General procedure for the synthesis of methyl 3-oxocyclopentanecarboxylate from methanol and 3-oxo-1-cyclopentanecarboxylic acid: 3-oxocyclopentane-1-carboxylic acid (10.0 g, 78.13 mmol, 1.0 eq.) was dissolved in methanol (100 ml) and the solution was cooled to 0 °C. Subsequently, concentrated sulfuric acid (2 mL) was slowly added and the reaction mixture was heated to 80 °C and maintained for 6 hours. The progress of the reaction was monitored by thin layer chromatography (TLC) and after confirming the complete consumption of the feedstock, the solvent was removed by evaporation under reduced pressure. The crude product obtained was quenched with water (100 mL) and subsequently extracted with ethyl acetate (2 x 100 mL). The organic phases were combined and washed sequentially with saturated sodium bicarbonate solution (1 x 100 mL) and distilled water (1 x 100 mL). The organic layer was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford the title product methyl 3-oxocyclopentanecarboxylate as a colorless liquid (10.0 g, 91.0% yield). The product was analyzed by LC-MS showing a UV inactive compound with a mass spectrometry calculated value of [M+H]+ of 142.06 and a measured value of [M+H2O]+ of 159.96.1H NMR (400 MHz, CDCl3) data were as follows: δ 3.73 (s, 3H), 3.17-3.09 (m, 1H), 2.55-2.24 (m, 4H). 2.21-2.04 (m, 2H).
