Scandium triflate Sc

Kobayashi has found that scandium triflate, Sc(OTf)3,36 and lanthanide triflate, Ln(OTf)3, are stable and can be used as Lewis catalysts under aqueous conditions. Many other Lewis acids have also been reported to catalyze Diels-Alder reactions in aqueous media. For example, Engberts reported37 that the cyclization reaction in Eq. 12.7 in an aqueous solution containing 0.010 M Cu(N03)2 is 250,000 times faster than that in acetonitrile and about 1,000 times faster than that in water alone. Other salts, such as Co2+, Ni2+, and Zn2+, also catalyze the reaction, but not as effectively as Cu2+. However, water has no effect on the endo-exo selectivity for the Lewis-acid catalyzed reaction. 

Scandium triflate (Sc(OTf)3) was also found to be an effective catalyst in aldol reactions in aqueous media1131 In many cases, SdOTf)3 is more active than Yb(OTf)3, as expected from the smaller ionic radius ofSdffl). 

Varela et al. [40] obtained similar results from 2,3,4,5-tetra-O-methyl-D-galac-tono-1,6-lactone (20). The homopolymerization of this lactone, promoted by aluminum isopropoxide [Al(0 Pr)3] or scandium triflate [Sc(OTf)3], was attempted. 

Other RE(OTf)3 were also examined as catalysts in the reaction of 1 with acetic anhydride (Table 2). Catalytic amounts of all the RE(OTf)3 listed effectively mediated the acylation of 1. Among these, scandium trifluoromethanesulfonate (scandium triflate, Sc(OTf)3)[6] or Yb(OTf)3 was superior to other RE(OTf)3 and afforded the acylation product 2 quantitatively. When, on the other hand, lanthanum trifluoromethanesulfonate (lanthanum triflate, La(OTf)3) was used, the yield of 2 was relatively low. The yields shown in Table 2 may reflect the catalytic activity of respective RE(OTf)3. 

Scandium triflate (Sc(OTf)3), which is commercially available, is a practical and useful Lewis acid catalyst for acylation of alcohols with acid anhydrides or the esterification of alcohols by carboxylic acids in the presence of... 

Novel and efficient [2 - - 3] cycloaddition reactions of NADH analogues with Q derivatives rather than the hydride-transfer reactions occur in the presence of scandium triflate, Sc(OTf)3, in MeCN to afford the cycloadducts (142). When 1 -benzyl-4-tert-butyl-1,4-dihydronicotinamide (t-BuBNAH) is used as an NADH analogue in the Sc +-catalyzed reaction with Q, the crystal structure of the cycloadduct was determined successfully, as shown in Fig. 53 (142). 

SC2395>. Reaction of o-phenylenediamine and an aryl aldehyde in the presence of a catalytic amount of scandium triflate Sc(OTf)3 gives 2-(aryl)benzimidazoles in moderate to good yields. In this transformation, oxygen serves as the oxidant (Scheme 302) <2004H(63)2769>. 

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. 

It was only in 1995 that the first structure of a hydrated salt of scandium containing only water molecules in its coordination sphere was reported. Refluxing scandium oxide with triflic acid leads to the isolation of hydrated scandium triflate Sc(03SCF3)3 9H20. It is isomorphous with the hydrated lanthanide triflates, containing tricapped trigonally prismatic coordinate scandium in the [Sc(H20)g] ions, with Sc—O (vertices) = 2.171(9) A and Sc—O (face capped) 2.47(2) A. 

Similarly, scandium triflate (Sc(OTf)3), zirconium triflate (Zr(OTf)4) and titanium chloro(tris)triflate (TiCl(OTf)3) were also used for the orf/zo-acylation of phenols and 1-naphthols using acid chlorides . ... 

Quite recently, it has been found that scandium triflate (Sc(OTf)rcatalyzed aldol reactions of silyl enol ethers with aldehydes can be successfully carried out in micellar systems [24], While the reactions proceeded sluggishly in pure water (without organic solvents), remarkable enhancement of the reactivity was observed in the presence of a small amount of a surfactant (cf. Section 4.5). 

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. 

Scandium triflate (Sc(OTf)3) was found to be an effective catalyst in the aldol reactions (Kobayashi et al. 1993b). The activities of various triflate catalysts were evaluated in the aldol reaction of 1-trimethylsiloxycyclohexene (2) with benzaldehyde in dichloromethane (table 7). While the reaction scarcely proceeded at -78°C in the presence of Yb(OTf)3 or Y(OTf)3, the aldol adduct was obtained in an 81% yield in the presence of Sc(OTf)3. Obviously, Sc(OTf)3 is more active than Y(OTf)3 or Yb(OTf)3 in this case. 

