Role du methyle 4β dans la formation des oxetanones en serie steroïde. Cas du cycle B.

The formation of oxetanones $\text{5}$ from bromoketonee $\text{2}$ requires the presence of a β-methyl group at C-4. The yield of the reaction $\text{2}$→$\text{5}$ is improved by addition of water to the medium.     

Rearrangement spinal en serie a/b cis : conversion du lithocholate de methyle en derives du d-homoandrostane

A new backbone rearrangement is observed in A/B $\text{cis}$ methyl lithocholate derivatives. It is initiated from the C-3 carbon either by dehalogenation of the chloroesters $\text{1}$ by AgSbFg₆ or by the action of the triflic anhydride on the si1y1ated ether $\text{2}$. This rearrangement leads to methyl diacholenate $\text{3}$ and new lactones in D-homoandrostane series $\text{5}$ and $\text{6}$. The differences of behaviour between A/B $\text{cis}$ and A/B $\text{trans}$ series and the mechanism of rearrangements are discussed.     

Echange de ligands mono- et penta-haptocyclopentadienyles en serie du titanocene

The action of cyclopentadienyl anions on the compounds CP₂TiA₂ is described (Cp  substituted or non-substituted cyclopentadienyl ring, A  Cl, n¹Cp or aryloxy group). In all cases the redistribution of cyclopentadienyl ligands, either by direct substitution at the n¹ or n⁵ ligands, or by intermolecular exchange of n¹ ligands, was observed.     

Copolymerisation alternee du methacrylate de methyle et du styrene complexes par du Chlorure de Zinc en milieu aqueux

In this paper we present some of our copolymerization results of methyl methacrylate with styrene in the presence of a complexing agent, zinc chloride. The reaction rates were studied as function of the level of complexing agent, water and time. It was found that the complexing agent level and the water level have opposite effect on the reaction yield, the reaction yield increasing as the level of the complexing agent is increased. The reaction time has also a positive effect on the yield. Using the interrelations between the various factors affecting the reaction an equation was derived; it relates the reaction yield with the following variables: monomers, complexing agent and water concentration as well as the reaction time. The experimental results were compared with theoretical values obtained from this equation and it showed a good fit.     

Processus de photopolymerisation du methacrylate de methyle en presence de chlorure de zinc

The photopolymerization of methylmethacrylate in solution or in bulk, initiated by DMPA (2,2-dimethoxy-2-phenylacetophenone) and BP (benzophenone), has been investigated in the presence of ZnCI₂ as a complexing agent. We have studied the steady state polymerization (measurement of R, and OT) and the behaviour of the excited states by laser spectroscopy. We have shown the following points: R_p and DP increase with [ZnCI₂]; the rate constant for propagation increases with [ZnC12]; the rate of initiation remains constant in presence of BP-ZnCl₂ but increases with DMPA-ZnCl₂. The results are accounted for by the results of laser spectroscopy.     

RMN du carbone-13 en serie cyclopropanique. Effets de substituants

Substituent effects on chemical shifts of cyclopropane derivatives are investigated by ¹³C NMR. When we introduce pairwise corrections in empirical correlations, the theoretical chemical shifts of trisubstituted cyclopropanes are in good agreement with experimental values.     

Interactions electroniques en serie organostannique aromatique : IV. Etude par spectroscopie infrarouge,correlation avec la RMN du fluor 19

The use of infrared spectroscopy allows the calculation of “pure” σ⁰_R(IR) and σ⁰_IR constants for organostannic substituents, as well as the existence of a relation between para-fluorine chemical shifts and σ⁰_IR.     

Stereochimie d'halogenation d'enols en serie exocyclique du cyclohexane

The steric course of the halogenation of exocyclic cyclohexyl enols E is not affected by the nature of halogenating species, medium, or substituent. In every case, equal amounts of axial and equatorial attack are formed. The results may be interpreted by a cyclic halogenation mechanism.     

Addition du chloracetate de methyle sur les olefines

α-Chloroesters add to olefins or dienes under redox catalysis by cuprous chloride in the presence of Bipy or Phen, leading to γ-chloroesters or unsaturated esters.     

Syntheses en serie racemique et en serie optiquement active d'une famille de derives oxygenes naturels de l'ombelliferone. Structure spatiale du (-)epoxy-3'6' auraptene

3'6'Epoxyaurapten and marmin were synthesized by a stereocontrolled way in racemic then in optically active forms from achiral precursors. The synthetic strategy is of biomimetic type. The reaction sequence involved a Sharpless asymmetric epoxidation as the key-step to induce chirality. Enantiomeric conversion gave rise to the opposite unnatural serie. The structural dimensions of (-)3'6'-epoxyaurapten have been ascertained by means of X-ray cristallography. This route allows the preparation of related molecules.     

