- R(-)PANTOYLLACTONE-β-D-GLUCOPYRANOSIDE: CHARACTERIZATION OF A METABOLITE FROM RICE SEEDLINGS
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A new derivative of pantoic acid, R(-)pantoyllactone-β-D-glucopyranoside, has been isolated from rice seedlings and its structure determined. β-Glucosidase hydrolysed it to D-glucose and R(-)pantoyllactone.Alkaline hydrolysis converted it to the salt of 2-R(-)pantoic acid β-D-glucopyranoside.It accumulated in rice shoots but not in roots. - Keywords: Oryza sativa; Gramineae; rice seedling; pantoyllactone glucoside; pantoic acid glucoside; new metabolite; NMR signal assignment; shoot to root distribution.
- Menegus, Faustino,Cattaruzza, Liliana,Ragg, Enzio,Scaglioni, Leonardo
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Read Online
- A new phenolic glycoside from Saprosma merrillii
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A new phenolic glycoside derivative, saproglucoside (1), along with five known phenolic glycoside derivatives (2–6) were isolated from the stems of Saprosma merrillii. The structure of the new compound 1 was determined by 1D and 2D NMR as well as by HRESIMS and hydrolysis. The inhibitory activities of all compounds against seven pathogenic bacteria and two cancer cell lines were evaluated.
- Zhou, Xue-Ming,Zheng, Cai-Juan,Song, Xiao-Ping,Chen, Guang-Ying,Cao, Yu-Hua,Huang, A-Qian,Su, Shao-Hui,Chen, Wen-Xing,Yang, Hui
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Read Online
- Copper-Mediated Synthesis of N-Acyl Vinylogous Carbamic Acids and Derivatives: Synthesis of the Antibiotic CJ-15,801
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(Equation presented) Copper(I)-mediated C-N bond formation has been employed to prepare both N-acyl vinylogous carbamic acids and ureas. The novel N-acyl vinylogous carbamic acid antibiotic, CJ-15,801, was synthesized using this methodology.
- Han, Chong,Shen, Ruichao,Su, Shun,Porco Jr., John A.
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Read Online
- Synthesis of (R)-pantoyl lactone by reduction of ketopantoate with formate and Proteus species
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(R)-Pantoyl lactone (ee > 97%) is obtained by stereoselective reduction of ketopantoate with resting cells of anaerobically grown Proteus vulgaris or Proteus mirabilis. Benzyl-viologen or safranine T have been used as electron mediators.
- Eck,Simon
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Read Online
- Optical Resolution of (R,S)-Pantolactone through Amide Formation
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The optical resolution of (RS)-pantolactone (1) is carried out through formation of diastereomeric amides.These are separated by a single hot washing with CH2Cl2 or CHCl3.The used asymmetric amine, (1R)-3-endo-aminoborneol (4), is readily accessible and can be recovered almost quantitatively after resolution.
- Fizet, Christian
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Read Online
- Synthesis of New Chiral Arene Ruthenium(II) Aminophosphinephosphinite Complexes and Use in Asymmetric Hydrogenation of an Activated Keto Compound
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The easy access to new arene-ruthenium(II)bisphoshine complexes bearing aminophosphine phosphinite ligands is presented.The complexes were prepared in two steps from 2 under mild conditions and were found to be effective precursors for the asymmetric hydrogenation of dihydro-4,4-dimethyl-2,3-furandione giving the corresponding pantolactone with up to 42percent enantiomeric excess.
- Hapiot, Frederic,Agbossou, Francine,Mortreux, Andre
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Read Online
- Industrial kinetic resolution ofd,l-pantolactone by an immobilized whole-cell biocatalyst
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Immobilized whole-cells ofPichia pastorisharboring recombinantd-lactonase were entrapped in calcium alginate gels and used as an efficient biocatalyst for catalytic kinetic resolution ofd,l-pantolactone. The immobilized whole-cell biocatalyst exhibited good catalytic stability, which was applied for stereospecific hydrolysis ofd-pantolactone for up to 56 repeated batch reactions without obvious loss in the catalytic activity and enantioselectivity.
- Huang, Liu-Nv,Luo, Wen-Fang,Tang, Yi-Bin,Yang, Liu,Zhang, Qiu-Hua
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p. 30373 - 30376
(2021/10/20)
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- NEW TRANSITION METAL CATALYST
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The present invention relates to specific transition metal catalysts and their use in chemical reactions.
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Page/Page column 10-11
(2021/05/15)
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- Synthesis method of chiral 2-hydroxy-1, 4-dicarbonyl compound and pantoic acid lactone
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The invention discloses a chiral 2-hydroxy-1, 4-dicarbonyl compound synthesized by catalyzing asymmetric Aldol reaction of fatty aldehyde and glyoxylate or fatty aldehyde and acylformaldehyde monohydrate by taking tetrapeptide TP or an enantiomer ent-TP thereof as a chiral catalyst, and application of a synthetic product. The method for synthesizing the chiral 2-hydroxy-1, 4-dicarbonyl compound through the asymmetric Aldol reaction is shown as a formula 1 and a formula 2. The asymmetric Aldol reaction of fatty aldehyde and glyoxylate or fatty aldehyde and acylformaldehyde monohydrate is catalyzed to synthesize the optically active 2-hydroxy-1, 4-dicarbonyl compound, then the optically active pantoic acid lactone can be further synthesized, and the method has advantages of mild reaction conditions, easy operation, low catalyst consumption, high yield and the like, and can synthesize the 2-hydroxy-1, 4-dicarbonyl compounds with two configurations by using tetrapeptide and the enantiomerthereof.
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Paragraph 0076-0078
(2020/11/10)
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- Catalyst Repurposing Sequential Catalysis by Harnessing Regenerated Prolinamide Organocatalysts as Transfer Hydrogenation Ligands
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A catalyst repurposing strategy based on a sequential aldol addition and transfer hydrogenation giving access to enantiomerically enriched α-hydroxy-γ-butyrolactones is described. The combination of a stereoselective, organocatalytic step, followed by an efficient catalytic aldehyde reduction induces an ensuing lactonization to provide enantioenriched butyrolactones from readily available starting materials. By capitalizing from the capacity of prolineamides to act as both an organocatalyst and a transfer hydrogenation ligand, catalyst repurposing allowed the development of an operationally simple, economic, and efficient sequential catalysis approach.
