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  • Azides, electrophilic  (4)
  • Oxepines  (3)
  • Ring expansion  (3)
  • Asymmetric synthesis  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Synthese mittlerer und großer Ringe, XXXI[1] Die [6](3,6)Oxepinophan-[6](2,5)Furanophan-Ringverengung mit Rutheniumtetroxid (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 1485-1494 
    Details
    ISSN: 0009-2940
    Keywords: Oxepines ; Furans ; Ruthenium tetroxide ; Iron complexes ; Heterophanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Medium and Large Rings, XXXI[1] - The [6](3,6)Oxepinophane-[6](2,5)Furanophane Ring Contraction with Ruthenium TetroxideA one-pot synthesis of the furanophanes 2a and 2b by ring contraction of the oxepinophanes 1a and 1b is described. Evidence is presented that the reaction proceeds by subsequent oxidation of two double bonds via the intermediates 3 and 4. On treatment with hydrochloric acid cis-4 gives 2a by 1,4-elimination of hydrogen peroxide. The oxidation of the [7](3,6)oxepinophane 1c leads to a complex mixture of the products 2d and 6-10. 2a undergoes Diels-Alder reactions with benzyne and 2,3-naphthalyne to give 11 and 12. The latter forms the stable iron tricarbonyl complex 13. The structures of 2c, 4, 10, 11, and 13 have been established by X-ray analyses.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250626
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  • 2
    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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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Axially Chiral Biaryls by Atropo-Diastereoselective Cleavage of Configurationally Unstable Biaryl Lactones with Menthol-Derived O-Nucleophiles (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 3047-3055 
    Details
    ISSN: 1434-193X
    Keywords: Axial chirality ; Biaryls ; Atropisomerism ; Dynamic kinetic resolution ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Configurationally unstable lactone-bridged biaryls 4 are cleaved atropo-diastereoselectively using chiral menthol-derived alkali metal alkoxides, to give axially chiral biaryl esters of type 5 in high yields and excellent diastereomeric ratios of up to 〉 99:1. The method permits the optional preparation of each of the two atropisomers from the same lactone precursor (“atropo-divergence”), simply according to the choice of the appropiate mentholate or its enantiomer as the O-nucleophile - or by the use of the mentholate in solution or in suspension. Undesired minor atropisomers of 5 possibly formed (if at all) can be recycled (“axially chiral economy”) by cyclization back to the lactone 4. For the preparation of larger amounts of enantiopure biaryl alcohols 9, an efficient reaction sequence was developed: alcoholysis of 4 → in situ reduction → crystallization. The synthetic value of these alcoholysis reactions for asymmetric biaryl synthesis is illustrated by the transformation of 5 into a broad series of enantiopure biaryls of type 6 with various functional groups ortho to the axis.
    Additional Material: 4 Tab.
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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Zwitterions as Intermediates in 1,3-Dipolar Cycloadditions of Electrophilic Azides to 2-Alkylidenetetrahydroimidazoles and 2-AlkylidenedihydrobenzimidazolesDedicated to Professor Günter Szeimies on the occasion of his 60th birthday. (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1551-1558 
    Details
    ISSN: 0947-3440
    Keywords: Ketene N,N-acetals, cyclic ; Imidazole, derivatives of ; Benzimidazole, derivatives of ; Azides, electrophilic ; Cycloaddition, 1,3-dipolar, nonconcerted ; Zwitterions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclic ketene N,N-acetals derived from imidazolidine (4a, c) and 2,3-dihydrobenzimidazole (6a-c) add methanesulphonyl azide (2a) or picryl azide (2f) to afford the zwitterions 5 and 7, respectively. The structure of 7d is elucidated by X-ray crystallography. Reversibility of formation and thermal stability of the N-sulphonyl zwitterions depend on the substitution pattern at the carbon atom to which the triazenide moiety is attached: In the case of a pair of geminal methyl groups (5a, 7a) formation is irreversible and decomposition by cyclisation and subsequent reactions occurs above -20°C, while in presence of a single alkyl group (7c, d) these processes require heating to 80°C and are accompanied by partial reversion to 2a and ketene N,N-acetals (6b, c). Cyclisation of the zwitterions yields intermediate spirocyclic [3 + 2] cycloadducts, which may undergo [3 + 2] cycloreversion into N-sulphonylimine 13 and diazo compound 14 or extrude molecular nitrogen to furnish ring-expanded 2-(sulphonylimino)piperazine derivatives (9, 11).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199619961009
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of Medium and Large Rings, XLIVPart XLIII: W. Tochtermann, L. Rodefeld, H. Dreeskamp, S. M. Sage, Liebigs Ann. 1996, 1959-1961.. Synthesis of Optically Active Bridged Bicyclobutane DerivativesDedicated to Professor Hans Paulsen on the occasion of his 75th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1125-1129 
    Details
    ISSN: 0947-3440
    Keywords: Oxepines ; Photoisomerization ; s-cis-Butadiene conformation ; Small ring systems ; Enantiomeric resolution ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation of the dihydrooxepine monoester (+)-4 gives the bridged bicyclobutane (+)-5 in 77% yield. On the other hand, the corresponding diester 1 yields the cyclobutene 2. Possible explanations for this differing behaviour are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970611
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  • 7
    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.
