Heterocyclic Synthesis with 4-Benzoyl-1-cyanoacetylthiosemicarbazide: Selective Synthesis of Some Thiazole, Triazole, Thiadiazine, Pyrrylthiazole, and Pyrazolo[1,5-a]triazine Derivatives

4-Benzoyl-1-cyanoacetylthiosemicarbazide undergoes coupling reaction with aromatic diazonium chloride to afford (arylhydrazono)thiosemicarbazide, which was reacted with phenacyl bromide regioselectivity to afford the thiazoline. The (arylhydrazono)thiosemicarbazide could be transformed into the pyrazolo1,5-a]triazine. Heterocyclization of 4-benzoyl-1-cyanoacetylthiosemicarbazide with α-haloketones (bromoacetone and phenacyl bromide), ethyl iodide, and ethyl bromoacetate furnished the pyrrylthiazoles, 1,2,4- triazole, and 1,3,4-thiadiazine. The latter was coupled with aromatic diazonium chloride to give the bis(arylhydrazono)‐thiadiazine. The mechanism for the formation of the title compounds was suggested and discussed.