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  • 1
    Book
    Book
    Bremen : Fachbereich Geowissenschaften, Universität Bremen
    Keywords: Dissertation ; Report ; Hochschulschrift ; Südpolarmeer ; Organischer Stoff ; Kohlenstoffisotop
    Type of Medium: Book
    Pages: 161 Seiten , Karten, Diagrame , 30 cm
    Series Statement: Berichte aus dem Fachbereich Geowissenschaften der Universität Bremen Nr. 5
    Language: German
    Note: Zsfassung in engl. Sprache , Zugl.: Bremen, Univ., Diss., 1989
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  • 2
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The year-round mooring station WS-1 is located at 62°26.5' S, 34°45.5' W, in a water depth of 3,880 m. This station is covered by sea ice for about 70% of the year (〉9 on ice-cover scale (ICS); see refs 1 and 2). We developed an automated Parflux Mk 5-25 time-series sediment trap3 at 863 ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 119 (1986), S. 589-615 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Photochemical Transformations, 64. The 3σ → 3π-Route to Oxepines/Benzene OxidesThe 7-oxanorbornadiene skeleton (8a), its 2,3-bis(trifluoromethyl) derivative (8b), and several 2,3-dicarboxylic esters with potential dipolarophilic groups at C-1 (16a - d, 17a - c) were synthesized and selectively transformed into the 3-oxaquadricyclanes (18a,b, 19a - d, and 20a - c) through sensitized (8a,b) or direct (16a - d, 17a - c) photoexcitation. In the thermolysis of these oxaquadricyclanes [18a(b): Ea(C6D6) = 32.6 ± 0.3 kcal/mol (32.2 ± 1.4 kcal/mol); lg A = 15.8 (14.5)] CF3(CH3CO2) substituents at C-2(3) favor the scission of the opposite (neighbouring) cyclopropane bonds. Competition experiments with dimethyl acetylenedicarboxylate as external dipolarophile support the stepwise mechanism of the oxaquadricyclane → oxepine conversion. The intramolecular carbonyl ylide-interception cannot compete with oxepine formation in 19a - d but is efficient in 20a - c. The unusually low activation barrier (Ea(C6D6) = 23.5 ± 1 kcal/mol; lg A = 11.6) and singular specifity in case of 20a is interpreted in terms of a concerted [π2 + σ2 + σ2]-cycloaddition to the bishomofuran unit of the oxaquadricyclane skeleton.
    Notes: Das 7-Oxanorbornadien-Grundgerüst (8a), das 2,3-Bis(trifluormethyl)-Derivat (8b) und diverse 2,3-Dicarbonester mit potentiell dipolarophilen Gruppen an C-1 (16a - d, 17a - c) wurden synthetisiert und durch sensibilisierte (8a,b) bzw. direkte Lichtanregung (16a - d, 17a - c) durchweg hochselektiv in die 3-Oxaquadricyclane (18a,b, 19a - d, 20a - c) umgewandelt. Bei der Thermolyse dieser Oxaquadricyclane [18a(b): Ea(C6D6) = 32.6 ± 0.3 kcal/mol (32.2 ± 1.4 kcal/mol); lg A = 15.8 (14.5)] begünstigen CF3(CH3CO2)-Reste an C-2(3) die Spaltung der gegenüberliegenden (benachbarten) Cyclopropanbindungen. Durch Konkurrenzversuche mit Acetylendicarbonsäure-dimethylester als externem Dipolarophil wird der Mehrstufen-Mechanismus der Oxaquadricyclan → Oxepin-Isomerisierung untermauert. Die intramolekulare Carbonylylid-Abfangreaktion kann in 19a - d nicht, wohl aber in 20a - c mit der Oxepinbildung konkurrieren. Deren im Falle von 20a außergewöhnlich niedrige Aktivierungsbarriere (Ea(C6D6) = 23.5 ± 1 kcal/mol; lg A = 11.6) und singuläre Spezifität werden im Sinne einer konzertierten [π2 + σ2 + σ2]-Cycloaddition an die Bishomofuran-Einheit des Oxaquadricyclan-Gerüstes interpretiert.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 327 (1985), S. 151-155 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXVI. Comparative U.V./Vis. Studies on 3-Methyl-2,4,6-triarylpyrylium Perchlorates
