, Ilaria,Grimaud, Laurence,Lakhdar, Sami
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p. 1237 - 1242
(2021/06/01)
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- α-Heteroarylation of Thioethers via Photoredox and Weak Br?nsted Base Catalysis
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We report the C-H activation of thioethers to α-thio alkyl radicals and their addition to N-methoxyheteroarenium salts for the redox-neutral synthesis of α-heteroaromatic thioethers. Studies are consistent with a two-step activation mechanism, where oxidation of thioethers to sulfide radical cations by a photoredox catalyst is followed by α-C-H deprotonation by a weak Br?nsted base catalyst to afford α-thio alkyl radicals. Further, N-methoxyheteroarenium salts play additional roles as a source of methoxyl radical that contributes to α-thio alkyl radical generation and a sacrificial oxidant that regenerates the photoredox catalytic cycle.
- Alfonzo, Edwin,Hande, Sudhir M.
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p. 6115 - 6120
(2021/08/16)
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- Photocatalytic deoxygenation of N-O bonds with rhenium complexes: From the reduction of nitrous oxide to pyridineN-oxides
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The accumulation of nitrogen oxides in the environment calls for new pathways to interconvert the various oxidation states of nitrogen, and especially their reduction. However, the large spectrum of reduction potentials covered by nitrogen oxides makes it difficult to find general systems capable of efficiently reducing variousN-oxides. Here, photocatalysis unlocks high energy species able both to circumvent the inherent low reactivity of the greenhouse gas and oxidant N2O (E0(N2O/N2) = +1.77 Vvs.SHE), and to reduce pyridineN-oxides (E1/2(pyridineN-oxide/pyridine) = ?1.04 Vvs.SHE). The rhenium complex [Re(4,4′-tBu-bpy)(CO)3Cl] proved to be efficient in performing both reactions under ambient conditions, enabling the deoxygenation of N2O as well as synthetically relevant and functionalized pyridineN-oxides.
- Anthore-Dalion, Lucile,Cantat, Thibault,Kjellberg, Marianne,Nicolas, Emmanuel,Ohleier, Alexia,Thuéry, Pierre
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p. 10266 - 10272
(2021/08/12)
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- A Lewis Base Nucleofugality Parameter, NFB, and Its Application in an Analysis of MIDA-Boronate Hydrolysis Kinetics
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The kinetics of quinuclidine displacement of BH3 from a wide range of Lewis base borane adducts have been measured. Parameterization of these rates has enabled the development of a nucleofugality scale (NFB), shown to quantify and predict the leaving group ability of a range of other Lewis bases. Additivity observed across a number of series R′3-nRnX (X = P, N; R′ = aryl, alkyl) has allowed the formulation of related substituent parameters (nfPB, nfAB), providing a means of calculating NFB values for a range of Lewis bases that extends far beyond those experimentally derived. The utility of the nucleofugality parameter is explored by the correlation of the substituent parameter nfPB with the hydrolyses rates of a series of alkyl and aryl MIDA boronates under neutral conditions. This has allowed the identification of MIDA boronates with heteroatoms proximal to the reacting center, showing unusual kinetic lability or stability to hydrolysis.
- García-Domínguez, Andrés,Gonzalez, Jorge A.,Leach, Andrew G.,Lloyd-Jones, Guy C.,Nichol, Gary S.,Taylor, Nicholas P.
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supporting information
(2022/01/04)
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- A Mild Method for Electrochemical Reduction of Heterocyclic N-Oxides
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Deoxygenation of heteroaromatic N-oxides is commonly accomplished using chemical or enzymatic methods. In this work, we report on an expedient protocol for electrochemical reduction of pyridine N-oxide derivatives under mild conditions. A diverse range of mono- and bis N-oxides were converted into the corresponding nitrogen bases in good yields. Importantly, the method is highly selective towards N-oxides and tolerates challenging halo and nitro substituents in the heteroaromatic ring.
- Fukazawa, Yasuaki,Rubtsov, Aleksandr E.,Malkov, Andrei V.
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supporting information
p. 3317 - 3319
(2020/05/25)
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- Light-driven activation of carbon-halogen bonds by readily available amines for photocatalytic hydrodehalogenation
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A straightforward protocol using readily available aromatic amines, N,N,N′,N′-tetramethyl- p-phenylenediamine or N,N′,N′-tetramethylbenzidine, as photocatalysts was developed for the efficient hydrodehalogenation of organic halides, such as 4′-bromoacetophenone, polyfluoroarenes, cholorobenzene, and 2,2′,4,4′-tetrabromodiphenyl ether(a resistant and persistent organic pollutant). The strongly reducing singlet excited states of the amines enabled diffusion-controlled dissociative electron transfer to effectively cleave carbon-halogen bonds, followed by radical hydrogenation. Diisopropylethylamine served as the terminal electron/proton donor and regenerated the amine sensitizers.
