Efficient synthesis of 2- and 3-substituted-2,3-dihydro [1,4]dioxino[2,3-b]pyridine derivatives

A versatile new approach for the synthesis in three steps of 2-substituted-2,3-dihydro[1,4]dioxino[2,3-b]pyridines B via a Smiles rearrangement using easily available reagents is described. A study illustrating the influence of experimental conditions on the progress of the reaction is reported.     

Application of Carbowax 20M as an open-tubular liquid phase in analyses of nutritionally important fats and oils.

In the first part, the reasons for the choice of Carbowax 20M-terephthalic acid as a liquid phase are indicated and the technique for preparation of columns is descirbed. The ECL of 14 to 24 carbon fatty acids (branched and positional isomers of unsaturated acids) as well as the accuracy of determination of some fatty acids, are presented. In the second part, examples of chromatograms are given as well as tables concerning the composition of various fats: vegetable oils, depot fats, and fats from organs of monogastric species, polygastric species, and fish.     

Preparation and properties of surface modified ceramic membranes. Part III. Gas permeation of 5 nm alumina membranes modified by trichloro-octadecylsilane

Stable trichloro-octadecyl silane (ODS) derivatives of a 5 nm γ-alumina ceramic membrane were prepared. Gas permeabilities of the untreated membrane did not show Knudsen diffusion at 20°C. Gas permeabilities of the ODS membrane were three orders of magnitude lower; He, Ne, Ar, CO₂, C₃H₈ have near constant permeabilities 360 mol s⁻¹ m⁻² bar⁻¹, except methane which has the highest permeability of the group, 481 mol s⁻¹ m⁻² bar⁻¹. The mechanism of diffusion is solution/diffusion. Remarkably, permeabilities of ODS-alumina membrane were reduced by 5 X after exposure to a pressure difference of 1 atm (active layer side) against vacuum for only 10 min. The effect was metastable but could be reversed on standing for several hours, reversal of pressure difference or after washing with (hydrocarbon solvent) toluene. The mechanism was presumed to be due to movement of the octadecyl-hydrocarbon chains of the silane monolayer causing a partially blocked pore structure; perhaps a unique example of self-fouling.     

Synthesis of new compounds containing the 2,3-dihydro[1,4]dioxino[2,3-b]pyridine heterocyclic system as a substructure

2,3-Dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,3′-pyrrolidine (8A) and 2,3-dihydro-spiro[1,4]dioxino[2,3-b]pyridine-3,4′-piperidine (9A) have been synthesized from 2-chloro-3-pyridinol. The corresponding 2,3′ (8B) and 2,4′ (9B) isomers were obtained via the Smiles rearrangement, while 9B was also selectively synthesized from 2-nitro-3-pyridinol. The separation of the isomers A and B under the sulfamide form was carried out by flash column chromatography. Subsequent transformations of the corresponding dioxinopyridine derivatives were described.     

Tumorhemmende wirkstoffe, XIII [1] aromatisch carbocyclisch und heterocyclisch substituierte 2-perfluoralkylpyrimido[1,2-a]benzimidazole

The interaction of 2-aminobenzimidazole with the appropriate β-diketones carrying fluoroalkyl groupings has led to the 2-perfluoroalkylpyrimido[1,2-a]benzimidazoles as follows: 4-phenyl-, 4-(2'-naphthyl)-, 4-(3'-pyridyl)-, 4-(2'-furyl)-, and 4-(2,-thienyl)-2-trifluoromethylpyrimido[1,2-a]benzimidazole, and 4-(2'-thienyl)-2-(heptafluoropropylpyrimido [1,2-a]benzimidazole.     

Synthesis of cone, partial-cone, and 1,3-alternate 25, 27-Bis

The preparation of 25,27-bis[1-(2-ethyl)hexyl]- and 25, 27-bis[1-(2-tert-butoxy)ethyl]calix[4]arene-crown-6 combining one polyether crown-6 and one alkylchain O-attached on each side of a calix[4]arene in the cone, partial-cone, and 1,3-alternate conformations are reported. The control over 25, 27-bisalkylcalix[4]arene-crown-6 conformation via varying specific reaction conditions was studied. The series of calix[4]arenes have been prepared by two routes, which differ in the order in which the alkyl or polyether groups were introduced. Moreover, methods have been developed to selectively prepare the cone and partial-cone conformers by using an appropriate base in the alkylation reactions. The conformations of these new derivatives have been probed by (1)H NMR analysis and X-ray crystallography. The (1)H and (13)C NMR spectra of 25,27-bis[1-(2-ethyl)hexyl]calix[4]arene-crown-6, 1, 3-alternate 1, cone 2, and partial-cone 3 are also discussed.     

First Synthesis of 1,3-Alternate 25,27-Dialkyloxy-5,17-diarylcalix[4]arenes-crown-6 as New Cesium Selective Extractants by Suzuki Cross-coupling Reaction

The synthesis of new 25,27-dialkyloxy-5,17-diarylcalix[4]arenes-crown-6 1a–f in 1,3-alternate conformation by Suzuki cross-coupling reaction is reported. Their conformation was determined using ¹H, ¹³C, 2D NMR and ROESY analysis, and X-ray crystallography. Extraction experiments using a two-phase solvent method involving sodium, potassium or cesium picrate showed good extraction of the cesium cation. The X-ray crystal structures of 1,3-alternate 25,27-dipropoxy-5,17-diphenylcalix[4]arene-crown-6 ether 1a and its cesium picrate complex were established. Solid-state data were used to determine the complexation behavior of these new ligands. The efficiency of calixarenes 1a–f for cesium ion extraction could be ascribed to the rigidity and flatness linkages caused by the aryl groups at the lower rim of the aromatic moieties in the calixarene skeleton. In addition, the introduction of these aromatic moieties in positions 5 and 17 enhanced the solubility of the metal complexes in organic media.     

Nonlinear Spherical Caps and Associated Plate and Membrane Problems

This paper deals with the existence and multiplicity problem of the equilibrium solutions of an elastic spherical cap within nonlinear strain theory. We pose the problem in the form of a three parameter bifurcation problem, one parameter being related to the load, the others to the geometry. When the geometrical parameters are different from zero, the so-called generic case, we revisit the nonuniqueness results, and explore the solutions in the parameter space. Then we analyze the formal limits as the geometrical parameters tend to zero. When the curvature tends to zero, we obtain from the nonlinear shell a von Kármán plate, a new, although natural, result. When the thickness parameter tends to zero, we get a nonlinear membrane problem. A study of the latter gives infinitely many solutions, and we discuss the construction, shapes, and stability in detail. This revised version was published online in August 2006 with corrections to the Cover Date.     

<Emphasis Type="Italic">L</Emphasis><Superscript>2</Superscript> Stability Estimates for Shock Solutions of Scalar Conservation Laws Using the Relative Entropy Method

We consider scalar nonviscous conservation laws with strictly convex flux in one spatial dimension, and we investigate the behavior of bounded L ² perturbations of shock wave solutions to the Riemann problem using the relative entropy method. We show that up to a time-dependent translation of the shock, the L ² norm of a perturbed solution relative to the shock wave is bounded above by the L ² norm of the initial perturbation.