- Vapor-phase photochemistry of dimethylpyridines
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Irradiation of dimethylpyridine vapors (2-5 Torr) at 254 nm results in the formation of two sets of isomerization products. One set, formed in the larger yield, is substantially quenched when the irradiations are carried out in the presence of 15-21 Torr of nitrogen and is not formed when the irradiations are carried out with light of λ > 290 nm. In addition, a second set of reactions, which involve the interconversion of 2,3- and 2,5- dimethylpyridines, is enhanced by the addition of nitrogen, and these reactions are the only photoisomerization reactions observed when the irradiations are carried out with light of λ > 290 nm. In addition to the photoisomerizations, four of the dimethylpyridines also undergo demethylation to yield monomethylpyridines, and 2,6-dimethylpyridine undergoes methylation to yield a trimethylpyridine product. A variety of crossover experiments confirmed that the photoisomerizations are intramolecular. Based on the major phototransposition products, the six dimethylpyridines can be divided into two triads. Interconversion of the three members of each triad results in the major phototransposition products. These intra-triad interconversions are suggested to occur via 2,6-bonding, originating in a vibrationally excited S2 (π,π*) state of the dimethylpyridine, followed by nitrogen migration and rearomatization. This allows nitrogen to insert within each carbon- carbon bond. Phototransposition of 2,6-dideuterio-3,5-dimethylpyridine to a mixture of 5,6-dideuterio-2,4-dimethylpyridine and 3,4-dideuterio-2,5- dimethylpyridine is consistent with this mechanism. In addition to these intra-triad reactions, 2,5-dimethylpyridine, a member of triad 1, was observed to interconvert with 2,3-dimethylpyridine, a member of triad 2. These inter-triad reactions are suggested to occur via interconverting Dewar pyridine intermediates, formed from the triplet state of the dimethylpyridines. These Dewar pyridine intermediates were also observed by 1H NMR spectroscopy after irradiation of the dimethylpyridines in CD3CN at -30 °C.
- Pavlik, James W.,Kebede, Naod,Thompson, Michael,Day, A. Colin,Barltrop, John A.
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- Synthesis, structural characterization, and coordination chemistry of (Trineopentylphosphine)palladium(aryl)bromide dimer complexes ([(Np3P)Pd(Ar)Br]2)
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A series of [(PNp3)Pd(Ar)Br]2 complexes (PNp3 = trineopentylphosphine, Ar = 4-tolyl, 4-tert-butylphenyl, 2-tolyl, 4-methoxy-2-methylphenyl, 2-isopropylphenyl, and 2,6-dimethylphenyl) were synthesized and structurally characterized by X-ray crystallography and density functional theory optimized structures. The trineopentylphosphine ligand is able to accommodate coordination of other sterically demanding ligands through changes in its conformation. These conformational changes can be seen in changes in percent buried volume of the PNp3 ligand. The binding equilibria of the [(PNp3)Pd(Ar)Br]2 complexes with pyridine derivatives were determined experimentally and analyzed computationally. The binding equilibria are sensitive to the steric demand of the pyridine ligand and less sensitive to the steric demand of the aryl ligand on palladium. In contrast to previous studies, the binding equilibria do not correlate with pyridine basicity. The binding equilibria results are relevant to fundamental ligand coordination steps in cross-coupling reactions, such as Buchwald-Hartwig aminations.
- Hu, Huaiyuan,Vasiliu, Monica,Stein, Trent H.,Qu, Fengrui,Gerlach, Deidra L.,Dixon, David A.,Shaughnessy, Kevin H.
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- Allosteric Effects in Ethylene Polymerization Catalysis. Enhancement of Performance of Phosphine-Phosphinate and Phosphine-Phosphonate Palladium Alkyl Catalysts by Remote Binding of B(C6F5)3
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Remote binding of B(C6F5)3 to (PPO)PdMeL (L = pyridine or lutidine) or {(PPO)PdMe}2 ethylene polymerization catalysts that contain phosphine-arenephosphinate or phosphine-arenephosphonate ligands (PPO- = [1-PAr2-2-PR′O2-Ph]-: Ar = R′ = Ph (1a); Ar = Ph, R′ = OEt (1b); Ar = Ph, R′ = OiPr (1c); Ar = 2-OMe-Ph, R′ = OiPr (1d)) significantly increases the catalyst activity and the molecular weight of the polyethylene (PE) product. In the most favorable case, in situ conversion of (1d)PdMe(py) to the base-free adduct {1d·B(C6F5)3}PdMe increases the ethylene polymerization activity from 9.8 to 5700 kg mol-1 h-1 and the Mn of the PE product from 9030 to 99 200 Da (80 °C, 410 psi). X-ray structural data, trends in ligand lability, and comparative studies of BF3 activation suggest that these allosteric effects are primarily electronic in origin. The B(C6F5)3 binding enhances the chain growth rate (Rgrowth) by increasing the degree of positive charge on the Pd center. This effect does not result in the large increase in the chain transfer rate (Rtransfer) and concomitant reduction in PE molecular weight seen in previous studies of analogous (PO)PdRL catalysts that contain phosphine-arenesulfonate ligands, because of the operation of a dissociative chain transfer process, which is inhibited by the increased charge at Pd.
