Non-photochemical route to tetrathiahelicenes through Pd-mediated heteroaryl-heteroaryl bond formation

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 peculiar electronic and chiroptical properties suitable for applications in optoelectronics [2], biology [3], and 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, limiting the scale-up. In our ongoing studies on the synthesis and functionalization of 7-TH derivatives, we have set up an innovative and non-photochemical procedure for the synthesis of 7,8-diaryl and dialkyl substituted 7-TH compounds, exploiting a Suzuki-type cross coupling and a Pd-catalyzed annulation with internal alkynes as key steps.