Franck Metras

Mechanism of thermal polymerization of cyanate ester systems : Chromatographic and spectroscopic studies

The mechanisms and kinetics of polymerization of mono- and difunctional cyanate esters are investigated using chromatographic (HPLC) and spectroscopic methods (UV, liquid and solid-state NMR, and FTIR). The results obtained after chromatographic separation and identification of the chemical species present in the reaction medium have enabled us to propose a reaction path and a kinetic model for these thermally polymerized systems. Finally, the polymerization of cyanate ester was studied in the presence of different catalysts (imidazole, AcAcCu and AcAcCr) added directly, without solvent, and showed their influence on mechanisms.

Nouvelle synthèse de spiro-orthoesters d-glucosidiques par photocyclisation stéréoselective d'hydroxyalkyl-d-glucosides

Abstract Irradiation of hydroxyalkyl glucosides in the presence of mercury(II) oxide and iodine gave glucosidic C-1-spiroorthoesters. Where the starting glycoside had CH2OH, the cyclization was regio- and stereo-specific by α-attack. The C-1-spiroorthoesters were readily available in a “one-pot synthesis” starting from glucosyl halides.

Réaction non classique au cours de l′alkylation des Halogénures d′éments de la colonne IVB par des Réactifs de Grignard; cas du t′trachlorure de silicium

Abstract The reaction of sterically hindered Grignanrd reagents with silicon tetrachloride leads before hydrolysis to important yields of dialkylmonochlorosilanes. The formation of such compounds results from the reduction of SiCl4 to HSiCl3 followed by alkylation with the Grignard reagent. The different steps of these transformations are proved by chemical and physicochemical ways.

Réaction non classique au cours de l'alkylation des halogénures d'éléments de la colonne IV B par des réactifs de grignard : I. Cas du tétrachlorure de germanium, mise en évidence et réactivité d'un intermédiaire à liaison GeMg

Abstract The reaction at low temperature (4°) of sterically hindered Grignard reagents with germanium tetrachloride leads after hydrolysis to important yields of trialkylgermanes. These compounds proceed by hydrolysis of an intermediate: R3GeMgX, which formation results from the reduction of GeCl4 to GeCl2, followed by insertion of GeCl2 into the Grignard reagent CMg bond. The different steps of these transformations are proved by chemical and physico-chemical ways.

On the Twist-Boat Conformation of the Tetrahydropyran Cycle in the Trioxa-Bis-Spiroketal Series

Abstract INTRODUCTION In the solid state the trioxa-bis-spiroketal 2 (fig. 1) has a twist-boat conformation (tetrahydropyran cycle) and its infrared absorption and nuclear magnetic resonance (1H at 250 MHz, 13C at 15,06 MHz) spectra let forsee the same conformation in solution.1.

An Example of Crossed Ship Conformation: The Tetrahydropyran Ring in Trioxa-bis-Spirocital Series

Abstract The three 3JHH coupling constants observed in the 1H NMR spectra (500 MHz) of trioxa-bis-spirocital 1 and 2 serve to calculate the dihedral angles Ψ(8,9) and Ψ(9,10) of these two molecules. The values obtained, 54° for 1, 25° for 2, reflect the change in conformation: chair → crossed ship when passing from 1 to 2. This change in conformation corresponds in 13C NMR to strong shielding (−3.6 to −5.5 ppm) of the lines of the carbons C8, C9 and C10.