Novel method for synthesis of polynuclear heterocyclic systems with a pyridazine ring

摘要

Examples of diazotization of 5-aminopyrazoles, which lead to pyrazolyl-5-diazonium salts, are well known [1, 2]. In the case of aminopyrazoles 1a-c, the reaction does not stop at the diazotization step. When they are nitrosated in acetic acid by sodium nitrite at room temperature, the intermediate diazo compound 2 undergoes an intramolecular azo coupling reaction to form 1-R~1-3-R~2-7,8-dimethoxypyrazolo[3,4-c]cinnolines 3a-c.