Hétérocyclisations intramoléculaires par réaction d'oxymercuration III. Régiosélectivité et stéréosélectivité de l'oxymercuration intramoléculaire de phénols orthoallyliques

The intramolecular heterocylization of ortho-allylic phenols by oxymercuration has been realized with compounds having different substituents on the allylic chain. In all cases, only the corresponding benzofuran is formed. However, with a substituent at the terminal carbon of the double bond, we also observed the formation of benzopyran. The influence of the solvent and the mercuric salt on the orientation of this reaction has been examined. There is evidence of a molecular rearrangement during the reduction.     

Stéréosélectivité et régiosélectivité de la réduction des cyclopropènes-2,3 et méthylène-2 cyclopropanes fonctionalisés en position 1

Reduction of 2 cyclopropenyl esters and alcohols with lithium aluminium hydride is selective; at low temperatures (0°) the double bond is not reduced, but at higher temperatures (65°) the reduction is complete and only the cyclopropylmethanol is obtained. The reduction of the double bond is regioselective (the most stable carbanion is formed) and stereospecific (the hydride attack on the double bond occurs cis to the functional group). This stereospecificity can be explained through the initial formation of an alkoxylaluminium hydride followed by an intramolecular reduction of the double bond. Similar results have been obtained in the reduction of functionalised methylenecyclopropanes.     

Sur les dérivés de la fluorénone VIII. Difluorénonyl-cétones,difluorényl-cétones et difluorényl-méthanes

By condensation of the chlorides of the four isomeric fluorenecarboxylic acids, respectively of the three 1-, 3- and 4-fluorenonecarboxylic acids with fluorene, followed by reduction of the obtained mono-respectively diketones, the four difluorenylmethanes I, II, III and IV are synthesized. The oxydation of the diketones gives the corresponding triketones. Starting from the chloride of 4-fluorenecarboxylic acid and 1-methylfluorene, a methyl derivative of IV is analogically obtained.     

Structure électronique de dérivés sulfurés : Partie V. spectres électroniques d''hétérocycles thio-carbonylés

The experimental and theoretical spectra of thiocarbonyl heterocyclic compounds with two heteroatoms in the position to the thiocarbonyl group have been studied.

The theoretical interpretation of the CNDO/S results including an extension to the third period, i.e. 3d orbitais, is in good agreement with the saturation effect as well as with the influence of the intracyclic heteroatoms on the typical absorptions of the thiocarbonyl group.     

Réduction alkylante de quelques composés hétéroaromatiques polyazotés

The reduction-aldylation of quinoxaline, phthalazine and pyrido[2,3-b] pyrazine by potassium borohydride in a carboxylic acid medium is described. Formic, acetic, chloroacetic and propinic acids were used. The diazine ring of the molecule was reduced and alkylated into an N,N¹-dialkyltetrahydro compound. With quinoxaline and formic acid, N-formylation may be an important factor. Sodium borodeuteride allows one to prepare an hexadeuterated compound.     

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.     

Propriétés chimiques du benzisosélénazole-1,2

The nitration and the bromination of 1,2-benzisoselenazole give mono derivatives at 5- or 7-position. With potassium amide 3-amino-1,2-benzisoselenazole is obtained from the unsubstituted ring. We observe a ring opening by action of organolithium compounds. We describe also the synthesis of functional derivatives at the 3-position from 3-styryl-1,2-benzisoselenazole and selenonaphthenequinone.     

Régiospécificité et stéréosélectivité de la cycloaddition de l'oxyde de benzonitrile sur les pyrazolines-3

Pursuing our study on the cycloaddition of benzonitrile oxide with Δ₃-pyrazolines (1,2), we can now affirm that this reaction is regiospecific and stereoselective. The behaviour in acidic medium was studied. We have then discussed the process of epimerization and degradation observed according to the C₄ substituent of the bicyclic molecule and the solvent used.     

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.     

