Visible-light induced synthesis of 8H-indolo[3,2,1-de]phenanthridin-8-ones and related heterocycles using benzothiadiazole as photocatalyst

A simple and mild approach to access polycyclic 8 H -indolo[3,2,1- de ]phenanthridin-8-ones through a visible-light induced free radical cyclization of (2-bromophenyl)(9 H -carbazol-9-yl)methanones using benzothiadiazole-containing photocatalyst is reported. This transition metal free method can be utilized for the synthesis of 7 H -thieno[2′,3′:4,5]pyrido[3,2,1- jk ]carbazol-7-one, 14 H -isoquinolino[4,3,2- kl ]phenoxazin-14-one, 14 H -isoquinolino[4,3,2- kl ]phenothiazin-14-one, and 10,11,12,13-tetrahydro-8 H -indolo[3,2,1- de ]phenanthridin-8-one. Moreover, some products were found to emit strong blue or green fluorescence.