- Wilders, Alison M.,Contrella, Nathan D.,Sampson, Jessica R.,Zheng, Mingfang,Jordan, Richard F.
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- Synthesis of 2-(lutidinyl)organoboranes and their reactivities against dihydrogen and pinacol borane
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Two 2,4,6-tris(trifluoromethyl)phenyl-substituted 2-(lutidinyl)organoboranes (5a and 5b) were prepared. These complexes can function as intramolecular vicinal B/N frustrated Lewis pairs to heterolytically activate dihydrogen. When these complexes were treated with HBpin, two different reaction pathways took place. Whereas the reaction between 5a and HBpin affords a formal ligand-redistribution product, the reaction of 5b with HBpin leads to a dearomative dehydroborylation product.
- Zheng, Junhao,Lin, Yue-Jian,Wang, Huadong
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- Suggestion of unexpected sulfur dioxide mechanism for deoxygenations of pyridine N-oxides with alkanesulfonyl chlorides and triethylamine
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The reaction mechanism for unusual deoxygenations of pyridine N-oxides with alkanesulfonyl chlorides and triethylamine was explored. Some experimental facts suggested that sulfur dioxide generated in the reaction system might be responsible for the deoxygenations without chlorinations of the pyridine nucleus.
- Morimoto, Yoshiki,Kurihara, Hajime,Shoji, Takamasa,Kinoshita, Takamasa
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- One-step 2,6-Lutidine Synthesis from Acetone, Ammonia and Methanol. Temperature-programmed Desorption-Reaction (TPDR)-Mass Spectrometry (MS) Study
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The temperature-programmed desorption-reaction (TPDR)-mass spectrometry (MS) technique has been employed to study the behaviour and the reactivity of the title reactant mixture over a catalyst of amorphous silica-alumina impregnated with Sb2O3 and CuO.This catalyst exhibited acidic and redox properties, leading to oxidation, dehydration and alkylation reactions.The formation of 2,6-lutidine takes place only at high temperature, requiring a high activation energy.The reaction mechanism involves alkylation of acetone by methanol to form methyl ethyl ketone, followed by reaction of the latter with ammonia to form an imine, then reaction of the imine with a second molecule of acetone, and finally, cyclisation to 2,6-lutidine.
- Vatti, Francesco P.,Forni, Lucio
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- A MILD DEOXYGENATION OF HETEROAROMATIC N-OXIDES WITH DIPHOSPHORUS TETRAIODIDE
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When treated with diphosphorus tetraiodide in dichloromethane under gentle reflux, the title N-oxides are easily deoxygenated to the parent bases in good yields.
- Suzuki, Hitomi,Sato, Naofumi,Osuka, Atsuhiro
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- NCP-Type Pincer Iridium Complexes Catalyzed Transfer-Dehydrogenation of Alkanes and Heterocycles?
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A series of NCP-type pincer iridium complexes, (RNCCP)IrHCl (2a—2c) and (BQ-NCOP)IrHCl 3, have been studied for catalytic transfer alkane dehydrogenation. Complex 3 containing a rigid benzoquinoline backbone exhibits high activity and robustness in dehydrogenation of alkanes to form alkenes. Even more importantly, this catalyst system was also highly effective in the dehydrogenation of a wide range of heterocycles to furnish heteroarenes.
