Two routes were proposed for the synthesis of pyrimido[4,5-d]pyrimidine derivatives from 5-acetyl-4-aminopyrimidines. Acylation of 5-acetyl-4-aminopyrimidines followed by cyclization by the action of NH4OAc made it possible to access pyrimido[4,5-d]pyrimidines with alkyl, aryl, and hetaryl substituents in positions 2 and 7. Reductive amination of the acetyl group in 5-acetyl-4-aminopyrimidines and subsequent cyclization with DMF–DMA or HC(OEt)3 resulted in the formation of 6-alkyl-3,4-dihydropyrimido[4,5-d]pyrimidines.
