Visible light-induced metal-free synthesis of quinoxalines using Rose Bengal as a photocatalyst

An efficient eco-friendly photocatalytic method was developed for the synthesis of pharmaceutically highly sought-after quinoxalines. This route is a simple condensation between o-phenylenediamine and an a-hydroxy ketone in methanol at room temperature in the presence of the organic dye Rose Bengal (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein) as a photocatalyst. Using this protocol, a library of examples with various o- phenylenediamines and a-hydroxy ketones was prepared. This is a practically useful method for the development of quinoxaline derivatives of biological importance in good to excellent yields.