Synthesis of some new benzimidazole‐5(6)‐carboxylic acids

The title compounds, 1,2‐dialkyl‐benzimidazole‐5(6)‐carboxylic acids34–45were prepared at four steps; 1) preparation of mono amide derivatives1–11by the reaction of methyl 3,4‐diaminobenzoate and substituted phenyl or phenoxyacetic acid chlorides; 2) preparation of the methyl benzimidazolecarboxyl‐ates12–22, with zinc chloride and dry hydrogen chloride gas; 3) alkaline hydrolysis of the esters23–33; and 4) substitution of the imidazole ring with benzyl orp‐fluorobenzyl bromide, in alkali medium. 2‐Aryl‐benzimidazole‐5(6)‐carboxylic acids50–53were preparedviathe oxidative condensation of 3,4‐diaminobenzoic acid and aromatic aldehydes with cupric ion.