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  • Wiley-Blackwell  (65)
  • BioMed Central  (25)
  • 1
    Electronic Resource
    Electronic Resource
    Cyclisch gekreuzt-konjugierte Bindungssysteme, 31. Das vinyloge Pentafulvalen Synthese, Zwölfelektronen-Cyclisierung, Cycloadditionen (1977)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 1382-1402 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Cyclic Cross-Conjugated Bond Systems, 31. The Vinylogous Pentafulvalene Synthesis, Twelve-Electron Cyclisation, CycloadditionsThe synthesis of the vinylogous pentafulvalene 1 (1,2-biscyclopentadienylideneethane, 6,6′-bifulvenyl, pentafulvadiene) is described. In solution, 1 is inert towards photoexcitation but cyclizes thermally rapidly and quantitatively (Ea = 20 ± 0.4 kcal/mole, lg A = 11.3 ± 0.3; ΔH≠ = 19.4 ± 0.4 kcal/mole; ΔS≠ = -9 ± 1 e. u.) to trans-8a,8b-dihydro-as-indacene (8). The stereochemistry in 8 and consequently the conrotatory nature of this electrocyclic process  -  probable for steric reasons and with twelve participating bonding electrons symmetry-allowed  -  has been established by the vicinal coupling constants in the unsymmetrical derivatives 19 (J8,9 = 12.7 Hz) and 23 (J10,11 = 11.7 Hz) and finally by proving the C2-symmetry in the symmetrical bisadduct 21 with the help of a chiral shift reagent. 8 is photolabile and on direct excitation is cleanly isomerized back to 1. With reactive dienophiles 1 and 8 yield [4 + 2]-addition products (15-17; 19, 21); a [π2s + π10a]-type addition hoped for 8 (e. g. to 18) cannot be verified.
    Notes: Die Synthese des vinylogen Pentafulvalens 1 (1,2-Biscyclopentadienylidenethan, 6,6′-Bifulvenyl, Pentafulvadien) wird beschrieben. Es ist photochemisch inert und cyclisiert thermisch rasch und quantitativ (Ea = 20 ± 0.4 kcal/mol; lg A = 11.3 ± 0.3; ΔH≠ = 19.4 ± 0.4 kcal/mol; ΔS≠ = -9 ± 1 e. u.) zu trans-8a,8b-Dihydro-as-indacen (8). Die Stereochemie von 8 und mithin der aus sterischen Gründen ohnedies wahrscheinliche, bei Beteiligung von 12 Elektronen symmetrieerlaubte konrotatorische Verlauf dieses elektrocyclischen Prozesses wird durch Vicinalkopplungen in den unsymmetrischen Folgeprodukten 19 (J8,9 = 12.7 Hz) und 23 (J10,11 = 11.7 Hz) und letztlich durch Nachweis der C2-Symmetrie im Bisaddukt 21 mit Hilfe eines chiralen Shiftreagenzes bewiesen. 8 öffnet bei der direkten Lichtanregung einheitlich zu 1. 1 und 8 gehen mit reaktionsfähigen Dienophilen [4+2]-Addition (15-17; 19, 21) ein; eine bei 8 angestrebte [π2s + π10a]-Addition (z. B. zu 18) ist nicht erreichbar.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19771100423
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  • 2
    Electronic Resource
    Electronic Resource
    Über den Einfluss der pKa*-Werte von Anilinen auf die Bildung und Folgereaktionen von substituierten Butadienen aus Cumalinsäure-methylester2. Mitt. über Chemie der Cumalinsäurederivate; 1. Mitt. [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1569-1576 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Influence of Aniline pKa* Values on the Formation and Reactivity of Substituted Butadienes from Methyl CoumalateThe product of the reaction between 2 equiv. of methyl coumalate (1) and 1 equiv. of a substituted aromatic amine depends on the pKa* value of the latter. Aromatic amines with pKa* values between 1.05 and 2.8 produce bicyclic lactones 4, whereas those with higher pKa* values also give 2-azabicyclo[3.3.1]nona-3,7-diene-9-carboxylic acids 9. The latter, products of the intramolecular Diels-Alder reaction 8 → 9, may in certain cases even prevail.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680608
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  • 3
    Electronic Resource
    Electronic Resource
    Reaktionen des Cumalinsäure-methylesters und Cumalinaldehyds mit ambidenten Nucleophilen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1467-1473 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of Methyl Coumalate and Coumalaldehyde with Ambident NucleophilesMethyl coumalate and coumalaldehyde show great diversity in their reactions with ambident nucleophiles both depending upon the 2H-pyran-2-one derivative and the nature of the ambident nucleophile used. The products are either pyridine or pyrimidine derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710610
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  • 4
    Electronic Resource
    Electronic Resource
    Eine neue Azepinring-Synthese (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 457-463 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: A New Azepine-Ring SynthesisA new one-step synthesis of an azepine ring is described. The 2H-pyran-2-one ring of methyl cumalate (8) or cumalaldehyde (2) upon reaction with an 1-aminoacryl derivative, e.g. 1 or 6, is opened with subsequent decarboxylation to give a 1-aminobutadiene derivative that undergoes an electrocyclic ring closure to the azepine ring (Schemes 1 and 2).
