3-Hydroxyanthranilic Acid → 2-Phenylbenzoxazole-4-carboxylic acid

Participants

Reaction Steps

To a suspension of 3-hydroxyanthranilic acid (0.300 g, 1.96 mmol) in toluene (10 mL) was added benzoyl chloride (0.830 g, 5.90 mmol) followed by pyridine (0.545 g, 6.92 mmol) at room temperature. The resulting mixture was stirred at room temperature for 30 min then heated to 80° C. for 1 hr. After this time the reaction was cooled and poured into a mixture of ethyl acetate (50 mL) and 5% aqueous hydrochloric acid (50 mL). Subsequent separation of the layers, drying the organic over MgSO4 and filtration afforded an orange solution. This solution was concentrated to an orange solid which was directly re-dissolved in xylenes (20 mL) and the solution treated with p-toluenesulfonic acid (0.800 g, 4.20 mmol). The reaction mixture was then heated to reflux for 6 hrs. After this time the reaction was cooled and poured into water (50 mL), the organic layer separated then washed with water (3×50 mL). The organic was dried over MgSO4, filtered and concentrated to an orange/brown solid. Re-crystallization of this solid from ethyl acetate afforded 0.412 g (88% yield) of 2-phenylbenzoxazole-4-carboxylic acid as a light yellow solid: 1H NMR (300 MHz, CD3OD) δ 11.58 (br s, 1H), 8.30 (m, 2H), 8.17 (dd, J=7.8, 0.8 Hz, 1H), 7.83 (dd, J=8.2, 0.8 Hz, 1H), 7.69-7.45 (m, 4H); MS (APCI) m/z 240 [M+H]+.

Provenance & Evidence