Facile construction of substituted pyrimido[4,5-d]pyrimidones by transformation of enaminouracil

The reaction of 6-amino-1,3-dimethylpyrimidine-2,4(1h,3h)-dione (1) as a binucleophile with primary aromatic or heterocyclic amines and formaldehyde or aromatic (heterocyclic) aldehydes in a molar ratio (1:1:2) gave the pyrimido[4,5-d]pyrimidin-2,4-dione ring systems 2–5. treatment of 1 with diamines and formalin in molar ratio (2:1:4) gave the bis-pyrimido[4,5-d]pyrimidin-2,4-diones 6–8. furthermore, substituted pyrimido[4,5-d]pyrimidin-2,4-diones with uracil derivative 11 or spiro indole 16 were synthesized. synthesis of pyrimido[4,5-d]pyrimidin-2,4-diones with different substitution at c-5 and c-7 was achieved to give 13 and 18, respectively.