Dimethylformamide → 2-Chloro-6-methoxypyridine-3-carbaldehyde

The 3-bromo-2-chloro-6-methoxy-pyridine (0.50 g, 2.26 mmol) obtained in (19-1) above was dissolved in toluene (dehydrated) (11 mL), and thereafter, n-butyllithium (1.46 mL, 2.3 mmol, 1.57 mmol/L hexane solution) was added dropwise to the solution at −78° C. in an argon atmosphere. The obtained mixture was stirred at the same temperature as described above for 30 minutes, and DMF (1.0 mL) was then added to the reaction solution. The obtained mixture was further stirred for 30 minutes. Thereafter, a saturated ammonium chloride water (20 mL) was slowly added to the reaction solution, and the temperature of the mixture was then increased to room temperature. The mixture was extracted with diethyl ether (20 mL) twice, and organic layers were gathered. The resultant was dried over anhydrous sodium sulfate and was then filtrated, followed by vacuum concentration. The obtained residue was purified by silica gel column chromatography (SiO2 30 g, hexane:ethyl acetate=95:5 to 80:20), so as to obtain 180 mg of 2-chloro-6-methoxy-3-pyridinecarboxaldehyde.