Palladium-catalyzed arylation reactions: A mechanistic perspective

After being restricted for the intramolecular formation of C-C bonds, the palladium catalyzed arylation reaction has been extended for the intermolecular synthesis of biaryls systems. Many of these reactions have been demonstrated to proceed by mechanisms that involve a concerted metalation-deprotonation, in which the base plays an important role in the proton abstraction. Other mechanisms based on electrophilic aromatic substitution and on Pd^II/Pd^IV or Pd^II/Pd^III catalytic cycles have also been proposed. This review summarizes the most important recent advancements on the mechanistic understanding of the different types of palladium-catalyzed arylations reactions.