Br[C:2]1[CH:3]=[C:4]2[C:9](=[C:10]([Cl:12])[CH:11]=1)[O:8][CH2:7][CH2:6][C:5]2([CH3:14])[CH3:13].[Li]CCCC.CN([CH:23]=[O:24])C>C1COCC1>[Cl:12][C:10]1[CH:11]=[C:2]([CH:23]=[O:24])[CH:3]=[C:4]2[C:9]=1[O:8][CH2:7][CH2:6][C:5]2([CH3:14])[CH3:13]6-Bromo-8-chloro-4,4-dimethyl-3,4-dihydro-2H-chromene (483 mg, 1.75 mmol) in THF (12.0 mL) under N2 atmosphere was cooled to −78° C., and n-BuLi (841 μL, 2.10 mmol) was added dropwise via a syringe. The reaction mixture was stirred at −78° C. for 10 minutes and then DMF (543 μL, 7.01 mmol) was added dropwise via a syringe. The resulting mixture was allowed to warm to room temperature and wet silica gel (5.0 g/0.5 mL of water) was added. The mixture was allowed to stir at room temperature for 10 minutes before it was filtered. The silica gel was rinsed with EtOAc, and the filtrate was concentrated under vacuum. The crude residue was purified by silica gel chromatography eluting with 0-20% EtOAc/hexanes to obtain the title compound as a white solid.
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