Green Synthesis of 2-Oxazolidinones by an Efficient and Recyclable CuBr/Ionic Liquid System via CO2, Propargylic Alcohols, and 2-Aminoethanols

Chao Bu,Francis Verpoort,Yongxing Zhang,Heriberto Díaz Velázquez,Minchen Du,Ye Yuan,Somboon Chaemchuen,Jia Hu,Cheng Chen,Yanyan Gong

doi:10.3390/catal11020233

Abstract

With the aim of profitable conversion of carbon dioxide (CO2) in an efficient, economical, and sustainable manner, we developed a CuBr/ionic liquid (1-butyl-3-methylimidazolium acetate) catalytic system that could efficiently catalyze the three-component reactions of propargylic alcohols, 2-aminoethanols, and CO2 to produce 2-oxazolidinones and α-hydroxy ketones. Remarkably, this catalytic system employed lower metal loading (0.0125–0.5 mol%) but exhibited the highest turnover number (2960) ever reported, demonstrating its excellent activity and sustainability. Moreover, our catalytic system could efficiently work under 1 atm of CO2 pressure and recycle among the metal-catalyzed systems.

Highlights

Carbon dioxide (CO2), as a potential inducement for the greenhouse effect, has caught great attention from governments and scientific institutions [1,2]
The strategy of CO2 capture and utilization (CCU) came up, which aimed at the profitable conversion rather than the unhelpful storage after CO2 was captured [17,18,19,20,21,22,23,24]
According to the previous literature, activation of hydroxyl groups in propargylic alcohols is the initial step of the three-component reaction, which could be monitored by the shape and chemical shift of the hydroxyl signal in 1H NMR [55,59,60]

Summary

Introduction

Carbon dioxide (CO2), as a potential inducement for the greenhouse effect, has caught great attention from governments and scientific institutions [1,2]. An optimal CuBr/1butyl-3-methylimidazolium acetate ([C4C1im][OAc]) catalytic system was obtained This system proved to inherit the merits from both ILs and metal-catalyzed systems, which could efficiently promote the reaction under 1 atm of CO2 pressure with a lowermost metal loading in the absence of any ligands, bases, and additives. It is worth noting that 0.5 mol% is the lowest metal loading ever reported among the metal-catalyzed systems, even the generally more active Ag catalysts could not reach this level This is the first reported metal-catalyzed system that could efficiently work under 1 atm of CO2 pressure. An experiment under the optimal conditions but without purging the system was performed; only moderate yields could be obtained (entry 10), indicating that lower CO2 partial pressure or lower CO2 purity was unfavorable for the reaction. This is the highest TON ever reported for this threecomponent reaction (Figure S1 and Table S1, supporting information)

Activation of the Hydroxyl Group

Proposed Catalytic Mechanism

Exploration of the NHC–Cu Complexes

Characterization

Conclusions