Réaction d'ylures stabilisés sur des aldéhydosucres: influence de divers facteurs dont la structure de l'aldéhydosucre sur le pourcentage d'isomères géométriques obtenu

Reactions of stabilized ylides with aldehydosugars: influence of some factors, particularly the structure of the aldehydosugar, on the ratio of the geometrical isomers formed Aldehydosugars bearing no cis-substituent on the C-atom β to the carbonyl group ( 2, 3, 6, 7 ) or bearing a substituent without an electron lone-pair ( 5 ) gave, upon treatment with acetylmethylidenetriphenylphosphorane, exclusively the E-isomer, this representing the classical behaviour of aldehydes. On the other hand, aldehydosugars having a lone-pair bearing substituent ( 1, 4, 8, 9 ) gave a mixture of E- and Z-isomers. In the case of most of the aldehydosugars of the latter type (giving some Z-isomer) a partial epimerization of the C-atom α to the carbonyl group took place when the solvent of the Wittig reaction was HCONMe₂. It is probable that the presence of an electron lone-pair in the adequate position inhibits the reversion of the kinetic erythro-betaine, allowing the formation of the Z-isomer and, in particular solvent conditions, a cycloelimination leading to the epimeric aldehydosugar which ultimately reacts to give the epimeric E-enone.     

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.     

Réactions de Friedel et Crafts de dérivés aromatiques sur les composés dioxo-1,4,2,3-non saturés. IV. Réactions des hydroxy-5-ouchloro-5-diméthyl-3,5- ou diméthyl-4,5-dihydro-2,5-furannones-2

Friedel-Crafts reactions of aromatic derivatives with 1,4-dicarbonyls 2,3-éthylenic compounds. Part IV. Reactions of 5-hydroxy or 5-chloro 3,5-dimethyl or 4,5-dimethyl 2 (5 H) furanones We studied the Friedel-Crafts reactions of 2-(5H)-furanones. In the presence of sulfuric acid and of an aromatic derivative, 5-hydroxy- or 5-chloro-5-methyl-2-(5H)-furanones with one methyl group either in the 3 position, or in the 4 position generally give the corresponding 5-aryl-2-(5H)-furanones, while with aluminium chloride, it is possible to obtain, when a reaction takes place, isomeric 1H-indenecarboxylic acids. However, in a particular case, an addition to the substrate's double bond is observed. The 3-aryl-5-hydroxy-tetrahydrofuran-2-one obtained is methylated in two ways and gives either a cyclic product, or a linear one. In two cases tautomerism between 1H-1-indenecarboxylic acid and 1H-3-indenecarboxylic has been shown by ¹H-NMR.     

Utilisation d'ylides du phosphore en chimie des sucres,X. Synthèse stéréospécifique de l'épimère en C3 du streptose et d'autres sucres ramifiés,dérivés de désoxy-5-pentoses, à groupements gem-hydroxy-formyle ou gem-hydroxy-hydroxyméthyle

The synthesis of branched-chain sugars of the gem-hydroxy-formyl and the gem-hydroxy-hydroxymethyl types is described. A 5-deoxy-1,2-O-isopropylidene-furanos-3-ulose is treated with cyanomethylene-triphenyl-phosphorane, yielding the two geometrical isomers of the corresponding branched-chain unsaturated sugar. Cis-dihydroxylation(KMnO₄) of these cyanomethylenic compounds affords stereoselectively and in high yield the gem-hydroxy-formyl branched chain sugars whose formyl group is on the more hindered face of the furanose ring. The hydroxymethyl analogues of the latter compounds are readily prepared by their borohydride reduction. This method constitutes a new general route to type A branched-chain sugars epimeric at the branching-point with the sugars which would have been obtained by the classical procedure involving Grignard reagents.     

Extension de la méthode du «logarithme limite» [1] pour la détermination de la composition et de la constante de stabilité des complexes

A study of the conditions of applicability to weak complexes of the relation log x = v log V + log (β_v,cC^c) = f(logV), where V and C are variable and constant total concentrations of the constituants of the complexe, shows that for conditions other than C ? V, another function φ(log V) accounts better for the formation equilibrium of the complexe. From f(log V) and φ (log V) a relation t(log V) is derived whose simple analysis permits the determination of the composition and the stability constant of weak complexes. Applications are given to 1:1, 1:2, 2:2 composition.     

