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  • 1
    Electronic Resource
    Electronic Resource
    1,3-Dipolare Cycloaddition elektrophiler Azide an cyclische Keten-N,X-acetale.  -  Stickstoff-Extrusion und Ringerweiterung der [3 + 2]-Cycloaddukte (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 1259-1269 
    Details
    ISSN: 0170-2041
    Keywords: [3 + 2] Cycloaddition ; [3 + 2] Cycloreversion ; Nitrogen extrusion ; Ketene N,X-acetals, cyclic ; Azides, electrophilic ; Amidines, cyclic N-sulfonyl- and N-picryl- ; Ring expansion of heterocycles ; 1,2-Shift of carbon, nitrogen or sulfur ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3-Dipolar Cycloaddition of Electrophilic Azides to Cyclic Ketene N,X-Acetals.  -  Extrusion of Molecular Nitrogen and Ring Expansion of the [3 + 2] Cycloadducts.The electrophilic azides 2 react with cyclic ketene N,X-acetals of type 7, e.g. 13, 15, 18, 21, 23, 25, and with the alkylidene-dihydroindoles 28 as well, to produce, besides molecular nitrogen, ring-expanded products of type 11 and 12, e.g. 14, 16, 19, 22, 24, 26, and 29 (path A), and/or N-sulfonylimines 10, viz. 17, 20, 27, and 31, besides diazo compounds (path B). The configurations of 16b, 19, 24a, and 26a are elucidated by means of X-ray diffraction analyses. The envelope conformations of the hetero rings of 19, 29 undergo ring inversion with rates in the range of the 1H NMR time scale [19: ΔG#c (285 K) = 54.8 kJmol-1, 29; ΔG#c (301 K) = 61.4, ΔG#c (314 K) = 60.7]. The formation of the ring-expanded products 11 and 12 is interpreted in terms of an initial [3 + 2] cycloaddition leading to unstable spiro compounds 8. Opening of their dihydro-1,2,3-triazole ring generates the zwitterions 9 which lose molecular nitrogen with concomitant ring expansion by a 1,2-shift of the more soft one of the atoms N and X.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201209
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  • 2
    Electronic Resource
    Electronic Resource
    5-Imino-1,4,5,6-tetrahydro-1,2,3,4-tetrazine aus 5-Alkyliden-4,5-dihydro-1H-tetrazolen und elektrophilen Aziden (1991)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1991 (1991), S. 409-416 
    Details
    ISSN: 0170-2041
    Keywords: [3 + 2] Cycloaddition ; 1H-Tetrazoles, 5-alkylidene-4,5-dihydro- ; Azides, electrophilic ; 1,2,3,4-Tetrazines, 5-imino-1,4,5,6-tetrahydro- ; Nitrogen 1,2-shift ; Ring expansion ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Imino-1,4,5,6-tetrahydro-1,2,3,4-tetrazines Formed from 5-Alkylidene-4,5-dihydro-1H-tetrazoles and Electrophilic Azides1)The electrophilic azides 1 react with the 5-alkylidenedihydrotetrazoles 8 already at low temperatures to produce high yields of the novel 5-iminotetrahydro-1,2,3,4-tetrazines 10 besides molecular nitrogen. The configurations of (Z)-10a, (E)-10c, (Z)-10d, and (E)-10h are elucidated by means of X-ray diffraction analyses. The formation of 10 is interpreted in terms of an initial [3 + 2] cycloaddition leading to the unstable spiro compounds 9. Ring opening of their dihydro-1,2,3-triazole ring generates the zwitterions 11 which lose molecular nitrogen with concomitant ring expansion of the dihydrotetrazole ring by a nitrogen 1,2-shift. The tetrazines 10a-c and e are also obtained when 8a is generated from the tetrazolium salt 7a and trapped „in situ“ by the azides 1a-c and e.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199119910176
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  • 3
    Electronic Resource
    Electronic Resource
    Ring Expansion of Heterocyclic Ketene N,X-Acetals and 2-Alkylidenedihydroindoles with Methanesulphonyl Azide by [3 + 2] Cycloaddition and Subsequent Extrusion of Molecular Nitrogen (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1541-1549 
    Details
    ISSN: 0947-3440
