CC1C=CC(S(O)(=O)=O)=CC=1.O.O1[C:17]2([CH2:22][CH2:21][CH:20]([CH2:23][C:24]([O:26][CH2:27][C:28]3[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=3)=[O:25])[CH2:19][CH2:18]2)[O:16]CC1.CC(C)=O.C(=O)(O)[O-].[Na+]>O>[O:16]=[C:17]1[CH2:22][CH2:21][CH:20]([CH2:23][C:24]([O:26][CH2:27][C:28]2[CH:29]=[CH:30][CH:31]=[CH:32][CH:33]=2)=[O:25])[CH2:19][CH2:18]1
p-Toluene sulfonic acidmonohydrate (207 mg, 1.21 mmol) was added to a mixture composed of benzyl 2-(1,4-dioxaspiro[4,5]decan-8-yl)acetate (7.0 g, 24.11 mmol), acetone (220 ml), and water (10 ml) at room temperature, and the mixture was stirred at 55° C. for 15 hr. The mixture was cooled with ice and was adjusted to pH 5 by the addition of solid sodium bicarbonate. The mixture was concentrated under reduced pressure, and the residue was chromatographed on silica gel column (hexane:ethyl acetate=85:15) to give the title compound as a colorless solid (5.1 g, yield 86%).
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