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

Abstract

he 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

Financial support from MICINN of Spain (CTQ2008-05409-C02-02 and CTQ2009-08328) and “Generalitat de Catalunya” (2009SGR637) is acknowledged. Spectroscopic data has been partially funded by the University of Girona under the project with reference STR-CT00059