General procedure for the synthesis of 5-fluoro-6-methoxynicotinic acid from 5-fluoro-6-methoxynicotinic acid methyl ester: 5-fluoro-6-methoxynicotinic acid methyl ester (3.5 g, 18.9 mmol) and potassium hydroxide (4.2 g, 61.5 mmol) were dissolved in methanol (70 ml), and the reaction was stirred at room temperature for 5 hours. After completion of the reaction, methanol was removed by concentration under reduced pressure, the residue was dissolved in water and the aqueous solution was washed with ether. Subsequently, the aqueous phase was acidified to pH=1 with dilute hydrochloric acid and extracted with ether. The organic layers were combined, washed with saturated brine, dried with anhydrous sodium sulfate, and finally concentrated under reduced pressure to give 5-fluoro-6-methoxynicotinic acid (3.2 g, 98% yield) as a white solid.
