- Manganese catalyzed asymmetric transfer hydrogenation of ketones
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The asymmetric transfer hydrogenation (ATH) of a wide range of ketones catalyzed by manganese complex as well as chiral PxNy-type ligand under mild conditions was investigated. Using 2-propanol as hydrogen source, various ketones could be enantioselectively hydrogenated by combining cheap, readily available [MnBr(CO)5] with chiral, 22-membered macrocyclic ligand (R,R,R',R')-CyP2N4 (L5) with 2 mol% of catalyst loading, affording highly valuable chiral alcohols with up to 95% ee.
- Zhang, Guang-Ya,Ruan, Sun-Hong,Li, Yan-Yun,Gao, Jing-Xing
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supporting information
p. 1415 - 1418
(2020/11/20)
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- Mechanochemical, Water-Assisted Asymmetric Transfer Hydrogenation of Ketones Using Ruthenium Catalyst
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Asymmetric catalytic reactions are among the most convenient and environmentally benign methods to obtain optically pure compounds. The aim of this study was to develop a green system for the asymmetric transfer hydrogenation of ketones, applying chiral Ru catalyst in aqueous media and mechanochemical energy transmission. Using a ball mill we have optimized the milling parameters in the transfer hydrogenation of acetophenone followed by reduction of various substituted derivatives. The scope of the method was extended to carbo- and heterocyclic ketones. The scale-up of the developed system was successful, the optically enriched alcohols could be obtained in high yields. The developed mechanochemical system provides TOFs up to 168 h?1. Our present study is the first in which mechanochemically activated enantioselective transfer hydrogenations were carried out, thus, may be a useful guide for the practical synthesis of optically pure chiral secondary alcohols.
- Kolcsár, Vanessza Judit,Sz?ll?si, Gy?rgy
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- Observation of hyperpositive non-linear effect in catalytic asymmetric organozinc additions to aldehydes
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Asymmetric amplification is a phenomenon that is believed to play a key role in the emergence of homochirality in life. In asymmetric catalysis, theoretical and experimental models have been investigated to provide an understanding of how chiral amplification is possible, in particular based on non-linear effects. Interestingly, it has been proposed a quarter century ago that chiral catalysts, when not enantiopure might even be more enantioselective than their enantiopure counterparts. We show here that such hyperpositive non-linear effect in asymmetric catalysis is indeed possible. An in-depth study into the underlying mechanism was carried out, and the scheme we derive differs from the previous proposed models.
- Geiger, Yannick,Achard, Thierry,Maisse-Fran?ois, Aline,Bellemin-Laponnaz, Stéphane
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supporting information
p. 1250 - 1256
(2020/07/25)
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- Asymmetric transfer hydrogenation of ketones promoted by manganese(I) pre-catalysts supported by bidentate aminophosphines
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A series of commercially available chiral amino-phosphines, in combination with Mn(CO)5Br, has been evaluated for the asymmetric reduction of ketones, using isopropanol as hydrogen source. With the most selective ligand, the corresponding manga
- Azouzi, Karim,Bruneau-Voisine, Antoine,Vendier, Laure,Sortais, Jean-Baptiste,Bastin, Stéphanie
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- RETRACTED ARTICLE: The Manganese(I)-Catalyzed Asymmetric Transfer Hydrogenation of Ketones: Disclosing the Macrocylic Privilege
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The bis(carbonyl) manganese(I) complex [Mn(CO)2(1)]Br (2) with a chiral (NH)2P2 macrocyclic ligand (1) catalyzes the asymmetric transfer hydrogenation of polar double bonds with 2-propanol as the hydrogen source. Ketones (43 substrates) are reduced to alcohols in high yields (up to >99 %) and with excellent enantioselectivities (90–99 % ee). A stereochemical model based on attractive CH–π interactions is proposed.
