Novel Regioselective Synthesis and Biological Activity of 6-Phenylazo and 3,6-Bis(arylazo)-7-hydroxy-1H-[1,2,4]triazolo[4,3-a]pyrimidin-5(4H)-one

Treatment of 6‐hydroxy‐5‐phenylazo‐2‐thioxo‐4(1H)‐pyrimidinone 1 with a series of hydrazonoyl halides 2 and N,2‐diaryl‐diazinecarbohydrazonoyl halides 9 in dioxane in the presence of triethylamine under reflux furnishes 6‐phenylazo and 3,6‐bis(arylazo)‐7‐hydroxy‐1H‐[1,2,4]triazolo[4,3‐a]pyrimidin‐5(4H)‐one derivatives 7 and 10, respectively. The biological activities of the products were evaluated.