[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.[F-].[Cs+].CC(O)(C)C.Cl>C(OC)(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]A mixture of 108 mg of 2,3-dihydro-7-methyl-2-(1-methylethyl)-4H, 5H-pyrano[4,3-b]pyran-4,5-dione, 200 mg of cesium fluoride and 5m1 of 2-methyl-2-propanol was stirred for 2 hours under reflux-heating. 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 86 mg of 4-hydroxy-6-methyl-3-(4-methyl-2-pentenoyl)-2-pyrone.
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