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  • Organic Chemistry  (42)
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  • 1
    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.
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  • 2
    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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  • 3
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 325 (1983), S. 729-741 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XVIII. 2-Alkoxy-2H-pyrans from Tetra- and Pentasubstituted Pyrylium SaltsAlkali alkoxides add regioselectively to 2,3,4,6-tetrasubstituted pyrylium salts 7 (R'= H), affording high yields of colourless crystalline 2-alkoxy-2H-pyrans 9. The latte are also formed simply on refluxing 7 in the corresponding alcohol with triethylamine as proton acceptor. 3,5-Dialkylsubstituted 2,4,6-triarylpyrylium salts react analogously. The 2H-pyran structure of the adducts obtained follows from their n.m.r., i.r., u.v. and mass spectra as well as from their reaction with tetracyanoethylene to cycloadducts of type 10. Acids regenerate from 9 the original pyrylium cations, whereas reaction of 9 with nitromethane or ethyl cyanoacetate provides benzene derivatives. -- The novel starting pyrylium salts 7b--o are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives
    Additional Material: 2 Tab.
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  • 5
    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.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 955-961 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXV. Quantum Chemical Calculations Concerning the Valence Isomerization of 2-Amino-2H-pyran and -thiopyranThe equilibrium 2-amino-2H-pyran 6 ⇌ 5-amino-2,4-dien-1-one 7 was investigated using the semi-empirical MINDO/3 and MNDO methods. In accordance with experimental findings for the substituted derivatives 1/2a-d, the introduction of a methyl group into the position 3 of 6 or the exchange of oxygen by sulfur shifts the equilibrium towards the cyclic structures 8 and 10, respectively. Polar solvents, the influence of which was estimated applying the reaction field approach as well as the solvaton theory, and entropy effects are calculated to favour the ring-open valence isomer 7. These results also correspond to experimental results.
    Additional Material: 3 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 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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  • 8
    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.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 287-302 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXI. Structure and Tautomerism of Pseudobases of Unsymmetrically Substituted 2,4,6-Triarylpyrylium SaltsHydrolytic ring opening of unsymmetrically substituted 2,4,6-triarylpyrylium salts 11 results in a mixture of two tautomeric pseudobases, the penten-1,5-diones 13 and 14. In crystalline state as a rule one of these tautomers markedly predominates, whereas in solution a rapid equilibrium establishment occurs which can be followed by 1H-n.m.r. and u.v. spectroscopy (equilibrium ratio nearly 1:1). The 1H-n.m.r. spectroscopic structural assignment of the two isomeric forms was supported by u.v. spectroscopic studies using 1:1 mixtures of the chromophoric partial systems ArCOCH=CHPh and ArCOMe or the pseudobases 10 of symmetrically substituted 2,4,6-triarylpyrylium salts 9 as reference systems. From the mass spectra of the pseudobases 10 and 13/14 follows that - if hydrolysis of 11 is performed in media containing H218O - mass spectrometric isotopic analysis of the resulting 18O-labelled pseudobases allows no information to be made about the regioselectivity of the ring opening. - Novel starting pyrylium salts of type 9 and 11 are characterized by u.v./vis data and by transformation into the corresponding pyridine derivatives.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 326 (1984), S. 647-656 
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrylium Compounds. XXII. 1H-N.M.R. and U.V. Spectroscopic Investigations on the Isomerization of Pseudobases of Unsymmetrically Substituted 2, 4, 6-Triarylpyrylium SaltsThe kinetics and mechanism of the isomerization of the title compounds, the pentene 1,5-diones 2 and 3, were studied by 1H-n.m.r. and u.v. spectroscopy. The equilibrium constants measured vary little near 1, indicating the small influence of substituents on the equilibrium position. The mutual rearrangement 2⇄3 proved to be a base-catalized reaction which is characterized by strictly linear Hammett correlation between 1g k and Σσp. The results obtained suggest resonance-stabilized anions of type4 as intermediates. - Pseudobases of 3-alkyl-2, 4, 6-triarylsubstituted pyrylium salts do not undergo a reversible isomerization.
    Additional Material: 2 Ill.
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