- Wang, Yulei,Qian, Lu,Huang, Zhidao,Liu, Guixia,Huang, Zheng
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- Mechanism of proton transfer to coordinated thiolates: Encapsulation of acid stabilizes precursor intermediate
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Earlier kinetic studies on the protonation of the coordinated thiolate in the square-planar [Ni(SC6H4R′-4)(triphos)]+ (R′ = NO2, Cl, H, Me or MeO) by lutH+ (lut = 2,6-dimethylpyridine) indicate a two-step mechanism involving initial formation of a (kinetically detectable) precursor intermediate, {[Ni(SC6H4R′-4)(triphos)]...Hlut}2+ (KR1), followed by an intramolecular proton transfer step (kR2). The analogous [Ni(SR)(triphos)]BPh4 {R = Et, But or Cy; triphos = PhP(CH2CH2PPh2)2} have been prepared and characterized by spectroscopy and X-ray crystallography. Similar to the aryl thiolate complexes, [Ni(SR)(triphos)]+ are protonated by lutH+ in an equilibrium reaction but the observed rate law is simpler. Analysis of the kinetic data for both [Ni(SR)(triphos)]+ and [Ni(SC6H4R′-4)(triphos)]+ shows that both react by the same mechanism, but that KR1 is largest when the thiolate is poorly basic, or the 4-R′ substituent in the aryl thiolates is electron-withdrawing. These results indicate that it is both NH...S hydrogen bonding and encapsulation of the bound lutH+ (by the phenyl groups on triphos) which stabilize the precursor intermediate.
- Alwaaly, Ahmed,Clegg, William,Harrington, Ross W.,Petrou, Athinoula L.,Henderson, Richard A.
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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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- Lewis Acidic Boranes, Lewis Bases, and Equilibrium Constants: A Reliable Scaffold for a Quantitative Lewis Acidity/Basicity Scale
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A quantitative Lewis acidity/basicity scale toward boron-centered Lewis acids has been developed based on a set of 90 experimental equilibrium constants for the reactions of triarylboranes with various O-, N-, S-, and P-centered Lewis bases in dichloromethane at 20 °C. Analysis with the linear free energy relationship log KB=LAB+LBB allows equilibrium constants, KB, to be calculated for any type of borane/Lewis base combination through the sum of two descriptors, one for Lewis acidity (LAB) and one for Lewis basicity (LBB). The resulting Lewis acidity/basicity scale is independent of fixed reference acids/bases and valid for various types of trivalent boron-centered Lewis acids. It is demonstrated that the newly developed Lewis acidity/basicity scale is easily extendable through linear relationships with quantum-chemically calculated or common physical–organic descriptors and known thermodynamic data (ΔH (Formula presented.)). Furthermore, this experimental platform can be utilized for the rational development of borane-catalyzed reactions.
- Mayer, Robert J.,Hampel, Nathalie,Ofial, Armin R.
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supporting information
p. 4070 - 4080
(2021/01/29)
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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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- 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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- 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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- Controlling Ligand Exchange through Macrocyclization
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Ligand exchange at a sterically hindered palladium center was investigated for six different ligands. The palladium atom was coordinated to a tridentate, NNN pincer bis(amido)pyridine macrocycle to produce a square-planar complex, in which an acetonitrile molecule occupies one of the coordination sites. Kinetic studies showed that ligand exchange at the palladium center proceeds through an associative mechanism and, as a consequence, is impeded by the small size of the metallomacrocycle cavity. The ligand-exchange rate on the palladium center between acetonitrile and six different ligands has been investigated and compared to the exchange rate on the corresponding open form. Our results demonstrate that macrocyclization of ligands is a way to modify the rate of guest exchange in a square-planar metal complex.
- Carta, Veronica,Mehr, S. Hessam M.,Maclachlan, Mark J.
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p. 3243 - 3253
(2018/03/25)
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- Nickel(I) Aryl Species: Synthesis, Properties, and Catalytic Activity
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In this work, Ni(I) aryl species that are directly relevant to cross-coupling have been synthesized. Transmetalation of (dppf)NiIX (dppf = 1,1′-bis(diphenylphosphino)-ferrocene, X = Cl, Br) with aryl Grignard reagents or aryl boronic acids in t
- Mohadjer Beromi, Megan,Banerjee, Gourab,Brudvig, Gary W.,Hazari, Nilay,Mercado, Brandon Q.
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p. 2526 - 2533
(2018/03/13)
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- Application of Silicon-Initiated Water Splitting for the Reduction of Organic Substrates
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The use of water as a donor for hydrogen suitable for the reduction of several important classes of organic compounds is described. It is found that the reductive water splitting can be promoted by several metalloids among which silicon shows the best efficiency. The developed methodologies were applied for the reduction of nitro compounds, N-oxides, sulfoxides, alkenes, alkynes, hydrodehalogenation as well as for the gram-scale synthesis of several substrates of industrial importance.
