Mono-lithiation of 2, 6-dibromopyridine by n-BuLi is complicated by deprotonation of the pyridine ring by the resulting mono-lithium species. This problem can be eliminated by a reverse addition, but this causes formation of the undesired dilithio species. However, rapid lithium-halogen exchange between 2, 6-dibromopyridine and 2, 6-dilithiopyridine produces 2-bromo-6-lithiopyridine cleanly. Thus, using reverse addition, the mono-lithiated pyridine ...
