A facile phase-transfer catalysed N-methylation of 2-substituted benzimidazoles

Abstract

N-Alkyl-2-acetylbenzimidazoles have been obtained by alkylating 2-acetylbenzimidazole in CH₃CN at RT for 30 min in over 90% yield using triethylbenzylammonium chloride as phasetransfer catalyst and anhyd. K₂CO₃ as base. When the same conditions are used to methylate simple 2-alkylbenzimidazoles, poorer results were obtained. Optimum conditions have been worked out for the methylation of simple 2-alkylbenzimidazoles by changing (a) the solvent, (b) the phase-transfer catalyst, (c) the concentration of the phase-transfer catalyst and (d) the type of phase-transfer catalysis itself. Using the optimised conditions, a number of l-methyl-2-alkylbenzimidazoles have been synthesised in a facile manner.