- Effect of support texture on enantioselective hydrogenation of (E)-α-phenylcinnamic acid with cinchonidine-modified palladium catalysts
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The texture of support materials has decisive influence on the behavior of cinchonidine-modified palladium catalysts in the enantioselective hydrogenation of (E)-α-phenylcinnamic acid, which suggests an important role of pore diffusion in the determinatio
- Nitta, Yuriko,Okamoto, Yasuaki
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- Base-controlled chemoselectivity: direct coupling of alcohols and acetonitriles to synthesise α-alkylated arylacetonitriles or acetamides
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We achieved chemoselective synthesis of α-alkylated arylacetonitriles and acetamides by combining Ir complex-catalysed direct coupling of alcohols and nitriles by a simple adjustment of the base. Methanol and ethanol performed well as the alkylating reagents. This method of acetonitrile alkylation provided a novel approach for carbon chain extension.
- Bai, Liang,Ge, Min-Tong,Li, Chen,Qiu, Yuan-Rui,Wang, Ying,Xia, Ai-Bao,Xu, Dan-Qian
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p. 15200 - 15204
(2021/09/06)
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- Metal-Free Hydrosilylation of Ketenes with Silicon Electrophiles: Access to Fully Substituted Aldehyde-Derived Silyl Enol Ethers
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Little-explored hydrosilylation of ketenes promoted by main-group catalysts is reported. The boron Lewis acid tris(pentafluorophenyl)borane accelerates the slow uncatalyzed reaction of ketenes and hydrosilanes, thereby providing a convenient access to the new class of β,β-di- and β-monoaryl-substituted aldehyde-derived silyl enol ethers. Yields are moderate to high, and Z configuration is preferred. The corresponding silyl bis-enol ethers are also available when using dihydrosilanes. The related trityl-cation-initiated hydrosilylation involving self-regeneration of silylium ions is far less effective.
- Roy, Avijit,Oestreich, Martin
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supporting information
p. 8273 - 8276
(2021/05/11)
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- Kinetic analysis of enantioselective hydrogenation of 2,3-(E)-diarylpropenoic acids over a chiral cinchona alkaloid-modified Pd/C catalyst
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Enantioselective hydrogenations of α,β-unsaturated carboxylic acids over cinchona alkaloid-modified Pd metal heterogeneous catalysts have received considerable attention because of scientific importance in molecular recognition catalysis as well as feasibility of industrial applications. In the present study, comprehensive kinetic analysis of the hydrogenation was conducted to disclose the crucial kinetic parameters controlling enantiodifferentiation and reaction rate with the combinations of four kinds of modifier and three kinds of substrate. Despite simplicity of the kinetic model, the present novel kinetic formulation allows us to describe the enantioselectivity as a function of modifier concentration, to estimate intrinsic enantioselectivity at the modified sites, to estimate respective reaction rates at the modified and unmodified sites, and to establish a correlation between the magnitude of ligand acceleration and kinetic parameters. The enantioselectivity is successfully correlated to the reaction rate. The adsorption strength of the modifier on Pd is suggested to decrease in the order, cinchonidine > cinchonine > quinine > quinidine. The roles played by benzylammine and the observed decrease in the selectivity at a high modifier concentration are also discussed. The kinetic model and formulation can be applied to analyze the catalytic behaviors and performance of Pt counterparts.
- Kim, Bokeun,Nakatsuji, Makoto,Mameda, Takuya,Kubota, Takeshi,Fujita, Morifumi,Sugimura, Takashi,Okamoto, Yasuaki
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p. 163 - 175
(2020/04/27)
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- Electrocatalytic asymmetric hydrogenation of α,β-unsaturated acids in a PEM reactor with cinchona-modified palladium catalysts
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We have developed an electrocatalytic asymmetric hydrogenation reaction using a proton-exchange membrane (PEM) reactor that employs a polymer electrolyte fuel cell and industrial electrolysis technologies. Reasonable enantioselectivities and excellent current efficiencies were obtained in the asymmetric hydrogenation of α-phenylcinnamic acid under mild conditions without adding a supporting electrolyte. The current density was crucial to achieving the improved results observed.
- Atobe, Mahito,Fukazawa, Atsushi,Hashimoto, Yasushi,Sato, Yasushi,Tanaka, Kenta
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- Kinetic analysis of the asymmetric hydrogenation of (: E)-2,3-diphenylpropenoic acid over cinchonidine derivative-modified Pd/C: Quinoline ring modification
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The effects of the quinoline ring modification of cinchonidine (CD) on the enantioselectivity of the asymmetric hydrogenation of (E)-2,3-diphenylpropenoic acid over chirally modified Pd/C were systematically analyzed from the kinetic points of view. The substitutions at the 2′- and/or 6′-positions of the quinoline ring of CD by a methyl, vinyl, n-butyl, or phenyl group decreased enantioselectivity over the whole range of the modifier concentration. Kinetic analysis allowed us to estimate the intrinsic enantioselectivity at modified sites and adsorption strength of the modifier. It is revealed that the substitutions reduce both the intrinsic enantioselectivity and adsorption strength of the parent modifier. The intrinsic enantioselectivity is correlated, most likely, to the modifier-substrate interaction strength. This journal is
- Fujita, Morifumi,Nakatsuji, Makoto,Okamoto, Yasuaki,Sugimura, Takashi
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p. 6573 - 6582
(2020/11/13)
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- Nickel-catalyzed hydrogen-borrowing strategy: Chemo-selective alkylation of nitriles with alcohols
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The first nickel-catalyzed hydrogen-borrowing alkylation of a series of aryl acetonitriles with a variety of aryl, heteroaryl, allylic and alkyl alcohols releasing water as the by-product (>33 examples, up to 90% yield) is reported.
- Banerjee, Debasis,Bera, Atanu,Bera, Sourajit
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p. 6850 - 6853
(2020/07/04)
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- Harnessing Applied Potential: Selective β-Hydrocarboxylation of Substituted Olefins
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The construction of carboxylic acid compounds in a selective fashion from low value materials such as alkenes remains a long-standing challenge to synthetic chemists. In particular, β-addition to styrenes is underdeveloped. Herein we report a new electrosynthetic approach to the selective hydrocarboxylation of alkenes that overcomes the limitations of current transition metal and photochemical approaches. The reported method allows unprecedented direct access to carboxylic acids derived from β,β-trisubstituted alkenes, in a highly regioselective manner.
