Ionic-liquid-supported reagents

Fig. 34 Preparation of a 4-thiazolidinone library using an ionic liquid support. Reagents and conditions a MW 100 °C, l-2h, open vessel b R"NH2, t-BuOK, MW 100-150°C, 10-20 min. R = H, Me, CH2COOH R = Pr, i-Pr, i-Bu, Bn, piperonyl, CH2CH(OMe)2, CH2CH CH2 R" = Pr, Bu, Bn, or cyclic derivatives as piperonyl, piperidine, pyrrolidine,...

Fig. 36 Synthesis of a polysubstituted pyran on ionic liquid support. Reagents and conditions a ethyl acetoacetate, MW 200 W, reflux, 10 min b arylidenemalononitriles, pyridine, MeCN, MW 200 W, reflux, 15-20 min c NaOMe, MeOH, rt, 6h...

Fig. 35 Preparation of 2-thioxo tetrahydropyrimidin-4-(lif)-ones on ionic liquid support. Reagents and conditions a R N = C = S, MeCN, rt, 18 h b Et2NH, MW, 120 °C, 15-45 min. R = Pr, i-PrCH2, PhCH2 R = Me, Bu...

Figure 5.4 shows several examples of ionic-liquid-supported (also called ion-supported) hypervalent iodlne(III) reagents [93], Ion-supported (diacetoxyiodo)arenes 98-100 are prepared by the peracetic oxidation of appropriate ion-supported aryl iodides [93-95], The ion-supported tosylates 101 and 102 are made by treatment of the appropriate acetates with toluenesulfonic acid in acetonitrile [95,96] and the ion-supported iodosylbenzenes 103 and 104 are prepared by treatment of appropriate diacetates with sodium hydroxide in water [93], Ion-supported derivatives 98-104 are thermally stable solids or viscous liquids that can be used as efficient recyclable hypervalent iodine(III) reagents. Reactions of these reagents with organic substrates produce the corresponding ion-supported aryl iodides as by-products, which can be easily recovered from the reaction mixture either by extraction into an ionic liquid phase or by simple filtration. 

Although the iodoarene can often be recovered and used in the synthesis of At2IX [53], this process could be facilitated by the use of solid supported diaryliodonium salts. Polymer-bound reagents have, however, met with limited success in applications, possibly because of chemoselectivity problems resulting in the nucleophiles being transferred to the polymer backbone [42,54], Ionic liquid-supported Ar2lX were recently synthesized and applied in chemoselective O-arylations without the need for chromatography [55]. 

Pd(0)-catalysed hydrostannation of alkynes HC=CCMc20H has been reported to proceed cleanly with the ionic liquid-supported organotin reagents RSnBu2Cl... 

Handy and Okello prepared ionic liquid-supported stable and recyclable hypervalent iodine(III) reagents 19 and 20 (Figure 6) and used in the preparation of a-fxmctionalized ketones [8]. The by-product supported monovalent iodine could be easily separated from the product and recycled without compromising the product yield. In 2006, Zhang et al. reported an environmentally benign ionic liquid-supported iodine(III) reagent 21 (Figure 6) which was foxmd to be quite effective in the selective oxidation of primary alcohols [9]. 

FIGURE 6 Representative ionic liquid-supported I(III) reagents. 

FIGURE 1 General techniques of ionic liquid-supported s3TYthesis a) supported substrates b) supported reagents c) supported catalysts. 

Ionic Liquid-Supported Hypervalent Iodine Reagent... 

C. Zhu, A. Yoshimura, Y. Wei, V.N. Nemykin, V.V. Zhdankin, Facile preparation and reactivity of bifunctional ionic liquid-supported hypervalent iodine reagent a convenient recyclable reagent for catalytic oxidation. Tetrahedron Lett. 53 (2012) 1438-1444. 

N. LouaisU, RD. Pham, F. Boeda, D. Faye, A.S. Castanet, S. Legoupy, Ionic liquid supported organotin reagents green tools for Stille crosscoupling reactions with brominated substrates, Eur. J. Org. Chem. (2011) 143-149. 

J. Vitz, D.H. Mac, S. Legoupy, Ionic liquid supported tin reagents for Stille cross coupling reactions. Green Chem. 9 (2007) 431-433. 

The application of modem solid-phase chemistry to metal catalyzed cross coupling reaction (including the Stille coupling) has been the subject of a very recent review by Testero and Matta. Ionic liquid supported tin reagents have also been developed." ... 

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. 

The microwave-assisted thionation of amides has been studied by Ley and coworkers using a polymer-supported thionating reagent [115]. This polymer-supported amino thiophosphate serves as a convenient substitute for its homogeneous analogue in the microwave-induced rapid conversion of amides to thioamides. Under microwave conditions, the reaction is complete within 15 min, as opposed to 30 h by conventional reflux in toluene (Scheme 7.95). The reaction has been studied for a range of secondary and tertiary amides and GC-MS monitoring showed that it proceeded almost quantitatively. More importantly, this work was the first incidence of the use of the ionic liquid l-ethyl-3-methylimidazolium hexafluorophosphate... 

Using day supported ammonium nitrate (dayan), selective deprotection of methoxyphenyl methyl (MPM) ether has been achieved recently using microwave irradiation in solvent-free conditions (Scheme 6.15) [56]. The same reagent has been used for the cleavage of tetrahydropyranyl (THP) ethers. A similar selective preparation and deavage of THP ethers has been achieved under microwave irradiation catalyzed by iodine [57] or neat reaction in an ionic liquid [28],... 

Organic Synthesis Using Microwaves and Supported Reagents 6.2.7.6 Solvent-free Synthesis of Ionic Liquids... 

Various solid-supported perruthenate reagents have been designed for the oxidation of alcohols.Solid-supported NMO has also been used. A number of perruthenate systems employing O2 as the terminal oxidant have also been reported. The use of ionic liquids based upon substituted imidazolium cations as alternative solvent media for the selective oxidation of alcohols to aldehydes and ketones has also been investigated. ... 

Figure 2.3-1 Substrate interactions with (I to r) solid-supported reagent, polymer gel supported reagent, task-specific ionic liquid.

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