General procedure for the synthesis of 3-methoxypyridin-4-aldehyde from (3-methoxypyridin-4-yl)methanol: Manganese dioxide (843 mg) was added to a solution of ethyl acetate (10 mL) in (3-methoxypyridin-4-yl)methanol (270 mg), and the reaction was carried out at reflux for 2 hours. Subsequently, manganese dioxide (167 mg) was added to the reaction system and refluxing was continued for 1 hour. After completion of the reaction, the mixture was cooled to room temperature and filtered to remove insoluble material. The filtrate was distilled under reduced pressure to remove the solvent, and the resulting residue was purified by silica gel column chromatography (eluent ratio: hexane/ethyl acetate = 1:1 → 0:1) to give 3-methoxypyridine-4-aldehyde (190 mg) as a white solid.