- Chen, Chuncheng,Duan, Ran,Meng, Di,Song, Wenjing,Wei, Yan,Zhao, Jincai,Zhen, Shengli,Zhu, Qian
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p. 1474 - 1479
(2020/04/29)
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- Photorelease of Pyridines Using a Metal-Free Photoremovable Protecting Group
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The photorelease of bioactive molecules has emerged as a valuable tool in biochemistry. Nevertheless, many important bioactive molecules, such as pyridine derivatives, cannot benefit from currently available organic photoremovable protecting groups (PPGs). We found that the inefficient photorelease of pyridines is attributed to intramolecular photoinduced electron transfer (PET) from PPGs to pyridinium ions. To alleviate PET, we rationally designed a strategy to drive the excited state of PPG from S1 to T1 with a heavy atom, and synthesized a new PPG by substitution of the H atom at the 3-position of 7-dietheylamino-coumarin-4-methyl (DEACM) with Br or I. This resulted in an improved photolytic efficiency of the pyridinium ion by hundreds-fold in aqueous solution. The PPG can be applied to various pyridine derivatives. The successful photorelease of a microtubule inhibitor, indibulin, in living cells was demonstrated for the potential application of this strategy in biochemical research.
- Dong, Zaizai,Fang, Xiaohong,Kou, Xiaolong,Tan, Weihong,Tang, Xiao-Jun,Wu, Yayun,Zhang, Zhen,Zhao, Rong,Zhou, Wei
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supporting information
p. 18386 - 18389
(2020/08/24)
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- Efficient Chemoselective Reduction of N-Oxides and Sulfoxides Using a Carbon-Supported Molybdenum-Dioxo Catalyst and Alcohol
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The chemoselective reduction of a wide range of N-oxides and sulfoxides with alcohols is achieved using a carbon-supported dioxo-molybdenum (Mo@C) catalyst. Of the 10 alcohols screened, benzyl alcohol exhibits the highest reduction efficiency. A variety of N-oxide and both aromatic and aliphatic sulfoxide substrates bearing halogens as well as additional reducible functionalities are efficiently and chemoselectively reduced with benzyl alcohol. Chemoselective N-oxide reduction is effected even in the presence of potentially competing sulfoxide moieties. In addition, the Mo@C catalyst is air- and moisture-stable, and is easily separated from the reaction mixture and then re-subjected to reaction conditions over multiple cycles without significant reactivity or selectivity degradation. The high stability and recyclability of the catalyst, paired with its low toxicity and use of earth-abundant elements makes it an environmentally friendly catalytic system.
- Li, Jiaqi,Liu, Shengsi,Lohr, Tracy L.,Marks, Tobin J.
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p. 4139 - 4146
(2019/05/27)
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- ZEOLITE CATALYST
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The present disclosure relates to the preparation of pyridine derivatives, such as α-picoline or α-parvoline, and catalysts useful for the selective preparation of such pyridine derivatives. Particularly, the present disclosure relates to the selective preparation of certain pyridine derivative using dealuminated zeolite catalysts.
- -
-
Paragraph 0107-0108; 0111-0122; 0126; 0134
(2019/05/22)
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- Axial coordination reactions with nitrogenous bases and determination of equilibrium constants for zinc tetraarylporphyrins containing four β, β ′-fused butano and benzo groups in nonaqueous media
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The axial coordination properties of six zinc tetraarylporphyrins with seven different nitrogenous bases were examined in CH2Cl2 for derivatives containing four β,β′-fused butano or benzo groups and the equilibrium constants (logK) determined using spectral titration methods. The examined compounds are represented as butano(YPh)4PorZn and benzo(YPh)4PorZn, where Por is the porphyrin dianion and Y is a CH3, H or Cl substituent on the para-position of each meso-phenyl ring of the macrocycle. The initial four-coordinate butano-And benzoporphyrins will axially bind one nitrogenous base to form five-coordinate derivatives in CH2Cl2 and this leads to a 4-22 nm red-shift of the Soret and Q bands. The logK values range from 1.98 to 4.69 for butano(YPh)4PorZn and from 3.42 to 5.36 for benzo(YPh)4PorZn, with the exact value depending upon the meso and β-substituents of the porphyrin and the conjugate acid dissociation constants (pKa) of the nitrogenous base.