- Passera, Alessandro,Mezzetti, Antonio
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supporting information
p. 187 - 191
(2019/12/11)
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- Highly Enantioselective Transfer Hydrogenation of Prochiral Ketones Using Ru(II)-Chitosan Catalyst in Aqueous Media
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Unprecedentedly high enantioselectivities are obtained in the transfer hydrogenation of prochiral ketones catalyzed by a Ru complex formed in situ with chitosan chiral ligand. This biocompatible, biodegradable chiral polymer obtained from the natural chitin afforded good, up to 86 % enantioselectivities, in the aqueous-phase transfer hydrogenation of acetophenone derivatives using HCOONa as hydrogen donor. Cyclic ketones were transformed in even higher, over 90 %, enantioselectivities, whereas further increase, up to 97 %, was obtained in the transfer hydrogenations of heterocyclic ketones. The chiral catalyst precursor prepared ex situ was examined by scanning electron microscopy, FT-mid- and -far-IR spectroscopy. The structure of the in situ formed catalyst was investigated by 1H NMR spectroscopy and using various chitosan derivatives. It was shown that a Ru pre-catalyst is formed by coordination of the biopolymer to the metal by amino groups. This precursor is transformed in water insoluble Ru-hydride complex following hydrogen donor addition. The practical value of the developed method was verified by preparing over twenty chiral alcohols in good yields and optical purities. The catalyst was applied for obtaining optically pure chiral alcohols at gram scale following a single crystallization.
- Sz?ll?si, Gy?rgy,Kolcsár, Vanessza Judit
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p. 820 - 830
(2018/12/13)
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- Towards practical earth abundant reduction catalysis: Design of improved catalysts for manganese catalysed hydrogenation
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Manganese catalysts derived from tridentate P,N,N ligands can be activated easily using weak bases for both ketone and ester hydrogenations. Kinetic studies indicate the ketone hydrogenations are 0th order in acetophenone, positive order in hydrogen and 1st order in the catalyst. This implies that the rate determining step of the reaction was the activation of hydrogen. New ligand systems with varying donor strength were studied and it was possible to make the hydrogen activation significantly more efficient; a catalyst displaying around a 3-fold increase in initial turn-over frequencies for the hydrogenation of acetophenone relative to the parent system was discovered as a result of these kinetic investigations. Ester hydrogenations and ketone transfer hydrogenation (isopropanol as reductant) are first order for both the substrate and catalysts. Kinetic studies also gained insight into catalyst stability and identified a working range in which the catalyst is stable throughout the catalytic reaction (and a larger working range where high yields can still be achieved). The new more active catalyst, combining an electron-rich phosphine with an electron-rich pyridine is capable of hydrogenating acetophenone using as little as 0.01 mol% catalyst at 65 °C. In all, protocols for reduction of 21 ketones and 15 esters are described.
- Widegren, Magnus B.,Clarke, Matthew L.
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p. 6047 - 6058
(2019/11/14)
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- Asymmetric Reduction of Prochiral Ketones by Using Self-Sufficient Heterogeneous Biocatalysts Based on NADPH-Dependent Ketoreductases
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The development of cell-free and self-sufficient biocatalytic systems represents an emerging approach to address more complex synthetic schemes under nonphysiological conditions. Herein, we report the development of a self-sufficient heterogeneous biocatalyst for the synthesis of chiral alcohols without the need to add an exogenous cofactor. In this work, an NADPH-dependent ketoreductase was primarily stabilized and further co-immobilized with NADPH to catalyze asymmetric reductions without the addition of an exogenous cofactor. As a result, the immobilized cofactor is accessible, and thus, it is recycled inside the porous structure without diffusing out into the bulk, as demonstrated by single-particle in operando studies. This self-sufficient heterogeneous biocatalyst was used and recycled for the asymmetric reduction of eleven carbonyl compounds in a batch reactor without the addition of exogenous NADPH to achieve the corresponding alcohols in 100 % yield and >99 % ee; this high performance was maintained over five consecutive reaction cycles. Likewise, the self-sufficient heterogeneous biocatalyst was integrated into a plug flow reactor for the continuous synthesis of one model secondary alcohol, which gave rise to a space-time yield of 97–112 g L?1 day?1; additionally, the immobilized cofactor accumulated a total turnover number of 1076 for 120 h. This is one of the few examples of the successful implementation of continuous reactions in aqueous media catalyzed by cell-free and immobilized systems that integrate both enzymes and cofactors into the solid phase.
