A green and metal-free one-pot three-component synthesis of thiazolobenzimidazoles in sustainable deep eutectic solvent

Abstract

We have developed a highly efficient and environmentally friendly synthetic procedure for the one-pot three-component synthesis of thiazolobenzimidazole derivatives. This method entails the reaction of 2-mercapto benzimidazole, chloroacetic acid, and aryl/heteroarylaldehydes in a deep eutectic solvent (DES). Our atom-economical approach capitalizes on a specially formulated deep eutectic solvent composed of choline chloride and urea [ChCl]: [urea]2, which serves as both a sustainable solvent and a reaction promoter. This innovative approach enables a seamless reaction under mild heating conditions in an open-air atmosphere, leading to product formation and achieving an outstanding yield of up to 90 % in a short interval of 40 minutes. Diversely substituted aldehydes are used to synthesize a total of 19 thiazolobenzimidazole derivatives. Significantly, our protocol obviates the necessity for bases, catalysts, and volatile and hazardous organic solvents, further enhancing its environmental sustainability. The DES employed in this process exhibits remarkable recyclability and reusability, retaining its catalytic activity over multiple cycles with negligible performance deterioration.