Analogies Photochimiques. III—Diméthyl-4,4 allyl-2 Cyclohexanone. Elimination Inattendue de C2H4O et Perte de 15 Unités de Masse

The mass spectrum of 4,4-dimethyl 2-allyl cyclohexanone shows an ion at m/z 122 resulting from the elimination of a neutral acetaldehyde molecule direct from the molecular ion. Deuterium labelling results show a complex decomposition pathway during which four hydrogen atoms transfer to the eliminated acetaldehyde molecule. The molecular ion of this compounds also loses a methyl group originating from the allyl substituent. The mechanisms are discussed in terms of photochemical analogies.     

Synthèse de sucres aminés ramifiés III. Synthèse et réactions de 1′α-amino-nitrile dérivé du di-O-isopropylidène-1,2:5,6-α-D-ribo-hexofurannosul-3-ose

The addition of cyanohydric acid to 1,2:5,6-di-O-isopropylidene-α-D -ribo-hexofurannos-3-ulose can be sterically controlled. Under kinetic conditions, the allo cyanohydrine epimer is formed, under thermodynamic conditions, the gluco epimer is formed. The configuration of these two products is proved by their chemical reactions. Hydration followed by hydrolysis of the nitrile group of the allo epimer (O-acetyl derivative) gives the 3-C-carboxy-1,2-O-isopropyloidene compound. This product forms the corresponding γ or δ-lactone with hydroxyl ( 5 ) or ( 6 ). On the other hand, after hydrolysis of 5,6-isopropylidene, the 3-O-acetyl derivative of the gluco epimer gives an acetyl migration from position 3 to position 5 and finally to position 6. By reaction of the allo epimer with NH₃ and CN^?, an aminonitrile is formed. The allo configuration is deduced from the above mentioned reaction and from IR. and NMR. data. Several acetylated and trifluoracetylated derivatives of these products are described. The oxidation of the nitrile group to the amide group is possible with both epimeric cyanohydrines and the amino-nitrile.     

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.     

Sur le mécanisme de la réaction de meth-cohn-tarnowski de préparation des thiocoumarines

Reaction of 2-t-butylthiobenzaldehyde with N-(2-dialkylaminoethyl)-cyanacetamides followed by heating of the resulting 3-(2-t-butylthiophenyl)-2-cyanoacrylamides in polyphosphoric acid leads to the formation of 3-carboxamido-2-imino-2H-benzo[b][l]thiopyrann intermediates which afford thiocoumarins on hydrolysis. The authors postulate the intermediate formation of a thiophenate ion by an electronic mechanism involving six centers.     

Etude par RMN du Proton de la Stéréochimie de Composés Ethyléniques Trisubstitués. Calcul Empirique et Calcul par Incréments de la Constante d'Ecran

The Pascual and Tobey approaches for evaluating the chemical shift of an olefinic proton have been tentatively applied to the case of substituents which often cause difficulties in signal assignment. The empirically calculated values of the differential shielding between olefinic protons in both Z and E configurations are compared to the experimental values of the chemical shifts in a series of 2-arylpropene nitriles. The Z configuration is proved to correspond to the less shielded nucleus and the observed solvent effects are consistent with this assignment. When the Z configuration predominates its nature has been unambiguously established by studying also the corresponding E isomer of which a very small quantity could be isolated. The results offer a good way for the computation of new substituent additive parameters (NH₂, OH, ONa).     

Etude de la réaction de l'acé'tylacé'tate d'éthyle avec les diamino-1,5 imidazoles

The condensation of 1,5-diaminoimidazoles with ethyl aceto-acetate gives two types of compounds: imidazo[1,5-b]-1,2,4-triazepinones and imidazo[4,5-b]pyridinones. The structure of these compounds is demonstrated by rmn and mass spectroscopy. The formation of imidazo[4,5-b]pyridinones from imidazo[1,5-b]-triazepinones through a new transposition is also shown.     

