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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 124 (1991), S. 827-832 
    ISSN: 0009-2940
    Keywords: Conformations, solid state ; Conformers in solution ; UV-Vis transition energies and CO/CO dihedral angles ; CO/CO rotational barriers ; Calculations, CNDO/S-CI, MMP1, PIMM / PE spectroscopy ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chromophoric Systems, 2. - Conformation and Absorption of Light in (2-Alkoxyvinyl)ethanedionesThe unusual color properties of yellow 1,2-bis(4,5-dihydrofuran-3-yl)ethane-1,2-dione (1) and colorless 1,2-bis(5,6-dihydro-4H-pyran-3-yl)ethane-1,2-dione (2) in the solid state and in solution are investigated by crystal structure analysis, UV-Vis, PE, and 13C-NMR spectroscopy as well as by reparameterized force-field calculations. Dione 1 takes an antiperiplaner CO/CO conformation of its chromophore in the solid state whereas dione 2 is twisted in this respect by 102°. In solution both chromophores are not planar, but 1 is less distorted (ca. 142°) than dione 2 (ca. 126°). The calculated rotational barrier for CO/CO twisting amounts to 0.9 kcal mol-1 for 1 and to 2.2 kcal mol-1 for 2.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1989 (1989), S. 527-531 
    ISSN: 0170-2041
    Keywords: Dehydroalanine esters, N-(arylmethylene)- ; Tetrahydropyridines ; 3,6-Diazabicyclo[3.2.1]oct-2-enes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: On the Dimerization Reaction of N-(Arylmethylene)dehydroalanine Methyl EstersN-(Arylmethylene)dehydroalanine esters are highly reactive compounds. They dimerize in a [4 + 2] cycloaddition reaction (Diels-Alder reaction) yielding rac-3,4,5,6-tetrahydropyridine derivatives 2 Which can be isolated under suitable conditions. In solution the dimers 2 tautomerize to give the enamines 3 which subsequently undergo a fast intramolecular cyclization reaction yielding the bicyclic compounds. 4. These 3,6-diazabicyclo[3.2.1]oct-2-ene derivatives 4 are formed diastereoselectively. The structure of 4 was established by X-ray analysis. The bicyclic diaminodicarboxylic esters 4 represent the stable final products of this series of transformations.
    Notes: N-(Arylmethylen)dehydroalaninester sind hochreaktive Verbindungen. Sie dimerisieren unter [4+2]-Cycloaddition (Diels-Alder-Reaktion) zu rac-3,4,5,6-Tetrahydropyridin-Derivaten 2, die unter geeigneten Bedingungen isoliert werden können. In Lösung tautomerisieren die Dimeren 2 zu Enaminen 3, die schnell intramolekular zum Bicyclus 4 reagieren. Diese 3,6-Diazabicyclo-[3.2.1]oct-2-en-Derivate 4 werden diastereoselektiv gebildet. Ihre Struktur wurde durch Röntgenstrukturanalyse geklärt. Die bicyclischen Diaminodicarbonsäureester 4 stellen die stabilen Endprodukte der gesamten Reaktionsfolge dar.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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