Facile Synthesis of 2‑Acylthieno[2,3‑b]quinolines via Cu-TEMPO-Catalyzed Dehydrogenation, sp2‑C–H Functionalization (Nucleophilic Thiolation by S8) of 2‑Haloquinolinyl Ketones

An efficient, solvent-free synthesis of 2-acylthieno­[2,3-b]­quinolines is reported from 2-halo-quinolinyl ketones through Cu-TEMPO catalyzed dehydrogenation, sp2-C–H functionalization using elemental sulfur as thiol surrogate (sulfur source) and tetrabutylammonium acetate as an ionic reaction medium. The optimized reaction conditions give excellent product yields under mild reaction conditions with chemoselectivity and broad functional group tolerance. The synthetic importance of the synthesized molecules is showcased further by Friedländer annulation, reduction, and alkene functionalization reactions.