- Bourgeois, Frederic,Medlock, Jonathan A.,Bonrath, Werner,Sparr, Christof
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supporting information
p. 110 - 115
(2019/12/30)
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- Preparation method of hydroxyaldehyde and method for resolving optical isomer by using electrodialysis technology
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The present invention provides a process for preparing hydroxyaldehydes using an immobilized catalyst, wherein the immobilized catalyst comprises a solid support and a tertiary amine-based functionalgroup. The invention also provides a method for preparing a polyhydroxy alcohol compound and a polyhydroxy acid compound. The invention further provides a method for splitting the optical isomer fromthe raceme through electrodialysis.
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- Peptide-Catalyzed Highly Asymmetric Cross-Aldol Reaction of Aldehydes to Biomimetically Synthesize 1,4-Dicarbonyls
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β-Turn tetrapeptides were demonstrated to catalyze asymmetric aldol reaction of α-branched aldehydes and α-carbonyl aldehydes, i.e. glyoxylates and α-ketoaldehydes, to biomimetically synthesize acyclic all-carbon quaternary center-bearing 1,4-dicarbonyls in high yield and excellent enantioselectivity under mild conditions. The spatially restricted environment of the tetrapeptide warrants high enantioselectivity and yield with broad substrates. Using this protocol, (R)-pantolactone, the key intermediate of vitamin B5, was readily accessed in a practical, efficient, and environmentally benign process from inexpensive starting materials.
- Da, Chao-Shan,Du, Zhi-Hong,Qin, Wen-Juan,Tao, Bao-Xiu,Wang, Pei,Xu, Yan-Li,Yuan, Meng
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supporting information
(2020/06/08)
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- STEREOSELECTIVE SYNTHESIS OF ENANTIOMERICALLY-ENRICHED PANTOLACTONE
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The present invention relates stereoselective synthesis of enantiomerically enriched pantolactone.
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Page/Page column 15
(2019/12/25)
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- Wittig Rearrangements of Boron-Based Oxazolidinone Enolates
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[2,3]-Sigmatropic rearrangements (Wittig rearrangements) of α-alkoxy oxazolidinone enolates are described. Whereas alkali metal enolates fail, owing to facile deacylation, boron enolates generated from di-n-butylboron triflate and triethylamine rearranged in good yields and high selectivities with exceptions noted. IR and NMR spectroscopies show the boron is chelated by the α-alkoxy group rather than the more distal oxazolidinone carbonyl in the complex and enolate. The rearrangement product contains a boron alkoxide that remains unchelated by either carbonyl. Optimization was guided by density functional theory computations, suggesting that valine-derived oxazolidinones would be superior to the phenylalanine-derived analogues.
- Zhang, Zirong,Collum, David B.
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p. 10892 - 10900
(2019/09/07)
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- A D - (-) - pantoic acid lactone synthesis method
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The invention discloses a vitamin B5 synthesis of key intermediate D - (-) - pantoic acid lactone synthetic method, using (R)- (+) - α - phenethylamine hydrochloride or sulfate as a chiral reagent with a racemic pantoic acid alkali metal salt reaction, filtering to remove the inorganic salt, the mother liquor is concentrated to get pantoic acid - (R)- phenethylamine diastereomers salt, by the re-crystallization or beating of the diastereoisomer of the double salt method to carry out the purification, filtering to obtain (D)- pantoic acid - (R)- phenethylamine salt, and (L)- pantoic acid - (R)- phenethylamine salt is dissolved in the solvent, (D)- pantoic acid - (R)- phenethylamine salt and then subjected to a decomposition, acidified cyclization to obtain D - (-) - pantoic acid lactone.
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Paragraph 0068; 0072; 0073
(2019/03/24)
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- A thermoregulated phase-separable chiral Pt nanocatalyst for recyclable asymmetric hydrogenation of α-ketoesters
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The design and preparation of a chiral Pt nanocatalyst system possessing thermoregulated phase-separation property and its application in recyclable asymmetric hydrogenation of α-ketoesters are presented.
- Xue, Xiuru,Wang, Yanhua,Han, Fu-She
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supporting information
p. 3346 - 3349
(2017/03/22)
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- Porous Aerogels from Shape-Controlled Metal Nanoparticles Directly from Nonpolar Colloidal Solution
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Porous architectures of noble metal nanocrystals are promising for many catalytic as well as for fuel cell applications. Here we present the synthesis of porous, extremely lightweight aerogels of self-supported Pt nanocubes and nanospheres by direct destabilization from nonpolar colloidal solution using hydrazine monohydrate (N2H4·H2O) as gelation reagent. The template-free voluminous lyogels of the Pt nanocrystals are converted to macroscopic solid aerogel monoliths by supercritical drying. The aerogels from Pt nanocubes mostly exhibit (100) as the exposed crystal facets throughout the entire monolithic surface, while the aerogels from quasi-spherical Pt nanocrystals exhibit many crystal facets such as (111) and (100). Furthermore, the aerogels exhibit remarkably low densities of ～0.19 g cm-3 ± 0.038 g cm-3 (～0.9% of bulk Pt) and a specific surface area in the range of ～6400-7000 m2 mol-1. The nanocube gels show better catalytic performance than the nanosphere gels when employed for asymmetric hydrogenation reaction, which is exemplarily shown for 4,4-dimethyldihydrofuran-2,3-dione to d-/l-pantolactone conversion with an excess of 9% for the d-enantiomer. Owing to their high specific surface area and certain type of exposed crystal facets, Pt aerogels developed here are highly promising for possible future applications in facet selective catalytic reactions.
- Naskar, Suraj,Freytag, Axel,Deutsch, Jens,Wendt, Natalja,Behrens, Peter,K?ckritz, Angela,Bigall, Nadja C.
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p. 9208 - 9217
(2017/11/20)
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- A ionic liquid under the conditions of the asymmetric hydrogenation process of synthesizing method of D - pantolactone
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The invention relates to a method for synthesizing D-pantolactone through asymmetric hydrogenation under an ionic liquid condition. The method adopts a homogeneous-phase asymmetric hydrogenation system which is composed of a chiral catalyst formed by chiral diphosphine ligand and a rhodium catalyst, a polyether alkyl guanidine salt ionic liquid, ketopantolactone and benzene or toluene; and asymmetric hydrogenation is carried out a certain reaction temperature and hydrogen pressure. According to the method provided by the invention, the immobilization effect of the ionic liquid on the chiral catalyst is utilized, separation and circulation of the chiral catalyst are realized through simple liquid-liquid separation, and the chiral catalyst can be cyclically used for a plurality of times; and the conversion rate of pantolactone or stereoselectivity of D-pantolactone is not obviously decreased.
