types of reactions. Further studies on the reaction of α-chloroformylarylhydrazines 1 with thiourea compounds confirmed a novel cyclization and de-cyclization mechanism, which led to give 2-arylhydrazinecarboximidamides 5 and 1,3,4-thiadiazolin-5-ones 6. In addition, various 1,3,4-oxadiazines 9 were obtained by reacting α-chloroformylarylhydrazines with α-cyclodiketones, showing ring cyclization was involved