We report a new method for preparation of hydroxyacids as precursors of benzolactones using a simple and an efficient electrochemical step. This gives in only four steps six- to eleven-membered lactones with high isolated yields from conveniently substituted aryl bromides. The lactonisation was performed according to the Yamamoto's process. 相似文献
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
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
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
The ability of tris[(S)-2-methylbutoxyl] aluminum to bring about asymmetric reduction of methyl ethyl ketone has been reinvestigated: only a low stereoselectivity has been observed. 相似文献
Previous low resolution studies indicated that, in the absorption spectrum, transitions to Rydberg states are far more sensitive to pressure than transitions to valence states in accordance with the complete vanishing of Rydberg bands and the deperturbation of the valence bands in the spectrum of NO trapped in a solid rare gas matrix. The present study of NO is the first extensive investigation of medium and high resolution molecular electronic spectra subjected to pressure of foreign gases. It is observed that, at the highest pressure attained (~1000 bar), almost all of the Rydberg bands have vanished whereas the remaining valence bands stay relatively sharp. While high pressure medium resolution spectra give information about the deperturbation of intensities and of vibrational spacings of the valence bands, inspection of low pressure high resolution spectra reveals that the rotational lines react to pressure in a way reflecting closely the degree of configuration mixing between Rydberg and valence states. 相似文献
Peracids in solution may undergo homolytic decomposition leading mostly to mixtures of acid and alcohols, these Latters being formed from either the peracid or the solvent The peracid behaves as source of radicals and also as substrate thus presenting two radicophile centers - with a nucleophilic radical (R' from peracid or S' from solvent) the site of attack is the 0-0 bond of the peracid yielding an alcohol (NuOH). The rate of this reaction increases with increasing nucleophilicity of the radical ; this reactivity is interpreted in terms of frontier orbital perturbation theory, taking into account both the orbital energy level difference and the orbital overlap.- when the radical is electrophilic, it abstracts rather the hydrogen of the peroxidic group Leading to decomposition of the peracid into acid.Hydrogen abstraction from the solvent may be also observed in appropriate cases : this process can be used for free radical hydroxylation of hydrocarbons.The relative importance of these three chain reactions in competition : 0-0 bound attack, hydrogen abstraction from the peracid and solvent transfer reaction were studied as a function of structure of the radicals, solvent properties and temperature. 相似文献