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  • 1
    Electronic Resource
    Electronic Resource
    Concave Pyridines for Selective Acylations of Polyols (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1077-1084 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Catalysis ; General base ; Macrocycles ; Molecular recognition ; Hydrogen bond ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Selectivity enhancements in the base-catalyzed acylation of polyols (1,2- or 1,3-alkanediol, partially protected glucoside) have been found with (bi)macrocyclic pyridines 2 and 9 as catalysts. The different selectivities obtained for concave pyridines of varying ring sizes (1 vs. 2) are probably caused by their different geometries as a number of X-ray analyses (1a, 1b, 2a, 2b, 2e, 9) indicate. The methyl glucoside 7 can selectively be acylated in 2-position.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Concave Reagents, 21Part 20: Ref.[1].. Selective Acylations of Primary and Secondary Alcohols by Ketenes (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 2099-2105 
    Details
    ISSN: 0947-3440
    Keywords: Bimacrocycle ; Base catalysis ; Hydrogen bond ; Molecular recognition ; Pyridine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Concave pyridines 1 were used to catalyze the addition of primary and secondary alcohols to ketenes 4, and the kinetic data of these catalyses were determined. In inter- and intramolecular competitions the use of 1e-g led to improved selectivities for the acylation of primary alcohols in comparison with secondary alcohols. All primary alcohols react at comparable rates. Observed rate constants were correlated with Taft's Es values. The starting materials and products were fully characterized.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961223
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Concave reagents, 9 Alcoholysis of diphenylketene catalyzed by concave pyridines and open-chain analogs (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 999-1002 
    Details
    ISSN: 0170-2041
    Keywords: Base catalysis ; Macrocycles ; Nucleophilicity ; Ketene ; Brønsted plot ; Pyridines ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pseudo-first-order rate constants k(obs) for the (concave) pyridine-catalyzed addition of ethanol to diphenylketene have been determined photometrically. The catalytic activity of the concave pyridines 1 or 2 is determined by their basicity and by their size. This effects a difference in k(obs) of up to three orders of magnitude. The decrease in catalytic activity by the concave shielding can be overcome by introduction of basicity-increasing substituents into the pyridine ring (i.e. 1q). An amine-alcohol complex is probably the reactive species in this catalysis as the slope β of 0.3-0.5 in a Brønsted plot supports.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1991199101173
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    Paper (German National Licenses)
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