90151-04-5

General procedure for the synthesis of 4-hydroxy-2-nitrobenzaldehyde from 4-methoxy-2-nitrobenzaldehyde: To a stirred solution of 4-methoxy-2-nitrobenzaldehyde (4.5 g, 24.84 mmol) in dichloromethane (100 mL) was added drop-wise boron tribromide (8 mL, 84.5 mmol) at 0 °C. The reaction mixture was continued to be stirred at 0°C for 30 minutes, then brought to room temperature and stirred for 4 hours. After completion of the reaction, the mixture was slowly poured into ice water (200 mL) and stirred continuously for two days. The aqueous phase was extracted twice with ethyl acetate. The organic layers were combined, washed sequentially with water and saturated saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by medium pressure liquid chromatography (MPLC) using a gradient elution of ethyl acetate/petroleum ether (1:15 to 1:5) to give 4-hydroxy-2-nitrobenzaldehyde (2.55 g, 61% yield) as an orange solid.

[1] Patent: WO2015/171610, 2015, A2. Location in patent: Paragraph 000656
[2] Patent: WO2010/48582, 2010, A1. Location in patent: Page/Page column 170-171