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Chimie moléculaire Paris Centre

Photoredox Catalysis: Trifluoromethylation and Beyond

Séminaire du Pr Munetaka Akita (Tokyo Institute of Technology, Yokohama)


.  Photoredox catalysis mediated by photo-sensitizers (e.g. [Ru(bipy)3]2+ and relevant Ir complexes) has attracted increasing attention as practical, green synthetic chemical processes, because they are visible light-promoted, redox-neutral reaction systems. Organyl radicals can be formally generated by 1e-oxidation and 1e-reduction of anionic and cationic species, respectively.  We have demonstrated that the action of the redox functions of the photo-excited catalyst (*PC) to organyl onium and ate species regarded as stabilized forms of them causes generation of organyl radicals with elimination of the auxiliary groups (X, Y).  Further functionalization (f) followed by reverse redox processes leads to a redox-neutral reaction system. Photoredox catalysis via oxidative quenching cycle is in particular effective for tri- and di-fluoromethylation of olefinic substrates, which is the main topic of the presentation. Electron transfer from the photoexcited metal species to an electrophilic CF3-reagent such as Umemoto’s reagent generates the key ·CF3 radical intermediate via homolytic bond cleavage (e.g. C-S bond) together with the cationic species of the catalyst.  Subsequent addition of the ·CF3 radical to the olefinic substrate followed by oxidation of the resultant carbon radical intermediate by the cationic metal species gives the carbocationic intermediate, which is trapped by nucleophiles to furnish the coupling products.  It is remarkable that the reactions are promoted not only by artificial light sources (e.g. Xe lamp and blue LED lamps) but also by sunlight. This concept can be extended to organyl radicals other than the ·CF3 radical.


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