• Lithiation with LDA occurs mainly ortho to F; subsequent carboxylation gives 5-chloro-2-fluorobenzoic acid in moderate yield: Tetrahedron Lett., 33, 7495 (1992). The selectivity is improved by the use of the superbasic combination of n-BuLi and KO-t-Bu, and the yield is increased to 86%: Tetrahedron Lett., 37, 6551 (1996).