Selectivity control during the solid supported protic acids catalysed synthesis of 1,2-disubstituted benzimidazoles and mechanistic insight to rationalize selectivity
作者:Dinesh Kumar、Damodara N. Kommi、Rajesh Chebolu、Sanjeev K. Garg、Raj Kumar、Asit K. Chakraborti
DOI:10.1039/c2ra21994h
日期:——
Selectivity control during the formation of 1,2-disubstituted benzimidazoles has been achieved for the reaction of o-phenylenediamine with aldehydes in the presence of solid supported protic acids as catalysts and choosing an appropriate reaction medium. Perchloric acid adsorbed on silica-gel (HClO4–SiO2) was found to be the most effective catalyst system for the synthesis of 1,2-disubstituted benzimidazoles in EtOH at rt. Apart from the catalyst and solvent, the electronic and steric factors of the aldehyde and the electronic factor of the o-phenylenediamine are also significant contributory factors in dictating the selectivity. An understanding of the mechanistic course of the formation of the 1,2-disubstituted benzimidazoles has been outlined that would rationalise the origin of selectivity control under the set experimental parameters.
在形成1,2-二取代苯并咪唑的反应中,已经实现了选择性控制,该反应是对邻苯二胺与醛类在固态酸催化剂的存在下进行的,同时选择了合适的反应介质。研究发现,吸附在硅胶上的高氯酸(HClO4–SiO2)是合成1,2-二取代苯并咪唑在室温下使用乙醇的最有效催化体系。除了催化剂和溶剂之外,醛的电子和空间因素以及邻苯二胺的电子因素也是决定选择性的显著因素。对于1,2-二取代苯并咪唑的形成机制的理解也已被概述,这将有助于解释在设定实验参数下选择性控制的来源。