- Ye, Lina,Fang, Yuanyuan,Ou, Zhongping,Wang, Liping,Xue, Songlin,Lu, Yang,Kadish, Karl M.
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p. 196 - 206
(2019/02/19)
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- Heterogeneously palladium-catalyzed acceptorless dehydrogenative aromatization of cyclic amines
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In this manuscript, we report an efficient heterogeneously catalyzed acceptorless dehydrogenative aromatization of cyclic amines under relatively mild conditions. In the presence of a supported catalyst Pd/LDH (LDH = layered double hydroxide), various kinds of structurally diverse cyclic amines including piperidines, tetrahydro(iso)quinolines, and indolines could be converted into the corresponding heteroarenes. Pd/LDH could be reused several times though its catalytic activity gradually declined due to the increase in the palladium particle size.
- Oyama, Takashi,Yatabe, Takafumi,Jin, Xiongjie,Mizuno, Noritaka,Yamaguchi, Kazuya
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supporting information
p. 517 - 520
(2019/06/11)
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- Mesoporous Aluminosilicates in the Synthesis of N-Heterocyclic Compounds
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Abstract: The catalytic properties of samples of amorphous mesoporous aluminosilicate ASM with different Si/Al molar ratios (40, 80, 160) were studied in the synthesis of practically important pyridines (by the interaction of С2–С5 alcohols with formaldehyde and ammonia, cyclocondensation of acetaldehyde and propionic aldehyde with ammonia), dialkylquinolines and alkyltetrahydroquinolines (by reaction of aniline with C3, C4 aldehydes) and alkyldihydroquinolines (by interaction of aniline with ketones, acetone and acetophenone). It is found that mesoporous aluminosilicate ASM sample with a molar ratio of Si/Al = 40, which has the highest acidity among the studied samples, exhibits the highest activity and selectivity in these reactions.
- Agliullin, M. R.,Bikbaeva, V. R.,Bubennov, S. V.,Filippova, N. A.,Gataulin, A. R.,Grigor’eva, N. G.,Kostyleva, S. A.,Kutepov, B. I.,Narender, Nama
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p. 733 - 743
(2020/02/25)
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- A mild and efficient H2O2 oxygenation of N-heteroaromatic compounds to the amine N-oxides and KI deoxygenation back to the tertiary amine with hexaphenyloxodiphosphonium triflate
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A mild and efficient method for the oxidation of N-heteroaromatic compounds to the corresponding N-oxides using H2O2 in the presence of hexaphenyloxodiphosphnium triflate (Hendrickson reagent) in EtOH at room temperature was reported. This methodology presented relatively fast and selective reactions to afford the N-oxides in good yields. The reverse reactions, deoxygenation reactions, were also carried out under the same reaction conditions by KI to produce the tertiary amines.
- Khodaei, Mohammad Mehdi,Alizadeh, Abdolhamid,Hezarkhani, Hadis Afshar
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p. 1843 - 1849
(2018/07/06)
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- Mild Deoxygenation of Sulfoxides over Plasmonic Molybdenum Oxide Hybrid with Dramatic Activity Enhancement under Visible Light
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Harvesting solar light to boost commercially important organic synthesis still remains a challenge. Coupling of conventional noble metal catalysts with plasmonic oxide materials which exhibit intense plasmon absorption in the visible light region is a promising option for efficient solar energy utilization in catalysis. Herein, we for the first time demonstrate that plasmonic hydrogen molybdenum bronze coupled with Pt nanoparticles (Pt/HxMoO3-y) shows a high catalytic performance in the deoxygenation of sulfoxides with 1 atm of H2 at room temperature, with dramatic activity enhancement under visible light irradiation relative to dark conditions. The plasmonic molybdenum oxide hybrids with strong plasmon resonance peaks pinning at around 556 nm are obtained via a facile H-spillover process. Pt/HxMoO3-y hybrid provides excellent selectivity for the deoxygenation of various sulfoxides as well as pyridine N-oxides, in which drastically improved catalytic efficiencies are obtained under the irradiation of visible light. Comprehensive analyses reveal that oxygen vacancies massively introduced via a H-spillover process are the main active sites, and the reversible redox property of Mo atoms and strong plasmonic absorption play key roles in this reaction. The catalytic system works under extremely mild conditions and can boost the reaction by the assistance of visible light, offering an ultimately greener protocol to produce sulfides from sulfoxides. Our findings may open up a new strategy for designing plasmon-based catalytic systems that can harness visible light efficiently.
