Scandium sulfonates

Scandium triflate and lanthanide triflates also catalyze alkylation by secondary methane-sulfonates. ... 

T. Akiyama, J. Iwai, Scandium Trifluoromethane-sulfonate-Catalyzed Chemoselective Allylation Reactions of Carbonyl Compounds with Tetraallylgermane in Aqueous Media Tetrahedron Lett. 1997,38, 853-856. 

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

Keimg et al. describes the optimization of 2-imino-piperazines using Lewis acids to catalyze the multicomponent a-amino amidine synthesis to make piperazines 39 (Scheme 6) [26]. A, Af -(jimethylethylenediamine 36 was used with an aldehyde 37 and isocyanide 38 in methanol with scandium (III) trifluoromethane sulfonate (Sc(OTf)3) as a catalyst to obtain the piperazine 39 in 57% yield. 

Aggarwal VK, Vennall GP, Davey PN, Newman C (1998) Scandium trifluoromethane-sulfonate, an efficient catalyst for the intermolecular carbonyl-ene reaction and the intramolecular cyclization of citronellal. Tetrahedron Lett 39 1997-2000... 

Kitazume and Zulfiqar have investigated the Claisen rearrangement of several aromatic allyl ethers in ionic Hquids, catalyzed by scandium(III) trifluoromethane-sulfonate [72]. The reaction initially gave the 2-aUylphenol but this reacted further to give 2-methyl-2,3-dihydrobenzo[b]furan (Scheme 5.1-41). The yields in this reaction were highly dependant on the ionic liquid chosen, with [EDBU][OTf giving the best yields (e.g., 91 % for R = 6-CH3). Reactions in [BMIMjlBFJ and [BMIM][PF j gave low yields (9-12 %). 

Scandium complexes readily with 8-hydroxyquinolinate ion. Many years ago, Sc(hq)3-Hhq, which was obtained from aqueous solution, was described,97 and this compound does not lose Hhq cleanly on heating but does so in benzene solution.98 However, it has been stated that the solid deposited at about pH 7 is in fact Sc(hq)3." More recently, stability constant values have been determined for the Sc3+/hq-/50% aqueous dioxane system and the corresponding 2-methyl-8-hydroxyquinoline system.100 Chinese workers, who are showing some interest in spectrophotometric analysis, have detected Sc3+ on the microgram scale by fluorometry using -5-sulfonate and cetyltrimethylammonium bromide as an extractant... 

Cyclocondensations of NADH analogues with / ara-benzoquinone are described in [368, 369]. For example, upon addition of dihydropyridine 338 to an acetonitrile solution of 339 in the presence of scandium trifluoromethane-sulfonate, the cycloaddition reaction occurs efficiently at room temperature, yielding cycloadduct 340 [368] (Scheme 3.113). This reaction passes via formation of a complex between azine and scandium trifluoromethanesulfonate. 

Against this background it is important that—quite fitting in this still new millennium— the first catalytic Friedel-Crafts acylations of (still relatively electron-rich) aromatic compounds were reported (Figure 5.35). Trifluoromethane sulfonates ( triflates ) of rare-earth metals, e. g., scandium(III)triflate, accomplish Friedel-Crafts acylations with amounts of as little as 1 mole percent. Something similar is true of the tris(trifluoromethanesulfonyl)-methides ( triflides ) of rare-earth metals. Unlike conventional Lewis acids, the cited rare-earth metal salts can form 1 1 complexes with the ketone produced, but these are so unstable that the Lewis acid can re-enter the reaction. Whether this works analogously for the third catalytic system of Figure 5.35 is unclear. 

Another variation on this theme is the use of a scandium salt of a hydrophobic polystyrene-supported sulfonic acid (PS-S03H) as an effective heterogeneous Lewis acid catalyst in aqueous media [149]. 

Grey anhydrous scandium triflate, [Sc(03SCF3)3] (triflate = trifluoromethane sulfonate), has been obtained by dehydration of the hydrate at 190 200 °C the hydrated salt was itself obtained from the reaction of hydrated scandium chloride and dilute triflic acid. [Sc(03SCF3)3], in which triflate is believed to act as a bidentate ligand (similar to perchlorate in 80(004)3), is not isomorphous with the lanthanide analogues. 

Kobayashi, S., Moriwaki, M., and Hachiya, I. 1995. The catalytic Fries rearrangement of acyloxy naphthalenes using scandium trifluoromethane-sulfonate as catalyst. /. Chem, Soc., Chem. Commun. 1527-1528. 

