In-situ formed aryl acid-triggered intramolecular dehydrative cyclization whilst supported Pd-catalyzed carbonylative synthesis of 2-aryl benzimidazoles

Herein, polystyrene supported palladium (Pd@PS) nanoparticles (NPs) catalyzed carbonylative synthesis of 2aryl benzimidazoles from aryl iodides and aromatic diamines has been introduced. In-situ formed aryl carboxylic acid was revealed as a catalyst for dehydrative cyclization of secondary (2 degrees) and tertiary (3 degrees) amides formed via aminocarbonylation between aryl iodides and aromatic diamines. Herein, oxalic acid acts as carbon monoxide (CO) and carbon dioxide (CO2) gases source plausibly leading to aminocarbonylation via CO gas as major pathway and carboxylation of aryl iodides via CO2 as minor pathway. The Pd@PS catalyst was found to be easily separable, air/moisture stable and recyclable under the targeted reaction conditions. In addition, the present protocol requires only catalytic amount of inorganic base (K2CO3) to achieve the highest yields of desired products.