- Kuwahara, Yasutaka,Yoshimura, Yukihiro,Haematsu, Kohei,Yamashita, Hiromi
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p. 9203 - 9210
(2018/06/25)
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- Spin-Center Shift-Enabled Direct Enantioselective α-Benzylation of Aldehydes with Alcohols
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Nature routinely engages alcohols as leaving groups, as DNA biosynthesis relies on the removal of water from ribonucleoside diphosphates by a radical-mediated "spin-center shift" (SCS) mechanism. Alcohols, however, remain underused as alkylating agents in synthetic chemistry due to their low reactivity in two-electron pathways. We report herein an enantioselective α-benzylation of aldehydes using alcohols as alkylating agents based on the mechanistic principle of spin-center shift. This strategy harnesses the dual activation modes of photoredox and organocatalysis, engaging the alcohol by SCS and capturing the resulting benzylic radical with a catalytically generated enamine. Mechanistic studies provide evidence for SCS as a key elementary step, identify the origins of competing reactions, and enable improvements in chemoselectivity by rational photocatalyst design.
- Nacsa, Eric D.,MacMillan, David W. C.
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supporting information
p. 3322 - 3330
(2018/03/13)
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- Silica-supported silver nanoparticles as an efficient catalyst for aromatic C-H alkylation and fluoroalkylation
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The efficient catalysis of oxidative alkylation and fluoroalkylation of aromatic C-H bonds is of paramount importance in the pharmaceutical and agrochemical industries, and requires the development of convenient Ag0-based nano-architectures with high catalytic activity and recyclability. We prepared Ag-doped silica nanoparticles (Ag0/+@SiO2) with a specific nano-architecture, where ultra-small sized silver cores are immersed in silica spheres, 40 nm in size. The nano-architecture provides an efficient electrochemical oxidation of Ag+@SiO2 without any external oxidant. In turn, Ag+@SiO2 5 mol% results in 100% conversion of arenes into their alkylated and fluoroalkylated derivatives in a single step at room temperature under nanoheterogeneous electrochemical conditions. Negligible oxidative leaching of silver from Ag0/+@SiO2 is recorded during the catalytic coupling of arenes with acetic, difluoroacetic and trifluoroacetic acids, which enables the good recyclability of the catalytic function of the Ag0/+@SiO2 nanostructure. The catalyst can be easily separated from the reaction mixture and reused a minimum of five times upon electrochemical regeneration. The use of the developed Ag0@SiO2 nano-architecture as a heterogeneous catalyst facilitates aromatic C-H bond substitution by alkyl and fluoroalkyl groups, which are privileged structural motifs in pharmaceuticals and agrochemicals.
- Khrizanforov, Mikhail N.,Fedorenko, Svetlana V.,Mustafina, Asiya R.,Kholin, Kirill V.,Nizameev, Irek R.,Strekalova, Sofia O.,Grinenko, Valeriya V.,Gryaznova, Tatiana V.,Zairov, Rustem R.,Mazzaro, Raffaello,Morandi, Vittorio,Vomiero, Alberto,Budnikova, Yulia H.
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supporting information
p. 9608 - 9616
(2018/08/06)
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- Visible-light-responsive catalysis of a zinc-introduced lacunary disilicoicosatungstate for the deoxygenation of pyridine N-oxides
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We herein report the synthesis and photoredox catalysis of a mononuclear zinc-introduced lacunary disilicoicosatungstate TBA7[{Zn(CH3CN)}(γ-SiW10O34){γ-SiW10O32(CH3CONH)}(μ-O)2] (II, TBA = tetra-n-butylammonium). POM II showed efficient photocatalytic activity in the selective deoxygenation of pyridine N-oxides under visible light irradiation (λ > 400 nm).
