• Lithiation at low temperatures with n-BuLi occurs ortho to F; subsequent reaction with electrophiles provides access to mixed dihalo derivatives such as 3-chloro-2-fluorobenzoic acid: Tetrahedron Lett., 36, 881 (1995). Improved yields are obtained by the use of the superbasic combination of n-BuLi and KO-t-Bu: Tetrahedron Lett., 37, 6551 (1996).