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Page/Page column 0021; 0027; 0030; 0033; 0036; 0039; 0042
(2017/08/24)
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- Missing Linker Defects in a Homochiral Metal-Organic Framework: Tuning the Chiral Separation Capacity
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Efficient chiral separation remains a very challenging task due to the identical physical and chemical properties of the enantiomers of a molecule. Enantiomers only behave differently from each other in the presence of other chiral species. Homochiral metal-organic frameworks (MOFs) have received much attention for their promising enantioseparation properties. However, there are still challenges to overcome in this field such as high enantiomeric separation. Structural defects play an important role in the properties of MOFs and can significantly change the pore architecture. In this work, we introduced missing linker defects into a homochiral metal-organic framework [Zn2(bdc)(l-lac)(dmf)] (ZnBLD; bdc = 1,4-benzenedicarboxylic acid, l-lac = l-lactic acid, dmf = N,N′-dimethylformamide) and observed an increase in enantiomeric excess for 1-phenylethanol of 35% with the defective frameworks. We adjusted the concentration of monocarboxylic acid ligand l-lactic acid by varying the ratio of Zn2+ to ligand from 0.5 to 0.85 mmol. Additionally, a defective framework was synthesized with propanoic acid as modulator. In order to elucidate the correlation between defects and enantiomeric excess, five characterization techniques (FTIR, TGA, 1H NMR, ICP, and PXRD) were employed. Full width at half-maximum analysis (fwhm) was performed on the powder X-ray diffraction traces and showed that the higher concentration of monocarboxylic acid MOFs were isostructural but suffered from increased fwhm values.
- Slater, Benjamin,Wang, Zeru,Jiang, Shanxue,Hill, Matthew R.,Ladewig, Bradley P.
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supporting information
p. 18322 - 18327
(2017/12/15)
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- Synthesis of vinylic iodides for incorporation into the C17-C27 fragment of bryostatins
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Vinylic iodides were identified as useful intermediates for the synthesis of the C17-C27 fragment of the bryostatins with control of the geometry of the exocyclic methoxycarbonylmethylene group. Following literature precedent, the Piers (E)-stereoselective addition of tributyltin hydride to an alkynoate followed by ester reduction and tin-iodine exchange gave vinylic iodides that could be used to form the C20-C21 bond of the bryostatins. Chelation controlled addition of lithiated 3-silyloxypropynes to 2-alkoxyaldehydes followed by reductive iodination was used to prepare vinylic iodides that could be used in the complementary assembly of the C21-C22 bond of the bryostatins. Initial studies of the synthesis of intermediates for metathesis studies using metal catalysed reactions of a vinylic iodide for C21-C22 bond formation were complicated by cyclisation reactions.
- Gregson, Thomas,Thomas, Eric J.
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p. 3316 - 3328
(2017/05/22)
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- Chiral imidazolidinone and proline-derived surface modifiers for the Pt-catalysed asymmetric hydrogenation of activated ketones
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A series of imidazolidinone and proline derivatives have been synthesised and tested with regard to their suitability for the chiral modification of platinum used for the asymmetric hydrogenation of activated ketones. Hydrogenations of ketopantolactone (KPL), methyl benzoylformate (MBF) and trifluoroacetophenone (TFAP) performed at low hydrogen pressures (1 and 10 bar) were selected as test reactions. With some of these synthethic modifiers, encouraging levels of enantioselectivity were achieved (up to 73.5:26.5 e.r.) without optimisation of the reaction conditions. Moreover, performance enhancement of l-proline derived-modifiers, as a consequence of molecular editing with fluorine, was found to be significant (OH → F, Δee up to 23%) contributing to the growing interest in modulating catalyst performance by fluorine introduction.
- Holland, Mareike C.,Meemken, Fabian,Baiker, Alfons,Gilmour, Ryan
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p. 335 - 345
(2015/02/19)
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- On-Column Reaction Set-Up for High-Throughput Screenings and Mechanistic Investigations
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A screening platform, which offers a high-throughput approach as well as an easy investigation of kinetic isotope effects, applicable to a wide range of reactions is presented. To illustrate the high potential of this approach, the asymmetric transfer hydrogenation of methyl benzoylformate with copper(II) bis(oxazoline) and Hantzsch ester was examined. Accordingly, the enantioselectivities of the reaction performed on-column in a microcapillary were comparable to standard reaction conditions, however, we were able achieve catalysis and analysis in a single step in less than 30 min. The throughput can be increased by simultaneous investigation of different substrates without increasing the overall analysis time. Use of di-deuterated Hantzsch ester allowed us to investigate the kinetic isotope effect of the transfer hydrogenation reaction only requiring a minute amount of the deuterated transfer hydrogenation reagent. Hence we were able to get further insights into the mechanism of the asymmetric transfer hydrogenation using Hantzsch ester as hydrogen source. The here presented technique is broadly applicable to study isotope effects on a very small scale, which is a rapid and an inexpensive alternative compared to conventional experiments.
- Stockinger, Skrollan,Troendlin, Johannes,Rominger, Frank,Trapp, Oliver
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p. 3513 - 3520
(2016/01/25)
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- Chemoenzymatic synthesis of vitamin B5-intermediate (R)-pantolactone via combined asymmetric organo- and biocatalysis
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The combination of an asymmetric organocatalytic aldol reaction with a subsequent biotransformation toward a "one-pot-like" process for the synthesis of (R)-pantolactone, which to date is industrially produced by a resolution process, is demonstrated. This process consists of an initial aldol reaction catalyzed by readily available l-histidine followed by biotransformation of the aldol adduct by an alcohol dehydrogenase without the need for intermediate isolation. Employing the industrially attractive starting material isobutanal, a chemoenzymatic three-step process without intermediate purification is established allowing the synthesis of (R)-pantolactone in an overall yield of 55% (three steps) and high enantiomeric excess of 95%.
- Heidlindemann, Marcel,Hammel, Matthias,Scheffler, Ulf,Mahrwald, Rainer,Hummel, Werner,Berkessel, Albrecht,Gr?ger, Harald
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p. 3387 - 3396
(2015/04/22)
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- Polystyrene-supported triphenylsilyl chloride for the silylation-based kinetic resolution of secondary alcohols
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A silyl chloride derivatized styrene polymer was employed in the silylation-based kinetic resolution of secondary alcohols for chromatography-free separation of alcohol enantiomers. Synthetically useful selectivity factors were obtained; furthermore, the polymer was recycled for use in a subsequent kinetic resolution, and it maintained its selectivity and integrity. Probability of precipitation: A silyl chloride polymer is employed in a kinetic resolution for the chromatography-free separation of enantiomers. After one enantiomer is covalently bonded to the polymer, it is precipitated from the solution for easy recovery. The polymer can also be recycled in subsequent kinetic resolutions without loss in selectivity.
- Akhani, Ravish K.,Clark, Robert W.,Yuan, Liang,Wang, Li,Tang, Chuanbing,Wiskur, Sheryl L.
