Palladium-Catalyzed Synthesis of Substituted Pyrido[2,3-d]pyridazines at Positions 5 and 8

Several synthetic strategies were developed for the preparation of highly substituted pyrido[2,3- d ]pyridazines. We particularly focused on the impact of the pyridine nitrogen atom on pyridazine ring reactivity toward aromatic substitutions, alkylations, or pallado-catalyzed cross-coupling reactions.