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  • Ab initio calculations  (1)
  • Bicyclo[1.1.1]pentane  (1)
  • 1
    ISSN: 0947-3440
    Keywords: Conjugation ; X-ray diffraction ; Molecular structures ; Ab initio calculations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Low temperature crystal structural studies of small cyclopropyl-conjugated unsaturated hydrocarbons reveal significant differences in bond lengths between carbon atoms mainly within the three-membered rings but also for adjacent C—C single bonds. The strongest influence of conjugation was observed for spiro[2.4]hepta-4,6-diene (1), where the difference in the lengths of three-membered ring bonds is 0.050 Å (X-ray). The same effect is also obvious from ab initio calculations at HF/6-31G(d) (to a minor extent) and MP2/6-31G(d) levels, as shown by a difference analysis of bond lengths which was performed in order to cancel out systematic errors and differences for both methods. Static difference electron density maps were derived from the experimental data by multipole refinements. These maps showed shifts of electron density to exocyclic locations within the planes of the three-membered rings and significant bond ellipticities for the adjacent single bonds. For 1,1-diethenylcyclopropane (4) a nonsymmetric conformation was found in the crystal lattice, very close to the global minimum structure calculated by ab initio methods.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-193X
    Keywords: Bicyclo[1.1.1]pentane ; Haloarenes, cross-coupling of ; Propellanes ; Palladium ; Catalysis ; Small-ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Radical addition reactions of organyl iodides 7a-s onto [1.1.1]propellane (2) followed by halogen-lithium exchange and transmetallation with zinc chloride, as well as additions of Grignard reagents to 2, have furnished a variety of 3-substituted bicyclo[1.1.1]pentyl-1-magnesium (14) and -zinc (19) derivatives. The latter have been coupled with various alkenyl, aryl, and biaryl halides and triflates under NiCl2dppe, Pd(PPh3)4, or PdCl2(dppf) catalysis to give a number of 1,3-disubstituted bicyclo[1.1.1]pentyl derivatives 17, 20, and 23, several of which exhibit liquid crystalline properties, in moderate to very good yields. The coupling products 20ca, 23ab, 23ae, 23ff, and 23fg have been further transformed to yield bicyclo[1.1.1]pentyl derivatives 32, 24ab, 24ae, 27ff, and 27fg, respectively, bearing alkynyl, cyano, and/or alkenyl groups.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
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