[Synthesis]
General procedure for the synthesis of (S)-(+)-2,2-dimethylcyclopropanecarboxylic acid from 2,2,2-difluorocyclopropanecarboxylic acid 2,2-difluoroethyl ester (60 g): in a 2L round-bottomed flask equipped with a stirrer, a pH meter, and a thermometer, 2,2,2-difluorocyclopropanecarboxylic acid 2,2-difluoroethyl ester (60 g), potassium hydrogen phosphate (2 mg) and water (600 mL) were added. Esterase (CLS-BC-21012, 1.5 g) was added to the reaction mixture and the reaction temperature was maintained at 40 °C. The pH of the reaction system was adjusted to 7.0 using 50% aqueous sodium bicarbonate.After the reaction was completed, the esterase was removed by filtration through filter paper, and 35% hydrochloric acid was slowly added to the filtrate to adjust the pH to 2.0.Subsequently, ethyl acetate (600 mL) was added to the mixture, and it was stirred for 15 min. The organic and aqueous phases were separated, and the organic phase was distilled to recover the solvent and low-boiling organics to afford (S)-(+)-2,2-dimethylcyclopropanecarboxylic acid (Yield: 49.1%, Purity: 99.0%, Optical purity: 99.1%). tlc Rf = 0.5 (n-hexane/ethyl acetate, 2:1). 1H NMR (CDCl3, 300MHz) δ: 1.55 ( dd, 1H, J = 7.95Hz, J = 5.42Hz), 1.19 (s, 3H), 1.16 (s, 3H), 1.13 (dd, 1H, J = 4.98Hz, J = 4.89Hz), 0.92 (dd, 1H, J = 7.98Hz, J = 4.42Hz). |