    Keywords: [3 + 2] Cycloaddition ; Ketene N,X-acetals, cyclic ; Azides, electrophilic ; Amidines, cyclic N-sulphonyl- ; Ring expansion of heterocycles ; 1,2-Shift of carbon, nitrogen, sulphur, or selenium ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Methanesulphonyl azide (2) reacts readily with isolated cyclic ketene N,X-acetals of type 1, viz. 10a, d, 15b, d, and 22a-c, or those that are generated in situ by deprotonation of the corresponding 2-alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b, and 18 → 19. Ring-expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2-shift of N (route A1 → 12, 24) or X (route A2 → 16, 20, 21). In addition, 3 may undergo [3 + 2] cycloreversion into N-sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25). The configurations of the cyclic N-sulphonylamidines 16b and 21b, the N-sulphonylimine 24 and the N-sulphonylamine 27 are elucidated by means of X-ray diffraction analyses. The ratio of the (useful) ring-expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α-carbon atom.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961008
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  • 4
    Electronic Resource
    Electronic Resource
    Synthese und Photolyse von 1,4,4-Trialkyl -4,5-dihydro-5-imino -1H-1,2,3-triazolen.  -  Regio- und diastereoselektive Bildung von (Z)-Aziridiniminen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2195-2202 
    Details
    ISSN: 0009-2940
    Keywords: [3 + 2] Cycloaddition ; [3 + 2] Cycloreversion ; 5H-Tetrazoles, 5-alkylidene-1,4-dihydro- ; Aziridinimines ; 1,2,3-Triazoles, 1,4,4-trialkyl-4,5-dihydro-5-imino- ; 1,2,3,4,6,7,8-Heptaazaspiro[4.4]nona-2,7-dienes ; Photolysis ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis and Photolysis of 1,4,4-Trialkyl-4,5-dihydro-5-imino-1H-1,2,3-triazoles.  -  Regio- and Diastereoselective Formation of (Z)-AziridiniminesThe novel 5-iminodihydro-1,2,3-triazoles 14 are synthesized from the 5-isopropylidenedihydrotetrazole 11 through a ring transformation involving cycloaddition and cycloreversion of alkyl azides 12. Thus, [3 + 21 cycloaddition of 11 and 12 pro- duces high yields of the spiro compounds 13. On thermolysis at 120- 130°C, the latter undergo clean [3 + 2] cycloreversion into methyl a i d e (12a) and the iminodihydro-1,2,3-triazoles 14, which exist as mixtures of diastereomers, e.g. (E)-/(Z)-14a = 955, or as a single stereoisomer (E)-14c. When toluene solutions of 14 are irradiated (≥ 1 280 mm) at - 60°C, the configuration of the products is under kinetic control. Irradiation of 14a affords a quantitative yield of the aziridinimines (E)-and (Z)-15a (11:89) besides molecular nitrogen. In order to allow the distinction between the least-motion and the non-least-motion path of product formation, the photolysis of iminodihydro-1,2,3-triazoles is studied which are labelled at N-1 by a deuterated methyl group (14b) or a neopentyl group (14c). Neither photolysis (λ ≥280 nm) nor heating to 120 to 130°C induces any scrambling of the alkyl groups attached to N-1 and the exocyclic nitrogen atom of 14b and c. The major product from (E)-/(Z)-14b (84%) is formed by the non-least-motion path leading diastereoselectively to (Z)-15 b, while the least-motion products (E)- and (Z)-17b (16%) exhibit a diastereo-meric ratio of 3: 1. Very similar results are obtained on photolysis of (E)-14c, except that the least-motion product (15%) arises only in a single configuration [(E)-l7c]. In the non-least-motion products (Z)-15b, c, the geometry of the Me—N=-C—N???—R group, fixed by the ring in 14b, c, is completely retained. Therefore, the (Z) diastereoselectivity is interpreted in terms of a one-bond cleavage leading to diazenyl-1,3-diazaallyl diradicals 22 having lifetimes too short for changes of their configuration which is determined by the structure of the precursor.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231118
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