The palladium-catalyzed arylation of thiophenes study of the catalytic system Original Research Article

The direct arylation of activated thiophenes was successful using a Heck type reaction with a mixture of Pd(OAc)2 and phase transfer agent as catalytic system. However, the competitive formation of biaryl resulting from an Ullmann type coupling may occur. To get a better understanding of the reaction mechanism and to find the best conditions, the reaction parameters have been studied. Several general features have been pointed out as a solid–liquid phase transfer catalysis occurring at the base interface, as the crucial role of the quaternary ammonium anion and the nature and/or the amount of the phase transfer agent that may favour thiophene arylation vs. biaryl formation.