Abstract New 6‐amino and 6,8‐diamino‐2‐aryl‐2,3‐dihydro‐4‐styryl‐1 H ‐pyrimido[4,5‐ b ][1,4]diazepines were obtained in the reaction of 2,4,5,6‐tetraaminopyrimidine 1a and 4,5,6‐triaminopyrimidine 1b with one equivalent of the diaryli dene acetones 2 in absolute ethanol with acetic acid as the catalyst. Structure analysis of 6‐amino and 6,8‐diamino‐2‐aryl‐2,3‐dihydro‐4‐styryl‐1 H ‐pyrimido[4,5‐ b ][1,4]diazepines 3a‐i, determined by detailed nmr measurements, reveals a high regioselectivity of this reaction.