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p. 1527 - 1530
(2015/05/27)
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- Monitoring surface processes during heterogeneous asymmetric hydrogenation of ketones on a chirally modified platinum catalyst by operando spectroscopy
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Surface processes occurring at the catalytic chiral surface of a cinchona-modified Pt catalyst during the asymmetric hydrogenation of activated ketones have been monitored for the first time using operando ATR-IR spectroscopy. Fundamental information about this catalytic system could be gained, including the chiral modification process of the catalyst, the surface interaction of reactant ketone with preadsorbed chiral modifier, the role of hydrogen as well as the influence of the product enantiomers in the catalytic cycle. The formation of a diastereomeric transient surface complex between ketone and chiral modifier was found to be related to the ketone consumption. Among the studied activated ketones, a correlation between stereoselection and the strength of the intermolecular hydrogen bond was identified. Dissociated hydrogen from the catalytic surface is found to play a crucial role in the formation of the diastereomeric surface complex.
- Meemken, Fabian,Hungerbuehler, Konrad,Baiker, Alfons
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supporting information
p. 8640 - 8644
(2014/08/18)
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- Modifier-substrate interactions of various types in the Orito reaction: Reversal of the enantioselection in the hydrogenation of ketopantolactone on Pt modified by β-isocinchonine and O-phenylcinchonidine
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The enantioselective hydrogenation of ketopantolactone (KPL) on Pt-alumina catalyst modified by β-isocinchonine (β-ICN) and O-phenylcinchonidine (PhOCD) in toluene, acetic acid and their mixtures under otherwise identical experimental conditions was studied. Reversal of the enantioselection was obtained dependent on the concentration of acetic acid (eemax = 17% (S) on Pt-PhOCD and 50% (R) on Pt-β-ICN, respectively). The possible role in enantioselection of adducts forming in the reaction mixture and the stability of PhOCD under the conditions of the hydrogenation was investigated by ESI-MS. The results of the nonlinear phenomenon measurements on β-ICN + PhOCD mixtures suggest that the intermediate surface complexes β-ICN-KPL and PhOCD-KPL responsible for the opposite enantioselection include different types of interactions and the enantioselection is directed by the competition between these interactions.
- Szollosi, Gy?rgy,Balázsik, Katalin,Bucsi, Imre,Bartók, Tibor,Bartók, Mihály
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- Iron-catalyzed hydrogenation for the in situ regeneration of an NAD(P)H model: Biomimetic reduction of α-Keto-/α-iminoesters
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Two irons for a smoother finish: An NAD(P)H model was regenerated readily in situ by iron-catalyzed reduction with molecular hydrogen. The subsequent biomimetic reduction of α-keto-/ α-iminoesters proceeded smoothly in the presence of an iron-based Lewis acid (LA) to provide α-hydroxyesters and amino acid esters in good to excellent yields (see scheme; NAD(P) +=nicotinamide adenine dinucleotide (phosphate), TM=transition metal). Copyright
- Lu, Liang-Qiu,Li, Yuehui,Junge, Kathrin,Beller, Matthias
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supporting information
p. 8382 - 8386
(2013/09/02)
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- Chiral rh/sio2 catalysts for enantioselective Hydrogenation reactions. the role of (S,S)-dipamp as chiral modifier and Stabilizer on metallic nanoparticles Synthesis
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Rhodium nanoparticles were successfully stabilized by the (S,S)-1,2-ethanediylbis[(2-ethoxyphenyl)phenylphosphine] ((S,S)-DIPAMP) deposited on SiO2 prepared by a facile reduction and impregnation method. The chiral catalysts obtained were efficient for the enantioselective hydrogenation reactions of prochiral compounds. The catalysts synthesized from [Rh(?-OMe)(COD)]2 in the presence of different amounts of a ligand used as chiral stabilizer, showed good metal dispersion. As shown by TEM, the metal particle size ranged between 1 and 2 nm using stabilizer and 9.1 nm was achieved without chiral ligand. Other techniques were used to characterize the chiral catalysts such as X-ray diffraction (XRD), electron diffraction, thermogravimetric analysis (TGA) and N2 adsorption-desorption isotherms. (S,S)-DIPAMP was used as the stabilizer of metal particles to prevent growing and agglomeration, and it also acts as chiral modifier inducing enantioselectivity in the asymmetric hydrogenation of 3,4-hexanodione (HD), ethyl pyruvate (EP), ketopantolactone (KP), and acetophenone (AP). Under specific conditions such as 25 C, 40 bar of H2 and substrate/Rh=100, 1%Rh-(S,S)-DIPAMP/SiO2 chiral catalysts showed excellent catalytic performance with conversion and enantiomeric excess (ee) levels up to 99% and 54% respectively.
- Mella, Claudio,Avila, Mauricio,Sanchez, Ariel,Marzialetti, Teresita,Reyes, Patricio,Ruiz, Doris
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p. 2125 - 2130
(2014/03/21)
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- Silylation-based kinetic resolution of α-hydroxy lactones and lactams
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A silylation-based kinetic resolution has been developed for α-hydroxy lactones and lactams employing the chiral isothiourea catalyst (-)-benzotetramisole and triphenylsilyl chloride as the silyl source. The system is more selective for lactones than lactams, and selectivity factors up to 100 can be achieved utilizing commercially available reagents.
- Clark, Robert W.,Deaton, T. Maxwell,Zhang, Yan,Moore, Maggie I.,Wiskur, Sheryl L.
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supporting information
p. 6132 - 6135
(2014/01/17)
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- Kinetic resolution of racemic 2-hydroxy-γ-butyrolactones by asymmetric esterification using diphenylacetic acid with pivalic anhydride and a chiral acyl-transfer catalyst
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Various optically active 2-hydroxy-γ-butyrolactone derivatives are produced via the kinetic resolution of racemic 2-hydroxy-γ-butyrolactones with diphenylacetic acid using pivalic anhydride and (R)-benzotetramisole ((R)-BTM), a chiral acyl-transfer catalyst. Importantly, the substrate scope of this novel protocol is fairly broad (12 examples, s-value; up to over 1000). In addition, we succeeded in disclosing the reaction mechanism to afford high enantioselectivity using theoretical calculations and expounded on the substituent effects at the C-3 positions in 2-hydroxylactones.
- Nakata, Kenya,Gotoh, Kouya,Ono, Keisuke,Futami, Kengo,Shiina, Isamu
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supporting information
p. 1170 - 1173
(2013/05/21)
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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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- NANOSTRUCTURED METALS
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The invention relates to a nanoparticulate material comprising long ultrathin metal nanowires, and to processes for making it. The nanoparticulate material may be used as a catalyst and, in the presence of a chiral modifier, can catalyse enantioselective reactions.