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 573-581 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 34. 2-Acetonyl-2H-thiopyrans from 2,4,6-Triarylthiopyrylium Salts2,4,6-Triarylthiopyrylium salts 4 react with acetone in the presence of amine salts of weak acids (e.g. piperidine acetate) to give the hithero unknown 2-acetonyl-2-H-thiopyrans 5, the structure of which was established by spectroscopic methods. Depending on the nature of the amine salt used, the enamine 6 or the enol 7 of acetone may function as attacking nucleophile. Using the 2,4,6-triphenyl derivative 5a as model compound, some typical reactions of 2-acetonyl-2H-thiopyrans were studied. With 2,4-dinitrophenylhydrazine, semicarbazide and thiosemicarbazide, the carbonyl derivatives 10a-c are formed. Hydrogen peroxide in acetic acid affords the S,S-dioxide 11. Methanolic sodium methoxide or sodium hydroxide in aqueous ethanol give rise to a ring transformation yielding 1,3,5-triphenylbenzene (12) and 2,4,6-triphenylacetophenone (13). Under similar conditions, benzaldehyde reacts with 5a to give 2′, 4′, 6′-triphenylchalcone (14). Perchloric acid regenerates from 5a the initial thiopyrylium perchlorate 4a.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 327 (1985), S. 983-997 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 30. C-Alkylation of 1,3,5-Triaryl-pentene-1,5-dione Enolates: A Simple Approach to 3-Alkylsubstituted 2,4,6-Triarylpyrylium Salts1,3,5-Triaryl-pentene-1,5-dione enolates (10), obtainable in crystalline form from 2,4,6-triarylpyrylium pseudobases (9) and sodium methoxide in benzene/ether, react in dipolar aprotonic solvents (e.g. DMSO, DMF) with various types of alkyl iodides to give C-alkylation products (11) which afford 3-substituted 2,4,6-triarylpyrylium salts (12) on treatment with perchloric acid. This reaction sequence proved to be a convenient synthetic route to pyrylium salts (12) having 3-oriented substituents such as normal or branched alkyl groups CnH2n+1 (e.g.n = 1-5), isotopically modified alkyl groups (e.g. C[2H3], C2[2H5]), allyl type substituents (e.g. CH2=CHCH2, MeCH=CHCH2, CH2, CH2=CMeCH2) or benzyl groups (e. g. PhCH2, 4-Br—C6H4CH2). Bifunctional alkylating agents (e.g. 1,4-diiodobutane, o-xylylenediiodide) resulted in a novel type of bispyrylium salts (14) with 3,3′-linkage. The pyrylium salts obtained were characterized by their 1H-n.m.r. and u.v. spectra as well as, in most cases, by transformation into the corresponding pyridine derivatives (13) and bispyridines (15) respectively.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 327 (1985), S. 529-535 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXVIII. Specifically Deuterated Carbo- and heterocycles via 2,4,6-Triaryl[3,5-2H2]pyrylium SaltsOn heating with catalytic amounts of bases(e.g. triethyl amine) in deuterated alcohols such as methan[2H]ol or ethan[2H]ol pseudobases of 2, 4, 6-triarylpyrylium salts 1 undergo fast1H/2H isotopic exchange reaction affording 1, 3, 5-triaryl[2, 4, 4-2H3]pent-2-ene-1,5-diones which with [2H] perchloric acid give highly deuterated 2, 4, 6-triaryl-[3, 5-2H] pyrylium perchlorates 8. These salts are obtainable also directly from 1 through a one-pot procedure by ring opening of the latter with deuterium oxide under the above-mentioned1H/2H isotopic exchange conditions followed by recyclization of the formed 1, 3, 5-triaryl[2, 4, 4-2H3]pent-2-ene-1, 5-diones with [2H]ClO4. Ring transformations of 2, 4, 6-triphenyl[3, 5-2H2]pyrylium perchlorate (8a) to 2, 4, 6-triphenyl[3, 5-2H2]nitrobenzene (9) 2, 4, 6-triphenyl[3, 5-2H2]pyridine (10), 1, 2, 4, 6-tetraphenyl[3, 5-2H2]pyrydinium perchlorate(11), 2, 4, 6-triphencyl[3, 5-2H2]thiopyrylium perchlorate(12), 2-benzoyl-3, 5-diphenyl[4-2H]furan (13), and 3, 5, 7-triphenyl-[4, 4, 6-2H3]4H-1, 2-diazepin (14) demonstrate the usability of pyrylium salts of type 8 as starting materials for syntheses of specifically deuterated carbo- and hetrocycles.