Heterocyclization of 1-aryl/alkyl-2-thiobiureas to 4-aryl/alkyl-3-substituted-Δ2-1,2,4-triazolin-5-ones

Synthesis of a range of 1,2,4-triazolin-5-ones has been carried out by thermally induced cyclization of 1-aryl/alkyl-2-alkyl isothiobiureas 4. The required isothiobiureas were generated in situ by the reaction of alkyl halides with 1-aryl/alkyl-2-thiobiureas 3 in acidic medium at reflux. The reaction proceeds after S-alkylation of the thiobiureas and is demonstrated by the isolation of the alkyl isothiobiurea intermediates and their subsequent acid catalyzed thermal cyclization.