Applications of fluorous chalcogenides and of radical cations in organic synthesis

Fluorous organosulfur and organoslenium reagents were synthesized and successfully applied in important organic transformations. Alkene radical cations were generated by a non-oxidative pathway and applied in the synthesis of heterocycles.;A meta-substituted fluorous aryl diselenide was synthesized and used to limit a rapid cyclopropylcarbinyl radical rearrangement under stannane-mediated conditions. In another system, a para-substituted fluorous aryl diselenide was shown to eliminate vicinal dimesylates, to give alkenes in good yields, through stoichiometric and catalytic pathways. Both of the fluorous diselenides were recovered in good yields with the help of a continuous extractor.;A fluorous sulfoxide was found to oxidize a wide range of primary and secondary alcohols with differing functionalities under Swern conditions. The reactions were high yielding and odorless, and the fluorous sulfoxide or the sulfide could be recovered for reuse through a simple continuous fluorous extraction. The mechanism of the fluorous Swern reaction was studied with deuterium labeling and found to be closely related to that of the standard Swern reaction. Oxidations of alcohols could also be performed with the fluorous sulfide under Corey-Kim conditions.;A borane:fluorous sulfide complex was prepared and used in the hydroborations of alkenes, and also in the reduction of various carbonyl functionalities. The reactions were performed in a biphasic system of FC-72 and an organic solvent with subsequent recycling of the fluorous sulfide by fluorous extraction. This complex has also been used in the asymmetric reduction of a ketone catalyzed by a chiral oxaborolidine catalyst.;Alkene radical cations generated by the radical ionic fragmentation of β-(phosphatoxy)alkyl radicals were shown to undergo efficient nucleophilic capture by amines, in exo or endo modes, leading to six and seven membered nitrogen heterocycles. Suitably engineered substrates were shown to undergo tandem radical/cationic cyclization, giving rise to indolizidines by a 6- exo/5-exo pathway. Unfavorable 6-endo and 7-endo cyclizations were also successfully accomplished and applied in the syntheses of complex heterocycles with bicyclic ring systems.