C([Mg]Br)C.C(OC)(=O)/C=C/CCC(OC)=O.[C:17]([CH:22]1[CH:26]([CH:27]=[CH2:28])[CH2:25][CH2:24][C:23]1=[O:29])([O:19][CH2:20]C)=[O:18].C(OC)(=O)C=C>C1COCC1.[Cu]Cl>[CH2:27]([CH:26]1[CH2:25][CH2:24][C:23](=[O:29])[CH:22]1[C:17]([O:19][CH3:20])=[O:18])[CH3:28]A round bottom flask was charged with copper(I) chloride (0.0575 g, 0.581 mmol) and purged with N2. A solution of 1M ethylmagnesium bromide in THF (23.2 mL, 23.2 mmol) was injected and the mixture was cooled to 0° C. A solution of (E)-dimethyl hex-2-enedioate (2 g, 11.6 mmol) in anhydrous THF (10 mL) was injected over 15 minutes, and the reaction was stirred for 30 minutes at 0° C. (E)-Dimethyl hex-2-enedioate was prepared as described in Nugent, William A. and Frank W. Hobbs, Jr. “Conjugate Addition-Cyclization of a Cyanocuprate: 2-Carboethoxy-3-vinylcyclopentanone.” Organic Syntheses. Vol. 66 (1988): pp. 52-59, using methyl acrylate (100.00 mL, 1110.5 mmol), anhydrous LiBF4 (9.109 g, 97.17 mmol), and tetrakis(acetonitrile)palladium (II) tetrafluoroborate (1.332 g, 2.998 mmol). The reaction was warmed to room temperature and stirred at room temperature for 1 hour. TLC (5:1 EtOAc/Hexanes) showed disappearance of the UV-active starting material spot. The reaction was concentrated to a solid under vacuum and partitioned between DCM and saturated aqueous NH4Cl. The organic was washed with brine and dried over anhydrous Na2SO4. The reaction produced methyl 2-ethyl-5-oxocyclopentanecarboxylate (1.88 g, 11.0 mmol, 95.1% yield) as an oil. 1H NMR (CDCl3, 400 MHz) δ 3.76 (s, 3H), 2.84 (d, 1H), 2.2-2.6 (m, 4H), 1.62 (m, 1H), 1.41-1.52 (m, 2H), 0.96 (t, 3H). MS (APCI+) [M+H]: 171.0.
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