General procedure for the synthesis of 3-chloro-5-methoxybenzaldehyde from 3-chloro-5-methoxybenzyl alcohol: 3-chloro-5-methoxybenzyl alcohol (5.0 g, 28.9 mmol) was mixed with 20% pyridinium chlorochromate (40 g, 37.8 mmol) loaded on alumina and the reaction was stirred for 1.25 h. The reaction was carried out with the addition of ether. Upon completion of the reaction, it was diluted with the addition of ether (200 mL) and subsequently filtered to remove the solid precipitate. The filtrate was concentrated under reduced pressure, and the resulting crude product was purified by silica gel column chromatography with the eluent being a mixed solvent of 40% dichloromethane and 60% petroleum ether, resulting in 3.8 g of the target product 3-chloro-5-methoxybenzaldehyde in 78% yield. The structure of the product was confirmed by 1H-NMR (CDCl3): δ 3.84 (s, 3H), 7.13 (s, 1H), 7.28 (s, 1H), 7.41 (s, 1H), 9.89 (s, 1H).