- Jeong, Jinu,Suzuki, Kosuke,Yamaguchi, Kazuya,Mizuno, Noritaka
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supporting information
p. 13226 - 13229
(2017/11/27)
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- Platinum-supporting hollandite-type vanadium-chromium mixed oxides as efficient heterogeneous catalysts for deoxygenation of sulfoxides under atmospheric H2 pressure
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Deoxygenation of sulfoxides to their corresponding sulfides is an important reaction, and the development of efficient heterogeneous catalysts that can utilize molecular hydrogen (H2) as a reducing agent is highly desired. In this study, we successfully developed a new concept in heterogeneous catalysts, platinum-supporting hollandite-type vanadium-chromium mixed oxide catalysts (Pt/V(1-x)Crx-Hol, x: Cr/(V + Cr) molar ratio of the precursor solution), for sulfoxide deoxygenation with H2. Hollandite-type vanadium-chromium mixed oxides (V(1-x)Crx-Hol) that did not support platinum could stoichiometrically deoxygenate methyl phenyl sulfoxide to methyl phenyl sulfide, and the V3+ species in V(1-x)Crx-Hol were oxidized to V4+ after deoxygenation. However, the V4+ species could not be re-reduced with H2. By supporting platinum nanoparticles on V(1-x)Crx-Hol, the re-reduction of the oxidized vanadium species with H2 became possible. Thus, in the presence of Pt/V(1-x)Crx-Hol, catalytic sulfoxide deoxygenation with H2 as the reducing agent can be realized; the deoxygenation occurs on V(1-x)Crx-Hol, and the role of platinum is to re-reduce the oxidized vanadium species with H2. In the presence of Pt/V0.7Cr0.3-Hol, various types of structurally diverse sulfoxides could be selectively converted into their corresponding sulfides under atmospheric H2 pressure (1 atm). In addition, the present system was applicable to the deoxygenation of pyridine N-oxides to their corresponding pyridines. The observed catalysis was truly heterogeneous, and the Pt/V0.7Cr0.3-Hol catalyst could be reused for sulfoxide deoxygenation, although the performance was reduced.
- Uematsu, Tsubasa,Ogasawara, Yoshiyuki,Suzuki, Kosuke,Yamaguchi, Kazuya,Mizuno, Noritaka
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p. 1912 - 1920
(2017/07/15)
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- Full Cleavage of C≡C Bond in Electron-Deficient Alkynes via Reaction with Ethylenediamine
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Reaction of 1,2-diaminioethane (ethylenediamine) with electron-deficient alkynes leads to full scission of the C≡C bond even in the absence of a keto group directly attached to the alkyne. This process involves oxidation of one of the alkyne carbons into C2 of a 2-R-4,5-dihydroimidazole with the concomitant reduction of the other carbon to a methyl group. The sequence of Sonogashira coupling with the ethylenediamine-mediated fragmentation described in this work can be used for selective formal substitution of halogen in aryl halides by a methyl group or a 4,5-dihydroimidazol-2-yl moiety.
- Vasilevsky, Sergei F.,Davydova, Maria P.,Mamatyuk, Victor I.,Tsvetkov, Nikolay,Hughes, Audrey,Baranov, Denis S.,Alabugin, Igor V.
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p. 421 - 429
(2017/04/07)
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- Producing pyridines: Via thermo-catalytic conversion and ammonization of glycerol over nano-sized HZSM-5
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In this study, nano-sized HZSM-5 catalysts with different Si/Al ratios were synthesized and employed for producing pyridines from glycerol via a thermo-catalytic conversion and ammonization (TCC-A) process. The catalytic performance of micro-sized HZSM-5 and nano-sized HZSM-5 was studied firstly. The nano-sized HZSM-5 showed better catalytic performance in pyridine production in the TCC-A process due to its smaller particle size. When the nano-sized HZSM-5 (Si/Al = 25) served as the catalyst, and the reaction temperature was about 550 °C with the weight hourly space velocity of glycerol to catalyst at 1 h-1 and the ammonia to glycerol ratio at 12:1, the highest yield of pyridines was up to 42.1%, which was much higher than that when using micro-sized HZSM-5 (35.6%) reported before. In addition, nano-sized HZSM-5 also showed a better catalytic performance than micro-sized HZSM-5 in the catalytic conversion of bio-derived furans to produce indoles. After five reaction/regeneration cycles, the catalytic performance of nano-sized HZSM-5 slightly decreased compared with the first run, but was still higher than that of micro-sized HZSM-5.
