- Towards a General Understanding of Carbonyl-Stabilised Ammonium Ylide-Mediated Epoxidation Reactions
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The key factors for carbonyl-stabilised ammonium ylide-mediated epoxidation reactions were systematically investigated by experimental and computational means and the hereby obtained energy profiles provide explanations for the observed experimental results. In addition, we were able to identify the first tertiary amine-based chiral auxiliary that allows for high enantioselectivities and high yields for such epoxidation reactions.
- Novacek, Johanna,Roiser, Lukas,Zielke, Katharina,Robiette, Rapha?l,Waser, Mario
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supporting information
p. 11422 - 11428
(2016/08/03)
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- Catalytic asymmetric aldol-type reaction of zinc enolate equivalent of amides
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Treatment of phenyl isocyanate with bis(iodozincio)methane gave a zinciomethylenated product, which acts as an amide-enoate equivalent. It did not react with an aldehyde efficiently, but gave the corresponding adduct in good yield in the presence of an aminoalcohol. Use of a catalytic amount of chiral aminoalcohol led the process to the catalytic asymmetric Aldol-type reaction.
- Haraguchi, Ryosuke,Matsubara, Seijiro
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supporting information
p. 3378 - 3380
(2013/07/26)
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- Dual catalyst system for asymmetric alternating copolymerization of carbon dioxide and cyclohexene oxide with chiral aluminum complexes: Lewis base as catalyst activator and lewis acid as monomer activator
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Optically active aluminum complexes such as Schiff base, binuclear β-ketoiminate, and bisprolinol complexes were found to promote asymmetric alternating copolymerizations of carbon dioxide and cyclohexene oxide. The aluminum Schiff base complexes-tetraethylammonium acetate afforded isotactic poly(cyclohexene carbonate)s with low enantioselectivities. Lewis bases having two coordinating sites were utilized to enhance activity and selectivity based on the binuclear structure of the aluminum β-ketoiminate clarified by X-ray crystallography. [2gAlMe]2-bulky bisimidazole produced the alternating copolymer with high enantioselectivity (62% ee). The polymerization is considered to preferentially proceed at more crowded, enantioselective site owing to coordination of bulky Lewis bases to aluminums in less enantioselective sites. 32AlMe-2-picoline also exhibited a high enantioselectivity (67% ee). Methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) was applied to perform faster and more enantioselective copolymerizations at low temperature (82% ee). The asymmetric copolymerizations were found to be significantly dependent on size of epoxide, temperature, and kind/amount of activators.
- Nishioka, Kiyoshi,Goto, Hidetoshi,Sugimoto, Hiroshi
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p. 8172 - 8192
(2013/01/15)
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- Enantioselective michael addition to α,β-Unsaturated aldehydes: Combinatorial catalyst preparation and screening, reaction optimization and mechanistic studies
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Shortcut to chiral catalysts: An efficient combinatorial strategy based on back reaction screening by ESI-MS allows rapid evaluation of organocatalysis for the asymmetric Michael addition to α,β-unsaturated aldehydes (see scheme). An unexpected nonlinear effect has been observed in this reaction, resulting from a double nucleophilic-electrophilic activation mechanism involving two catalyst molecules "Chemical Equation Presented"
- Fleischer, Ivana,Pfaltz, Andreas
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supporting information; experimental part
p. 95 - 99
(2010/03/26)
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- Synthesis and crystal structure of the chiral β-amino alcohol (S)-α,α-diphenyl-2-pyrrolidine methanol
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Optically pure (S)-α,α-diphenyl-2-pyrrolidine methanol was prepared from L-proline via protection of the amino group, reaction with the Grignard reagents and deprotection of the amino-protected groups in 54.4% yield. The synthetic conditions to prepare (S)-α,α-diphenyl-2- pyrrolidinemethanol were optimised. Single crystal X-ray diffraction analysis revealed that the molecular structure of the compound was enantiomerically pure. The crystals are orthorhombic, space group P2(1)2(1)2(1), with unit cell parameters a = 8.9000(18) A, b = 9.2405(18) A, c = 16.671(3) A, V = 1371.1(5) A3, Dx = 1.227 g cm -3, Z =4, T = 113(2)K, F(000) = 628, R1 = 0.0335 and wR2 = 0.0707. The absolute structure parameter was -1.6(17).
- Zhang, Yu-Mei,Liu, Peng,Zhang, Hong-Li
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experimental part
p. 610 - 612
(2011/03/18)
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- Asymmetric reduction of ketimines with trichlorosilane employing an imidazole derived organocatalyst
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Organocatalysts for the asymmetric reduction of ketimines are presented that function well at low catalyst loadings providing chiral amines in good yield and enantioselectivity, the latter appearing to be independent of the ketimine substrate geometry.
- Gautier, Franois-Moana,Jones, Simon,Martin, Stephen J.
