Structure cristalline et configuration relative d'un complexe du titanocene presentant une chiralite plane et une chiralite centree sur l'atome de titane

The crystalline structure of the racemic form m.p. 164° C of the compound (h⁵ -3-MeC₅H₃C(Me₂)C₆H₅)(h⁵-C₅H₅)Ti (2,6-Me₂C₆H₃O)Cl has been determined by X-ray diffraction to establish the relative configuration of the two chiral moieties. This compound may be used further as a reference for studies on dynamic stereochemistry around the titanium atom. A systematic absolute nomenclature is proposed for this type of structure.     

Transfert de chiralite par hetero-ene synthese intramoleculaire

The first example of transfer of axial chirality into central chirality during a reaction of hetero-ene synthesis performed with optically active γ-allenic aldehyde is reported.     

Alkylation selective de substituants aromatiques actives par un greffon chrome carbonyle

The complexes (C₆H₅X)Cr(CO)₃, where X is COCH₃, CH₂,CO₂CH₃ and CH₃ are readily alkylated by either sodium hydride in DMF or by potassium tert-butoxide in DMSO. The activating influence brought about by the electron-withdrawing effect of the Cr(CO)₃ group can be modified by replacement of a carbonyl group by P(OPh)₃ or CS which lead to mono or dialkylated products respectively.     

Heteroallenes comportant un atome de phosphore dicoordonne

Abstract

The first stable heterocumulenes with dicoordinated phosphorus were obtained. The chemical properties of the new heterocumulenes are discussed.     

Essais d'isolement de complexes catalytiques dimerisables par fixation sur un support polymere

Iridium pyridino phosphino complexes extremely active in olefin hydrogenation catalysis, were anchored on highly crosslinked polystyrene—divinyl-benzene macroporous resins carrying well dispersed phosphine groups. Although the catalytic sites are totally dispersed, the catalysts are more or less rapidly deactivated. An alternative cause of deactivation might be a dissociation process followed by dimerization of the dissociated complex.     

Premier heteroallene stable comportant un atome de phosphore dicoordonne.

The first stable heterocumulene with dicoordinated phosphorus t-BuP=C=NBu-t was obtained from t-BuP(SiMe₃)NBu-t. The I.R. and Mass Spectrum as well as the NMR (¹H, ¹³C, ³¹P) data are discussed. The chemical properties of the new heterocumulene are also described.     

Influence d'un ou de plusieurs groupements tertiobutyle sur le comportement magnétooptique du doublet libre d'un atome de phosphore tricoordonné

A magnetooptical study of some halogenotertiobutylphosphines is performed in order to improve the so-called regular relationship which seemed to exist between the magnetic rotation, ?dP, of the lone pair and the bond angles in PX₃ compounds. It is clearly shown that, in any case, ?dP is largely lower than the extreme value which was observed in PX₃ molecules for which XPX=100°. Thus, the existence of the previously invoked relationship vanishes and the question remains as to why there exists a maximum of ?dP for XPX of 100°.     

Synthesis de carbodiimides par photoaddition de nitrenes sur les isonitriles

The photochemical addition of nitrenes to isonitriles leads to carbodiimides or/and ureas. The application of this reaction to 1-isocyano sugars offers an approach to the synthesis of glycosylbarbiturates.     

Synthese de derives de la tobrosamine par addition d'acide hydrazoique sur un systeme enonique dans la serie hydrate de carbone

Derivatives of a new diaminotrideoxy-d-ribo-hexopyranose, a component of the antibiotic tobramycin, have been prepared by addition of the elements of hydrazoic acid to the α, β-unsaturated ketone 8. After 5 min only the kinetically favored product 13 was observed, which is gradually transformed into the thermodynamically more-stable substance 20. The equilibrium mixture after 5 hours contained d-erythro and d-threo isomers 20 and 13 in the ratio 6:4 The d-erythro azide 20 was converted into the derivatives of di-N-acetyl tobrosamine.     

Etude par RMN d'une inversion de cycle de quelques benzodiazépinones

The NMR spectra of five benzodiazepinones are determined over a range of temperature. They indicate that the seven ring has a twist-boat shape, which inverts more or less rapidly according to the nature of substituents. The activation parameters and the rates of inversion are determined and the substituent effects are discussed.     

Etude d'une resine epoxy chargee avec un noir de carbone

We studied the electrical conductivity σ and the glass transition temperature Tg of an epoxy resin filled with a carbon black. It could be shown that σ and Tg depend on the volume concentration of carbon black and that the concentration dependence of Tg is sensitive to the thermal conditions of polymerization.     

Detection d'une activite optique au niveau d'un atome de vanadium a environnement pseudo-teraerique chiral

Dissymmetrical vanadocenes CpCp′V are prepared by reduction of the corresponding dichlorides CnCp′VCl₂ (Cp = C₅H₅ ; (Cp′ = C₅H₄R). Like vanadocene they display a carbeno? behavior and can be coordinated to CS₂ and acetylenic compounds. The addition of dissymmetrical acetylenes involve the formation of a chiral center at vanadium. This chirality is detected by partial chromatographic separation of diastereoisomers CpCp″V* (RCCR*) which bear a second chiral center on acetylenic ligand.