It has been shown that chalcones react with 5,6-diamino-4-hydroxypyrimidine to form 2,3-dihydro-1H-pyrimido-1,5-diazepines but aromatic aldehydes and methyl ketones give the monoazomethines.The mechanism and tendency to form the 7-membered ring are
Orlov, V. D.,Kolos, N. N.,Zhidkova, E. V.,Papiashvili, I. Z.