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