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  • 1
    Electronic Resource
    Electronic Resource
    Diastereoselective Synthesis of 1-Hydroxy-Substituted Benzo[b]quinolidines and 11-Hydroxy-Substituted Azepino[1,2-b]isoquinolines via Hetero-Ene Cyclization (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 533-540 
    Details
    ISSN: 0947-3440
    Keywords: Ene reaction ; Benzo[b]quinolidines ; Azepino[1,2-b]isoquinolines ; Lewis acid catalysis ; Nitrogen heterocycles ; Cyclizations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (L)-Phenylalanine 4 can be converted to N-(4-methyl-3-pentenyl)tetrahydrosisoquinoline-3-carbaldehyde 10 and the corresponding homologous aldehyde 19 in 4 and 5 steps, respectively, by employing the Pictet-Spengler reaction as the key step. After Lewis acid catalyzed cyclization of 10 and 19 the cis-configured 1-hydroxybenzo[b]quinolizidine 21a and 11-hydroxyazepino[1,2-b]isoquinoline 22a were obtained with high diastereoselectivities. Compound 21a, which was characterized by X-ray structure analysis, displays a fishbone pattern of endless zig-zag chains connected via intermolecular hydrogen bonds in the solid state.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970314
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  • 2
    Electronic Resource
    Electronic Resource
    Diastereoselective Synthesis of 1-Hydroxy-Substituted Benzo[b]quinolidines and 11-Hydroxy-Substituted Azepino[l,2-b]isoquinolines via Hetero-Ene Cyclization (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1041-1041 
    Details
    ISSN: 0947-3440
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970538
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  • 3
    Electronic Resource
    Electronic Resource
    Enantioselective Cathodic Reduction of 4-Methylcoumarin: Dependence of Selectivity on Reaction Conditions and Investigation of the MechanismDedicated to Professor Dieter Seebach on the occasion of his 60th birthdayElectroorganic Synthesis, Part 64. Part 63: K. Möller, H. J. Schäfer, Electrochim. Acta 1997, 42, 1971-1978. (1997)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 2011-2024 
    Details
    ISSN: 0947-6539
    Keywords: enantioselective protonations ; kinetics ; quantum chemical calculations ; reductions ; voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cathodic reduction of 4-methylcoumarin (1) in acidic methanol/water in the presence of yohimbine leads to formation of a mixture of the hydrogenation product 4-methyl-3,4-dihydrocoumarin (2), with an enantiomeric excess (ee) of (R)-2 of 0-67%, and the hydrodimer 3. The relative yields of 2 and 3 and the ee of 2 depend on a number of experimental parameters such as pH, supporting electrolyte, working potential, and the concentrations of substrate and yohimbine, as demonstrated by a series of preparative-scale experiments. In addition, a series of voltammetric and kinetic measurements were carried out to investigate the influence of the individual experimental parameters. Three mechanistic possibilities have been examined, and by combination of the analytical data with the results of the preparative experiments, a single model is put forward which is in accord with the available results. The main features of the mechanistic model can be summarized as follows: 1) under acidic conditions (pH 2-3) the electroactive species is a complex between 1 and H3O+, the reduction of which leads to an enolic radical; 2) this radical is not reduced at the working potential but tautomerizes into the more easily reduced keto radical or dimerizes; 3) the keto radical is reduced and further protonated; 4) the function of the yohimbineH+ is to catalyze the tautomerization and enantioselectively protonate the final carbanion. Additionally, we conclude that the concentration of yohimbine in the immediate vicinity of the electrode is considerably higher than its stoichiometric concentration. Quantum chemical calculations demonstrate that si protonation of the intermediate anion by yohimbineH+ to give (R)-2 is energetically favored.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19970031216
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  • 4
    Electronic Resource
    Electronic Resource
    Notiz über eine einfache Synthese des tert-Butylmalondialdehyds (1974)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 107 (1974), S. 3454-3456 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19741071030
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  • 5
    Electronic Resource
    Electronic Resource
    Notiz zum Mechanismus der Japp-Klingemann-Reaktion von 1,3-Dialdehyden (1976)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 109 (1976), S. 3735-3737 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19761091126
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  • 6
    Electronic Resource
    Electronic Resource
    A Fourier Transform Ion Cyclotron Resonance Study of the Structure of some Phenyl-substituted 2-Azaallenium Ions (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 3877-3883 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Eine Fourier-Transform-Ionen-Cyclotron-Resonanz-Studie zur Struktur von Phenyl-substituierten 2-Azaallenium-IonenDurch Protonenabstraktionsreaktionen in Kombination mit Deuterium-Markierungsexperimenten wird gezeigt, daß die Ionen 1-3, die durch Elektronenstoß aus Benzylidenaminen durch Alkylradikal-Abspaltung aus der α-Position erzeugt werden, die Struktur von Phenyl-substituierten 2-Azaallenium-Ionen besitzen. Die durch die Deprotonierung entstehenden Moleküle zeigen sehr hohe Gasphasenbasizitäten (größer als 231.7 kcal/mol).
