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  • 1
    Electronic Resource
    Electronic Resource
    Probing for Steric and Electronic Effects in Diastereoselective Dioxirane Epoxidations Compared to The Oxygen Transfer by Peroxy Acids (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 547-551 
    Details
    ISSN: 0947-3440
    Keywords: Dioxiranes ; Diastereoselectivity ; Epoxidations ; Spiro transition states ; Peracids ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spiro transition state for the oxygen transfer by dioxiranes is substantiated by the fact that no enhanced steric effects are observed when dioxiranes with alkyl groups of different size are employed, as manifested by the same (within the experimental error) diastereoselectivities in the epoxidation of 2-menthene and 1,3-dimethylcyclohexene for different dioxiranes. The π-facial selectivity (anti attack) in the epoxidation of the acetate and the methyl and trimethylsilyl ether derivatives of 2-cyclohexenol derives from steric interactions, whereas a pronounced electronic effect (electrostatic repulsion) is held responsible for the high anti selectivity of peroxides such as ascaridol and 3-hydroperoxycyclohexene. Quite generally, dioxiranes display only slightly higher diastereoselectivities than mCPBA in sterically controlled epoxidations of cycloalkenes.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970316
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  • 2
    Electronic Resource
    Electronic Resource
    1-Methylgeraniol as Novel Regio- and Diastereoselective Probe for Hydrogen Bonding in Hydroxy-Assisted Oxygen-Transfer Reactions (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1365-1369 
    Details
    ISSN: 0947-3440
    Keywords: Epoxidations ; Diastereoselectivity ; Hydrogen bonding ; 1-Methylgeraniol ; Chemoselectivity ; Peroxides ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral 1-methylgeraniol has been designed and applied for epoxidation reactions as a mechanistic probe, which allows to assess simultaneously in one and the same molecule regio- and stereochemical information. Of the two trisubstituted double bonds, the terminal 7,8 one reflects kinetic preferences on account of its greater π nucleophilicity, the 3,4 one with the chiral allylic hydroxy functionality expresses diastereoselective directivity through hydrogen bonding. The combination of regio- and stereoselectivity provides a novel and powerful mechanistic tool to differentiate electronic and steric effects of oxidants. Thus, various epoxidizing agents have been employed and the mechanistic implications derived from the product ratios are well in line with those reported, which exemplifies the validity of the probe.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970713
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