- Gevorgyan, Ashot,Mkrtchyan, Satenik,Grigoryan, Tatevik,Iaroshenko, Viktor O.
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p. 375 - 382
(2018/06/04)
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- Osmium Hydride Acetylacetonate Complexes and Their Application in Acceptorless Dehydrogenative Coupling of Alcohols and Amines and for the Dehydrogenation of Cyclic Amines
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The preparation of new osmium hydride complexes, starting from OsH6(PiPr3)2 (1) and OsH2Cl2(PiPr3)2 (2), and their catalytic activity in acceptorless dehydrogenative coupling of alcohols and amines and in dehydrogenation of cyclic amines are reported. Complex 1 reacts with acetylacetone (Hacac) to give the classical trihydride OsH3(acac)(PiPr3)2 (3). The protonation of 3 with triflic acid (HOTf) produces the release of H2 and the formation of the unsaturated osmium(IV) dihydride [OsH2(acac)(PiPr3)2]OTf (4), which is also prepared by starting from 2 via the intermediate OsH2Cl(acac)(PiPr3)2 (5). Treatment of an acetylacetone solution of 5 with KOH affords Os(acac)2(PiPr3)2 (6). In the presence of 5 mol % of KOH, complexes 3-6 promote the coupling of benzyl alcohol and aniline to give N-benzylideneaniline and H2. Under the same conditions, complex 3 catalyzes a wide range of analogous couplings to afford a variety of imines, including aliphatic imines, with yields between 90 and 40% after 1-48 h. Complex 3 also catalyzes the dehydrogenation of cyclic amines. According to the amount of H2 released by each 1 g of employed substrate, the amines have been classified into three classes: poor (1,2,3,4-tetrahydroquinaldine, 2-methylindoline, and 2,6-dimethylpiperidine), moderate (1,2,3,4-tetrahydroquinoline and 6-methyl-1,2,3,4-tetrahydroquinoline), and good hydrogen donors (1,2,3,4-tetrahydroisoquinoline).
- Esteruelas, Miguel A.,Lezáun, Virginia,Martínez, Antonio,Oliván, Montserrat,Onate, Enrique
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p. 2996 - 3004
(2017/08/21)
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- Reversible Interconversion between 2,5-Dimethylpyrazine and 2,5-Dimethylpiperazine by Iridium-Catalyzed Hydrogenation/Dehydrogenation for Efficient Hydrogen Storage
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A new hydrogen storage system based on the hydrogenation and dehydrogenation of nitrogen heterocyclic compounds, employing a single iridium catalyst, has been developed. Efficient hydrogen storage using relatively small amounts of solvent compared with previous systems was achieved by this new system. Reversible transformations between 2,5-dimethylpyrazine and 2,5-dimethylpiperazine, accompanied by the uptake and release of three equivalents of hydrogen, could be repeated almost quantitatively at least four times without any loss of efficiency. Furthermore, hydrogen storage under solvent-free conditions was also accomplished.
- Fujita, Ken-Ichi,Wada, Tomokatsu,Shiraishi, Takumi
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supporting information
p. 10886 - 10889
(2017/08/30)
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- Deoxygenation of tertiary amine N-oxides under metal free condition using phenylboronic acid
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A simple and efficient method for the deoxygenation of amine N-oxides to corresponding amines is reported using the green and economical reagent phenylboronic acid. Deoxygenation of N,N-dialkylaniline N-oxides, trialkylamine N-oxides and pyridine N-oxides were achieved in good to excellent yields. The reduction susceptible functional groups such as ketone, amide, ester and nitro groups are well tolerated with phenylboronic acid during the deoxygenation process even at high temperature. In addition, an indirect method for identification and quantification of tert-amine N-oxide is demonstrated using UV–Vis spectrometry which may be useful for drug metabolism studies.
- Gupta, Surabhi,Sureshbabu, Popuri,Singh, Adesh Kumar,Sabiah, Shahulhameed,Kandasamy, Jeyakumar
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supporting information
p. 909 - 913
(2017/02/15)
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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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- Palladium-catalyzed Heck-type reaction of oximes with allylic alcohols: Synthesis of pyridines and azafluorenones
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We describe herein a palladium-catalyzed Heck-type reaction of O-acetyl ketoximes and allylic alcohols to synthesise pyridines. This protocol allows the robust synthesis of pyridines and azafluorenones in good to excellent yields with tolerance of various functional groups under mild conditions. The reaction is supposed to go through an oxidative addition of oximes to palladium(0) complexes, generating an alkylideneamino-palladium(ii) species, which is utilized as a key intermediate to capture the nonbiased alkenes for carbon-carbon bond formation.
