[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.O.O.[OH-].[Li+].Cl>COC(C)(C)C>[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]To a mixture of 200 mg of 2, 3-dihydro-7-methyl-2-(1-methylethyl)-4H,5H-pyrano[4,3-b]pyran-4,5-dione and 10 ml of water, 200 mg of lithium hydroxide monohydrate were added and stirred at room temperature for 1 hour. After that, methylt-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 178 mg of 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone.
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