Le réarrangement [1,2] de Wittig: contribution à l'étude de son mécanisme et de ses applications
The importance of catalysis in chemistry has not to be proved anymore. Be it homogeneous or heterogeneous catalysis, the constant progresses observed in that field proves its obvious interest. The asymmetric homogeneous catalysis is a method of choice to synthesize chiral substances. Indeed, it allows the obtention of these compounds in an enantioselective way. During transition metal mediated catalytic asymmetric reactions, the chirality is induced by the presence of organic monodentate or bidentate chiral ligand, directly linked to the metal. Very good results were obtained in this kind of reaction with chiral ligands based on binaphthyl skeleton. Initially, this thesis work consisted in the study of the double [1,2] Wittig rearrangement of binaphthyl ethers. It was shown, for allyl carbanion, that only one diastereoisomer is formed during the rearrangement among the three possible one. This diastereoisomer has a C2 symmetry axis and the absolute configuration of the two new asymmetric centers created was assigned. On the other hand, for benzyl or benzhydril carbanions, the results are differents. For the former, the three possible diastereisomer are formed with the unsymmetrical one as the major compound. In the latter case, no rearrangement takes place and only starting material is recovered after neutralization of the reaction mixture. Then, the potential of double [1,2] Wittig rearrangements applied to allyl binaphthyl ethers was evaluate in order to synthesize homochiral compounds usable in asymmetric homogeneous catalysis. It was shown that this transformation could be used to give access to the enantiopur acid 1,1'-binaphtyl-2,2'-dicarboxylic which finds applications in the field of the asymmetric catalysis. The high diastereoselectivity observed during this double rearrangement allowed to develop the kinetic resolution of the binaphthyl skeleton by means of the asymmetric epoxidation according to the conditions described by K.B Sharpless and T Katsuki. Finally, taking profit of the high diastereoselectivity already mentioned, it was possible to elaborate out a new phosphorus ligand whose stereoinduction capacity was evaluated for catalytic asymmetric hydrosilylation.
Section de chimie et génie chimique
Faculté des sciences de base
Institut des sciences et ingénierie chimiques
Jury: Alexandre Alexakis, Dominique Michel, Stefan Pitsch, Ursula Röthlisberger
Public defense: 2005-9-16
Record created on 2005-07-12, modified on 2016-08-08