Br[C:2]1[CH:7]=[C:6]([O:8][CH2:9][CH3:10])[C:5]([F:11])=[CH:4][C:3]=1[F:12].[Li]CCCC.[B:18](OC)([O:21]C)[O:19]C>C1COCC1>[CH2:9]([O:8][C:6]1[C:5]([F:11])=[CH:4][C:3]([F:12])=[C:2]([B:18]([OH:21])[OH:19])[CH:7]=1)[CH3:10]To 97D (670 mg, 2.83 mmol) in THF (10 mL) was added n-BuLi (1.6M in hexane, 2.3 mL) at −78° C. After stirring for 15 min, trimethyl borate (0.634 mL) was introduced. The mixture was stirred from −78° C. to rt for 5 h before it was quenched by 1N HCl. It was extracted with ethyl acetate. The organic extract was washed with saturated Na2S2O3, brine and dried over MgSO4. The crude product was purified by column chromatography to give 97E (400 mg, 70% yield) as a solid.
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