Novel approach towards 2-substituted aminobenzimidazoles on imidazolium ion tag under focused microwave irradiation

Abstract

We have developed an efficient, parallel synthesis of 2-substituted aminobenzimidazoles via intramolecular ring closing reactions of imidazolium ion tag immobilized o-phenylenediamine with various isothiocyanates. The methodology is based on the attachment of 4-fluoro-3-nitro benzoic acid into the imidazolium ion tag, which enables the S(N)Ar reactions with different amines followed by neutral reduction to furnish o-phenylenediamines under microwave irradiation. The substituted isothiocyanates are reacted with o-phenylenediamines to form monothiourea, which is further activated by methyl iodide to undergo desulfurization in one pot manner. The ionic liquid bound 2-substituted aminobenzimidazoles were finally cleaved from the support with sodium methoxide to generate target compounds in good yields and high purities with two points of structural diversity. This synthetic protocol has promising features of extremely short reaction time, operational simplicity, good yields, as well as widespread applications, leading to a facile and straightforward admittance to structurally diverse 2-substituted aminobenzimidazole analogues with potential bioactivities. (C) 2011 Elsevier Ltd. All rights reserved.