- Benítez-Mateos, Ana I.,San Sebastian, Eneko,Ríos-Lombardía, Nicolás,Morís, Francisco,González-Sabín, Javier,López-Gallego, Fernando
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p. 16843 - 16852
(2017/11/16)
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- Iron-catalyzed asymmetric hydrosilylation of ketones
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A series of iron complexes of chiral iminopyridine-oxazoline (IPO) ligands have been synthesized. The most sterically hindered iron catalyst exhibits excellent activity (up to 99% yield) and high enantioselectivity (up to 93% ee) in asymmetric hydrosilylation of aryl ketones. This journal is
- Zuo, Ziqing,Zhang, Lei,Leng, Xuebing,Huang, Zheng
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supporting information
p. 5073 - 5076
(2015/03/30)
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- Chiral ruthenium catalyst immobilized within magnetically retrievable mesoporous silica microcapsules for aqueous asymmetric transfer hydrogenations
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The preparation of magnetically separable silica microcapsules that incorporate in their inner shell a chiral catalyst and their application in asymmetric transfer hydrogenation reactions are described. The preparation method is based on the emulsification of an oil phase containing chloroform, a modified Noyori Ru-TsDPEN catalyst, tetraethoxysilane (TEOS), and hydrophobic magnetic nanoparticles in water in the presence of an appropriate surfactant, followed by an interfacial polycondensation process under basic conditions to generate a silica shell around the oil droplets. The resulting catalytic microreactors can be considered a "quasi-homogeneous" system because the immobilized chiral catalyst reacts in a homogeneous zone, the microcapsule core filled with an organic solvent. The catalytic activity was tested in the asymmetric transfer hydrogenation of ketones in an aqueous medium. The catalytic reactions took place only in the presence of surfactants. In addition, the judicious selection of the surfactant plays a crucial role in enhancing the reaction progress through the emulsion-solid transfer (EST) approach. The catalytic activity of the Ru-TsDPEN catalyst immobilized within the silica microcapsules was superior to the same catalyst supported on silica microspheres or linked to the backbone of a silica sol-gel matrix, which indicates the importance of the homogeneous zones for the reactions. We report the design of a "quasi-homogeneous" catalytic system, based on a modified Noyori Ru-TsDPEN catalyst confined within mesoporous silica-based microreactors, for the efficient asymmetric transfer hydrogenation of ketones in water. The new system demonstrates excellent reactivity and enantioselectivity characteristic of homogeneous catalysts, but can be easily recovered.
- Zoabi, Amani,Omar, Suheir,Abu-Reziq, Raed
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p. 2101 - 2109
(2015/05/05)
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- Asymmetric hydrosilylation of ketones catalyzed by zinc acetate with hindered pybox ligands
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A highly efficient asymmetric hydrosilylation (AHS) of a wide variety of prochiral aryl ketones catalyzed by zinc acetate with TPS-he-pybox (tert-butyldiphenylsilyl hydroxyethyl pybox) ligand has been successfully developed. Cheap and readily available chiral Lewis acids based on zinc salts have been used as promising catalyst for the reduction of aryl ketones under mild conditions at room temperature leading to chiral alcohols in excellent yields and good to high enantioselectivities (up to 85% ee).
- Lowicki, Daniel,Bezlada, Agata,Mlynarski, Jacek
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supporting information
p. 591 - 595
(2014/05/20)
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- Chirally functionalized SBA-15 as efficient heterogeneous catalyst for asymmetric ketone reduction
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Chiral amine catalyst was synthesized using (1R, 2S)-(-)-norephedrine and 5-chlorosalicylaldehyde by reductive amination. The structure of the catalyst was confirmed using 1H-NMR and 13C-NMR spectroscopic method. The catalyst was immobilized onto SBA-15 via covalent bonding using 3-chloropropyltrimethoxysilane as a reactive surface modifier under reflux condition using toluene as a solvent. The supported chiral catalyst was characterized using various physico-chemical techniques like XRD, SEM, N 2 adsorption isotherm, FTIR and UV-DRS to study the morphology, pore dimension, functional group analysis and catalyst loading in the mesoporous material. The immobilized catalyst was studied for prochiral ketone reduction using 30 mol% of chiral catalyst and boranedimethylsulphide as a stoichiometric reductant in toluene under inert atmosphere for 30 minutes. Secondary alcohols were formed up to 79% enantiomeric excess for selective ketones. Catalyst was recycled from the reaction mixture and used for further reaction without much effect on the catalytic conversion. Copyright
- Balakrishnan, Umesh,Velmathi, Sivan
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p. 3079 - 3086
(2013/08/25)
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- Effect of substituents on enantioselectivity in chiral oxazaborolidine mediated asymmetric ketone reduction reaction
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Various new chiral ligands have been synthesized by the condensation of different esters of L-Valine with different substituted salicylaldehydes in order to find the most effective catalyst for the enantioselctive ketone reduction. Chiral amine synthesized from L-Valine methyl ester and 5-chloro salicylaldehyde is found to catalyse the enantioselective reduction of prochiral ketone with high yield (99%) and enantiomeric excess (91%) with 20 mol% of the catalyst using borane dimethylsulphide as a stoichiometric reducutant. Different subsituted prochiral ketones have also been reduced in high yield upto 90% and the corresponding secondary alcohols are formed with good enantiomeric excess upto 99%. The mechanism of this reduction can be very well explained by considering a plausible mechanism for the CBS catalyst.
