In a round-bottomed flask, 5-fluoro-2-methoxypyridine-3-carbaldehyde (37, 0.500 g, 3.22 mmol) was dissolved in a solvent mixture of 30 mL of 1,4-dioxane and 10 mL of water, to which was added sodium chlorite (0.6734 g, 5.957 mmol) and sulfamic acid (2.39 g, 24.6 mmol) in that order. The reaction mixture was stirred at room temperature for 5 min and then poured into 100 mL of water and extracted with 100 mL of ethyl acetate. The organic layer was washed with water and brine sequentially, dried over anhydrous magnesium sulfate, filtered and the filtrate was concentrated in vacuum to give the crude product 5-fluoro-2-methoxynicotinic acid (150, 512 mg), which was used directly in the subsequent reaction.
