52126-90-6Relevant articles and documents
Chemoenzymatic synthesis of vitamin B5-intermediate (R)-pantolactone via combined asymmetric organo- and biocatalysis
Heidlindemann, Marcel,Hammel, Matthias,Scheffler, Ulf,Mahrwald, Rainer,Hummel, Werner,Berkessel, Albrecht,Gr?ger, Harald
, p. 3387 - 3396 (2015)
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%.
A novel class of fluorinated cinchona alkaloids as surface modifiers for the enantioselective heterogeneous hydrogenation of α-ketoesters
Mondelli, Cecilia,Bucher, Christoph,Baiker, Alfons,Gilmour, Ryan
, p. 87 - 91 (2010)
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.
A density functional study of the hydrogenation of ketones catalysed by neutral rhodium-diphosphane complexes
Agbossou-Niedercorn, Francine,Paul, Jean-Francois
, p. 4338 - 4348 (2006)
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.
Fine tuning the "chiral sites"; on solid enantioselective catalysts
Diezi, Simon,Mallat, Tamas,Szabo, Andras,Baiker, Alfons
, p. 162 - 173 (2004)
A fundamental point in the mechanism of enantioselective hydrogenation over chirally modified metals is the nature of "chiral sites" developed by adsorption of the modifier on the metal surface. Despite considerable effort toward unraveling the adsorption mode of the modifier by surface science techniques, most of these spectroscopic measurements were done under conditions relatively far from those met under real reaction conditions. Here we applied a truly in situ "synthetic" approach, the systematic variation of the structure of the chiral modifier used for enantioselective hydrogenation over 5 wt% Pt/Al2O3. We have synthesized various O-alkyl, -aryl, and -silyl derivatives of cinchonidine (CD) and tested them in the enantioselective hydrogenation of ethyl pyruvate, ketopantolactone, 4,4,4-trifluoroacetoacetate, and 1,1,1-trifluoro-2,4-diketopentane. With increasing bulkiness of the ether group, the ee gradually decreased or even the opposite enantiomer formed in excess (up to 53% ee). We propose that the increasing bulkiness of the ether group prevents the strong, π-bonded adsorption of the quinoline ring of CD close to parallel to the Pt surface. In this tilted position the modifier adsorbs weaker via the quinoline N and also the position of the interacting function, the quinuclidine N, is shifted. This shift results in a different shape and size of the "chiral pocket" available for adsorption of the activated ketone substrate. The weaker adsorption of the bulky ether derivatives was proved by UV-vis spectroscopy and by the nonlinear behavior of modifier mixtures. The tilted adsorption mode was corroborated by the lower hydrogenation rate of the quinoline ring of the ether derivatives, relative to that of CD.
Palladium and rhodium complexes with planar-chiral carborane ligands
Brunner, Henri,Apfelbacher, Andreas,Zabel, Manfred
, p. 917 - 924 (2001)
Base degradation of the prochiral 1-diphenylphosphanyl-2-phenyl-1,2-dicarba-closo-dodecaborane (1) affords the planar-chiral 7-diphenylphosphanyl-8-phenyl-7,8-dicarba-nido-undecaborate anion (2). Resolution of the racemic anion carried out using a well-established procedure, gave the internally diastereomeric palladium complexes 3R-R and 3R-S. These complexes were separated by fractional crystallization. A single-crystal X-ray analysis of 3R-R established the exo-nido bonding of the carborane ligand via the phosphorus atom and the adjacent BH group, and the (R) configuration of the carborane ligand. The enantiomerically pure anions of 2 were liberated from the diastereomerically pure palladium complexes 3R-R and 3R-S, respectively, by subsequent addition of HCl and NaCN. The exo-nido-rhodium-carborane complexes 4-8 were prepared by heating 2eR or 2eS with [Rh(COD)Cl]2 and/or a chiral chelating phosphane, such as DIOP and BINAP, under reflux. The chiral complexes were tested under enantioselective catalysis conditions such as hydrogenation of acetamidocinnamic acid, hydrogenation of ketopantolactone, and hydrosilylation of acetophenone.