- Zheng, Meifang,Chen, Pengquan,Wu, Wanqing,Jiang, Huanfeng
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supporting information
p. 84 - 87
(2015/12/26)
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- A molecular iron catalyst for the acceptorless dehydrogenation and hydrogenation of N-heterocycles
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A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A trans-dihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments.
- Chakraborty, Sumit,Brennessel, William W.,Jones, William D.
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supporting information
p. 8564 - 8567
(2014/07/07)
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- Selective catalytic transfer dehydrogenation of alkanes and heterocycles by an iridium pincer complex
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Catalytic alkane dehydrogenation is a reaction with tremendous potential for application. We describe a highly active PSCOP-pincer iridium catalyst for transfer dehydrogenation of cyclic and linear alkanes. The dehydrogenation of linear alkanes occurs under relatively mild conditions with high regioselectivity for a-olefin formation. In addition, the catalyst system is very effective in the dehydrogenation of heterocycles to form heteroarenes and olefinic products.
- Yao, Wubing,Zhang, Yuxuan,Jia, Xiangqing,Huang, Zheng
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supporting information
p. 1390 - 1394
(2014/03/21)
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- Iridium-catalyzed direct dehydroxylation of alcohols
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Iridium-catalyzed direct dehydroxylation of alcohols with hydrazine was developed through a combination of the oxidation of alcohols and the Wolff-Kishner reduction. This protocol is simple to perform and highly efficient for a series of primary, benzylic and allylic alcohols. Iridium-catalyzed direct dehydroxylation of alcohols with hydrazine is developed through a combination of the oxidation of alcohols and Wolff-Kishner reduction. This protocol is simple to perform and highly efficient for a series of primary alcohols, especially benzylic and allylic ones. Copyright
- Huang, Jian-Lin,Dai, Xi-Jie,Li, Chao-Jun
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supporting information
p. 6496 - 6500
(2013/11/06)
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- Direct vicinal disubstitution of diaryliodonium salts by pyridine N-oxides and N-amidates by a 1,3-radical rearrangement
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Paired off: The title reaction leads to a series of o-pyridinium phenols (1) and anilines (2). The experimental and computational studies indicate that the key step involves homolytic cleavage to give a radical pair, which undergoes solvent-cage recombination to give the product. Copyright
- Peng, Jing,Chen, Chao,Wang, Yong,Lou, Zhenbang,Li, Ming,Xi, Chanjuan,Chen, Hui
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supporting information
p. 7574 - 7578
(2013/07/26)
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- Dimerization of ethylene by nickel phosphino-borate complexes
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Trifluoroborate-functionalized phosphine ligands react with a variety of nickel(II) precursors to cleanly yield a number of κ2(P,F)- bound nickel complexes, which were characterized crystallographically. In comparison to related palladium complexes, ancillary ligands in the nickel complexes were observed to be generally more weakly bound, and the trifluoroborate ligands were more easily displaced by coordinating solvents that did not cause a similar displacement in a related palladium system. Such weaker ligand coordination resulted in a much faster dimerization of ethylene. Experiments conducted under constant ethylene pressure saw the suppression of the isomerization of 1-butene observed in related palladium complexes; higher oligomers were also generated under such conditions.
- Gutsulyak, Dmitry V.,Gott, Andrew L.,Piers, Warren E.,Parvez, Masood
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p. 3363 - 3370
(2013/07/19)
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- Generation and reactions of pyridyllithiums via Br/li exchange reactions using continuous flow microreactor systems
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A continuous flow microreactor method for generating and carrying out reactions on pyridyllithiums has been developed based on Br/Li exchange reactions of bromopyridines and dibromopyridines. The reactions can be carried out without using cryogenic conditions by virtue of short residence times and efficient heat transfer, while very low temperatures such as-78 or-110°C are required for conventional batch macro methods. Moreover, sequential introduction of two different electrophiles has been successfully achieved using dibromopyridines in an integrated flow microreactor system composed of four micromixers and four microtube reactors.
