[CH3:1][O:2][C:3](=[O:20])[CH:4]([C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=1[Cl:19])N1CC(=O)CC(S)C1.CC(OC(CP(OC)(OC)=O)=O)(C)C.[H-].[Na+].ClCCl>C1COCC1>[CH3:1][O:2][C:3](=[O:20])[CH2:4][C:13]1[CH:18]=[CH:17][CH:16]=[CH:15][C:14]=1[Cl:19]The crude (2-chlorophenyl)-(3-mercapto-5-oxopiperidin-1-yl)-acetic acid methyl ester (0.36 g, 1.14 mmol) was dissolved in THF (5 mL, argon sparged) and added to a mixture of tert-butyl P,P-dimethylphosphonoacetate (0.50 g, 2.23 mmol) and 60% sodium hydride (0.075 g, 1.87 mmol) in THF (4 mL, argon sparged), at room temperature under an argon atmosphere. After 20 minutes, dichloromethane (25 mL, argon sparged) was added and the mixture was washed with water (25 mL, argon sparged). The dichloromethane solution was dried over sodium sulfate, filtered, and concentrated under reduced pressure. The remaining yellow oil was purified by column chromatography on silica gel (15 g), eluting with heptane-ethyl acetate (4:1, argon sparged) to provide 3-tert-butoxycarbonylmethylene-5-mercaptopiperidin-1-yl)-(2-chlorophenyl)-acetic acid methyl ester (0.28 g, 59% yield) as a clear gel that was kept under an argon atmosphere at low temperature to prevent oxidation to the disulfide. 1H NMR (300 MHz, CDCl3/TMS): δ=7.60-7.15 (m, 4H), 5.55 (m, 1H), 4.77 (m, 1H), 3.67 (s, 3H), 3.20-2.00 (m, 7H), 1.41 (m, 9H). 13C NMR (75 MHz, CDCl3/TMS): δ=170.63 (2×), 165.26 (2×), 151.09 (3×), 134.64, 133.11 (4×), 129.83 (5×), 127.21, 118.35 (2×), 80.32 (2×), 67.57 (5×), 57.28 (6×), 52.28, 42.49-40.14 (8×), 34.54, 28.38 (2×). HRMS (DIP-CI): Calculated for (M+H+): 412.1349. found 412.1312.
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