4-Hydroxy-5-bromopyrimidines containing a variety of electron-releasing substituents in the 2-and 6-positions react readily with 0-aminothiophenoxide ion to produce 4-hydroxy-5-(o- aminoarylthio) pyrimidines. The products cyclize with ease by warming in dilute aqueous or alcoholic acid, to produce lOH-pyrimid0 [5, 4-b][1, 4]-benzothiazines. The parent compound of this new ring system was prepared from the 2-hydroxy derivative by ...