- Xu, Lujiang,Yao, Qian,Zhang, Ying,Fu, Yao
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p. 86034 - 86042
(2016/11/09)
-
- Preparation of an Arenylmethylzinc Reagent with Functional Groups by Chemoselective Cross-Coupling Reaction of Bis(iodoazincio)methane with Iodoarenes
-
Palladium-catalyzed cross-coupling reaction of bis(iodozincio)methane with iodoarenes carrying various functionalities such as ester, boryl, cyano, and halo groups proceeded chemoselectively to give the corresponding arenylmethylzinc species efficiently. The moderate reactivity of the gem-dizinc reagent imparted functional group tolerance to the process. The transformations from iodoheteroarenes were also performed; in the case of iodopyridine derivatives, the nickel-catalyzed reaction gave the corresponding organozinc species efficiently. The obtained arenylmethylzinc species underwent the copper-mediated coupling reaction with a range of organic halides.
- Shimada, Yukako,Haraguchi, Ryosuke,Matsubara, Seijiro
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p. 2395 - 2398
(2015/10/19)
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- Dynamic Covalent Chemistry of Nucleophilic Substitution Component Exchange of Quaternary Ammonium Salts
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Dynamic covalent libraries (DCLs) of quaternary ammonium cations were set up by reversible nucleophilic substitution (SN2′ and SN2) exchange reactions of ammonium salts and tertiary amines. The reactions were conducted at 60 °C to generate thermodynamically and kinetically controlled mixtures of quaternary ammonium compounds and tertiary amines, and were accelerated by using iodide as a nucleophilic catalyst. Microwave irradiation was used to assist the exchange reaction between the pyridinium salts and pyridine derivatives. Finally, experiments towards the generation of dynamic ionic liquids were performed. The results of this study pave the way for the extension of dynamic combinatorial chemistry to nucleophilic substitution reactions.
- Kulchat, Sirinan,Lehn, Jean-Marie
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p. 2484 - 2496
(2015/11/02)
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- One-Pot Defunctionalization of Lignin-Derived Compounds by Dual-Functional Pd50Ag50/Fe3O4/N-rGO Catalyst
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Generation of hydrogen from renewable sources and its safe utilization for efficient one-pot upgrading of renewable biofuels are a challenge. Bimetallic PdAg catalyst supported on Fe3O4/nitrogen-doped reduced graphene oxide (N-rGO) were synthesized for hydrogen generation from formic acid with high TOF (497 h-1 at 50 °C), and the hydrogen was subsequently utilized in situ for selective defunctionalization of lignin-derived chemicals with preserved aromatic nature at ambient pressure. Hydrodeoxygenation of aromatic aldehydes and ketones gave excellent yields (99% at 130 °C) with no use of additives. Furthermore, hydrogenolysis of β-O-4 and α-O-4 C-O model compounds produced only two products with high selectivity at 120 °C, which is an efficient and versatile one-pot platform for valorization of lignin biomass.
- Singh, Ajay K.,Jang, Seungwook,Kim, Jae Yul,Sharma, Siddharth,Basavaraju,Kim, Min-Gyu,Kim, Kyung-Rok,Lee, Jae Sung,Lee, Hong H.,Kim, Dong-Pyo
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p. 6964 - 6972
(2015/11/18)
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- Quantitative evaluation of the stability of gem -diaurated species in reactions with nucleophiles
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The reactivity of diaurated species toward nucleophiles was investigated. The reaction yields vinyl gold species and is described as simple SN2 ligand exchange at gold. Using suitably strong nucleophiles, equilibrium constants were determined to measure the stability of various diaurated species. On the basis of these equilibrium constants the influence of ligand and the nature of vinyl cores on the stability were analyzed. These results have direct implication for gold catalysis: it was demonstrated that vinyl gold intermediates bind the catalytic LAu+ species generally stronger than an alkyne (the substrate) by a factor of 106-109. This demonstrates that the formation of diaurated species from vinyl gold intermediates is thermodynamically favored in a catalytic reaction.
- Zhdanko, Alexander,Maier, Martin E.
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supporting information
p. 2000 - 2006
(2013/05/08)
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- Electrochemical coupling of mono and dihalopyridines catalyzed by nickel complex in undivided cell
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One step nickel-catalyzed electroreductive homocoupling among 2-bromopicolines and 2-bromopyridine has been investigated by our group in an undivided cell and using zinc or iron as sacrificial anode. In this work, it was developed mono and dihalopyridines coupling to obtain possible products from heterocoupling. A series of reactions were carried out in order to develop a synthetic method for the preparation of unsymmetrical 2,2′-bipyridines and 2,2′:6′,2″-terpyridines. Statistical yields (50%) were observed for 2-bromopyridines/2-bromo-6-methylpyridine heterocoupling. In a preliminary study devoted to terpyridines preparation, good results were obtained for 2,6-dihalopyridines homocoupling, affording 2,6-dichloro-2, 2′-bipyridine (46%) and 2,6-dibromo-2,2′-bipyridine (56%), at controlled reaction time. At major reaction time, it was observed that the direct electroreduction of the 2,6′-dihalo-2,2′-bipyridines intermediates and 2,6″-dihalo-2,2′:6′,2″-terpyridines products on the cathode surface. A reasonable isolated product yield of 6,6″-dimethyl-2,2′:6′,2″-terpyridine (10%) was only observed in the reaction between 2,6-dichloropyridine and 2-bromo-6- methylpyridine (1:2).