Réactions d'addition-élimination à partir d'hétérocycles germaniés du type I. Cas des dioxolannes germaniés

Addition-elimination reactions from germanium heterocycles I. Germadioxolanes (X?Y?O) The reactivity of 2-germa-1,3-dioxolanes is studied with unsaturated compounds such as carbonyl compounds (aldehydes and ketones) or heterocumulenes (PhNCO, PhNCS). The formation of mono- and di-insertion derivatives is observed. The structure of these adducts is established and their decomposition process, at atmospheric pressure or at high pressure, is precised. The mechanism of these addition-elimination reactions is established from 4,5-disubstitued germadioxolanes. The reaction takes place under steric control. The consecutive elimination reaction proceeds by a mechanism of intramolecular nucleophilic substitution.     

Régiospécificité de la cycloaddition des diarylnitrilimines sur quelques dérivés indoliques

In this paper, we describe the results of a study of the reaction of diaryl nitrilimines with N-ethylindole ( 1 ) and 2-methoxycarbonyl-N-ethylindole ( 2 ). The regioselectiivity of the reaction is reversed when going from 1 to 2 as it has been spectroscopically and chemically demonstrated.     

Recherches sur la stéréochimie des diènes fonctionnnels—XI: Interprétation théorique des déplacements chimiques de stéréoisomères D'éthoxybutadiènes-1,3

A theoretical analysis of the proton chemical shifts of alkoxy-1,3-diene stereoisomers is proposed. The diamagnetic contribution is calculated from π and σ theoretical indices obtained by the CNDO/2 method. This effect depends on the stereochemistry of the molecule and the charges and chemical shifts alternate in the same way. The diamagnetic part is often small compared to the experimental value, however, and the paramagnetic contribution Δδ_p is important. Δδ_p is difficult to explain with the usual models of anisotropic and electric contributions, but the results give useful information on the conformations of the molecules.     

Le mécanisme de la réduction polarographique des dérivés ditosyloxylés et son implication en électrochimie préparative

The cleavage of a single SO₂? O bond occurs during the polarographic reduction of a tosyloxy group (p? CH₃C₆H₄SO₂O = TsO) in aprotic medium and intramolecular cyclisation may ensue when a second TsO group is present on the same molecule. The polarographic behaviour of aliphatic ditosyloxy derivatives is discussed on the assumption that oriented vicinal derivatives at the interface assume a conformation which resembles the geometry of the transition state for an intramolecular elimination with anchimeric assistance of one of the tosyloxy groups. This situation favours the electron transfer, whereas the same geometric requirements hinder the intramolecular interaction of the TsO groups of the oriented non-vicinal derivatives. This interpretation agrees well with the fact that the large scale electrolysis of vicinal ditosyloxy derivatives give much higher yield of cyclic ethers than the higher homologues. It is also shown that intramolecular interaction between TsO groups can occur through an intervening double bond in a non-vicinal derivative.     

Phosphates D'énols: XI—Étude en Spectrométrie de Masse des Dérivés Diméthyliques

The mass spectrometric study of a series of enolic phosphates of type A leades to fragmentation patterns influenced by the nature of the substituents (R, R′ and R″). It is generally observed that a simple or double hydrogen rearrangement occurs with the loss of the enolic groups. When R and R′ are alkyl groups, the migrating groups are the hydrogen atoms on the alkyl group at position 1. When there is no alkyl group at position 1, the hydrogen atoms of the alkyl group at position 2 induce the rearrangement process. Finally, if R, R′ and R″ are hydrogen atoms, the loss of the enolic chain occurs without any rearrangement.     

Une synthèse générale des tétraazamacrocycles mono-C-fonctionnalisés

A General Synthesis for Mono-C-Functionalized Tetrazamacrocycles A new synthesis, under usual conditions of concentration, medium, and temperature, of a series of mono-C-functionalized tetraazamacrocycles is given. The method may easily be generalized. The new procedure allows the modification of the length of the side-chain or the size of the cavity by choosing fitted staring materials. The key intermediate has a tosylated linear side-chain susceptible to be transformed into a large variety of functional groups.     

