Claude Biran

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, CH2ue5fbCHCH2COR, 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 CH2ue5fbCHCH2COR lead uniquely to the trans-,propenylketones, MeCHue5fbCHCOR.

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 SiClue5f8Mgue5f8HMPT 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.

L'électrosynthèse, une voie simple d'accès aux di- et polysilanes

Abstract Electrochemical reduction of chlorosilanes, at constant current intensity, in a single compartment cell fitted with a sacrificial aluminium anode, is a practical and convenient route to di-, tri-, and poly-silanes.

Silylation par des chlorosilanes de polyènes conjugués obtention de dérivés monosiliciés y-éthyléniques par scission Si-C

Summary In the presence of magnesium and in hexamethylphosphoric triamide (HMPT), trimethylchlorosilane reacts with 2,6-dimethyl-2,4,6-octatriene to lead only to one disilylated derivative with 1,4-addition of trimethylsilyl groups. Silylation of dienes has been especially worked out with butadiene and carried out with isoprene: particularly with dimethyldichlorosilane, the corresponding silacyclopentenes have been synthetized with satisfactory yields. The disilylated compounds prepared all undergo acid cleavage of one allylic Si-C bond, with allylic rearrangement. These reactions can be explained both by steric and electronic reasons.

Creation de la liaison silicium-carbone par silylation reductrice de composes fonctionnels allyliques et benzyliques; influence des groupes SiMe3 sur la stabilisation des anions

Abstract The Me3SiCl/Mg/HMPT system reacts with several functional substituted benzylic or allylic compounds (alkoxysilanes, ethers, amines etc.) and leads to a reduction of the function with C-silylation. These reactions generally need catalysts (transition metal complexes), except with α-silylated or with trityl compounds, when stabilization of the intermediate carbanions, especially by the trimethylsilyl group, takes place.

Stereoselective electrochemical synthesis of silyl enol ethers using a sacrificial magnesium anode

Abstract The 2-pyrrolidone magnesium salt electrogenerated in an undivided cell fitted with a sacrificial magnesium anode allowed the stereoselective synthesis of Z-silyl enol ethers upon deprotonation of enolizable ketones in the presence of a complexing agent.

Molar scale electrosynthesis of ethyl-2,2-difluoro-2-trimethylsilylacetate, a difluoromethylene building block precursor

Abstract Ethyl-2,2-difluoro-2-trimethylsilylacetate has been prepared by electrolysis of ethyl-2-chloro-2,2-difluoroacetate in one step, at a molar scale, in the presence of a large excess of chlorotrimethylsilane. The transfer of the ethyl-2,2-difluoroacetate moiety to various electrophiles has been achieved.

Electrosynthèse en chimie organosilicique: silylation sélective de polychlorométhanes

Abstract Silylation by electroreduction of carbon tetrachloride, chloroform or methylene chloride is more selective than the common organometallic route. Me 3 SiCCl 3 (94%) and (Me 3 Si) 2 CCl 2 (68%) were thus obtained from CCl 4 , Me 3 SiCHCl 2 (94%) and (Me 3 Si) 2 CHCl (56%) from CHCl 3 and Me 3 SiCH 2 Cl (90%) from CH 2 Cl 2 . Complete silylation of polychloromethanes was also successful by electrosynthesis and gave satisfactory yields.

Sur une nouvelle synthese d'acylsilanes

Abstract In the presence of a stoichiometric amount of CuI, Ph3SiLi reacts with MeCOCl, EtCOCl and t-BuCOCl, to give the corresponding acylsilanes in high yields.

Magnesium bis(diisopropylamide), a useful reagent for regio- and stereoselective synthesis of kinetic silyl enol ethers

Abstract Less highly substituted silyl enol ethers are regiospecifically prepared in high yield, around room temperature under kinetic conditions, from unsymmetrical cyclic ketones and magnesium bis(diisopropylamide) [(DA) 2 Mg] in THF/heptane. This high regioselectivity is markedly higher than these reported for bromomagnesium diisopropylamide (DAMgBr); it is also similar to this of LDA/DME at −78°C, but (DA) 2 Mg can be used at room temperature. In addition, a high E-enolization stereoselectivity is observed for benzylic ketones, reverse of this obtained with LDA.