An efficient method for the synthesis of 7H-benzo[4,5]isothiazolo[3,2-b]quinazolin-7-ones from the reaction of 2-arylquinazolin-4(3H)-ones and elemental sulfur is described. The rhodium-catalyzed C-H activation of 2-arylquinazolinones and cyclization with elemental sulfur via one-step formation C-S/N-S bonds to give the corresponding 7H-benzo[4,5]isothiazolo[3,2-b]quinazolinones in good to high yields with good functional group tolerance.