Step 3. (3-methoxy-5-nitrophenyl)methanol (75 g, 0.41 mol) was dissolved in dichloromethane (1.5 L) and cooled below 10°C. Under stirring, pyridinium dichromate (382 g, 1.02 mol) and silica gel (382 g) were added in batches. After addition, the reaction mixture was brought to room temperature and stirring was continued for 3 hours. The progress of the reaction was monitored by thin layer chromatography (TLC) (Expanding agent: petroleum ether/ethyl acetate = 3:1, Rf = 0.6) to confirm the complete conversion of the raw material. Upon completion of the reaction, the crude product was purified by fast column chromatography (eluent: dichloromethane) to afford 3-methoxy-5-nitrobenzaldehyde as a yellow solid (170 g, 76% yield in 3 batches).
[1] Patent: WO2013/148365, 2013, A1. Location in patent: Paragraph 0095
[2] Journal of Medicinal Chemistry, 2004, vol. 47, # 11, p. 2897 - 2905
[3] MedChemComm, 2018, vol. 9, # 8, p. 1293 - 1304
