Pyridazino[3,4‐ b ]quinoxalines and their reduced derivatives. Preparation and structure

The reaction of o ‐phenylenediamine with a β‐ketoacid, leads in most cases to quinoxalinones. Their structure has been determined as well as that of their corresponding hydrazones. The reaction of hydrazine with these quinoxalinones gives dihydropyridazino[3,4‐ b ]quinoxalines, the structure of which has been ascertained. It has been shown that among the six possible formulas, the only 1,2‐dihydro structure fits with the spectroscopic data. On the contrary, N ‐substituted o ‐phenylenediamines lead to 2,10‐dihydro derivatives. The electrochemical behavior of the 2,10‐dihydro‐10‐methyl‐3‐phenylpyridazino[3,4‐ b ]quinoxaline has been investigated. It has also been shown that the 3,4,6‐trichloropyridazine reacts with o ‐phenylenediamines to give 5,10‐dihydropyridazino[3,4‐ b ]quinoxalines. These compounds can be oxidized to give the new heterocycle pyridazino[3,4‐ b ]quinoxaline.