[CH3:1][C:2]1[O:3][C:4]2[C:13]3[C:12](=[O:14])[CH2:11][CH2:10][C:9]=3[CH:8]=[CH:7][C:5]=2[N:6]=1.[CH3:15][C:16]([CH3:18])=O.IC#N>O1CCCC1>[CH3:1][C:2]1[O:3][C:4]2[C:13]3[C:12](=[O:14])[C:11](=[C:16]([CH3:18])[CH3:15])[CH2:10][C:9]=3[CH:8]=[CH:7][C:5]=2[N:6]=12-Methyl-6,7-dihydro-8H-indeno[5,4-d][1,3]oxazol-8-one (1.87 g, 10.0 mmol), acetone (3.68 mL, 50.0 mmol) and ICN Alumina B (manufactured by ICN, Akt.1, 20 g) were suspended in tetrahydrofuran (50 mL), and the mixture was stirred at 50° C. for 9 hr. Acetone (3.68 mL, 50.0 mmol) was added, and the mixture was further stirred for 12 hr. The reaction solution was filtered, and the filtrate was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate/hexane=10/90→50/50) to give the title compound (742 mg, yield 33%).
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