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.