Transposition oxy-cope assistee par le trifluoroacetate mercurique en quantite stoechiometrique et en quantite catalytique

Tertiary 1,5-hexadien-3-ols are transformed at room temperature into δ-ethylenic ketones in 35-90%, yields under two sets of conditions: treatment with one molar equivalent of mercuric trifluoroacetate followed by demercuration of the intermediate α-mercuro ketone with sodium borohydride; and treatment with 0.2 molar equivalent of t of lithium trifluoroacetate or trifluorométhansulfonate. The reactions are highly stereoselective, the E isomer of the ketone forming 80-95% of the product. The highest selectivity was observed under the second conditions.     

Reaction des hexadiene-1,5 ols-3 avec le trifluoroacetate mercurique ; transposition d'oxy-cope a temperature ambiante.

Tertiary 1,5-hexadien-3-ols $\text{1}$ are transformed to δ-ethylene ketones $\text{2}$ in 35–75 % yield by treatment with one equivalent of mercuric trifluoroacetate and subsequent demercuration using sodium borohydride (Scheme 1, Table).     

Le dosage de traces d'argent dans le zinc extra-pur par activation neutronique

Below the p.p.m. level, the determination of silver in zinc by non-destructive γ-spectrometry is no longer feasible due to the activation of the matrix element. The activated zinc is dissolved in nitric acid, sulfamic acid and silver carrier are added, and ^110mAg (253 d) is obtained in a radiochemically pure state after two successive electrolyses on gold cathodes.After two days of irradiation in a thermal neutron flux of the order of 3.10¹³ n/cm²/sec (BR₂-Mol), 30 ng of silver can easily be evaluated with an error of 5%. Data obtained by integral γ-counting or by γ-spectrometry are compared.     

Mecanisme d'ignifugation d'elastomeres organosiliciques par le platine

The role of platinum and of some mineral oxides in improving the thermal stability of a silicone rubber has been studied by temperature-programmed thermogravimetric analysis and by isothermal pyrolysis. Platinum has no significant influence on the scission of side chains. It limits the rupture of the polymer backbone by preventing the formation of a transition complex involved in silicone degradation. Mineral oxides combine with certain products of the thermal decomposition of the polymer.     

Transposition des oxirannes-ethanols par l'intermediaire d'alcoxyetains

Oxiraneethoxytributyltins prepared from the corresponding oxiraneethanols, on heating at ～ 200° gave, after demetalation with isophthallic acid, 2-oxetanemethanols and/or 3-oxolanols. As appears from about thirty rearrangements the choice between oxetane and oxolane formation is dependent on: (1) the relative degree of substitution of the oxirane ring; cyclization occuring predominantly at the more substituted carbon; and (2) the configuration of the oxirane ring, when both its ends are equally substituted; cis form being more suitable for generation of the smaller ring. The reaction is shown to proceed with inversion of configuration at the site of oxygen attack. The results of attempts to perform the rearrangement in dilute-phase or through alkaline metal alkoxides in various media support the conclusion that there is a large contribution by electrophilic assistance to the oxirane opening. Such assistance can be efficiently provided by a tin atom in a push-pull mechanism which accomodates all the facts. The present method of oxiraneethanol rearrangement may offer a convenient route to functional oxetanes.     

Dilactones macrocycliques chirales derivees d'aminoacides. Synthese assistee par les organostannes ; proprietes complexantes

Three chiral macrocyclic dilactones containing L-glutamic or L-cystine moiety are synthetised by a simple method based on a tin “template-driven” process. Complexing properties are examined.     

Metallation des halogenures d'aryle par le tributylstannyllithium dans le tetrahydrofuranne

The metallation of aryl halides with tributylstannyllithium in THF proceeds via at least three different mechanisms whose relative rates depend on the nature of the halogen, the substrate and the experimental conditions. In the case of aryl bromides, a halogenmetal exchange (major process) is competing with a radical mechanism. With aryl chlorides, an arynic process, a halogenmetal exchange and a radical mechanism are involved. Finally, with aryl fluorides, the arynic process is usual, but it may be strongly competed by a radical mechanism whenever suitable experimental conditions are arranged.     

Photooxygenations par transfert d'electron sensibilisees par le dicyano-9,10 anthracene. Role du solvant et formation d'oxygene singulet.

Photooxygenation of naphtalenic compounds sensitized by electron acceptors like 9,10 dicyanoanthracene (DCA) is shown to proceed by two distinct ways depending on the solvent polarity. In a polar solvent superoxide ion (O₂^-.) as well as singlet oxygen (¹O₂★) are involved while in a non polar solvent only singlet oxygen is produced.     

Modification chimique du polybutadiene-1,2 par le phosphonate d'éthyle

The addition of diethyl phosphonate [HPO(OEt)₂] (I) to carbon-carbon double bonds of 1,2-polybutadiene is studied, in order to obtain functionalised polymers with phosphonate pendent groups. The interest is to obtain structures soluble in organic solvents, such as benzene or chloroform. The reaction is mainly catalysed by peroxides, tert.-butyl hydroperoxide being the most efficient. Study of the influence of various parameters (temperature, solvent and catalyst nature, concentrations of the various reaction components) has shown that the addition competes with cyclisation and, mostly, cross-linking reactions. (I) Addition and reticulation rates are closely dependent: increase of the first is always accompanied by increase of cross-linking. Whatever the reaction conditions may be with the considered 1,2-polybutadiene, gelation is complete as soon as the modification yield exceeds 6%. The polymer structures have been studied by ¹H-NMR and i.r., by comparison with those of the addition compounds obtained with model molecules (3-ethyl 1-pentene, 4-octene, 1,6-heptadiene).     

Transposition des oxirannes-ethanols par l'intermediaire d'alcoxyetains. Influence de la configuration de l'oxiranne

The transposition of oxirane-ethanols, through alkoxytin compounds, into oxetane-2-methanols and/or oxolan-3-ols (tetrahydrofuran-3-ols) is dependent upon the oxirane configuration. Cis configuration is more suitable for the formation of the smallest ring. Steric hindrance is not sufficient enough to explain the results.