- Nagaki, Aiichiro,Yamada, Daisuke,Yamada, Shigeyuki,Doi, Masatomo,Ichinari, Daisuke,Tomida, Yutaka,Takabayashi, Naofumi,Yoshida, Jun-Ichi
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p. 199 - 207
(2013/03/28)
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- Rapid and selective in situ reduction of pyridine- N -oxides with tetrahydroxydiboron
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Pyridine-N-oxides are often used as reactive precursors in the syntheses of substituted pyridines. Isolation and subsequent reduction of the associated pyridine-N-oxide intermediates can be challenging. We have discovered that tetrahydroxydiboron functions as a mild, versatile, and remarkably selective reducing agent for pyridine-N-oxides and may be used in an in situ fashion, thus obviating the isolation of N-oxide-containing intermediates. Georg Thieme Verlag Stuttgart New York.
- Londregan, Allyn T.,Piotrowski, David W.,Xiao, Jun
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supporting information
p. 2695 - 2700
(2014/01/06)
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- Compositions and Methods Related to Acid Stable Lipid Nanospheres
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The present invention relates generally to the fields of chemistry and biochemistry. More particularly, it concerns methods and compositions for the use of fatty asparagine, fatty cysteine, and fatty serine derivatives.
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- Reduction of amine N-oxides by diboron reagents
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Facile reduction of alkylamino-, anilino-, and pyridyl-N-oxides can be achieved via the use of diboron reagents, predominantly bis- (pinacolato)- and in some cases bis(catecholato)diboron [(pinB)2 and (catB)2, respectively]. Reductions occur upon simply mixing the amine N oxide and the diboron reagent in a suitable solvent, at a suitable temperature. Extremely fast reductions of alkylamino- and anilino-N-oxides occur, whereas pyridyl-N-oxides undergo slower reduction. The reaction is tolerant of a variety of functionalities such as hydroxyl, thiol, and cyano groups, as well as halogens. Notably, a sensitive nucleoside N-oxide has also been reduced efficiently. The different rates with which alkylamino- and pyridyl-N-oxides are reduced has been used to perform stepwise reduction of the N,N-dioxide of (S)-(-)-nicotine. Because it was observed that (pinB)2 was unaffected by the water of hydration in amine oxides, the feasibility of using water as solvent was evaluated. These reactions also proceeded exceptionally well, giving high product yields. In constrast to the reactions with (pinB)2, triethylborane reduced alkylamino-N oxides, but pyridine N-oxide did not undergo efficient reduction even at elevated temperature. Finally, the mechanism of the reductive process by (pinB)2 has been probed by 1H and 11B NMR. (Figure presented) ; 2011 American Chemical Society.
- Kokatla, Hari Prasad,Thomson, Paul F.,Bae, Suyeal,Doddi, Venkata Ramana,Lakshman, Mahesh K.
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experimental part
p. 7842 - 7848
(2011/12/01)
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- GOLD CATALYZED HYDROAMINATION OF ALKYNES AND ALLENES
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Methods are provided for the catalytic hydroamination of compounds having an alkyne or allene functional group, in which the compound is contacted with ammonia or an amine in the presence of a catalytic amount of a gold complex under conditions sufficient for hydroamination to occur.
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Page/Page column 21; 2/13
(2010/01/29)
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- C-Terminally Pegylated Growth Hormones
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Conjugated growth hormones of the structure (I) are provided together with methods for manufacturing said conjugates. The conjugates are useful in therapy.
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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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- Photophysics of a series of efficient fluorescent pH probes for dual-emission-wavelength measurements in aqueous solutions
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This paper evaluates the 5-aryl-2-pyridyloxazole backbone to engineer donor-acceptor fluorescent pH probes after one- or two-photon absorption. Parent fluorophores, as well as derivatives that can be used to label biomolecules, can be easily obtained in good yields. These molecules exhibit a large one-photon absorption in the near-UV range, and a strong fluorescence emission that covers the whole visible domain. The 5-aryl-2-pyridyloxazole derivatives also possess significant cross sections for two-photon absorption. Upon pyridine protonation, large shifts were observed in the absorption spectra after one- and two-photon excitation, as well as in the emission spectra. This feature was used to measure the pKa of the investigated compounds that range between 2 and 8. In most of the investigated derivatives, the pKa increased upon light excitation and protonation exchanges took place during the lifetime of the excited state, as shown by phase-modulation fluorometry analysis. Several 5-aryl-2-pyridyloxazole derivatives are suggested as efficient probes to reliably measure the pH of aqueous solutions by means of ratiometric methods that are dependent on fluorescence emission.
- Charier, Sandrine,Ruel, Odile,Baudin, Jean-Bernard,Alcor, Damien,Allemand, Jean-Francois,Meglio, Adrien,Jullien, Ludovic,Valeur, Bernard
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p. 1097 - 1113
(2007/10/03)
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- New phenylalanine derivatives
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Specified phenylalanine derivatives and analogues thereof have an antagonistic activity to α4 integrin. They are used as therapeutic agents for various diseases concerning α4 integrin.
