Polymer scandium catalyst

It was also found that MC Sc(OTf)3 was effective for the activation of carbonyl compounds. The polymer scandium catalysts such as Nafion-Sc, polyallylscan-... 

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. 

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. 

The use of solid supported, recyclable catalysts, is a well-assessed technique in classic organic chemistry, and many exhaustive reviews dealing with this subject are available [105, 115]. The use of solid supported catalysts for library synthesis in solution has also been reported. Among others, Kobayashi et al. presented the use of a new supported scandium catalyst for 3CC reactions leading to solution libraries of amino ketones, esters, and nitriles (24-member model discrete library) [116], or to quinolines (15-member model discrete library) [117], and Jang [118] presented a polymer bound Pd-catalyzed Suzuki coupling of organoboron compounds with halides and triflates. This area was also briefly reviewed recently [119]. 

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. 

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... 

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). ... 

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... 

In another procedure, the preparation of the polymer-supported scandium catalyst was performed according to Scheme 8.17 [70], Polystyrene, cross-linked with divinylbenzene, was treated with 5-phenylvaleryl chloride in carbon disulfide in the presence of aluminum trichloride. The carbonyl groups were then reduced using aluminum trichloride-lithium aluminum hydride in diethyl ether to afford double spacer resin. After sulfonation (chlorosulfonic acid/acetic acid), resin was treated with scandium(III) chloride in acetonitrile at room temperature to give the polymer-supported scandium chloride. Finally, it was treated with trifluo-romethanesulfonic acid to afford the immobilized triflate. 

Alternatively, the authors have evaluated the polymer-bound scandium(III) bis (trifluoromethanesulfonate) as catalyst, and it proved to be slightly more active than the previous one. In a series of runs, the authors have re-evaluated the method and produced a library of 50 a-aminonitriles starting fi om ahphatic and aromatic aldehydes. In all runs, the reported yields were >99.6%. 

Recently, rare-earth metal complexes have attracted considerable attention as initiators for the preparation of PLA via ROP of lactides, and promising results were reported in most cases [94—100]. Group 3 members (e.g. scandium, yttrium) and lanthanides such as lutetium, ytterbium, and samarium have been frequently used to develop catalysts for the ROP of lactide. The principal objectives of applying rare-earth complexes as initiators for the preparation of PLAs were to investigate (1) how the spectator ligands would affect the polymerization dynamics (i.e., reaction kinetics, polymer composition, etc.), and (2) the relative catalytic efficiency of lanthanide(II) and (III) towards ROPs. 

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... 

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