[OH-].[Na+].C[O:4][C:5]([C:7]1[C:8]2[CH:9]=[CH:10][CH2:11][O:12][C:13]=2[CH:14]=[CH:15][CH:16]=1)=[O:6]>CO.O>[O:12]1[C:13]2[CH:14]=[CH:15][CH:16]=[C:7]([C:5]([OH:6])=[O:4])[C:8]=2[CH:9]=[CH:10][CH2:11]1A solution of NaOH (7.26 mmol) in a mixture of MeOH (5.4 mL) and water (12.1 mL) is added to 2H-chromene-5-carboxylic acid methyl ester (4.84 mmol). The mixture is stirred at 55° C. for 3 h, partially concentrated in vacuo to remove MeOH and made acidic by addition of aq. HCl (1.0M). The desired carboxylic acid precipitates and is collected by filtration. 1H-NMR (DMSO-d6): δ=4.75 (bs, 2H); 5.99-6.05 (m, 1H); 6.98 (d, J=7.78 Hz, 1H); 7.19 (t, J=7.78 Hz, 1H); 7.25 (d, J=10.3 Hz, 1H); 7.40 (d, J=7.78 Hz, 1H); 13.0 (bs, 1H).
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