Synthesis of 1, 2, 4-triazoles and thiazoles from thiosemicarbazide and its derivatives

The use of thiosemicarbazide in organic synthesis has become a classical strategy for the synthesis of several heterocycles. Their reactions with compounds containing C=O and C=N groups is an elegant method for the preparation of biologically active compounds viz. triazoles and thiazoles. The case of forming C-N and C=N bonds as opposed to N-N bond formation is reflected in their extensive use for the preparation of these heterocycles. As the internal nitrogen atom of the hydrazine fragment is a softer nucleophilic centre than the more powerful terminal nitrogen, reagents susceptible to nucleophilic attack by the terminal nitrogen undergo cyclisation to afford the aforesaid heterocycles in excellent yields, even under mild reaction conditions. The present review attempts to summarise the cyclisation reactions of thiosemicarbazide derivatives yielding 1, 2 4-triazoles and thiazoles.