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Page/Page column 12
(2012/06/16)
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- Enantiodivergent syntheses of pantolactone and pantothenic acid from d -mannitol
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Efficient synthetic routes to both the enantiomers of pantolactone and pantothenic acid have been developed starting from d-mannitol-based d-glyceraldehyde acetonide through its conversion into a protected pantoic acid intermediate followed by either cyclization or amide bond formation with a -amino ester, and subsequent appropriate deprotection. Georg Thieme Verlag Stuttgart . New York.
- Sanyal, Ishita,Barman, Piyalideb,Banerjee, Asishkumar
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experimental part
p. 1102 - 1108
(2012/05/04)
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- Histidine-catalyzed asymmetric aldol addition of enolizable aldehydes: Insights into its mechanism
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Extensive studies of asymmetric cross-aldol addition between enolizable aldehydes are described and provide a deeper insight into histidine-catalyzed aldol additions. In particular, aspects of enantio- as well as diastereoselectivity of these reactions are discussed. Rules and predictions of configurative outcome are explained by using different transition-state models. These discussions are confirmed by extensive computations.
- Scheffler, Ulf,Mahrwald, Rainer
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experimental part
p. 2310 - 2330
(2012/05/20)
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- New phenomenon in competitive hydrogenation of binary mixtures of activated ketones over unmodified and cinchonidine-modified Pt/alumina catalyst
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Competitive hydrogenations of eight binary mixtures of ethyl pyruvate (EP), methyl benzoylformate (MBF), ketopantolactone (KPL), pyruvic aldehyde dimethyl acetal (PA) and trifluoroacetophenone (TFAP) on platinum/alumina catalysts unmodified (racemic hydrogenation) and modified by cinchonidine (chiral hydrogenation) were studied under the experimental conditions of the Orito reaction. Reaction rates of chiral and racemic hydrogenations were determined and relative adsorption coefficients were calculated. In the competitive chiral hydrogenation of EP + MBF, EP + TFAP and KPL + MBF binary mixtures a new phenomenon was observed: namely the EP and KPL are hydrogenated faster than MBF and TFAP, whereas in racemic one the MBF and TFAP are hydrogenated faster than EP or KPL. Effects of the activated ketones structure on their reactivity and the stability of the surface complexes are discussed. It was found that differences in rate enhancement are caused by the differences both in the adsorptivity and in the reactivity of adsorbed substrates and adsorbed intermediate complexes.
- Balázsik, Katalin,Szori, Kornél,Szollosi, Gy?rgy,Bartók, Mihály
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experimental part
p. 1410 - 1414
(2012/07/31)
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- Enantioselective hydrogenation of α-ketoesters over alkaloid-modified platinum nanowires
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A green process for enantioselective hydrogenation of α-ketoesters over cinchona alkaloid-modified platinum (Pt) nanowires has been developed. Pt nanowires with a diameter of ～1 nm were successfully synthesized, and used for the asymmetric hydrogenation of α-ketoesters in the presence of cinchona alkaloids under a low pressure at room temperature in water. Quantitative yields and excellent enantioselectivity of up to 78% were achieved. The catalyst along with the modifier was recycled multiple times without any significant loss in activity or selectivity. To our knowledge, such a catalyst system is unprecedented for asymmetric hydrogenation of α-ketoesters. The Royal Society of Chemistry.
- Erathodiyil, Nandanan,Gu, Hongwei,Shao, Huilin,Jiang, Jiang,Ying, Jackie Y.
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experimental part
p. 3070 - 3074
(2011/12/16)
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- Influence of support acid-base properties on the platinum-catalyzed enantioselective hydrogenation of activated ketones
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The influence of support acidity and basicity was investigated in the enantioselective hydrogenation of methyl benzoylformate and ketopantolactone on cinchonidine-modified Pt/Al2O3-SiO2 and Pt/Al2O3-Cs2O catalysts. Two series of flame-derived 4.7 wt.% Pt/Al2O3 catalysts in which the acid-base properties of the support were systematically varied by introducing SiO2 (5-80 wt.%) or Cs2O (0.25-10 wt.%) were applied. Addition of SiO2 improved the enantioselectivity with a maximum at 30 wt.%. Enantioselectivity correlated well with the acidity of the catalysts characterized by TPD of NH3 and with the selectivity to hydrogenolysis of methyl cyclohexyl ketone to ethylcyclohexane. On the contrary, doping with Cs was detrimental to the formation of the (R)-alcohols and the drop in enantioselectivity could unambiguously be attributed to the basicity of the support characterized by TPD of CO2. The critical impact of support ionicity on the electronic properties of Pt, and thus on the adsorption and interaction of the reaction components on the metal surface, was further proven by the good correlation between the enantioselectivities of all catalysts and the ratio of CO adsorbed in bridged to linear (B/L) geometry. The practical importance of our findings is demonstrated by the best ee (94 ± 0.5%) achieved so far in the industrially relevant hydrogenation of ketopantolactone to (R)-pantolactone.
- Hoxha, Fatos,Schimmoeller, Bjoern,Cakl, Zdenek,Urakawa, Atsushi,Mallat, Tamas,Pratsinis, Sotiris E.,Baiker, Alfons
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experimental part
p. 115 - 124
(2010/06/12)
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- Ferrocenyl-aryl based trans-chelating diphosphine ligands: Synthesis, molecular structure and application in enantioselective hydrogenation
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Potentially trans-chelating diphosphine ligands based on a ferrocenyl-aryl backbone were synthesised in a four-step sequence and the molecular structures in the solid state of two representatives were determined by X-ray diffraction. High throughput screening of these ligands in rhodium-, ruthenium- and iridium-mediated hydrogenations of a variety of alkenes and ketones revealed that these ligands can deliver high enantioselectivity for alkenes (up to 98% ee) but are less selective when ketones are used as the substrates. The coordination behaviour of one ligand in its square planar palladium and platinum dichloride complexes was studied by 31P NMR and only trans-chelated complexes, together with oligomeric by-products, were observed. Reaction with the (p-cymene)ruthenium dichloride dimer, [RuCl2(pcymene)] 2, resulted in a mixture of diastereomeric complexes.
