Abstract 4, 5-dihydro-3 (2H) pyridazinones such as CI-914, CI-930 and pimobendan along with tetrahydropyridopyridazine (endralazine) and perhydropyridazinodiazepine (cilazopril) have been used as potent positive inotropes, antihypertensives as well as platelet aggregation inhibitors. Accordingly, the present work involves the synthesis of 24 target compounds; 4, 5-dihydro-3 (2H) pyridazinones in addition to seven reported intermediates ...