- Oliveira, Jadson L.,Silva, Maria J.,Florêncio, Tupolevck,Urgin, Karne,Sengmany, Stéphane,Léonel, Eric,Nédélec, Jean-Yves,Navarro, Marcelo
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experimental part
p. 2383 - 2390
(2012/04/17)
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- METHOD FOR RAPIDLY METHYLATING HETEROAROMATIC ARENE AND METHOD FOR PRODUCING TRACER FOR USE IN PET
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Provided is a method whereby a heteroaromatic ring aryl can be very rapidly methylated at a high yield. In an N-alkyl-2-pyrrolidinone, a heteroaromatic ring aryltrialkylstannan is cross-coupled with methyl iodide in the presence of a palladium complex, a phosphine ligand, a cuprous halide, a carbonic acid salt and/or an alkali metal fluoride to thereby rapidly methylate the heteroaromatic ring aryl. (Formula shows a case wherein the heteroaromatic ring aryl is a pyridyl group.)
- -
-
Page/Page column 5-6
(2011/11/06)
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- Highly efficient gold nanoparticle catalyzed deoxygenation of amides, sulfoxides, and pyridine N-oxides
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Selective deoxygenation is one of the most important reactions in the areas of total synthesis, biological chemistry, and transformation of renewable biomass resources.To date, many useful methods for the selective deoxygenation of oxygen-containing organic molecules, such as amides, nitro compounds, epoxides, sulfoxides, and those with Noxide groups, have been developed. However, these methods often include stoichiometric reactions. Some successful catalysts have been reported,but most of them are homogeneous systems and still suffer from low activities and selectivities, harsh reaction conditions, and tedious workup procedures. Therefore, further development of highly efficient heterogeneous catalysts for selective deoxygenations is highly desired.
- Mikami, Yusuke,Noujima, Akifumi,Mitsudome, Takato,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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experimental part
p. 1768 - 1772
(2011/03/21)
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- Dissection of complex molecular recognition interfaces
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The synthesis of a family of zinc porphyrins and pyridine ligands equipped with peripheral H-bonding functionality has provided access to a wide range of closely related supramolecular complexes featuring between zero and four intramolecular H-bonds. An automated UV/vis titration system was used to characterize 120 different complexes, and these data were used to construct a large of number of different chemical double mutant cycles to quantify the intramolecular H-bonding interactions. The results probe the quantitative structure-activity relationship that governs cooperativity in the assembly of complex molecular recognition interfaces. Specifically, variations in the chemical structures of the complexes have allowed us to change the supramolecular architecture, conformational flexibility, geometric complementarity, the number and nature of the H-bond interactions, and the overall stability of the complex. The free energy contributions from individual H-bonds are additive, and there is remarkably little variation with architecture in the effective molarity for the formation of intramolecular interactions. Intramolecular H-bonds are not observed in complexes where they are geometrically impossible, but there are no cases where excellent geometric complementarity leads to very high affinities. Similarly, changes in conformational flexibility seem to have limited impact on the values of effective molarity (EM). The major variation that was found for all of the 48 intramolecular interactions that were examined using double mutant cycles is that the values of EM for intramolecular carboxylate ester-phenol H-bonds (200 mM) are an order of magnitude larger than those found for phosphonate diester-phenol H-bonds (30 mM). The corresponding intermolecular phosphonate diester-phenol H-bonds are 2 orders of magnitude more stable than carboxylate ester-phenol H-bonds, and the large differences in EM may be due to some kind of compensation effect, where the stronger H-bond is harder to make, because it imposes tighter constraints on the geometry of the complex.
- Hunter, Christopher A.,Misuraca, Maria Cristina,Turega, Simon M.
