Synthesis of Azonia Aromatic Compounds by Photocyclization

Photocyclization provided a good route to prepare azonia derivatives of fused polycyclic aromatic compounds such as benzo [c] phenanthrene, benzo [ghi] perylene, benzo [a] coronene, picene, and [6] helicene. The photoreactions could be classified into four types; (A) photocyclization of 1-styrylpyridinium salts to benzo [a] quinolizinium derivatives, (B) photocyclizaiton of styrylquinolizinium salts to fused azonia compounds, (C) photocyclization of 2-styrylpyridine derivatives to benzo [c] quinolizinium salts, and (D) photocyclization of 1, 2-diarylpyridinium salts.The photocyclization occurred when the bond order (Prs*) between atoms r and s, involved in the cyclization in the excited state, has a negative value.