With n-BuLi at -30 o, selective metallation occurs by exchange with one Br atom: J. Org. Chem., 16,1485 (1951). In contrast, using LDA in THF at -100 o, lithiation can be accomplished at the 4-position. Subsequent reaction with an electrophile can be followed by lithiation with n-BuLi to give 3-bromo-4,5-disubstituted pyridines: Tetrahedron Lett ., 37, 2565 (1996).