Synthese en serie dedoublee d''un precurseur tricyclique du nor-18 methyl-8β-oestradiol

A diastereoisomeric mixture of cis- and trans-(10aR)- 7-hydroxy-10a-methyl-1-oxo-1,2,3,4,4a,9,10,10a-phenanthrene was synthesised from 2-methyl-1,3-cyclohexanedione. The enantiomers were separated at an early stage in the synthesis via a cyclohexane-carboxylic acid intermediate and no racemisation or inversion occurred at any step. The products are precursors of 8β-methyl 18-nor estradiol and of 8β-méthyl 18-nor 9β-estradiol respectively.     

Polymeres cryptants: Application a la polymerisation du methacrylate de methyle

The purpose of the present work, relative to anionic polymerization, is to describe the use of cryptands fixed on polymers in order to prepare alkali salts of radical anions complexed in tetrahydrofuran. All these new species initiate the polymerization of methyl methacrylate. The presence of complexed ion pairs increases the syndiotactic structure. The polymerization seems to obey Bernoullian statistics.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—II Comportement de la polymerisation en fonction de la temperature et de la composition du magnesien

The polymerization of methylmethacrylate initiated by tert butyl-magnesium chloride in tetrahydrofuran has been studied in terms of yield and balance-sheet. It has been shown that only the symmetrical form of the Grignard reagent is efficient in initiating the polymerization. Initiation, propagation and termination mechanisms have been proposed.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—III: Parametres thermodynamiques des propagations iso- et syndiotactique en fonction de la composition du magnesien

The thermodynamics of the polymerization of methylmethacrylate have been carefully studied for various MgCl₂/tBu₂Mg ratios. Assumptions have been made on the stereospecificity of the anionic propagation of MMA. The complex behaviour of the propagation mechanisms may result from possible (donor-acceptor) equilibria between monomer and ether on the one hand, and different magnesium compounds on the other.     

Etude enthalpique de l'interaction du chelate Eu(DPM)3 avec une serie de pyridines en solution

Résumé Les constantes d'équilibre et les variations d'enthalpie entre une série de pyridines méthylées et le chélate tris(dipivaloylméthanato) europium (III) ont été déterminées à 36° dans le chloroforme par des mesures calorimétriques. Nous constatons que la chaleur de complexation de l'adduit 1/1 est sensible à l'encombrement stérique du ou des méthyles en de l'hétéroatome. Cependant, lorsque le rapport des concentrations entre la base et le chélate est supérieur à l'unité, l'enthalpie de la réaction est modifiée. Dans ce cas, nous attribuons cette modification à l'existence d'un équilibre supplémentaire entre le chélate et les bases conduisant à la formation de l'adduit 1/2.

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Equilibrium constants and enthalpy changes are reported between a series of substituted methylpyridines and the chelate tris(dipivaloylmethanato)europium(III) in chloroform solution at 36° as obtained by calorimetric measurements. The 11 adduct enthalpies are ordered in agreement with the electronic and steric effects of the methyl group in a to the heteroatom. Some anomalies are observed when the concentration ratio between ligand and chelate is higher than unity. These findings conform with the hypothesis of the existence of a supplementary equilibrium which may be assigned to the formation of the 12 adduct.

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Zusammenfassung Es wird über durch kalorimetrische Messungen ermittelte Gleichgewichtskonstanten und Enthalpie-Änderungen zwischen einer Reihe substituierter Methylpyridine und dem Tris(dipivaloylmethanato)-Europium (III) Chelat in Chloroform bei 36° berichtet. Die 1/1 Addukt-Enthalpien befinden sich in Übereinstimmung mit dem elektronischen und sterischen Effekt der Methylgruppe im a des Heteroatoms. Einige Anomalien werden beobachtet, wenn das Konzentrationsverhältnis zwischen dem Liganden und dem Chelat höher als eins ist. Diese Feststellungen sind im Einklang mit der Hypothese der Existenz eines supplementären Gleichgewichts und können der Bildung des 1/2-Adduktes zugeordnet werden.

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, , // () 36°. 11 , - . , . . . 12.

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Les auteurs souhaitent exprimer ici leurs remerciements au Docteur J. F. Gal pour l'intérêt qu'il a porté á ce présent travail.     

Sur la non-equivalence des liaisons CH du groupement methyle dans les complexes cristallises de trans-bromotetracarbonyle methyle carbyne de chrome

The syntheses, ³¹P{¹H} NMR spectra, and a structure of “mixed” 1,5-cyclo-octadienebis(tertiary phosphine)dirhodium complexes possess a rhodiumrhodium bond, briding diphenylphosphido and two different stereochemistries around the rhodium atoms. One rhodium is tetrahedral and surrounded by four phosphorus atoms and the other rhodium (bonded to COD) is nearly planar.