Visible-light-promoted organic-dye-catalyzed sulfonylation/cyclization to access indolo[2,1-a]isoquinoline derivatives

An efficient visible-light-promoted organic-dye-catalyzed radical cascade cyclization was developed for the rapid synthesis of sulfonyl-substituted indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolin-6(5H)-ones. Using the economical and environmentally benign Eosin B as the photocatalyst, a wide range of indolo[2,1-a]isoquinoline derivatives were obtained in moderate to good yields. Mechanistic studies indicate that a sulfonyl radical pathway is involved in this reaction. Compared with previous works, this protocol has the advantages of being metal- and base-free, using visible light as a traceless energy source, simple operation and mild reaction conditions, all of which make this methodology more attractive.