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Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Regiocontroled Pd-catalysed C5-arylation of 3-substituted thiophene derivatives using a bromo-substituent as blocking
Mariem Brahim1, Hamed Ben Ammar2, Jean-François Soulé3
1Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes "Organométalliques: Matériaux et Catalyse", Campus de Beaulieu, 35042 Rennes, France. Tel.: 00-33-2-23-23-63-84; Laboratoire de Synthèse Organique Asymétrique et Catalyse Homogène, (UR 11ES56) Université de Monastir, Faculté des Sciences de Monastir, avenue de l'environnement, Monastir 5000, Tunisia.
Abstract:
The use of a bromo-substituent as blocking group at the C2-position of 3-substituted thiophenes allows the regioselective introduction of aryl substituents at C5-position via Pd-catalysed direct arylation. With 1 mol % of a phosphine-free Pd catalyst, KOAc as the base and DMA as the solvent and various electron-deficient aryl bromides as aryl sources, C5-(hetero)arylated thiophenes were synthesized in moderate to high yields, without cleavage of the thienyl C-Br bond. Moreover, sequential direct thienyl C5-arylation followed by Pd-catalysed direct arylation or Suzuki coupling at the C2-position allows to prepare 2,5-di(hetero)arylated thiophenes bearing two different (hetero)aryl units in only two steps. This method provides a "green" access to arylated thiophene derivatives as it reduces the number of steps to prepare these compounds and also the formation of wastes.
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