Carbon Dioxide → 3-Bromo-5-chloro-2-fluorobenzoic acid

A solution of 2-bromo-4-chloro-1-fluorobenzene (4.31 g, 20 mmol) was added dropwise to a −78° C. solution of LDA in THF (prepared from diisopropylamine (3.38 ml, 24 mmol) and n-BuLi (1.6 M, 13.1 ml, 21 mmol)). The mixture was stirred at −78° C. for 1 h, and then was transferred slowly (˜30-60 min) via cannula to a stirred −78° C. mixture of dry ice and THF (40 ml). The mixture was stirred at −78° C. for 1 h, and then was allowed to warm to rt (gas evolution). The mixture was concentrated, and was then treated with 50 ml of 1 N sodium hydroxide solution. The mixture was extracted with ethyl acetate (discarded). The aqueous layer was acidified with 1N hydrochloric acid, and then was extracted with chloroform (3×400 ml). The chloroform extract was dried over sodium sulfate, filtered, and concentrated to provide the crude title compound. The product was contaminated with a small amount of the isomeric product 2-bromo-6-chloro-3-fluorobenzoic acid. 1H NMR for title compound 3-Bromo-5-chloro-2-fluorobenzoic acid: (400 MHz, CDCl3) δ 7.93 (dd, 1H, J=2.8, 5.6 Hz), 7.79 (dd, 1H, J=2.8, 5.6 Hz) ppm.