- Alkayal, Anas,Buckley, Benjamin R.,Malkov, Andrei V.,Montanaro, Stephanie,Tabas, Volodymyr,Wright, Iain A.
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supporting information
(2020/02/13)
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- Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions
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A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2-based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.
- Gevorgyan, Ashot,Hopmann, Kathrin H.,Bayer, Annette
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p. 2080 - 2088
(2020/02/20)
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- Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters
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A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.
- Greenhalgh, Mark D.,Laina-Martín, Víctor,Neyyappadath, Rifahath M.,Qu, Shen,Smith, Andrew D.,Smith, Samuel M.
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supporting information
p. 16572 - 16578
(2020/09/09)
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- Cobalt-Catalyzed Asymmetric Hydrogenation of α,β-Unsaturated Carboxylic Acids by Homolytic H2 Cleavage
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The asymmetric hydrogenation of α,β-unsaturated carboxylic acids using readily prepared bis(phosphine) cobalt(0) 1,5-cyclooctadiene precatalysts is described. Di-, tri-, and tetra-substituted acrylic acid derivatives with various substitution patterns as well as dehydro-α-amino acid derivatives were hydrogenated with high yields and enantioselectivities, affording chiral carboxylic acids including Naproxen, (S)-Flurbiprofen, and a d-DOPA precursor. Turnover numbers of up to 200 were routinely obtained. Compatibility with common organic functional groups was observed with the reduced cobalt(0) precatalysts, and protic solvents such as methanol and isopropanol were identified as optimal. A series of bis(phosphine) cobalt(II) bis(pivalate) complexes, which bear structural similarity to state-of-the-art ruthenium(II) catalysts, were synthesized, characterized, and proved catalytically competent. X-band EPR experiments revealed bis(phosphine)cobalt(II) bis(carboxylate)s were generated in catalytic reactions and were identified as catalyst resting states. Isolation and characterization of a cobalt(II)-substrate complex from a stoichiometric reaction suggests that alkene insertion into the cobalt hydride occurred in the presence of free carboxylic acid, producing the same alkane enantiomer as that from the catalytic reaction. Deuterium labeling studies established homolytic H2 (or D2) activation by Co(0) and cis addition of H2 (or D2) across alkene double bonds, reminiscent of rhodium(I) catalysts but distinct from ruthenium(II) and nickel(II) carboxylates that operate by heterolytic H2 cleavage pathways.
- Chirik, Paul J.,Shevlin, Michael,Zhong, Hongyu
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supporting information
(2020/03/13)
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- Direct synthesis of in-situ chirally modified palladium nanocrystals without capping agents and their application in heterogeneous enantioselective hydrogenations
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Shape-controlled metal nanocrystals possess the advantages of specific atomic arrangement on the surface and uniform size, which can act as ideal model catalysts for heterogeneous enantioselective catalytic studies. Nevertheless, capping agents are commonly retained on the surface of the as-synthesized metal nanocrystals, which may hinder the necessary interaction between the substrate and the chiral modifiers coadsorbed on the metal surface for chiral recognition. In this paper, we directly synthesized dendritic or cubic palladium nanocrystals in-situ modified by chiral modifiers such as cinchonidine (CD) or S-proline through a one-pot strategy by replacing the conventional capping agents with the chiral modifiers. The as-prepared CD-modified Pd nanodendrite catalyst already exhibits enantioselectivity in the asymmetric hydrogenation of (E)-α-phenylcinnamic acid without subsequent chiral modification processes. The in-situ S-proline-modified Pd nanocube catalyst shows higher enantioselectivity than nanocubes synthesized with polyvinylpyrrolidone (PVP) or cetyltrimethylammonium bromide (CTAB) as traditional capping agents in asymmetric hydrogenation of acetophenone. Chiral modifiers have dual functions (both shape-control agents and catalytic functional molecules), which can not only eliminate the adverse effect of traditional capping agents (such as PVP) on heterogeneous enantioselective hydrogenations but also simplify the follow-up chiral modification step of metal catalysts, providing a simple and efficient synthetic protocol to directly prepare in-situ chirally modified metal nanocrystal catalysts.
- Gao, Xiuyun,Chen, Xueying,Li, Zhen Hua,He, Heyong
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p. 6100 - 6110
(2019/06/24)
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- Deracemizing α-Branched Carboxylic Acids by Catalytic Asymmetric Protonation of Bis-Silyl Ketene Acetals with Water or Methanol
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We report a highly enantioselective catalytic protonation of bis-silyl ketene acetals. Our method delivers α-branched carboxylic acids, including nonsteroidal anti-inflammatory arylpropionic acids such as Ibuprofen, in high enantiomeric purity and high yields. The process can be incorporated in an overall deracemization of α-branched carboxylic acids, involving a double deprotonation and silylation followed by the catalytic asymmetric protonation.
- Mandrelli, Francesca,Blond, Aurélie,James, Thomas,Kim, Hyejin,List, Benjamin
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p. 11479 - 11482
(2019/07/18)
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- Photocarboxylation of Benzylic C-H Bonds
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The carboxylation of sp3-hybridized C-H bonds with CO2 is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C-H bonds with CO2 into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated in situ. The resulting benzylic carbanion reacts with CO2 to generate the corresponding carboxylic acid after protonation. The reaction proceeded without the addition of any sacrificial electron donor, electron acceptor or stoichiometric additives. Moderate to good yields of the desired products were obtained in a broad substrate scope. Several drugs were successfully synthesized using the novel strategy.
- Meng, Qing-Yuan,Schirmer, Tobias E.,Berger, Anna Lucia,Donabauer, Karsten,K?nig, Burkhard
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supporting information
p. 11393 - 11397
(2019/08/20)
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- Palladium-catalyzed α,β-dehydrogenation of acyclic ester equivalents promoted by a novel electron deficient phosphinooxazoline ligand
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A unique example of Pd-catalyzed decarboxylative dehydrogenation of fully substituted N-acyl allyl enol carbonates is enabled by a new electron deficient phosphinooxazoline (PHOX) ligand. The reaction proceeds from the Z-enol carbonate to provide dehydrogenation products exclusively in high E/Z selectivity, while the E-enol carbonate provides the α-allylation product with only minor dehydrogenation. The reaction proceeds with a broad scope of Z-enol carbonates derived from N-acyl indoles to furnish acyclic formal α,β-unsaturated ester equivalents.
