The general procedure for the synthesis of 2-chloro-3-methylbenzaldehyde from (2-chloro-3-methylphenyl)methanol is as follows:
1. dichloromethane (30 mL) was cooled to -78 °C under nitrogen protection, and a solution of DCM (10 mL) with oxalyl chloride (1.34 mL, 15.2 mmol, 1.2 eq.) and DMSO (2.2 mL, 31.7 mmol, 2.5 eq.) was added sequentially.
2. After stirring the reaction mixture for 15 minutes, a solution of 2-chloro-3-methylbenzyl alcohol (2 g, 12.7 mmol, 1 eq.) in DCM (12 mL) was added slowly and dropwise.
3. After continuing the reaction for 30 minutes, triethylamine (9.03 mL, 63.5 mmol, 5 eq.) was added in a single addition and the reaction mixture was slowly warmed to room temperature over a period of 1 hour.
4. After completion of the reaction, the reaction was quenched with saturated aqueous sodium bicarbonate (50 mL) and the aqueous layer was extracted with DCM (2 x 50 mL).
5. The organic phases were combined, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to remove the solvent to give 2-chloro-3-methylbenzaldehyde as a yellow oil (1.8 g, 91.4% yield).
6. The product was characterized by 1H NMR (300 MHz, CDCl3): δ= 10.53 (1H, s, CHO), 7.81-7.74 (1H, m, ArH), 7.53-7.46 (1H, m, ArH), 7.34-7.23 (1H, m, ArH), 2.46 (3H, s, CH3).
