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Synthesis of methyl 6-bromo-5-fluoro-pyridinecarboxylate: Concentrated sulfuric acid (4.2 eq.) was slowly added to a methanol (0.2 M) solution of 6-bromo-5-fluoro-2-pyridinecarboxylic acid (1.0 eq.) and the reaction mixture was stirred at room temperature. The progress of the reaction was monitored by LC/MS and the reaction was completed after about 2 hours. The reaction mixture was diluted with ethyl acetate and saturated aqueous sodium bicarbonate solution was added slowly to quench the reaction. The mixture was transferred to a partition funnel and extracted with ethyl acetate. The organic phases were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford methyl 6-bromo-5-fluoropyridinecarboxylate as a white solid (yield >99%). The product was characterized by LC/MS: m/z = 233.9/235.9 ([M+H]+), retention time Rt = 0.69 min.

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