To a methanolic (35 mL) suspension of cis-1,3-cyclopentanedicarboxylic anhydride (3.0 g, 21 mmol) was added sodium methanolate (1.2 g, 21 mmol) in batches at room temperature. After 1 h of reaction, the resulting clarified solution was evaporated, alkalized with 1 M NaOH solution and washed twice with ethyl acetate (EtOAc). Subsequently, the aqueous layer was acidified with 1 N HCl to pH about 2 and extracted with dichloromethane (CH2Cl2, 3 x 25 mL). The organic phases were combined, dried over anhydrous sodium sulfate (Na2SO4) and evaporated to afford cis-3-(methoxycarbonyl)cyclopentanecarboxylic acid (2.7 g, 75%) as a clear oil. The product was characterized by 1H NMR (400 MHz, CDCl3): δ 3.70 (s, 3H), 2.76-2.94 (m, 2H), 2.28 (dt, J = 13.3, 8.0 Hz, 1H), 2.15 (dt, J = 13.3, 9.1 Hz, 1H), 1.89-2.07 (m, 4H). The mass spectrum (APCI+) showed a m/z of 173.2 (C8H12O4, [M+H]+).
