Lithiation with n-BuLi occurs selectively at the 2-position, giving e.g. on carboxylation, 3-bromothiophene-2-carboxylic acid in good yield: Synthesis, 327 (1980). With 2 eq. of n-BuLi the dilithio-derivative is obtained, providing a useful route to 2,3-disubstituted thiophenes: Synthesis, 545 (1972).
Metallation with LDA at low temperature results, not in the expected 5-lithio-derivative, but in rearrangement to 2,4-dibromo-5-lithiothiophene, an example of the "base-catalyzed halogen dance": Synthesis, 771 (1989).
