Unequivocal synthesis of 2,3,6-triazaphenothiazine and two new tetraazaphenothiazine heterocycles

This paper describes the unequivocal synthesis of three new heterocycles: 2, 3, 6-triazaphenothiazine ( 7 ) and 2, 3, 6, 9-tetraazaphenothiazine ( 18 ), both parents of the respective ring systems and the 6, 8-dihydro-7, 9-di-oxo derivative of 2, 3, 6, 8-tetrahydrophenothiazine ( 12 ). These compounds were obtained by base-catalysed condensation of 4, 5-dichloropyridazine ( 8 ) with the appropriate o-amino-heterocyclic thiols 9, 11, 16 . In contrast, reaction of 2, 3, 5-trichloropyrazine ( 20 ) with 4, 6-diaminopyrimidine-5-thiol ( 21 ) and 2-amino-6-picoline-3-thiol ( 28 ) gave 5-chloro-2, 3-bis(diaminopyrimidinyl-5-thio)pyrazine ( 33 ) and 5-chloro-2, 3-bis(2-amino-6-picolinyl-3-thio)pyrazine ( 29 ), respectively. Chloropyrazine ( 34 ) and 3-aminopyridine-2(1H)-thione ( 9 ) followed the latter reaction path to 2-(3-amino-2-pyridyl) pyrazinyl sulfide ( 35 ) in good yields. Structural assignments were based on their infrared, ultraviolet, nmr and mass spectra.