An Efficient Synthesis of Benzimidazole Derivatives Using a New Binuclear Cu-Bis-Salen Complex at Room Temperature

Abstract

Benzimidazole derivatives have attracted a significant attention in recent years because of their medicinal applications as antiviral, antiulcer, antifungal, antihypertensive, anticancer, and antihistamine compounds [1]. Apart from therapeutic applications, benzimidazoles also play an important role as intermediates in different organic reactions. Two general methods are reported for the synthesis of 2-substituted benzimidazoles; (1) coupling of phenylenediamines and carboxylic acids or their derivatives (nitriles, imidates, or orthoesters) as well as (2) a two-step procedure that consists of the oxidative cyclodehydrogenation of aniline Schiff’s bases, which are often generated in situ from the condensation of phenylenediamines with aldehydes [2]. However, most of these methods involve drastic reaction conditions, tedious work-up procedures and low yields [3]. The additional serious drawbacks relate to the use of homogeneous catalysts that are somewhat modified in the work-up procedure and cannot be recovered. In continuation of our work on the development of low loaded, environmentally sound, affordable, stable and selective catalysts for greener organic reactions, herein we report the use homogeneous effective catalytic system based on bis-Cu(II)-salen complex for the synthesis of benzimidazole compounds under mild reaction conditions. This homogeneous catalytic system possesses inherent advantages for benzimidazole synthesis including high activity, low metal loading in the catalyst as well as the use of a relatively inexpensive transition metal (Cu) system that prepared by accessible and cheap starting materials.