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 359-372 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Pyrylium Compounds. 31. Reaction of 3-Alkyl-2,4,6-triarylpyrylium Salts with 1,3-Diketonates: A Method for the Preparation of 3-Acylsubstituted BenzophenonesReaction of 3-alkyl-2,4,6-triarylpyrylium salts with 1,3-diketones in the presence of one equivalent of triethylamine or potassium tert-butoxide does not lead  -  as originally suspected  -  to the primary adducts of 2H-pyran structure 6, but to the open-chain valence isomers 7. Treatment of the latter with one equivalent of tert-butoxide in tert-butyl alcohol gives the same 3-alkyl-2,4,6-triarylacetophenones 9 which are obtained directly from 5, 1,3-diketones and two equivalents of potassium tert-butoxide. However, on treating 7 with aqueous ethanolic sodium hydroxide 3-acylsubstituted benzophenones 10 are formed in good yields. The reaction sequence 5→7→10 can also be performed through a one-pot-procedure.  -  The i.r., u.v., n.m.r. and mass spectroscopic data of the novel products 7, 9, and 10 are reported.
    Notes: No abstract.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 373-379 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 32. 2-Methoxy-2H-thiopyrans from 2,4,6-Triaryl-thiopyrylium SaltsReaction of 2,4,6-triarylthiopyrylium salts 1 with sodium methoxide in absolute methanol yields isolable 2-methoxy-2H-thiopyrans 2, the structure of which was proved spectroscopically. Using the 2,4,6-triphenyl derivative 2a as model compound, the behaviour of the 2-methoxy-2H-thiopyran system towards some nucleophiles and electrophiles was studied. Thus, on heating with ethanol the 2-ethoxy-2H-thiopyran 3 is formed. Nitromethane and ethyl cyanoacetate react with 2a in the presence of triethylamine to give 2,4,6-triphenylbenzene (6) and 2,4,6-triphenylbenzonitrile (7), respectively. Electrophiles (e. g. mineral acids or acyl halides) regenerate from 2a the starting thiopyrylium system; the same principle underlies the formation of 2,4,6-triphenylthiopyrylium perchlorate (1a) and 2-methoxy-3-methyl-2,4,6-triphenyl-2H-pyran (5) from 2a and 3-methyl-2,4,6-triphenylpyrylium perchlorate (4).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 328 (1986), S. 567-572 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. 33. 2-Dialkylamino-2H-thiopyrans from 2,4,6-Triaryl-thiopyrylium Salts2,4,6-Triaryl-thiopyrylium salts 7 react with dialkylamines in diethyl ether to give stable crystalline 2-dialkylamino-2H-thiopyrans 8, the structure of which is in accordance with their u.v., n.m.r. and mass spectra. The chemical properties of 8 parallel those of structurally analogous 2-alkoxy- and 2-dialkylamino-2H-pyrans and 2-alkoxy-2H-thiopyrans. Thus, on heating 2-dimethylamino-2,4,6-triphenyl-2H-thiopyran (8a) with methanol the corresponding 2-methoxy-2H-thiopyran 9 is formed. Nitromethane and ethyl cyanoacetate give rise to ring transformations yielding 1,3,5-triphenyl benzene (10) and 2,4,6-benzonitrile (11), respectively. From 8a electrophiles (e.g. mineral acids, methyl iodide, benzoyl chloride) regenerate the initial thiopyrylium system by taking over the dialkylamino group.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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