- Fulton, Tyler J.,Wu, Brenda,Alexy, Eric J.,Zhang, Haiming,Stoltz, Brian M.
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supporting information
p. 4104 - 4109
(2019/06/20)
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- New Strategy for Forging Contiguous Quaternary Carbon Centers via H 2 O 2 -Mediated Ring Contraction
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Stereospecific construction of contiguous quaternary carbon centers constitutes a major challenge in natural product synthesis. A general protocol that enables stereospecific construction of all stereoisomers of such a moiety remains elusive. In this article, we will discuss the oxidative ring contraction of all-substituted cyclic α-formyl ketones mediated by H 2 O 2, which provides a facile access to the stereospecific construction of contiguous quaternary carbon centers.
- Hu, Jiadong,Yu, Xin,Xie, Weiqing
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p. 2517 - 2524
(2017/09/28)
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- Nucleophilic Arylation of N,O-Ketene Acetals with Triaryl Aluminum Reagents: Access to α-Aryl Amides through an Umpolung Process
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A novel approach for the umpolung α-arylation of amides is presented. By the nucleophilic phenylation of O-silyl N,O-ketene acetals, generated in situ from N-alkoxy amides, a phenyl group can be introduced onto the α-carbon atom of amides through N?O bond cleavage in a two-step, one-pot process. The asymmetric synthesis of α-aryl amides through the diastereoselective arylation of a chiral N,O-ketene acetal is also described.
- Takeda, Norihiko,Futaki, Erika,Kobori, Yukiko,Ueda, Masafumi,Miyata, Okiko
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p. 16342 - 16346
(2017/12/04)
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- Copper-catalyzed carboxylation of hydroborated disubstituted alkenes and terminal alkynes with cesium fluoride
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A protocol for the hydrocarboxylation of disubstituted alkenes and terminal alkynes providing access to different secondary carboxylic acids and malonic acid derivatives has been developed. This methodology relies on an initial hydroboration using 9-BBN followed by carboxylation with carbon dioxide in the presence of a copper catalyst and the additive, cesium fluoride. Different cyclohexene, styrene, and stilbene derivatives could be utilized, and alkynes could be transformed into their corresponding dicarboxylic acids in good yields. Finally, six different terpenoids were carboxylated using the developed procedure. (Chemical Equation Presented).
- Juhl, Martin,Laursen, Simon L. R.,Huang, Yuxing,Nielsen, Dennis U.,Daasbjerg, Kim,Skrydstrup, Troels
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p. 1392 - 1396
(2017/05/24)
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- Adsorption and performance of chiral cinchona alkaloid modifiers over Pd/C catalyst for enantioselective hydrogenation of α-phenylcinnamic acids
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The enantioselective hydrogenation reactions of α-phenylcinnamic acid (PCA) and 4,4′-dimethoxy α-phenylcinnamic acid (DMPCA) were carried out over chiral cinchona alkaloidmodified Pd/C. Two sets of the modifiers were employed to get deeper insights into the effects of relative adsorption strength between the modifier and the substrate on the enantioselectivity; cinchonidine (CD)/cinchonine (CN) and quinine (QN)/quinidine (QD). The performances of the two sets of modifiers were compared by systematically varying the modifier concentration over a wide range. It was clearly substantiated that the origin of the low selectivity observed with QN/QD at an ordinary concentration is primarily due to its weak adsorption strength on Pd metal surface, which originates from the steric hindrance of the methoxy substituent at C6. A new modifier, 6-hydroxy CD, was found to exhibit a performance comparable to that of CD, implying that the steric hindrance of the 6-methoxy group of QN/QD is much more influential than the electronic effects.
- Nakatsuji, Makoto,Misaki, Tomonori,Okamoto, Yasuaki,Sugimura, Takashi
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p. 1187 - 1191
(2016/11/02)
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- Enantioselective hydrogenation of α-phenylcinnamic acids over cinchonidine-modified Pd/C commercial catalysts
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Enantioselective hydrogenation of α-phenylcinnamic acid (PCA) and p,p′-dimethoxyphenylcinnamic acid (DMPCA) was studied over a variety of commercial 5 % Pd/C catalysts to reveal catalyst properties suitable for obtaining high enantioselectivity. The catalysts were characterized by CO adsorption, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). It is confirmed that pretreatment at 353 K under atmospheric pressure of H2 before modification with cinchonidine is very effective for all the Pd/C catalysts used here to improve the selectivity and reaction rate. It is suggested that the distribution of Pd metal particles is crucial to attain high selectivity (ee% = 79 ± 1 for PCA, 89 ± 2 for DMPCA): a uniform or eggshell-type distribution of Pd is more suitable than an egg-white or egg-yolk-type distribution. It is also suggested that the dispersion of Pd metal particles controls the enantioselectivity over cinchonidine (CD)-modified Pd/C catalysts. XPS techniques are proposed to provide a convenient method to find desirable catalysts. The choice of such Pd/C catalysts could facilitate high-throughput guided study on highly enantioselective hydrogenation of α,β-unsaturated carboxylic acids.
