Cercosporin-bioinspired photoreductive activation of aryl halides under mild conditions

Abstract Bioinspired by the naturally-occurring cercosporin-driven infection process of plant pathogenic fungi Cercospora sp., here we took advantage of the photophysical properties of cercosporin, and used it as a metal-free photocatalyst to develop an unprecedented cercosporin-driven photocatalysis under mild conditions. Furthermore, the forming conditions and excited-state dynamics of radical anions of cercosporin have been systematically investigated. In particular, transient femtosecond absorption spectroscopy was employed to unveil the excited-state dynamics of cercosporin, a key step that dictates its function in photocatalysis. We showed that cercosporin was able to be sufficiently activated through a two-step excitation, ultimately boosting its photocatalytic activity for the reductive activation of substrates with very low reactivity. Since large quantities of cercosporin can be easily produced through microbial fermentation like other commercially available perylenequinonoid pigments, such as hypocrellin A and hypocrellin B, we expect that all advantages of these naturally-occurring perylenequinonoid pigments as green photocatalysts can be further explored to a wide range of synthetic transformations.