Cl[C:2](=[O:8])[C:3]([O:5][CH2:6][CH3:7])=[O:4].[CH:9]([O:11][CH2:12][CH3:13])=[CH2:10].C(N(CC)CC)C>C([O-])(=O)C.[Pd+2].C([O-])(=O)C>[CH2:6]([O:5][C:3](=[O:4])[C:2](=[O:8])/[CH:10]=[CH:9]/[O:11][CH2:12][CH3:13])[CH3:7]Reference: Dujardin, G; Rossignol, S.; Brown, E. Synthesis, 1998, 763-770. Add ethyl chlorooxoacetate (67 mL, 600 mmol) to a solution of palladium acetate (1.35 g, 6 mmol), ethyl vinyl ether (315 mL, 3.3 mol), and triethylamine (125 mL, 900 mmol) at ambient temperature. Heat to 55° C. for 24 hours, cool to room temperature, then partition the reaction mixture between diethyl ether and water. Concentrate under reduced pressure the organic layer to obtain (E)-4-ethoxy-2-oxo-but-3-enoic acid ethyl ester (72 g, 70%) as a brown oil. 1H NMR (400 MHz, CDCl3): δ 7.84 (d, J=13.2 Hz, 1H), 6.15 (d, J=13.2 Hz, 1H), 4.29 (q, J=7.6 Hz, 2H), 4.03 (q, J=6.8 Hz, 2H), 1.34 (m, 6H).
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