Yield:-

Reaction Conditions:

with p-benzoquinone in 1,4-dioxane at 80;

Steps:

General Procedure A: Synthesis of 2-Substituent-1H-benzimidazole-4/5-carboxylic acids (Compounds 6-13).

General procedure: Appropriate aldehyde 3 (1.5 mmol) was added to the solution of 2,3/3,4-diaminobenzoic acid 2 (1.0 mmol) in dioxane (10 mL). 1,4-Benzoquinone was added and the solution was heated to 80 °C and stirred for about 6-9 h.Then, the solution was cooled to room temperature. The separated solid crystals were filtered, washed with ethanol and ether, dried. The products were used in the next step without further purification.

References:

Wubulikasimu, Reyila;Yang, Yanbing;Xue, Fei;Luo, Xianjin;Shao, Dongping;Li, Yuhuan;Gao, Rongmei;Ye, Weidong [Bulletin of the Korean Chemical Society,2013,vol. 34,# 8,p. 2297 - 2304]