Boric Acid-Catalyzed Direct Condensation of Carboxylic Acids with Benzene-1,2-diamine into Benzimidazoles
作者:Nenad Maraš、Marijan Kočevar
DOI:10.1002/hlca.201100064
日期:2011.10
applicability of boric acid catalysis for the direct condensation of carboxylic acids with benzene‐1,2‐diamine to give 2‐substituted benzimidazoles was investigated. It was found that catalytic amounts (5–10 mol‐%) of boric acid efficiently promote the cyclocondensation of aliphatic carboxylic acids in refluxing toluene. In addition, the relatively neutral conditions allow the use of acid‐sensitive substrates
研究了硼酸催化用于羧酸与苯1,2-二胺直接缩合生成2取代的苯并咪唑的适用性。发现催化量(5-10 mol%)的硼酸可有效促进脂肪族羧酸在回流甲苯中的环缩合。此外,相对中性的条件允许使用酸敏感的底物,并引起某些经典方法无法观察到的特定转化和选择性。发现苯甲酸的反应性低于脂族酸,因此需要回流二甲苯以提高效率。苯硼酸由于与苯1,2-二胺缩合生成2-苯基苯并二氮杂硼酸酯而迅速消耗,因此被发现是无活性的催化剂。