Ruthenium(II)-catalyzed synthesis of 2-arylbenzimidazole and 2-arylbenzothiazole in water

Abstract

Benzimidazoles/benzothiazoles are heterocyclic compounds which contain a five membered heteroatom and a benzene ring. They constitute a crucial structural unit of numerous bioactive compounds and natural products. Since the compounds containing benzimidazole/benzothiazole core and their derivatives possess interesting biological activity, steady efforts are being made on the development of an improved synthetic methodology for the synthesis of these biologically important class of compounds. Inspired by their biological properties, synthesis of 2-arylbenzimidazoles and 2-aryl benzothiazoles has been attempted using N^O chelate ruthenium(II)-catalyst in water. A series of 2-arylbenzimidazoles and 2-arylbenzothiazoles including a few new derivatives have been prepared by the reaction of ortho-phenylenediamine or ortho-aminothiophenol with aromatic aldehydes in the presence of 5 mol% of ruthenium(II)-catalyst under nitrogen without the use of additive in water. This reaction was extended to various heteroaromatic aldehydes obtaining up to 88% yield of the desired 2-arylbenzimidazoles/2-arylbenzothiazoles. In a few cases, a small amount of diarylated compounds was formed depending on the aldehydes used. Additionally, antibiotic properties of the synthesized compounds have been screened using the standard disc diffusion method.