C([O:3][C:4]([CH:6]1[CH2:10][CH:9]=[C:8]([CH3:11])[CH2:7]1)=[O:5])C.[OH-].[Na+]>CO>[CH3:11][C:8]1[CH2:7][CH:6]([C:4]([OH:5])=[O:3])[CH2:10][CH:9]=1A solution of the 3-Methyl-cyclopent-3-enecarboxylic acid ethyl ester (255 mg, 1.65 mmol) in MeOH (4.0 mL) and 10% aq. NaOH (3.3 mL, 8.25 mmol) was heated at 50° C. for 16 h, reaction mixture was cooled to room temperature, solvent was evaporated, diluted with water. The aqueous solution was washed with ether, and acidified with aq. 1 N HCl, extracted with ether. The ethereal solution was washed with brine and dried. Evaporation of the solvent furnished the 3-Methyl-cyclopent-3-enecarboxylic acid (200 mg, 97% yield). 1H NMR (CDCl3, 400 MHz), 5.27 (brs, 1H), 3.26-3.17 (m, 1H), 2.7-2.55 (m, 4H), 1.74 (s; 3H).
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