The cyclization of a variety of substituted anilines 271 with ketones 274 in the presence of scandium trifluoromethane sulfonate under MWI at 150 oC produced 2,2,4-substituted 1,2-dihydroquinolines 275 within 50 min in 30-79% yields. Under conventional conditions at room temperature for about 2-6 h, the yields were 59-98% (Scheme 57) (02TL3907). 

Lim et al. used a palladium complex for the cationic polymerization of TH F and the ROMP of NB [10]. The same group also showed that even condensation and chain polymerization could be performed simultaneously in one step (Scheme 11.45). This was achieved by the use of unimolecular compounds which can simultaneously act both as an initiator for chain polymerization, and as an end-capper for condensation polymerization. The method provides a simple means of combining NMRP with a condensation polymerization to yield interesting and useful block copolymers [207]. Another interesting new system for the combination of chain (AROP of CL) and step (dehydration polycondensation) polymerizations for polyester-based new material, in which scandium trifluoromethane sulfonate catalyzed both polymerization modes, was reported by Takasu et al. (Scheme 11.46) [208]. 

Catalytic systems comprising of sulfonated calix[n]arenes with alkyl group at the lower rim (n = 4, 6) and scandium inflate were used for the Mukaiyama aldol addition (Scheme 4.14). It was established that cahxarenes stabilized labile silyl enol ester and allowed reaction to be carried out in water [66]. 

MCSc(OTf)3] = Microencapsulated scandium trifluoro methane sulfonate... 

Partial hydrolysis of the aqua ion produces a bridged dimeric species, the [(H20)5Sc(0H)2Sc(H20)5]" + ion, which has been found in three salts, [(H20)5Sc(/u.-0H)2Sc(H20)s] X4 2H2O (X = Cl, Br), and also a benzene sulfonate [(H20)5Sc(/x-0H)2Sc(H20)5] (C6H5S03)4-4H20. In view of the tendency of many of the hydrated lanthanide halides to contain coordinated halide ions, the chlorides in particular, the absence of halide from the coordination sphere of scandium in these compounds is remarkable. 

Fe -montmorillonite [4], scandium triflate [Sc(OTf)3] [5], polystyrene sulfonate [6], and acidic styrol resin (DOOl) [7] in the presence or absence of solvent(s) at room temperature. 

A supported scandium catalyst prepared fi-om sulfonated polystyrene resin was found to be an effective catalyst for Mukaiyama aldol reactions in water, the use of this solvent being crucial for the reaction. The catalyst was easily recovered by a simple filtration and reused without any loss of catalytic activity (Scheme 8.7). Other similar work... 

A nanostructured scandium-containing polymer was also successfully used in the condensation of aldehydes, aromatic amines, and silyl enol ethers to give the corresponding /3-aminoketones, but the observed diastereoselectivities were moderate. Cai and coworkers reported the use of sulfonated amino acids as efficient Bronsted catalysts in direct diastereo-and regioselective Mannich reactions in water. ... 

Preparative Methods scandium triflate is commercially available. On the other hand, it can also be prepared from the corresponding oxide (SC2O3) and aqueous trifluoromethane-sulfonic acid (TfOH). After filtration and concentration of the clear aqueous solution in vacuo, the resulting hydrated salt is dried in vacuo (<1 mmHg) at 200 °C for 40 h to afford the anhydrous trifiate, which is stored over P2O5. 

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. 

One more example is related to the Unalool oxidation with hydrogen peroxide using a [Ln(OH)(H20)(naphthalenedisulfonate)], where Ln=Nd, Pr, La [104], though the nature of the active sites is not quite clear, since the MOF contains no transition metal ions, like Ti, Fe, Co, and so on. Similarly, oxidation of methylphenylsulfide to sulfoxide and sulfone with H O is catalyzed by scandium ions in a [Sc2(bdc)3] MOF [105]. Among other oxidation reactions, the use of a Cu-MOF ([Cu3(btc)J) in the conversion of phenols to higher phenols deserves attention and the nature of activity is not so elusive [106]. 

Catalytic amounts of scandium triflate [Sc(OTf)3] were found to greatly increase the rate of oxidation of sulfides by 60% H2O2 [30] The reaction is run at room temperature in methylene chloride containing 10% ethanol. The reaction shows quite a high selectivity for sulfoxide with sulfones being formed in only 2-4%. 

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