Supports, functional, ionic liquid

Ionic liquid supports, functional 115 Isocyanides, PS-oxazaphospholidine 148 Isoquinolines 252 Isoxazoles 95... 

Microwave-Enhanced Synthesis Using Functional Ionic Liquid Supports. 115... 

Abstract Current microwave-assisted protocols for reaction on solid-phase and soluble supports are critically reviewed. The compatibility of commercially available polymer supports with the relatively harsh conditions of microwave heating and the possibilities for reaction monitoring are discussed. Instrmnentation available for microwave-assisted solid-phase chemistry is presented. This review also summarizes the recent applications of controlled microwave heating to sohd-phase and SPOT-chemistry, as well as to synthesis on soluble polymers, fluorous phases and functional ionic liquid supports. The presented examples indicate that the combination of microwave dielectric heating with solid- or soluble-polymer supported chemistry techniques provides significant enhancements both at the level of reaction rate and ease of purification compared to conventional procedures. 

Preparation of a 4-thiazolidinone Library Employing a Functional Ionic Liquid Support... 

These supported cycloadducts were then treated with a base (LiOH, NaOH) in a mixture of water and alcohol to give the expected free acid derivatives. However, while the latter compounds were readily recovered, the same was not true for the ionic liquid 4b, which was obtained as a dark brown liquid impure by NMR analysis. Very likely, the basic hydrolysis of the ester function caused the deprotonation of the imidazolium ring leading to a series of undesired side-reactions. Therefore, milder reaction conditions were explored to cleave the Diels-Alder product from the ionic liquid support. Handy and Okello found that the best method was the cyanide-mediated transesterification that gave the corresponding methyl esters 9-11 and allowed recover of 4b in at least 90% yield. It was also demonstrated that the recovered 4b could be used for further supported syntheses. In fact, in two subsequent mns the yields of the final ester compound were similar, indicating that the ionic liquid 4b could be efficiently recycled. 

Liu Y, Wang S-S, Liu W, Wan Q-X, Wu H-H, Gao G-H (2009) Transition-metal catalyzed carbon-carbon couplings mediated with functionalized ionic liquids, supported-ionic liquid phase, or ionic liquid media. Curr Org Chem 13 1322-1346... 

Zhang YJ, Li JH, Niu L et al (2005) Electrochemical functionalization of single-walled carbon nanotubes in large quantities at a room-temperature ionic liquid supported three-dimensional network electrode. Langmuir 21 4797-4800... 

The synthesis of P-lactams in ionic liquids, using functionalized ionic liquid as soluble supports, has been reported. p-Lactams have been isolated in elevated yields and high cis/trans ratio, according to a rather wearisome procedure and long reaction times. 

The same authors have also reported 1,3-dipolar cycloadditions using 2-hydroxy and 3-hydroxybenzaldehydes grafted on a soluble ionic liquid support [62]. New benzaldehyde-supported ionic liquids were prepared via two different routes. In the first approach the synthesis started from an N-alkylimidazole and 2-chloroethanol, thermolysis of which, followed by anion exchange to form the BF4 or PF ionic liquid, gave the desired supports. After esterification with an acid-functionalized 2-hydroxybenzaldehyde, excellent yields of the benzaldehyde-supported ionic liquids were obtained. The synthetic approach is shown in Scheme 7.13. 

Synthesis of thiazolidinones [PEG -RMIM]X ionic liquids have been used for rapid synthesis of a small library of amido 4-thiazolidinones from amine, aldehyde, and mercaptoacid components (Scheme 7.22) [74]. In an initial feasibility study, acid-functionalized benzaldehydes were first coupled to the [PEG -RMIM]X ionic liquids. Imines were formed by reaction of the supported aldehydes with primary amines. The reactions were run in open vessels. Optimum results were obtained by irradiating the reaction mixture with low power at 100 °C for 20 min. The imines were then condensed with mercaptoacids to give the desired thiazolidinones which were then cleaved from the ionic liquid support by amide formation. Microwave irradiation was again used in this cleavage step. The procedure entailed addition of a small amount of solid potassium tert-butoxide to a premixed mixture of the amine and supported thiazolidinone and microwave exposure for 10-20 min at 100 or 150 °G depending on the amine used. In another study, a series of one-... 

Song et al. [46] have used a carboxyl-functionalized ionic liquid as soluble support to synthesize a small library of 4-aminophenyl ethers via Williamson reaction and extracting with ethyl acetate in good yields (75-80%) and purities (99%). The recovered ionic liquid support was reused several times with consistent loading capacity (Scheme 5.5-30). 

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. 

In addition to the examples described above, functionalized ionic liquids have been recently introduced as microwave-compatible soluble supports [137,138]. 

Sulfonamido-l,3,4-oxadiazoles 141 Sulfonyloximes 147 Supports, functional, ionic liquid 115 Suzuki couplings 21,122 Suzuki-Miyaura reaction 164... 

Work with supported ionic liquids was extended to a cationic polymer, poly (diallyldimethylammonium chloride), which has quaternary ammonium functional groups (Fig. 16) 268). The extra-structural counter anion is Cl . The polymer was applied to simultaneously incorporate an ionic liquid and a transition-metal catalyst via a simple mixing of the components. Wilkinson s catalyst and [BMIM]PF6 were... 

The hydrophobicity of ionic liquids was found to be particularly beneficial for lipase PS-C-catalyzed transesterification of 2-hydroxymethyl-1,4-benzodioxane in the presence of vinyl acetate (277). The hydrophobic [BMIMJPFg functioned as a better promotional medium than methylene chloride and hydrophilic [BMIM]BF4, with either supported or unsupported enzyme for the catalytic transesterifications. The ionic liquid not only acted as a medium but also as a permanent host for the enzymes, so that the enzyme-ionic liquid system could be recycled several times without substantial diminution in lipase activity. 

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