Synthesis of analogues of the 2,3,6-triazaphenothiazine ring system

Article abstract of DOI:10.1002/jhet.5570200141

Treatment of 2,3-dichloroquinoxalines with 2-amino-6-picoline-3-thiol gave a mixture of 2,3-bis(2-amino-6-picolinyl-3-thio)quinoxalines (16, R = H, Cl) and 2,3-bis (N,N-dimethylamino)quinoxalines (15, R = H, Cl) separated by fractional crystallization. A similar reaction of 3-amino-6-methoxypyridine-2(1H)-thione (9) with 4,5-dichloropyridazin-3(2H)-one (21) gave 4-chloro-5-(3-amino-6-methoxypyridyl-2-thio)pyridazin-3(2H)-one (22). Concentrated hydrochloric acid-catalysed cyclization of 22 gave the nonrearranged 7-methoxy-2,3,6-triazaphenothiazin-1(2H)-one. The action of compound 22 in refluxing glacial acetic acid gave, on the other hand, 7-methoxy-2,3,6-triazaphenothiazin-4(3H)-one via a Smiles rearrangement. These cyclized compounds are the first known derivatives of the new 2,3,6-triazaphenothiazine ring system.