ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    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
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Desaminierungsreaktionen, 55. Zerfall von 2-Cyannorbornan-2-diazonium-Ionen (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 1503-1508 
    Details
    ISSN: 0009-2940
    Keywords: α1-Cyanodiazonium ions ; Carbocations, destabilized ; Wagner-Meerwein rearrangement ; 6,2-H Shifts ; Stereoselectivity ; Diazonium ions ; Deamination reactions ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deamination Reactions, 55[1]. - Decomposition of 2-Cyanonorbornane-2-diazonium IonsThe epimeric 2-aminonorbornane-2-carbonitriles (8a and 9a) were prepared from norbornane-2-one (7). The nitrous acid deamination reactions of 8a and 9a afforded the nitro compounds 15c and 16c in low exo/endo ratios, presumably by way of 2-cyano-2-norbornyl radicals (12). The major ionic process was found to be a Wagner-Meerwein rearrangement, leading to 1-cyano-2-norbornyl cations (10) and products 14 derived therefrom. Minor amounts (≤10%) of 2-hydroxynorbornane-2-carbonitriles (15a, 16a) provide suggestive, albeit inconclusive evidence for the trapping of 2-cyano-2-norbornyl cations (11). The decomposition of the endo diazonium ions 9c is also associated with norbornyl → norpinyl rearrangement, giving rise to 17 (≤9%). Stereochemical studies with optically active precursors point to intervention of the 7-bridged norbornyl cation 13 and of the edge-protonated cyclopropane 25. The formation of both species is clearly promoted by the cyano group.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260637
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Desaminierungsreaktionen, 51. Zerfall von Bicyclo[3.1.0]hexan-exo-6-diazonium-Ionen (1989)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 122 (1989), S. 389-392 
    Details
    ISSN: 0009-2940
    Keywords: Bicyclo[3.1.0]hex-6-yl derivatives ; Diazonium ions ; Electrocyclic reactions ; Nucleophilic displacement ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deamination Reactions, 51. - Decomposition of Bicyclo-[3.1.0]hexane-exo-6-diazonium lonsThe nitrous acid deamination of the amine 13, the copper(II)-induced cleavage of the nitrosourea 19, and the thermolysis of the nitrosoamide 20 were used to generate the diazonium ion 7. In contrast to previous work, performed in the presence of base, the neutral to weakly acidic conditions of the present study afforded substantial fractions (30-40%) of bicyclo[3.1.0]hex-exo-6-yl products (15). Small quantities of bicyclo[3.1.0]hex-endo-6-yl (14), bicyclo[3.1.0]hex-2-yl (25, 26), and 3-cyclohexen-1-yl (27) derivatives were also detected, the latter arising by a 1,3-hydride shift. These results, unprecedented with higher homologs of 7, suggest a largely „classical“ bicyclo[3.1.0]hex-6-yl cation (21) as the initially formed intermediate. Capture of 21 is thought to compete with disrotatory transformation to the cyclohexenyl cation 12.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19891220231
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Nitrogen as Leaving Group: Aliphatic Diazonium Ions (1976)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 15 (1976), S. 251-261 
    Details
    ISSN: 0570-0833
    Keywords: Nitrogen ; Leaving groups ; Diazonium ions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nitrogen is one of the best known leaving groups. Decomposition of aliphatic diazonium ions has rendered carbocations (carbon cations) accessible in cases where the solvolysis of halides or sulfonic esters follows different pathways. The limits of unassisted decomposition are seen in primary diazonium ions, where the participation of external nucleophiles and of neighboring groups in the elimination of nitrogen becomes noticeable. Cyclopropanediazonium ions occupy a position intermediate between aliphatic and aromatic diazonium ions. New versatile methods of generating aliphatic diazonium ions facilitate their preparative use.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.197602511
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...