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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 58 (1993), S. 6814-6817 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-1948
    Keywords: Asymmetric catalysis ; Hydrogenations ; Hemilabile ligand ; Hydroxy phosphane ; Methoxy phosphane ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The influence of two threo-arranged methoxy or hydroxy groups as hemilabile ligands in seven-membered (diphosphane)RhI chelates upon the asymmetric hydrogenation is studied. In comparison to the parent complex based on 1,4-bis(diphenylphosphanyl)butane (DPPB) a lowering of the reaction rate is caused by the hemilabile ligands. The catalyst bearing the hydroxy groups gives significantly higher enantioselectivities than the corresponding methoxy complex (by ca. 35 % ee). X-ray structural analysis reveals that the oxygen atom of the hydroxy group is by 0.9 Å closer to the metal center than that of the methyl ether. 31P-NMR studies give evidence that the dihydroxy diphosphane ligand binds at low temperature exclusively in the η3-coordination mode, whereas for the dimethoxy complex also an η2-coordinated isomer can be found. These differences in complexation could be responsible for the superior enantioselectivities achieved with this and other hydroxy catalysts.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1707-1712 
    ISSN: 0009-2940
    Keywords: Amphiphiles ; Carbohydrates ; Fluoro-D-glucoses ; Fluoro Sugars ; Liquid crystals ; Mesogens ; Scyllitol derivatives ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Liquid Crystalline Compounds, 79[1a].-Amphiphilic and Mesogenic Carbohydrates, V[1b].-Amphiphilic Fluoroglucose and Fluoroscyllitol DerivativesIn order to look at the influence of the OH-F substitution in the cyclic, hydrophilic section (head group) of amphiphilic sugars and of scyllitol derivatives on their liquid crystalline properties for the first time, we synthesized various differently structured fluoro-D-glucose derivatives [2-O-decyl-α-D-glucopyranosyl fluoride (4), 4-O-tetradecyl-α-D-glucopyranosyl fluoride (5), 6-O-hexadecyl-α-D-glucopyranosyl fluoride (6), 6-deoxy-6-fluoro-2,3-di-O-hexadecyl-D-glucopyranose (9), 2-deoxy-2-fluoro-4,6-O-alkyliden-D-glucopyranosen (11a-d), 3-deoxy-3-fluoro-5,6-di-O-tetradecyl-D-glucofuranose (15)] as well as the 2-deoxy-2-fluoro-2,3,4,5,6-tetra-O-hexyl-scyllo-in-osit (19). Substitution of an OH group for a fluorine atom in amphiphilic derivatives destabilizes the thermotropic mesophase as it was to be expected so that either no or only narrowrange mesophases result. Both thermotropic and lyotropic liquid crystal phases occur in the series of 2-deoxy-2-fluoro-D-glucopyranose acetals 11 which are discussed in detail and which are compared with the analogous 2-hydroxy derivatives 12. Only 11c-d are thermotropic fluoro mesogens.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 767-773 
    ISSN: 0009-2940
    Keywords: Ether phosphanes ; Hydroxyalkylphosphanes ; Rhodium ; Asymmetric hydrogenation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically pure 1,4-bis(diphenylphosphanyl)-2-hydroxy-butane (2) and its methyl ether 1 can be conveniently prepared by starting from chiral pool substances such as malic or L-ascorbic acid. Different pathways to these compounds were elucidated. In one case an interesting migration of an acetalic OH-protective group was observed. The reaction of the bisphosphanes with Rh1 or PdII gave uniform metal complexes. On the basis of X-ray structural analysis, NMR and IR data it was concluded that in the investigated precatalysts of the type [Rh(COD)(bisphosphane)]BF4 a coordination of the alkoxy or hydroxy oxygen to the metal does not take place. Nevertheless, significant differences in enantioselectivity and activity could be observed when several prochiral substrates were hydrogenated.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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