Dérivés de sucres à groupement gem-dihalogénoéthényle

Carbohydrate Derivatives Bearing a gem-Dihalogenoethenyl Group Treated with the appropriate Wittig reagent, aldehydosugar derivatives ( 1–13 ) led in good to excellent yields to the expected gem-difluoro, gem-chlorofluoro-and/or gem-dichloroenoses ( 14–29 ). Examples of their dibromo analogues had been previously described (see e.g. [1]) but the diiodo derivatives could not be isolated, The influence of the conditions on the yields is reported as well as spectroscopic properties (particularly the long-range ¹³C, ¹⁹F- and ¹H, ¹⁹F-coupling constants) of these new enoses.     

Etude par Résonance Magnétique Nucléaire de dérivés anthracéniques: II—Anisotropie magnétique du phényle et effets steriques

The peri effect induced by the phenyl group has been studied in the anthracene series by means of ¹H and ¹³C n.m.r. The chemical shifts of overcrowded protons can be explained by a combination of magnetic anisotropy and steric effects. Steric contributions amount to c. 25% of the phenyl induced shift at the peri position. Amongst published ring-current theories, only the model of Johnson and Bovey is capable of describing correctly the shielding region of the phenyl group. The unexpected shieldings and deshieldings, observed by ¹³C n.m.r. in the case of very hindered derivatives, is probably due to distortions of the anthracene skeleton.     

Applications de la Résonance Dynamique du Proton et du Carbone-13 à l'Etude d'Azines Hétérocycliques. Mécanismes de Formation et d'Isomérisation

A ¹H and ¹³C n.m.r. study of heterocyclic azines is presented and the influence of Z/E isomerism on the ¹³C chemical shifts is examined. The kinetic study of the formation and Z/E isomerization of these compounds has been carried out and mechanisms of these reactions are discussed.     

Action de nucléophiles simples sur un bromoénurononitrile,précurseur et équivalent synthétique partiel d'un ynurononitrile

Reactions of Mononucleophiles with a Bromoenurononitrile, Precursor and Partial Synthetic Equivalent of an Ynurononitrile Several mononucleophiles (bases) have been reacted with one or the other of the geometrical isomers of the bromoenurononitrile 1. Depending on the nucleophile and the conditions, many different mechanistic pathways were followed, f. ex.: with OH^?, stereospecific elimination from (Z)- 1 leading to 2 , with N^?₃ and F^?, stereospecific E-A_N reactions leading from (Z)- 1 to (Z)- 8 and (Z)- 12 respectively, with PhCH₂SH, conjugate nucleophilic addition to 7, with Me₂NH, conjugate nucleophilic addition followed by a S_N2 to 11 , as well as several cases of nonstereoselective, probably A_N-E, reactions leading to 3,6,9 and 10. In spite of their diversified reactivity, bromoenurononitriles like 1 , partial synthetic equivalent of 2 , constitute useful synthetic intermediates.     

Résonance magnétique nucléaire du noyau 14N par Transformée de Fourier

¹⁴N-NMR. measurements using the Fourier Transform technique are presented and compared to C. W. experiments. The F. T. technique is especially advantageous for relaxation time measurements. However, since ¹⁴N-nuclei may have widely different relaxation times, it is often not possible to have optimal gain in sensitivity (as compared to C. W. measurements) in a single F. T. experiment for different ¹⁴N-nuclei contained in the same sample. Different experiments have to be performed, optimizing the spectrometer parameters for each ¹⁴N-resonance of appreciably different linewidth. The technique is applied to three different problems. ¹⁴N-relaxation in symmetrical ammonium salts is shown to arise from reorientation of the water dipoles. The use of a double spin-probe, ¹³C-¹⁴N, allows the determination of the electric field gradients in cyclic ammonium salts. The electronic distribution is especially distorted from tetrahedral symmetry in the highly strained N, N-dimethyl-aziridinium cation. Finally, electric and dynamic effects in ion pairing may be studied as shown on the case of tetrabutylammonium iodide in water and in benzene.     

