C([O-])([O-])=O.[K+].[K+].[CH:7]1([C:12]([OH:14])=[O:13])[CH2:11][CH:10]=[CH:9][CH2:8]1.[CH2:15](Br)[C:16]1[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=1>C(#N)C>[CH:7]1([C:12]([O:14][CH2:15][C:16]2[CH:21]=[CH:20][CH:19]=[CH:18][CH:17]=2)=[O:13])[CH2:11][CH:10]=[CH:9][CH2:8]1K2CO3 (35.0 g, 255 mmol) was added to a solution of cyclopent-3-enecarboxylic acid (20.0 g, 178 mmol) in acetonitrile (500 mL) followed by addition of benzyl bromide (36.6 g, 214 mmol). The reaction mixture was stirred for 12 h at ambient temperature. The mixture was filtered and washed with acetonitrile (200 mL). The filtrate and washings were combined and concentrated to dryness. The residue was purified by flash column chromatography on silica gel (hexane/EtOAc=10:1) to afford benzyl cyclopent-3-enecarboxylate (26.5 g, 74% yield) as an oil.
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