Synthesis of Thiadiazole-Containing Polycyclic Aromatic Systems

Significance

The synthesis of phenanthro[9,10-c]-1,2,5-thiadiazole-1,1-dioxide (2) was achieved in nearly quantitative yield using a chlorosulfonic acid promoted Scholl reaction. Various other Brønsted and Lewis acids were also screened, though chlorosulfonic acid proved to be optimal in terms of yield and reaction time. This preparation, which uses benzil as a precursor to 1, is less expensive than a known route involving the acid-catalyzed condensation between sulfamide and 9,10-phenanthrenedione (a relatively more costly starting material). In addition, a new polycyclic aromatic derivative 3,6-dibenzophenanthro[9,10-c]-1,2,5-thiadiazole-1,1-dioxide (4), was also obtained in fair yield using the same reagent.