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- New phenylalanine derivatives
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Specific phenylalanine derivatives or pharmaceutically acceptable. salts thereof have an antagonistic effect on the α4 integrins and, therefore, are usable as therapeutic agents or preventive agents for diseases in which α4 integrin-depending adhesion process participates in the pathology, such as inflammatory diseases, rheumatoid arthritis, inflammatory bowel diseases, systemic lupus erythematosus, multiple sclerosis, Sj?gren's syndrome, asthma, psoriasis, allergy, diabetes, cardiovascular diseases, arterial sclerosis, restenosis, tumor proliferation, tumor metastasis and transplantation rejection.
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- EPOTHILONE DERIVATIVES, METHOD FOR PRODUCING SAME AND THEIR PHARMACEUTICAL USE
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This invention relates to the new epothilone derivatives of general formula I, 1in which substituents Y, Z R2a, R2b, R3, R4a, R4b, D—E, R5, R6, R7, R8 and X have the meanings that are indicated in more detail in the description. The new compounds interact with tubulin by stabilizing microtubuli that are formed. They are able to influence the cell-splitting in a phase-specific manner and are suitable for treating malignant tumors, for example, ovarian, stomach, colon, adeno-, breast, lung, head and neck carcinomas, malignant melanomas, acute lymphocytic and myelocytic leukemia. In addition, they are suitable for anti-angiogenesis therapy as well as for treatment of chronic inflammatory diseases (psoriasis, arthritis). To avoid uncontrolled proliferation of cells and for better compatibility of medical implants, they can be applied or introduced into polymer materials. The compounds according to the invention can be used alone or to achieve additive or synergistic actions in combination with other principles and classes of substances that can be used in tumor therapy.
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- Nanoscale faceted polyhedra
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The subject invention pertains to nanoscale polyhedron-shaped molecules having molecular building blocks connected at their vertices. The subject invention also concerns methods of producing nanoscale polyhedrons utilizing a self-assembly reaction. The resultant molecules are faceted polyhedra that are porous, chemically robust, contain chemically accessible sites on their facets, and which are neutral and soluble in common laboratory solvents. The nanoscale polyhedrons can exhibit additional desirable physical properties, such as ferromagnetic properties.
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- A method for producing pyridine bases
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A method for producing pyridine bases which comprises reacting in a gas-phase an aliphatic aldehyde, aliphatic ketone or mixture thereof with ammonia in the presence of a zeolite comprising titanium and/or cobalt and silicon as zeolite constituent elements in which the atomic ratio of silicon to titanium and/or cobalt is about 5 to 1000 gives improved yield.
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- Efficient catalytic conversion of pyridine N-oxides to pyridine with an oxorhenium(V) catalyst
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(Equation Presented) The compound CH3Re(O)(SR)2PPh3, where (SR)2 represents the dianion of 2-(mercaptomethyl)thiophenol, catalyzes the rapid and efficient transfer of an oxygen atom from a wide range of ring-substituted pyridine N-oxides to triphenylphosphine, yielding the pyridines in high yield.
- Wang, Ying,Espenson, James H.
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p. 3525 - 3526
(2007/10/03)
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- A mild deoxygenation of heteroaromatic N-oxides by formamidinesulfinic acid
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Various heteroaromatic N-oxides were efficiently deoxygenated to the corresponding bases under mild conditions using formamidinesulfinic acid (thiourea S,S-dioxide).
- Balicki, Roman,Chmielowiec, Urszula
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p. 1105 - 1107
(2007/10/03)
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- Method for the demethoxycarbonylation of porphyrinic compounds such as pheophorbides
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An improved method for the demethoxycarbonylation of porphyrinic compounds such as pheophorbides involving reacting the starting porphyrinic compound with a high boiling point solvent to which a selected amount of water has been added.
