An efficient and highly selective multicomponent synthesis of 4-aminoimidazo[1,2-a][1,3,5]triazines, which are 5-aza-7-deaza-isosteres of adenine, was developed. The reaction of 2-aminoimidazoles, triethyl orthoformate and cyanamide under microwave irradiation proceeded regioselectively to provide a library of novel 5-aza-7-deaza-adenines in good yields and purity. The developed method was demonstrated to be scalable and highly reproducible in three different monomode microwave reactors. A rearrangement was proposed to explain the high selectivity of the reaction.