Polycyclic pyridazines. II [3]. Synthesis of pyrazolo[4′,3′:5,6]pyrido[2,3‐ d ]pyrid‐azine derivatives from dimethyl pyrazolo[3,4‐ d ]pyrid‐azine‐5,6‐dicarboxylates as the key intermediates

The synthesis of the novel pyrazolo[4′,3′:5,6]pyrido[2,3‐ d ]pyridazine ring system and some of its derivatives has been accomplished such as 4‐amino‐1‐phenyl‐5,8‐dioxo‐, 4‐amino‐5,8‐dioxo‐, 1‐phenyl‐5,8‐dioxo‐, 5,8‐dioxo‐, 5,8‐dichloro‐1‐phenyl‐, 5‐ethoxy‐1‐phenyl‐ and 8‐ethoxy‐1‐phenylpyrazolo[4′,3′:5,6]pyrido[2,3‐ d ]pyrid‐azines.