磺酸型离子液体催化芳甲胺与邻苯二胺 “一锅”合成苯并咪唑

One-pot synthesis of benzimidazoles via benzylamine and o-phenylenediamine catalyzed by sulfonic acidic ionic liquid

摘要:

以磺酸型离子液体1-甲基-3-（3-磺丙基）咪唑盐酸盐（[MIMPs]Cl）为催化剂，催化芳甲胺与1,2-苯二胺“一锅”好氧氧化缩合，合成相应的苯并咪唑，并通过1H NMR对产物的结构进行了表征。首先，以苄胺与邻苯二胺合成2-苯基苯并咪唑为模型反应，筛选出离子液体催化剂并优化了反应条件，即：基准底物量25 mol%的离子液体[MIMPs]Cl为催化剂，0.1 MPa氧气作氧化剂，N,N-二甲基甲酰胺为溶剂，苄胺与邻苯二胺的投料摩尔比为2.5:1，反应温度100 ℃，反应时间20 h。在该条件下2-苯基苯并咪唑的收率达到91.3%。然后，将该方法用于取代的其它底物，也取得较好的结果，表明其底物适用性广泛。该方法以分子氧为唯一氧化剂，无过渡金属存在，因而对环境友好，适合于药物中间体的合成。

Abstract:

The ionic liquid 1-methyl-3-(3-sulfopropyl)imidazolium chloride ([MIMPs]Cl) as a catalyst demonstrates high efficiency in the one-pot aerobic oxidative condensation of arylmethylamines with 1,2-phenylenediamines to give benzimidazoles. The products were characterized by 1H NMR. First, the condensation of benzylamine with o-phenylenediamine to give 2-phenylbenzimidazole was used as a model reaction to screen the catalysts and optimize the reaction conditions, which were found to be [MIMPs]Cl with 25 mol% of basic substrate as catalyst, oxygen of 0.1 MPa as oxidant, dimethylformamide (DMF) as solvent, benzylamine to o-phenylenediamine molar ratio of 2.5:1, reaction temperature of 100 ℃, and reaction time of 20 h. Under the optimal conditions, the yield of 2-phenylbenzimidazole reached 92%. Then, the method was applied to other substituted substrates and good to excellent results were obtained, indicating its broad substrate tolerance. This strategy is benign to the environment and suitable for the synthesis of pharmaceutical intermediates due to its advantage of using molecular oxygen as the oxidant under metal-free conditions.