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.     

Sels d'atdp—19: Cinetique de decomposition d'un chlorure d'atdp en chlorure d'alkyle et HMPT. Effet de solvant et effet de sel

The kinetics of decomposition of the 2-methyl-1-pentyloxy(trisdimethylamino)phosphonium chloride, was measured in several solvents. The experimental kinetic order towards the chloride anion was in the range from 2, in a dissociating solvent, to 1 in non dissociating solvents. Hence we afford experimental confirmation of an earlier prevision in the literature. A linear correlation of log k with the dielectric constants of the solvents was found in the case of the systems exhibiting first order kinetics, contrasting with the classical correlation in $\text{1}\text{?}$, generally observed for the reactions between ions of opposite charge. The salt effect has been measured and interpreted. It allows the performance of kinetic runs for non hindered, very labile ATDP salts, by their replacement by a mixture of an ATDP perchlorate and an aryloxyphosphonium chloride, both of which are stable.     

Effets cinetiques de sels lors de la methanolyse de l'acetate de phenyle par catalyse basique en milieu methanolique: Etude perturbationnelle des effets de sels lors de l'hydrolyse ou de la méthanolyse d'esters aliphatiques ou aromatiques

Methanolysis of phenyl acetate shows a slight rate increase in the presence of NaClO₄ or NaBr or a rather large rate decrease in the presence of LiClO₄ or LiBr. These results are different from those obtained for alkaline hydrolysis of an aliphatic ester. They are interpreted in terms of a frontier orbital controlled reaction. For aliphatic esters, complexation phenomena

is predominant; for aromatic esters, due to a stabilisation of the π^* CO orbital energy level, two opposite effects are possible:

complexation inducing a rate increase, and association of the nucleophile HO^- or CH₃O^- with M⁺ leading to a rate decrease. The relative importance of these two opposite effects depends on the nature of the ester.     

Stereochimie et mecanisme de l'ouverture par les amines d'ions N-alcoxypyridinium : Formation competitive d'un ylure endocyclique; application a une nouvelle conversion heterocyclique

The N-alkoxypyridinium salt 1, with pyrrolidine, piperidine and diethylamine, undergoes reversible ring opening in acetonitrile. This competes with irreversible cyclization of an ylide to the bicyclic intermediate 3 which suffers subsequent ring opening to 3-ω-aminobutadienylisoxazol-4 ones in methanol. The different courses of the reaction is tentantively explained by means of HSAB theory. Stereochemistry of the primary open products is consistent with a disrotatory ring opening of cis-dihydropyridine adducts resulting from amine addition to the salt 1 or to the bicyclic ion 3. These primary products are further isomerized and all-trans structures have been isolated in the case of isoxazoline derivatives. Conversion of an N-alkoxypyridinium salt to substituted butadienylisoxazolones exemplifies a new type of heterocyclic ring transformation that can be described by the PARC-ANRO sequence: Proton Abstraction, Ring Closure—Addition of a Nucleophile, and Ring Opening.     

Photolyse d'oxazirannes V. Comparaison entre le réarrangement thermique et photochimique d'oxazirannes à jonction spirannique

Thermolysis and photolysis of spiro-oxaziridines have been compared. These reactions proceed with the same regioselectivity.     

Analyse conformationnelle a l'aide de la notation des angles de torsion—II: Controle conformationnel de l'ouverture de monoepoxydes de dienes cisoides et transoides s'effectuant avec deplacement allylique de l'olefine

Taking advantage of the torsion angle notation and using only the assumption of the maintenance of orbital overlap during the reaction it is possible to analyse and interpret the steric course of the 1,4-opening of cisoïd and transoïd diene monooxide incorporated in mono or polycyclic structures. The stereochemistry of the reverse reaction, corresponding to diene monoepoxide formation from a γ-bromo-α,β-unsaturated-cyclohexanol can also be predicted.     

Heterocyclisation des α-acylaminoamides—IV : Mecanismes d'ouverture et de formation du cycle amino-5 oxazole

It was established by using ¹⁸O enriched water that the 5-aimno-oxazole cycle is opened via a nucleophilic attack of water on the 5 position. The mechanism of the heterocyclisation of ¹⁸O enriched α-acylaminoamides by trifluoracetic anhydride has been studied. Two cyclisation reactions occur, involving the attack of the anhydride by the amidic O atoms.     

