Scandium polymer-supported

A partially soluble polyallylscandium triflamide ditriflate 45 was prepared and used to catalyze a three-component coupling reaction.67 An aldehyde, an aromatic amine, and an alkene were mixed in the presence of the catalyst to afford tetrahydroquinolines (equation 17). The catalyst was recovered from the reaction mixtures by precipitation with hexane and could be recycled without loss of activity. Another polymer-supported scandium catalyst was prepared by treating Nafion with scandium chloride to afford the Nafion-scandium catalyst 46.68 This catalyst was used in allylation reactions of carbonyl compounds by tetraallyltin (equation 18). It could be easily recovered by filtration and reused without appreciable loss of activity. 

Kobayashi, S. Nagayama, S. A New Methodology for Combinatorial Synthesis. Preparation of Diverse Quinoline Derivatives Using a Novel Polymer-Supported Scandium Catalyst, J. Am. Chem. Soc. 1996, 118, 8977. 

In order to increase the throughput of the system, the authors subsequently investigated the use of an alternative catalyst, polymer-supported scandium triflate (PS-Sc(OTf)2) 135. As Table 18 illustrates, compared to PS-RuC13 133, the PS-Sc(OTf)2 135 was found to be a more active catalyst toward the Strecker reaction and afforded the target a-aminonitriles in... 

Kobayashi and Nagayama [26] have reported the preparation of a library of quinoline derivatives using a novel polymer-supported scandium catalyst (Fig. 8) in a three-component coupling reaction. The scandium catalyst has the advantage of being partially soluble in the dichloromethane/acetonitrile mixtures but can be precipitated by the addition of hexanes and thus be removed quantitatively by filtration. 

Kobayashi S, Nagayama S, A new methodology for combinatorial synthesis. Preparation of diverse quinoline derivatives using a novel polymer-supported scandium catalyst, J. Am. Chem. Soc., 118 8977-8978, 1996. 

Rare earth metal triflates are recognized as a very efficient Lewis acid catalysts of several reactions including the aldol reaction, the Michael reaction, allylation, the Diels-Alder reaction, the Friedel-Crafts reaction, and glycosylation [110]. A polymer-sup-ported scandium catalyst has been developed and used for quinoline library synthesis (Sch. 8) [111], because lanthanide triflates were known to be effective in the synthesis of quinolines from A-arylimines [112,113]. This catalyst (103) was readily prepared from poly(acrylonitrile) 100 by chemical modification. A variety of combinations of aldehydes, amines, and olefins are possible in this reaction. Use of the polymer-supported catalyst has several advantages in quinoline library construction. 

The throughput of the system was subsequently doubled as a result of employing polymer-supported scandium triflate [PS-Sc(OTf)2] (79) as the Lewis acid catalyst, under the aforementioned reaction conditions. Using this approach, the authors demonstrated the generality of the technique, synthesizing a 10 x 5 array of a-aminonitriles, derived from 10 aliphatic and aromatic aldehydes and five amines. The chemoselectivity of the technique was also demonstrated using the reaction of 4-acetylbenzaldehyde (80) and 2-phenylethylamine (81) (Scheme 6.22) whereby 2-(4-acetylphenyl)-2-(phenethylamino)acetonitrile (82) was obtained, in 99.8% yield, as the sole reaction product. 

Recently, scandium triflate [Sc(OTf)3] was found to be stable in water and successful Lewis acid catalysis was carried out in both water and organic solvents [6-8]. Sc(OTf)3 coordinates to Lewis bases under equilibrium conditions, and thus activation of carbonyl compounds using a catalytic amount of the acid has been achieved [6,7]. In addition, effective activation of nitrogen-containing compounds such as imines, amino aldehydes, etc. has been performed successfully [8]. Encouraged by the characteristics and the usefulness of Sc(OTf)3 as a Lewis acid catalyst, a polymer-supported scandium catalyst was prepared. 

The unique selectivities obtained using the polymer-supported catalyst can be explained by the following equations. A catalytic amount of a scandium Lewis... 

In Sects. 1 and 2, polymer-supported scandium Lewis acids based on Nation and a polyacrylonitrile derivative were discussed. While several useful reactions... 

