Aza analogues of pteridine. VIII. 3-Amino- from 3-Alkoxy-pyrimido[5,4-e]-as-triazin- 5-ones prepared by cyclization of 3-Ethoxy-1,2,4-triazines or other means

Syntheses of hitherto unknown 3-aminopyrimido[5,4-e]-as-triazin-5-ones are described. One route involves selective hydrolysis of 3,5-di- or 3,5,7-tri-alkoxypyrimidotriazines at the 5-position followed by aminolysis. Another is exemplified thus: 3-ethoxy-5-methoxypyrimidotriazine (2a) is converted by methanolic hydrochloric acid into methyl 6-amino-3-ethoxy-1,2,4-triazine-5-carboxylate (3a) which then undergoes successive ammonolysis to the corresponding amide (3b), cyclization by triethyl orthoformate-acetic anhydride to 3-ethoxypyrimidotriazin-5-one (1d) and final ammonolysis to the corresponding amine (1a). The second route may be modified to furnish 3-aminopyrimidotriazine- 5,7-dione (5c) and its 6-methyl derivative (5d). Dehydration of the above amide (3b) with phosphoryl chloride gives both the corresponding nitrile (3h) and an unusual hydrolytic product, 6-amino-3- ethoxytriazin-5-one (6). The ionization constants and the u.v., N.M.R. and mass spectra are discussed.