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Acetic anhydride (200 μL, 218 mg, 2.13 mmol) was added dropwise to a solution of phenol 5 (315 mg, 1.64 mmol) in pyridine (1.5 mL) at room temperature. The mixture was stirred for 14 hours before the solvent was removed. The residue was purified by chromatography (10:1, hexanes:EtOAc) to afford 6 (337 mg, 88%) as a colorless oil: 1H NMR (CDCl3, 400 MHz) δ 7.95-7.90 (m, 2H), 7.11 (d, J=8.2 Hz, 1H), 5.92-5.83 (m, 1H), 5.12-5.03 (m, 2H), 3.88 (s, 3H), 3.33 (d, J=6.5 Hz, 2H), 2.29 (s, 3H); 13C NMR (CDCl3, 100 MHz) δ 169.2, 166.8, 153.0, 135.6, 132.7, 132.4, 129.4, 128.4, 123.0, 117.2, 52.6, 35.0, 21.3; IR (neat) νmax 3080, 3005, 2980, 2953, 2916, 2845, 1765, 1722, 1639, 1609, 1589, 1493, 1437, 1418, 1369, 1285, 1263, 1190, 1163, 1121 cm−1; HRMS (ESI+) m/z 235.1076 (M+H+, C13H15O4 requires m/z 235.0970).

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2. customThe residue was purified by chromatography (10:1, hexanes:EtOAc)