The synthesis of azoniadithia[6]helicenes

A new short‐step synthesis of 8a‐azonia[6]helicene (1) and the novel dithieno derivatives (2 and 3) is described. Double photocyclization of 2,8‐distyrylquinolizinium salt (8) gave 1 in 35% yield. Similarly, 2,8‐bis[2‐(2‐thienyl)vinyl]‐ and 2,8‐bis[2‐(3‐thienyl)vinyl]‐quinolizinium salts (9 and 10) afforded new azonia[6]helicenes containing two thiophene rings at the ends of helix, that is 7a‐azonia‐3,12‐dithia[6]helicene (2) and 7a‐azonia‐1,14‐dithia[6]helicene (3), in 43 and 35% yields, respectively. The total assignment of their 1H‐ and 13C‐nmr spectra was performed by utilizing two‐dimensional and NOE nmr spectroscopic methods.