Transpositions a etapes multiples d'epoxydes sesquiterpeniques—I : Action de l'acide formique sur l'epoxyde de cyperene. Correlation entre le cyperene et l'α-cedrene

Cyperene epoxide 2, on treatment with formic acid, gives about ten products of which the two major ones have been isolated and characterised. The allylic alcohol 3 is the product of an allylic rearrangement. The diol 5 is produced by a multistep rearrangement, the mechanism of which is remarkable in that the first elementary step cannot be concerted. The structure of the diol 5 has been confirmed by correlation with α-cedrene.     

L'extraction des lanthanides et des actinides par les oxydes d'alkylphosphine: Tome 1. l'extraction de l'acide nitrique par l'oxyde de tri-n-butylphosphine

The distribution of TBPO, water and nitric acid has been measured between an aqueous phase and various inert diluents at 25°. This study allowed the determination of the apparent stability constants for two molecular complexes, TBPO . HNO₃ (K₁=17.5±1.3 (M/l)^-2 (benzene); 20.1±0.8 (M/l)^-2 (toluene); II±2(M/l)^-2 (n-hexane) and TBPO . 2HNO₃.H₂O (K₂=(2.9±0.3) 10^-3(M/l)^-2 (benzene)).     

Sels d'alkyloxyphosphonium—XV: Activation de l'hydroxyle anomere des 2,3,4,6-tetra-o-acyl-d-glucopyranoses—II. Preparation d'orthoesters et de thioglucosides

The joint action of tris(dimethylamino)phosphine (TDAP)-carbon tetrachloride on a tetra-O-acyl-2,3,4,6-d-glucopyranose yields two anomeric oxyphosphonium chlorides (ATDP salts). One of these anomeric forms is stable and the corresponding α-hexafluorophosphate is isolable as a solid. The alcohols react with the mixture of ATDP chlorides to yield 1,2-orthoesters, while thiophenol reacts to give the thioglucoside. These results are discussed and interpreted.     

Étude de l'erreur acide de l'électrode de verre en milieu aqueux: Tome III. Solutions mixtes d'acide et de sel alcalin

The acid error of the glass electrode is studied in mixed solutions of acid and alkaline salt with common anion. Measurements have been made by direct comparison with the hydrogen electrode. The experimental results confirm the view that the acid error arises from anion penetration into the glass. An empirical equation is proposed in which this error is expressed in terms of cation concentration in mixed solution.     

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.     

Analyse conformationnelle a l'aide de la notation des angles de torsion—IV: Interpretation et prevision du cours sterique de l'addition conjuguee d'anions sur les cyclopenten-2 ones

With the help of the torsion angle notation the steric course of anion conjugate addition to cyclo-pentenones can be interpreted or predicted, taking into account the maintenance of orbital overlap and the least amount of structural distortion during the reaction.     

Reactivite des epoxydes—II: Influence du milieu reactionnel lors de l'ouverture des epoxydes par les amidures de lithium

The suppression of α-elimination during opening of epoxides by lithium amides (RRNLi) is possible by the use of HMPT as a solvent. This solvent effect is general and is of some interest for the preparation of allylic alcohols by epoxides opening with lithium amides. Formation of by-products such as ketones or aminoalcohols is also avoided in this polar solvent.     

Effets de cryptands et activation de bases—II: Genese d'enolates et essais d'activation de LiH,NaH et KH dans l'ether,le THF et le benzene

The generation of the lithium, sodium and potassium enolates of cyclohexanone using LiH, NaH and KH has been investigated. The utilization of macrocyclic ligands (which selectively complex the metal cation) activated the alkaline hydride reagent. However, the most dramatic effect was the activation of the enolate, enabling proton abstraction from the solvent.     

Alcaloïdes des Homalium: Structure de l'homaline,de l'hopromine,de l'hoprominol et de l'hopromalinol

L'étude chimique de quatre alcaloïdes: homaline, hopromine, hoprominol et hopromalinol, isolés de l'Homalium pronyense Guillaum., aétéeffectuée. La structure du principal d'entre eux, I'homaline, est démontrée commeétant celle du butylène 5-5′ di(méthyl-1 phényl-2 oxo-4 diaza-1,5 cyclooctane)-(2S,2′S). Ces quatre bases constituent un nouveau type d'alcaloïde. La présence dans leur molécule deséléments de la spermine permet de les rattacher au groupe des “Alcaloïdes macrocycliques dérivés de la spermine et de la spermidine?d.¹³