Keywords: Cyanopurines / Amines / Rearrangement / Pyrimido [5,4-d]pyrimidines 7,pyrimidines 4 were isolated in very good yields by treatment of 9-aryl-6-cyanopurines 1 with primary amines. Nucleophilic attack of the amine on C8 of the purine ring was followed by ring-opening of the imidazole unit, and subsequent intramolecular cyclization involving the newly formed amidine group and the cyano substituent in the pyrimidine ring produced the 7,8-dihydropyrimido[5,4-d]pyrimidine structure 4. When ammonia was used instead of primary amines, compound 4 rapidly reacted further to afford the more stable pyrimido [5,4-d]pyrimidine 6 as

Fused pyrimidine derivatives R 0515An Efficient Synthesis of 7,8-Dihydropyrimido[5,4-d]pyrimidines. -Two types of fused pyrimidines are formed by the reaction of cyanopurines (I) with excess ammonia or primary amines. The major pathway involves nucleophilic attack of the amine on C-8 of the purine ring followed by ring-opening of the imidazole and ring-closure on the cyano group in the C-6 purine position. In the case of ammonia, the stable amino tautomers (II) are isolated instead of iminopyrimidines. This type of compound is also formed by the reaction of hydrazine (III) with purine (Ic). -(CARVALHO, M. A.; ESPERANCA, S.; ESTEVES, T.; PROENCA*, M. F.; Eur. J. Org. Chem. 2007, 8, 1324-1331; Dep. Quim., Univ. Minho, P-4710 Braga, Port.; Eng.) -Klein 25-157