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  • 1
    Digitale Medien
    Digitale Medien
    Diels-Alder Reactions of Tetradehydrodianthracene with Electron-Rich Dienes (1996)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1996 (1996), S. 1795-1800 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Tetradehydrodianthracene ; Diels-Alder reactions ; Diradical ; Stretched bond ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Tetradehydrodianthracene (TDDA; 1) reacts with electronrich dienes such as butadiene, cyclopentadiene and o-quinodimethane under ambient conditions. Only 1:1 products 5-8 were observed even with a large excess of the diene and under drastic conditions (though two strained and highly pyramidalized double bonds are available). The enhanced reactivity of TDDA compared with its mono Diels-Alder adducts is mainly due to the through-bond and through-space interaction of the two olefinic double bonds. During the cycloaddition one of the olefinic bonds in TDDA is converted into an extremely long C-C single bond (〉 1.65 Å). Attempts to cleave the strained π-bond thermochemically to form a diradical 13 afforded product 14a that was formed via a formal intramolecular homo 1,3-sigmatropic shift.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.199619961113
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  • 2
    Digitale Medien
    Digitale Medien
    Electrophilic additions to tetradehydrodianthracene (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1283-1289 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Electrophilic addition ; Tetradehydrodianthracene ; Solvent effects ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: 5,12:6,11-Di[1,2]benzenodibenzo[a,e]cyclooctene (tetrade-hydrodianthracene, TDDA) (1) reacts with halogens to give transannular (anti) 4, 5 and ring-opened (syn) products 6, 7. The product ratio shows a remarkable solvent dependence. Solvents of medium polarity favor anti addition, whereas syn addition is observed both with increasing and decreasing polarity. For instance, chlorine in toluene adds 100% syn, in dichloroethane 56 % anti, and in trifluorethanol again 100% syn. It is concluded that, depending on solvent polarity, three different mechanisms for electrophilic addition are operative.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.1995199507170
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  • 3
    Digitale Medien
    Digitale Medien
    Diels-Alder Reactions of Tetradehydrodianthracene with Electron-Deficient DienesDedicated to Professor Dr. Miha Tisler on the occasion of his 70th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1473-1479 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Tetradehydrodianthracene ; Diels-Alder reactions ; Cycloadditions ; Tetrazines ; Steric hindrance ; Kinetics ; Semiempirical calculations ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Theoretical calculations and simple MO considerations predict that a coplanar and spatially close arrangement of double bonds in structures such as tetradehydrodianthracene 1, should both lower the LUMO and raise the HOMO energy of the π system. Thus the reactivity in Diels-Alder reactions towards electron-rich, as well as electron-deficient, dienes should be enhanced. The first effect has already been shown in a previous paper, the latter statement is now also confirmed by the reactivity of 1 in Diels-Alder reactions with inverse electron demand. In [4 + 2] cycloaddition reactions of 1 with 1,2,4,5-tetrazines 2 the electronic effect of 3,6 substituents in tetrazines is far outweighed by steric factors resulting in an unexpected reactivity sequence: 2a ≫ 2b ≈ 2c 〉 2d.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.199719970726
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