- Linking BINOL: C2-symmetric ligands for investigations on asymmetric catalysis
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The synthesis of new C2-symmetric chiral ligands consisting of two binaphthol units linked by a short bridge is described. These ligands can be used for investigating catalytic asymmetric reactions which utilize BINOL or related ligands as was
- Vogl, Erasmus M.,Matsunaga, Shigeki,Kanai, Motomu,Iida, Takehiko,Shibasaki, Masakatsu
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- Highly regioselective ring opening of oxiranes with phenoxides in the presence of β-cyclodextrin in water
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Highly regioselective ring opening of oxiranes to β-hydroxy ethers with phenoxides has been achieved in impressive yields in the presence of β-cyclodextrin as catalyst and water as solvent.
- Surendra,Krishnaveni, N. Srilakshmi,Nageswar,Rao, K. Rama
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p. 4994 - 4995
(2007/10/03)
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- Linked-BINOL: An Approach towards Practical Asymmetric Multifunctional Catalysis
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The development and application of a novel linked-1,1′-binaphthol (linked-BINOL) as an approach towards practical asymmetric multifunctional catalysis is described. Linked-BINOL was first designed to increase the stability of a Ga-Li-BINOL complex against
- Matsunaga, Shigeki,Ohshima, Takashi,Shibasaki, Masakatsu
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- Conformationally controlled intramolecular charge transfer complexes
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Trans-1-acceptor-2-donor-substituted cyclohexanes (1), as well as their 4- (or 5-)methyl-substituted homologues (2), have been prepared and are shown to form intramolecular charge-transfer (donor-acceptor) complexes. These weak complexes are turned on and off by the chair-chair interconversion of the cyclohexane ring. The CT absorptions have been measured and the equilibrium constants for the ring reversal have been determined by UV/vis spectroscopy at 298 K, as well as by NMR spectroscopy at two temperatures: at 183 K, by direct comparison of signals due to the two chair conformations, and at 300 K, by comparison of calculated and measured widths of the α-proton signals. The Gibbs free energies assigned to the donor-acceptor interactions range between 0 and -1 kcal mol-1. A crystal structure of one of the complexes (1b) confirms the intramolecular donor-acceptor alignment and interaction. The regioisomers of the methyl-substituted complexes were characterized by NOE interaction between the methyl and an α-proton cis to it.
- Kost, Daniel,Peor, Na'Ama,Sod-Moriah, Gali,Sharabi, Yifat,Durocher, David T.,Raban, Morton
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p. 6938 - 6943
(2007/10/03)
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- Catalytic enantioselective meso-epoxide ring opening reaction with phenolic oxygen nucleophile promoted by gallium heterobimetallic multifunctional complexes
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The catalytic enantioselective meso-epoxide ring opening reaction with phenolic oxygen nucleophile (4-methoxyphenol) is described for the first time herein. This reaction was first found to be promoted by (R)-GaLB (Ga = gallium, L = lithium, B = (R)-BINOL), giving a variety of epoxide opening products in good to high ee (67-93% ee). However, chemical yield was only modest (yield 31-75%), despite the use of more than 20 mol % GaLB. This was due to the undesired ligand exchange between BINOL and 4-methoxyphenol, which resulted in the decomplexation of GaLB. Application of various known chiral ligands such as 6,6'-bis((triethylsilyl)ethynyl)-BINOL and H8-BINOL were examined, but satisfactory results were not obtained. To overcome this problem a novel linked-BINOL containing coordinative oxygen atom in the linker has been developed. By linking two BINOL units in GaLB, the stability of the Ga-complex was greatly improved. Using 3-10 mol % (R,R)-Ga-Li-linked- BINOL complex, a variety of epoxide opening reactions were found to proceed smoothly, affording products in analogous ee (66-96% ee) and in much higher yield (yield 67-94%) compared to (R)-GaLB. The structure of the LiCl free Ga- Li-linked-BINOL complex was elucidated by X-ray analysis. This is the first X-ray data for an asymmetric catalyst containing gallium. The possible mechanism of the entitled reaction is also discussed, based on the X-ray structure of the Ga-complex.
- Matsunaga,Das,Roels,Vogl,Yamamoto,Iida,Yamaguchi,Shibasaki
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p. 2252 - 2260
(2007/10/03)
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- A Convenient Enantioselective Synthesis of trans-2-Aryloxycyclohexan-1-ols Using Pig Liver Acetone Powder (PLAP) as Biocatalyst
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Pig liver acetone powder (PLAP) has been used as a biocatalyst for enantioselective hydrolysis of racemic trans-1-acetoxy-2-aryloxycyclohexanes to produce the resulting (R,R)-2-aryloxycyclohexan-1-ols upto >99percent enantiomeric purities. (R,R)-Selectivity in this hydrolysis of racemic trans-2-aryloxycyclohexyl acetates was explained on the basis of Jones' three dimensional active site-model.
- Basavaiah, Deevi,Krishna, Peddinti Rama,Bharathi, Tirumala K.
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p. 439 - 454
(2007/10/02)
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- Conformationally Controlled Intramolecular Charge Transfer Complexes
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The formation of intramolecular charge transfer complexes between an electron-poor 3,5-dinitrobenzoyl fragment and electron-rich 4-substituted phenoxy fragments can be controlled by restricting the conformation of substituted cyclohexanes containing these
- Raban, Morton,Durocher, David T.
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p. 5125 - 5128
(2007/10/02)
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