Functionalization of the 3‐Position of Thiophene and Benzo[b]thiophene Moieties by Palladium‐Catalyzed CC Bond Forming Reactions using Diazonium Salts

AbstractThe palladium‐catalyzed Matsuda–Heck and Suzuki–Miyaura cross‐couplings of 2‐methoxycarbonylthiophene‐3‐diazonium tetrafluoroborate 1 were performed to synthesize a series of thiophene derivatives functionalized in the β‐position. Good to excellent yields of the cross‐coupling products were obtained using palladium acetate [Pd(OAc)2], a ligandless palladium catalyst, without a base, at room temperature, under aerobic conditions and with short reaction times. A diazotization and cross‐coupling sequence can also be performed in a one‐pot process avoiding the isolation of the thiophenediazonium salt derivative. In addition, 2‐methoxycarbonylbenzo[b]thiophene‐3‐diazonium tetrafluoroborate 8 was also efficiently arylated by applying the same Suzuki–Miyaura optimized reaction conditions.