Design and Synthesis of Acridine-Based Ionic Photocatalyst for Decarboxylation of Aryl Carboxylic Acids to Achieve α-Arylation of Chromones/Naphthoquinones

Photocatalytic decarboxylation of aryl carboxylic acids has emerged as a promising strategy for generating aryl radical precursors. However, the insufficient photo-oxidation capacity of conventional photocatalysts limits the implementation of this strategy. Therefore, in order to break through this limitation, a transition metal Cu modified acridin-based ionic photocatalyst (AIPC-Cu) was designed and synthesized based on the excellent photocatalytic activity of the acridine moiety. A series of photoelectric performance tests demonstrated that introducing transition metal Cu into acridine based photocatalysts could significantly enhance their photo-oxidation performance. AIPC-Cu was used as the photocatalyst for the decarboxylation of aryl carboxylic acids to develop α-arylation reaction of chromones and naphthoquinones, and a series of flavonoids and 2-arylchromone derivatives were obtained in good yields. This strategy does not require preactivation of aryl carboxylic acids and has high functional group tolerance that can be successfully applied to the synthesis of challenging natural products without any protection procedures. Control experiments revealed that the decarboxylation system proceeds via the free radical pathway. AIPC-Cu as a high photo-oxidizing activity photocatalyst (E0 up to +2.64 V vs SCE) has the advantages of good stability and recyclability. This provides a new idea for the decarboxylation strategy of aryl carboxylic acids and the design of sustainable photocatalysts.