Heterocyclic Tautomerism. IX. Structural Revision of a Series of Pharmacologically Active Pyridazines

Abstract

On the basis of ¹H n.m.r. n.O.e. Measurements and an X-ray crystal structure determination, it is shown that a large series of pharmacologically active pyridazine derivatives should be represented as aromatic pyridazine tautomers [e.g. (1b)-(3b)], rather than the previously reported arylidene-4,5-dihydropyridazines [e.g. (1a)-(3a)]. Crystals of (7b) are monoclinic, P2₁/c, a 13.312(3), b 7.269(1), c 11.753(2) Ǻ, β 101.38(3)°, Z = 4; the structure was refined to a conventional R[I > 2σ(I)] 0.037.