52126-90-6Relevant academic research and scientific papers
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%.
Enantioselective catalysis. Part 147. A Rh(cod) complex with the chiral [Pt2S2{(-)diop}2] ligand
Brunner, Henri,Weber, Matthias,Zabel, Manfred
, p. 6 - 12 (2003)
The trinuclear complex [Pt2Rh(μ3-S)2 {(-)-diop}2(cod)]Cl (3) was synthesized starting from the chiral "ligand" [Pt2(μ-S)2{(-)-diop}] (2) and [Rh(cod)Cl]2, and characterized by X-ray crystallography. Compound 3 was used as a catalyst in the hydrosilylation of acetophenone with diphenylsilane and in the hydrogenation of ketopantolactone.
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.
Rhodium(I) bis(aminophosphane) complexes as catalysts for asymmetric hydrogenation of activated ketones
Roucoux, Alain,Suisse, Isabelle,Devocelle, Marc,Carpentier, Jean-Francois,Agbossou, Francine,Mortreux, Andre
, p. 379 - 382 (1996)
The synthesis of new homochiral bis(aminophosphanes) (BAMP) 1-5 and their application in rhodium based asymmetric hydrogenation of dihydro-4,4-dimethyl-2,3-furandione 12 and N-benzylbenzoylformamide 14 are presented. Under mild conditions, the hydrogenations led to high enantiomeric excesses (up to 87% and 75% ere respectively for both substrates).
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.
Determination of Enantiomeric Excess and Degree of Hydrogenation in the Enantioselective Hydrogenation of Ketopantolactone
Brunner, H.,Forster, St.
, p. 659 - 663 (1992)
A new gas chromatographic method for the simultaneous determination of the degree of hydrogenation of ketopantolactone and the enantiomeric excess of pantolactone does not require any derivatisation. Keywords.Ketopantolactone; Enantioselective hydrogenation; Catalyses with phospines; Gaschromatography on Chirasil-L-Val
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.
Inversion of enantioselectivity in the hydrogenation of ketopantolactone on platinum modified by ether derivatives of cinchonidine
Diezi, Simon,Szabo, Andras,Mallat, Tamas,Baiker, Alfons
, p. 2573 - 2577 (2003)
Asymmetric hydrogenation of ketopantolactone was studied on a 5 wt% Pt/Al2O3 catalyst in the presence of cinchonidine and its O-methyl, -ethyl, -phenyl and -trimethylsilyl derivatives. Inversion of enantioselectivity with the latter two bulky substituents proved that in the enantiodifferentiating step cinchonidine adsorbs via the quinoline ring lying approximately parallel to the Pt surface. The striking nonlinear effect observed with cinchonidine-O-phenyl-cinchonidine mixtures is attributed to differences in the adsorption strength and geometry of the modifiers.
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.
Continuous enantioselective hydrogenation of activated ketones
Kuenzle,Hess,Mallat,Baiker
, p. 239 - 241 (1999)
Heterogeneous enantioselective hydrogenation of activated ketones in a fixed-bed reactor was achieved by continuous feeding of minute amounts of chiral modifier to the reactant stream. The potential of this concept is illustrated using the hydrogenation of ketopantolactone and ethyl pyruvate over Pt/alumina modified by cinchonidine. Production rates and enantiomeric excesses (ee) achieved without optimization at room temperature and 40 bar were 94 mmol/gcat·h and 83.4% ee for ketopantolactone, and 23 mmol/gcat·h and 89.9% ee for ethyl pyruvate. Transient measurements by stopping of the cinchonidine flux indicate that continuous feeding of the modifier in ppm concentration is essential.
