2-phenyl-1,2,4-triazolo(1,5-c)(1,3)benzoxazin-5-one

Triethylamine (0.42 mL) and triphosgene (0.15 g) were added to a solution of 3-phenyl- 5-(2-hydroxyphenyl)-1,2,4-triazole (1.26 mmol) in anhydrous tetrahydrofuran (10 mL). The mixture was stirred at room temperature for 9 days. On the third and sixth days further triethylamine (0.42 mL) and triphosgene (0.15 g) were added. The mixture was eventually diluted with water and the resulting solid was collected and washed with water. Yield 93%.