General procedure for the synthesis of 5-bromo-3-fluoro-2-hydroxybenzene-1,2-diol from 5-bromo-3-fluoro-2-hydroxybenzaldehyde: Water was added slowly and dropwise to a solution of 5-bromo-3-fluoro-2-hydroxybenzaldehyde (40 g, 183 mmol) in tetrahydrofuran (THF, 260 mL). Sodium hydroxide (NaOH) solution (0.05N, 720 mL, 37 mmol) was added at 0 °C, followed by 30% hydrogen peroxide (H2O2) solution (90 mL). The reaction mixture was stirred at room temperature for 2 hours, then a second portion of 30% hydrogen peroxide (90 mL) was added. After continued stirring for 4 hours, the mixture was cooled to 0°C and washed with cold water. The pH was adjusted to 10-11 by adding sodium hydroxide solution (2N, 112 mL) and stirring was continued for 0.5 h. The reaction was subsequently quenched with concentrated hydrochloric acid (HCl). The pH was adjusted to 2-3 with hydrochloric acid at 0 °C. The reaction mixture was extracted with dichloromethane (250 mL x 3), the organic phases were combined and washed with brine (300 mL x 2), dried over anhydrous sodium sulfate (Na2SO4), and concentrated to give 5-bromo-3-fluorobenzene-1,2-diol (37 g, 98% yield) as a yellow oil. lc-MS (m/z): 205 [ M-H]-.
