Synthesis of α ‐(Fluorophenyl)pyridine by Palladium‐Catalyzed Cross‐Coupling Reaction

A series of α ‐(fluoro‐substituted phenyl)pyridines have been synthesized by means of a palladium‐catalyzed cross‐coupling reaction between fluoro‐substituted phenylboronic acid and 2‐bromopyridine or its derivatives. The reactivities of the phenylboronic acids containing di‐ and tri‐fluoro substituents with α ‐pyridyl bromide were investigated in different catalyst systems. Unsuccessful results were observed in the Pd/C and PPh 3 catalyst system due to phenylboronic acid containing electron‐withdrawing F atom(s). For the catalyst system of Pd(OAc) 2 /PPh 3 , the reactions gave moderate yields of 55% –80%, meanwhile, affording 10% –20% of dimerisation (self‐coupling) by‐products, but trace products were obtained in coupling with 2,4‐difluorophenylboronic acids because of steric hinderance. Pd(PPh 3 ) 4 was more reactive for boronic acids with sterically hindering F atom(s), and the coupling reactions gave good yields of 90% and 91% without any self‐coupling by‐product.