J. Dunogues

A new practical synthesis of silyl enol ethers : Part.I. From simple aldehydes and ketones

Abstract A new, practical route to enoxysilanes is described from simple enolizable aldehydes or ketones, using the trimethylchlorosilane-sodium iodide—tertiary amine reagent in acetonitrile. From certain aldehydes, an onium intermediate has been isolated. A conformational study of this onium intermediate and a thermal unimolecular syn-elimination process may explain the stereoselectivity of the reaction. Such an interpretation can be extended to all the aldehydes and ketones considered, Steric factors related to the nature both of the carbonyl derivative and of the amine play a capital role for the regio- as well as for the stereo-control of the reaction

Si-C-N ceramics with a high microstructural stability elaborated from the pyrolysis of new polycarbosilazane precursors

Novel polycarbosilazanes (PCSZs) were prepared by stepwise synthesis and thermal crosslinking of polysilasilazane (PSSZ) copolymers. Their pyrolysis under inert gas, producing Si-C-N ceramics, was investigated up to 1600 °C by analyses performed on the solids (elemental analysis; EPMA; TGA, density; 1H, 13C and 29Si solid state NMR, i.r. XRD, electrical conductivity) and analyses of the evolved gases (gas chromatography and mass spectrometry). From 250 to 450 °C, a first strong weight loss was observed, which was due to the formation and elimination of low-boiling-point oligomers. The weight loss closely depends on the cross-linking degree of the ceramic precursor resulting from the PSSZ/PCSZ conversion. Then, the organic/inorganic transition took place between 500 and 800 °C, proceeding via evolution of gases (mainly H2 and CH4) and yielding a hydrogenated silicon carbonitride. This residue remained stable up to 1250 °C although it progressively lost its residual hydrogen as the temperature was raised. Then, crystallization occurred between 1250 and 1400 °C, yielding β-SiC crystals surrounded by free-carbon cage-like structures. Finally, above 1400 °C, the remaining amorphous Si-C-N matrix underwent a decomposition process accompanied by nitrogen evolution and a second substantial weight loss. At 1600 °C, the pyrolytic residue was a mixture of β-SiC and free carbon. So, the amorphous silicon carbonitride resulting from the pyrolysis of PCSZ precursors was found to be appreciably more thermally stable than the previously reported Si-C-O ceramic obtained by pyrolysis of polycarbosilane precursors.

Nouvelles Méthodes de création de liaisons siliciumcarbone À partir de chlorosilanes VI. Double silylation en 1,4 de dienes conjugués

Abstract In hexamethylphosphoric triamide and in the presence of magnesium, triorganochlorosilanes react with conjugated dienes to yield 1,4-addition products. In the aliphatic series the diorganodichlorosilanes lead to the formation of 1-sila-3-cyclopentenes.

Addition d'hydrocarbures silicies possedant une liaison SiC activee a des composes carbonyles : I. Additions au chloral

Abstract In the presence of a Lewis acid catalyst, silylated hydrocarbonds having an activated SiC bond (allyl-, aryl-, vinyl-, ethynyl- or propargyl-silanes) add to chloral and give after hydrolysis the corresponding α-trichloromethylated carbinols; this type of reaction is original in this series. Likewise allyltrimethylsilane adds to chloroacetone.

A new practical synthesis of silyl enol ethers : II. From α,β-unsaturated aldehydes and ketones

Abstract In acetonitrile as the solvent and in the presence of a tertiary amine the trimethylchlorosilane/sodium iodide (trimethyliodosilane “in situ”) reagent provides the corresponding siloxy dienes when reacted with α,β-unsaturated series. These reactions occurs via the formation of 1,2 or -1,4 onium salt intermediates.

Synthese nouvelle d'allylcetones par voie organosilicique

Abstract In the presence of a Lewis acid (AlCl3, InCl3, GaCl3), acyl chlorides react with allyltrimethylsilane to give the corresponding allyl ketones, CH2CHCH2COR, in good yields. Substituted allylsilanes, synthesized by 1,4-disilylation of conjugated dienes, give a similar reaction. The electrophilic substitution of SiMe3 by a COR group occurs with allylic rearrangement and therefore silylated β,γ-ethylenic ketones, , are obtained. In most cases the allylic ketones prepared isomerize easily to the corresponding conjugated ketones; ketones having the formula CH2CHCH2COR lead uniquely to the trans-,propenylketones, MeCHCHCOR.

Silylation d'hydrocarbures mono-aromatiques mono- ou disubstitues

Abstract In the presence of lithium and in tetrahydrofuran as solvent, trimethylchlorosilane reacts at 0–10°C, in an inert atmosphere, with monoaromatic mono- or disubstituted hydrocarbons, to give the corresponding 1,4-disilyl derivatives. In the case of ortho -xylene and cumene, disilylation is accompanied by tetrasilylation, whereas phenyltrimethylsilane can lead to the tetrasilylated derivative in quantitative yields. 1,3-Dichlorotetramethyldisiloxane reacts with benzene to give: Most of the products described are new compounds.

Application du systeme Me3SiClLiTHF a la synthese d'acylsilanes, d'alcools, d'aldehydes, d'esters et de nitriles C-silicies

Abstract Synthesis of C -silylated products by silylation of various functional saturated derivatives (aldehydes, nitriles, acid anhydrides and esters), by mens of the Me 3 SiClLiTHF system used at 0–10°C, is described. Most of the products obtained are new. A mechanism explaining the formation of these derivatives is proposed.

Nouvelle méthode de création de la liaison silicium-carbone à partir de chlorosilanes VII. C-silylation d'esters

Abstract The trimethylchlorosilane/magnesium/hexamethylphosphoric triamide system reacts with methyl benzoate to lead to an O - and C -silylated mixed ketal, which under hydrolysis easily gives benzoyltrimethylsilane (new preparative method of this compound), but which in basic media is converted to an unexpected siloxanic isomer. Under the same conditions trimethylsilyl benzoate gives, after hydrolysis, an α- C -disilylated alcohol.

C-silylation et duplication réductrice observées lors de l'action de Me3SiClMgHMPT sur des composés carbonylés α-éthyléniques. : Application à la préparation d'εdicétones à partir de cétones α-éthyléniques

Abstract Two reactions, the 1,4-disilylation and the reductive duplication accompanied by O -silylation, can chiefly occur by action of the Me 3 SiClMgHMPT system on various α-ethylenic carbonylated compounds. When the sequence of such derivatives is conjugated with another group , the 1,4-disilylation is the main reaction and affords upon hydrolysis the corresponding derivative β-silylated with respect to the carbonyl group (new illustrative example: the pseudo-ionone). In contrast to this, when the sequence is not conjugated with another group, the reductive duplication accompanied by O -silylation occurs and leads, after hydrolysis, to the corresponding e-diketone (examples: methylbutenone, 2-cyclohexenone and isophorone). Such a reaction can be used in organic synthesis to prepare e-diketones from α-ethylenic ketones. A mechanism permitting homogeneous interpretation of all our results in this domain is proposed.