General procedure for the synthesis of 2,3-dichloro-5-formylpyridine from 5,6-dichloro-3-pyrimidinemethanol: To a 500 mL round-bottomed flask was added an anhydrous dichloromethane (150 mL) solution of 2,3-dichloro-5-hydroxymethylpyridine (64.810 g, 50.0 mmol), followed by manganese oxide (43.5 g, 0.50 mol). The reaction mixture was stirred at 25 °C for 48 hours. Upon completion of the reaction, it was filtered through Celite and the filtrate was concentrated under reduced pressure. The resulting crude product was purified by silica gel column chromatography using ethyl acetate (0%-40%)/hexane gradient elution to afford 2,3-dichloro-5-formylpyridine (7.2 g, 90% yield). The product was confirmed by 1H NMR (400 MHz, CDCl3): δ10.08 (1H, s), 8.77 (1H, d, J=1.97 Hz), 8.25 (1H, d, J=1.97 Hz). the LC/MS analysis showed the molecular ion peak (M+1) was 176.
