Etude par RMN. de polyaminocarboxylates de terres rares,III. Hydroxyéthyliminodiacétates de praséodyme

¹H—NMR. has been used to study the chemistry of the hydroxyethyliminodiacetate complexes of praseodymium in aqueous solution. The ligand exchanges by spontaneous dissociation of the metal-bis-hydroxyethyliminodiacetate (1:2 complex) and of the metal-bis-hydroxyethyliminodiacetate hydroxocomplex, by acid catalysed dissociation of the 1:2 complex, and by a bimolecular process involving the free ligand and the 1:2 complex or the ternary hydroxo-complex. The ligand exchange rate constants are given and the mechanisms discussed.     

Préparation de dérivés de sucres acétyléniques terminaux et d'acides ynuroniques par réaction de Wittig. Note de laboratoire

Synthesis of Terminal Acetylenic Sugars Derivatives and Ynuronic Acids Derivatives by Use of a Wittig Reaction The method described for the preparation of terminal acetylenic sugars presents two advantages over earlier procedures: no new asymmetric center is created and the chain can be extended by one or more C-atoms. The method also allows preparation of ynuronic acids. The aldehydosugars derivatives 1–7 gave in good to excellent yields the corresponding gem-dibromoenoses 8–14 from which either the terminal acetylenic sugars derivatives 15–21 or the ynuronic acids 22–24 were easily prepared. A few examples of 1,3-dipolar cycloadditions (leading to 28–30 ) with these acetylenic sugar derivatives are also described.     

Diénamines hétérocycliques. III. Réexamen de la réaction de la base de Fischer avec le tétracyanoéthylène

Heterocyclic dienamines III. A re-examination of the reaction of Fischer's base on tetracyanoethylene Depending on the order of addition, Fischer's base 5 (1,3,3-trimethyl-2-methylidene-indoline) reacts 1:1 with tetracyanoethylene to give either the tricyanovinylation product 6 or the spiro compound 7 . A skeletal rearrangement of a zwitterionic intermediate can explain the formation of the spiro compound. The latter undergoes a thermal isomerization yielding by ring expansion the tetrahydroquinoléine 8 . On reaction with LiAlH₄ or CH₃ONa 7 and 8 lead both to triazatetracycles. All structures are assigned on the basis of spectral data.     

Nouveaux exemples de radicaux libres stables de dérivés hétérocycliques de sucres. Communication préliminaire

Some more examples of stable free radicals of carbohydrate heterocyclic derivatives 2-Glycosyl-4,4,5,5-tetramethylimidazoline- 3-oxide-1-oxyls and 2-glycosyl-4,4,5,5-tetramethylimidazoline 1-oxyls have been prepared in nine carbohydrate series, which proves the generality of the method. The hyperfine coupling constant between the free electron and the α-proton of the glycosyl group is never very large (0-2.3 G) but a correlation between its value and the structure of the aglycone has been noted. Free radicals of that type, stable in aqueous solutions, are potentially interesting for biological studies.     

Application de la réaction de Wittig à la synthèse de dérivés de bromoénosuloses et d'esters bromoénuroniques. Note de laboratoire

Use of the Wittig reaction for the synthesis of derivatives of bromoenosuloses and bromoenuronic esters Treatment of 3-O-benzyl (or 3-O-methyl)-1, 2-O-isopropylidene-α-D -xylo-pentodialdo-1, 4-furanoses ( 2 or 1 ) with acetylbromomethylidenetriphenylphosphorane ( 3 ), benzoylbromomethylidenetriphenylphosphorane ( 4 ) or bromoethoxycarbonylmethylidenetriphenylphosphorane ( 5 ) gave in good to excellent yields the expected enose ( 6--11 ). In all cases but one ( 8 where some 10% of the E-isomer was formed) the reaction led to the exclusive formation of the Z-isomer whose configuration was established by NMR.     

17O-RMN. d'éthers,de cétones et d'esters cycliques. Détermination de constante de couplage quadrupolaire

¹³C- and ¹⁷O-relaxation times measured in cyclic ethers, cyclic ketones, and lactones allowed the determination of the quadrupolar interaction at the O-site. Values obtained for six-membered rings can be used as standard values for ethers (χ = 13 MHz), ketones (χ = 10.5 MHz), and esters (χ = 11.5 MHz for dicoordinated and 9.5 MHz for monocoordinated O-atom). Even within a series, no correlation is found between the ¹⁷O-chemical shift and the value of quadrupolar interaction.     

Dérivés de l'hydroxyméthyl-5 furfural. I. Synthése de dérivés du di- et terfuranne

Addition of α, β-unsaturated sulfones or ketones to 5-hydroxmethyl-furaldehyde or related furanaldehydes in the presence of a thiazolium salt gives di or tetraketonic furan compounds. Dehydrative cyclizationled to di- and terfuryl derivatives.     

Dérivés C-glycosyliques. VII. Synthèse et réactions de nitrones dérivées de sucres. Communication préliminaire

The syntheses of three types of sugar nitrones (aldonitrone, ketonitrone and α-β unsaturated aldonitrone) are described. On 1,3-dipolar cycloaddition with phenylacetylene, the aldonitrone gave two Δ₄-isoxazolines epimeric at the new asymetric carbon, while the same reaction on the ketonitrone led to a spiro-Δ₄-isoxazoline. The reaction of these nitrones with carbon nucleophiles like phenylethynylmagnesium bromide constitutes a novel chain-extension reaction in carbohydrate chemistry.     

