Ligand Combination Approach in Pd‐Catalyzed Direct C−H Arylation of Benzothiazole and Benzoxazole

Abstract The use of ligand combination approach in the Pd catalyzed direct C−H arylation of benzothiazole and benzoxazole is demonstrated. The combination of two ligands phenanthroline monohydrate (Phen.H 2 O) and triphenylphosphine (PPh 3 ) with Pd‐catalyst have offered the best catalytic properties in the C−H bond arylation reactions than either of two ligands employed separately in the reactions. This protocol exhibits a wide substrate scope affording C2 arylated benzothiazole and benzoxazole derivatives in excellent yields. Mechanistic studies including kinetic isotope effect (KIE), H/D exchange and competition experiments show that the C−H bond activation of benzothiazole and benzoxazole is very facile under reaction conditions. Furthermore, different mechanistic pathways originated from the catalytically active species such as Pd(η 2 ‐dba)L (dba=dibenzylidene acetone) and Pd(PPh 3 ) 2 were investigated using computational methods. The computational results suggest that the generation of catalytically active species from Pd 2 (dba) 3 is endoergic process and Phen ligand can initiate this step. On the other hand, the presence of PPh 3 could be crucial for the oxidative addition of aryl halides which is the rate‐determining step of the reaction.