    Notes: No abstract.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720306
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  • 5
    Electronic Resource
    Electronic Resource
    Distamycin-NA: A DNA Analog with an Aromatic Heterocyclic Polyamide Backbone. Part 1. Synthesis and structural analysis of monomers and dimers containing the nucleobase uracil (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 14-34 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the monomeric building block 13 and its constitutional isomer 12 of a new type of DNA analog, distamycin-NA, is presented (Schemes 1 and 2). This building block consists of a uracil base attached to a thiophene core unit via a biaryl-like axis. Next to the biaryl-like axis on the thiophene chromophore, a carboxy and an amino substituent are located allowing for oligomerization via peptide coupling. The proof of constitution and the conformational preferences about the biaryl-like axis were established by means of X-ray analyses of the corresponding nitro derivatives 10 and 11. Thus, the uracil bases are propeller-twisted relative to the thiophene core, and bidentate H-bonds occur between two uracil bases in the crystals. The two amino-acid building blocks 12 and 13 were coupled to give the dimers 15 and 16 using dicyclohexylcarbodiimide (DCC) in THF/LiCl and DMF, respectively. While the dimer 15 showed no atropisomerism on the NMR time scale at room temperature, its isomer 16 occurred as distinct diastereoisomers due to the hindered rotation around its biaryl-like axis. Variable-temperature 1H-NMR experiments allowed to determine a rotational barrier of 19 ± 1 kcal/mol in 16. The experimental data were complemented by AM1 calculations.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19980810103
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  • 6
    Electronic Resource
    Electronic Resource
    N, N, N′,N′-Tetrabutyl-3,6-dioxaoctan-dithioamid, ein ionophor mit Cd2+-Selektivität, Röntgenstrukturanalyse des Cd2+-Komplexes (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 1297-1303 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N, N, N′,N′-Tetrabutyl-3,6-dioxaoctan-dithioamid, an Ionophore with Cd2+-SelectivityThe CdCl2-complex of N, N, N′, N′-tetrabutyl-3, 6-dioxaoctanedithioamide crystallizes with the composition [Ligand. Cd2Cl4] in space group P1, a= 14.140, b= 10.025, c= 12.173 Å, α = 95.59°. β = 102.06°. γ = 85.50° Z= 2. Each ligand coordinates two Cd2+-ions. Adjacent cations are bridged by two Cl+-ions such that infinite bands along the b-axis are formed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650420
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  • 7
    Electronic Resource
    Electronic Resource
    Chemie der Cumalinsäurederivate. I. Synthese und Diels-Alder-Reaktionen von 1-Arylamino-2-methoxycarbonylbutadienen (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2769-2777 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nucleophilic attack of substituted anilines at position 6 of methyl coumalate (1) opens the α-pyrone ring to form 4-arylamino-3-(methoxycarbonyl)butadien-1-carboxylic acid 2 (Scheme 1). The latter are easily decarboxylated at room temperature in polar aprotic solvents to 1-arylamino-2-(methoxycarbonyl)butadiene 4 which smoothly undergo regio- and stereospecific Diels-Alder reactions with different dienophiles.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660845
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  • 8
    Electronic Resource
    Electronic Resource
    Über die Reaktion einiger 2H-Pyran-2-on-Derivate mit primären Aminen (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 407-416 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Reaction of Some 2H-Pyran-2-one Derivatives with Primary AminesThe versatile reactivity of 6-unsubstituted 2H-pyran-2-ones towards aliphatic and aromatic amines has been studied. It was found that the result of the reaction depends not only on the substitution of 2H-pyran-2-ones and on the structure of amines, but also on the stoichiometric ratio of reacting compounds.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740218
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  • 9
    Electronic Resource
    Electronic Resource
    Eine neue einfache Synthese spirocyclischer 1H-Chinolin-Derivate (1992)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 75 (1992), S. 1274-1280 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New and Simple Method for the Synthesis of Spirocyclic la-QuinolinesThe reaction of anilines with (+)-(R)-pulegone in toluene at temperatures between 125 and 150° with 4-toluenesulfonic acid or I2 as catalysts leads to diastereoisomeric mixtures of spiro[cyclohexane-1,2′(1′H)-quinoline] derivatives (see 1-4, Scheme 1; Table). The diastereoisomers are separated by column chromatography, and the structure of the single isomers is determined by NMR-spectroscopic methods. A reaction mechanism proceeding via several 6π-electrocyclic rearrangements and H-shifts is proposed for the formation of 1H-quinolines 1-4 (Scheme 2). This mechanism is in accordance with the results of the reaction of 2-isopropenylaniline with 3-methylcyclohexanone which leads to a stereoisomeric mixture of 3,4′-dimethylspiro[cyclohexane-1,2′(1H)-quinolines] (Scheme 3).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19920750428
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  • 10
    Electronic Resource
    Electronic Resource
    Säurekatalysierte Umsetzungen von 2- Vinylanilin-Derivaten mit 1-Benzyl- und 1-Methylpiperidin-4-on: Eine Elegante Synthese Neuer Polycyclischer Indol-Derivate (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1469-1475 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acid-Catalyzed Reactions of 2-Vinylaniline Derivatives with 1-Benzyl- and 1-Methylpiperidin-4-one: An Elegant Synthesis of New Polycyclic Indole DerivativesThe reaction of 2-vinylaniline derivatives with 1-benzylpiperidin-4-one or 1-methylpiperidin-4-one in toluene at temperatures between 115 and 120° with toluene-4-sulfonic acid as catalyst leads in good yields to a new class of polycyclic indole derivatives (Scheme 1, Table 1). The structure of the new diastereoisomerically pure racemic compounds 1-5 is determined by NMR-spectroscopic methods. A reaction mechanism proceeding via cyclization of enamine 9, leading to a racemic, tricyclic reactive intermediate 10, and subsequent intramolecular 1,5-dipolar cyclization as key steps in proposed for the formation of octahydropyrido[4′,3′:4]cyclobut[1,2-b]indoles 1-5. The scope and limitations of the new method are discussed (see Table 2).
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760407
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