[OH:1][C:2]1[CH:11]=[C:10]2[C:5]([C:6]([CH3:17])=[C:7]([CH2:13][C:14]([OH:16])=[O:15])[C:8](=[O:12])[O:9]2)=[CH:4][CH:3]=1.S(=O)(=O)(O)O.[CH2:23](O)[CH3:24]>C(OCC)(=O)C>[OH:1][C:2]1[CH:11]=[C:10]2[C:5]([C:6]([CH3:17])=[C:7]([CH2:13][C:14]([O:16][CH2:23][CH3:24])=[O:15])[C:8](=[O:12])[O:9]2)=[CH:4][CH:3]=17-Hydroxy-4-methylcoumarin-3-acetic acid (1) (1 gm, 4.3 mmol) was suspended in anhydrous ethanol (15 mL), concentrated sulfuric acid (1.5 mL) was added and the mixture was heated at reflux for 1 hour. The reaction mixture was cooled to room temperature, diluted with ethyl acetate (100 mL), washed with 5% NaHCO3 (5×50 mL), water (2×50 mL), saturated NaCl (2×50 mL) dried with sodium sulfate, filtered and the filtrate was evaporated under reduced pressure to give 1.04 gm (4.0 mmol, 92% yield of 2 as a white solid. 1H NMR (CDCl3 /DMSO-d6): 1.19 (3H,t), 2.29 (3H,s), 3.57 (2H,s), 4.06 (2H,q), 6.65 (1H,d), 6.73 (1H,dd), 7.44 (1H,d).
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