1655-07-8

1461-96-7

The general procedure for the synthesis of cis-1,2-cyclopentanedicarboxylic acid from ethyl 2-oxocyclohexanecarboxylate was as follows: bromine (112.8 g, 705.6 mmol) was slowly added dropwise to a solution of ethyl 2-oxocyclohexanecarboxylate (120 g, 705.6 mmol) dissolved in chloroform (360 ml) at 0 °C. The reaction mixture was stirred at room temperature overnight and then washed sequentially with sodium bicarbonate solution (2 x 200 ml) and brine (2 x 100 ml). The organic layer was dried over anhydrous sodium sulfate and concentrated and the resulting residue was added slowly and dropwise to a pre-cooled aqueous solution of potassium hydroxide (168 g, 3 mol) (960 ml). The reaction mixture was continued to be stirred at 0 °C for 6 h and subsequently extracted with ether. The aqueous phase was adjusted to pH 5 with 4.0 M hydrochloric acid and extracted again with ether. All organic layers were combined, washed with brine (200 ml), dried, filtered and concentrated to give a yellow oil. The oil was crystallized by mixed solvent ethyl acetate/ether to give cis-1,2-cyclopentanedicarboxylic acid as colorless crystals (70 g, 63% yield). Mass spectrum (electrospray ionization): 159 [M + H]+.