Pyrimidothiazines are a class of heterocyclic compounds that have been described as corrosion inhibitor for carbon steel in 1.0 M HCl, Filament temperature sensitive protein Z (FtsZ) inhibitors, 15-LO inhibitory activities, anti-inflammatory and antipyretic.1 The main synthetic methods for the formation of various bicyclic pyrimidothiazines involve the reaction of pyrimidine-2-thiones with urea, 1,2-epoxy-3-chloropropane, 3-bromopropanoic acid derivatives, acetylene dicarboxylates or DMF-DMA and carbon disulfide.2 In view of these observations and in continuation of our studies on developing the new routes for the synthesis of various fused heterocyclic derivatives containing pyrimidine core,3 herein we report a simple and efficient method for the synthesis of new fused dipyrimido[2,1-b:4\\\',5\\\'-d][1,3]thiazines as a novel heterocyclic system. In addition, we present our findings on the regiochemistry of the reaction by performing x-ray analysis.

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