D. Mesnard

Structural changes of Ce-Pr-O oxides in hydrogen: a study by in situ X-ray diffraction and Raman spectroscopy

Ce–Pr–O mixed oxides prepared by coprecipitation and calcined at 1173 K reveal a non stoichiometric structure with oxygen vacancies in the bulk. In situ XRD and Raman spectroscopy were used to investigate these properties simultaneously and identified a thermal expansion coefficient twice as high as that of pure ceria at room temperature and the presence of a Raman band at 560 cm−1, characteristic of the oxygen vacancies. These results confirm that praseodymium atoms are able to induce oxygen mobility in the bulk at 298 K. This is due to a structure containing a high number of anionic vacancies pre-existing at ambient temperature.

Action de silanes propargyliques sur des derives carbonyles α-ethyleniques

Abstract Propargylsilanes RCCCH 2 Si(CH 3 ) 3 easily react with dialkyl alkylidenemalonates, in the presence of TiCl 4 , to lead to the only product corresponding to an 1,4-addition; the reaction takes place with propargylic rearrangement.

Etude du comportement d'organometalliques (M = Zn, Mg, Li) vis a vis d'enynes conjuges : I. Cas des carbures: HCCC(R)C(R)(R); influence de la structure sur la reactivite et la regioselectivite

Abstract Reactive organometallic compounds such as allyl-zinc, -magnesium, -lithium and saturated lithium compounds are shown to readily undergo addition reactions with conjugated enynes: HCCC(R)C(R)(R), but the reactivity is reduced when the steric hindrance around the double bond is increased. With each organometallic compound used, this reaction is regioselective: 3,4 addition with organozinc compounds, 1,2 addition with organolithium compounds (allyl, butyl) and both 1,2 and 1,4 addition with organomagnesium compounds.

Bis(trimethylsilyl)-1,3 alcynes-1 : Preparation a partir de silanes propargyliques et application a la synthese de silanes alleniques α-fonctionnels

Abstract 1,3-bis(trimethylsilyl)-1-alkynes may be obtained from trimethylsilyl propargylsilanes by metallation with n-butyllithium following by reaction with trimethylsilylchloride; these silanes easily react with acetals, in the presence of titanium tetrachloride, to produce α-functional allenyltrimethylsilanes.

Alcynylsilanes fonctionnels. I, Synthèse régiospécifique par voie organozincique d'alcools homopropargyliques trialkylsilylés α'- ou ω'-chlorés

In many cases, the reaction between α- or ω-chloro carbonyl derivatives and organozincs prepared from halides R3SiCCCH2Br is chemo- and regioselective: it affords, in a good yield, trialkylsilyl homopropargylic alcohols α′- or ω′-substituted by a chlorine atom. This behaviour is different of this of organoaluminiums which lead mainly to trialkylsilyl α-allenyl α′- or ω′-chlorinated alcohols.

Allénylsilanes fonctionnels: synthése régiosélective par voie organoaluminique d'alcools alléniques triméthylsilylés α′ - ou ω′-chlorés

Abstract In many cases, the reaction between α- or ω-chloro carbonyl derivatives and organoaluminium compound prepared from Me3Si−CC−CH2Br is chemo- and regioselective: it affords, in a good yield, trimethylsiyl α′ - or μ′-substituted by a chlorine atom; some of these functional alcohols have produced oxygenated heterocycles.

Synthèse régiospécifique d'amines tertiaires à groupe secondaire bi-insaturé

Abstract We describe the regiospecific preparation of tertiary amines with a symmetrical (or dissymmetrical) doubly unsaturated secondary group, by reaction of an allylic, vinylic or acetylenic organometallic derivative with a dialkylformamido acetal, a chlorinated iminium salt or an alkynyl aminoether.

Allénylsilanes fonctionnels: II. Synthèse par voie organoaluminique du 2-triméthylsilylbuta-2,3-diénal et application a la synthèse d'alcools secondaires α-alléniques triméthylsilylés

Abstract The 2-trimethylsilyl-2,3-butadienal is easily prepared, in good yield, by the reaction at −80°C between triethylorthoformate and the organoaluminum compound prepared from Me3SiCC-CH2Br. The resulting conjugated aldehyde reacts readily with various organometallic compounds (containing Al, Mg, Zn) to produce alcohols resulting from an 1,2-addition only, but for the saturated or phenylic magnesium derivatives which also give products from 1,4-addition.

Alcynylsilanes fonctionnels: III. Synthèse régiosélective par voie organozincique de 1-triméthylsilyl-4-éne-1-ynes fonctionnels☆

Abstract The organozinc prepared from trimethylsilylpropargylbromide regiospecifically reacts with triple bond of monosubstituted α-accetylenic alcohols, ethers, amines and bromides, to lead to functional 1-trimethylsilyl-4-en-1-ynes in good yield. These derivatives are easily desilylated to produce functional 1-en-4-ynes.

Alcynylsilanes fonctionnels II. Synthèse en une étape par voie organozincique d'éthers-oxydes cycliques à substituant propargyltrialkylsilyle☆

Abstract A convenient one-pot synthesis of alkynylsilanes bearing a cyclic ether group is described.