PMGB

To a mixture of 4-(6-acetyl-3-oxo-2H-benzo[b][1,4]oxazin-4(3H)-yl)butanoate (1.3 g, 0.003 mol), urea hydrogen peroxide (0.85 g, 0.009 mol) and sodium bicarbonate (0.76 g, 0.009 mol) in anhydrous dichloromethane (10 mL) under nitrogen atmosphere at ice-bath temperature was added trifluoroacetic anhydride (0.8 mL, 0.006 mol) drop-wise over a period of 10 minutes. The reaction mixture was gradually warmed to room temperature and stirred for 24 h. The reaction mixture was diluted with 50 mL dichloromethane and washed with saturated sodium bicarbonate solution (50 mL), dried over sodium sulfate and evaporated under reduced pressure to give ethyl 4-(6-acetoxy-3-oxo-2H-benzo[b][1,4]oxazin-4(3H)-yl)butanoate, isolated as a pale yellow oil (1.36 g, 99% yield, NMR complies).