Scandium trifluoromethanesulfonate

Solubility soluble in H2O, alcohol, acetonitrile, and most polar organic solvents. 

Preparative Methods scandium triflate is commercially available. On the other hand, it can also be prepared from the corresponding oxide (SC2O3) and aqueous trifluoromethanesulfonic 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 triflate, which is stored over P2O5. 

Handling, Storage, and Precautions the anhydrous triflate is fairly hygroscopic (not decomposed, forms a hydrate) and must be kept in a desiccator over P2O5 and freshly dried in vacuo ( 1 mmHg) at 200 °C for 1 h before using. 

Sc(OTf)3 also catalyzes aldol-type reactions of silyl enolates with acetals. For example, the reaction of 3-phenylpropionaldehyde dimethyl acetal with the ketene silyl acetal of methyl isobutyrate proceeds at 0°C to room temperature to give the desired adduct in 97% yield (eq 2)  

Sc(OTf)3 is effective in the aldol-type reaction of silyl enolates with aldehydes in aqueous media (H2O-THF) without any significant decomposition of the water-sensitive silyl enolates. Thus, aldehydes available in aqueous-solution such as formaldehyde and chloroacetaldehyde can be directly used to afford the corresponding aldol adduct in high yield (eq 3).  

Masaharu Sugiura Shu Kobayashi The University of Tokyo, Tokyo, Japan 

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. 

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Rare earth metals and scandium trifluoromethanesulfonates (lanthanide and scandium triflates) are strong Lewis acids that are quite effective as catalysts in... 

Allylations, allenylations, and propargylations of carbonyl compounds in aqueous media can also be carried out with preformed organic tin reagent, rather than the use of metals.86,87,88 For example, the allylation reaction of a wide variety of carbonyl compounds with tetraal-lyltin was successfully carried out in aqueous media by using scandium trifluoromethanesulfonate (scandium triflate) as a catalyst (Eq. 8.40).89 A phase-transfer catalyst (PTC) was found to help the allylation mediated by tin at room temperature without any other assistance.90... 

Interestingly, salts other than tin(ll) bis-(2-ethylhexanoate) such as scandium and tin trifluoromethanesulfonate [41 3], zinc octoate [44, 45], and aluminum acetyl acetonate [45] were reported to mediate the ROP of lactones. As far as scandium trifluoromethanesulfonate is concerned, the main advantage is the increase of its Lewis acidity enabling the polymerization to be carried out at low temperatures with acceptable kinetics. Later, faster kinetics were obtained by extending the process to scandium trifluoromethanesulfonimide [Sc(NTf2)3] and scandium nonafluorobutanesulfonimide [Sc(NNf2)3] and to other rare earth metal catalysts (metal=Tm, Sm, Nd) [46]. 

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. 

The above acid-catalyzed polycondensations were carried out at more than 100 °C, whereas Takasu et al. reported room temperature polyesterification with scandium trifluoromethanesulfonate [Sc(OTf)3] or scandium trifluo-romethanesulfoimide [Sc(NTf2)3] [27,28]. Thus, the direct polycondensation of methylsuccinic acid and 1,4-butanediol proceeded in bulk under reduced pressure (0.3-30 mmHg) using 1.4 mol % of Sc(OTf)3 at 35 °C for 96 h to afford poly(butylene methylsuccinate) with Mn of 12400 (Scheme 5). When HfCl4-(THF)2 was used in this room temperature polymerization instead of Sc(OTf)3, only low molecular weight polyester (Mn = 1100) was afforded. The scandium catalysts did not promote transesterification ethanol selectively reacted with acetic acid even in the presence of equimolar methyl acetate. 

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. 

The element scandium (Sc) is in group 3 (above La and Y), and its radius is appreciably smaller than those of any other rare earth elements. Scandium is uncommon probably because of the lack of rich sources and difficulties of separation. Its chemical behavior is known to be intermediate between that of aluminum and lanthanides [1]. Use of scandium in organic synthesis was rather limited before scandium trifluoromethanesulfonate (Sc(OTf)3) was first introduces as a promising Lewis add in 1993 [2],... 

The use of a scandium trifluoromethanesulfonate catalyst has also been reported for aza-Diels-Alder reactions. The reaction of benzaldehyde and amine 104 in [emim][OTf] as the ionic liquid led to the in situ formation of the corresponding imine. Cycloaddition of this imine with Danishefsky s diene gave the A -aryl-6-phenyl-5,6-dihydro-4-pyridone 105 in a quantitative yield (Scheme 44). 

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