- Sato, Haruka,Mameda, Takuya,Nakai, Kengo,Misaki, Tomonori,Haruyama, Yuichi,Sonobe, Seiji,Kubota, Takeshi,Okamoto, Yasuaki,Sugimura, Takashi
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- EXAFS Characterization of Pd Catalysts for Enantioselective Hydrogenation of α-Phenylcinnamic Acid: Pretreatment Effects and Thiol Adsorption
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Abstract: The effects of the pretreatment and Pd-distribution on the enantioselective hydrogenation of α-phenylcinnamic acid over cinchonidine-modified Pd/C and Pd/Al2O3 were studied by use of EXAFS techniques combined with thiol ads
- Kubota, Takeshi,Sato, Haruka,Uchida, Takayuki,Kim, Tae Yeon,Omata, Koji,Misaki, Tomonori,Okamoto, Yasuaki,Sugimura, Takashi
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p. 2430 - 2440
(2016/11/25)
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- Systematic methodology for the development of biocatalytic hydrogen-borrowing cascades: Application to the synthesis of chiral α-substituted carboxylic acids from α-substituted α,β-unsaturated aldehydes
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Ene-reductases (ERs) are flavin dependent enzymes that catalyze the asymmetric reduction of activated carbon-carbon double bonds. In particular, α,β-unsaturated carbonyl compounds (e.g. enals and enones) as well as nitroalkenes are rapidly reduced. Conversely, α,β-unsaturated esters are poorly accepted substrates whereas free carboxylic acids are not converted at all. The only exceptions are α,β-unsaturated diacids, diesters as well as esters bearing an electron-withdrawing group in α- or β-position. Here, we present an alternative approach that has a general applicability for directly obtaining diverse chiral α-substituted carboxylic acids. This approach combines two enzyme classes, namely ERs and aldehyde dehydrogenases (Ald-DHs), in a concurrent reductive-oxidative biocatalytic cascade. This strategy has several advantages as the starting material is an α-substituted α,β-unsaturated aldehyde, a class of compounds extremely reactive for the reduction of the alkene moiety. Furthermore no external hydride source from a sacrificial substrate (e.g. glucose, formate) is required since the hydride for the first reductive step is liberated in the second oxidative step. Such a process is defined as a hydrogen-borrowing cascade. This methodology has wide applicability as it was successfully applied to the synthesis of chiral substituted hydrocinnamic acids, aliphatic acids, heterocycles and even acetylated amino acids with elevated yield, chemo- and stereo-selectivity. A systematic methodology for optimizing the hydrogen-borrowing two-enzyme synthesis of α-chiral substituted carboxylic acids was developed. This systematic methodology has general applicability for the development of diverse hydrogen-borrowing processes that possess the highest atom efficiency and the lowest environmental impact. This journal is
- Knaus, Tanja,Mutti, Francesco G.,Humphreys, Luke D.,Turner, Nicholas J.,Scrutton, Nigel S.
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p. 223 - 233
(2015/02/19)
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- Substrate dependent ligand acceleration in enantioselective hydrogenation of (E)-2,3-diarylpropenoic acid on cinchonidine-modified Pd/C
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The hydrogenation of substituted 2,3-diarylpropenoic acids over cinchonidine-modified Pd/C showed obvious ligand acceleration effects with the substrates yielding over 90% enantiomeric excess (ee). 2,3-Di(methoxyphenyl)propenoic acid exhibited profound ligand acceleration, and its hydrogenation rate relative to the rate on unmodified Pd/C was 370%, yielding 91%ee. 3-(p-Fluorophenyl)-2-(o-methoxyphenyl)propenoic acid showed 92%ee with an activity increase of 230%. It is considered that the difference is caused by the ortho-methoxy substituent on the α-phenyl ring. The substituent effect of the ortho-substituent on the α-phenyl ring demands the presence of an electron-donor substituent on the β-phenyl ring. A remarkable substituent effect was observed with 3-(p-methoxyphenyl)-2-(o-methoxyphenyl)propenoic acid, which attained up to 93%ee. The factors affecting enantioselectivity results are analyzed for each substituent.
- Mameda, Takuya,Nakai, Kengo,Misaki, Tomonori,Okamoto, Yasuaki,Sugimura, Takashi
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p. 129 - 133
(2015/03/04)
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- Carbonaceous materials as catalyst supports for the enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Effect of the support acidity
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A systematic comparative study of carbonaceous materials as catalyst supports for the asymmetric heterogeneous hydrogenation of (E)-α-phenylcinnamic acid (PCA) was performed to investigate the influence of the supports on the enantioselectivity. A series of Pd-based catalysts supported on activated carbon (AC), graphene oxide (GO), or carbon nanotubes (CNTs) was prepared using deposition methods. The hydrogenation reactions of PCA were conducted with/without the pretreatment of the prepared catalysts, and the results showed a significant drop of enantiomeric excess (ee) when the Pd/GO catalyst was used (27%) compared to that obtained from the Pd/AC (70%) and Pd/CNTs (66%) catalysts. This drop of ee values was assigned to the abundance of acidic sites present on the Pd/GO catalyst, as revealed by TGA, FT-IR, and TPD-NH3 analyses. The effect of the support acidity on the ee was ascribed to the preferential adsorption mode of cinchonidine (CD) on the GO surface via electrostatic interactions between the negatively charged oxygen functional groups present on the GO surface and the positively protonated amine groups of the CD molecule.
- Trung, Tran Si Bui,Kim, Yeonwoo,Kang, Sungho,Kim, Sehun,Lee, Hangil
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p. 319 - 325
(2015/09/01)
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- Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation
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The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)-2,3-diphenylpropenoic acid, (E)-2-(2-methoxyphenyl)-3-phenylpropenoic acid, (E)-2,3-di-(4-methoxyphenyl)phenylpropenoic acid and (E)-2-(2-methoxyphenyl)-3-(4-fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO- around 1394 cm-1 and νC-C of the -C-COO- moiety at 951 cm-1. In these series the plane of the α-phenyl group (γCH out-of-plane vibrations at 850-700 cm-1) is almost parallel to the silver surface, while the β-phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in-plane mode) at 1075 cm-1, νCC (ring breathing mode, in-plane) at 1000 cm-1 and γCCC (out-of-plane mode) around 401 cm-1. The other class of propenoic acids (cinnamic acid, (E)-2-phenyl-3-(4-methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm-1 in the FT-Raman spectra of methanolic solutions.
