Stereoselective synthesis of functionalised triol units by SnCl4 promoted allylation of α-benzyloxyaldehydes: crucial role of the stoichiometry of the Lewis acid

Enantiomerically pure syn-anti and syn-syn configured triol units are efficiently synthesized by the SnCl₄ mediated allylation of chiral α-benzyloxyaldehydes with the uniquely functionalised allylstannane 9. Remarkably, the stereochemistry of the adducts is solely governed by the amount of Lewis acid employed.     

Preparation d'esters par deshydrogenation d'alcools primaires en phase liquide catalysee par l'oxyde de cuivre - observations preliminaires

Linear primary alcohols with at least 7 carbon atoms are quite quantitatively transformed in esters, by CuO, at temperatures > 170°, without air in liquid phase. Preponderant influence of carbon in position 2 is evidenced. In the same conditions lactones are obtained from diols, and benzylic alcohols undergoes, by hydride transfer, a disproportionation into toluene, benzaldehyde and water.     

Novel RPLC stationary phases for lipophilicity measurement: solvatochromic analysis of retention mechanisms for neutral and basic compounds

An RPLC was developed to rapidly determine lipophilicity of neutral and basic compounds using three base deactivated RPLC stationary phases particularly designed for the analysis of basic compounds, namely, Supelcosil ABZ(+)Plus, Discovery RP Amide C16, and Zorbax Extend C18. The work consisted of three sets of experiments. In the first log kw values of neutral compounds were extrapolated using hydroorganic mobile phases at different compositions. Good correlation between log kw and log Poct indicated that the method was appropriate for these supports, without adding a silanol masking agent. In the second set of experiments, isocratic log k values of neutral and basic compounds were measured with three different mobile phases. The best estimation of lipophilicity was obtained for neutral and basic compounds when the secondary interactions were strongly reduced (i. e., when basic compounds were under their neutral form). In the third set of experiments, isocratic retention factors of basic compounds (in their neutral form) were measured with a high-pH mobile phase, on a chemically stable support (Zorbax Extend C18). Under these chromatographic conditions, correlation between the isocratic retention factors and log Poct (log D10.5) for basic compounds was similar to that for neutral compounds.     

The acidity functions of trifluoroethanol and hexafluoroisopropanol,and their mixtures with water

Acidity measurements in trifluoroethanol and hexafluoroisopropanol as solvents, and in their mixtures with water, are reported. The hydrogen electrode and the glass electrode were used for pH measurements. The “experimental” autoprotolysis constants were determined from measurements in strongly acidic (trifluoromethanesulfonic) media and in strongly basic (alcoholate) media: for trifluoroethanol, pK = -log K/mol² l^-2 = 15 and for hexafluoroisopropanol, pK = 14.8. Evaluation of the pH-indicator potential systems with reference to the ferrocene/ferricinium couple gives the acidity function R₀(H). The values obtained are compared to the H₀ values evaluated in the same conditions.     

Ion-pair formation observed in a pulsed-field ionization photoelectron spectroscopic study of HF

The pulsed-field ionization (PFI) photoelectron (PE) spectrum of HF has been recorded at the chemical dynamics beamline of the advanced light source over the photon energy range 15.9-16.5 eV using a time-of-flight selection scheme at a resolution of 0.6 meV. Rotationally-resolved structure in the HF+(X 2 pi 3/2, 1/2, v+ = 0, 1) band systems are assigned. The spectral appearance of these systems agrees with a previous VUV laser PFI-PE study. Importantly, extensive rotationally-resolved structure between these two vibrational band systems is also observed. This is attributed to ion-pair formation via Rydberg states converging on the v+ = 1 vibrational levels of the HF+(X 2 pi 3/2, 1/2) spin-orbit states. These Rydberg states are assigned to the 1 sigma+ part of the nd-complexes (sigma, pi, and delta). Ion-pair formation is observed in this study by the detection of F- ions. Some partially rotationally-resolved structure in a previously published threshold photoelectron spectrum is similarly attributed to ion-pair formation (F- detection) through a combination of the v+ = 17 level of the (A 2 sigma+) 3s sigma Rydberg state and the (X 2 pi 3/2, 1/2, v+ = 1) 7d Rydberg states. On the basis of the present study, an accurate experimental value for the dissociation energy of the ground state of HF has been obtained, D0(HF) = 5.8650(5) eV.     

Eight-vertex tetrametallic structures derived from cubanes: a close relationship between bisdisphenoidal metallaborane and organometallic clusters

The metallaborane Cp4Co4B4H4 and the organometallic cluster Cp4Fe4C4H4 (Cp = eta5-cyclopentadienyl) not only are isoelectronic but also exhibit completely analogous eight-vertex bisdisphenoidal structures. Such structures, as well as the tetracapped tetrahedral structure of the Cp4Fe4(mu3-CO)4 precursor to Cp4Fe4C4H4, can be derived from a cube by insertion of diagonals in each of the six faces. Furthermore, the formation of Cp4Fe4C4H4 from Cp4Fe4(mu3-CO)4 can be described as a double diamond-square-diamond process preserving D2d symmetry throughout the process.     

A facile three-step synthesis of (±)-crispine A via an acyliminium ion cyclisation

A high yielding cyclisation of the readily available N-(4,4-diethoxybutyl)-2-(3,4-dimethoxyphenyl)acetamide to 8,9-bis(methyloxy)-2,3,6,10b-tetrahydropyrrolo[2,1-a]isoquinolin-5(1H)-one is described. The latter can be reduced with either AlH₃ or BH₃ to (±)-crispine A in an overall yield of 55%.     

Synthesis of 4H-3,1-benzoxazin-4-ones and 4-(3H)quinazolinones from anthranilic acids and their derivatives by the use of triphenyl phosphite and pyridine

A series of 2-substituted 4H-3,1-benzoxazinones and 2,3-disubstituted 4-(3H)quinazolinones have been synthesized in mild conditions by the use of triphenyl phosphite and pyridine as cyclising medium. Benzox-azinones are produced either by ring closure of 2-(acylamino)benzoic acids or in the reaction of benzoic acid with anthranilic acids. In the presence of aniline, the reaction leads to quinazolinones.     

On the mechanism of conformational interconversion in cyclohexene derivatives

The free energy barriers to ring inversion for 3,3-dimethylcyclohexene, 4,4-dimethylcyclohexene and 3,3,6,6-tetramethylcyclohexene were determined by low temperature PMR studies. The results were interpreted in terms of a mechanism whereby the boat conformation is of highest energy on the energy profile for conformational interconversion. The very high ΔG^≠ value for 3,3,6,6-tetramethylcyclohexane (8·4 kcal/mole) is considered a reflection of the serious non bonded interaction that exists between methyl groups at the “prow” positions of the boat form.     

Photoinduced morphism of gemini surfactant aggregates

The photochemical behaviour of an azobenzene chromophore inserted in a gemini surfactant imparts photocontrol to the resulting amphiphile assemblies, including the collapse, upon irradiation, of the multi lamellar vesicles formed in aqueous solution.