Photoredox catalysis promoted by photo-sensitizers (e.g. [Ru(bipy)3]2+ and relevant cyclometalated pyridylphenyl-Ir complexes: M) has attracted increasing attention as practical, green synthetic chemical processes, because they are visible light-promoted, redox-neutral reactions.We have demonstrated that photoredox catalysisis a powerful synthetic tool, in particular, for trifluoromethylationof olefinic substrates, which is the topic of the presentation. Typical examples involve (a) trifluoromethylation of 1,1-diarylethenes and alkenylborates giving substituted products, (b) oxy- and amino-trifluoromethylation giving 3,3,3-trifluoro-propanol and -propylamine derivatives, respectively, (c) lactonazation via intramolecular versions of (b), and (d) keto-trifluoromethylation giving 1,1,1-trifluoroethyl ketone derivatives.As a typical example, a proposed mechanism for (b) is shown in the scheme. The photo-excited species of the catalyst (M*) undergoes a sequential 1e-reduction/1e-oxidation process. When M* is combined with an electrophilic trifluoromethylating reagent such as Umemoto's reagent, SET from M* generates the key �CF3 radical together with the cationic metal species M+. Subsequent addition of the �CF3 radical to the olefinic substrate followed by oxidation of the resultant carbon radical intermediate by M+gives, in addition to M of the ground state, the carbocationic intermediate, which is trapped by nucleophiles to furnish the coupling product. The sequential redox processes make the system redox-neutral.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.

Trifluoromethylation by photoredox catalysis

248th National Meeting (2014)

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