General procedure for the synthesis of 3-chloro-2-methoxybenzaldehyde from 3-chloro-2-methoxybenzyl alcohol: Manganese dioxide (16 g, 184 mmol) was added to a solution of 3-chloro-2-methoxybenzyl alcohol (5.68 g, 33 mmol) in dichloromethane (300 mL). The reaction mixture was heated at 45°C for 2.5 hours followed by stirring at room temperature for 18 hours. Upon completion of the reaction, the mixture was filtered through Arbocel (R) and the filter cake was washed with dichloromethane. After combining the filtrates, it was concentrated under reduced pressure to give 3-chloro-2-methoxybenzaldehyde as a yellow oil in 92% (5.2 g) yield. The product was characterized by 1H NMR (CDCl3, 400 MHz) with chemical shifts of δ 4.02 (s, 3H), 7.19 (m, 1H), 7.63 (d, 1H), 7.79 (d, 1H), 10.40 (s, 1H).
