[Cl:1][C:2]1[CH:3]=[CH:4][C:5]2[O:9][CH:8]([CH2:10][OH:11])[CH2:7][C:6]=2[CH:12]=1.CC1(C)N([O])C(C)(C)CCC1.[O-:24]Cl.[Na+].Cl>O.CC#N>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]2[O:9][CH:8]([C:10]([OH:24])=[O:11])[CH2:7][C:6]=2[CH:12]=1
To a solution of (5-chloro-2,3-dihydro-1-benzofuran-2-yl)methanol (2 g, 11 mmol), KHCO3 (4.32 g, 43 mmol, 4 eq) and TEMPO (20 mg, 0.13 mmol, 0.1 eq) in water (8 ml) and CH3CN (18 ml) was added NaOCl (20 ml, aq. 15%, ˜4 eq) dropwise with stirring at 0° C. and stirred for 1 hour. The mixture was diluted with water (200 ml) and adjusted to pH˜4 with hydrogen chloride (2N). After extraction with ethyl acetate (3×200 ml), the organic layers were combined, washed with brine (200 ml), dried over anhydrous sodium sulfate, filtered, and then concentrated under vacuum. The crude material was purified by silica gel chromatography using 1% methanol in dichloromethane to elute. The product-containing fractions were combined and concentrated under vacuum to afford 5-chloro-2,3-dihydro-1-benzofuran-2-carboxylic acid as a yellow solid (1.6 g, 74%). 1H NMR (300 MHz, CDCl3): δ 7.05-7.22 (m, 2H), 6.83 (d, J=8.4 Hz, 1H), 5.20-5.30 (m, 1H), 3.56-3.65 (m, 1H), 3.33-3.45 (m, 1H)
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