Synthesis of 5-Methyl-1,2,4-triazolo[1,5-a]pyrimidin-7(4H)-one in Supercritical Carbon Dioxide

5-Methyl-1,2,4-triazolo[1,5- a ]pyrimidin-7(4 H )-one, an intermediate product in the synthesis of the antiviral drug Triazid®, was obtained for the first time by condensation of 3 H -1,2,4-triazol-5-amine with ethyl acetoacetate in the presence of a catalytic amount of ZnCl 2 in supercritical carbon dioxide (200 bar) under solvent-free conditions. Depending on the temperature and reaction time, the conversion was 90%.