The general procedure for the synthesis of 2-bromo-5-methylbenzaldehyde using 2-bromo-N-methoxy-N,5-dimethylbenzamide as starting material was as follows: 2-bromo-N-methoxy-N,5-dimethylbenzamide (656 mg, 2.54 mmol) was dissolved in tetrahydrofuran (THF, 20 mL). The reaction system was cooled to -78 °C, followed by the slow addition of 1.0 M solution of diisobutylaluminum hydride (DIBAL-H) (7.62 mL, 7.62 mmol). The reaction temperature was maintained at -78 °C with stirring for 1 hour. Upon completion of the reaction, the reaction was quenched with acetone and stirred at room temperature with the addition of Rochelle salt solution. The reaction mixture was extracted with dichloromethane (DCM). The organic phases were combined, dried with anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure to afford the target product 2-bromo-5-methylbenzaldehyde (500 mg, 99% yield) as a colorless oil. It was analyzed by liquid chromatography-mass spectrometry (LC-MS), and its molecular ion peak (M + H)+ was 199.21.