Porous Aerogels from Shape-Controlled Metal Nanoparticles Directly from Nonpolar Colloidal Solution
Naskar, Suraj,Freytag, Axel,Deutsch, Jens,Wendt, Natalja,Behrens, Peter,K?ckritz, Angela,Bigall, Nadja C.
, p. 9208 - 9217 (2017)
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.
Synthetic modifiers for platinum in the enantioselective hydrogenation of ketopantolactone: A test for the mechanistic models of ketone hydrogenation
Orglmeister, Elisabeth,Mallat, Tamas,Baiker, Alfons
, p. 78 - 86 (2005)
Various derivatives of (R)-1-(1-naphthyl)-ethylamine have been synthesized and tested as chiral modifiers of Pt/alumina in the enantioselective hydrogenation of ketopantolactone. The best modifiers (ee up to 79%) possess an ester function in the α-position to the amino group. The modifiers performed far better in AcOH than in toluene, indicating that protonation of the N atom is important in enantioselection. The striking non-linear behaviour of modifier mixtures with cinchonine indicates that the alkaloid adsorbs much stronger on Pt than the naphthylethylamine derivatives. Two mechanistic models are proposed for interpretation of the results, involving an N-H-O or N +-H-O bond between the amine-type modifier and the keto carbonyl O atom of ketopantolactone, in apolar and protic media, respectively. In both cases the H atom originates from the modifier and not from the substrate ("half-hydrogenated-state"). The higher ee achieved in acidic medium is attributed to the better proton donor ability of the protonated amine modifiers. The models are applicable also to the hydrogenation of ethyl pyruvate.
Hydrogenation of α-ketoesters and ketopantolactone on rhodium modified by cinchona and isocinchona alkaloids
Hoxha, Fatos,Mallat, Tamas,Baiker, Alfons
, p. 11 - 19 (2007)
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.
Catalytic asymmetric hydrogenation of activated keto compounds by some homogeneous and silica-supported di(μ-carboxylato)bis(aminophosphinephosphinite)dirhodium complexes
Carpentier,Agbossou,Mortreux
, p. 39 - 42 (1995)
New soluble and silica-supported rhodium complexes have been synthesized and tested as catalyst precursors for the enantioselective hydrogenation of α-ketoesters and an α-ketoamide. The homogeneous catalysts have been found to be efficient in terms of activity and asymmetric induction (up to 94% enantiomeric excess). On the other hand, the heterogenized systems exhibited lower performances and were gradually deactivated.
Enantioselective Hydrogenation of Ketopantolactone: Effect of Stereospecific Product Crystallization during Reaction
Schuerch,Kuenzle,Mallat,Baiker
, p. 569 - 571 (1998)
The hydrogenation of ketopantolactone over cinchonidine-modified Pt/alumina has been reinvestigated, focussing on the misleading effect of stereospecific product crystallization during reaction at medium to high conversions. The appropriate choice of reaction conditions afforded 91.6 ± 0.5% ee to R-(-)-pantolactone.
Role of guiding groups in cinchona-modified platinum for controlling the sense of enantiodifferentiation in the hydrogenation of ketones
Hoxha, Fatos,Koenigsmann, Lucia,Vargas, Angelo,Ferri, Davide,Mallat, Tamas,Baiker, Alfons
, p. 10582 - 10590 (2007)
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.
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
Szollosi, Gy?rgy,Balázsik, Katalin,Bucsi, Imre,Bartók, Tibor,Bartók, Mihály
, p. 81 - 85 (2013)
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.
Preparation method of hydroxyaldehyde and method for resolving optical isomer by using electrodialysis technology
-
, (2020/12/15)
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.
Catalyst Repurposing Sequential Catalysis by Harnessing Regenerated Prolinamide Organocatalysts as Transfer Hydrogenation Ligands
Bourgeois, Frederic,Medlock, Jonathan A.,Bonrath, Werner,Sparr, Christof
supporting information, p. 110 - 115 (2019/12/30)
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.
