Br[C:2]1[CH:3]=[CH:4][C:5]2[N:6]([CH3:15])[C:7]3[C:12]([C:13]=2[CH:14]=1)=[CH:11][CH:10]=[CH:9][CH:8]=3.[Li]CCCC.CN([CH:24]=[O:25])C>C1COCC1>[CH3:15][N:6]1[C:5]2[CH:4]=[CH:3][C:2]([CH:24]=[O:25])=[CH:14][C:13]=2[C:12]2[C:7]1=[CH:8][CH:9]=[CH:10][CH:11]=2To a solution of 2b (1.8 g, 6.9 mmol) in dried THF (45 mL) was added n-BuLi (3.3 mL 8.3 mmol) at −78° C. The resulting mixture was stirred at −78° C. for 1 h and then added with dried DMF (8 mL). The reaction mixture was allowed to warm to room temperature and stirred overnight before quenched with aqueous ammonia chloride solution. Water was added and extracted with ethyl acetate three times. The combined organic phase was washed with brine and dried over anhydrous sodium sulfate. After removing the solvent, the residue was purified by silica gel chromatography using ethyl acetate and petroleum ether (EA:PE=1:4) as eluent to afford 3b (0.86 g) in 60% yield. 1H NMR (400 MHz, CDCl3) δ 9.58 (s, 1H), 7.79 (s, 1H), 7.49 (d, J=7.6 Hz, 1H), 7.41 (d, J=8.8 Hz, 1H), 7.09 (t, J=7.6 Hz), 6.90 (t, J=7.6 Hz, 1H), 6.77 (d, J=8.0 Hz, 1H), 6.61 (d, J=8.4 Hz, 1H), 3.00 (s, 3H). 13C NMR (400 MHz, CDCl3) δ 190.9, 143.2, 140.5, 127.4, 125.8, 122.7, 121.7, 119.6, 119.4, 108.3, 107.6, 28.0.
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