TSIL Supports

One of the main limitations of traditional solid or soluble supports is their low loading capacity which is related to the molecular weight of these polymers. Loadings of over 1 mmol g of polymer are rarely reached. Also, these polymers are used diluted either as suspensions or in solution in some molecular solvent. Then, we should consider the loading of the suspension or the solution that will be used for the reaction to be carried out. Most of the time low loadings such as 0.1 mmol g  

The loading capacity of the TSOSs and TSILs can be easily increased by using polyfunctional cations. For example, an ammonium cation can be substituted by at most four functional substituents. These kind of multifunctional salts have been prepared [18,21] and their loading capacity is reported in Table 5.5-6. This loading capacity could even be increased by dendrimerization if necessary [10]. 

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Viewed in conjunction with the solid-like, nonvolatile nature of ionic liquids, it is apparent that TSILs can be thought of as liquid versions of solid-supported reagents. Unlike solid-supported reagents, however, TSILs possess the added advantages of kinetic mobility of the grafted functionality and an enormous operational surface area (Figure 2.3-1). It is this combination of features that makes TSILs an aspect of ionic liquids chemistry that is poised for explosive growth. 

Supported analogs of ionic liquid catalysts Task specific ionic liquids (TSIL) Telomerization in ILs... 

Wu et alP have synthesized a TSIL having 2,2,6,6-tetramethylpiper-idine-l-oxyl (TEMPO) appended to an imidazolium cation for the oxidation of alcohols to corresponding carbonyl compounds. These reactions have shown high yields similar to non-supported TEMPO, but with the additional advantage of easy separation of products. 

Pure TSILs, a New Class of Soluble Supports for Synthesis... 

Nonetheless some examples using neat TSIL turned out to be successful, such as the application of the Knoevenagel condensation on supported benzaldehyde [30], Using piperidine as a catalyst under microwave heating conditions, olefins could be... 

Indeed, BTSILs strategy turned out to be really efficient, especially in terms of kinetics compared to using pure TSILs as supports for synthesis. However, if adding an IL matrix enhanced all physical characteristics of the assembly and allowed for modulation of reactivity, it is rather difficult to separate the synthetic OS supported intermediates from the matrix without releasing them from the support. As a result, the concept of BTSIL was extended to the use of molecular solvents which could be removed after reaction under reduced pressure. 

A new strategy for the synthesis of polyhydroquinolines from task-specific ionic liquids (TSIL) as a soluble support was developed. The preparation of the polyhydroquinolines by a three-component reaction was achieved by using ionic liquid... 

Some potential applications for TSILs have been briefly highlighted in Figs. 2.3-3 and 2.3-4. Many more examples can be found throughout this book. The reader interested in catalytic applications of TSILs is referred to Chapter 5, Section 5.3 for more details. Section 5.5 describes explicitly the role of task-specific ionic liquids as new liquid supports in combinatorial syntheses. This section also provides more details on the synthetic procedures leading to the specific functionalized ionic liquids that have turned out to be particularly suitable for this purpose. While Section 5.6 expands on the role of alkoxysilyl functionalized ionic liquids for surface modification in the preparation of supported ionic liquid phase (SILP) catalysts, Section 6.3 is devoted to the synthesis of nanoparticles and nanostructures in which TSILs often play a decisive role as templates or particle stabilizing agents. 

Here we provide a comprehensive review of new task-specific ionic liquids (TSILs) and binary task-specific ionic liquids (BTSILs) as functional ionic liquids designed as alternate soluble supports for supported organic synthesis (SPOS) and combinatorial chemistry. The applications of these supports are based mainly on imida-zolium, ammonium and pyridinium salts. The versatility of the supports has been... 

TSILs used as soluble supports usually contain functionalized cations. There are several ways to incorporate functionality into an ionic stmcture. The most vyidely used method relies on the alkylation of a nucleophile such as a tertiary amine. 

Supported liquid acrylic esters have been prepared from hydroxylated imidazolium-based TSILs and used neat in (4-1-2) Diels-Alder cydoadditions. First, Handy et al. [31] used a fructose-derived ionic liquid to support acryUc acid and performed the Diels-Alder cycloaddition with several dienes induding cydopenta-and cydohexadienes and butadiene derivatives at 120 °C for 12 h in the presence of hydroquinone (Scheme 5.5-25). 

A microwave dielectric heating assisted TSIL phase synthesis [45] of 1,4-dihydropyridines, 3,4-dihydropyrimidin-2(lH)-ones, pyridines and polyhydroquinolines using a TSIL as a soluble support was described. The efficiency of the ionic liquid phase organic synthesis (loLiPOS) methodology was demonstrated by using a one-pot three-component condensation. The stmcture of the intermediates... 

A microwave-assisted hquid phase Gewald synthesis [48] of 2-aminothiophenes was developed using the TSIL, l-(2-hydroxyethyl)-3-methylimidazohum tetrafluo-roborate, [2-(OH)EMIM][BF4] as soluble support. This new synthetic method is simple and eflEcient, and the products are obtained in good to excellent yields with high purities, without the need for chromatographic purification. 

In summary, these TSILs offer several advantages over the usual supports ... 

At present the key challenges in using this type of support are the limited stability of the imidazolium cation in the presence of base and the viscosity of these TSILs, since the more they are substituted the more viscous they become. Therefore, it is difficult to handle and stir them, necessitating the use of MW for heating, for example. 

Lab on a Chip System Using a TSIL as a Soiubie Support... 

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