- Firkala, Tams,Tlas, Emlia,Kristyn, Sndor,Sz?ll'si, Gy?rgy,Drotr, Eszter,Mink, Jnos,Mihly, Judith
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p. 1102 - 1109
(2016/01/26)
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- Soluble polymer supported 2-imidazolidinone chiral auxiliary and method for manufacturing the same
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The present invention relates to a chiral auxiliary agent and a manufacturing method thereof and, more specifically, to a 2-imidazolidinone chiral auxiliary agent supported onto a polymer soluble in an organic solvent and a manufacturing method thereof. The chiral auxiliary agent in the present invention shows effects of being easy to separate reaction products and the chiral auxiliary agent after a termination of a reaction while fulfilling an economic efficacy of chiral auxiliary molecules by being supported onto the polymer soluble in the organic solvent.COPYRIGHT KIPO 2015
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Paragraph 0092; 0097-0101
(2017/01/02)
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- Palladium nanocarbon catalysts (Pd/CNT) as potential enantioselective heterogeneous systems. the behavior in the hydrogenation and hydroarylation of unsaturated substrates
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Hydroxy-CNT were modified with optically active α-amino acids. The resulting chiral derivatives were directly palladated with Pd2dba3 and used to catalyze the hydrogenation of α-acetamidostyrene and α-phenylcinnamic acid as well as t
- Abramova,Turova,Davidovich, Yu. A.,Sokolov
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p. 216 - 218
(2015/10/05)
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- Hydrodecarboxylation of Carboxylic and Malonic Acid Derivatives via Organic Photoredox Catalysis: Substrate Scope and Mechanistic Insight
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A direct, catalytic hydrodecarboxylation of primary, secondary, and tertiary carboxylic acids is reported. The catalytic system consists of a Fukuzumi acridinium photooxidant with phenyldisulfide acting as a redox-active cocatalyst. Substoichiometric quantities of Hünigs base are used to reveal the carboxylate. Use of trifluoroethanol as a solvent allowed for significant improvements in substrate compatibilities, as the method reported is not limited to carboxylic acids bearing α heteroatoms or phenyl substitution. This method has been applied to the direct double decarboxylation of malonic acid derivatives, which allows for the convenient use of dimethyl malonate as a methylene synthon. Kinetic analysis of the reaction is presented showing a lack of a kinetic isotope effect when generating deuterothiophenol in situ as a hydrogen atom donor. Further kinetic analysis demonstrated first-order kinetics with respect to the carboxylate, while the reaction is zero-order in acridinium catalyst, consistent with another finding suggesting the reaction is light limiting and carboxylate oxidation is likely turnover limiting. Stern-Volmer analysis was carried out in order to determine the efficiency for the carboxylates to quench the acridinium excited state.
- Griffin, Jeremy D.,Zeller, Mary A.,Nicewicz, David A.
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supporting information
p. 11340 - 11348
(2015/09/21)
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- Palladium-Catalyzed ?±-Arylation of Aryl Acetic Acid Derivatives via Dienolate Intermediates with Aryl Chlorides and Bromides
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To date, examples of ?±-arylation of carboxylic acids remain scarce. Using a deprotonative cross-coupling process (DCCP), a method for palladium-catalyzed ?3-arylation of aryl acetic acids with aryl halides has been developed. This protocol is applicable to a wide range of aryl bromides and chlorides. A procedure for the palladium-catalyzed ?±-arylation of styryl acetic acids is also described.
- Sha, Sheng-Chun,Zhang, Jiadi,Walsh, Patrick J.
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supporting information
p. 410 - 413
(2015/03/04)
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- Oxidative rearrangement of malondialdehyde: Substrate scope and mechanistic insights
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A novel oxidative rearrangement of malondialdehyde was described. Under the effect of H2O2, malondialdehyde smoothly transferred to carboxylic acid with C-C bond cleavage in good to excellent yields. Mechanistic studies showed that this reaction proceeded via the formation of a 1,2-dioxolane intermediate, followed by concert C-C, O-O, C-H bond cleavage and a hydride shift.
- Yu, Xin,Liu, Zheng,Xia, Zilei,Shen, Zhigao,Pan, Xixian,Zhang, Hui,Xie, Weiqing
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p. 53397 - 53401
(2015/01/16)
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- GUANIDINE DERIVATIVES AS TRPC MODULATORS
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The present invention is directed to guanidine derivatives as inhibitors of transient receptor potential canonical channels (TRPC channels), in particular TRPC3 and/or TRPC6 and/or TRPC7 activity, more particularly TRPC6 activity. Also provided herein are processes for preparing compounds described herein, intermediates used in their synthesis, pharmaceutical compositions thereof, and methods for treating or preventing diseases, conditions and/or disorders mediated by TRPC channels (Formula (I))
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Page/Page column 43
(2014/02/16)
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- A Palladium-catalyzed three-component-coupling strategy for the differential vicinal diarylation of terminal 1,3-dienes
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A palladium-catalyzed intermolecular vicinal diarylation of terminal 1,3-dienes using aryldiazonium tetrafluoroborates and arylboronic acids is reported. Using this technology, two different arenes are regioselectively introduced in a vicinal fashion across the terminal alkene of a variety of terminal 1,3-dienes at ambient temperature. Through the action of a chiral bicyclo[2.2.2]octadienyl ligand at -20 °C, good enantioselectivity has also been achieved.
- Stokes, Benjamin J.,Liao, Longyan,De Andrade, Aline Mendes,Wang, Qiaofeng,Sigman, Matthew S.
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supporting information
p. 4666 - 4669
(2015/01/09)
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- Application of acyclic chiral auxiliaries on alkylation reactions
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The application in alkylation reactions of an acyclic chiral auxiliary is described. The synthesis is straightforward from a chiral primary amine and a double acylation. A characteristic of this auxiliary is its modular design formed by an achiral part (acyl) and a chiral component (primary amine) so it can be tuned for different reactions without difficulty. The alkylation proceeds with excellent diastereoselectivity because the conformational flexibility of the enolate is restricted by the formation of a chelate and the allylic 1,3-strain.
- Gardu?o-Castro, Monserrat H.,Hernández-Rodríguez, Marcos
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supporting information
p. 193 - 196
(2014/01/06)
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- Enantioselective hydrogenation of α,β-unsaturated carboxylic acid over cinchonidine-modified Pd nanoparticles confined in carbon nanotubes
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We report the enantioselective hydrogenation of α,β-unsaturated acid catalyzed by Pd nanoparticles in carbon nanotubes (CNTs) taking the advantage of the channels as nanoreactors. The Pd nanocatalyst inside the channels of CNTs shows higher activity and e
- Guan, Zaihong,Lu, Shengmei,Li, Can
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- Walphos versus biferrocene-based walphos analogues in the asymmetric hydrogenation of alkenes and ketones
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Two representative Walphos analogues with an achiral 2,2″- biferrocenediyl backbone were synthesized. These diphosphine ligands were tested in the rhodium-catalyzed asymmetric hydrogenation of several alkenes and in the ruthenium-catalyzed hydrogenation of two ketones. The results were compared with those previously obtained on using biferrocene ligands with a C 2-symmetric 2,2″-biferrocenediyl backbone as well as with those obtained with Walphos ligands. The application of one newly synthesized ligand in the hydrogenation of 2-methylcinnamic acid gave (R)-2-methyl-3- phenylpropanoic acid with full conversion and with 92% ee. The same ligand was used to transform 2,4-pentanedione quantitatively and diastereoselectively into (S,S)-2,4-pentanediol with 98% ee.
