Studies on the Heterocyclic Compounds. XIX. A Novel Ring Isomerization of 3-Ylideneaminoimidazo [4, 5-c] pyridazines

Abstract

Several 3-ylideneaminoimidazo [4, 5-c] pyridazines (IV and VI) were synthesized for the investigation of the ring isomerization reaction. The reactions of IVa, IVb, IVc, and IVd with 5% or 50% acetic acid gave VIII as the ring isomerization product. Similarly IVe afforded X. In the case of IVd, intermediate product (IXd) was obtained by the reaction with 50% acetic acid. This compound (IXd) was converted to VIII by the treatment with 70% acetic acid. The possible reaction mechanism was proposed.