Carbenoides de zinc et cyclopropanations enantioselectives (French text)

This thesis represents an ensemble of realizations accomplished in the area of asymmetric cyclopropanations under the Simmons-Smith/Furukawa conditions.; At first we will characterize spectroscopically and by X-ray crystallography the Simmons-Smith (IZnCH₂I), Furukawa (Zn(CH₂I) ₂) and for the first time Denmark's (Zn(CH₂CI)₂) reagents by generating stable bipyridine complexes. We have also demonstrated that these species can act as cyclopropanating reagents for allylic ethers in the presence of ZnI₂.; This thesis will highlight our findings regarding the development of a Lewis acid-catalyzed cyclopropanation of allylic alcohols with bis(iodomethyl)zinc. Iodo and chloro-methylzinc alkoxides (ROZnCH₂-Hal where Hal = CI or I) are stable, monomers in solution and tetramers in the solid state. They also are not prone to undergo cyclopropanation at low temperature, but the addition of a Lewis acid in catalytic amounts induces the cyclopropanation reaction. Using this procedure, we demonstrated that the Lewis acid-catalyzed pathway significantly overwhelms the uncatalyzed one. These results have induced the elaboration of a catalytic system for the cyclopropanation of allylic alcohols.; A catalytic asymmetric system for the cyclopropanation of allylic alcohols has been developed. Our studies indicate that 0.25 equiv of the catalyst (TADDOL-Ti( iOPr)₂) are necessary to induce high levels of selectivities and yields. This system is compatible with allylic alcohols substituted by an aryl or heteroaryl group, alkyl groups are however less tolerated and modest selectivities are obtained for these examples.; An asymmetric stoichiometric system has also been developed in our research group using a chiral ligand for the enantioselective cyclopropanation of allylic alcohols. This system has been extended to allylic alcohols with vinylic C-Sn and C-I bonds, thus giving access in good yields and excellent enantiomeric ratios to a variety of synthetically useful synthons. This methodology was also surprisingly selective for homo and bishomoallylic alcohols. Chiral cyclopropylmethylamines can be obtained through the enantioselective cyclopropanation of allylic carbamates; however the enantiomeric ratios in these cases were low. Finally, we have reported the first example of asymmetric intramolecular cyclopropanation using a zinc reagent which allows us to access bicyclic systems. From a mechanistic standpoint, we have synthesized a variety of useful dioxaborolane as ligands for the Charette-Juteau enantioselective cyclopropanation reaction. We have successfully crystallized a dioxaborolane having a 2-naphthyl group and thus confirmed the structure of these ligands. Our NMR experiments confirmed an interaction between the boron atom on the ligand and the allylic alkoxide generated in the reaction media; however we believe that the diastereomeric species inducing chirality is a boronic ester instead of the borate intermediate initially proposed.