Cyclodeshydration d'alcool-phenols induite par l'h.m.p.a. nouvelle voie d'acces aux dihydrobenzofurannes et dihydrobenzopyrannes

Substituted benzodihydrofurans and benzodihydropyrans 2 were obtained by heating alcohol-phenols 1 in HMPA. New cyclic alkyl phenyl dimethylaminophosphoramidates 3 were also isolated. Their thermolysis was studied. This and other considerations show that bis(dimethylamino)phenol alkyl phosphorodiamidate 4 and by-product 3 are intermediates of an alternative two or threestep reaction pathway. This mechanistic study gave indications on choice of best experimental conditions for this new cyclodehydration method.     

Ouverture d'epoxydes par des acides organiques dans L'H.M.P.T.: nouvelle voie d'acces a des desoxypentopyranosides

The opening of pyranic epoxides with organic acids in HMPA leads to regioselectively esterified methyl deoxy$\text{threo}$pentopyranosides; one of them is a convenient intermediate to provide $\text{erythro}$ isomers.     

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)).     

1H-NMR-spektroskopische konformationsanalyse von halogenierten thymidinabkömmlingen: I. konformation von thymidin, 3',5'-didesoxy-3'-chlor-5'-fluor-thymidin und 3', 5'-didesoxy-3',5'-difluor-thymidin

An improved method is given for determining the conformation of furanoid nucleosides by ¹H-NMR-spectra analysis using halogen-substituted thymidines as examples. The state of the three equilibria - ring-puckering, rotation about the C₄-C₅- bond and about the glycosidic bond - are influenced by the halogen substituents. Compared with thymidine the 3'-chlorine substituent shifts the furanose conformation to conformers, where the 3'-chlorine substituent is equatorial. The 5'-fluorine substituent increases the contribution of the G-G-rotamer and the ratio of syn-conformation. The relationships between the conformers in the pseudo-rotatory cycle and the population of the C_4'-C_5' rotamers are discussed.     

39. Symposium für Theoretische Chemie

Das 39. Symposium für Theoretische Chemie (STC 2003) fand unter dem Titel „Molecular Spectroscopy and Dynamics”︁ vom 28. September bis 2. Oktober 2003 in Gwatt am Thuner See (Schweiz) statt. Etwa 160 Tagungsteilnehmer hatten die Möglichkeit, sich in Vorträgen und auf Postersitzungen über aktuelle Forschungsarbeiten aus vielen Bereichen der Theoretischen Chemie zu informieren.     

Hydroboration d'amines insaturees: V. Nouvelle voie d'access aux aminoalkylidenecycloalkanes

Hydroboration of various 1-bromopropargylamines by borinane and 3,6-dimethylborepane has led to α-bromovinylboranes. Treatment of these compounds with iodine in basic media, only gives aminoalkylidenecycloalkanes with excellent yields.     

Sur l'Utilisation d'une electrode ponctuelle dans les cellules à oxyde electrolyte solide. II. Application a la détermination des tensions d'oxydoreduction des defauts ponctuels dans l'electrolyte

A method is described for direct measurement of oxidoreduction potential of point defects dissolved in solid electrolytes. Measurements were carried out with several solid oxide electrolytes based on zirconia ZrO₂ and hafnia HfO₂.Results allowed us to determine more accurately the electrolytic behaviour of these materials and the reactions involved in the electrochemical blackening of zirconia.     

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.     

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.     

Etude des aldimines lithiees: II. Preparation d'aldehydes a groupement halogenovinylique. Application a la synthese d'oxo-3 cyclopentenes et d'aldehydes γ acetyleniques

The condensation of metallated aldimines, prepared from activated lithium dialkylamides, with different dihalogenoalkenes gives aldehydes with a halogenovinylic group. Acidic hydrolysis of these aldehydes leads directly to cyclopentenones. When treated with an excess of activated amide, halogenovinylic aldimines give γ-acetylenic aldehydes.     

Metathese d'acetates d'alcools ω-insatures : Synthese de pheromones d'insectes

Esters of alkenoic acids, including insect pheromones as examples, have been synthesized using alkene metathesis reactions.