The synthesis of new azoniathiahelicenes

Synthesis of new azonia derivatives of thia[6]helicene (1) and thia[7]helicene (2) is described. The Knoevenagel condensation of 2-methylbenzothieno[3,2-a]quinolizinium salt (8) with appropriate arylaldehydes yielded 2-(arylvinyl)benzothieno[3,2-a]quinolizinium salts (9 and 10), respectively. Photocyclization of 2-styrylbenzothieno[3,2-a]quinolizinium salt (8) gave 7a-azonia-5-thia[6]helicene (1) in 63% yield. Similarly, 2-[2-(2-naphthyl)vinyl]benzothieno[3,2-a]quinolizinium salt (10) afforded 7a-azonia-5-thia[7]helicene (2) in 56% yield. The complete and unambiguous assignment of their 1H- and 13C-nmr spectra was performed by utilizing two-dimensional nmr spectroscopic methods.