Catalyst-Free Synthesis of Benzimidazole and Benzothiazole Derivatives by the Cleavage of the C–C Double Bond of 5-Arylidenepyrimidine-2,4,6- (1H,3H,5H)-triones

Background: Benzimidazole and benzothiazole subunits exist in many biologically active molecules, natural products, and synthetic compounds. These compounds have recently gained widespread interest due to their key role in medically important compounds, such as those exhibiting anticancer activity, antimicrobial activity, inhibition of hepatitis C virus NS5B polymerase, p38 kinase inhibitory activity, and anti-inflammatory activity. Methods: 2-Substituted benzimidazole and benzothiazole derivatives have been synthesized by the condensation of 1,2-phenylenediamine or 2-aminobenzothiophenol with 5-arylidenepyrimidine-2,4,6-(1H,3H, 5H)-trione derivatives via cleavage of C-C double bond without using a catalyst in EtOH under reflux conditions. Results: We report here a very simple, novel, efficient, and catalyst-free method for the synthesis of benzimidazole and benzothiazole in good to excellent yields from the treatment of 1,2-phenylenediamine and 2-aminothiophenol with various 5-arylidenepyrimidine-2,4,6(1H,3H,5H)-trione, respectively. This reaction proceeds via cleavage of a C=C double bond and elimination of barbituric acid. Conclusion: This method appears to be general for the synthesis of benzimidazoles and benzothiazoles using 5-arylidenepyrimidine-2,4,6-(1H,3H,5H)-trione derivatives containing various aromatic and heteroaromatic aldehydes such as furfural and thiophene-2-carbaldehyde with electron-withdrawing and electron-releasing groups.