98% concentrated sulfuric acid (6.5 mL) was slowly added dropwise to a mixture of 3-bromophenol (5.00 g, 28.9 mmol) and DL-malic acid (2.60 g, 19.4 mmol) at 0 °C. The reaction system was warmed to 120 °C and the reaction was continuously stirred for 6 hours. Upon completion of the reaction, the mixture was carefully poured into crushed ice and the precipitated solid product was collected by filtration. The filter cake was washed well with water to remove residual sulfuric acid. Subsequently, the solid was dissolved in dichloromethane (CH2Cl2), dried by addition of anhydrous magnesium sulfate (MgSO4) and concentrated under reduced pressure to remove the solvent. Purification by silica gel column chromatography (eluent ratio of dichloromethane:hexane=1:1, v/v) afforded the target product 7-bromo-2H-benzopyran-2-one in white powder form (yield: 34%). The structure of the product was confirmed by nuclear magnetic resonance hydrogen (1H NMR, 400 MHz, CDCl3) and carbon (13C NMR, 75 MHz, CDCl3) spectra: 1H NMR δ 6.44 (d, J = 9.6 Hz, 1H), 7.33-7.43 (m, 2H), 7.52 (d, J = 2.0 Hz, 1H), 7.66 (d, J = 9.6 Hz, 1H); 13C NMR δ 117.01, 117.90, 120.29, 125.93, 128.02, 128.97, 142.92, 154.40, 160.01.
