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

摘要

N-Alkyl-2-acetylbenzimidazoles have been obtained by alkylating 2-acetylbenzimidazole in CH_3CN at RT for 30 min in over 90% yield using triethylbenzylammonium chloride as phase transfer catalyst and anhyd.K_2CO_3 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 1-methyl-2-alkylbenzimidazoles have been synthesised in a facile manner.