    Notes: It is shown by proton abstraction reactions in combination with deuterium labelling that the initial structure of the ions 1-3 generated by electron impact from some benzylideneamines through loss of an alkyl radical via α-cleavage is indeed that of phenyl-substituted 2-azaallenium ions. The deprotonated species appear to have very high gas-phase basicities, that are higher than 231.7 kcal/mol.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831161211
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  • 7
    Electronic Resource
    Electronic Resource
    The Structure of 2-Azaallenium Cations (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 3365-3373 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zum Bau von 2-Azaallenium-KationenEntsprechend einer Röntgenstrukturanalyse kristallisiert das 2-Azaallenium-hexachloroantimonat 23 in der Topologie eines Allens (Geometrie 1a) und nicht eines 2-Azaallyl-Kations (1b). Ab-initio-Molekülorbital- (3-21 G Basissatz) und semiempirische MNDO-Rechnungen für das unsubstituierte 2-Azaallenium-Kation und einige mono- und disubstituierte Derivate (24) bestätigen die experimentellen Befunde: In vielen Fällen ist die Allengeometrie 24a stabiler als die 2-Azaallylium-Form 24b. Elektronenspendende Substituenten verringern den Energieunterschied zwischen 24b und 24a. Ein diaminosubstituiertes Allylium-Kation 24b ist energetisch stabiler als die entsprechende Allenium-Form 24a. Ganz allgemein sind substituierte 2-Azaallenium-Kationen um das zentrale Stickstoffatom sterisch flexibel. Verbindung 23 wurde nach einer neuen Synthese hergestellt.
    Notes: According to an X-ray structural analysis, the 2-azaallenium hexachloroantimonate 23 crystallizes with the topology of an allene (geometry 1a) and not of a 2-azaallyl cation (1b). Ab initio molecular orbital calculations (3-21 G basis set) and semiempirical MNDO calculations for the unsubstituted 2-azaallenium cation and for some mono- and disubstituted derivatives (24) confirm the experimental results: In many cases the allenium geometry 24a is more stable than the 2-azaallylium form 24b. Electron-releasing substituents reduce the energy difference between 24b and 24a. With two amino substituents the allylium geometry 24b is energetically preferred to the allenium form 24a. In general, substituted 2-azaallenium salts are sterically flexible around the central nitrogen atom. Compound 23 was synthesized by a new method.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841171205
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  • 8
    Electronic Resource
    Electronic Resource
    Massenspektrometrische Untersuchung von Stickstoff-Verbindungen, XXXV. Phenylsubstituierte 2-Azaallenium-Ionen in der Gasphase (1982)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 115 (1982), S. 2626-2634 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Mass Spectrometric Investigation of Nitrogen Compounds, XXXV. Phenyl-substituted 2-Azaallenium Ions in the Gas PhaseThe gas phase chemistry of metastable phenyl-substituted 2-azaallenium ions (2a,b,c) is characterized by intramolecular electrophilic substitution reactions; these processes are energetically favoured in comparison with various phenyl and hydrogen migrations, in spite of the fact that the latter may give rise to the formation of more stable intermediates (nitrilium ions). As a direct consequence of the electrophilic substitution, 2a, c decompose via loss of HCN, whereas from 2b PhCN is eliminated unimolecularly. The combination of experimental investigations, employing [2H]-and [13C]-labelled precursors, and MNDO calculations allows to give a detailed description of the chemistry of isolated 2a,b,c cations.
