Excitation of organocatalytic intermediates and application in new radical processes
Free radical chemistry offers a powerful tool to the construction of pharmaceuticals, agrochemicals and materials. One reason for the extensive use of this branch of organic synthesis is the orthogonality of radical processes compared to classical polar pathways. During the last century, the main methodology to reach the radical domain relied on the use of initiators, stoichiometric redox agents and harsh conditions. The recent advent of photoredox catalysis provided a new method for the generation of open-shell intermediates.
The objective of this thesis was to demonstrate how classic organocatalytic intermediates can trigger redox pathways upon photo-excitation. It has been shown how, a new class of dithiocarbamate catalyst (DTC), can be exploited to activate acyl and carbamoyl chlorides through nucleophilic acyl substitution. Subsequent photolysis of the intermediate provided easy access to the corresponding C(sp2) radicals, which could be trapped by electron-poor olefins in a Giese-type addition. The mildness of DTC photochemical activation strategy was exploited to develop an asymmetric γ-alkylation of enals. Exploiting the action of a secondary amine catalyst, it was possible to elicit the in situ formation of chiral dienamines which intercepted the radicals, generated by the DTC platform, with high selectivity. Finally, based on the previous knowledge on vinylogous radical chemistry it has been demonstrated how dienamines can undergo Electron Donor-Acceptor (EDA) complex formation with perfluoroalkyl iodides. Visible-light excitation of such complexes triggered the formation of perfluoroalkyl radicals, which could be intercepted by the chiral dienamines with high levels of regio- and enantio-selectivity. Overall the transformation provided a rare example of enantioselective γ-perfluoroalkylation of enals.