Synthesis of tetrathia[7]helicenes promoted by Pd-catalysed cross coupling reactions

Tetrathia[7]helicenes (7-TH), formed by thiophene and benzene rings ortho-fused in an alternating fashion, are emerging as one of the most popular class of chiral helical-shaped molecules [1], thanks to their unique electronic and optical properties suitable for applications in optoelectronics [2], biomolecular recognition [3], and asymmetric catalysis [4]. Despite all these potential advantages, most of the synthetic methodologies to prepare 7-TH systems involve oxidative photochemical cyclization processes, which require specific equipment, highly diluted solutions, and can limit the scale-up of the synthesis of these derivatives. In our ongoing studies on the preparation of 7-TH derivatives, we have set up an innovative and non-photochemical synthesis of 7,8-diaryl substituted 7-TH compounds, exploiting Suzuki-type reactions and Pd-catalysed annulation with diaryl alkynes. [1] Dova, D.; Cauteruccio, S.; Prager, S.; Dreuw, A.; Graiff, C.; Licandro E. J. Org. Chem. ASAP (DOI: 10.1021/acs.joc.5b00243) [2] Bossi, A.; Licandro, E.; Maiorana, S.; Rigamonti, C.; Righetto, S.; Stephenson, G. R.; Spassova, M.; Botek, E.; Champagne, B. J. Phys. Chem. C 2008, 112, 7900. [3] Cauteruccio, S.; Bartoli, C.; Carrara, C.; Dova, D.; Errico, C.; Ciampi, G.; Dinucci, D.; Licandro, E.; Chiellini, F. Chem. Plus. Chem. 2015, 80, 490. [4] Cauteruccio, S.; Dova, D.; Benaglia, M.; Genoni, A.; Orlandi, M.; Licandro, E. Eur. J. Org. Chem. 2014, 2694