Alcoxyflurophosphoranes. II—Monoalcoxyfluorophosphoranes possédant un centre d'asymétrie; diastéréotopie des fluors apicaux

Twenty-six monoalkoxyfluorophosphoranes bearing an asymmetric substituent of types R¹PF₃(OR²*)( 1 ), R¹*PF₃(OR²) ( 2 ), R¹R³PF₂(OR²* 3 ) and R₂¹PF₂(OR²*)( 4 ), have been prepared. The non-equivalence of the axial fluorine atoms is observed in the ¹⁹F NMR spectra for the compounds of types 1 δ_F′a – δ_F′a ～ 0·5 to 3·8 ppm, J(F_aF′_a) ～ 10 Hz, 2 δ_Fa – δ_F′a ～ 1·1 to 1·5 ppm, J(F_aF′_a) ～ 14 Hz and 3 δ_Fa – δ_Fa ～ 0·2 ppm, J(F_aF′_a) ～ 10 Hz but not for those of type 4 R₁²PF₂(OR²*). Its origin is assigned to the diastereotopic character of these fluorines. The possibility of a hindered rotation of the substituents as the origin of the phenomenon is excluded. The preparation of sec-BuPF₄ and EtPhPF₃ is also reported.     

Etudes stéréochimiques XIV. Adduits de Diels-Alder en série résiniques; action des peracides et ouvertures acido-catalysées d'époxydes

Studies in Stereochemistry XIV. Diels-Alder adducts in the resin series; action of peracids and acid-catalysed ring opening of epoxides The synthesis of Diels-Alder compounds of type 2 with a 17-nor-13(14)-atisène skeleton is described (cf. Schemes 1–3). Depending on the nature and configuration of substituents R¹ and R² on the carbon atoms 15 and 16, an epoxide ( 24–33 ) or a ketone ( 35–38 ) or a mixture of epoxide, ketone and lactone is obtained by the action of p-nitroperbenzoic acid on the double bond of these adducts (cf. Scheme 4). A simplified reaction scheme is suggested to explain the formation of the various products. In an acid-catalysed reaction, the epoxides isomerize mainly into ketones. Nevertherless, in some cases, dienes (e.g. 52 ) or hydroxy-γ-lactones of (13R*, 14S*)-configuration (e.g. 50 ) resulting from the opening of the epoxide ring with retention of configuration were obtained.     

Dérivés Alléniques de l'Étain,du Plomb et du Mercure. Signes Relatifs des Constantes de Couplage Métal-Proton á Travers Deux et Quatre Liaisons

Satellites corresponding to metal-proton coupling constants through two and four bonds are observed in PMR spectra of Pb, Sn and Hg allenic derivatives. The relative signs of these coupling constants are deduced from analysis of the satellite spectra: ²J(X? H) and ⁴J(X? H) are of opposite signs for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and of same sign for X = ¹⁹⁹Hg. Probable absolute signs of reduced coupling constants are discussed in relation to published data: ²K(X? C? H) is probably positive for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and ¹⁹⁹Hg. ⁴K(X? C?C?C? H) is probably negative for X = ²⁰⁷Pb, ¹¹⁹Sn, ¹¹⁷Sn and positive for X = ¹⁹⁹Hg.     

Dérivés d'énose- et d'ynosephosphonates et composés voisins. Communication préliminaire

Derivatives of enose- and ynosephosphonates and related compounds. Preliminary communication The gem-dibromo terminal enoses 1 and 7 are convenient sources of glycosylacetylenes which upon reaction with phosphorus electrophiles gave the phosphorusbearing acetylenic sugars 4, 5 and 8 . Compounds 5 and 8 underwent cycloaddition reactions leading to isoxazolyl-C-glycosides 6 and 9 respectively. The nitroolefinic sugar derivative 11 gave upon bromination-dehydrobromination the first example of a new kind of potentially useful synthetic intermediates, the gem-bromonitroenose 12 . The enosephosphonate 13 was also prepared from 11 . The diglycosylhydroxylamine 18 represents another type of phosphorus-bearing acetylenic sugar derivative. Some ¹H- and ¹³C-NMR. data relative to the new types of phosphorus-containing sugar derivatives synthesized are given.     

Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation pour le fluorure d'acroyle et l'acroléine

The NMR spectrum of acrolein and acroyl fluoride (CH₂?CH? COX with X?H and F) oriented in a nematic phase has been measured and information about conformational equilibrium s-cis ? s-trans has been obtained. The barrier to internal rotation of the COX group has been studied with various hypotheses. Good agreement between experimental and calculated spectra has been obtained using the potential equation V(?) = Σ_nV_n(1 – cos n?)/2, with V₁ = ?200 cal mol^?1, V₂ = 1500 cal mol^?1 and V₃ = 400 cal mol^?1 for the fluorine compound, and V₁ = 1200 cal mol^?1, V₂ = 3000 cal mol^?1 and V₃ = 2000 cal mol^?1 for acrolein; this last compound is found to be mostly in the s-trans conformation.     

Préparation de phosphonates de sucres ramifiés par addition nucléophile conjuguée. Communication préliminaire

Preparation of unsaturated sugars phosphonates using nucleophilic conjugate addition Different types of phosphorus nucleophiles underwent conjugate addition reaction with one of the branched-chain sugars 4, 5 or 11 the addition taking place either on the endo or the exo face of the furanose ring (or on both faces in the case of 11 ). The configuration at C(3) of these new phosphorus-bearing types of sugars as well as the configuration at the phosphorus atom of the cyclic phosphinates 9 and 10 was established by NMR. (³J_P,H–C(2), ³J_P,C(1)). Small amounts (7%) of the spiro enol phosphonate 16 were formed when 11 reacted with trimethyl phosphite.     

Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R-3 et R-5 cyano-4 cyclohexènes deutériés (R=méthyl ou t-butyl)

For trans-3-R- and 5-R-1-acetoxy-4-cyanocyclohexene-6,6-d₂ the molar fractions of diequatorial conformers are 0.83 (3-methyl), 0.68 (5-methyl), 0.57 (3-tert-butyl) and 0.55–0.69 (5-tert-butyl). For the last two compounds the values of the coupling constants are in agreement with the hypothesis of an ee?aa equilibrium. For the cis isomers, the molar fractions of equatorial alkyl conformers are 0.76 (3-methyl and 5-methyl) and 1.0 (3-tert-butyl and 5-tert-butyl). The cis-1-acetoxy-3-tert-butyl-4-methoxycarbonyl-cyclohexene presents a conformational heterogeneity. The conformational free energy of the methyl group in position 4 has been evaluated as ?0.6 kcal mol^?1 (2.5 kJ mol^?1).     

Interactions intramoleculaires: XXII—Constantes de couplage, équilibres conformationnels et interactions gauches avec un groupement t-butyle (molécules cyclohexéniques deutériées)

The NMR parameters are determined for a series of disubstituted (R = CH₃, (CH₃)₃C; X = COOCH₃, CN) and specifically deuterated cyclohexenes. The ³ J(HH), ³J(HD), ⁴J(HH) and ⁵ J(HH) coupling constants are used to evaluate the conformational equilibria. Three of the five compounds with an allylic t-butyl substituent, are conformationally heterogeneous; these equilibria, and those between stereoisomers are used for an analysis of this phenomenon, carried out within the framework of the hypothesis of additivity of conformational free energies and gauche interactions.     

La luminescence différée du styrène en solution vitreuse dans le méthylcyclohexane

The trapping of electrons and styrene cations and anions has been studied in a methylcyclohexane glass by the techniques of deferred luminescence. Radiothermoluminescence curves consist of two peaks, at 90 and 95°K, in this matrix. The second peak increases linearly with styrene concentration up to 2 × 10^?2M when it reaches a constant value, whereas the first peak increases from 10^?4 to 10^?3M and then decreases at higher concentrations and is not discernible at concentrations above 10^?2M. We propose two mechanisms which are qualitatively consistent with this behavior and are based essentially on the recombination of styrene cations with thermally detrapped electrons in the first peak and with anions in the second peak. Photothermoluminescence (i.e., thermoluminescence after photoionization with ultraviolet light) similarly consists of the 90 and 95°K peaks for a 10^?3M solution and of the 95° peak alone for a 10^?d M solution. Radiophotoluminescence excitation spectra at 77°K, corresponding to absorption spectra of trapped electrons and styrene anions, show that anions are the predominant negative species in 10^?2 molar solution, and trapped electrons in 10^?3 molar solution. Spectral analysis of radiothermoluminescenece shows the presence of two emission bands, one of which is identical with styrene fluorescence excited by the 254 Nm mercury line (λ_max = 292, 302, 307, and 317 Nm). The other band has three fairly poorly resolved maxima at 474, 486 and 496 nm and seems to correspond to the fluorescence of C₆H₅?H-CH₃ radicals formed during radiolysis.     