Utilisation d'ylides du phosphore en chimie des sucres VII. Synthèse de sucres ramifiés des types «streptose» et «apiose». Communication préliminaire

A new high-yielding route to branched-chain sugars of the streptose or the apiose type having at the branching point a configuration epimeric with that which would be obtained by the classical synthesis using Grignard reagents is described. The main steps are the preparation of branched-chain unsaturated cyano sugars by reaction of cyanomethylene triphenylphosphorane with keto sugars and the cis-dihydroxylation (KMnO₄) of the so obtained cyano sugars. The cis and the trans isomers of a series of cyanovinylidenic sugars have been separated and the stereodependence of the long-range coupling constants in this class of compounds has been examined.     

Détermination de la forme la plus stable de l'ortho-dichlorofluorure de benzyle par RMN en phase nématique

The value of direct couplings in o-dichlorobenzylfluoride, obtained from nematic phase NMR, lead to the conclusion that the most stable form is such that the fluorine atom is in a plane perpendicular to the benzene ring. However, the complete intepretation of these couplings in terms of geometrical parameters tends to indicate a modification of orientation with internal rotation of CH₂F.     

Sur la synthèse de quelques furochromènes,analogues pharmacochimiques de la xanthylétine et de la séseline

Some furochromenes substituted at the 2-position by an electron-attracting group were obtained starting from ortho-hydroxyformyl derivatives of 2,2-dimethyl-2H-chromene following various processes which are indicated. These new furochromenes are pharmacochemical analogues of some natural pyranocoumarins, and as such they are potential photosensitizers.     

Utilisation d'ylides du phosphore en chimie des sucres. XI. Synthèse des quatre didésoxy-3, 5-méthyl-3-pentoses parl'intermédiaire de sucres insaturés ramifiés

Treated with methylthiomethylenetriphenylphosphorane, 5-deoxy-1,2-O-iso-propylidene-β-D -threo- and -α-D -erythro-furanos-3-uloses led with good yields to a mixture of the cis-trans isomers of the corresponding methylthiovinylidenic sugars. There was no inversion of configuration at C(4) with the thero-furanosulose and a small one (7%) with its erythro isomer. These unsaturated branched-chain thio-sugars are useful synthetic intermediates. For examples, the desulfurization-hydrogenation (Raney Nickel) of each of these alkenes afforded in good yield two 3-deoxy-3-C-methyl-pentoses epimeric at C(3) and having the same configuration at C(4) as the starting alkenes. In all cases the isomer formed by attack from the less hindered face of the double bond was the preponderant one.     

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.     

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).     

Réactions du diazométhane III. Etude de la réaction d'insertion entre diazométhane et phénylcarbamates: comportement de la N-(phénoxy-carbonyl)-aniline et de la N-(p-nitrophénoxy-carbonyl)-aniline

Diazomethane reacts with N-(p-nitrophenoxy-carbonyl)-aniline giving on the one hand p-nitroanisole and phenylisocyanate, the latter being transformed into N-phenyl-β-propiolactam, and on the other hand N-(p-nitrophenoxy)-acetanilide by insertion. N-(phenoxy-carbonyl)-aniline does not react. The insertion reaction seems to depend on the heterolysis of the bond between the oxygen of the p-nitrophenoxy group and the carbamic carbonyl function, which is strongly polarized (existence of a mesomeric nitro-phenoxonium). The insertion is equally influenced y the nature of the radical R attached to the carbamic nitrogen: with R = ? CH₂COOC₂H₅ the reaction yields only isocyanate, with R = ? C₆H₅ it yields at the same time the isocyanate and the insertion product.     

Etude par Spectrométrie de Masse de la Fragmentation d'une Série de Diols Aliphatiques

The mass spectrometric fragmentation of a series of diols having the general formula HO? (CH₂)_n? OH with n = 2-11 has been studied. Extensive labelling of n-butane-1,4 diol and n-hexane-1,6 diol with deuterium allows fragmentation modes to be proposed. The labelling reveals that intramolecular exchange of H atoms often precedes the fragmentation and becomes more important when the length of the chain increases.     

A propos de la structure de pyrimidines obtenues par condensation de l'acide cyanacétique et de monoalkylurées

Classically, the condensation of cyanoacetic acid and monoalkylurea gives 1-alkyl-6-amino-1,2,3,4-tetrahydropyrimidine-2,4-dione. However, this was verified only in two instances involving a long and delicate synthesis. The structure of the N′-cyanoacetyl-N-isobutylurea, an intermediate in the preparation of this type of pyrimidine, was confirmed by nmr. This method is capable of extension.