Wang Huan, Zhao Yanfei, Zhang Fengtao, Wu Yunyan, Li Ruipeng, Xiang Junfeng, Wang Zhenpeng, Han Buxing, Liu Zhimin
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Colloid and Interface and Thermodynamics, CAS, Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun North First Street 2, 100190, Beijing, P. R. China.
University of Chinese Academy of Sciences, Beijing, 100049, P. R. China.
Angew Chem Int Ed Engl. 2020 Jul 13;59(29):11850-11855. doi: 10.1002/anie.202004002. Epub 2020 May 11.
O-heterocycles have wide applications, and their efficient and green synthesis is very interesting. Herein, we report hydrogen-bonding catalyzed ring-closing metathesis of aliphatic ethers to O-heterocycles over ionic liquid (IL) catalyst under metal- and solvent-free conditions. The IL 1-butylsulfonate-3-methylimidazolium trifluoromethanesulfonate ([SO H-BMIm][OTf]) is discovered to show outstanding performance, better than the reported catalysts. An interface effect plays an important role in mediating the reaction rate due to the immiscibility between the products and the IL catalyst, and the products can be spontaneously separated. NMR analysis and DFT calculation suggest that a pair of cation and anion of [SO H-BMIm][OTf] could form three strong H-bonds with an ether molecule, which catalyze the ether transformation via a cyclic oxonium intermediate. A series of O-heterocycles including tetrahydrofurans, tetrahydropyrans, morpholines and dioxane can be obtained from their corresponding ethers in excellent yields (e.g., >99 %). This work opens an efficient and metal-free way to produce O-heterocycles from aliphatic ethers.
O-杂环具有广泛的应用，其高效绿色合成非常有趣。在此，我们报道了在无金属和无溶剂条件下，离子液体（IL）催化剂催化脂肪醚通过氢键催化闭环复分解反应生成O-杂环。发现离子液体1-丁基磺酸根-3-甲基咪唑三氟甲磺酸盐（[SO₃H-BMIm][OTf]）表现出优异的性能，优于已报道的催化剂。由于产物与离子液体催化剂不互溶，界面效应在调节反应速率中起重要作用，产物可自发分离。核磁共振分析和密度泛函理论计算表明，[SO₃H-BMIm][OTf]的一对阳离子和阴离子可与醚分子形成三个强氢键，通过环状氧鎓中间体催化醚的转化。一系列O-杂环，包括四氢呋喃、四氢吡喃、吗啉和二氧六环，可以从它们相应的醚中以优异的产率（例如，>99%）获得。这项工作为从脂肪醚生产O-杂环开辟了一条高效且无金属的途径。
