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  • 1
    Electronic Resource
    Electronic Resource
    Pericyclic Domino reactions with 3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine: A convenient entry into azo cage compounds (1997)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 339 (1997), S. 623-632 
    Details
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,6-Bis(trifluoromethyl)-1,2,4,5-tetrazine (1) characterized by a highly reactive, electron deficient diazdiene system reacted with several cyclic and acyclic bis-dienophiles to yield the cage compounds 11, 19a, b, 31a, b and 41 in a pericyclic homo-domino reaction in good yields. The first step of the domino reactions is an inverse electron demand inter-molecular Diels-Alder addition followed by elimination of nitrogen to give 4,5-dihydropyridazines which then undergo a terminal ring closure to yield the cage compounds. The solvent employed and the reaction temperature is of crucial importance. Whereas in nitromethane and at elevated temperatures the main products are the cage compounds, at lower temperature and in dichloromethane as solvent the initially formed 4,5-dihydropyridazines are frequently converted to 1,4-dihydropyridazines by a 1,3-H-shift. Treatment of the tetrazine 1 with cyclooctatriene 23 did not lead to a cage compound in any case; instead via valence tautomeric species octa-1,3,5,7-tetraene 23a and bicyclo[4.2.0]octa-2,4-diene 23b the twofold pyridazine-substituted butadienes 24 and 26 together with the tricyclic cyclobuta[f]phthalazine 25 were formed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.199733901111
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  • 2
    Electronic Resource
    Electronic Resource
    A Novel Cycloocta[d]-/Barreleno[d]pyridazine RearrangementDedicated to Prof. Dr. Dr. h.c. F. Eiden on the occasion of his 70th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 661-666 
    Details
    ISSN: 0947-3440
    Keywords: Cyclooctatetraene-bicyclooctatriene valence tautomerism ; [4+2] Cycloadditions, inverse ; Cycloocta[d]pyridazine ⇛ barreleno[d]pyridazine rearrangement ; [1, 3]-Carbon migration ; Catalysis, 1,3-tautomerization with 2-hydroxypyridine ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As part of the valence tautomeric system cyclooctatetraene (2) bicyclo[4.2.0]octa-2,4,7-triene (3), the monocyclic polyene (2) reacts as a dienophile with the diazadiene 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine (1) to form after N2-elimination two products: The 1 : 1-adduct 6, a cycloocta[d]pyridazine, and the tetracyclic bis-Diels-Alder cycloadduct 9. Depending on solvent polarity and temperature, compound 6 displays interesting novel rearrangements. On refluxing in nonpolar solvents like toluene, compound 6 yields the barreleno[d]pyridazine 13 in high yield. Compound 13 can be oxidized with 4-phenyltriazolinedione 14 to the barreleno[d]pyridazine 15. When the more polar nitromethane is used as a solvent, heating of 6 at 90° 2°C surprisingly leads to the dihydrocycloocta[d]pyridazine 18 in a multistep reaction including proton-shift tautomerism and [1, 5]-sigmatropic rearrangement. The structures of the compounds 15 and 18 were assigned by the spectral data and verified by X-ray crystallography.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950493
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  • 3
    Electronic Resource
    Electronic Resource
    [4+ + 2] Cycloadditions with an N-Methyl-4H-pyrazolium cation as electron-deficient diazadiene systemDedicated to Prof. Dr. Hans Möhrle on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1313-1318 
    Details
    ISSN: 0947-3440
    Keywords: 4H-Pyrazole synthesis ; Dimethoxycarbene ; Diels-Alder reactions, „inverse“ ; Isopyrazolium ketal cations ; Phthalazinecarboxylates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3,6-Diphenyl-1,2,4,5-tetrazine (6) reacts with dimethoxycarbene (7), generated from the 1,3,4-oxadiazoline 8, to yield the 4H-pyrazole 10. This is alkylated to the N-methyl-4H-pyrazolium tetrafluoroborate 12 in high yield. The alkylated, cationic azine system of 12 serves as electron-deficient diene in a [4+ + 2] cycloaddition with inverse electron demand and reacts diastereoselectively with several cyclic olefins as electron-rich dienophiles. The initially formed cationic [4+ + 2] adduct, e.g. 15, is unstable and rearranges probably via 16 to a racemic phthalazinecarboxylic ester of type 17. The crystal structures of the epoxyphthalazinecarboxylic ester 25 and of the trans-annulated cycloocta[d]pyridazine 27 were determined by X-ray diffraction. In contrast to the cyclic olefins, cyclooctyne (28) reacts with the pyrazolium cation 12 to yield the cyclooctapyridiazinium tetrafluoroborate 30 via the cycloadduct 29.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507174
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  • 4
    Electronic Resource
    Electronic Resource
    Positional and Facial Selectivity in Diels-Alder Reactions of (-)-(aS,7S)-Colchicine: Synthesis of Novel Analogues of the Alkaloid (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 851-857 
