An efficient green synthesis of some new 4H-pyrimido[2,1,b]benzimiazoles and 4H-pyrimido[2,1,b]benzothiazoles promoted by guanidinium chloride

A facile and highly efficient protocol was applied successfully to synthesize 4H-pyrimido[2,1,b]benzimiazoles and 4H-pyrimido[2,1,b]benzothiazoles through one-pot three-component cyclocondensation reactions of 2-aminobenzimidazole or 2-aminobenzothiazole with dimedone and aromatic aldehydes in the presence of guanidinium chloride under solvent-free conditions. The reactions using guanidinium chloride provided high to excellent yields of the products.  The key advantages of this process are operational simplicity, inexpensive catalyst, short reaction time, simple workup and non-chromatographic purification, which make it an attractive route for the synthesis of benzimidazolo/benzothiazolo quinazolinones. Due to these advantages, several benzimidazolo/benzothiazolo quinazolinones as important pharmaceutical molecules can be prepared in high yield and high purity.