2-Chloro-5-(methoxymethoxy)pyridine-4-carboxaldehyde (12 g, 59.52 mmol, 1.00 eq.) was used as a starting material, which was dissolved in tetrahydrofuran (80 mL) and 3M hydrochloric acid (130 mL) was added. The reaction mixture was stirred at 60°C for 1 hour. After completion of the reaction, the mixture was cooled to room temperature and the pH was adjusted with 5% aqueous sodium carbonate to 7. The organic layer was separated and the aqueous layer was extracted with ethyl acetate (400 mL). The organic layers were combined, dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography, the eluent was ethyl acetate/petroleum ether (1:3), to obtain 2-chloro-5-hydroxypyridine-4-carbaldehyde (6g, yield 64%) as a light yellow solid. the TLC detection conditions: petroleum ether/ethyl acetate = 2:1, Rf = 0.3.
