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.     

Etude du mecanisme de la cyclotrimerisation catalytique de l'hexyne-3 par l'intermediaire d'un complexe cyclobutadienique du nickel

The reduction of nickel halide by metals in low oxidation states, in a boiling solution of 3-hexyne in tetrahydrofuran leads to catalytic and quantitative cyclotrimerisation of the unsaturated compound. During the reaction, tetraethylcyclobutadienenickel(II) dibromide can be isolated in appreciable yield. A mechanism is proposed for the cyclotrimerisation.     

Etude de la structure des oligomeres de l'isoprene desactives par les halogenures d'alcoyle

The deactivation of oligoisoprenyllithium RM_n^?, Li⁺ by an alkyl halide R′X yields two kinds of products: RM_nR′ and RM_nR; the microstructure of the isoprenic units in the oligomer is mainly 4,1 and 4,3 and it is determined by the addition to the active chain of an isoprene molecule or of the alkyl halide molecule. The microstructures of RM_nR′ and of RM_nR are different. The results indicate two kinds of halogen-lithium reactions leading to the products RM_nR: between the excess of initiator RLi and the alkyl halide or between oligoisoprenyllithium and the alkyl halide.     

Reaction de perhalostyrenes avec les organolithiens. Preparation d'aryl-1 alcynes-1 ramifies par l'intermediaire d'aryl fluoro acetylenes

Organolithium compounds react with 1-aryl 2-chloro 1,2-difluoroethylene to give derivatives of type ArCCR¹. Hydrolysis of the intermediate carbanionic species yields the corresponding α,β-difluorostyrenes.     

Influence de la solvatation par le tert-butanol sur la structure et la reactivite de l'enolate de potassium de l'acetylacetate d'ethyle en presence de couronne ou de cryptand. etude par spectrometrie infra-rouge et cinetique

The structure and the nucleophilic reactivity of crowned (18-crown-6) or cryptated {cryptand (2.2.2)} potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF). In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hydrogen-bonded to the solvent, is in a “transoid” (non chelating) conformation. Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME). In contrast to what is observed in tert-butanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME; in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation. The solvation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C₆D₆-t-BuOH, THF-t-BuOH). The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.     

Effet de longueur d'onde et controle par la geometrie de l'etat fondamental de la photoisomerisation de derives de l'hexatriene-1,3,5

Irradiations at different wavelengths (313, 254, 229 and 214 nm) of the 4 geometric isomers of 5-phenyl-1,3,5-heptatriene show that the photochemical behaviour of these trienes is mainly controlled by their ground state equilibrium.     

Forme des cristallites d'oxyde de cadmium produits par decomposition de l'hydroxyde

The structural transformation that occurs in the cadmium hydroxide decomposition reaction has the morphological and crystallographic character of a martensitic transformation. The authors predict the shape of the oxide crystallites produced during the reaction, viz., small platelets developed parallel to the (111) oxide planes. The difficulty in assessing their shape by analysis of X-ray diffraction line profiles is discussed. Electron microscope and X-ray diffraction results are presented and it is shown that the oxide crystallite shape is dependent on whether the precursor is hydroxide or carbonate.     

Etude des solutions solides d'oxyde de lithium dans l'oxyde de nickel. II. Influence de la pression d'oxygene et mecanismes d'incorporation

The formation of solid solutions of lithium and nickel oxides, containing more than 2 at Li %, requires the presence of oxygen under a pressure which must exceed 10^?3 torr at 933 K. Solid solutions containing a maximum of 2 at Li % however can be prepared under a reduced pressure of oxygen (< 10^?4 Torr). Mechanisms are proposed to explain, in both cases, the incorporation of lithium ions in the nickel-oxide lattice.     

Obtention d'un oxiranne far actiom de l'ozone sur un vinylsulfure

Ozone reacts with one vinyl sulphide and gives an oxirane, this fact confirms that oxirane is probably an intermediate in course of reactions of ozone with vinyl derivatives which give products containing unmodified hydrocarbon chains.     

Influence de la longueur d'onde sur la photoisomerisation de derives de l'hexatriene-1,3,5

Kinetic studies of photoisomerization of 1-phenyl 6-methyl-cyclohexa-1,3-diene, and of the four isomeric 5-phenylhepta-1,3,5-trienes, have been performed at 313, 254, 228 and 214 nm. Photoreactions of these compounds are dependent on the wavelength of irradiation. Photolysis at short wavelength of Z,E-5-phenylhepta-1, 3,5-triene initiates a new reaction, sigmatropic [1,5] hydrogen migration, forming an ene-allenic compound. Thermal reactivity data for polyenic compounds supports the assigned structures.     

Etude de l'equilibre entre l'oxyde de nickel et l'oxygene. Essai d'interpretation des lois de variation de la conductivite electrique en fonction de la temperature

In a previous paper we have shown that at 740°C and under an oxygen pressure less than 1,3 torr the electrical conductance G of a NiO powder reaches rapidly an apparently stabilized signal G_i which sharply decreases after a sufficiently long time to a G₀ value independent of P_O2.From this observation we have studied the influence of the temperature successively on the electrical conductance G_i and G₀. The Arrhenius law is only verified for the G₀ = f(T) curve. G₀ appears as the representative value of the gas-solid equilibrium.     

Sur la reactivite des organomagnesiens derivant de l'addition d'organomagnesiens allyliques sur l'isoprene

Contrary to a recent report, it is shown that allylic Grignard reagents prepared by treating allylic Grignard reagents with isoprene and a catalytic amount of Cp₂TiCl₂ react normally with carbon dioxide and carbonyl compounds: a complete allylic rearrangement is observed.