- Balakrishnan,Ananthi,Velmathi
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experimental part
p. 1157 - 1164
(2011/10/13)
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- Asymmetric reduction of ketones by phosphoric acid derived catalysts
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A new path to chiral alcohols: Asymmetric reduction of ketones was achieved utilizing a chiral Bronsted acid as precatalyst for the first time. Using catecholborane as the reducing agent, a highly enantioselective formation of chiral secondary alcohols was found with a broad substrate scope. Mechanistic studies indicate that phosphoryl catechol borate derived from the reaction of the Bronsted acid with catecholborane produced the active catalyst (see scheme).
- Zhang, Zuhui,Jain, Pankaj,Antilla, Jon C.
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supporting information; experimental part
p. 10961 - 10964
(2012/01/02)
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- Preparation and characterization of chiral oxazaborolidine complex immobilized SBA-15 and its application in the asymmetric reduction of prochiral ketones
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The immobilization of chiral oxazaborolidine complex in the wellordered mesochannels of SBA-15 is demonstrated by a postsynthetic approach using 3-aminopropyltriethoxysilane as a reactive surface modifier. The immobilized catalysts are characterized by va
- Balakrishnan, Umesh,Ananthi, Nallamuthu,Selvan, Sakthivel Tamil,Pal, Ravindra,Ariga, Katsuhiko,Velmathi, Sivan,Vinu, Ajayan
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experimental part
p. 897 - 903
(2010/08/04)
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- Chiral ligand derived from (1S,2R)-norephedrine as a catalyst for enantioselective prochiral ketone reduction
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Chiral oxazaborolidines derived from (1S,2R)-(+)-norephedrine and substituted salicylaldehydes were employed in the asymmetric reduction of prochiral ketones using borane dimethyl sulfide as a reducing agent. The secondary alcohols were formed in excellent yields (45-99.8%) with enantioselectivities up to 99.8%. The effect of the substitution in the aromatic ring of the ligand was discussed with the enantioselectivity of the product.
- Balakrishnan, Umesh,Ananthi, Nallamuthu,Velmathi, Sivan
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experimental part
p. 1150 - 1153
(2009/09/27)
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- Chemoenzymatic synthesis of stannylated metomidate as a precursor for electrophilic radiohalogenations - Regioselective alkylation of methyl 1H-imidazole-5-carboxylate [1]
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Metomidate (ee 99%) substituted with iodine in the phenyl ring was prepared from (S)-1-(4-iodophenyl)ethanol (ee >98%) obtained by lipase-catalysed resolution and methyl 1H-imidazole-5-carboxylate. The two fragments were joined highly regioselectively (al
- Hammerschmidt, Friedrich,Simov, Biljana Peric,Schmidt, Susanne,Schneider, Sabine,Zolle, Ilse
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p. 229 - 239
(2007/10/03)
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- Ruthenium(II) complexes of monodonor ligands: Efficient reagents for asymmetric ketone hydrogenation
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A series of BINOL-derived ligands have been prepared and incorporated into ruthenium(II) complexes containing a diamine ligand. The complexes have proven to be excellent catalysts for the asymmetric hydrogenation of ketones, giving reduction products with enantiomeric excesses of up to 99%.
- Xu, Yingjian,Clarkson, Guy C.,Docherty, Gordon,North, Carl L.,Woodward, Gary,Wills, Martin
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p. 8079 - 8087
(2007/10/03)
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- Radiolabelled phenylethyl imidazole caboxylic acid ester derivatives
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Halogenated carboxylic ester derivatives of phenylethyl imidazole, and their method of preparation are disclosed. Radio-halogenated forms of these compounds are ideally suited for positron-imaging of the adrenal glands, as it is known that these compounds demonstrate a selective and high rate of accumulation in the adrenals. The method of preparing these derivatives proceeds by the conversion of a stable, non-radioactive intermediate having trialkylstannyl leaving groups. These intermediates are efficiently converted to the corresponding halogenated forms by substitution of the trialkylstannyl group with the halogen or radiohalogen.
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Page/Page column 5-6
(2008/06/13)
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