General procedure for the synthesis of 2-bromooxazole-4-carboxylic acid from ethyl 2-bromooxazole-4-carboxylate: ethyl 2-bromo-1,3-oxazole-4-carboxylate (2.5 g, 11.36 mmol) was dissolved in a mixed solvent of THF and methanol (9:1, v/v/v), and 1 M aqueous lithium hydroxide (22.73 mL, 22.73 mmol) was slowly added. The reaction mixture was stirred at room temperature for 1 h. The reaction mixture was diluted with water and the pH was adjusted with dilute hydrochloric acid to 2. The precipitate was filtered and dried to give 2-bromoxazole-4-carboxylic acid (1.1 g). The filtrate was extracted three times with ethyl acetate, the organic phases were combined, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give 2-bromoxazole-4-carboxylic acid (0.85 g). The total yield was 88%. Mass spectrometry analysis showed m/z [M+H]+ of 192.0.
