- Electrostatic repulsion and hydrogen-bonding interactions in a simple N-aryl-L-valinamide organocatalyst control the stereoselectivity in asymmetric aldol reactions
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A novel stereocontrol method for asymmetric aldol reactions of aldehydes with ketones is described. The stereoselectivity of the products is controlled by the electrostatic repulsion and hydrogen-bonding interactions of an N-aryl-L-valinamide catalyst. Th
- Tanimura, Yuya,Yasunaga, Kenji,Ishimaru, Kaori
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p. 6535 - 6539
(2013/11/06)
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- Reversal of selectivity in acetate aldol reactions of N-acetyl-(S)-4- isopropyl-1-[(R)-1-phenylethyl]imidazolidin-2-one
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Synergistic effects of the exo- and endocyclic chiral centers of an imidazolidinone-based auxiliary were investigated in the perspective of acetate aldol reactions. The reversal in diastereoselectivity was accomplished by lithium and titanium enolate reactions, which proceed through proposed open and closed transitions states, respectively. The aldol adducts were used in the stereoselective synthesis of fluoxetine.
- Khatik, Gopal L.,Kumar, Varun,Nair, Vipin A.
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p. 2442 - 2445
(2012/07/03)
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- Chiral calcium catalysts for asymmetric hydroamination/cyclisation
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Calcium complexes supported by chiral 1,2-diamines have been shown to be efficient catalysts for the asymmetric hydroamination of amino-olefin substrates; the calcium complexes [Ca(NNR){N(SiMe3) 2}(THF)] (R = tBu, iPr, Ph, 4-C 6H4F) give enantioselectivities of up to 26% which marks a significant increase based upon literature precedence. The structure of [Ca(NNPh){N(SiMe3)2}(py)] has been computed with density functional methods.
- Wixey, James S.,Ward, Benjamin D.
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p. 5449 - 5451
(2011/06/28)
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- Methods and compositions for treating amyloid-related diseases
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Methods, compounds, pharmaceutical compositions and kits are described for treating or preventing amyloid-related disease.
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Page/Page column 136
(2010/11/24)
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- Synthesis of an enantiomerically pure resorcinarene with pendant L-valine residues and its attachment to a polysiloxane (Chirasil-Calix)
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The synthesis of a new enantiomerically pure resorcinarene by reaction of all resorcinic groups with N-bromoacetyl-L-valine-tert-butyl-amide is described. The chiral macrocyclic product was chemically bonded to a poly(hydro)dimethylsiloxane by hydrosilylation using a platinum catalyst. The resulting chiral polysiloxane Chirasil-Calix can be used as chiral stationary phase (CSP) in capillary gas chromatography.
- Ruderisch, Alexander,Pfeiffer, Jens,Schurig, Volker
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p. 2025 - 2030
(2007/10/03)
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- Peptide-titanium complex as catalyst for asymmetric addition of hydrogen cyanide to aldehyde
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The complex of titanium ethoxide and an acyclic dipeptide ester whose terminal amino group is modified to a salicylal-type Schiff base catalyzes the asymmetric addition of hydrogen cyanide to aldehydes with high enantioselectivity. In the reaction of benzaldehyde and hydrogen cyanide, (R)-mandelonitrile is obtained with an enantiomeric excess of 90% when N-((2-hydroxy-1-naphthyl)methylene)-(S)-valyl-(S)-tryptophan methyl ester is employed. In place of the dipeptide, the amide derivatives of an amino acid modified by substituted salicylaldehyde, such as N-(3,5-dibromosalicylidene)-(S)-valine piperidide, exhibit an entirely opposite stereoselectivity to yield S-cyanohydrins with optical purities up to 97% ee. This novel peptide-titanium complex, therefore, enables us to afford optically active cyanohydrins of both absolute configurations by using natural S-amino acids as chiral auxiliaries.
- Nitta, Hideaki,Yu, Donghai,Kudo, Masanobu,Mori, Atsunori,Inoue, Shohei
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p. 7969 - 7975
(2007/10/02)
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