    Details
    ISSN: 0947-3440
    Keywords: Colchicine, diene properties of ; Positional selectivity ; Stabilized exciplex through hydrogen bonding ; π-Facial diastereoselectivity ; Photooxygenation ; Solvent effects ; Cycloadditions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positional and facial selectivity in Diels-Alder reactions of several hetero- and carbodienophiles with (-)-(aS,7S)-colchicine (1) has been examined. In all cases, cycloaddition occurred with high positional selectivity at the 8,12-positions of the alkaloid and preferentially from the diene face syn to the allylic substituent at the stereogenic center C-7. The observed high π-facial diastereoselectivity is independent of the polarity of the solvent used and is therefore probably a consequence of steric factors. The structures of the Diels Alder-adducts of 1 with singlet oxygen, N-phenyl-1,2,4-triazolinedione (PTAD) and trans-cyclooctene, 4,5, and 15, respectively, were assigned on the basis of spectral data and verified by X-ray crystallography.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970510
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  • 5
    Electronic Resource
    Electronic Resource
    Dihydrocolchicine 8,12-Endoperoxide: A Novel Starting Material for Convenient Syntheses of the Allocolchicinoids N-Acetylcolchinol O-Methyl Ether and Androbiphenyline (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 2275-2279 
    Details
    ISSN: 0947-3440
    Keywords: Semisynthetic colchicine analogues ; Endoperoxide transformations ; Colchicine-allocolchicine rearrangement ; Axial chirality ; Biaryls ; Alkaloids ; Colchicum autumnale ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Optically pure dihydrocolchicine-8,12-endoperoxide 2 is used as the starting material for the synthesis of some bioactive allocolchicinoids. Depending on the reaction conditions and reagents employed, different modifications of the C ring of colchicine (1) are achieved. Triphenylphosphane deoxygenation of 2 leads to the well known N-acetylcolchinol O-methyl ether (NCME, 6, 40% yield from 1). Treatment of the endoperoxide 2 with CH3OH/CH2Cl2/silica gel provides the plant alkaloid androbiphenyline (11) in a yield of 60% from 1. Triethylamine-catalysed transformation of 2 yields (-)-colchicine-8,12-dione (12) (17% yield), together with a mixture of interconverting tetracyclic hemiketals 8a and 8b. For the formation of the allo colchicinoids 6 and 11 plausible reaction pathways are suggested. In contrast to what is found in the literature, the assignment of the absolute configuration of natural (-)-colchicine (1), and the allo-congeners 6 and 11, should be (M,7S) or (aR,7S) instead of (aS,7S).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719971115
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  • 6
    Electronic Resource
    Electronic Resource
    Cyclopentadienylidene, XIII1) Schwefelanaloga des Sesquifulvalens (1975)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1975 (1975), S. 331-341 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclopentadienylidenes, XI11 1). - Sulfur Analogs of SesquifulvaleneCondensation of the substituted cyclopentadienes 2, 5, 7, 8 with 1-thiopyrones 3a and b in acetic anhydride yields the cyclopentadienylidenethiopyrans 4, 6, 9, 10. Structural elucidation is based on 1H-NMR data. - Both electrophilic additions, which are regiospecific, and electrophilic substitutions with 4 and 6 are described, as are typical IR absorptions and characteristic electronic spectra of the thio analogs of sesquifulvalene.
    Notes: Die substituierten Cyclopentadiene 2, 5, 7, 8 reagieren mit den 1-Thiopyronen 3a und b in Acetanhydrid zu den Cyclopentadienylidenthiopyranen 4, 6, 9, 10, deren Konstitution durch 1H-NMR-Untersuchungen bestimmt wird. - Regiospezifisch verlaufende elektrophile Additionen und elektrophile Substitutionen mit 4 und 6 werden beschrieben. Die für Schwefelanaloga des Sesquifulvalens typischen IR-Banden und ihr charakteristisches Absorptionsverhalten in Elektronenspektren werden diskutiert.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197519750218
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  • 7
    Electronic Resource
    Electronic Resource
    Cyclopentadienylidene, VI1) Cyan-substituierte Heterosesquifulvalene mit Sauerstoff als Heteroatom (1970)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 732 (1970), S. 131-138 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclopentadienylidenes, VI1). Cyano-substituted Heterosesquifulvalenes Containing Oxygen as Hetero AtomCondensation of mono- and dicyano-substituted cyclopentadienes with 2,6-dimethyl-γ-pyrone in acetic anhydride yields the isomeric heterosesquifulvalenes 5a-d and 7a, b, respectively. Their structures are distinguished by NMR. The amphoteric character of the heterosesquifulvalenes permits electrophilic substitution in the five-membered ring and nucleophilic O/N-exchange in the six-membered ring. 5a-d and 7a, b exhibit strong infrared maxima near 1650 and 1350 cm-1; the ultraviolet absorption spectra show a characteristic maximum near 430 nm.
