Methyl 5-bromo-6-methylpyridine-2-carboxylate (7.00 g, 30.6 mmol, 1.00 eq.) and tetrahydrofuran (150 mL) were added to a 250 mL round-bottom flask under nitrogen protection. The reaction system was cooled to -78 °C and a hexane solution of diisobutylaluminum hydride (60 mL, 1 mol/L) was added slowly and dropwise. After keeping the reaction at -78 °C for 60 min, the reaction was quenched with aqueous ammonium chloride (50 mL). The reaction mixture was extracted with ethyl acetate (2 x 100 mL), the organic phases were combined, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (eluent: ethyl acetate/petroleum ether=10/90) to afford 5-bromo-6-methylpyridine-2-carboxaldehyde (4.90 g, 76% yield) as a light yellow solid. The structure of the product was confirmed by 1H NMR (300 MHz, CDCl3) and LC-MS (ESI): 1H NMR δ 10.04 (s, 1H), 8.02 (d, J=8.1 Hz, 1H), 7.67 (d, J=8.4 Hz, 1H), 2.78 (s, 3H); LC-MS (ESI, m/z): 200 [M+H]+.
