功能化的离子液体: 手性离子液体的合成与应用

手性在化学中占有重要地位. 利用离子液体特殊的结构可调性质, 将手性引入到离子液体结构中, 可以获得具有手性的离子液体, 从而可能广泛应用于手性合成、手性分离、手性催化等领域. 汇总了至今报道的手性离子液体, 从离子液体功能化设计的角度探讨其合成方法. 针对手性离子液体可能的发展方向, 再次强调了由天然手性源设计合成离子液体遵循的三个标准.     

Synthesis and characterization of novel chiral imidazolium and pyridinium ionic liquids derived from tartaric acid and 2-oxazolidinone

Abstract

Novel chiral imidazolium and pyridinium ionic liquids based on tartaric acid and 2-oxazolidinone were designed. Symmetrical dicationic ionic liquids based on tartaric acid have been synthesized and characterized. These chiral ionic liquids were designed by employing very short and simple methods. Incorporation of alkyl halide over tartaric acid and 2-oxazolidinone is an important step. N-methyl imidazole and pyridine were used for preparation of quaternary salts. These ionic liquids have been evaluated for the asymmetric sulfide oxidation. Chiral ionic liquids based on tartaric acid showed superior chiral inducing property as compare to 2-oxazolidinone based chiral ionic liquids.     

Natural terpene derivatives as new structural task‐specific ionic liquids to enhance the enantiorecognition of acidic enantiomers on teicoplanin‐based stationary phase by high‐performance liquid chromatography

We present the specific cooperative effect of a semisynthetic glycopeptide antibiotic teicoplanin and chiral ionic liquids containing the (1R ,2S ,5R )‐(–)‐menthol moiety on the chiral recognition of enantiomers of mandelic acid, vanilmandelic acid, and phenyllactic acid. Experiments were performed chromatographically on an Astec Chirobiotic T chiral stationary phase applying the mobile phase with the addition of the chiral ionic liquids. The stereoselective binding of enantiomers to teicoplanin in presence of new chiral ionic liquids were evaluated applying thermodynamic measurements and the docking simulations. Both the experimental and theoretical methods revealed that the chiral recognition of enantiomers in the presence of new chiral ionic liquids was enthalpy driven. The changes of the teicoplanin conformation occurring upon binding of the chiral ionic liquids are responsible for the differences in the standard changes in Gibbs energy (ΔG ⁰) values obtained for complexes formed by the R and S enantiomers and teicoplanin. Docking simulations revealed the steric adjustment between the chiral ionic liquids cyclohexane ring (chair conformation) and the β‐d ‐glucosamine ring of teicoplanin and additionally hydrophobic interactions between the decanoic aliphatic chain of teicoplanin and the alkyl group of the tested salts. The obtained terpene derivatives can be considered as “structural task‐specific ionic liquids” responsible for enhancing the chiral resolution in synergistic systems with two chiral selectors.     

Recent developments on chiral ionic liquids: design, synthesis, and applications

The recent progress in chiral ionic liquids with respect to their syntheses and applications in enantioselective reactions and chiral recognition is described. In addition to the conventional chiral ionic liquids derived from chiral natural products, a library of novel chiral spiro compounds, including spiro bis(pyridinium) and spiro bis(imidazolium) salt, is also described.     

Functionalized Chiral Ionic Liquids: A New Type of Asymmetric Organocatalysts and Nonclassical Chiral Ligands

By judiciously anchoring functional groups onto chiral ionic liquids, functionalized chiral ionic liquids (FCILs) are emerging as a new type of asymmetric organocatalysts and nonclassical chiral ligands. This Focus Review highlights the applications of FCILs from the viewpoint of asymmetric catalysis. We focus mainly on the de novo designed and synthesized FCILs which likely still maintain the typical ionic liquids properties, and in a few cases relevant ionic liquid immobilized chiral catalysts are briefly discussed.     

Combinatorial synthesis of functionalized chiral and doubly chiral ionic liquids and their applications as asymmetric covalent/non-covalent bifunctional organocatalysts

A facile combinatorial strategy was developed for the construction of libraries of functionalized chiral ionic liquids (FCILs) including doubly chiral ionic liquids and bis-functional chiral ionic liquids. These FCIL libraries have the potential to be used as asymmetric catalysts or chiral ligands. As an example, novel asymmetric bifunctional catalysts were developed by simultaneously incorporating functional groups onto the cation and anion. The resultant bis-functionalized CILs showed significantly improved stereoselectivity over the mono-functionalized parent CILs.     

Synthesis of novel chiral imidazolium-based ionic liquids derived from isosorbide and their applications in asymmetric aza Diels-Alder reaction

A novel family of chiral imidazolium-based ionic liquids containing a chiral moiety and a free hydroxyl function has been designed and synthesized using isosorbide as a biorenewable substrate. These chiral ionic liquids were found to catalyze the aza Diels-Alder reaction to give good yields and moderate diastereoselectivities. Chiral ionic liquids are recycled while their efficiency is preserved.     

Symmetry Breaking in Chiral Ionic Liquids Evidenced by Vibrational Optical Activity

Ionic liquids (ILs) are receiving increasing interest for their use in synthetic laboratories and industry. Being composed of charged entities, they show a complex and widely unexplored dynamic behavior. Chiral ionic liquids (CILs) have a high potential as solvents for use in asymmetric synthesis. Chiroptical methods, owing to their sensitivity towards molecular conformation, offer unique possibilities to study the structure of these chiral ionic liquids. Raman optical activity proved particularly useful to study ionic liquids composed of amino acids and the achiral 1‐ethyl‐3‐methylimidazolium counterion. We could substantiate, supported by selected theoretical methods, that the achiral counterion adopts an overall chiral conformation in the presence of chiral amino acid ions. These findings suggest that in the design of chiral ionic liquids for asymmetric synthesis, the structure of the achiral counter ion also has to be carefully considered.     