    Notes: Für die Gasphasenchemie metastabiler phenylsubstituierter 2-Azaallenium-Ionen (2a,b,c) sind intramolekulare elektrophile Substitutionen charakteristisch; diese sind energetisch günstiger als diverse Phenyl- und Wasserstoff-Wanderungen, obwohl letztere zu thermochemisch stabileren Zwischenprodukten (Nitrilium-Ionen) führen. Als Folge der elektrophilen Substitution zerfallen 2a und 2c unimolekular unter HCN-Eliminierung, während aus 2b PhCN eliminiert wird. Experimente unter Benutzung [2H]- und [13C]-markierter Substrate liefern zusammen mit MNDO-Rechnungen ein detailliertes Bild für die Chemie von „isolierten“ 2a,b,c-Kationen.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19821150725
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  • 9
    Electronic Resource
    Electronic Resource
    Zur Struktur von N-Methylencarbonsäureamiden: Röntgenstrukturergebnisse, spektroskopische Untersuchung und quantenmechanische Berechnungen (1984)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 117 (1984), S. 1597-1605 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Structure of N-Methylenecarboxamides: X-Ray Data, Spectroscopy, and Quantum Mechanical CalculationsN-(Diphenylmethylene)acetamide (1) has been studied by X-ray crystallography as an example for the polyfunctional, highly reactive N-methyleneamides. The dihedral angle (C = N - C = O = 73°) and the bond lengths indicate that there is only little interaction between the C = O and the C = N groups. Extensive ab initio 3-21G calculations for the parent molecule H2C = N - CH = O (2) predict a C - N rotational barrier of ca. 4 kcal/mol with a cisoid form (C = N - C = O = 23°) as the most stable structure. MNDO data as well as spectroscopic properties (IR, 13C NMR) suggest high molecular flexibility due to the many electronic interactions possible for the nitrogen atom.
    Notes: Als Beispiel für die polyfunktionellen N-Methylencarbonsäureamide wurde N-(Diphenylmethylen)acetamid (1) röntgenographisch untersucht. C = N - C = O-Torsionswinkel (73°) und Bindungslängen deuten auf nur geringe Wechselwirkungen zwischen C = O- und C = N-Molekülteil. Ausführliche ab initio-3-21G-Berechnungen am Grundsystem H2C = N - CH = O (2) sagen eine C - N-Rotationsbarriere von ca. 4 kcal/mol voraus, wobei als stabilste Struktur eine cisoide Form (C = N - C = O-Winkel = 23°) gefunden wurde. MNDO-Daten und spektroskopische Untersuchungen (IR, 13C-NMR) deuten ebenfalls auf hohe molekulare Beweglichkeit, die vor allem durch die vielfältigen elektronischen Wechselwirkungsmöglichkeiten des Stickstoffatoms verursacht wird.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19841170428
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  • 10
    Electronic Resource
    Electronic Resource
    Strukturuntersuchungen zum System 1,3-Dialkoxy-2-aza-allenium-Ionen/1,3-Dialkoxy-2-aza-allyl-Kationen (1985)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 118 (1985), S. 3632-3642 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structural Study of the System 1,3-Dialkoxy-2-aza-allenium Ions/1,3-Dialkoxy-2-aza-allyl CationsThe title system (I/II) is experimentally accessible by regiospecific alkylation at the carbonyl oxygen of alkyl N-acylimidates 4 using trialkyloxonium salts. According to an X-ray investigation (3a), the salts 3 form a compromise structure between both isomeric forms, the alkoxy substituents being in exo positions in s-cis-conformations (C — N — C-bond angle 133.0°, torsional angle 70.4°). Quantum mechanical calculations (3-21G ab initio) for the parent substance N-formylformimidic acid 6a predict preferred nitrogen protonation giving 7a. Oxygen protonation leading to the allenic structure 8a is disfavoured by 11.4 kcal/mol. The allenic- (8a) and the allyl structure (9a) differ by only ca. 5 kcal/mol and indicate therefore enormous structural flexibility of the title system. 1H NMR spectra support the existence of chiral isomers of 3a at low temperatures; at higher temperatures rapid equilibration takes place.
    Notes: Das Titelsystem (I/II) konnte durch regiospezifische Alkylierung am Carbonylsauerstoffatom von N-Acylimidsäureestern 4 mit Trialkyloxonium-Salzen präparativ zugänglich gemacht werden. Die Salze 3 liegen im Kristall nach einer Röntgenstrukturbestimmung (3a) als Kompromißform aus beiden Strukturtypen I und II vor, wobei die Alkoxysubstituenten exo in s-cis-Konformation stehen (C — N — C-Winkel 133.0°, Torsionswinkel 70.4°). Quantenmechanische Berechnungen (3-21G-ab initio) sagen für die Stammverbindung, die N-Formylformimidsäure 6a, eine bevorzugte Protonierung am Stickstoffatom zum Ion 7a voraus, eine Sauerstoffprotonierung zur allenartigen Struktur 8a soll um 11.4 kcal/mol ungünstiger sein. Allen- (8a) und Allyl-Form (9a) sind nur um ca. 5 kcal/mol verschieden und sollten daher extrem leicht ineinander übergehen. 1H-NMR-Spektren bestätigen das Vorliegen chiraler, allenartiger Strukturen 3a bei tiefer Temperatur, bei erhöhter Temperatur tritt rasche Äquilibrierung ein.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19851180917
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