Substitution électrophile aromatique dans l'anhydride sulfureux liquide. Etude cinétique de la réaction de bromation d'anisoles monosubstitués. Transmission des effets électroniques et caractéristiques de l'état de transition

Reactivity-structure correlations for anisole and eleven of its substituted derivatives established from bromination rate constants in liquid SO₂, unlike observations in water, show the reaction to be highly sensitive to substituent effects, (ρ = ?7.1; ρ = ?10.51). This result is ascribed to the solvation of the methoxy group which decreases the conjugation of para-substituted (ρ = ?9.70) compared to that of ortho-substituted derivatives (ρ = ?8.86). The highly solvated transition state lies far from reactants on the reaction coordinate and the positive charge developed in this state is nearly unity.     

Synthèse par cyclisation nucléophile de dérivés de sucres portant un hétérocycle inséré en spiro. Note de Laboratoire

Synthesis of Sugar Derivatives Bearing a Spiro Heterocycle via Nucleophilic Cyclization Treated with the 1,4-binucleophiles 1,2-diaminoethane, 2-aminoethanol, 2-aminoethanethiol, L -cysteine, o-phenylenediamine, o-aminophenol or o-aminothiophenol the ketosugar derivative 1 gave in good yields the corresponding spiro derivatives 2–8 . In each case, the reaction was stereospecific leading to the isomer bearing the N-atom on the endo face of the bicyclic starting material. Starting from the sugar enone 9 , the aromatic 1,4-binucleophiles led stereospecifically to the spirobenzo [b]-diazepine 10 , -oxazepine 11 or -thiazepine 12 . In one case, an imine (13) was isolated. As 13 cyclized to 6 , the intermediate formation of these kind of derivatives could be considered as a common step for all these reactions.     

Étude spectrophotométrique UV. de solutions diluées de chromate dans l'acide sulfurique concentré

Dilute solutions ( < 1· 10^?4M ) of CrO₄K₂ in concentrated sulfuric acid, were investigated spectrophotometrically. Spectral, kinetic and equilibrium studies confirm the instability of Cr^VI species and their conversion to Cr^V complexes, as proposed by MISHRA & SYMONS . Reaction mechanisms are proposed.     

Radicaux libres dérivés de sucres. Partie. VII. Analogues de nucléosides marqués par un spin. Communication préliminaire

Sugar Free Radicals. VIII. Spin-Labeled Nucleosides Analogs A series of 5′-deoxy-5′-hydroxylamino derivatives of adenosine and uridine have been prepared by reduction of the corresponding oxime or nitrone. ‘Second generation’ 3′-deoxy-3′-N-aryl(or N-alkyl) hydroxylamino-β-D -xylofuranosyluracils have also been synthesized by a one-pot reaction including the following elementary steps: deblocking of the starting material, reduction of the 3′-deoxy-3′-oximinouridine, condensation of the resulting hydroxylamine with an aldehyde, reduction of the nitrone formed. The deoxy-hydroxylaminonucleosides oxidized spontaneously in the air (or in presence of traces of PbO₂) to give the corresponding nitroxide free radicals, ESR spectra of which furnished useful informations on their structures. Some of these modified nucleosides bore notable cytotoxic or antiviral activities.     

Spectrométrie de Masse d'Hétérocycles. VIII—Edude de Dérivés du Dioxasilolanne-1,3,2

The fragmentation mechanisms of 1,3-dioxasilolane have been investigated. These fragmentations lead principally to ‘silyl’ ion formation, or involve cleavage of the bonds α and β to the silicon as for hydrogen migrations.     

Etude par spectrométrie de masse de l'ionisation de benzonitriles,de phénylacétonitriles et de N,N-diméthylanilines substitués

Molecular ionization potentials for series of compounds of the type X? C₆H₄? CN, X? C₆H₄CH₂? CN and X? C₆H₄? N(CH₃)₂ have been measured using the retarding potential difference technique (RPD. technique). The effect of the various substituents X is better correlated through the electrophilic Brown σ_p⁺ constants than through Hammett's σ_p values. No meta-para orientation effect is observed. For all the disubstituted phenyl compounds studied, the effect of the second substituent is affected by the electron-releasing power of the original substituent. Ionization potentials calculated by using the semi-empirical method of equivalent orbitals are in good agreement with the experimental values.     

Polymérisation anionique de l'isoprène: Nature de la paire d'ions et stéréospécificité. II. Influence de la nature du solvant

The present work reports some new results on the dependence between the stereospecificity of the anionic propagation of isoprene and the nature of the active centers. The stereospecificity of the propagation of macroheterobicylce separated ion pairs does not depend on the nature of the alkali counterions, and the microstructure of the polyisoprenes obtained does not differ from that of those produced by free ions. Variations in the microstructure were observed in the propagation of contact ion pairs, depending on the nature of the cation and the solvent used. These variations are likely to be related to the degree of intimacy of the contact ion pairs. There are two main factors which affect the stereospecificity of the propagations in different ways: the size of the cation and the donating power of the solvent. Finally, the external solvation of the propagation ions pairs was confirmed by the microstructure of polyisoprenes synthesized in mixed (inert + donor) solvents.     

Etude de la réactivité de la fonction carbonyle avec le cétène en présence d'un alcoxyde de titane. 2e communication. A propos de l'interprétation de quelques spectres RMN de β-hydroxyesters formés

The NMR. spectra of a serie of β-hydroxyesters have been studied. It has been found that the methylene protons are magnetically nonequivalent only when the substituents on the center of asymmetry of I or II are very different. The magnetically non-equivalence of the isopropylmethylprotons arise when the β-hydroxyesters contain an aromatic or aromatic conjugated group directly bonded to the asymmetric carbon. The interpretation of this finding is proposed.     

Alcoylation d'acridanone-9. Premiers exemples de O-alcoylation dans cette série de composés

The results of nucleophilic substitution of the 2-methoxy-9-acridone are discussed in terms of competition between both ionic sites N^? and O^?, of the molecule. They are the first examples of O-alkylation of substituted 9-acridone.