Synthesis of Acridinium Photocatalysts via Site-Selective C-H Alkylation

Acridinium dyes have been broadly used as photocatalysts, but it remains synthetically challenging to fine-tune their catalytic performance by functionalization of their structural cores. Acridinium photocatalysts are usually prepared through de novo synthesis, which involves difficult steps and requires sensitive organometallic reagents. Herein, we report a modular and scalable synthesis of acridinium photocatalysts with diversely functionalized core structures through site-selective late-stage C(aryl)H alkylation. The alkylation is achieved by inducing cross-coupling between acridinium salts and organotrifluoroborates with visible light, followed by electrocatalytic dehydrogenation. The late-stage diversification is compatible with organotrifluoroborates bearing a broad array of electronically and sterically diverse substituents, allowing rapid and convenient access to a library of 3,6-functionalized acridinium photocatalysts with novel photocatalytic properties. A four-step continuous-flow reactor system was also developed to achieve 3,6-dialkylation of acridinium dyes without need for intermediate manipulation. [GRAPHICS] .

Automated summary

This study presents a modular and scalable synthesis of acridinium photocatalysts through site-selective late-stage C(aryl)H alkylation, allowing for the diversification of core structures and the access to novel photocatalytic properties.