Diastéréotopies dans la série du benchrotrène

¹H and ¹³C spectra of mono-and disubstituted (benzene)-tricarbonylchromium complexes have been analysed. The influence of the substituents is discussed and special attention is paid to the diastereotopy resulting from different types of chirality. The racemic pseudosymmetric isomer and the two meso pseudoasymmetric isomers of the glycols (OC)₃CrC₆H₄(CHOHCH₃)₂ are compared. The stereochemical requirements are also examined.     

Synthèse de flavones et de xanthones dans la série du benzo[4,5]thiophène

We describe the first synthesis of 2-arylbenzo[4,5]thieno-[2,3-b]pyran-4-one and of 2-arylbenzo [4,5] thieno [3,2-b] pyran-4-one, from benzo [4,5] thiophene and we have extended these cyclizations to obtain the heterocyclic analogs of the xanthones.     

Processus de rotation empéchée autour de la liaison C?N dans les anilines

In anilines, intramolecular exchange of amino protons appears at low temperatures. Relations between activation parameters and electronic effects of substituents are studied and NMR parameters discussed.     

Utilisation de la RMN a champs forts dans la série du norbornène: triméthylsilyl-endo-3 bicyclo (2.2.1) heptène-5

High field NMR spectroscopy, double resonance and INDOR experiments are used for unambiguous assignment of the endo configuration of 3-trimethylsilyl-5-norbornene. Chemical shifts and coupling constants have been accurately determined and tested by computer simulation. Some ‘non W’ long range couplings are demonstrated.     

Isolement et identification de la C-galactosyl-8 apigénine dans les tiges feuillées de Carlina acanthifolia

Isolation and Identification of 8-C-Galactosylapigenin from Leaves of Carlina acanthifolia 8-C-galactosylapigenin was isolated from the leaves of Carlina acanthifolia (Compositae). This identification represents only the third report of a mono C-galactosylapigenin in plants and the first report in the Compositae.     

Recherches dans la série des cyclitols XXXIX RMN. de protons d'hydroxyles de cyclopentane- et de cyclopentène-polyols

Several mono-, di-, and tri-hydroxy derivatives of cyclopentane and cyclopentene have been studied by NMR. spectroscopy. The chemical shifts and the coupling constants of the OH groups have been correlated with their position, with their configuration and, in some cases, with their conformation.     

Recherches dans la série des cyclitols,XLI. Synthèses de deux cyclopentane-pentols

Two new cyclopentane-pentols, namely the 1, 2, 3, 4/5- and 1, 2, 3/4, 5-isomers have been prepared by hydroxylation of the three 3, 4, 5-trihydroxy-1-cyclopentenes. The stereoselectivity of some hydroxylating agents is discussed.     

Déplacements Chimiques du Carbone 13, Constantes de Couplage 1J(CH) et 3J(CH) dans une série de dérivés trisubstitués du benzène

¹³C chemical shifts, 1-bond and 3-bond (meta) ¹³C? H coupling constants have been determined in a series of trisubstituted benzene; the substituents are Cl, NH₂, N(C₂H₅)₂, N(iC₃H₇)₂, N(C₂H₄)₂O. Chemical shifts are only in moderate agreement with the usual additivity rules. Additivity rules relative to the above mentioned coupling constants are proposed. With few exceptions, the difference between predicted and observed values is less than 10%.     

Fonctionnalisation benzylique en série arène chrome tricarbonyle. Contrôle électronique de la régiospécificité de la réaction

The regiospecificity of the benzylic functional group of arenetricarbonylchromium cannot be explained by preferential attack at the carbon which is eclipsed by the chromium-carbonyl bond. Electronic effects in directing the regiospecificity of benzylic attack was found to predominate.     

Recherches dans la série des cyclitols,XL. Préparation de cyclopentane-triols et de cyclopentène-triols et -diols

Two as yet unknown cyclopentene-triols have been prepared. The replacement of the halogen of cyclopentene derivatives brominated in the allylic position has been investigated. In the presence of dimethyl sulfoxide and sodium hydrogen carbonate, the bromine of some of the above mentioned allylic derivatives or the tosyloxy group of a dibenzoyloxy-monotosyloxy-cyclopentane derivative is replaced by a hydroxyl group without formation of any keto compound. The mechanism of action of the substitution agents is discussed.     

Polymérisation anionique des diènes. III. Etude thermodynamique de la propagation du butadiène et de i'isoprène par les organo-alcalins

The present work is concerned with the influence of the polymerization temperature on the propagation mechanisms of polyisoprenyl- and polybutadienyl-alkali metals. The thermodynamic parameters of the contact ion pairs and free ions propagations have been calculated. With Li⁺ in dioxane solvent, the vinyl propagation is stereospecific (for isoprene, the propagation is mainly 4–3). In comparison with benzene, the vinyl propagation of the polydienyl-Li contact ions pairs should be due to complexation of Li⁺ by dioxane, an electron donor having a weak dielectric constant. In general, the stereospecificity of the propagation of contact ion pairs decreases with increasing counterion size; little difference has been observed with K⁺ and Cs⁺ ion pairs in dioxane and benzene media. For isoprene, the methyl substituant should have chiefly a steric effect in the propagation of free ions, whereas it should confer a polar character to the isoprene molecule in the presence of ions pairs.     