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- Application of non-steady-state kinetics to resolve the kinetics of proton-transfer reactions between methylarene radical cations and pyridine bases
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Apparent deuterium kinetic isotope effects (KIE(app)) of four different methylarene radical cation-pyridine base reactions in dichloromethane (0.2 M tetrabutylammonium hexafluorophosphate) were observed to increase toward a constant value with increasing extent of reaction. The reactions were studied by derivative cyclic voltammetry (DCV), and rate constants were assigned by comparing the experimental with the theoretical DCV data. The kinetic results rule out a simple second-order proton-transfer reaction and implicate a mechanism in which a complex is first formed that then undergoes proton transfer, followed by separation of the products. That KIE(app) are extent of reaction-dependent is observed before steady-state is reached. The concurrent analysis of kinetic data for the reactions of both ArCH3(·+) and ArCD3(·+) with bases under non-steady-state conditions facilitates the resolution of the apparent rate constant [k(app) = k(f)k(p)/(k(b) + k(p))] into the microscopic rate constants (k(f), k(b), and k(p)) for the individual steps. The KIE(app) observed during proton-transfer reactions need not be the real kinetic isotope effects (KIE(real)). Having access to the microscopic rate constants for the steps in which the proton is transferred allows KIE(real) to be evaluated and compared with the corresponding KIE(app). The present study shows that the KIE(real) are much greater than the KIE(app) derived in the usual way from the rate of the overall reaction.
- Parker, Vernon D.,Zhao, Yixing,Lu, Yun,Zheng, Gang
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p. 12720 - 12727
(2007/10/03)
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- Selective deoxygenation of heteroaromatic N-oxides with olefins catalyzed by ruthenium porphyrin
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A new convenient method of deoxygenation of heteroaromatic N-oxides is described. Ruthenium porphyrin was used as a catalyst and this method expressed high yields for o-substituted pyridine N-oxides, quinoline N-oxide derivatives, acridine N-oxide, etc. under mild conditions. Moreover, nitro-, benzyloxy-, and ketone carbonyl groups, which can be affected by the usual deoxygenation methods such as catalytic hydrogenation or borane reduction, were retained.
- Nakagawa, Hiroshi,Higuchi, Tsunehiko,Kikuchi, Kazuya,Urano, Yasuteru,Nagano, Tetsuo
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p. 1656 - 1657
(2007/10/03)
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- Zeolite-Catalyzed Isomerization of Aromatic Amines to Methyl-Aza-Aromatics
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The scope and mechanism of the isomerization of arylamines to methyl-substituted aromatic heterocycles have been studied.Aniline, toluidines, naphthylamines and m-phenylenediamine all reacted to the corresponding ortho-methyl-substituted aza-aromatiics when exposed to high NH3 pressure and elevated temperature in the presence of acid catalysts.Zeolites with a three-dimensional pore structure, especially H-ZSM-5, showed the best performance.Optimum reaction conditions are around 600 K and 10 MPa.Two mechanisms which had been proposed earlier for this apparent N-ortho C exchange reaction proved untenable.Neither incorporation of the N atom into the aromatic ring nor a mechanism based on an intramolecular Ritter reaction could explain the required high NH3 pressure or the product distribution.Two new mechanisms are proposed which can explain all observations.In both mechanisms, reaction starts with addition of NH3 to the arylamine, followed by ring opening.In one mechanism an alkyno-imine intermediate is formed; in the other mechanism an enamino-imine intermediate is formed through a reverse aldol reaction.In both cases ring closure and NH3 elimination lead to the required aromatic heterocycles.The high NH3 pressure is explained by the need to add NH3 to the aromatic ring, and the high temperature by the need to desorb NH3 from the acid sites.
- Stamm, T.,Kouwenhoven, H. W.,Seebach, D.,Prins, R.
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p. 268 - 282
(2007/10/02)
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- 6-amido-1-methyl carbapenems
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New antibacterial 6-amido-1-methylcarbapenems and process for their synthesis involving new azetidinone intermediates.
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- Entropy barriers to proton transfer
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Proton transfer between sterically hindered pyridines and amines proceeds through locked-rotor, low-entropy intermediates. The reactions exhibit slow kinetics (efficiencies of 0.1-0.0001) and large negative temperature coefficients (up to k = CT-8.7). The rates become slower and the temperature dependencies steeper with increasing steric hindrance. The observations are reproduced by a multiple complex-switching RRKM model that allows several alternative complexes to be rate controlling: a series of loose complexes, a locked-rotor tight complex that occurs before the formation of a hydrogen-bonded complex, and a complex located at the central barrier. The rate-limiting transition state shifts from the loose to the tight and central-barrier complexes with increasing temperature. The model suggests that at elevated temperatures, above 1000 K, ion-molecule reactions will become slow even for unhindered, small reactants. Ion kinetics may then become similar to neutral radical kinetics.
- Meot-Ner, Michael,Smith, Sean C.
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p. 862 - 869
(2007/10/02)
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