Easy Strategy for the Synthesis of New 5,6-Dihydro-[1,2,4]triazolo[4,3-a][1,3,5]triazine Derivatives

New substituted 5,6-dihydro[1,2,4]triazolo[4,3-a][1,3,5]triazines were synthesized by cyclocondensation of N-alkyl(aryl)-N′-(4H-1,2,4-triazol-3-yl)ethan- and -propanimidamides with benzaldehyde or ethyl methyl ketone in the presence of p-toluenesulfonic acid in 1,4-dioxane under reflux. The reaction tolerated a broad substrate scope and provided good yields (43–64%). The structure of the newly synthesized compounds was confirmed by elemental analyses and IR, 1H and 13C NMR, and mass spectra.