Water mediated expeditious and highly selective synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles by Dowex 50W: fluorescence properties of some representative compounds

Dowex 50W in aqueous medium proved to be a very efficient and reusable catalyst for the highly selective synthesis of 2-aryl-1-arylmethyl-1H-benzimidazoles in excellent yields from a wide variety of substituted ortho-phenylenediamines and aromatic aldehydes. A new technique for work-up has been developed that eliminates column chromatography for purification. The products can serve in further functionalization to produce molecular diversity including ionic liquids. Detailed DFT (Density Functional Theory) calculations have been done to establish the mechanism and justify the formation of the selective regioisomer from unsymmetrical ortho-phenylenediamine. The X-ray crystal data of one such product has been reported that clearly reveals the formation of one particular regioisomer. The fluorescence spectroscopic properties of some representative compounds have been studied in three solvents, dichloromethane, acetonitrile, methanol and their quantum yields calculated. The presented methodology has the advantages of one-pot operation and minimal environmental impact.