Abstract 2, 4-Disubstituted thiosemicarbazides were allowed to react with α- bromoacetophenone to give the anticipated 2, 3-dihydro-6H-1, 3, 4-thiadiazines, whereas with β-propiophenone and γ-butyrophenone to afford the unexpected 2, 3-dihydro-1, 3, 4- thiadiazole. The reaction mechanism was also discussed.
