A Convenient Synthesis of 3,4-Disubstituted-1,2,4-Thiadiazole-5(4H)-Thiones

3,4-Disubstituted-1,2,4-oxadiazole-5(4H)-ones were obtained from the reaction of substituted amide oximes with ethylchloroformate. These compounds were treated with P2S5 to give corresponding 1,2,4-oxadiazole-5-thiones. Rearrangement of 1,2,4-oxadiazole-5-thiones, catalysed by metallic copper, yielded 1,2,4-thiadiazole-5-ones. The reaction of 1,2,4-thiadiazole-5-ones with P2S5 gave 1,2,4-thiadiazole-5-thiones.