[O:1]=[C:2]1[CH:8](C(OC)=O)[CH2:7][C:6]2[CH:13]=[CH:14][CH:15]=[CH:16][C:5]=2[CH2:4][CH:3]1C(OC)=O.[OH-].[K+]>C(O)C>[CH:13]1[C:6]2[CH2:7][CH2:8][C:2](=[O:1])[CH2:3][CH2:4][C:5]=2[CH:16]=[CH:15][CH:14]=1The crude dimethyl 7-oxo-6,7,8,9-tetrahydro-5H-benzo[7]annulene-6,8-dicarboxylate was dissolved in 200 mL of ethanol (EtOH) and then 100 mL of 2 N KOH. The resulting mixture was refluxed at 85° C. for 17 h. After cooling to ambient temperature, the volatiles were evaporated. To the residue was added 120 mL of 2N HCl at 0° C., the crude product was extracted by EtOAc (200 mL×2). The combined extracts were washed with brine. After being dried (MgSO4), filtered, and concentrated, the residue was purified by flash column chromatography on silica gel (hexanes/EtOAc 8:1) to afford 6.6 g (57%) of 8,9-dihydro-5H-benzo[7]annulen-7(6H)-one as a white solid: mp 40-41° C.; 1H NMR (300 MHz, CDCl3) δ: 7.21 (m, 4H), 2.94-2.90 (m, 4H), 2.63-2.60 (m, 4H); LC-MS: 161 (M+H)+.
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