Abstract 8-Phenylpyrido [3, 4-d] pyridazines bearing various amino substituents at C-5 (7a-d, 8) were prepared from ethyl 5-benzyl-4-pyridazinecarboxylate 1 via the fused pyridone 5. The isomeric 4-phenylpyrido [2, 3-d] pyridazines having the amino functions attached to C-2 (10a-f) were obtained by a one-pot cyclization of the amino ketone 1 with appropriate acetamide acetals. These novel triazanaphthalene derivatives are of interest as ...