- Schuecker, Raffael,Mereiter, Kurt,Spindler, Felix,Weissensteiner, Walter
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scheme or table
p. 1063 - 1074
(2010/06/17)
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- Substrate-controlled adsorption of cinchonidine during enantioselective hydrogenation on platinum
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It is commonly accepted that the origin of enantioselection on chirally modified metals is the control of the adsorption and reactivity of the substrate by the chiral environment of the modifier. Here, we provide the first experimental evidence to a mutual process, namely, that the substrate controls the adsorption and reactivity of cinchonidine (CD) on the metal surface. Our approach is to follow the competing hydrogenation of the quinoline ring, the anchoring moiety of CD, in the presence or absence of an activated ketone substrate. On Pt/Al2O3 in the weakly interacting solvent toluene, CD (and 10,11-dihydro-CD) favors a C(4′) - pro(S) adsorption geometry and saturation of the heteroaromatic ring gives 1′,2′, 3′,4′(S),10,11-hexahydro-CD {(S)-CDH6} in excess. Addition of methyl benzoylformate, ketopantolactone, or ethyl pyruvate inverts the dominant conformation of CD to C(4′) - pro(R) as indicated by the major product (R)-CDH6, and even the rate is higher by about 30% ("inverse ligand acceleration"). Acetic acid that interacts strongly with CD exerts a similar effect on quinoline hydrogenation. In contrast, the product α-hydroxyester interacts weakly with CD, decelerates the hydrogenation of the quinoline ring and the de of CDH6 depends on the chirality of the α-hydroxyester. These unexpected observations provide a fundamentally new insight into the complexity of the surface conformation of CD and the origin of high enantioselectivity on cinchona-modified Pt.
- Schmidt, Erik,Mallat, Tamas,Baiker, Alfons
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experimental part
p. 140 - 150
(2010/09/09)
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- Enantioselective ketoester reductions in water: A comparison between microorganism-and ruthenium-catalyzed reactions
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In the search for green chemistry methods for the enantioselective reduction of ketoesters Saccharomyces cerevisiae-and ruthenium-catalyzed reactions in water have been investigated. The highest enantiomeric excesses for the reduction of α-and β-ketoesters have been obtained by S. cerevisiae. Chiral ruthenium catalysts are active for the reduction of all ketoesters with low to moderate enantioselectivities depending on the nature of the substrate and ligand. Interestingly, for several substrates both enantiomers of the hydroxyesters have been obtained according either to the catalytic method or to the structure of the ligand.
- Zeror, Saoussen,Collin, Jacqueline,Fiaud, Jean-Claude,Zouioueche, Louisa Aribi
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experimental part
p. 1211 - 1215
(2010/10/20)
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- A novel class of fluorinated cinchona alkaloids as surface modifiers for the enantioselective heterogeneous hydrogenation of α-ketoesters
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Novel C-9 fluorinated cinchona alkaloid derivatives were investigated as chiral surface modifiers for the platinum-catalyzed asymmetric heterogeneous hydrogenation of α-ketoesters. Enantioselectivities approaching those observed with the parent alkaloids were obtained, and direct comparison with conformationally labile deoxycinchonidine confirmed that the C-9 fluorine atom is important for performance. In this study, the 9-fluoro derivative of cinchonidine was shown to effect the reduction of ketopantolactone to (R)-pantolactone in quantitative yield with good levels of enantioinduction (57% ee) providing preliminary validation for this novel class of surface modifiers.
- Mondelli, Cecilia,Bucher, Christoph,Baiker, Alfons,Gilmour, Ryan
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experimental part
p. 87 - 91
(2010/11/17)
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- Chiral mixed secondary phosphine-oxide-phosphines: High-performing and easily accessible ligands for asymmetric hydrogenation
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P&O: Combining secondary phosphine oxides (SPOs) with phosphines leads to highly effective chiral bidentate ligands for transition-metal-based catalysts. JoSPOphos and TerSPOphos are readily accessible from inexpensive starting materials. The steric and electronic properties of these modular ligands can be easily tuned. In the asymmetric hydrogenation of functionalized alkenes, their rhodium complexes reacted to give enantioselectivities of up to 99% ee and turnover frequencies of up to 20000 h-1 Chemical equation Presented
- Landert, Heidi,Spindler, Felix,Wyss, Adrian,Blaser, Hans-Ulrich,Pugin, Benoit,Ribourduoille, Yann,Gschwend, Bjoern,Ramalingam, Balamurugan,Pfaltz, Andreas
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experimental part
p. 6873 - 6876
(2010/12/19)
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- A mild and chemoselective method for the deprotection of tert-butyldimethylsilyl (TBDMS) ethers using iron(III) tosylate as a catalyst
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The most common method for the deprotection of TBDMS ethers utilizes stoichiometric amounts of tetrabutylammonium fluoride, n-Bu4N+F- (TBAF), which is highly corrosive and toxic. We have developed a mild and chemoselective method for the deprotection of TBDMS, TES, and TIPS ethers using iron(III) tosylate as a catalyst. Phenolic TBDMS ethers, TBDPS ethers and the BOC group are not affected under these conditions. Iron(III) tosylate is an inexpensive, commercially available, and non-corrosive reagent.
- Bothwell, Jason M.,Angeles, Veronica V.,Carolan, James P.,Olson, Margaret E.,Mohan, Ram S.
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supporting information; experimental part
p. 1056 - 1058
(2010/04/05)
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- Toward preparative resolution of chiral alcohols by an organic chemical method
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Asymmetric alcohols were resolved as 1-α-O-alkyl-2,3-unsaturated hexosides. After separation of diastereoisomers, the auxiliary and the enantiomeric alcohol were recovered by transglycosidation. Potential applications include resolution of labile secondary and tertiary alcohols, difficult by existing techniques, and enhancement of ees of chiral alcohols produced enzymatically or by synthetic catalytic methods. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010.
- Malic, Nino,Moorhoff, Cornelis,Sage, Valerie,Saylik, Dilek,Teoh, Euneace,Scott, Janet L.,Strauss, Christopher R.
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supporting information; experimental part
p. 398 - 402
(2010/06/14)
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- Magnetically separable Pt catalyst for asymmetric hydrogenation
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A magnetic Pt/SiO2/Fe3O4 catalyst consisting of chirally modified platinum supported on silica coated magnetite nanoparticles was prepared using an easy synthetic route and successfully applied for the enantioselective hydrogenation of various activated ketones. The magnetic catalyst modified with cinchonidine showed a catalytic performance (activity, enantioselectivity) in the asymmetric hydrogenation of various activated ketones in toluene comparable to the best known Pt/alumina catalyst used for these reactions. The novel catalyst can be easily separated from the reaction solution by applying an external magnetic field and recycled several times with almost complete retention of activity and enantioselectivity.
