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  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 147-153 
    ISSN: 0899-0042
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the chiral 9,12-dimethyl-4-oxa[7]paracyclophane 3 was achieved by the dithia route with subsequent sulfone pyrolysis. The conformational flexibility of the oxamethylene bridge with local Cs symmetry is evident from low temperature NMR experiments. Experimentally, an activation enthalpy of 11.4 kcal/mol is found for this process, which is in good agreement with the rotational barrier derived from semiempirical AM1 calculations (10.2 kcal/mol). Ab initio Hartree-Fock geometry optimizations have been performed for 3 and the corresponding hydrocarbon 9,12-dimethyl[7]paracyclophane 4. The distance of the O-atom to the center of the benzene ring in the structure of 3 is only 2.784 Å, i.e., significantly closer than the analogous C4-benzene ring distance in the slightly more strained 4 (3.112 Å). The enantiomeric separation of (±3) has been achieved by HPLC and the circular dichroism (CD) spectrum is reported. Ab initio all-electron DFT/SCI calculations of the CD spectrum are in good agreement with the experimental data and reveal the importance of p(O-atom)→ π* charge-transfer type excited states at relative low energies (6.6 eV, 188 nm) responsible for an intense negative CD band. The benzene type π → π* states are energetically lowered by 0.4-0.8 eV due to the boat-type deformation of the benzene moiety. By comparison of theoretical and experimental CD data the absolute configuration of 3 is assigned as (-)-(S). Chirality 10:147-153, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0947-3440
    Keywords: Cinnoline pyrolysis ; Circular dichroism ; Cyclophanes ; Dimethylbiphenylene synthesis ; Sulfone pyrolysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of 1,8-disubstituted biphenylenes by pyrolysis of azo compounds has been optimized. By means of a continuously working pyrolysis apparatus, the cis isomer 2 can be reliably produced on a gram scale. The chiral syn-[2.2]biphenylenophane 12 has been synthesized by an intermolecular cyclization reaction, subsequent oxidation of the sulfur atoms and pyrolytic extrusion of sulfur dioxide. In an analogous manner, the [2.2]biphenylophane 13 was obtained. The separation of the racemates of the hydrocarbons 12 and 13 could be achieved using a stationary chiral HPLC phase. Compound 12 preferentially adopts a syn conformation in the solid state. The CD spectra of 12 and 13 are compared.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    ISSN: 0009-2940
    Keywords: Chirality ; Circular dichroism ; Conformational mobility ; Cyclophanes ; [n]Phanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Deformed Chiral [n]MetacyclophanesThe new dithiametacyclophane 3c and the thiaazametacyclophanes 6a, b are chiral, but do not contain chirality centres. They are obtained by cyclization of 1,3-propanedithiol (2), or of the thiaza precursors 5a, b, with the bis(bromomethyl) compounds 1, 4a, b. The dynamic behaviour of the aliphatic chains in 3c, and 6a, b (flipping/rotation) have been studied by dynamic NMR. X-ray analyses of 3c and 6a document the out-of-plane deformation of the boat-shaped benzene ring. The circular dichroism of enantiomer-enriched 3c is reported.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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