- Zirakzadeh, Afrooz,Gross, Manuela A.,Wang, Yaping,Mereiter, Kurt,Weissensteiner, Walter
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p. 1945 - 1952
(2014/05/20)
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- Biferrocene-based diphosphine ligands: Synthesis and application of walphos analogues in asymmetric hydrogenations
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A total of four biferrocene-based Walphos-type ligands have been synthesized, structurally characterized, and tested in the rhodium-, ruthenium- and iridium-catalyzed hydrogenation of alkenes and ketones. Negishi coupling conditions allowed the biferrocene backbone of these diphosphine ligands to be built up diastereoselectively from the two nonidentical and nonracemic ferrocene fragments (R)-1-(N,N-dimethylamino)ethylferrocene and (SFc)-2- bromoiodoferrocene. The molecular structures of (SFc)-2- bromoiodoferrocene, the coupling product, two ligands, and the two complexes ([PdCl2(L)] and [RuCl(p-cymene)(L)]PF6) were determined by X-ray diffraction. The structural features of complexes and the catalysis results obtained with the newly synthesized biferrocene-based ligands were compared with those of the corresponding Walphos ligands.
- Zirakzadeh, Afrooz,Gross, Manuela A.,Wang, Yaping,Mereiter, Kurt,Spindler, Felix,Weissensteiner, Walter
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supporting information
p. 1075 - 1084
(2013/04/23)
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- Anomalous ligand acceleration on cinchona-modified Pd/C during asymmetric hydrogenation of properly substituted phenylcinnamic acid
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The hydrogenation of 4,4'-dimethoxy-α-phenylcinnamic acid over Pd/C showed a large ligand acceleration effect when a cinchonidine modifier was used; the hydrogen rate increased to 370% relative to the reaction rate on unmodified Pd/C and resulted in a 91% enantiomeric excess (ee). Another good substrate, 4-fluoro-2'-methoxyphenylcinnamic acid, also resulted in a high ee value of 92%; however, the rate increased only to 230% when this modifier was used. On the basis of the difference in the degree to which the reaction rate was accelerated, the eemax for each substrate was analyzed.
- Ogawa, Hiroyuki,Mameda, Takuya,Misaki, Tomonori,Okamoto, Yasuaki,Sugimura, Takashi
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p. 813 - 815
(2013/09/02)
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- Heterogeneous enantioselective hydrogenation of hydroxy-substituted (E)-2,3-diphenylpropenoic acids over Pd/Al2O3 modified by cinchonidine
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The enantioselective hydrogenation of (E)-2,3-diphenylpropenoic acids substituted by hydroxyl group has been studied over Pd/Al2O 3 catalyst modified by cinchonidine. The effect of the acidic hydroxyl substituents was compared with that of the methoxy group in the same position. The para-hydroxyl substituent on the 3-phenyl ring had similar effect on the enantioselectivity as the methoxy group, whereas the meta positioned decreased the optical purity of the saturated acid. This was explained by different origin of the increase in the enantioselectivity obtained in the presence of electron releasing substituents in these positions. Although, the para-hydroxyl group on the 2-phenyl ring had beneficial influence on the enantioselectivity of the hydrogenation of the mono-substituted acid, in the presence of fluorine or hydroxyl group on the 3-phenyl ring the effect of the two substituents was not additive. This study demonstrated that the cinchonidine-modified Pd catalyst is appropriate for the preparation of several hydroxy-substituted 2,3-diphenylpropionic acids in good optical purities, extending the scope of this catalytic system to new types of versatile chiral building blocks.
- Sz?ll?si, Gyo?rgy
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experimental part
p. 345 - 351
(2012/06/18)
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- Enantioselective iridium-catalyzed hydrogenation of α-arylcinnamic acids and synthesis of (S)-equol
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By using iridium catalyst based on chiral spiro phosphine-oxazoline ligands, the hydrogenation of α-arylcinnamic acids was accomplished under ambient pressure and low catalyst loading (as low as 0.01 mol %), providing useful 2,3-diarylpropionic acids in high yields with excellent enantioselectivities (up to 99% ee). A catalytic enantioselective synthesis of (S)-equol with the present hydrogenation reaction as a key step was accomplished starting from commercially available starting materials in six steps with 48.4% overall yield.