- Panella, Barbara,Vargas, Angelo,Baiker, Alfons
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scheme or table
p. 88 - 93
(2009/04/10)
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- Shape-selective enantioselective hydrogenation on Pt nanoparticles
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The structure sensitivity of enantioselective hydrogenations on chirally modified metals was investigated using Pt nanoparticles of different shapes. All three samples had an average particle size of 10 nm, but the fraction of dominantly cubic, cubooctahedral, and octahedral particles varied with decreasing {100} and increasing {111} faces in the same order. In the absence of chiral modifier the hydrogenation of ethyl pyruvate was independent of the shape of the Pt nanoparticles; variation of the specific reaction rates did not exceed the experimental error on all self-prepared catalysts and on a commercial Pt/Al2O3 used as reference. Addition of cinchonidine or quinine induced a significant rate enhancement by a factor of 4-15, and the rate was always higher with quinine. Also, 72-92% ees were achieved, and the reaction was shape selective: both the rate and the ee increased with increasing Pt{111}/Pt{100} ratio. A similar correlation in the hydrogenation of ketopantolactone confirmed that decarbonylation or aldol-type side reactions of ethyl pyruvate were not the reason for structure sensitivity. A combined catalytic and theoretical study revealed that the probable origin of the particle shape dependency of enantioselective hydrogenation is the adsorption behavior of the cinchona alkaloid. DFT studies of cinchonidine interacting with Pt(100) and Pt(111) terraces indicated a remarkably stronger interaction on the former crystallographic face by ca. 155 kJ/mol. The higher adsorption strength on Pt(100) was corroborated experimentally by the faster hydrogenation of the homoaromatic ring of the alkaloid, which fragment interacts the strongest with Pt during its adsorption. Thus, an ideal catalyst for the hydrogenation of activated ketones contains dominantly Pt{111} terraces, which crystallographic face is more active and affords higher enantioselectivity, combined with the higher stability of the modifier.
- Schmidt, Erik,Vargas, Angelo,Mallat, Tamas,Baiker, Alfons
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scheme or table
p. 12358 - 12367
(2009/12/27)
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- Additional data to the origin of rate enhancement in the enantioselective hydrogenation of activated ketones over cinchonidine modified platinum catalyst
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Kinetic behaviour of different substrates such as purified ethyl pyruvate, dimer containing (20%) ethyl pyruvate, methylbenzoyl formate and ketopantolactone was investigated in both racemic and enantioselective hydrogenation over Pt/Al2O3 catalysts. Upon introducing the chiral modifier by injection under condition of racemic hydrogenation an immediate increase in reaction rate is observed in the case of all substrates. Consequently, significant rate enhancement (RE) was obtained in the case of all substrates. The RE increased in the following order: ketopantolactone ethyl pyruvate methylbenzoyl formate. This order does not follow the ability of substrates to be involved in various undesired side reactions with the formation of poisonous surface residues. Accordingly, results obtained in this study confirm that the RE must be an intrinsic feature of the asymmetric hydrogenation of activated ketones in the presence of cinchona alkaloids. However, our results also indicate that the poisoning effect by organic residues originated from ethyl pyruvate cannot be neglected.
- Talas, Emilia,Margitfalvi, Jozsef L.,Egyed, Orsolya
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experimental part
p. 191 - 198
(2011/03/17)
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- Asymmetric histidine-catalyzed cross-aldol reactions of enolizable aldehydes: Access to defined configured quaternary stereogenic centers
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(Chemical Equation Presented) A histidine-catalyzed asymmetric direct cross-aldol reaction of enolizable aldehydes is described. In contrast to proline, histidine is able to clearly differentiate the reactivity of various aldehydes. In addition, this appr
- Markert, Morris,Scheffler, Ulf,Mahrwald, Rainer
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supporting information; experimental part
p. 16642 - 16643
(2010/02/16)
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- New data to the origin of rate enhancement on the Pt-cinchona catalyzed enantioselective hydrogenation of activated ketones using continuous-flow fixed-bed reactor system
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A study on the origin of rate enhancement (RE) in the enantioselective heterogeneous catalytic hydrogenation of methyl benzoylformate (MBF), ketopantolactone (KPL) and pyruvic aldehyde dimethyl acetal (PA) under the Orito reaction conditions over Pt catalyst modified with parent cinchona alkaloids, as compared to the unmodified catalyst is presented. The hydrogenations were carried out in continuous-flow fixed-bed reactor system over 20-100 mg Pt/Al2O3 catalyst in 1 mL min-1 flow of toluene/acetic acid 9/1 solvent mixture under 40-80 bar H2 pressure, at 283 or 293 K using 0.044-2 mM modifier concentration and 45 mM substrate concentration. Our results obtained using racemic hydrogenations followed by three changes of the chiral modifier (on the same catalyst) supported the so-called "ligand acceleration" phenomenon in the enantioselective hydrogenation of activated ketones such as MBF, KPL and PA. In our opinion, RE produced by the first modifier added after racemic hydrogenation can also be explained by the purifying effect of the cinchona. REs observed following further exchanges of modifiers are indicative of the intrinsic character of the phenomenon. This research suggested that the origin of enantiodifferentiation and rate enhancement is the same, namely, both may be traced back-probably in different ways-to the role of the intermediate complexes of the hydrogenation, to its formation and transformation, which in turn depends on numerous factors.
- Szoellosi, Gyoergy,Cserenyi, Szabolcs,Fueloep, Ferenc,Bartok, Mihaly
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experimental part
p. 245 - 253
(2009/03/11)
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- DIPHOSPHINES AND METAL COMPLEXES
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Compounds of the formulae (I) and (II), or a mixture of these enantiomers, where R'1 is C1-C4-alkyl and n is 0, 1 or 2; R1 is C1-C8-alkyl, C2-C8-alken-1-yl, -CH2-OR or - CH2-NR5R6; the two radicals R2 are identical or different and are each hydrogen or a monovalent radical of an electrophilic organic compound, or one R2 has this meaning and the other R2 is hydrogen; sec-phos is a secondary phosphino group; R is C1-C8- alkyl and R5 and R6 are each C1-C6-alkyl or R5 and R6 together form tetramethylene, pentamethylene or 3-oxa-1,5-pentylene, are ligands for metal complexes which can be used as valuable homogeneous catalysts for asymmetric syntheses. The compounds are obtained by a novel process in which 3,3'-metallated 1,1'-di-R1-2,2'- dibromoferrocenes are firstly reacted with sec-phos halide, the bromine atoms are then replaced by lithium and the substituent R2 is subsequently introduced by reaction with an electrophilic organic compound or with water.
