Couplage selectif d'azaallyllithium et d'arylallenes : synthese generale d'arylmethylenepyrrolidines

1–3 Cycloaddition of 1,3-diphenyl-2-azallyllithium with arylallenes affords a general synthetic method for arylmethylenepyrrolidines, a new class of five-membered-heterocycles.     

Assistance d'un groupe voisin pour des tosylates secondaires β substitues diequatoriaux dans l'hexafluoroisopropanol 97%

Solvolysis rates in methanol and 97% hexafluoroisopropanol (HFIP) for four β-methyl and β-phenyl bicyclic tosylates, show that solvent nucleophilic assistance is operating in the former solvent. However, in 97% HFIP, for three of the mentioned compounds, the mechanism involves π or σ neighboring group assistance. The factors influencing the occurrence of these processes are discussed. Owing to these possible neighbouring group assistances in non-nucleophilic solvents used to obtain k_c reference mechanisms, it is concluded that the k_a/k_c ratio which was proposed as a quantitative evaluation of solvent nucleophilic assistance must be used with caution.     

Dimerisation oxydante d'anions de sulfones (XXI)

Cupric salts, particularly triflates, convert α-sulphonyl carbanions into α-disulphones. Allylphenylsulphones couple preferentially in the 3-3′ mode.     

Couplage des sulfones allyliques avec des reactifs de grignard en presence de cuivre synthese d'olefines

A convenient synthesis of di- and trisubstituted olefins using the coupling of Grignard reagents with allylic sulphones in the presence of copper II acetylacetonate is reported. The influence of sulphone, Grignard reagent and solvent on the regio- and stereoselectivity is discussed.     

Method d'estimation des limites d'inflammabilite

We have employed the criteria defined by the CHETAH (ASTM) program to predict the lower and the upper flammability limits of various organic compounds. The results obtained for molecules containing carbon, hydrogen, oxygen and nitrogen are, in most cases, in good agreement with experimental values. The difficulties encountered when the molecule contains a heteroatom can be overcome by knowledge of the stoichiometric conditions of the combustion reactions.     

Determination de la constante d'acidite intrinseque d'un echangeur d'ions carboxylique

To obtain the intrinsic acidity constant of a carboxylic ion-exchanger, we propose a method of graphical double extrapolation. The results for an ion-exchanger made of polyvinyl alcohol grafted with acrylic acid are close to those published for the corresponding linear polyacid.     

Synthese ambidoselective d'enamines et d'imines siliciees

Trimethylchlorosilane reacts with organotin imines or enamines leading mainly (or only) to the corresponding silicon enamine. In contrast, the silylation of lithium or magnesium iminates gives only the isomeric imine when the nitrogen is hindered by bulky groups (i-Pr, t-Bu).The study of the NSi ? CSi equilibration shows clearly that in both cases the isomer obtained is the kinetic product of each reaction.These results show that a proper choice of both the metal associated with the iminate and of the iminate itself allows the formation of each isomer in a pure state.     

Coupures alcalines d'ethers bi-tertiaires et d'alcools

Heating αα′-tetrasubstituted ethers with sodium amide at 225–300° leads to smooth cleavage of one of the α-substituents, which is reduced in the process; the Intermediacy of an alkoxide ion is postulated, and a high yield cleavage of a tertiary alkoxide is indeed observed.     

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.