- Stereoselective substitution of α-aminoalkylferrocenes with diorganozincs. A fast synthesis of new chiral FERRIPHOS ligands for asymmetric catalysis
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A direct stereoselective substitution of α-aminoalkylferrocenes of type 3 with organozinc reagents provides chiral ferrocenes which can be converted to the FERRIPHOS ligands of type 1 in a one-pot procedure. These FERRIPHOS ligands have been used for the Rh-catalyzed asymmetric hydrogenation of an enol acetate with 94.9% ee.
- Lotz, Matthias,Ireland, Tania,Almena Perea, Juan J.,Knochel, Paul
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- Stereoregularity of poly(lactic acid) and their model compounds as studied by NMR and quantum chemical calculations
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In order to understand the origin of the tacticity splitting in the NMR spectra of poly(lactic acid), monomer and dimer model compounds were synthesized and their 1H and 13C NMR chemical shifts were observed. Two stable conformations were obtained from Ramachandran map calculated as a function of the internal rotation angles for the monomer model using Gaussian 09 calculations. Four preferred conformations were selected and optimized for each dimer model. The conformations of neighboring residues were energetically interdependent. The 1H and 13C chemical shifts for dimer model compounds were calculated by averaging the occurrence probabilities obtained from the optimized conformational energies and the calculated chemical shift of each conformation. It was confirmed that the solvent effect on the tacticity-dependent relative chemical shifts was small from the NMR experiments of the model compound observed in different solvents, dimethyl sulfoxide, chloroform, and chloroform/carbon tetrachloride (20/80 v/v) mixture. Good agreement between observed and calculated chemical shifts was obtained for the relative chemical shifts of isotactic and syndiotactic 1H and 13C NMR peaks of the dimer model compounds. The observed tacticity splitting of poly(lactic acid) at the diad level was rationalized on the basis of these chemical shift calculations.
- Suganuma, Koto,Horiuchi, Ken,Matsuda, Hironori,Cheng,Aoki, Akihiro,Asakura, Tetsuo
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- Ruthenium- and lipase-catalyzed inversion of l-lactates
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The ruthenium catalyzed inversion of l-lactic acid esters in the presence of Novozym 435 is described which give d-lactates in good yields and with >99% ee. 2012 Elsevier Ltd. All rights reserved.
- Shuklov, Ivan A.,Dubrovina, Natalia V.,Schulze, Joachim,Tietz, Wolfgang,Kühlein, Klaus,B?rner, Armin
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- New ferrocenyl ligands with broad applications in asymmetric catalysis
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A new synthetic approach allows the synthesis of taniaphos- analogous ligands 2 with inverted α configuration (Sp, αS). This new class of ferrocenyl ligands displays excellent enantioselectivity and enhanced reactivity in several types of asymmetric hydrogenation reactions (e.g. 1→).
- Lotz, Matthias,Polborn, Kurt,Knochel, Paul
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- Ruthenium Tetroxide Catalyzed Oxidations of Aromatic and Heteroaromatic Rings
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In order to determine the absolute stereochemistry of several aromatic and heterocyclic alcohols, it was necessary to oxidize protected derivatives to mono- and dicarboxylic acids of established configuration.A recently improved procedure utilizing aqueous sodium periodate in the presence of catalytic quantities of ruthenium tetroxide has been used to oxidize a number of compounds to the desired acids in satisfactory yield.The oxidations of (-)-α-(2-thienyl)ethyl acetate, (-)-α-(2-furyl)ethyl acetate, and several substituted α-phenylethyl acetates to (S)-O-acetyllactic acid have been used to confirm their absolute stereochemistries.However, α-(2-pyridyl)ethyl acetate was inert, and α-(3-phenanthryl)ethyl acetate yielded a complex reaction mixture.Prior conversion of the pyridine derivative to its N-oxide and of the substituted phenanthrene to the 9,10-dibromo derivative permitted each compound to be degraded to O-acetyllactic acid.
- Kasai, Masaji,Ziffer, Herman
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- The assignment of the configuration for α-hydroxy acid esters using a CEC strategy
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A simple and efficient 1H NMR method for determining the absolute configuration of chiral α-hydroxy acid esters using a competing enantioselective conversion (CEC) strategy was developed. The α-hydroxy acid esters were acylated in the presence
- Peng, Ruixue,Lin, Lili,Zhang, Yuheng,Wu, Wangbin,Lu, Yan,Liu, Xiaohua,Feng, Xiaoming
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p. 5258 - 5262
(2016/07/06)
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- Dynamic kinetic resolution of α-substituted β-ketoesters catalyzed by Baeyer-Villiger monooxygenases: Access to enantiopure α-hydroxy esters
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BVMOs make a play: The dynamic kinetic resolution of racemic α-alkyl-β-ketoesters was performed through a selective Baeyer-Villiger oxidation employing different Baeyer-Villiger monooxygenases (BVMOs) in mild basic media. The product diesters were obtained with excellent yields and enantioselectivities, and used as precursors for optically active α-hydroxy esters.
- Rioz-Martínez, Ana,Cuetos, Aníbal,Rodríguez, Cristina,De Gonzalo, Gonzalo,Lavandera, Iván,Fraaije, Marco W.,Gotor, Vicente
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supporting information; experimental part
p. 8387 - 8390
(2011/10/09)
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- Efficient and highly enantioselective Rh-catalyzed hydrogenations of unsaturated lactate precursors with chiral bisphospholanes as ligands
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The current invention relates to an asymmetric hydrogenation process of prochiral α-acetoxy acrylic acid esters for the synthesis of enantiopure lactic acid esters by the use of Rh-catalyzed bisphospholane ligands in a unit using an autoclave, and a distillation process. In a first process step α-acetoxy acrylic acid esters (1) and Rh-catalyzed bisphospholane ligands are dissolved in a solvent as substrate solution, in a second process step the substrate solution is added to an evacuated autoclave, in a third process step H2 is fed into the autoclave, in a fourth process step the asymmetric hydrogenation reaction is carried out under H2-pressure, and in a fifth process step the reaction product composed of solvent, lactic acid esters (2), remaining α-acetoxy acrylic acid esters (1) and Rh-catalyzed bisphospholane ligands is transferred into a distillation unit, is being distilled and enantiopure lactic acid esters (2) are separated from solvent, α-acetoxy acrylic acid esters (1) and Rh-catalyzed bisphospholane ligands. In this process propylene carbonate is used as solvent in the first process step, and the distillation is performed in a Spaltrohrkolonne in the fifth process step.
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Page/Page column 6
(2010/01/29)
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- Synthesis of a new class of chiral 1,5-diphosphanylferrocene ligands and their use in enantioselective hydrogenation
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A new family of ferrocenylphosphane ligands has been prepared. Their flexible synthesis allows many structural modifications. The asymmetric induction of these ligands was examined in the hydrogenation of functionalized C=C, C=O, and C=N bonds. The enantioselectivity of the reaction was strongly dependent on the substituent R at the position α to the ferrocene moiety. In many cases, both enantiomeric β-hydroxyesters of the reduction product can be obtained by simply replacing a dimethylamino group in the ligand with a methyl group.
- Ireland, Tania,Tappe, Katja,Grossheimann, Gabi,Knochel, Paul
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p. 843 - 852
(2007/10/03)
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