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supporting information; experimental part
p. 582 - 594
(2011/04/16)
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- METHOD OF RAPID METHYLATION, KIT FOR PREPARING PET TRACER AND METHOD OF PRODUCING PET TRACER
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It is intended to provide a method of rapid methylation of an aromatic compound or an alkenyl compound, which is capable of obtaining an aromatic compound or an alkenyl compound labeled with a methyl group or a fluoromethyl group under a mild condition rapidly in high yield using an organic boron compound whose toxicity is not so high as a substrate; a kit for preparing a PET tracer to be used in the same, and a method of producing a PET tracer using the same. In an aprotic polar solvent, methyl iodide or X-CH2F (wherein X is a functional group which can be easily released as an anion), an organic boron compound in which an aromatic ring or an alkenyl group is attached to boron are subjected to cross-coupling in the presence of a palladium(0) complex, a phosphine ligand, and a base.
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Page/Page column 9
(2009/07/10)
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- Chemoselective hydrogenation of nitroarenes and deoxygenation of pyridine N-oxides with H2 catalyzed by MoO2Cl2
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A chemoselective and highly efficient hydrogenation of nitroarenes and deoxygenation of pyridine N-oxides using a cheap and environmentally friendly H2/MoO2Cl2 system has been developed.
- Reis, Patrícia M.,Royo, Beatriz
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scheme or table
p. 949 - 952
(2009/05/27)
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- Palladium(0)-mediated rapid methylation and fluoromethylation on carbon frameworks by reacting methyl and fluoromethyl iodide with aryl and alkenyl boronic acid esters: Useful for the synthesis of [11C]CH 3-C-and [18F]FCH2-C-containing PET tracers (PET = positron emission tomography)
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The rapid methylation and fluoromethylation on aryl and alkenyl carbon frameworks by reacting methyl and fluoromethyl iodide with aryl and alkenyl boronates have been studied with the focus on the realization of the synthesis of [11C]CH3- and [18F]FCH2-labeled positron emission tomography (PET) tracers. The coupling of methyl iodide and pinacol phenylboronate (40 equiv) is accomplished in > 91% yield within 5 min at 60 °C under the conditions of [Pd2(dba)3]/P(o- CH3C6H4)3/K2CO 3 (0.5:2:2; dba = di-benzylideneacetone) in DMF. The reaction shows a high generality and is applicable to various types of aryl and alkenyl boronates, giving the corresponding methylated derivatives in high yields (80-99). This reaction is also useful for the rapid incorporation of the fluoromethyl group. Thus, this boron protocol provides a firm chemical basis for the synthesis of 11C- and 18F-incorporated PET tracers and can be used as a complementary method for [11C]methylation together with our previous and ongoing processes using organotributylstannanes.
- Doi, Hisashi,Ban, Ikuya,Nonoyama, Akihito,Sumi, Kengo,Kuang, Chunxiang,Hosoya, Takamitsu,Tsukada, Hideo,Suzuki, Masaaki
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experimental part
p. 4165 - 4171
(2009/12/01)
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- Displacement of neutral nitrogen donors by chloride in AuCl3(am) (am = pyridines and amines): Kinetics and DFT calculations show the effects of basicity and π-acceptor ability
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The kinetics of the process AuCl3(am) + Cl- → AuCl4- + am (am = sp2 N-donor isosteric pyridines with different π systems and sp3 amines; they cover a wide range of basicity) have been studied in methanol at 25°C. The reactions obey the usual two-term rate law observed in substitutions on square-planar complexes. The second-order rate constants, k2, are very sensitive to the nature of the leaving group, and plots of log k2 against the pKa of the conjugate acids are linear, with the same slope, -0.68, for both normal pyridines and pyridines with a more extended π system, such as 4-cyanopyridine, isonicotinic acid, methyl isonicotinate and 4-acetylpyridine. The reactivity of the considered N-donors is different and follows the order sp3 N-donors > normal pyridines > π-extended pyridines. This result, with the support of ground-state DFT calculations on the AuCl3(am) derivatives, is explained on the basis of an Au-N bond enforcement due to an increased π-back-donation contribution. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Pitteri, Bruno,Bortoluzzi, Marco
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p. 4456 - 4461
(2008/03/12)
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- Deoxygenation of pyridine N-oxides with dimethylthiocarbamoyl chloride
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(Chemical Equation Presented) Treatment of pyridine N-oxides with dimethylthiocarbamoyl chloride in boiling acetonitrile effects chemoselective deoxygenation to pyridines.
- Ponaras, Anthony A.,Zaim, Oemer
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p. 487 - 489
(2008/03/29)
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