[CH3:1][C:2]1[O:11][C:10](=[O:12])[C:9]2[C:8](=[O:13])[CH2:7][CH:6]([CH:14]([CH3:16])[CH3:15])[O:5][C:4]=2[CH:3]=1.[OH-].[K+].C(OC)(C)(C)C.Cl>CO>[OH:5][C:4]1[CH:3]=[C:2]([CH3:1])[O:11][C:10](=[O:12])[C:9]=1[C:8](=[O:13])[CH:7]=[CH:6][CH:14]([CH3:15])[CH3:16]In 10 ml of methanol, 222 mg of 2, 3-dihydro-7-methyl-2-(1-methylethyl)-4H, 5H-pyrano[4,3-b]pyran-4,5-dione were dissolved, and 200 mg of potassium hydroxide were added thereto and stirred at room temperature for 1 hour. After that, methyl t-butyl ether and 3% hydrochloric acid were added to the reaction mixture. The separated organic layer was washed with saturated brine once, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give 130 mg of 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone. 1H-NMR (CDC13, TMS) δ (ppm): 1.13 (6H, d), 2.27 (3H, s), 2.60 (1 H, m), 5.93 (1H, s), 7.23 (1H, dd), 7.58 (1H, d).
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