Abstract The synthesis of novel 1, 2, 3-thiadiazol derivatives containing 2H-benzo [b][1, 4] oxazin-3 (4H)-one moiety as one of the substituents has been reported. A combined application of H 3 PO 4/(CF 3 CO) 2 O mediated acylation followed by Hurd–Mori reaction has been explored to synthesize these compounds. The scope and limitation of this strategy along with the reaction mechanism of the key step is discussed.