An early example of a Diels-Alder reaction catalyzed by a polymer-supported Lewis acid involves the use of copper-loaded polystyrene-based polymers in the reaction of furan with 2-cyanoacrylonitrile [41]. Nafion-supported scandium... 

Synthesis of a quinoline library using a polymer-supported scandium catalyst... 

Scandium triflate-catalyzed aldol reactions of silyl enol ethers with aldehyde were successfully carried out in micellar systems and encapsulating systems. While the reactions proceeded sluggishly in water alone, strong enhancement of the reactivity was observed in the presence of a small amount of a surfactant. The effect of surfactant was attributed to the stabiMzation of enol silyl ether by it. Versatile carbon-carbon bondforming reactions proceeded in water without using any organic solvents. Cross-linked Sc-containing dendrimers were also found to be effective and the catalyst can be readily recycled without any appreciable loss of catalytic activity.Aldol reaction of 1-phenyl-l-(trimethylsilyloxy) ethylene and benzaldehyde was also conducted in a gel medium of fluoroalkyl end-capped 2-acrylamido-2-methylpropanesulfonic acid polymer. A nanostmctured, polymer-supported Sc(III) catalyst (NP-Sc) functions in water at ambient temperature and can be efficiently recycled. It also affords stereoselectivities different from isotropic solution and solid-state scandium catalysts in Mukaiyama aldol and Mannich-type reactions. 

Related Reagents. Related polymer-supported scandium tri-flates, i.e. Nafion-Sc, MC Sc(OTf)3, PA-Sc-TAD, and a polymer-supported scandium that works efficiently in water. A Lewis acid-surfactant combined scandium catalyst, scandium tris(dodecylsulfate). ... 

Mg(ll), Ca(ll), and Zn(ll) Lewis Acids, Boron(lll) Lewis Acids, Al( ,Lgwis cids, Ga(lll) Lewis Acids, ln(llljrtewis Acids, Si(IV) Lewis Acids, Sh(ll) and Sn(IV) Lewis Acids, Bismuth(lll) Lewis Acids, Scandium and Yttrium Lewis cids. Lanthanide Lewis Acid, Titanium Lewis Acid, Zr(IV) and Hf(IV) Lewis Acids, llransition Metal Lewis Acids, Cu(l) anc u(ll) Lewis Acids, Ag(l) and Au(l) Lewis Acids, Polymer-supported Metal... 

Based on Mannich-type reactions of N-acryliminoacetates with silyl enol ethers, a new method for the preparation of N-acylated amino acid derivatives via nucleophilic addition to N-acrylimino ester has been developed using a polymer-supported amine and scandium catalysts (Scheme 12.5) [9]. Ethyl N-benzoyl-2-bromoglycine was used as a substrate. It could be readily converted to reactive N-acrylimino ester in situ by treatment with a base. Immobilizations of the amine and the scandium species into polymeric supports prevented loss of activity of the catalyst. The method is simple and provides a convenient method for the preparation of N-acrylated amino acid derivatives. 

Since the discovery of Sc(OTf)3 as a water-compatible Lewis acid, several immobilized scandium catalysts that work efficiently in water have been developed. Polymer-supported scandium-based Lewis acid (7) worked well in several carbon-carbon forming reactions in water (Schemes 12.67-12.69) [168]. It was suggested that the spacer could help to form hydrophobic reaction environments in water. As expected, (7) was easily recovered and reused. 

Hydrophobic polymer-supported scandium catalyst has been developed by Kobayashi, which is highly active for carbon-carbon bond-forming reactions in water. Organic reactions in water without the use of any harmful organic... 

Since the discovery of scandium triflate as a water-compatible Lewis acid, several supported scandium catalysts that work efficiently in water have been developed. Polymer-supported... 

A hydrophobic polymer-supported scandium(III) catalyst was also successfully used in the Michael reaction of unsaturated ketones with silyl enol ethers. Recently, an amphiphilic resin-supported rhodium/phosphine complex was used as catalyst in the 1,4-addition of various boronic acids to enones in water at 25°C. High yields were obtained and the catalyst was easily separated and subjected to a second and third round of reactions with no decrease in activity. ... 

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