Azaanthraquinone PCET Catalysis Enables Chemoselective Decarboxylative Functionalization of Diverse Carboxylic Acids

The advancement of a proton-coupled electron transfer (PCET) strategy holds significance to expand the synthetic applicability and energy efficiency of photoredox chemistry. However, the current implementation of this strategy is typically narrow in terms of the redox potential and reaction efficiency. In this study, a novel PCET catalyst containing an azaanthraquinone skeleton has been developed for the decarboxylative functionalization of a wide range of carboxylic acids, including aromatic and perfluoroalkyl carboxylic acids. By integrating the aza-arene and benzoquinone moieties into a single molecule, this catalyst suppresses the previously problematic back electron transfer (BET) through rapid intersystem crossing from singlet to triplet states and the facilitated electron transfer from the substrate to the excited triplet catalyst via PCET. This catalyst enables a variety of decarboxylative functionalization reactions from challenging substrates, such as benzoic acids and fluoroalkanoic acids, to proceed under mild conditions with high chemoselectivity.