Microwave-assisted linear approach toward highly substituted benzo[d]oxazol-5-yl-1H-benzo[d]imidazole on ionic liquid support.

A novel and efficient diversity-oriented synthetic approach was employed to access the benzo[d]oxazol-5-yl-1H-benzo[d]imidazole on ionic liquid support, which helps to absorb microwave irradiation. In this paper, we successfully coupled 4-hydroxy-3-nitrobenzoic acid onto ionic liquid-immobilized o-phenylenediamine, which subsequently underwent an acid mediated, ring closure reaction leading to benzimidazole derivatives. After hydrogenation of the nitro group to an amine, the resulting ionic liquid conjugate was reacted with 1,1-thiocarbonyldiimidazols to yield an ionic liquid tagged-benzoxazol. Final skeletal diversity of the present scaffold was further achieved by S-alkylation with alkyl and aryl bromides. The benzo[d]oxazol-5-yl-1H-benzo[d]imidazole was finally cleaved smoothly from the ionic liquid support with sodium methoxide in methanol under microwave irradiation. This methodology has provided access to a small, diverse library by straightforward and simple operations and could be applied readily in various drug discovery programs.