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DOI: 10.1055/sos-SD-012-00657

Grimmett, M. R.Science of Synthesis, (200212599.

N-Alkylbenzimidazoles have lower melting and boiling points than the unsubstituted derivatives because N-substitution decreases intermolecular hydrogen bonding. Although methyl and methylene groups do not easily take part in carbanion-type reactions, such as those of toluene, metalation can occur at NCH2 or NMe in some circumstances. When 1-[(phenylsulfanyl)methyl]-1H-benzimidazole is treated with butyllithium at low temperatures, the initial metalation site is C2. As the temperature is increased, however, a rather unstable product of lithiation at the N-methylene group results. Such a carbanion is readily trapped by weak electrophiles. If the 2-position is blocked, or if the corresponding sulfoxide or sulfone substrates are involved, exclusive exocyclic lithiation occurs.[‌347‌] 2-Substituted 1-(benzotriazolylmethyl)benzimidazoles are even more readily lithiated at the α-carbon.[‌350‌]