Comparison of methods of synthesis of 5-methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one in supercritical carbon dioxide

For the optimization of the method of synthesizing 5-methyl-1,2,4-triazolo[1,5-a]pyrimidine-7(4H)-one (an intermediate of the antiviral drug Triazid®) by cyclocondensation of 5-amino-3-H-1,2,4-triazole (aminotriazole) with acetoacetic ester, various conditions (reaction in supercritical carbon dioxide in the presence of acetic acid, organic solvents, as well as Lewis acid (ZnCl2, TiO2, and SiO2) or inorganic additives) for this reaction were studied. By comparison of the yields of the reaction products, it was concluded that the most preferable conditions are pure supercritical CO2 in the presence of acetic acid or ZnCl2 at a temperature of 150-190 °C.