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  • 8
    Electronic Resource
    Electronic Resource
    The Reaction of Dimethyl 10-Oxo-3,6-hexanooxepine-4,5-dicarboxylate with Sodium Methoxide/Methanol - A Reinvestigation (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 507-508 
    Details
    ISSN: 1434-193X
    Keywords: Oxepines ; Bicyclopentyl derivatives ; X-ray analysis ; Correction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of the title compound 1 with sodium methoxide in ether in the presence of methanol leads to the bicyclopentyl derivative 3. The structure of 3 was established by X-ray analysis. The structure 2 proposed earlier has to be corrected in favour of 3.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis, Crystal Structure, and Circular Dichroism Spectra of (1S)-4,8-Diphenylbarbaralane-2,6-dicarbonitrile - Chiroptical Properties of the Transition State of a Degenerate Cope Rearrangement (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1811-1823 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Automerisation ; Circular dichroism ; Conformation analysis ; Enantiomeric resolution ; Polycycles ; Solid-state structures ; Solvent effects ; Thermochromism ; Transition states ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Diphenylbicyclo[3.3.1]nonane-2,6-dione rac-3 is resolved in 57 % overall yield by chromatographic separation of the diastereomeric (R)-N-(1-phenylethyl)carbamates 9 which are obtained from (R)-(1-phenylethyl) isocyanate (8) and the 6-hydroxydiphenylbicyclo[3.3.1]nonan-2-ones endo- and exo-4. The enantiomers (1R)- (e.r. = 98:2) and (1S)-3 (e.r. = 97:3) are regenerated from 9 by reduction with lithium aluminium hydride followed by Swern oxidation of the resulting diols 5. The title compound (1S)-1 is synthesised in three steps from (1S)-3 in improved yield on the route that had led to rac-1. The absolute configurations are established by X-ray diffraction analyses of the carbamates endo-(1R)-9 and exo-(1S)-9. X-ray diffraction analyses were also performed of the camphanoate (1R)-7, the intermediates rac-endo-4 and (1S)-3, and the title compound (1S)-1. Hydroxy ketone rac-endo-4 adopts similar conformations in the solid state and in solution as shown by a comparison of vicinal 1H,1H coupling constants from proton spectra with those calculated from torsional angles in the crystal. The molecular structures of (1S)-1 and (1S)-3 closely resemble those of the corresponding racemates investigated previously. These results show (i) that intermolecular interactions in the solid state are of minor importance and (ii) that the unusually long C2-C8 distance of (1S)-1 and rac-1 (168 pm) is a molecular but not an averaged property due to a non-degenerate Cope rearrangement in the crystal. CD spectra are reported for (1R)- and (1S)-3, the unsaturated dicarbonitrile (1S)-13, and (1S)-1. The CD spectrum of (1S)-1 exhibits a weak positive band at 459 nm where rac-1 shows a temperature-dependent absorption which has been assigned to the higher, vibronic state represented by rac-1*. The intensity of the weak CD band depends on the temperature and the solvents in the same way as the UV/Vis absorption of rac-1. This supports the conclusion that both bands originate from the same source, viz. the transition state 1* of the degenerate Cope rearrangement 1 ⇄ 1′.
    Additional Material: 11 Ill.
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  • 10
    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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