Stereochimie de la des benzoates d'argent sur des diesters iododesoxy ns: I- Action des benzoates d'argent sur des di-o-aroyl-1,2 iododesoxy-3 ns-glycerols

The stereochemistry of the reaction of silver benzoates on chiral di-O-aroyl-1,2 iododeoxy-3-sn-glycerols has been reinvestigated. The reaction proceeds either with or without neighbouring group participation, depending on : - possible electrophilic assistance by the silver ion to the ionisation of the substrate (occuring only with dissociated silver salts), - ability of substituants R¹ and R² on the substrates to stabilize a positive charge. Rearrangements are at minimum with R¹ and R² electronreleasing groups in the substrate, silver salts un-or weakly dissociated and bearing a good nucleophile. For one case, a regio- and stereo specific reaction is observed.     

Studies on the 4-benzoylpyridine-3-carboxamide entity as a fragment model of the Isoniazid-NAD adduct

An ortho-metallation-electrophilic substitution sequence was employed as a key step to build the 4-benzoylpyridine framework. It was found that 4-benzoylpyridine-3-carboxamide and an N-pyridyl alkylated derivative both exist in a unique cyclized hemiamidal structure, not in the usually expected keto-amide open form. These structures represent fragment models of the Isoniazid-NAD adducts involved in the mechanism of action of the antituberculous drug Isoniazid.     

Scope, limitations and mechanistic aspects in the selective homogeneous palladium-catalyzed reduction of alkenes under transfer hydrogen conditions

A new and efficient mild Pd/P(t-Bu)₃ catalyst for selective reduction of various alkenes under transfer hydrogen conditions has been developed leading to the corresponding saturated derivatives in chemical yields varying from 65 to 98%. Mechanistic rationale of this reaction has been also demonstrated.     

Bicyclic aziridines as intermediates in the photolysis of polycyclic aromatic azides.

According to the subsequent treatment, azepines $\text{16}$, $\text{17}$, $\text{19}$ or 1,2-dihydro derivatives $\text{18}$ and $\text{20}$ are obtained in the photolysis in basic medium of β-anthracenic azides $\text{7b}$ and $\text{7c}$ and provide strong evidence for the intermediate formation of bicyclic aziridines.     

Vapor Pressure and Solid Phases of Methanol below Its Triple Point Temperature

We present an experimental work devoted to study of the thermodynamical properties of solid methanol. We combine Fourier transform infrared spectroscopy (FTIR) and mass spectrometry (MS) to measure, for the first time, the vapor pressure of various methanol solid phases and determine their Clausius-Clapeyron equations. We perform our experiments between T = 130 K and the triple point temperature T(t) = 175.61 K. When methanol is condensed from its vapor below T(t), we observe three different solid phases depending on temperature. A condensation at T = 130 K forms a metastable phase with an enthalpy of sublimation deltaH(metastable-vapor) = 42.9 +/- 0.5 kJ.mol(-1). Upon heating, this phase transforms itself at T approximately 145 K to the alpha-phase that has an enthalpy of sublimation deltaH(alpha-vapor) = 46.9 +/- 0.2 kJ.mol(-1). Cooling the alpha-phase does not lead back to the metastable phase, whereas heating this alpha-phase leads to the beta-phase occurrence at T(alpha-beta) = 157.36 K. This latter one is stable until T(t) and has an enthalpy of sublimation deltaH(beta-vapor) = 44.2 +/- 0.5 kJ.mol(-1).     

Probing electrochemical properties of pi-conjugated thienylenevinylenes/fullerene C(60) adducts by ESI/MS: evidence for dimerized cation-radicals

Oligothienylenevinylenes/C(60) dyads n-C and triads n-C(2) are studied by electrospray mass spectrometry. A clear correlation is observed between the nature of the charged species detected by mass spectrometry, i.e. protonated molecule [M + H], (+) cation radical M(+.) and dication M(++), and the oxidation potentials of the molecules. Moreover, under defined solubility conditions, mass spectrometry provides conclusive evidences for the reversible dimerization of cation-radicals of n-C(2) compounds.     

Nachweis von C (15)-epimeren Coleonen C und D in der Natur und ihre Bedeutung für den sterischen Verlauf der Bildung des Spirocyclopropanrings

Natural Occurrence of C(15)-Epimeric Coleons C and D and its Significance to the Stereochemistry of the Formation of a Spirocyclopropanring In a previous paper some evidence was presented for a predominant occurrence of epimeric coleons ((15S)-coleon C ((15 S)- 1a ), and (15S)-coleon D ((15S)- 2a )) in Plectranthus lanuginosus [1], The proposed structures have now been proven by careful comparison of their physical data with those of the already described C(15)-epimers whose structures were deduced by X-ray analysis of a derived cis-diketone 3 [5], Examination of the epimeric purity of coleons possessing a 2-hydroxy-1-methylethyl side-chain (coleons C , D , H , I , I ′ and derivatives) isolated from seven different species (Coleus, Plectranthus and Solenostemon) has shown that these coleons always occur as a mixture of C(15)-epimers, although in most cases with one predominant epimer. The consequences for the stereochemistry of the postulated in vivo formation of the methyl-substituted spirocyclopropane substructure is discussed.     

Gibbs functions for transfer of divalent metal cations from water to water + methanol mixtures using potentiometry, polarography and solubility measurements

Gibbs functions for transfer from water to methanol and to a full range of water + methanol mixtures were obtained for Cu²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ using potentiometric or polarographic measurements in these solvents. In addition, data were obtained from the solubility products of the alkaline-earth iodates. From values obtained by the different methods and literature data, a table of selected values is given.