Synthesis Of Poly(Ethylene Glycol) Grafted Functionalized Ionic Liquids And Their Applications In Organic Synthesis

Ionic liquids (ILs) have peculiar properties including excellent thermal stability, easy recyclability and highly designable ability. Functionalized ionic liquids (FILs), which incorporate additional functional groups as a part of the cation and/or anion, have attracted considerable attention in recent years. Poly(ethylene glycol)(PEG) have been introduced as reaction medium, supports for the immobilization of catalyst and phase transfer catalysts, because of their particular advantages such as inexpensive, nontoxic and thermally stable. In view of these excellent properties of ILs and PEG, the synthesis and application of PEG grafted FILs have been attracted the attention of researchers.Herein, a series of PEG grafted coordinated functionalized ionic liquids and PEG grafted basic functionalized ionic liquids were designed and synthesized. In addition, their applications in the organic synthesis reaction were investigated.PEG grafted diol-functionalized ionic liquid was prepared and used as a ligand for copper-catalyzed amination reaction. A series of aryl halides with different substituents could react with aqueous ammonia at100～120℃for12～48h to give the corresponding aromatic primary amines in84～98%yields. The catalyst CuI/[diol-PEG1000-DIL][PF6] could be reused for at least five times without obvious loss of catalytic activity.PEG grafted hydroxyquinoline functionalized ionic liquid was synthesized. It was firstly applied as a ligand for copper-catalyzed N-arylation reaction. A series of aryl halides with different substituents could react with nitrogen-containing heterocycles at120℃for6～48h to give the corresponding N-arylation products in36～96%yields. The catalyst Cu2O/[HQ-PEG1000-DIL][BF4] could be easily recovered and reused for at least five runs without significantly decrease of product yield.Then, it was also applied as a ligand for palladium-catalyzed Heck reaction under solvent-free conditions. A series of aryl halides with different substituents could react with olefins at100～120℃for2～24h to give the corresponding coupling products in48～98%yields. The catalytic system Pd(OAc)2/[HQ-PEGiooo-DIL][BF4] could be reused for at least five times without obvious loss of catalytic activity.PEG grafted salicylaldoxime functionalized ionic liquids were prepared and used as ligands for palladium-catalyzed Suzuki-Miyaura raction in water. A series of aryl halides with different substituents could react with aromatic boronic acids at100～120℃for12～48h to give the corresponding biphenyl compounds in83～96%yields. The catalyst Pd(OAc)2/[salox-PEG1000-DIL][BF4] could be easily recovered and reused for at least five runs with some extent decrease in its activity.PEG grafted primary amine functionalized ionic liquid was synthesized. It was used as the catalyst for the synthesis of substituted tetrahydrobenzo[b]pyrans through a three-component condensation of aromatic aldehydes, malononitrile and dimedone in86～96%yields within10～30min at100℃in water. Furthermore, the catalyst could be easily recovered and reused for at least five runs without obvious loss of catalytic activity.PEG grafted triethylamine functionalized ionic liquid was synthesized. It was used as the catalyst for the synthesis of substituted pyrano[2,3-c]pyrazoles through a four-component reaction of aromatic aldehydes, malononitrile, ethyl acetoacetate, hydrazine hydrate or phenylhydrazine in86～94%yields within10～30min at100℃in water. The catalyst could be reused for at least five times without obvious loss of catalytic activity.PEG grafted piperidine functionalized ionic liquid was prepared. It was firstly used as the catalyst for the synthesis of substituted2-amino-2-chromenes through a three-component reaction of aromatic aldehydes, malononitrile and naphthol in81～96%yields within8～40min at100℃in aqueous media. Then, it was also applied as the catalyst for the synthesis of substituted3,4-dihydropyrano[3,2-c]chromenes through a three-component reaction of aromatic aldehydes, malononitrile and4-hydroxycoumarin in85～96%yields within6～30min at100℃in aqueous media. In addition, the catalyst could be easily recovered and reused for at least five runs without obvious loss of catalytic activity and significantly decrease of product yield.PEG grafted functionalized ionic liquids, which grafted the classic ligands of organic small molecules (such as ethylene glycol,8-hydroxy quinoline, salicylaldoxime) and common organic bases (such as triethylamine, piperidine) through covalent bonding, provided a strong guarantee for efficient recycling and active maintenance of the catalyst, and thus achieved a greater degree of green reaction.