Applications de la Chimie Radicalaire des Xanthates : Synthèse d'Alpha Céto Vinyl Carbinols, Synthèse stéréosélective de Sulfones Vinyliques et d'Alcènes, Induction de la Chiralité sur des Systèmes Cycliques, Approche à la Synthèse des Sesquiterpènes de type eudesmane, Approche à la Synthèse du (+)-Maritimol - Synthèse du fragment C16-C30 du dolabélide C

摘要

The goal of my first project was to synthesize α-keto vinyl carbinols using xanthate radical chemistry. The sequence starts with the addition of an α-keto radical generated from the corresponding O-ethyl xanthate to vinyl ethyl sulfide. The xanthate adduct undergoes pyrolytic elimination, leading to a mixture of vinylic sulfides and allylic sulfides. The sequence ends with the irreversible Mislow-Evans rearrangement of the corresponding allylic sulfoxides to give the desired α-keto vinyl carbinol moiety. My second project deals with the development of a new methodology for the transfer of chirality by the use of an all carbon tether. Using the xanthate transfer process, we have developed an efficient approach to the stereocontrolled formation of carbon-carbon bonds. A methyl ketone is used as a temporary tether for an alpha-xanthanyl ketone moiety. A xanthanyl radical transfer from this group enables difunctionalization of proximal alkenes with complete control of the stereochemistry. The substrates for this transformation include 4-acetylcyclohexenes conveniently generated by Diels-Alder reactions. The approach shares some features with Stork's silicon-tethered radical cyclization method. Nevertheless, the successful use of 6-exo cyclization and also functionalization of tri- and tetra-substituted olefins is made possible thanks to the reversible nature of xanthate transfer reactions. Quaternary stereogenic centers can therefore be generated in a stereocontrolled manner. The original radical transfer process can be used as a platform for further carbon-carbon bond formation. In addition, the original methyl ketone is regenerated using a modified Beckman fragmentation reaction. I have also been working towards the development of a new methodology that allows the introduction of an unsaturation in a controlled manner. (E)-Vinylsulfones can be synthesized with excellent diastereoselectivity with the use of xanthates and simple aldehydes and ketones and then converted selectively into (E) and (Z) disubstituted and trisubstituted alkenes. My last project concerns the total synthesis of the (+)-Maritimol using radical reactions to build quickly the diterpenoid scaffold. I am currently working on the construction of the fourth and last cycle using a Robinson annelation. I have had previous experience with the total synthesis of natural products during the first year of my Ph.D . At that time, I successfully synthesized the C16-C30 fragment of the Dolabelide C.