- Yang, Shuang,Zhu, Shou-Fei,Zhang, Can-Ming,Song, Song,Yu, Yan-Bo,Li, Shen,Zhou, Qi-Lin
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experimental part
p. 5172 - 5178
(2012/07/31)
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- Efficient cluster-based catalysts for asymmetric hydrogenation of α-unsaturated carboxylic acids
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The new clusters [H4Ru4(CO)10(μ-1,2-P- P)], [H4Ru4(CO)10(1,1-P-P)] and [H 4Ru4(CO)11(P-P)] (P-P=chiral diphosphine of the ferrocene-based Josiphos or Walphos ligand families) have been synthesised and characterised. The crystal and molecular structures of eleven clusters reveal that the coordination modes of the diphosphine in the [H4Ru 4(CO)10(μ-1,2-P-P)] clusters are different for the Josiphos and the Walphos ligands. The Josiphos ligands bridge a metal-metal bond of the ruthenium tetrahedron in the "conventional" manner, that is, with both phosphine moieties coordinated in equatorial positions relative to a triangular face of the tetrahedron, whereas the phosphine moieties of the Walphos ligands coordinate in one axial and one equatorial position. The differences in the ligand size and the coordination mode between the two types of ligands appear to be reflected in a relative propensity for isomerisation; in solution, the [H4Ru4(CO)10(1,1-Walphos)] clusters isomerise to the corresponding [H4Ru4(CO) 10(μ-1,2-Walphos)] clusters, whereas the Josiphos-containing clusters show no tendency to isomerisation in solution. The clusters have been tested as catalysts for asymmetric hydrogenation of four prochiral α-unsaturated carboxylic acids and the prochiral methyl ester (E)-methyl 2-methylbut-2-enoate. High conversion rates (>94 %) and selectivities of product formation were observed for almost all catalysts/catalyst precursors. The observed enantioselectivities were low or nonexistent for the Josiphos-containing clusters and catalyst (cluster) recovery was low, suggesting that cluster fragmentation takes place. On the other hand, excellent conversion rates (99-100 %), product selectivities (99-100 % in most cases) and good enantioselectivities, reaching 90 % enantiomeric excess (ee) in certain cases, were observed for the Walphos-containing clusters, and the clusters could be recovered in good yield after completed catalysis. Results from high-pressure NMR and IR studies, catalyst poisoning tests and comparison of catalytic properties of two [H4Ru4(CO)10(μ-1,2-P-P)] clusters (P-P=Walphos ligands) with the analogous mononuclear catalysts [Ru(P-P)(carboxylato)2] suggest that these clusters may be the active catalytic species, or direct precursors of an active catalytic cluster species. Copyright
- Moberg, Viktor,Duquesne, Robin,Roehrs, Oliver,Nachtigall, Jonny,Nordlander, Ebbe,Contaldi, Simone,Monari, Magda,Damoense, Llewellyn,Green, Michael,Hutton, Alan T.,Santelia, Daniela,Haukka, Matti
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p. 12458 - 12478,21
(2020/08/24)
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- Fundamental insights into the enantioselectivity of hydrogenations on cinchona-modified platinum and palladium
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The influence of the configuration at the C8 and C9 positions of cinchona alkaloids was investigated by comparing the efficiency of cinchonidine, cinchonine, and 9-epi-cinchonidine as chiral modifiers. In the hydrogenation of ketones (methyl benzoylformate, ketopantolactone, methylglyoxal dimethylacetal, 2,2,2-trifluoroacetophenone) on Pt, a change in the configuration at C9 did not affect the absolute configuration of the main products; however, the ees and rates dropped significantly. In the hydrogenation of α-functionalized olefins (E-2-methyl-2-hexenoic acid, 2-phenylcinnamic acid, and 4-methoxy-6-methyl-2H-pyran-2-one) on Pd, replacement of cinchonidine or cinchonine by epi-cinchonidine diminished the rates and almost eliminated the enantioselection, indicating that a subtle combination of C8 and C9 configurations is required on Pd. DFT calculations of the adsorption of the modifiers and the nonlinear behavior of modifier mixtures revealed that the lower reaction rates observed for 9-epi-cinchonidine-modified surfaces cannot be related to different adsorption strength of this modifier. Additionally, substrate-modifier docking interactions are presented.
- Schmidt, Erik,Bucher, Christoph,Santarossa, Gianluca,Mallat, Tamas,Gilmour, Ryan,Baiker, Alfons
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experimental part
p. 238 - 248
(2012/06/01)
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- Substituent position-driven reaction pathways in the heterogeneous one-pot reduction/asymmetric hydrogenation of nitro-substituted (E)-2,3- diphenylpropenoic acids over Pd catalyst
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The reaction pathway in the heterogeneous enantioselective hydrogenation of nitro-substituted (E)-2,3-diphenylpropenoic acids over Pd catalyst modified by cinchonidine is determined by the position of the substituent. The reaction route was indicated by the H2 consumption curve and enantioselectivity of the final amino acid or 3-phenyl-1,2,3,4-tetrahydro-2- quinolone formed by intramolecular amidation. The obtained enantioselectivities were low with the exception of acids bearing nitro substituent in para position on the 3-phenyl moiety, the latter resulting in good, up to 80 % optical purity. The present study is the first to report the enantioselective heterogeneous catalytic preparation of 1,2,3,4-tetrahydro-2-quinolones and presents an attractive method for obtaining optically enriched 3-(4-aminophenyl)-2- phenylpropionic acids. ARKAT-USA, Inc.
- Szoelloesi, Gyoergy,Bartok, Mihaly
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experimental part
p. 16 - 27
(2012/03/11)
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- Highly enantioselective direct alkylation of arylacetic acids with chiral lithium amides as traceless auxiliaries
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A direct, highly enantioselective alkylation of arylacetic acids via enediolates using a readily available chiral lithium amide as a stereodirecting reagent has been developed. This approach circumvents the traditional attachment and removal of chiral auxiliaries used currently for this type of transformation. The protocol is operationally simple, and the chiral reagent is readily recoverable.
- Stivala, Craig E.,Zakarian, Armen
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supporting information; experimental part
p. 11936 - 11939
(2011/09/19)
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- Palladium supported on detonation nanodiamond as a highly effective catalyst of the C=C and C≡C bond hydrogenation
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Palladium loaded on detonation nanodiamond was used for the first time as a catalyst for the C=C and C≡ C bond hydrogenation. By the example of tolane hydrogenation, the Pd(0)/nanodiamond was found to greatly surpass in catalytic activity other Pd(0)/nanocarbon catalysts.
- Turova, Olga V.,Starodubtseva, Eugenia V.,Vinogradov, Maxim G.,Sokolov, Viacheslav I.,Abramova, Natalya V.,Vul', Alexander Ya.,Alexenskiy, Alexander E.
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experimental part
p. 577 - 579
(2011/12/22)
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- METHOD FOR PRODUCING OPTICALLY ACTIVE ESTER AND METHOD FOR PRODUCING OPTICALLY ACTIVE CARBOXYLIC ACID
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Disclosed is a method for producing an optically active ester by highly selectively esterifying one enantiomer of a racemic carboxylic acid, while producing an optically active carboxylic acid which is the other enantiomer. An optically active ester is produced while producing an optically active carboxylic acid at the same time by reacting a racemic carboxylic acid with a specific alcohol or phenol derivative in the presence of benzoic anhydride or a derivative thereof and a catalyst such as tetramisole or benzotetramisole, thereby selectively esterifying one enantiomer of the racemic carboxylic acid.
