[CH2:1]([O:3][C:4]([C:6]1[CH2:10][C:9]([O-:11])=[C:8](C(OC)=O)[C:7]=1[CH2:16][CH3:17])=[O:5])[CH3:2].[Na+].[Cl-].[K+].CC(O)=O.C([O-])(O)=O.[Na+]>C1(C)C=CC=CC=1.O>[CH2:16]([C:7]1[CH:6]([C:4]([O:3][CH2:1][CH3:2])=[O:5])[CH2:10][C:9](=[O:11])[CH:8]=1)[CH3:17]In a 5 L round bottom flask, sodium 4-(ethoxycarbonyl)-3-ethyl-2-(methoxycarbonyl)cyclopenta-1,3-dienolate (316 g, 1205 mmol, [Example #1, step E]), KCl (126 g, 1687 mmol), and AcOH (241 mL, 4218 mmol, JT Baker) in toluene (1850 mL) and water (130 mL) were heated at reflux for about 6 h. The reaction mixture was allowed to cool to ambient temperature for about 16 h. The reaction mixture was added dropwise to an aqueous solution of NaHCO3 (3.5 L, 8%). The aqueous layer was extracted with MTBE (2×1.5 L). The combined organic layers were washed with brine (1 L), dried over anhydrous MgSO4, filtered, and concd under reduced pressure. The crude material was purified by vacuum distillation (80-98° C., 0.6 mmHg) to give ethyl 2-ethyl-4-oxocyclopent-2-enecarboxylate (160.4 g, 69%): 1H NMR (400 MHz, CDCl3) δ 6.05-6.02 (m, 1H), 4.28-4.14 (m, 2H), 3.75 (m, J=0.9, 1.8, 3.8, 6.7, 1H), 2.69 (dd, J=3.1, 18.4, 1H), 2.61 (dd, J=6.9, 18.4, 1H), 2.52 (dq, J=7.4, 24.2, 1H), 2.40 (dq, J=7.4, 16.1, 1H), 1.30 (t, J=7.2, 3H), 1.21 (t, J=7.4, 3H).
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