The lithiation of 1-(phenylthiomethyl)benzimidazole and related compounds

Abstract

1-(Phenylthiomethyl)benzimidazole is lithiated initially at the 2-position and at low temperatures the 2-lithio derivative reacts with active electrophiles to form 2-substituted products. At higher temperatures rearrangement occurs to a rather unstable methylene-lithiated isomer, which can be trapped by weaker electrophiles. Lithiation can be directed exclusively to the methylene group by: (a) using the corresponding sulphoxide or sulphone, or (b) blocking the 2-position with a t-butyl or phenyl (not methyl) group.