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Page/Page column 7
(2010/09/18)
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- An effective kinetic resolution of racemic α-arylpropanoic acids, α-arylbutanoic acids, and β-substituted-α-arylpropanoic acids with bis(9-phenanthryl)methanol as a new achiral nucleophile in the asymmetric esterification using carboxylic anhydrides and the acyl-transfer catalyst
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A general method for the kinetic resolution of racemic α-arylalkanoic acids with achiral alcohols is described. It was determined that bis(9-phenanthryl)methanol is a suitable nucleophile which reacts with the intermediary mixed anhydrides generated from aromatic anhydrides with α-arylpropanoic acids or β-substituted-α-arylpropanoic acids in the presence of (+)-benzotetramisole to produce the corresponding optically active esters with high ee's under very mild conditions.
- Nakata, Kenya,Onda, Yu-Suke,Ono, Keisuke,Shiina, Isamu
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experimental part
p. 5666 - 5669
(2010/11/18)
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- Cinchona methyl ethers as modifiers in the enantioselective hydrogenation of (E)-2,3-diphenylpropenoic acids over Pd catalyst
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The enantioselective hydrogenation of (E)-2,3-diphenylpropenoic acids over Pd/Al2O3 modified by (R)C8(S)C9 cinchona ethers resulted in the inversion of the sense of the enantioselectivity. To find the explanation of the phenomenon, the interaction of acids bearing different substituents with cinchona alkaloids was studied in solution by NMR spectroscopy and experiments using mixtures of modifiers were carried out. The prominent non-linear behaviour obtained revealed the altered adsorption of the cinchona methyl ethers when compared with the parent alkaloids. The investigations indicated that the interaction of the ether derivatives with the unsaturated acids is more flexible and the presence of the methyl group reshapes the chiral surface sites. The combination of these effects complemented by the bulkiness of the diaryl substituted acrylic acids may lead to the inversion of the docking preference of the substrates in the altered chiral pocket of the adsorbed modifier and consequently results in decrease in the enantioselectivity or even in the inversion of its sense. Novel evidence on the ligand-accelerated mechanism in the enantioselective hydrogenation of (E)-2,3-diphenylpropenoic acids over cinchona alkaloid-modified Pd in the presence of benzylamine was also presented.
- Szllsi, Gyoergy,Herman, Beata,Fueloep, Ferenc,Bartok, Mihaly
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experimental part
p. 259 - 267
(2011/02/27)
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- Acceleration of enantioselective hydrogenation of olefins over Pd/C by cinchonidine as a chiral modifier. Comparison with cinchonine, pseudoenantiomer
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The performance of cinchonidine (CD) and cinchonine (CN) as chiral modifiers in enantioselective hydrogenation over Pd/C were compared in different concentrations. The catalytic hydrogenation with CD always occurred in better ee and at faster rate than that with CN. The difference is not attributable to the adsorption properties of the modifiers, but to the intrinsic enantio differentiation that accompanies the reaction acceleration.
- Sugimura, Takashi,Ogawa, Hiroyuki
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supporting information; scheme or table
p. 232 - 233
(2010/08/22)
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- Is amine addition vital for highly enantioselective hydrogenation of α,β-unsaturated carboxylic acid over cinchonidine-modified palladium?
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Benzylamine (BA) is a commonly employed additive for the hydrogenation of α,β-unsaturated acids over the cinchonidine-modified palladium catalyst, but the BA addition effects largely depend on the reaction solvent. In toluene, BA is not required to obtain the high enantioselectivity. Quicker desorption of the product due to weaker acidity in toluene than in a commonly used wet dioxane reasonably explains both the kinetic properties and the product selectivities.
- Kim, Tae Yeon,Sugimura, Takashi
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experimental part
p. 58 - 62
(2010/11/16)
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- Reactions of chlorine substituted (E)-2,3-diphenylpropenoic acids over cinchonidine-modified Pd: Enantioselective hydrogenation versus hydrodechlorination
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The effect of the chlorine position on the C-Cl bond hydrogenolysis and the enantioselective hydrogenation of Cl substituted (E)-2,3-diphenylpropenoic acid derivatives has been studied over cinchonidine-modified Pd/Al2O 3. In contrast to the fast hydrodechlorination of the β-phenyl-para-Cl substituted acids the Cl on the α-phenyl ring was barely hydrogenolized. These observations were interpreted by the different arrangements of the two phenyl rings on the surface, with the α- and β-phenyl rings adsorbed tilted and parallel, respectively. The results confirmed the beneficial effect of the α-phenyl-ortho-substituents on the chiral discrimination, thus the 2,3-diphenylpropionic acids substituted by Cl on the α-phenyl ring could be prepared in good yields and optical purities. The conclusions were used for the rational design of an acid, i.e. (E)-2-(2-methoxyphenyl)-3-(3,4-difluorophenyl)propenoic acid, which afforded the best optical purity (ee up to 95% at 295 K) described until now in this heterogeneous system.
- Szllsi, Gy?rgy,Hermán, Beáta,Szabados, Erika,Fül?p, Ferenc,Bartók, Mihály
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experimental part
p. 28 - 36
(2011/02/24)
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- Friedel-Crafts alkylation of benzene with 1,2-diphenyl-2-propanol, 1-chloro-2,3-diphenylpropane and 2-methyl-1-phenyl-2-butanol
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The alkylation of benzene with 1,2-diphenyl-2-propanol (1) using AlCl 3/CH3NO2 catalyst gave a mixture of 1,2,2- (4) and 1,1,2-triphenylpropane (5) as product alkylates. With 85% H 2SO4 catalyst, the product consisted of E-1,2-diphenylpropene (6) after 2 h of a mixture of 5 and 6 after 18 h. Similar alkylation of benzene with 1-chloro-2,3-diphenylpropane (2) using AlCl 3 catalyst gave a mixture consisting of 4, 5 and 6. Finally, alkylation of benzene with 2-methyl-1-phenyl-2-butanol (3) using AlCl 3/CH3NO2 gave 2-methyl-1,1-diphenylbutane (10) as sole product alkylate. The identities of the products were confirmed spectroscopically and by comparison with unequivocally prepared samples. Mechanisms are proposed to rationalise the observed results.
- Khalaf, Ali A.,Awad, Ibrahim M.,El-Emary,El-Aal, H.A.K. Abd
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experimental part
p. 595 - 600
(2011/08/21)
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