Studies on condensed Systems of Aromatic Nitrogenous Series. XXIV. Synthesis of 4-Substituted 1H-Imidazo[4, 5-c]pyridines

The evidences that the reported 6-chloro-3, 4-diaminopyridine was actually 2-chloro-3, 4-diaminopyridine (X) were presented. By employing X 4-amino-1H-imidazo[4, 5-c]-pyridine (IV) was prepared via 4-chloro-1H-imidazo[4, 5-c]pyridine (III). An alternative synthetic method leading to IV was devised using 1H-imidazo[4, 5-c]pyridine 5-oxide (II) as a key intermediate as follows. Oxidation of 1H-imidazo[4, 5-c]pyridine (I) with hydrogen peroxide in acetic acid afforded the cerresponding 5-oxide (II); treatment of II with boiling phosphoryl chloride gave rise to III. 3-Nitro-2, 4-dichloropyridine, useful intermediate for the synthesis of IV (via 3-nitro-2, 4-diaminopyridine→2, 3, 4-triaminopyridine) was prepared by N-oxide-phosphoryl chloride reaction from 3-nitro-4-chloropyridine 1-oxide. Comparison of the several routes leading to IV has been made from a standpoint of the over-all yield.