A facile and green method for the synthesis of 4-amino-1,2-dihydrobenzo[4,5]imidazo[1,2- a]pyrimidine-6-carbonitrile derivatives has been developed by one-pot condensation of 2-aminobenzimidazole, aldehydes, and malononitrile catalysed by ammonium acetate in ethanol. The inexpensive and readily available catalyst and easy workup is environmentally friendly.