Étude des spectres infrarouges de divers dialcoyl-diméthoxy-stannanes

The infrared absorption spectra of some dialkyldimethoxystannanes have been investigated in the 400–1500 cm^?1 region. The bands associated with v_s(SnC₂) and v_s(SnO₂) vibrations have been found at 510–521 cm^?1 and 466–475 cm^?1. The group of bands between 560 and 620 cm^?1 is assigned jointly to v_a(SnC₂) and v_a(SnO₂) vibrations. v(C? O) of the methoxy groups linked to tin appears at 1064–1068 cm^?1.     

Etude Stéréochimique par RMN 1H de Tetrahydropyrannes β-Chlorés α-Substitués

The ¹H NMR study of 2-alkyl-3-chlorotetrahydropyrans, obtained by reaction of Grignard reagents with a mixture of cis/trans-2,3-dichlorotetrahydropyrans, shows cis/trans configuration of two isomers in which the alkyl substituents are exclusively in the equatorial position. 3-Chloro-2-phenyltetrahydropyran exists in trans (eq-eq) configuration only. The ¹H NMR study of cis/trans 2-alkoxy (or aryloxy)-3-chlorotetrahydropyrans, obtained by reaction of alcohols or phenol with 2,3-dichlorotetrahydropyrans, shows the axial position of the alkoxy (or aryloxy) substituent.     

Etude par Résonance Magnétique Nucléaire de dérivés phosphores. Etude de dithiaphospholanes-1,3,2

The proton NMR spectral analysis of eight different 1,3,2-dithiaphospholanes with various groups attached to the phosphorus atom has been performed. The AA′BB′X (X phosphorus atom) system shows that the two ³J(P? S? C? H) coupling constants have a small magnitude and opposite signs. Using the ³J(HH) values, the torsion about the C₄—C₅ bond has been evaluated. The conformational requirements in the two isomers of the 2 phenyl-4-methyl-1,3,2-dithiaphospholane are also discussed.     

Etude Conformationnelle par Résonance Magnétique Nucléaire Protonique des Dérivés de la O-Isopropylidène-2′,3′ Adénosine

Conformational analysis using ¹H n.m.r. data (δ, ³J and NOE) has been carried out on several derivatives of 2′,3′,-O-isopropylideneadenosine bearing various substituents at positions C-5′, C-8 and N-6. Conformational modifications are assigned to specific interactions between the sugar and purine moieties and also to solvent effects.     

Structure cristalline et moléculaire d'un dérivé méthyl-hexopyranoside à C(4) hybridé sp2

The derivative C₁₃H₁₉NO₅ crystallizes in space group P2₁2₁2₁ with a = 9.371, b = 11.815, c = 13.207 Å and Z = 4. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0.058. The pyranose ring exists in the ³S₁ conformation (or in the equivalent, but here structurally less consistent, ⁰S₄ conformation). The dioxolane ring has an envelope conformation. Strong intramolecular interactions between the bulky substituents suggest that the ensuing strain energy is assumed, for a significant part, by the twisted-boat conformation of the pyranose ring.     

Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation de la monofluoroacétone

The NMR spectra of monochloro-, monobromo- and monofluoroacetone (CH₃? CO? CH₂X with X = Cl, Br, F) oriented in a nematic phase have been measured and the direct dipolar coupling constants determined. The barrier to internal rotation for the CH₂F group has been studied for fluorine compound using various hypotheses. The best agreement with IR data has been obtained using the potential equation V(θ) = Σ_n V_n × (1 – cos nθ)/2 and a Boltzmann distribution of the CH₂F group (V₁ = 250 ± 50 cal.mol^?1, V₂ = 1650 ± 100 cal.mol^?1, V₃ = ?1000 ± 100 cal.mol^?1).