On treatment with Mg: J. Org. Chem., 49, 4518 (1984), or n-BuLi: Tetrahedron, 48, 4379 (1992), benzyne is generated, which undergoes [4+2] cycloadditions with furans or pyrroles.
Whereas n-BuLi effects bromine-metal exchange, lithiation with LDA at -75o results in deprotonation ortho to F; subsequent reaction with electrophiles provides access to mixed dihalo derivatives such as 3-bromo-2-fluorobenzoic acid: Tetrahedron Lett., 36, 881 (1995). Improved yields are obtained by the use of lithium 2,2,6,6-tetramethylpiperidide (LTMP) as base: Tetrahedron Lett., 37, 6551 (1996).