Oxydations et halogénations régiosélectives et réactions carbéniques de dérivés de sucres portant un groupement thioéther

Regioselective Oxidations, Regioselective Halogenations and Carbene Reactions of Sugar Derivatives Bearing a Thioether Group Regioselective stoechiometrically controlled procedures are described for the oxidation of thiosugars either at the sulfur atom (to sulfoxides or sulfones) or at a hydroxymethylene group (to ketosugars). Ruthenium tetraoxide reacted at both sites. Chloration (SO₂Cl₂) of β-ketothioether sugar derivative 3 took place exclusively at C(6). Evidence is given that a chlorosulfonium intermediate C was formed when the dichloroketothiosugar derivative 6 was treated with SO₂Cl₂. The carbene generated from the tosylhydrazone 16 rearranged to the enoses 17–20 , the migrating group coming in equal proportions from C(4) and C(6). Some stereochemical aspects of these reactions are discussed.     

Détermination de constantes de stabilité de chélates par résonance magnétique nucléaire du proton

In a solution containing an excess of two metal ions in regard to a ligand (e.g. NTA) a competitive equilibrium is established. The measure, by proton NMR. spectroscopy, of the individual concentrations of both chelates, and eventually of the free ligand, allows to determine the ratio of the stability constants of the two complexes. As an illustration the ratios of the stability constant of the 1:1 nitrilotriacetate chelates of Pb and Zn, respectively Mo and W, were determined.     

Contribution à l'étude de l'ionisation des films insolubles de polyélectrolytes stéréoréguliers

The surface potentials of monolayers of poly(methacrylic acid) (PMA) have been studied as a function of the pH of the subsolution. The influence of the macromolecular configuration on the properties of the ionizable groups was more particularly investigated. Orientation of molecules in the monolayer may be imposed by the stereoregularity of PMA (isotactic, atactic) and by the nature of the interface (air–water, cyclohexane–water). The results are analyzed in terms of theories of the ionic double layer (Gouy model, Donnan equilibrium) which permit the determination of the degree of ionization α of the film. The value of α gives indications about the orientation of specific groups of the macromolecular chain, i.e., of the ionized monomer units. Indeed, at the air–water interface, the film of isotactic PMA is more acid than that of the atactic sample, and at the cyclohexane–water interface, the degree of ionization is greater than at the air–water interface. These properties are the consequence of a modification of orientation of the hydrophilic groups with respect to the aqueous phase as a function of the stereoregularity of the sample and the nature of the interface. The variation of α with the pH of the substrate phase may be used to calculate an intrinsic dissociation constant K_s° of the molecules in the film. The value of K_s° is not modified by spreading conditions and remains very similar to that obtained in solution.     

Hétérocycles contenant du phosphore: XXVII—Etude par Résonance Magnétique Nucléaire de quelques dérivés des dioxa-et dithiaphospholanes-1,3,2 monosubstitués en 4

The ¹H n.m.r. spectra of some derivatives of 4-methyl (or 4-phenyl) 1,3,2-dioxa- and 1,3,2-dithiaphospholanes are analysed. The configurational study of the compounds has been investigated. The torsional angle of the C₄? C₅ fragment is calculated and the ring conformation in solution is discussed.     

Étude D'une Série de Phénoxazines et D'azaphénoxazines par Spectrométrie de Masse

Mass spectra of substituted phenoxazines and azaphenoxazines have been determined and are discussed here. These compounds are characterised by hydrogen on the heterocyclic nitrogen and aromatic rings with nitro groups and chlorine as substituents. The fragmentation patterns are explained by known mechanisms. An interpretation of almost all the peaks is offered. The presence of the substituents causes a complete change in the fragmentation patterns compared with the unsubstituted phenoxazine. This is due to changes in charge localisation, caused by the substituents. Isomerisation of the nitro group to the nitroso group gives rise to a particular fragmentation route.