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Hydrogen‐Bonding Catalyzed Ring‐Closing C−O/C−O Metathesis of Aliphatic Ethers over Ionic Liquid under Metal‐Free Conditions
Author(s) -
Wang Huan,
Zhao Yanfei,
Zhang Fengtao,
Wu Yunyan,
Li Ruipeng,
Xiang Junfeng,
Wang Zhenpeng,
Han Buxing,
Liu Zhimin
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202004002
Subject(s) - ionic liquid , chemistry , catalysis , trifluoromethanesulfonate , metathesis , ring closing metathesis , oxonium ion , salt metathesis reaction , ether , metal , hydrogen bond , molecule , polymer chemistry , organic chemistry , medicinal chemistry , ion , polymerization , polymer
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 3 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 3 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.