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  • Substitution, nucleophilic  (3)
  • Alkyl-bridged ions  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Umlagerungen von 1,4,4- und 2,2,5-Trimethylbicyclo[3.2.1]oct-6-yl-Kationen (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 237-240 
    Details
    ISSN: 0009-2940
    Keywords: Bicyclo[3.2.1]oct-6-yl cations ; Wagner-Meerwein rearrangements ; Alkyl-bridged ions ; Conformational effects ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rearrangements of 1,4,4- and 2,2,5-Trimethylbicyclo[3.2.1]oct-6-yl Cations1,4,4-Trimethylbicyclo[3.2.1]oct-6-yl cations (18) are generated from the tosylhydrazone 7, by nitrous acid deamination of the amines 6 and 8, and by acetolysis of the brosylates 21 and 24. The product distributions are but slightly affected by the configuration (exo vs. endo) of the leaving groups. The predominant product, 1,4,4-trimethylbicyclo[3.2.1]octan-exo-6-ol (11) is formed without significant redistribution of a 6-2H label. The degenerate Wagner-Meerwein rearrangement of the parent bicyclo[3.2.1]oct-6-yl cation is virtually eliminated by the presence of two methyl groups at C-4. Enhanced conformational strain, raising the barrier to ring flipping, accounts for these observations. Minor products (12, 13) arise from a 7,6-hydride shift of 18, followed by Wagner-Meerwein rearrangement. When the 2,2,5-trimethylbicyclo[3.2.1]oct-6-yl cation (19) is generated directly from the tosylhydrazone 17, the tertiary alcohol 13 is obtained as the major product. The conformational barrier to Wagner-Meerwein rearrangement is compensated by the incipient stabilization of the tertiary carbocation 20.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240136
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  • 2
    Electronic Resource
    Electronic Resource
    Umlagerungen von Tricyclo[3.2.1.12,4]non-6-yl-, Tricyclo[4.2.1.12,5]dec-3-yl- und Tricyclo[4.2.2.12,5]undec-3-yl-Kationen (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1297-1300 
    Details
    ISSN: 0009-2940
    Keywords: Wagner-Meerwein rearrangement ; Carbocations, tricyclic ; Substitution, nucleophilic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rearrangements of Tricyclo[3.2.1.12,4]non-6-yl, Tricyclo[4.2.1.12,5]dec-3-yl, and Tricyclo[4.2.2.12,5]undec-3-yl CationsThe tricyclic ketones 5, 9, 13, and 24 were prepared by modified or novel routes. The corresponding tosylhydrazones 10, 11, 14, and 25 were photolyzed in 0.5 N NaOH (NaOD) to generate the title cations 2, 15-17, and 28, respectively, by way of diazonium precursors. The distribution of deuterium labels revealed rapid degenerate Wagner-Meerwein rearrangements of 2 and 28 contrasting the unsymmetrical behavior of the parent bicyclo[3.2.1]oct-6-yl cation (1). The virtually irreversible rearrangement of 17 to 15, on the other hand, mirrors the preferred chair conformation of 1. The results with tricyclic carbocations support our previous explanation for the exceptional reactivity of 1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250542
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  • 3
    Electronic Resource
    Electronic Resource
    Umlagerungen von 5,5,6,6-Tetraalkyl-2-norbornyl-Kationen (1991)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 241-245 
    Details
    ISSN: 0009-2940
    Keywords: 2-Norbornyl cations, 5,5,6,6-tetramethyl- ; Tetracyclo[4.2.2.12,5.01,6]undec-3-yl cations ; Wagner-Meerwein rearrangements ; Alkyl-bridged ions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Rearrangements of 5,5,6,6-Tetraalkyl-2-norbornyl CationsWhen the 6,6-dimethyl-2-norbornyl cation (9) is generated from the tosylhydrazone 5 by way of the diazonium ion 8, a 2H label is distributed equally between positions 1 and 2 of the exo-alcohol 10. The degeneracy of 9, previously derived from solvolytic studies, is thus confirmed for the deaminative route. 5,5,6,6-Tetramethyl-2-norbornanone (25) and tetracyclo[4.2.2.12,5.01,6]undecan-3-one (31) are prepared by using Diels-Alder methodology. The corresponding tosylhydrazones 26 and 32 are employed as precursors for the 5,5,6,6-tetramethyl-2-norbornyl and tetracyclo[4.2.2.12,5.01,6]undec-3-yl cations (11 and 12). Again, the distributions of 2H labels are close to 1 : 1. The angular distortions expected from repulsive interactions of the methyl groups in 11 and from cyclobutane annulation in 12 do not affect the relative energies of the bridged ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19911240137
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  • 4
    Electronic Resource
    Electronic Resource
    Desaminierungsreaktionen, 54. Zerfall von 1-Cyan-1-propandiazonium-Ionen (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1499-1502 
    Details
    ISSN: 0009-2940
    Keywords: α1-Cyanodiazonium ions ; α1-Cyanoalkyl radicals ; Carbocations, destabilized ; Substitution, nucleophilic ; Deamination reactions ; Diazonium ions ; Radicals ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deamination Reaction, 54[1]. - Decomposition of 1-Cyano-1-propanediazonium IonsThe nitrous acid deamination of 2-aminobutanenitrile (9) was studied with regard to product distribution and stereochemistry. The formation of 2-(hydroxyimino)butanenitriles (21, 22; 8 - 28%) indicates the intervention of 1-cyanopropyl radicals (24) that are captured by NO. The polar reactions lead mainly to elimination (10 - 13) and nucleophilic substitution (14 - 16), rearrangement playing a minor role. (R)-9 was prepared from (R)1-2-aminobutanoic acid. The nitrous acid deamination of (R)-9 afforded the cyanohydrin 16 with 81% net inversion. Owing to destabilization of the carbocation 26 by CN, the SN2 route of nucleophilic displacement is preferred over SN1. The influence of CN is shown to be smaller than that of CF3.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260636
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  • 5
    Electronic Resource
    Electronic Resource
    Reaktionen Pentafluorethyl-substituierter Bicyclo[2.1.1]hexan-Derivate (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 409-414 
    Details
    ISSN: 0009-2940
    Keywords: Carbocations, destabilized ; Solvolysis rates ; Wagner-Meerwein rearrangement ; Substitution, nucleophilic ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Pentafluoroethyl-Substituted Bicyclo[2.1.1]hexane DerivativesThe effect of inductively electron-withdrawing substituents on the generation of 2-bicyclo[2.1.1]hexyl cations was probed by means of pentafluoroethyl groups. 2-Pentafluoroethyl-2-bicyclo[2.1.1]hexyl brosylate (4a) and triflate (4b) were found to rearrange with formation of the analogous 1-pentafluoroethyl-2-bicyclo[2.1.1]hexyl sulfonates 5a, b. Solvolytic displacement did not compete with the rearrangement but occurred on 5b at elevated temperatures. Deuterium labels revealed that the rearrangement proceeded stereospecifically, with the sulfonate departing and rebonding on the same side of the molecular plane. Complete inversion was observed during solvolysis of 5b in aqueous dioxane while some retention (16%) occurred in trifluoroacetic acid. Predominant inversion even with the analogous diazonium ion in water attests to the reluctant formation of 1-pentafluoroethyl-2-bicyclo[2.1.1]hexyl cations. Solvolysis rates of 4a, b and 5b were in close agreement with those of the analogous cyano derivatives, thus confirming that the resonance interaction of α1-cyano groups with carbocations is small.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260218
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