Synthesis of the oxime ethers containing pyridazinones

Compounds 1 a ∼ f were synthesized from 4, 5-dichloropyridazinone 4 under two different conditions (NaH/DMF or NaOH/acetone). The nucleophilic substitution of 4-chloro-5-(β-bromo-ethoxy)-pyridazinone 3 with aromatic aldehyde (ketone) oximes afforded exclusively the product 2 in the condition of PTC. However, it led to a mixture of 1 and 2 reacting with alphatic ketone oximes. The regioselectivity of the reaction affacted by nucleophiles and reaction conditions was also discussed.