A facile synthesis of 5(6)-(chloromethyl)benzimidazoles: Replacement of a sulfonic acid functionality by chlorine

Valuable new synthetic intermediates, 5(6)-(chloromethyl)benzimidazoles, were prepared by the facile elimination of sulfur dioxide under the influence of thionyl chloride from benzimidazole-5(6)-methane-sulfonic acids easily obtained from (3,4-diaminophenyl)methanesulfonic acid with formic-, or trifluoroacetic acid. Both reaction steps involved only acidic conditions, thus the synthesis of polysubstituted 5(6)-(chloromethyl)benzimidazoles incorporating base-sensitive substituents became possible.