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supporting information; experimental part
p. 229 - 231
(2009/03/11)
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- Amine-catalyzed cyclizations of tethered α,β-unsaturated carbonyl compounds
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(Chemical Equation Presented) Various linked unsaturated dicarbonyl compounds were cyclized by dienamine catalysis. Depending on the substrates, alternative pathways were observed, leading to mono- and bicyclic products in high enantiomeric excess.
- De Figueiredo, Renata Marcia,Froehlich, Roland,Christmann, Mathias
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p. 1450 - 1453
(2008/12/22)
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- Design and evaluation of inclusion resolutions, based on readily available host compounds
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Resolution of enantiomers through selective crystallisation of diastereomeric inclusion compounds can extend the scope of traditional racemate resolution beyond salt forming compounds. To assess the practical value of this approach the literature was carefully screened and promising results were checked. Also an extensive range of new inclusion hosts suitable for resolution processes, derived from simple hydroxy- and amino acids were prepared and tested. Several techniques, including the Dutch Resolution approach utilizing mixtures of resolving agents, were applied. Over 70 potential resolving agents were tested in combinations with 34 racemates (over 100 racemates if literature results are included). Reproducibility of literature results was found to be problematic. Also the number of successful new resolutions found was very limited: only two efficient resolutions out of 1200 combinations of racemate and resolving agent tested in over 10.000 experiments! Crystal studies of representative combinations of resolving agents and inclusion compounds revealed some of the causes for the low rate of success in inclusion resolution. Compared to diastereomeric salts, the absence of strong electrostatic interactions substantially reduces the probability of forming crystals including both components. Molecular structure features allowing formation of intricate intramolecular and intermolecular H-bond networks were found to be responsible for inclusion crystal formation, and for the quality of the ensuing resolution through selective diastereomer crystallisation, in the successful cases. Whereas diastereomeric salt resolution continues to be of scientific and industrial interest, inclusion resolution should be viewed as of very limited scope; useful in specific instances, but lacking the wide applicability of classical resolution. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
- Mueller, Simona,Afraz, Marcel Cyrus,De Gelder, Rene,Ariaans, Gerry J. A.,Kaptein, Bernard,Broxterman, Quirinus B.,Bruggink, Alle
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p. 1082 - 1096
(2007/10/03)
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- Diastereospecific synthesis of (S,S)-2-substituted-4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes
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(S,S)-2-substituted-4,4-diphenyl-3,1-oxazabicyclo[3.3.0]octanes were synthesized from aldehydes and (S)-2-(hydroxy-diphenylmethyl)pyrrolidine, which was obtained from L-proline. The stereospecificity of the condensation reaction was discussed. The stereo-structure of each product in the condensation was found to be in agreement with the product of a similar reaction of (S)-phenylglycinol with an aldehyde. The method was found to be useful for the synthesis of cis 3,1-oxazabicyclo[3.3.0]octane derivatives.
- Zuo, Gang,Zhang, Qihan,Xu, Jiaxi
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- Asymmetric carbonyl reduction with borane catalyzed by chiral phosphinamides derived from L-amino acid
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Two types of chiral phosphinamide catalysts 3a-d and 4a-c were prepared from L-phenylalanine and L-proline, respectively. Their applications in the asymmetric borane reduction of prochiral ketones were investigated. The chiral secondary alcohols were obtained with excellent chemical yields and moderate to high enantiomeric excesses.
- Li, Kangying,Zhou, Zhenghong,Wang, Lixin,Chen, Qifa,Zhao, Guofeng,Zhou, Qilin,Tang, Chuchi
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- Lanthanide Lewis acid-mediated enantioselective conjugate radical additions
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(figure presented) Lanthanide triflates along with proline-derived ligands have been found to be efficient catalysts for enantioselective conjugate addition of nucleophilic radicals to enoates. N-Acyl oxazolidinones, when used as achiral additives, gave meaningful enhancements in the ees for the product.
- Sibi, Mukund P.,Manyem, Shankar
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p. 2929 - 2932
(2007/10/03)
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- An L-proline-based β-amino tertiary thiol: Synthesis and use as a catalyst in the enantioselective addition of diethylzinc to aldehydes
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Two independent routes for the synthesis of the novel β-amino tertiary thiol 1 have been developed. Utilisation of this thiol in the enantioselective addition of diethylzinc to aldehydes provided (R)-secondary alcohols in ees of up to 64%.
- Gibson, Colin L.
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p. 1551 - 1561
(2007/10/03)
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- Convenient method for the synthesis of chiral α,α-diphenyl-2-pyrrolidinemethanol
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A simplified, convenient synthesis of chiral α,α-diphenyl-2-pyrrolidine-methanol involving one step N-and O-protection of S-proline using ethylchloroformate followed by Grignard addition-alkaline hydrolysis (KOH/CH3OH) is described.
- Kanth, J. V. Bhaskar,Periasamy, Mariappan
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p. 5127 - 5132
(2007/10/02)
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