    Notes: Mono- und Dicyan-substituierte Cyclopentadiene reagieren mit 2.6-Dimethyl-γ-pyron in Acetanhydrid zu den isomeren Heterosesquifulvalenen 5a-d bzw. 7a und b, deren Konstitution durch NMR-Messungen bestimmt wird. Der amphotere Charakter der Heterosesquifulvalene erlaubt elektrophile Substitution am Fünfring und nucleophilen O/N-Austausch im sechsgliedrigen Ring. 5a-d und 7a, b zeigen in den IR-Spektren intensive Banden bei ca. 1650 und 1350 cm-1; die Elektronenspektren weisen ein charakteristisches Maximum im Gebiet von 430 nm auf.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.19707320112
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  • 8
    Electronic Resource
    Electronic Resource
    Cyclopentadienylidene, X. Dipyridinoheterosesquifulvalene (1972)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 757 (1972), S. 93-99 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclopentadienylidenes, X. - DipyridinoheterosesquifulvalenesReaction of 9-diazo-1,8-diazafluorene (2) with 2,6-dimethylpyrane-4-thione (3a) or with 2,6-dimethyl-1-thiapyrane-4-thione (3b) yields the corresponding dipyridinoheterosesquifulvalenes 1a and b. With n-butylamine compound 1a forms the nitrogen analog 1c by O/N-exchange. NMR- and ultraviolet absorption spectra of the π-bases 1 and of the conjugate acids 4 are discussed and compared with those of the dibenzoheterosesquifulvalene 5.
    Notes: 9-Diazo-1.8-diaza-fluoren (2) reagiert mit 2.6-Dimethyl-pyran-4-thion (3a) bzw. mit 2.6-Dimethyl-1-thia-pyran-4-thion (3b) zu den entsprechenden Dipyridinoheterosesquifulvalenen 1a und b. Aus 1a entsteht mit n-Butylamin durch O/N-Austausch das entsprechende Azaloge 1c. NMR-und Elektronenspektren der π-Basen 1 und der konjugaten Säuren 4 werden diskutiert und mit denen des Dibenzoheterosesquifulvalens 5 verglichen.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.19727570111
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesen in der Thietan-Reihe, III1) 2,8-Dithiadispiro[3.1.3.1]decan und sein Sauerstoffanalogon (1974)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1974 (1974), S. 1328-1332 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Syntheses in the Thietane Series, III1). - 2,8-Dithiadispiro[3.1.3.1]decane and its Oxygen AnalogueThe syntheses of the dispiro compound 2a, of the oxygen analogue 8 and of the unsymmetrical dispiro compound 11 are described. The structure of 2a is supported by the electronic spectrum and by comparison with that of the trispiro compound 5a. Hence an alternative structure 4 can be ruled out.
    Notes: Es wird eine Synthese der Dispiroverbindung 2a, des entsprechenden Sauerstoffanalogons 8 und der unsymmetrischen Dispiroverbindung 11 beschrieben. Die Struktur von 2a wird durch das Elektronenspektrum und durch dessen Vergleich mit dem der Trispiroverbindung 5a gestützt. Eine denkbare Alternative 4 kann ausgeschlossen werden.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197419740820
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  • 10
    Electronic Resource
    Electronic Resource
    Polycarbonylverbindungen, XXV. Versuche zur Synthese des Tetrathioquadratsäure-dimethylesters (1979)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1979 (1979), S. 595-604 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Polycarbonyl Compounds, XXV. - Attempted Synthesis of Dimethyl TetrathiosquarateTreatment of the 1,2-dithiosquaricdiamide 6 with excess methanethiol leads, depending on the reaction conditions, to various products. At elevated temperature the expected dimethyl tetrathiosquarate (4) is not obtained; instead the “1,3-dithiosquaricdiamide” 7 is formed via intermolecular migration of the amino functions as indicated by crossover experiments. At room temperature, on the other hand, two equivalents of methanethiol add to 6 to form the salt 17, which undergoes twofold alkylation with methyl iodide to give 19. Solvolysis of this compound by H2S yields a precursor of 4, the monothioketal 22, the chemical properties and spectral data of which are discussed.
    Notes: Die Umsetzung des Dithioquadratsäurediamids 6 mit überschüssigem Methanthiol führt je nach den Reaktionsbedingungen zu verschiedenen Produkten. Bei erhöhter Temperatur entsteht nicht der erwartete Tetrathioquadratsäure-dimethylester (4), sondern, wie Kreuzungsexperimente beweisen unter intermolekularer Wanderung der Aminfunktionen das, “1,3-Dithioquadratsäurediamid” 7. Im Gegensatz dazu erhält man bei Raumtemperatur unter Addition von zwei Äquivalenten Methanthiol an 6 das Salz 17, das nach zweifacher Alkylierung mit Methyliodid zu 19 und anschließender Solvolyse mit H2S zu einer Vorstufe von 4 führt, dem Monothioketal 22, dessen chemische Eigenschaften und spektrale Daten diskutiert werden.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197919790502
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