“Cationic” Suzuki–Miyaura Coupling with Acutely Base-Sensitive Boronic Acids

Fast,
base-promoted protodeboronation of polyfluoroaryl and heteroaryl
boronic acids complicates their use in Suzuki–Miyaura coupling
(SMC) because a base is generally required for catalysis. We report
a “cationic” SMC method using a PAd3-Pd catalyst
that proceeds at rt in the absence of a base or metal mediator. A
wide range of sensitive boronic acids, particularly polyfluoroaryl
substrates that are poorly compatible with classic SMC conditions,
undergo clean coupling. Stoichiometric experiments implicate the intermediacy
of organopalladium cations, which supports a long-postulated cationic
pathway for transmetalation in SMC.