[OH:1][C:2]1[CH:10]=[CH:9][CH:8]=[C:7]2[C:3]=1[C:4](=[O:24])[N:5]([CH2:12][CH:13]([C:18]1([CH3:23])OCC[O:19]1)[C:14]([O:16][CH3:17])=[O:15])[C:6]2=[O:11].O.C1(C)C=CC(S(O)(=O)=O)=CC=1>CC(C)=O.O>[OH:1][C:2]1[CH:10]=[CH:9][CH:8]=[C:7]2[C:3]=1[C:4](=[O:24])[N:5]([CH2:12][CH:13]([C:18](=[O:19])[CH3:23])[C:14]([O:16][CH3:17])=[O:15])[C:6]2=[O:11]Methyl 3-(4-hydroxy-1,3-dioxo-1,3-dihydro-isoindol-2-yl)-2-(2-methyl-[1,3]dioxolan-2-yl)propionate (0.84 g, 2.51 mmol) was dissolved in 24 mL of a solvent mixture of acetone/water (v/v=5/1), and p-toluenesulfonic acid monohydrate (about 0.19 g) was then added to the obtained solution. The resulting mixture was refluxed at 100° C. for 2 days. After the reaction was completed, the reaction mixture was concentrated under a reduced pressure and then extracted with dichloromethane. The desired product was obtained (0.55 mg, 75%) by performing column chromatography (eluent: n-hexane/ethyl acetate=2/1).
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