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Page/Page column 41-42
(2008/06/13)
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- DIPHOSPHINE LIGANDS
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Compounds of the formulae I and Ia in the form of mixtures of diastereomers or pure diastereomers, (I), (Ia), where R1 is a hydrogen atom or C1-C4-alkyl and R'1 is C1-C4-alkyl; X1 and X2 are each, independently of one another, a sec-phosphino group; T is C6-C20-arylene or C4-C18- heteroarylene having heteroatoms selected from the group consisting of O, S, -N= and N(C1-C4-alkyl); v is 0 or an integer from 1 to 4; X1 is bound in the ortho position relative to the T-C* bond; Q is vinyl, methyl, ethyl, -CH2-OR, -CH2-N(C1-C4-alkyl)2 or a C- or S-bonded chiral group which directs metals of metallation reagents into the ortho position; R is hydrogen, a silyl radical or an aliphatic, cycloaliphatic, aromatic or aromatic-aliphatic hydrocarbon radical which has from 1 to 18 carbon atoms and is unsubstituted or substituted by C1-C4-alkyl, C1-C4-alkoxy, F or CF3; are ligands for metal complexes as homogeneous catalyst in asymmetric syntheses.
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Page/Page column 40-41
(2008/06/13)
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- Hydrogenation of α-ketoesters and ketopantolactone on rhodium modified by cinchona and isocinchona alkaloids
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Various Rh catalysts and cinchona-type modifiers were tested in the hydrogenation of ethyl pyruvate, ethyl 3-methyl-2-oxobutyrate, and ketopantolactone. The experiments were completed with the study of the nonlinear behavior of modifier mixtures, and UV and NMR analysis of hydrogenation of the modifiers. From this study, β-isocinchonine emerged as an outstanding modifier of Rh/Al2O3 that gave up to 68% ee in the hydrogenation of ketopantolactone to (R)-pantolactone in toluene, at full conversion and without the formation of any detectable byproducts. Careful prereduction of the catalyst at elevated temperature is critical to achieve good enantioselectivity. The loss of ee, or even the formation of the opposite enantiomer in small excess, in protic solvents is attributed to the formation of solvent-substrate and solvent-modifier complexes that disturb the enantioselection on cinchona-modified Rh. In the weakly interacting solvent toluene, only a few ppm of β-isocinchonine related to ketopantolactone was sufficient to induce enantioselection. This unique feature of the conformationally rigid isocinchona alkaloid is attributed to the stronger adsorption on Rh and weaker adsorption on Al2O3, and to the higher resistance against hydrogenation of its quinoline ring "anchoring moiety" compared with the corresponding values of cinchonine and cinchonidine.
- Hoxha, Fatos,Mallat, Tamas,Baiker, Alfons
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- Role of guiding groups in cinchona-modified platinum for controlling the sense of enantiodifferentiation in the hydrogenation of ketones
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Systematic structural variations of cinchona-type modifiers used in the platinum-catalyzed hydrogenation of ketones give insight into the adsorption mode of the modifier and its interaction with the substrate on the platinum surface under truly in situ conditions. The performance of a new modifier, O-(2-pyridyl)-cinchonidine, is compared to that of O-phenyl-cinchonidine and cinchonidine (CD). In the hydrogenation of ethyl pyruvate, ketopantolactone, and 2-methoxyacetophenone, CD gives the (R)-alcohol in excess. Introduction of the bulky O-phenyl group favors the (S)-enantiomer, whereas upon replacement of the phenyl by a 2-pyridyl group the (R)-alcohol is again the major product. This finding is particularly striking, because the two ether groups have virtually identical van der Waals volumes. A catalytic study including the nonlinear behavior of modifier mixtures, and attenuated total reflection infrared spectroscopy of the solid-liquid interface in the presence of hydrogen, revealed the adsorption mode and strength of the modifiers on Pt. Theoretical calculations of the modifier-substrate interactions offered a feasible explanation for the different role of the bulky ether groups: repulsion by the phenoxy and attraction by the 2-pyridoxy groups. Simulation of the interaction of o-pyridoxy-CD with ketopantolactone on a model Pt surface suggests that formation of two N-H-O-type H-bonds-involving the quinuclidine and pyridine N atoms, and the two keto-carbonyls in the substrate-controls the adsorption of the substrate during hydrogen uptake. This mechanistic study demonstrates the potential of insertion of suitable substituents into CD and their influence on adsorption and stereocontrol on the platinum surface.
- Hoxha, Fatos,Koenigsmann, Lucia,Vargas, Angelo,Ferri, Davide,Mallat, Tamas,Baiker, Alfons
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p. 10582 - 10590
(2008/02/13)
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- Calcium pantothenate. Part 2. Optimisation of oxynitrilase-catalysed asymmetric hydrocyanation of 3-hydroxy-2,2-dimethylaldehyde: Synthesis of (R)-pantolactone
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The synthesis of (R)-pantolactone via oxynitrilase-catalysed asymmetric hydrocyanation of 3-hydroxy-2,2-dimethylaldehyde has been investigated. (R)-Oxynitrilases from almonds as well as from apple and plum kernels were employed as catalysts in the form of defatted meal. A number of factors influencing the hydrocyanation process have been studied and the conditions optimised using statistical methods. (R)-Pantolactone with 74% yield and 30% ee has been synthesised.
- Synoradzki, Ludwik,Rowicki, Tomasz,Wlostowski, Marek
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p. 103 - 108
(2012/12/21)
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- A density functional study of the hydrogenation of ketones catalysed by neutral rhodium-diphosphane complexes
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The potential energy profile of RhI-catalysed hydrogenation of ketones has been computed for the simple model system [Rh{H3POCH 2CH2N(H)PH3}(Cl)] using DFT calculations. The general sequence of the catalytic cycle involves coordination of the carbonyl derivative to the neutral RhI complex followed by oxidative addition of molecular hydrogen providing rhodium dihydride intermediates. The latter are converted into alkoxy hydrides by a migratory insertion reaction. Reductive elimination of the alcohol and substitution of the latter by the incoming substrate completes the catalytic cycle. Intermediates and transition states of all catalytic steps have been located. Two isomeric derivatives bearing the model substrate have been found for the [Rh{H3POCH2CH 2N(H)PH3}(Cl)(H2CO)] complex. Eight diastereomeric pathways have been followed for the cis addition of molecular hydrogen to [Rh{H3POCH2CH2N(H)PH 3}(Cl)(H2CO)] leading to eight distinct isomeric dihydride intermediates. Four dihydride complexes can be considered as the more accessible compounds. The site preference for migratory insertion and transition states discriminates the main path of the catalytic reaction. Migratory insertion to form the alkoxy hydride constitute the turn over limiting step of the process. The potential energy profile has been found to be smooth without excessive activation barriers. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Agbossou-Niedercorn, Francine,Paul, Jean-Francois
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p. 4338 - 4348
(2008/03/27)
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