Other methods of esterification that do not utilize a carbodi-imide coupling method have also been explored. For example, the stereoselective esterification of 20-(S)-camptothecin, a hindered 3 ° alcohol, with amino acid derivatives was accomplished with the use of scandium triflate (Sc(OTf)3) in high yields while retaining the integrity of the amino acid stereocenter (eq 9). ... 

Scandium triflate [Sc(OTf)3] is a new type of Lewis acid that is different from typical Lewis acids such as AICI3, BF3, SnCU, etc. While most Lewis acids are decomposed or deactivated in the presence of water, Sc(OTf)3 is stable and works as a Lewis acid catalyst in water solution. Many reactions proceed smoothly when this reagent is used in catalytic quantities, while stoichiometric amounts of conventional Lewis acids are needed in the same reactions. Moreover, many nitrogen-containing compounds such as imines and hydrazones are also successfully activated by a catalytic amount of Sc(OTf)3 in both organic and aqueous solvents. Sc(OTf)3 can be recovered almost quantitatively after reactions are complete and can be reused. While lanthanide triflates [Ln(OTf)3] have similar properties, the catalytic activity of Sc(OTf)3 is higher than that of Ln(OTf)3 in several cases. 

For MMA polymerization, the addition of a Lewis acid, specifically scandium triflate [Sc(OTf)3], is known to increase the fraction of isotactic triads and enhance the rate of polymerization. Similar stereocontrol was observed for RAFT polymerization with cumyl dithiobenzoate and Sc(OTf)3. However, these RAFT polymerizations gave only poor control over molecular weight and polydispersity. Our NMR analyses confirm that the poor... 

Effect of scandium triflate [Sc(OTf J concentration on RAFT poiymerization of MMA with methyi cyanoisopropyi trithiocarbonate (13) and azobis(isobu1yronitriie) initiator at 6o°C ... 

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. 

Diels-Alder reactions constitute one of the most important methodologies for the constructuction of a cyclic molecular framework. Lanthanide Lewis acid catalyzed Diels-Alder reaction was pioneered by Danishefsky et al., who revealed that NMR shift reagent Eu(hfc)3 served as chiral catalyst in hetero Diels-Alder reaction of silyloxydiene and aldehydes [32]. Later, although Yb(OTf)3 was first introduced for Diels-Alder reactions as an effective catalyst among lanthanide triflates, scandium triflates (Sc(OTf)3), classified as rare earth metal triflate, has gained popularity as a superior catalyst for Diels-Alder reactions [11, 33]. This section highlights several examples of the reactions where lanthanide triflates displayed preferable performance over scandium triflates. 

Pioneering work by Lubineau and coworkers showed that the aldol type reaction between a silyl enol ether and an aldehyde (the so-called Mukaiyama aldol reaction) occurred in water at room temperature with high syn stereoselectivity, albeit in low yields.However, the development of water-tolerant Lewis acids for this reaction has led to improved rates and chemical yields. Various lanthanides triflates, such as ytterbium triflate [Yb(OTf)3], scandium triflate [Sc(OTf)3], gadolinium triflate [Gd(OTf)3], or lutetium triflate [Lu(OTf)3], have been found to afford the aldol products between various aldehydes and silyl enol ethers in high yields in aqueous media, with good to moderate syn/anti diastereoselectivi-ties (Scheme 8.3, Table 8.1). ... 

Figure 4.7 UV-vis absorption spectra observed in Sc -coupled electron transfer from CoTPP (1.0 x 10" M) to O2 (air saturated, 2.6 x 10 M) in the presence of scandium triflate (Sc(OXf)3 1.7 x 10 M) in MeCN at 298 K.

We tested the reactions of imines with silyl enolates in the presence of 5 mol% of lanthanide triflates (Ln(OTf)3) and scandium triflate (Sc(OTf)3), and selected examples are shown in Table 8.10 [49]. In most cases, the reactions proceeded smoothly in the presence of 5mol% of Yb(OTf)3 (a representative lanthanide triflate) to afford the corresponding p-aminoester derivatives in good to high yields. Yttrium triflate (Y(OTf)3) was also effective, and the yield was improved when Sc(OTf)3 was used as a catalyst instead of Yb(OTf)3. Not only silyl enolates derived from esters, but also... 

Kerr and coworkers have also successfully reported the use of cobalt hexacarbonyl cyclopropanes in [3-1-2] cycloadditions with nitrones via a purported Nicholas-type reaction in the presence of scandium triflate (Sc(OTf)3) to afford a variety of oxazines in high yields (Scheme 10.9) [11]. 

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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