Synthesis of 3‐amino‐5 H ‐1,2,3‐triazino[5,4‐ b ]indol‐4‐one. New compounds with blood platelet antiaggregation activity

Starting with 3‐aminoindole‐2‐carbohydrazide 1 a series of arylidene hydrazones 2 was obtained with good yields (79–85%). Upon treating 2 with nitrous acid a series of 3‐arylidineamino‐5 H ‐1,2,3‐triazino[5,4‐ b ]indol‐4‐ones 3 was obtained (80–86%). The reaction of 4‐methoxybenzylidene derivative 3e with hydrazine hydrate, in ethanol, gave 3‐amino‐5 H ‐1,2,3‐triazino[5,4‐ b ]indol‐4‐one 4 (64%). However, by treating 3e in boiling hydrate, 3‐aminoindole‐2‐carbaldehyde azine 5 was obtained (44%). By boiling 1 in N,N ‐dimethylformamide, 3‐amino‐5 H ‐pyrimido[5,4‐ b ]indol‐4‐one, 6 was obtained (52%).