C[Si]([N-][Si](C)(C)C)(C)C.[K+].[Br:11][C:12]1[CH:13]=[CH:14][C:15]2[O:19][CH2:18][C:17](=O)[C:16]=2[CH:21]=1.[Cl-].[NH4+].[C:24]([O:27][CH2:28][CH3:29])(=[O:26])[CH3:25]>O1CCCC1.C1(C)C=CC=CC=1>[CH2:28]([O:27][C:24](=[O:26])[CH2:25][C:17]1[C:16]2[CH:21]=[C:12]([Br:11])[CH:13]=[CH:14][C:15]=2[O:19][CH:18]=1)[CH3:29]
To a solution of triethyl phosphonoacetate (6 ml, 30.2 mmol) in dry tetrahydrofuran (200 ml) at -78° C. was added a solution of potassium bis(trimethylsilyl)amide in toluene (58 ml of a 0.5M solution). After stirring for 2 hours at -78° C., 5-bromobenzofuran-3-one (5.5 g, 26 mmol) was added dropwise. The resulting solution was stirred 1 hour at -78° C. and overnight at room temperature. Saturated aqueous ammonium chloride solution and ethyl acetate were added. The organic layer was separated and evaporated to dryness to give the crude title compound which was purified by column chromatography on silica using dichloromethane, followed by column chromatography on alumina using dichloromethane. 5-Bromobenzofuran-3-ylacetic acid ethyl ester was obtained as a low melting solid (4.2 g, 57%). mp 38-40° C. 1H NMR (250 MHz, CDCl3) δ 1.28 (3H, t, J=7 Hz), 3.65 (2H, d, J=1 Hz), 4.20 (2H, q, J=7 Hz), 7.36 (1H, s), 7.38 (1H, d, J=2 Hz), 7.63 (1H, s), 7.71 (1H, d, J=2 Hz).
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