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121.
An efficient route to chiral chromene and tetrahydroquinoline ring models 3 and 4 was developed by means of the vanadium epoxidation of chiral homoallylic alcohols 12 and 19 followed by an intramolecular epoxide opening of 3,4-epoxy alcohols 14 and 20. The configuration of all compounds was confirmed using NMR analysis. 相似文献
122.
Salpin JY Mormann M Tortajada J Nguyen MT Kuck D 《European journal of mass spectrometry (Chichester, England)》2003,9(4):361-376
The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C(7)H(9)(+) ions, [CHT + H](+). The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 +/- 4 kJ mol(-1), was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C(7)H(9)(+) population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 +/- 4 kJ mol(-1), and the heat of formation of the cyclo-C(7)H(9)(+) ion, deltaH(f)(0)([CHT + H](+)) = 884 +/- 4 kJ mol(-1). Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H((1))](+), generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 +/- 2 kJ mol(-1) and deltaH(f)(0)(300)([CHT + H((1))](+)) = 892 +/- 2 kJ mol(-1). However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C-C bond formation, generating protonated norcaradiene [NCD + H](+), a valence tautomer being 19 kJ mol(-1) more stable than [CHT + H((1))](+). The 1,4-dihydrotropylium ion, [CHT + H((3))](+), generated by protonation of CHT at C-3, is 17 kJ mol(-1) less stable than [CHT + H((1))](+). The bicyclic isomer [NCD + H](+) is separated by relatively high barriers, 70 and 66 kJ mol(-1) from the monocyclic isomers, [CHT + H((1))](+) and [CHT + H((3))](+), respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H((1))](+) does not rearrange to the bicyclic isomer [NCD + H](+) under mild protonation conditions. 相似文献
123.
Jean-Yves Saillard Samia Kahlal Vincent Ferrand Helen Stoeckli-Evans Georg Süss-Fink 《Journal of organometallic chemistry》2001,620(1-2):119-126
Triruthenium clusters containing a methylphenylsulfoximido cap or bridge, Ru3(CO)9(μ2-H)[μ3-NS(O)MePh] (1), Ru3(CO)10(μ2-H)[μ3-NS(O)MePh] (2), Ru3(CO)8(μ3-η2-CPhCHBu)[μ3-NS(O)MePh] (3), Ru3(CO)9(μ3-η2-PhCCCCHPh)[μ2-NS(O)MePh] (4), and Ru3(CO)7(μ2-CO)(μ3-η2-PhCCCCHPh)[μ3-NS(O)MePh] (5) have been examined by EHT and DFT calculations in order to analyze the bonding present in the clusters and to establish the electron counting. They clearly show that a μ3-sulfoximido group is not a 3e− ligand as one may be led to think at first sight, but rather acts as a three-orbital/5e− system, i.e. should be considered as isolobal to an N---R− ligand. Because of some delocalization of its π-type orbitals on the sulfur and oxygen atoms, it is expected to bind slightly less strongly to metal atoms than classical imido ligands. Once in a μ2 coordination mode, the sulfoximido ligand retains a lone pair on its pyramidalized N atom and becomes a two-orbital/3e− ligand. It follows that clusters 1, 2, 4 and 5 are electron-precise, whereas cluster 3 is electron deficient with respect to the 18e− rule but obeys the polyhedral skeletal electron pair electron-counting rules. Consistently, all the calculated clusters exhibit large HOMO–LUMO gaps and no trace of electron deficiency can be found in their electronic structures. 相似文献
124.
Jean-Yves Piquemal Sabine Halut Jean-Marie Brgeault 《Angewandte Chemie (International ed. in English)》1998,37(8):1146-1149
Model compounds for silica surfaces modified with metal complexes are provided by the mononuclear anionic diperoxo species 1 and the dinuclear complex anions 2 (M = Mo, W). They were obtained in fair to nearly quantitative yields by the reactions of Ph3SiOH and [Ph2Si(OH)]2O, respectively, with an aqueous solution of [MO(O2)2(H2O)2]. 相似文献
125.
Jean-Franois Devaux Pierre Fraisse Issam Hanna Jean-Yves Lallemand 《Tetrahedron letters》1995,36(52):9471-9474
An unprecedented remote effect of the hydroxyl group on π-facial selectivity was observed in the addition of Grignard reagents to bicyclo[2.2.2]octan-2-ones, where nucleophilic attack occured from the slerically more hindered face. 相似文献
126.
Bachir Zouchoune Jean-Yves Saillard Jean-François Halet 《Journal of Cluster Science》2007,18(3):720-728
DFT calculations show that the optimal metal valence electron (MVE) count of omnicapped cubic rhodium clusters containing
more than eight terminal ligands, is 114. For such a count, a closed-shell configuration is computed with a substantial HOMO-LUMO
gap. The presence of more than eight terminal ligands in the clusters favors highly distorted cubic architectures with capping
ligands asymmetrically bound to the distorted metallic square faces. Removal of terminal ligands leads to the replacement
of bonding M–L electron pairs by nonbonding electron pairs localized on the metal atoms, giving rise to unchanged MVE count. 相似文献
127.
Sans résumé
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128.
129.
We first build the moduli spaces of real rational pseudo-holomorphic curves in a given real symplectic 4-manifold. Then, following the approach of Gromov and Witten [3, 19, 11], we define invariants under deformation of real symplectic 4-manifolds. These invariants provide lower bounds for the number of real rational J-holomorphic curves which realize a given homology class and pass through a given real configuration of points. Mathematics Subject Classification (2000) 14N10, 14P25, 53D05, 53D45 相似文献
130.
Jean-Yves Charbonnel 《Mathematische Annalen》1980,250(1):1-34
Sans résumé 相似文献