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  • 1
    Electronic Resource
    Electronic Resource
    Nucleophile Singulett-Carbene in der [4 + 1]1-Cycloaddition mit 1,2,4,5-Tetrazinen: Eine neue Isopyrazol-Synthese (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 733-738 
    Details
    ISSN: 0009-2940
    Keywords: Singlet carbenes ; [4 + 1] Cycloadditions ; Isopyrazoles ; Diels-Alder reactions ; [4 + 2] Cycloreversion ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Nucleophilic Singlet Carbenes in the [4 + 1] Cycloaddition with 1,2,4,5-Tetrazines: a New Synthesis of IsopyrazolesA series of 3,6-disubstituted 1,2,4,5-tetrazines 6, including C6H5, SCH3, SO2CH3, N(CH3)2, CF3, CO2CH3 groups, has been submitted to [4 + 1] cycloaddition with the nucleophilic singlet carbenes 4, 15, and 20, which are generated from the precursors 1, 11 and 19, resp. In all cases isopyrazoles (4H1-pyrazoles) 9, 10, 18, and 21 are isolated in good yields. They are formed in a two-step reaction sequence with the [4 + 1] cycloadducts of type 8 as intermediates which eliminate nitrogen by subsequent [4 + 2] cycloreversion. The acceptor-substituted isopyrazole 9e is characterized as an electron-deficient diene by some Diels-Alder reactions with inverse electron demand leading to the expected azo-bridged cycloadducts 23, 25, 27, 29, and 31 without acid catalysis or application of higher pressure. With cyclooctyne (32), the [4 + 2] cycloaddition is followed by a [4 + 2] cycloreversion with formation of the cyclopentacyclooctene 34.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260325
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  • 2
    Electronic Resource
    Electronic Resource
    Wanzlick-Carbene in der [4 + 1]-Cycloaddition mit Bis(methylthio)- und Bis(trifluormethyl)-1,2,4,5-tetrazin (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1803-1806 
    Details
    ISSN: 0009-2940
    Keywords: Singlet carbenes ; [4 + 1] Cycloadditions ; 1,2,4,5-Tetrazines ; SEAr reactions, intramolecular ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Wanzlick Carbenes in the [4 + 1] Cycloaddition Reaction with Bis(methylthio)- and Bis(trifluoromethyl)-1,2,4,5-tetrazineThe 3,6-disubstituted 1,2,4,5-tetrazines 3 and 4 have been submitted to a [4 + 1] cycloaddition reaction with the nucleophilic singlet carbenes (Wanzlick carbenes) 2a-d, which are generated from the precursors 1a-d. With 3 as diazadiene the expected spiro compounds 6a-d are formed. In contrast to this presumed two-step reaction sequence of 3, with the tetrazine 4 the cascade cycloaddition/cycloelimination is surprisingly followed by an intramolecular electrophilic aromatic substitution to yield the chiral tetracyclic compounds of type 8 with high diastereoselectivity. The crystal structure of 8d has been determined by X-ray diffraction methods.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19941270933
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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
    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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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Polycarbonylverbindungen, XXIX. Schwefelhaltige Dicyanmethylen-“Pseudooxokohlenstoff”-Anionen (1980)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1980 (1980), S. 1409-1418 
    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, XXIX.  -  Sulfur Containing Dicyanomethylene-“Pseudooxocarbon” AnionsNucleophilic replacement reactions of malononitrile at the aryl-substituted deltic acid amidinium cation 5, at 1,2-dithiosquaric acid bis(dimethylamide) (13), or at croconic acid dimethyl ester (20) lead to the corresponding dicyanomethylene derivatives 6, 14, or 21, respectively, which on subsequent sulfhydrolysis yield the novel sulfur containing delocalized “pseudooxocarbon” anions 8, 15, or 22, respectively. Alkylation reactions of these anions as well as spectroscopic data are reported.
    Notes: Nucleophile Austauschreaktionen von Malononitril am arylsubstituierten Dreiecksäureamidiniumkation 5, am 1,2-Dithioquadratsäurebis(dimethylamid) (13) oder am Krokonsäure-dimethylester (20) führen zu den entsprechenden Dicyanmethylenderivaten 6, 14 bzw. 21, die durch anschließende Sulfhydrolyse zu den neuen schwefelhaltigen, delokalisierten “Pseudooxokohlenstoff” Anionen 8, 15 bzw. 22 reagieren. Alkylierungsreaktionen an diesen Anionen und ihre spektroskopischen Daten werden mitgeteilt.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198019800909
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  • 10
    Electronic Resource
    Electronic Resource
    Cyclopenta[C]pyran und sein 6-tert-Butyl-Derivat (1988)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1988 (1988), S. 855-860 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclopenta[C]pyran and Its 6-tert-Butyl DerivativeThree-step syntheses of the hitherto unknown cyclopenta[C]pyran (2) and its 6-tert-butyl derivative 12 are described. The 1H-NMR, 13C-NMR, and electronic spectra of the lemon-yellow isooxalenes are compared with those of other pseudoazulenes.
    Notes: Wir beschreiben dreistufige Synthesen des bisher unbekannten Cyclopenta[C]pyrans und dessen 6-tert-Butyl-Derivats 12. Die 1H-NMR-, 13C-NMR- und Elektronenspektren der zitronengelben Isooxalene werden mit denen anderer Pseudoazulene verglichen.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198819880907
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