Reactivite d'hydrocarbures methylenecyclo-hexaniques—I : Stereochimie de la reaction d'oxymercuration-demercuration

Methylenecyclohexanes, prepared in excellent yield by Corey and Chaykovsky then Cornforth reactions, give on oxymercuration followed by reductive demercuration tertiary alcohols resulting from axial attack by solvent. The attack takes place trans to the substiuent when the latter is at the 2 position. α-Hydroxy or methoxy compounds behave similarly to each other. For acetoxy compounds, the cis alcohols are obtained preferentially, by intramolecular attack of acetoxy group on the mercurinium ion intermediate. The results can be explained satisfactorily on the assumption that the factors inducing stereochemistry are short distance interactions.     

Rearrangements des halohydrines en presence de carbonate d'argent sur celite-II: Halohydrines cyclohexaniques substituees

Silver carbonate on Celite reacts with trans-diaxial halohydrins of the cyclohexane series, giving epoxides. cis-Bromohydrins, where the bromine atom is axial, lead to ketones.     

Adsorption d'eau sur la kaolinite: Influence de la nature des sites actifs

Water adsorption on kaolinite is a specific cooperative adsorption which does not satisfy the fundamental hypothesis of the BET theory.The adsorption isotherms on different homoionic samples show the effect of the hydration energy of the active sites (exchangeable cations) on quantitative adsorption data.The corresponding calorimetric curves present a maximum which characterizes interactions in the adsorbed phase. A relationship is apparent between these interactions and the electric field or the polarizability of the fixed cation, these factors determining the nature of the bond between the surface and cation.From the experimental data, we may propose an approximative value for the number of molecules which compose the primary hydration sheath of the active sites.     

Action des halogenures d'alkylmagnesium sur les pyrones-2—VI : Etude de la regioselectivite de l'ion enolate intermediaire de la reaction

Grignard reagents normally react with 2H-pyrones to yield unsaturated ketols, dihydropyranols, dienones and 2H-pyrans. In some cases, products are obtained by attack on the most sterically crowded position of the enolate ion. Since steric hindrance is an unsatisfactory basis for predicting the reactivity, we have applied a theoretical study to this problem. The model used is based on an enlarged electronic delocalization in the transition state, and allows the interpretation of the regioselectivity of the reaction.     

Stereochimie de la stannylation d'halogenures allyliques en serie cyclohexenique

cis- and trans-5-Methyl-2-cyclohexenyl chlorides were matallated by trimethylstannyllithium and tributylstannyllithium giving the corresponding allyltin compunds with inversion of configuration as shown by ¹³C and ¹¹⁹Sn NMR spectroscopy.     

Stereochimie de la cycloadditton des diarylnitrilimines sur les n-alkyl et les dialkyl-1,2 dihydro-1,2 isoquinoleines

The PMR spectroscopic properties (60 MHz) of cycloadducts of diarylnitrilimins towards 1,2-dihydroisoquinolines mono alkylated at the N-atom or dialkylated at the C¹ -carbor and N-atoms have been studied.Date allow us to determine the stereochemistry of the cycloaddition reaction which is regio and diastereospecific. Configuration and conformation of the cycloadducts are specified.     

Stereochimie de l'action des organomagnesiens et des organolithiens sur les dimethyl-1,2 alcoxy-1 silacyclobutanes

The reaction of organomagnesium organolithium compounds (alkyl, aryl, allyl and benzyl derivatives) with 1,2-dimethyl-1-alkoxy-l-silacyclobutanes proceeds with retention of configuration at the silicon atom. Stereochemical results are discussed in terms of the S_N2Si mechanism. The proposed configurations are supported by ¹H and ¹³C NMR data.     

Oxydations par le carbonate d'argent sur celite—VII : Oxydations de diols

The oxidation of several secondary-tertiary α diols by silver carbonate on Celite is described. In the steroid series, a 17α,20α diol leads to the related ketol, whereas its 17α,20β isomer is either not affected by the reagent, or slowly cleaved to give a 17-keto steroid.     

Oxydations par le carbonate d'argent sur celite—XIII : Preparation de lactones

Silver carbonate on Celite oxidizes primary 1,4-, 1,5-, and 1,6-diols and primary-tertiary diols into lactones in high yield. Primary—secondary diols lead to mixtures of hydroxy-ketones and lactones. Details are given on the synthesis of (±) mevalonolactone.     

Action des halogenures d'alkylmagnesium sur les pyrones-2—V : Action de l'iodure de methylmagnesium sur des alkylpyrones-2 non substituees en position 4

To check if only 4-substituted 2-pyrones lead to 2H-pyrans with Grignard reagents, the reactions of 4-unsubstituted 2-pyrones with methylmagnesium iodide have been studied. From 3, 5, 6 trisubstituted 2-pyrones, 2H-pyrans may be obtained; but 5,6-disubstituted 2-pyrones give only linear products.     

