A simple, efficient, eco-friendly, and cost-effective method has been developed for the synthesis of N-methyl-3-nitro-4-phenyl-1,4-dihydrobenzo[4,5]imidazo[1,2-a] pyrimidin-2-amine derivatives using 1H-benzo[d]imidazol-2-amine, aldehydes and (E)-N-methyl-1-(methylthio)-2-nitroethenamine, in the presence of catalytic amount of p-toluenesulfonic acid (p-TSA) in ethanol under reflux conditions. The advantages of this method are the use of an inexpensive and readily available catalyst, shorter reaction times, a wide range of functional group tolerance, and high yield of products via a simple experimental and work-up procedure.