Carbon Dioxide → 4-Ethoxy-3-hydroxypyridine-2-carboxylic acid

A stirred solution of 11 (2.9 g) in THF (50 mL) under an argon atmosphere was cooled to ≦−70° C. To this was slowly added t-BuLi (8 mL, 1.5M pentane solution) while keeping the reaction temperature at ≦−66° C. After the addition was complete, the mixture was stirred at ≦−70° C. for 45 minutes and then poured into a slurry of crushed dry ice in ether. The resulting mixture was stirred until it reached room temperature, then the solvents were evaporated. THF (25 mL) and 4N HCl (15 mL) were added to the residue and the resulting mixture was stirred at room temperature for two hours. At the end of this period, the insoluble material was filtered, washed with a small volume of THF and air dried to give the title compound as a white solid (1.05 g). Preparation of 6-Bromo-3-Benzyloxy-4-Methoxypyridine-2-Carboxylic Acid (16) and its Acid Chloride (3) (See Scheme 4). a. Preparation of Methyl 4,6-Dibromo-3-Hydroxypyridine-2-Carboxylate (14).