Comptes Rendus de l'Académie des Sciences - Series IIC - Chemistry最新文献

This review summarizes a new efficient carbon–carbon bond-forming reaction based on sulfanyl radical addition–cyclization, which proceeds by the formation of a carbon-centered radical species generated by the addition of a sulfanyl radical to a multiple bond and then intramolecular addition of the resulting carbon-centered radical to a multiple bond. The synthetic potentiality was demonstrated by the syntheses of anantine, oxo-parabenzlactone, cispentacin, vitamin D, and α-kainic acid.

A photoreductive cyclization has been used to synthetize the bicyclic core of (±)-bisabolangelone.

On treatment with SmI₂ in THF, 1-ferrocenyl-3-phenyl-2-propen-1-one and its related ferrocene-substituted enones underwent cyclodimerizations to give aldols (2a–g) with 3,4-trans configuration. Further reduction by using increased amounts of SmI₂ produced the corresponding diols. The stereoselectivity in this study was comparable with that in the SmI₂-promoted cyclodimerization of chalcones, but in contrast to that in the SmI₂-promoted cyclization-aldol reaction of 1,1’-dicinnamoylferrocenes. The thienyl- and furyl-substituted enones 5a and 5b could be visualized as an extended system of conjugated ketones, so that the SmI₂-mediated coupling reactions occurred preferably by linkages of β-carbons with thiophene or furan rings, giving compounds 8a,b and 9a,b.

1,5-Hydrogen atom transfer from α, β and γ carbons of cycloalkanones to an alkenyl or aryl radical on a side chain has been studied systematically. Deuterium labeling experiments and theoretical calculations were used to delineate this process. The results indicate that 1,5-hydrogen atom transfer is controlled mostly by conformational factors.

In the domains of chemical catalysis and analytical chemistry, the modification of metal electrodes by the deposition of multilayers was developed about twenty years ago. The purpose of our work was to compare the behavior of an electrode prepared with a substituted polyaniline with that of electrodes regularly used in analytical chemistry: platinum, platinized platinum and glassy carbon. We initially present results obtained with poly-2,5-dimethoxyaniline (PDMAn) on two classic systems: the couple Fe(CN)₆^3–/Fe(CN)₆^4– and the couple O₂/OH^–. The first example is often studied during training in electrochemistry because of the good results generally obtained. Levich’s equation is effectively well verified. On the other hand, reduction of oxygen and oxidation of OH^– ions are always limited by the rate of the electron transfer reactions. It seems to us that the study of the behavior of these two systems with platinum electrodes covered with PDMAn, platinized or not, could be interesting. The oxidation of isopropanol in a weakly acid medium was also investigated. In the field of analytical chemistry, a more detailed study is mandatory before deciding on the possibility of using electrodes modified with films of substituted polyaniline. An electrode, which would not be platinized, does not seem useful; the use of electrodes prepared with platinized polymers deposited on substrates less expensive than platinum, (glassy carbon for example), may be more interesting. It seems that H₂O₂ formation over a wide domain of potential would be the best result for oxidations and new experiments will be investigated.

Phosphomolybdic compounds were first described as active catalysts in heterogeneous catalytic reactions some twenty-five years ago. Research on these catalysts underwent a huge acceleration when an industrial application in the oxidation of methacrolein to methacrylic acid was reported. They were later developed with success as catalysts for the oxidative dehydrogenation of isobutyric acid into methacrylic acid for which they surpass in many aspects the FePO catalysts. More recently phosphomolybdic catalysts were shown to be very efficient for the oxidation of light alkanes. The structure of these ionic solids with discrete cations and anions can be defined at the molecular level of the heteropolyanion 〚PMo₁₂O₄₀〛^3–, this feature makes them attractive for fundamental studies on catalytic reaction mechanism or catalytic site visualization. In the latter case they represent a unique model of a mixed oxide cluster that can be advantageously used to design new catalysts. Starting from the acid H₃〚PMo₁₂O₄₀〛 two substitution types leading to important modifications of the catalytic properties are possible: (i) the substitution of protons with counter-cations, (ii) the substitution of molybdenum in the anions. This review addresses the effect of transition metals substituting protons on both catalytic and physicochemical properties. It will focus on the influence of iron, copper and vanadyl directly introduced as counter-cations and that of vanadium initially substituting molybdenum in the anion but which moves out due to a partial rebuilding of the anions under catalytic reaction conditions. These transition metals have important and complex effects and have been widely studied. In both cases alkaline metals substituting protons have been also studied.

This note presents a characterization method of the ‘adhesion’ of a coating by acoustic emission technique. In situ acoustic emission measurements which were investigated in terms of amplitude, absolute energy, position of the event, etc. were performed on WC–Co coated specimens prepared by HVOF (high velocity oxy fuel) during four-point bending tests. The microscopic observations of the specimens show two types of cracks: transversal cracks (regularly spaced on the coating surface) and interfacial cracks. Acoustic emission results show two different types of acoustic events in terms of absolute energy and amplitude, which are representative of two cracking mechanisms.

The electronic structures of the sesquioxide In₂O₃ and Sn-doped In₂O₃ are examined both self-consistently within the ab initio local density functional theory and using the non self-consistent extended Hückel method. A direct band gap and a wide dispersion of the bottom of the conduction band are obtained in the non-doped case. In the doped case, a narrow, half-filled band assigned to Sn is found at the bottom of the conduction band, in agreement with the metallic and transparent characteristics observed experimentally.

Lactols are compounds of increasing interest in the synthesis of active pharmaceutical derivatives. Nevertheless, the product obtained by the reduction of the carbonyl group of coumarin has been described only twice, and without definition of its precise chemical structure. Since these studies, doubts have been raised about the existence of a monomeric or dimeric form. Our study has led us to conclude definitely that the single dimeric form exists and to precisely define the spectral properties of the two diastereoisomers.

The continuous measure of quantitative chirality by the least squares method is extended to weighed sets. It is shown that a pairwise correspondence between the atoms of the enantiomers is obtained when all weights are equal.