[CH3:1][O:2][P:3]([O:16][CH3:17])([CH2:5][C:6]([O:8][CH2:9][C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1)=[O:7])=[O:4].[Li+].C[Si]([N-][Si](C)(C)C)(C)C.C1C(=O)N([Br:35])C(=O)C1.[Cl-].[NH4+]>C1COCC1>[CH2:9]([O:8][C:6](=[O:7])[CH:5]([Br:35])[P:3]([O:16][CH3:17])([O:2][CH3:1])=[O:4])[C:10]1[CH:15]=[CH:14][CH:13]=[CH:12][CH:11]=1
To a solution of benzyl dimethyl phosphonoacetate (1.94 g, 7.5 mmol) in THF (15 mL) cooled to −78° C. in a dry ice/isopropanol bath was added LHMDS (9.0 mL of a 1 M solution in THF, 9.0 mmol). The reaction was allowed to warm to 10° C. over 30 min, then recooled to 78° C. NBS (1.6 g, 9.0 mmol) was added as a solution in THF (20 mL), and the reaction was allowed to warm to room temperature over 18 h. Saturated ammonium chloride was added to quench any remaining base, and the reaction was concentrated to dryness. Ethyl acetate was added, and the organic layer was washed with water and brine, and dried over sodium sulfate. The crude product was obtained as a yellow oil and was subsequently purified by flash column chromatography on silica gel eluting with 30% ethyl acetate in hexanes to afford the desired product, bromo-(dimethoxy-phosphoryl)-acetic acid benzyl ester, as a pale yellow oil, 1.61 g (63%). 1H NMR (300 MHz, CDCl3): δ 7.36 (m, 5H), 5.24 (s, 2H), 4.44 (d, J=14.1 Hz, 1H), 3.83 (q, J=4.8 Hz, 6H). LC-MS m/z=417 [C11H15O5P+H]+.
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