Lithiation of the unprotected acid, with 2.2 moles of s-BuLi in the presence of TMEDA, occurs at the 2-position; subsequent reaction with hexachloroethane or dibromotetrachloroethane provides access to 2-chloro-3-fluoro- and 2-bromo-3-fluorobenzoic acid respectively: Tetrahedron Lett., 36, 881 (1995); Bull. Soc. Chim. Fr., 133, 133 (1996).
