A novel palladium-catalyzed synthesis of 2-arylbenzimidazoles

Article abstract of DOI:10.1021/jo00077a019

A new method for the preparation of 2-arylbenzimidazoles based on the palladium-catalyzed carbonylation, coupling, and cyclization of haloaromatics and o-phenylenediamines is described. Reactions were run in DMAc at 145°C for 18 h, under 95 psig CO, with 1.5 mol% PdCl₂L₂ as catalyst and in the presence of 1.2 equiv of 2,6-lutidine to give 70-98% yield of desired products. This route is tolerant of a variety of functional groups and nicely complements the classical route where the desired benzoic acid derivatives are unavailable. The selection of an appropriate base is crucial for the formation of 2-arylbenzimidazoles. Intermolecular bis-acylation to form bisamides occurs if the base is too strong. Weak bases allow side reactions with amide solvents to occur, leading to substituted benzamides and alkyl benzimidazoles.