Direct Arylation Under Catalysis Of An Oxime-Derived Palladacycle

Substituted biaryls are importrant building blocks for the syntheses of diverse naturalproducts, medicinal agents, organic materials, crystals and ligands. Currently, among the vastmethods for biaryl linkages, the direct arylation of arenes by catalytic C-H activation is widelychosen for aryl-aryl bond formation because of its well atom economy and friendly reactionconditions. A variety of transition metals, such as Fe, Co, Ni, Cu, as well as noble metals Pd, Rh,Ru, Ir, have been discovered to promote efficiently the direct coupling reaction.Palladium-catalyzed intermolecular or intramolecular direct coupling reaction in presence ofphosphine ligand is undoubtedly among the most important and reliable methods. However,most of phosphine ligands are air/moisture sensitive and toxic, which limited their large-scaleapplication. Therefor, it is necessary to develop phosphine-free methods for direct arylation.During the past decades, oxime-derived palladacycles, due to their accessibility, thermalstability, and high catalytic activity, have expressed pivotal activity in a wide variety of C-Ccoupling reactions, such as Heck, Suzuki, Sonogashira, Stille coupling. In these C-C couplingreactions, the intermediate Pd~0species have been proposed to generate from oxime palladacyclesand the processes operate through Pd~0-Pd~â…¡mechanism, which lead us to considering oximepalladacycles as homogeneous phosphine-free catalysts in the direct arylation coupling. Herein,we demonstrate the potential activity of oxime palladacycle to mediate inter-or intramoleculardirect coupling reaction.The direct arylation of benzothiazole with iodobenzene was chosen as model reaction.Solvent, base, reaction temperature, time and catalyst loading were tested toward to optimumconditions. The new catalyst system is applicable for the2-arylation of benzothiazole by usingaryl bromides and iodides. In addition, this method is especially suitable for the intramoleculardirect coupling of bromo-and iodoamides, as well as chloroamides, to achieve the rapidsynthesis of benzo[c]phenanthridine alkaloids.