3-Alkoxymethyl-1-(1R,2S,5R)-(−)-menthoxymethylimidazolium salts-based chiral ionic liquids

A new group of imidazolium salt-based chiral ionic liquids have been prepared and characterized. The chiral ionic liquids obtained are stable in air, in contact with water and popular organic solvents. Their physicochemical properties, single-crystal X-ray structures, antimicrobial activities, and antielectrostatic effects have been determined. The chiral ionic liquids synthesized have proven to represent not only potential new solvents in asymmetric synthesis but also effective disinfectants with antielectrostatic activity.     

手性离子液体的合成及其应用

近年来对离子液体的研究已取得了显著进展,并已在许多领域得到了广泛应用。手性离子液体(CILs)作为离子液体家族新成员,引起越来越多的兴趣。本文综述了手性离子液体的合成以及应用,并对以后的研究方向作了展望。     

Synthesis of chiral ionic liquids from natural amino acids

For the first time, chiral imidazolium ionic liquids containing one chiral carbon (10a-c) were synthesized from the natural amino acids by a simple and straightforward procedure. The characteristics of the chiral ILs are very similar to the popular ionic liquids.     

Chiral pool based synthesis of pyrrolidinium ionic liquids

Chiral ionic liquids show promising applications in various different fields. A series of pyrrolidinium-based chiral ionic liquids bearing a chiral cation, a chiral anion or both was prepared in good yields using an efficient, economic and simple pathway. The chirality was introduced using (l)-lactate and (l)-menthol derivatives. The resultant chiral compounds were characterized by both spectroscopy and polarimetry. We envision that these new chiral compounds can serve as effective reaction media and chiral catalysts for asymmetric reactions, which are presently being investigated in our lab.     

Enantioselective allylation of aldehydes catalyzed by chiral indium(III) complexes immobilized in ionic liquids

In the presence of chiral catalytic complexes prepared from In(OTf)3 and chiral PYBOX ligands, allytributylstannane reacted with aldehydes in ionic liquids to afford the corresponding homoallylic alcohols in high enantioselectivities (86-94% ee) and good yields (68-89%); the chiral catalysts immobilized in ionic liquids could be reused with comparable enantioselectivities and yields.     

(S)-Histidine: the ideal precursor for a novel family of chiral aminoacid and peptidic ionic liquids

(S)-Histidine is shown to be a powerful chiral precursor for the construction of a new series of imidazolium-containing chiral ionic liquids, in which the chiral bifunctional unit of the aminoacid remains unchanged. These ionic materials can be used as building blocks for the synthesis of peptidic ionic liquids.     

Recent progress of task‐specific ionic liquids in chiral resolution and extraction of biological samples and metal ions

Ionic liquids have been functionalized for modern applications. The functional ionic liquids are also called task‐specific ionic liquids. Various task‐specific ionic liquids with certain groups have been constructed and exploited widely in the field of separation. To take advantage of their properties in separation science, task‐specific ionic liquids are generally used in techniques such as liquid–liquid extraction, solid‐phase extraction, gas chromatography, high‐performance liquid chromatography, and capillary electrophoresis. This review mainly covers original research papers published in the last five years, and we will focus on task‐specific ionic liquids as the chiral selectors in chiral resolution and as extractant or sensor for biological samples and metal ion purification.     

Novel imidazolium chiral ionic liquids that contain a urea functionality

Nine chiral room temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a imidazolium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 1-(3-aminopropyl)imidazole and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts, which are presently being investigated in our laboratory.     

Synthesis of functionalized chiral ammonium,imidazolium, and pyridinium-based ionic liquids derived from (−)-ephedrine using solvent-free microwave activation. Applications for the asymmetric Michael addition

An efficient procedure for the synthesis of functionalized chiral ammonium, imidazolium, and pyridinium-based ionic liquids derived from (1R, 2S)-ephedrine using solvent-free microwave activation has been described. Good yields were obtained in very short reaction time. These chiral ionic liquids were used as chiral reaction media for the asymmetric Michael addition, giving good yields and moderate enantioselectivities.     

Design and synthesis of pyridinium chiral ionic liquids tethered to a urea functionality

Nine chiral room-temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a pyridinium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 2-(aminomethyl)pyridine and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts for asymmetric reactions, which are presently being investigated in our laboratory.     

S-Substituted-2-mercaptobenzthiazolium-based chiral ionic liquids: efficient organocatalysts for enantioselective sodium borohydride reductions of prochiral ketones

Novel chiral ionic liquids having chirality in their cationic part have been synthesized for evaluation of their catalytic potential as organocatalysts in sodium borohydride reduction of prochiral ketones to yield optically active secondary alcohols. The chiral ionic liquids have been synthesized from the reaction of (?)-menthol or (?)-borneol, chloroacetic acid and S-methyl/benzyl-2-mercaptobenzthiazole. The synthesized chiral ionic liquids have been characterized by ¹H, ¹³C NMR and Mass spectrometry. Moderate to excellent enantiomeric excess (ee > 99%) has been obtained in asymmetric sodium borohydride reduction of prochiral ketones using these salts as chiral catalysts.     

Chiral pyridinium-based ionic liquids containing the (1R,2S,5R)-(−)-menthyl group

A novel class of chiral pyridinium salts in which the chirality resides in the cation have been prepared and characterized. The physicochemical and anti-microbial properties have been determined. The group of prepared salts contained chiral ionic liquids and decomposable chiral pyridinium chlorides.