[OH:1][C:2]1[CH:11]=[CH:10][C:5]2[CH2:6][O:7][B:8]([OH:9])[C:4]=2[CH:3]=1.[H-].[Na+].Br[C:15]([CH3:22])([CH3:21])[C:16]([O:18][CH2:19][CH3:20])=[O:17].Cl>CN(C=O)C>[CH2:19]([O:18][C:16](=[O:17])[C:15]([O:1][C:2]1[CH:11]=[CH:10][C:5]2[CH2:6][O:7][B:8]([OH:9])[C:4]=2[CH:3]=1)([CH3:22])[CH3:21])[CH3:20]
H181 (150 mg, 1.0 mmol) was dissolved in DMF (7.0 mL) and cooled to 0° C. with ice bath. To this solution under nitrogen were added in sequence NaH (60% in mineral oil, 160 mg, 4.0 mmol) and ethyl 2-bromo-2-methylpropanoate (0.59 mL, 4.0 mmol). The reaction mixture was stirred for 1 d then treated with 1.0 M HCl (10.0 mL). After extraction with ethyl acetate, the organic phase was washed with water and brine, and dried over anhydrous Na2SO4. The residue after rotary evaporation was purified by column chromatography over silica gel to give the title compound (161 mg, 61% yield). 1H NMR (300 MHz, CDCl3): δ 7.23 (d, J=8.1 Hz, 1H), 7.16 (d, J=2.4 Hz, 1H), 7.04 (dd, J=8.4 & 2.7 Hz, 1H), 5.04 (s, 2H), 4.25 (q, J=6.9 Hz, 2H), 1.60 (s, 6H) and 1.26 (t, J=7.2 Hz, 3H) ppm; Mp: 63-66° C.
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