Green Syntheses of N-Alkyl-2-styrylbenzimidazoles

Abstract

Simple and green methodologies for the syntheses of 2-styrylbenzimidazoles (3a-c) and its N-alkyl derivatives (7a-i) have been developed. o-Phenylenediamine (1) was condensed with cinnamic acids (2a-c) resulting in 2-styrylbenzimidazoles (3a-c) using glycerol as a green and efficient solvent. 3 were also prepared alternatively by the condensation of 2-methylbenzimidazole (4) with benzaldehydes (5a-c) using glycerol as solvent. 2-Styrylbenzimidazoles (3a-c) and 2-methylbenzimidazole (4) were alkylated independently to obtain N-alkyl-2-styrylbenzimidazole (7a-i) and N-alkyl-2-methylbenzimidazole (6a-c), respectively using DMS/DES/PhCH₂Cl applying green methods such as simple physical grinding of reactants in solid phase, treating reactants in PEG-600 as a solvent in solution phase and using microwave irradiation of reactants respectively. Compounds 7a-i could also be prepared, alternatively, by heating 6a-c with 5a-c in glycerol at 180 °C for 3-4 h.