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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 23 (1984), S. 1-19 
    ISSN: 0570-0833
    Keywords: Cycloaddition ; Allyl cations ; Cations ; Synthetic methods ; Cycloheptanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of allyl cations and 1,3-dienes affords seven-, five-, and six -membered rings as well as products of electrophilic substitution and linear 1:1-adducts. In this review article, preparative and mechanistic advances are summarized with special emphasis on the synthesis of seven-membered carbocycles. For the first time, a comprehensive mechanistic description is presented: Three classes A, B, and C correlate product type and stereochemistry with the nucleophilicity of the diene, the electrophilicity of the allyl cation intermediate, and the donor capacity of the group Y attached to the central carbon of the allylic moiety. The problem “allylic resonance versus nucleophilic participation of Y” is discussed and experimental evidence is adduced for some participation of Y as a function of its nucleophilicity. For cyclopentenyl cations, enhanced charge separation and electrophilicity are postulated, even when Y is a good donor, due to the structurally enforced polarity of the π-allyl system.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 12 (1973), S. 819-835 
    ISSN: 0570-0833
    Keywords: Allyl cations ; Cyclization ; Cyclopentanes ; Cycloaddition ; Cycloheptanes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cycloaddition of allyl cations to conjugated dienes offers an efficient and general tool for the construction of seven-membered carbocycles. The silver salt route is highly suitable for generating allyl cations and can be used even in most difficult cases, i. e. for elusive and intractable allyl cations such as 2-methylallyl, 2-methoxyallyl, and the parent allyl cation. Cycloadditions to the 2-methoxyallyl cation come very close to the prototype of a 6π, 7C reaction, since the carbonyl group introduced into the new ring can either be used for further transformations or be removed altogether. The combination of an allyl cation with π reactants, especially conjugated dienes, is a powerful and strongly convergent synthetic method since it permits one-step assembly, from a C3 and a C4 unit, of a cluster of up to four chiral centers in a ring which is larger than six-membered. Allyl cations combine with electron-rich 2π systems to form novel five-membered rings. The nature of the organometallic intermediates has been elucidated in many cases.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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