Thiopyran-Fused Mono and Double Helicenes with Low Band Gaps via Simultaneous Ring Expansion and 6- endo Cyclizations.

Mono and double helicenes ( M5 , M6 , D5 , and D6 ) containing six-membered thiopyran rings have been successfully prepared via simultaneous ring expansion and 6- endo cycloisomerizations from the corresponding precursors with five-membered thiophene rings. Although D5 and D6 exhibit similar chemical structures, they demonstrate completely different helical structures because of their distinct steric clashes caused by the incorporated methyl groups. Moreover, all of the thiopyran-fused helicenes exhibit broad absorption bands covering the visible and near-infrared regions.