9-phenyl-10-methylacridinium: a highly efficient and reusable organocatalyst for mild aromatization of 1,4-dihydropyridines by molecular oxygen.

The mild, efficient, and general aerobic aromatization of Hantzsch 1,4-dihydropyridines was realized at room temperature with 5 mol % of 9-phenyl-10-methylacridinium perchlorate as the photocatalyst, which could be easily recovered and reused.