3(2H)-pyridazinone derivatives and related analogues was synthesized. Substituted 3(2H)-pyridazinones and their 4,5-dihydro analogues were alkylated by omega-haloalkyl cyanides at the N-2 position under phase-transfer catalyticreaction, and the nitrile group was converted to the thio amide group by treatment with hydrogen sulfide alone or with the appropriate primary or secondary amines. Various substituents