Trimethyl orthobeznoate → 6-Chloro-2-phenyl-benzoxazole-4-carboxylic acid

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A 25-mL, round bottomed flask equipped with a magnetic stirrer was charged with 2-amino-5-chloro-3-hydroxybenzoic acid (0.931 g, 4.96 mmol), trimethyl orthobenzoate (7.23 g, 39.7 mmol), and pyridinium p-toluenesulfonate (0.062 g, 0.248 mmol). After stirring at 90° C. for 1 h, the reaction was diluted with hexanes (30 mL) filtered, and the filter cake dried in a vacuum oven at 40° C. to afford 0.455 g (33% yield) of 6-chloro-2-phenyl-benzoxazole-4-carboxylic acid as a brown solid: 1H NMR (500 MHz, DMSO-d6) δ 8.24 (m, 3H), 7.84 (s, 1H), 7.65 (m, 3H); MS (ESI) m/z 272 (M−H).

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