Rearrangements d'allyloxy-pyridines catalyses par les complexes du platine(o)

Zerovalent Platinum complexes catalyse the conversion of allyloxy-pyridines into N-allyl pyridones. The results can be rationalized by assuming an intermediate π allylic complex.     

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.     

Mecanisme de l'homologation directe d'acetyleniques en allenes

Homologation of a terminal acetylene to an allene is easily accomplished in a “one-flask” process, via a Mannich base which is transformed to the desired allene by a 1–5 hydrogen shift.     

Esterifications selectives induites par proximite au sein d'un complexe du platine (II)

The proximity induced by the coordination within a platinum (II) complex of pyridinic and olefinic ligands, respectively bearing a hydroxyl group (primary, secondary or tertiary) and an acetic acid-carboxylic acid mixed anhydride results in the preferred esterification of these alcohol functions rather than a primary alcohol in the same solution. Moreover it allows a very selective attack at one of the two mixed anhydride carbonyl groups which leads to the formation of Pt(II) complexes containing a macroligand that spans trans positions.     

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.     

Les organosiliciques comme agents de synthese d'acetals β-halogenes

The reactions of unsaturated aldehydes and ketones with diols in presence of halogenosilane lead to the synthesis of halogenoacetals in yields of 60–97 %.     

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).     

Mecanisme d'hydrolyse en milieu basique aqueux d'esters allophaniques,modeles de carboxybiotine

This work is dealing with basic hydrolysis in water of allophanic esters as possible models of carboxybiotin. A complex mechanism is involved likely due to competition of nucleophilic attack on the two carbonyl groups of the substrate. The rate of hydrolysis is significantly increased by metallic cation (Mg⁺⁺), a specific effect which allows to consider characterization of selectivity of bond breaking between nitrogen and carboxylate group with other nucleophiles.     

Alkylamidation d'organometalliques par les sels d'oxoimminium-1,3 cycliques

Dialkylcuprolithium reagents are efficiently condensed at low temperature onto N-Methyl 2-(2,4,6-trimethyl) cyclo 1,3-oxoimminium salts giving rise specifically to the corresponding alkylamides.