Streamlined Synthesis of Aminoacridinium Photocatalysts with Improved Photostability

The efficient synthesis of photocatalysts with improved photostability from readily available resources is a requirement for more sustainable and scalable photocatalysis. Herein, we describe a strategy utilizing a high-yielding threefold C–N cross-coupling selective for three out of six arylbromide sites to avoid alkyl groups in the final catalyst structure. A subsequent triple metalation to form 1,5,5′-trifunctional organometallic reagents enables the coupling and cyclization with simple esters, whereas a third unreacted functionality is hydrolyzed upon acidic quench. This short reaction sequence results in bis(diarylamino)acridiniums with dramatically increased photostability, allowing us to lower the catalyst loading to 0.10 mol % without loss in yield.