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  • 1
    Electronic Resource
    Electronic Resource
    Ring Expansion of 2-Alkylidenedihydroquinazolines to Iminodihydro-1,4-benzodiazepines by Methanesulfonyl and Trifluoromethanesulfonyl Azide (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1577-1587 
    Details
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Polycycles ; Ring expansion ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinazolinium hexafluorophosphates 9 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinazolines 10, which were investigated by NMR spectroscopy. Trapping with methanesulfonyl azide (5a) of 10 in situ or subsequent treatment with trifluoromethanesulfonyl azide (5b) gives mixtures of colourless (15) and intensely yellow N-sulfonylimino-1,4-benzodiazepines 16 along with products due to cleavage of the exocyclic double bond of 10, viz. 11 and 13. The ethylidene compound 10b yields the bicyclic products 18 and 19, apparently by complex sequences of reactions that are triggered by removal of the acidic proton at C-2 of 16b and 16f. The structures of the products are based on spectroscopic evidence and X-ray diffraction analyses performed on 15b, 16d, 16e, and 19.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    An Attempted Synthesis of 2,6-Bis(phenylazo)barbaralane (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1733-1738 
    Details
    ISSN: 0947-3440
    Keywords: Azo compounds ; Cyclizations ; Hydrazones ; Michael additions ; Nitrogen heterocycles ; Oxidations ; Polycycles ; Rearrangements ; Strained molecules ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the unsaturated ketone 6 with phenylhydrazine fails to afford the unsaturated phenylhydrazone 3 but gives the tricyclic phenylhydrazoketone exo-8, which is oxidised with iron(III) chloride to yield the phenylazoketone exo-9. The configuration of exo-9 is elucidated with the help of an X-ray diffraction analysis. The unsaturated phenylazo compound 14 is obtained from Meerwein's diketone 10 in two ways. Iodination of the phenylhydrazone 11 in the presence of pyridine followed by elimination of pyridinium iodide from the bispyridinium salt 13 with aqueous sodium hydroxide in dimethyl sulphoxide furnishes 14 in low yield. A somewhat better yield is more conveniently achieved when the dibromodiketones exo,exo- and exo,endo-12 are allowed to react with phenylhydrazine in the presence of pyridine. Bromination of 14 with N-bromosuccinimide in cyclohexane as solvent affords the labile dibromide 15. Both reagents employed, viz. the zinc/copper couple in refluxing tetrahydrofuran and butyllithium at low temperature, fail to convert 15 into the hoped-for bis(phenylazo)barbaralane 1 but instead give rise to the formation of the isomer 17, either by cyclisation of the intermediate anion 16 or by rearrangement of 1.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970815
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  • 4
    Electronic Resource
    Electronic Resource
    Ring Expansion of 2-Alkylidenedihydroquinolines to 2-Iminodihydro-1-benzazepines by Phenyl, Methanesulphonyl, and Trifluoromethanesulphonyl Azide[1] (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 507-520 
    Details
    ISSN: 1434-193X
    Keywords: Azides ; Cleavage reactions ; Cycloadditions ; Nitrogen heterocycles ; Photolysis ; Ring expansion ; Spiro compounds ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---2-Alkyl-1-methylquinolinium hexafluorophosphates 1 are deprotonated by sodium or potassium hydride to afford solutions of 2-alkylidenedihydroquinolines 2, which are investigated by NMR spectroscopy. 1,3-Dipolar cycloaddition of phenyl azide to 2 yields the spirocyclic products 10. While, at 80-110 °C, the [3 + 2] cycloaddition that afforded (u)-10f is reversible and accompanied by epimerisation to give (l)-10f, thermolysis of the dimethyl compounds 10b and d affords the ring-expanded products 14b and d, respectively, in good yields along with molecular nitrogen. Irradiation of 10d with light of λ 〉 320 nm results in the formation of similar amounts of 14d and [3 + 2] cycloreversion products, viz. 2-diazopropane (5b) and the N-phenylimine 15d. - Trapping of 2 by methanesulphonyl azide (18a) gives mixtures of the products of ring expansion (21b, d-f, 10-50 %) and [3 + 2] cycloreversion (22a, d, 10-80 %) of the apparently very labile intermediate spirocyclic cycloadducts 19. The ratio of 21 vs. 22 is significantly improved when 18a is replaced by trifluoromethanesulphonyl azide (18b), which affords the iminodihydrobenzazepines 21i-k in 50-75 % yield. The structures of the products are based on NMR evidence and X-ray diffraction analyses performed with 21b, d, and (ax,E)-21e.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 5
    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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  • 6
    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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