A convenient and efficient method for the synthesis of fluorinated phenanthridin-6(5H)-ones from the corresponding 2-isocyanato-1,1′-biphenyls mediated by trifluoromethanesulfonic acid in chlorobenzene is described. The reaction uses readily available starting materials, takes place under very mild reaction conditions (r. t.) and provides access to biologically promising fluorinated heterocycles in good to excellent yields. Synthesized compounds were tested in vitro for cytotoxicity in MDCK cell line and for antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1).