Syntheses of Fused Thiophenes: [7]Helicene and Double Helicene Bearing Chiral Alkyl Chains

In this paper, an efficient synthesis of the two attractive fused thiophenes: [7]helicene (1) and double helicene (2) bearing chiral chains was developed via multi-step moisture sensitive reactions in ca. 10.5 % and ca. 6.0 % isolated yields, respectively, with dithieno[2,3-b:3',2'-d]thiophene (7) as a starting material. However, 1 and 2 showed no optical rotations due to the too weak contribution from chiral induction of the chiral chain, (S)-3,7-dimethyl-octyl group in the formation of helicenes. Keywords: [7]helicene, chiral chain, double helicene, thiophene-based, synthesis