Synthesis of new 1,2,4‐triazolo[4,3‐ b ]pyridazines and related compounds

The synthesis of novel 6‐[4‐(1 H ‐imidazol‐1‐yl)phenyl]‐1,2,4‐triazolo[4,3‐ b ]pyridazines 8a‐f and related compounds is described. Although the intermediate hydrazine derivatives 7 and 9 possess good positive inotropic activity, the fused bicyclic pyridazines 8a‐f are significantly less potent than the 3(2 H )‐pyridazinone 5. Compounds 8a‐f are potent but nonselective inhibitors of cardiac phosphodiesterase.