[CH3:1]C([O-])(C)C.[K+].[CH2:7]([CH:9]1[CH2:13][C:12](=O)[CH2:11][CH:10]1[C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH3:8]>[Br-].C[P+](C1C=CC=CC=1)(C1C=CC=CC=1)C1C=CC=CC=1.C1COCC1>[CH2:7]([CH:9]1[CH2:13][C:12](=[CH2:1])[CH2:11][CH:10]1[C:15]([O:17][CH2:18][CH3:19])=[O:16])[CH3:8]A solution of KOt-Bu (3.65 g, 32.6 mmol) and methyltriphenylphosphonium bromide (11.6 g, 32.6 mmol) in THF (69.5 mL) was cooled to about −10° C. A solution of ethyl 2-ethyl-4-oxocyclopentanecarboxylate (4.00 g, 21.7 mmol) in THF (17.4 mL) was added dropwise while the temperature was kept at about 0° C. The reaction mixture was allowed to warm to ambient temperature and stirred for about 16 h. The insoluble material was removed by filtration. The filtrate was concd under reduced pressure. The resulting material was purified by silica gel (120 g) chromatography eluting with a gradient of 0-20% EtOAc in heptane to provide ethyl 2-ethyl-4-methylenecyclopentanecarboxylate (2.55 g, 64%) as a colorless liquid: 1H NMR (d-DMSO) δ 4.88-4.78 (m, 2H), 4.16-3.96 (m, 2H), 2.66-2.31 (m, 4H), 2.24-1.82 (m, 2H), 1.50 (m, 1H), 1.35-1.22 (m, 1H), 1.18 (t, 3H), 0.85 (m, 3H).
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