Recherches dans la série des cyclitols XXXVII Etude par spectrométrie de masse

Low resolution mass spectra of cyclohexane-triols, -tetrols, -pentols and -hexols and of some of their deuterium labelled derivatives have been measured. The results indicate that for some geometrical isomers quantitative differences between ion intensities are significant, allowing to deduce the stereochemistry of the molecule from its mass spectrum. In all these compounds the electron impact induced elimination of water occurs mainly by interaction between OH groups. There is a correlation between the relative abundance of (M – H₂O)⁺ and (M ?2 H₂O)⁺ ions and the number of axial hydroxyls in the more stable conformation of the molecule. Difficulties encountered in deducing fragmentation patterns, and determination of number and position of deuterium atoms in the molecule of ms-inositol are discussed.     

Etude dans la série des pyrrolidinones. IV. Formation de quelques dérivés de l'acide L méthylène bis N-(oxo-5 pyrrolidine carboxylique-2)

Starting from the readily available 5-oxo-2-carboxypyrrolidine, methylene-bis-(N-5-oxo-2-carboxypyrrolidine) was prepared and transformed into a diamine, then into two isomeric diols, which cyclised into one ether. The meso configuration has been assigned for this ether. The reduction of both diols and ether was complete and gave rise to methylene-bis-N-pyrrolidine.     

Recherches dans la série des cyclitols XLIV. Synthèses de cycloses dérivés du cyclopentane

The conversion to free ketoses by transketalisation of ethylene-ketal and/or isopropylidene derivatives of polyhydroxy-cyclopentanones has been investigated. The preparation of 2, 3-dihydroxy-cyclopentanone and of 2, 3-dihydroxy-cyclopentenone has been described.     

Copolymérisations de l'acrylonitrile. XII. Phénomènes de solvatation préférentielle et effet de conversion dans la copolymérisation (acrylonitrile–styrène)

Kinetic deviations with the conversion observed in free-radical-initiated [acrylonitrile (A)–styrene (S)] copolymerization carried out in DMF solution have been interpreted in terms of preferential solvation of the polymer by one of the monomers or the solvent. First it is well established that the initial styrene content of the PAS copolymer increases if a slight amount of polymer is introduced before the beginning of polymerization. Next the preferential solvation has been studied and characterized in various solvents (toluene or DMF) from the results of differential refractometry at dialysis equilibrium of the ternary solution (solvent–monomer–polymer) versus its solvent mixture. It was found that the most polar monomer, acrylonitrile, is already adsorbed by the polymer, mostly in copolymerizations carried out in DMF, from initially rich acrylonitrile mixtures. It is suggested that this phenomenon implies a heterogeneous repartition of the monomer mixture in the solution, which may affect the kinetic copolymerization when the conversion increases.     

Systèmes aromatiques à 10 électrons π derivés de l'aza-3a pentalène. XVII. Tautomérie azido/tétrazole dans la série du pyrazole

The IR and NMR study of twelve 3- (or 5-) azidopyrazoles shows that the azide is the only tautomer present under neutral conditions. The most stable isomer (tautomer) is 3-azido in N-acetyl and N-H derivatives. 3-Azidopyrazoles are the only polyazoles in which coupling with the N-H in NMR (solvent: DMSO) is observed. In a basic medium, the corresponding anions of the 3-azidopyrazoles N-H are formed: these anions slowly evolve, following first-order kinetics, to the bicyclic anions of pyrazolo-[1,5-d] tetrazoles, derived from 3a-azapentalene. This evolution has been checked by means of IR and NMR spectroscopy.     

Polymérization anionique de l'isoprène par les insertions ternaires graphite–métal alcalin–solvant

The examination by HR–NMR of the microstructure of polyisoprenes synthesized in the presence of alkali metal–graphite compounds reveals that the polymerization has an anionic character. The microstructure of the polymers depends on the nature of the active centers, which depends on the solvent used in the preparation of the graphite compounds or as polymerization medium. With powdered alkali metal–graphite compounds, the propagation does not differ from the anionic one occurring in a homogeneous medium. Except for K–graphite, an enhancement of the 1–4 addition mode is observed if grains of Li or Na–graphite are used in mass polymerization. This change in the microstructure could be explained by the competition between the rate of propagation and the rate of diffusion of the growing chains from the grains to the homogeneous phase of the polymerization medium.     

Etude de copolymères ABS (acrylonitrile–butadiène–styrène): Solvatation préférentielle du polybutadiène par les promoteurs

ABS resins formed by copolymerization of styrene and acrylonitrile (AN) in presence of polybutadiene, consist of a mixture of SAN graft copolymer on polybutadiene (PBut) and of ungrafted SAN copolymer (styrene-co-acrylonitrile). The kinetic study was completed by showing a preferential solvation of polybutadiene by the initiator. This solvation effect was studied as a function of the concentration ratio SAN/PBut and in relation with the type of initiator. The adsorption of initiator appeared to be maximum when its solubility parameter (σ) is close to that of polybutadiene. As a function of the polybutadiene characteristics, this selective adsorption can be given by where I₁ is the quantity of initiator in the polybutadiene medium, I is the total amount of peroxide, [PBut] is the concentration of polybutadiene, and M?_n its molecular weight. It has been shown furthermore that the preferential solvation of polybutadiene by the benzoyl peroxide can be increased by addition of SAN or acrylonitrile. The consequences of this solvation effect on the characteristics of the grafting reaction, more precisely on the molecular weight of grafted and ungrafted SAN and on the rate of polymerization, were examined.     

Etude en RMN du 13C des Effets de Substituant sur les Déplacements Chimiques du Carbone dans les Méthyl Tétrahydrofurannes

Carbon-13 nuclear magnetic resonance spectra have been recorded and interpreted for some methyltetrahydrofurans. The effects of a methyl substituent on the ring carbon atoms are discussed in terms of steric hindrance and conformational equilibrium.