Titrage potentiometrique des thiols en milieu organique a l'aide d'une electrode a monocristal de sulfure d'argent: Comparaison avec une electrode argent-sulfure d'argent classique

The responses of the silver sulfide membrane electrode (the so-called sulfideselective membrane electrode) to different primary and aromatic thiols and to hydrogen sulfide have been studied in an ethanol-benzene mixture. They have not been found in good agreement with the Nernst relationship. However, this electrode can readily be used to follow, by potentiometry, the precipitation of thiols and thiol-hydrogen sulfide mixtures with silver ions. The observed potential breaks are similar to those obtained with a conventional silver-silver sulfide electrode. As it needs neither pretreatment nor maintenance, the silver sulfide membrane electrode is therefore suitable for determining hydrogen sulfide and thiols in petroleum products by potentiometric titration.     

Transpositions a etapes multiples d'epoxydes sesquiterpeniques—II : Action d'acides de lewis sur l'epoxyde de cyperene

Cyperene epoxide 1, on treatment with stannic chloride, gives the cyclopentanone 2 (70% yield) and the methyl ketone 3 (10% yield) by multi-step rearrangements comprising six elementary rearrangements. At least two of these elementary rearrangements cannot be concerted and it seems that in such compact globular polycyclic systems, the bond which migrates is not necessarily the one which is the better geometrically disposed for migration, but the one which would give a thermodynamically more stable product.Treatment of cyperene epoxide 1 with activity grade 1 alumina leads to two conjugated dienes which are the dehydration products of a rearranged allylic alcohol.     

Structure du reactif d'ivanov et de quelques organometalliques issus des derives phenylacetiques—II : Stereochimie de la condensation avec la t-butyl-4 cyclohex-anone

Ivanov reagent and some other analogous reagents (phenyl acetique serie) have been condensed with t-Bu-4 cyclohexanone in order to complete investigation of the reactive species. In all the cases, equatorial attack is highly predominant; it let suppose that enolate, detected by NMR, is the reactive species.     

Etudes sur le mecanisme de la metathese des olefines : IV. Echanges d'hydrure et carbenes

The possibility of exchanging hydrogen atoms between the catalyst and the substrate in olefin metathesis was examined. Exchange was observed at a high catalyst/olefin ratio, although virtually no exchange was observed at low ratio, Alkylidenetungsten, formed from WCl₆ and dimetallic derivatives of methane (i.e. CH₂M₂), proved to be efficient catalysts for olefin metathesis. It was concluded from these experiments and from those described earlier that olefin metathesis takes place by addition of an alkylidenetungsten to an olefin followed by fission of the resulting cyclobutane. A solution was proposed to the question raised by the Chauvin mechanism, namely the initiation, which was linked to the formation of alkyltungsten by addition of alkyl- or hydrido-tungten to olefins, followed by appropriate transformation to alkylidenetungsten compounds.     

Etude dans la serie des organosilylazoles : I. Action des halogenures d'alkyle,des chlorures d'acide et des cetones halogenees

The reactivity of organosilylamines of imidazole, pyrazole, 1,2,4-triazole and benzotriazole towards alkyl halides, acidic chlorides and halogenated ketones has been studied. Except for 1-trimethylsilylimidazole, which gives a mixed quaternary salt, reactions with primary halides lead to the corresponding 1-alkylated heterocyclic compounds in high yields; in each case only one isomer is obtained (1-alkyl-1,2,4-triazole and 1-alkylbenzotriazole). Similarly acidic chlorides give 1-acylated derivatives in quantitative yields. Finally α- or β-halogenated ketones show different behaviour and give the addition or substitution products.     

Addition regioselective d'enolates de cetones aux α-enones: Influence des facteurs steriques sur l'orientation et la reversibilite des reactions

Regio and stereochemistry in the addition of preformed magnesium and lithium ketone enolates (1 to 8) to α-enones (10 and 11) have been examined. When the substitution degree of the enolate is increased the formation of δ-diketone is favoured; nevertheless a good efficiency in the synthesis of the γ-ethylenic β-ketols (1-2 addition) is obtained via bromomagnesium enolates (EMgX) under kinetic conditions. Lithium enolate (ELi) and, chiefly magnesium enolates (E₂MgX) give preferentially the Michael addition. Reversibility from 1-2 to 1-4 addition is commonly observed but the stereochemistry, if any, of the diastereoisomeric δ-diLetones may be quite different when using EMgBr or E₂Mg as starting enolates.     

Organocuivreux vinyliques : IV. Etude de la regioselectivite de l'addition d'un alkylcuivre sur des alcynes β et γ fonctionnels

The syn addition of alkylcopper compounds to various alkynes HCC(CH₂)₂Z (n = 2, 3, Z = X, NEt₂, SEt, OR) shows a regio-selectivity dependant on various factors, the major factors being the nature of the function and the solvent. The vinylcopper derivatives thus obtained have been carboxylated, iodinated and alkylated.     

Action des reactifs de grignard sur les dithioesters : Addition carbophile d'organomagnesiens insatures. synthese de cetones β-ethyleniques

Reactions of allyl, benzyl, propargyl and vinyl Grignard reagents with methyl dithioacetate give dithioacetals (or hemidithioacetals) resulting from a carbophilic addition process. Reactions with various allylic organomagnesium compounds always involve an “inversion” of the allylic chain and direct carbophilic addition, rather than initial thiophilic addition followed by [2.3] sigmatropic shift. Three methods for the synthesis of β-unsaturated ketones are described, showing the potential synthetic uses of the reactions of Grignard reagents with dithioesters.