Unveiling the potency of a phenalenyl-based photocatalyst for intramolecular dehydrogenative lactonization

Abstract

Here, an intramolecular dehydrogenative lactonization reaction has been accomplished by combining a phenalenyl-based organic photocatalyst and a Co(III) co-catalyst. Due to its extremely high excited state redox potential, the phenalenyl motif could directly oxidise carboxylic acid derivatives to generate carboxyl free radicals without the assistance of an external base. This protocol allows access to multiple 4-aryl-2H-chromen-2-ones by using the external oxidant K₂S₂O₈ and shows diverse functional group tolerance for biaryl-2-carboxylic acids. Moreover, the reaction was performed on a bulk scale with a very good yield.