Scandium triflate catalyst

Allenyltrimethylsilanes add to ethyl glyoxalate in the presence of a chiral pybox scandium triflate catalyst to afford highly enantioenriched homopropargylic alcohols or dihydrofurans, depending on the nature of the silyl substituent (Tables 9.39 and 9.40) [62]. The trimethylsilyl-substituted silanes give rise to the alcohol products whereas the bulkier t-butyldiphenylsilyl (DPS)-substituted silanes yield only the [3 + 2] cycloadducts. A bidentate complex of the glyoxalate with the scandium metal center in which the aldehyde carbonyl adopts an axial orientation accounts for the observed facial preference ofboth additions. 

Elsewhere, Faita et al. (438) bound the Evans chiral auxiliary to Wang or Merrifield resin for use as a dipolarophile in cycloadditions with C,N-diphenyl-nitrone. Yields on both resins are significantly reduced in comparison to the solution phase reaction (43-20% compared to 95%) but are unaffected by addition of magnesium perchlorate or scandium triflate catalyst. A one-pot process has been reported by Hinzen and Ley (439) that oxidizes secondary hydroxylamines to the... 

Several catalysts have been found for the ring opening of epoxides. For instance, cyclohexene oxide gave an excellent yield of the trans-fi-amino alcohol when treated with either aromatic or aliphatic amines in the presence of a scandium triflate catalyst.21 Aromatic epoxides react in a regiospeciflc reaction at the benzylic carbon when treated with aromatic amines and scandium triflate but at the least substituted carbon of the epoxide ring when aliphatic amines react. Electronic effects are more important in the reactions of the aromatic epoxides whereas steric factors control the reaction with aliphatic epoxides. 

A variety of carbon and sulfur nucleophiles displace Meldrum s acid as the leaving group in what is thought to be an 5 1 reaction of indoylmethyl derivatives of Meldrum s acid, giving substituted indolemethanes in the presence of a scandium triflate catalyst. Yields range from moderate to excellent (38-100%). ... 

Scheme 8.17 Preparation of the Polymer-Supported Scandium Triflate Catalyst.

It turned out that the dodecylsulfate surfactants Co(DS)i Ni(DS)2, Cu(DS)2 and Zn(DS)2 containing catalytically active counterions are extremely potent catalysts for the Diels-Alder reaction between 5.1 and 5.2 (see Scheme 5.1). The physical properties of these micelles have been described in the literature and a small number of catalytic studies have been reported. The influence of Cu(DS)2 micelles on the kinetics of quenching of a photoexcited species has been investigated. Interestingly, Kobayashi recently employed surfactants in scandium triflate catalysed aldol reactions". Robinson et al. have demonshuted that the interaction between metal ions and ligand at the surface of dodecylsulfate micelles can be extremely efficient. ... 

Benzyl and allyl alcohols which can generate stabilized caibocations give Friedel-Crafts alkylation products with mild Lewis acid catalysts such as scandium triflate. ... 

Skraup/Doebner-von Miller-type reactions with lanthanide catalysts under microwave radiation are efficient for a variety of different anilines. For example, cyclisation of aniline 44 with acetone in the presence of scandium triflate gave the desired product 45 in excellent yield. 

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

Scandium triflate [33] is a more active catalyst than the lanthanide triflates and the cycloadditions can also be carried out in aqueous media (Chapter 4). The catalyst is easily recovered from the aqueous layer after the reaction is completed, and can be reused. Some of the cycloadditions carried out in DCM and catalyzed by Sc(OTf)3 are summarized in Table 3.2. 

Scandium triflate is also an effective catalyst for dioxolane formation.246... 

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... 

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). 

The advantages of using ionic liquids as solvents for Diels-Alder reactions are exemplified by the scandium triflate catalysed reactions [14] in [bmim][PFg], [bmim][SbF6] and [bmim][OTf] for the reaction shown in Scheme 7.6. Whilst the nature of the anion seems to have little effect, all these solvents give rate enhancements for a range of Diels-Alder reactions compared to when the reactions are carried out in dichloromethane (DCM). Also, the selectivity towards the endo product is higher than in conventional solvents. As well as the enhanced rates and selectivities, the products can also be removed by extraction with diethyl ether and the ionic liquid and catalyst can immediately be reused. Experiments... 

Although the above demonstrated that product control could be achieved in scC02, the difference in selectivity was relatively small. However, later work using a Lewis acid catalyst, scandium triflate, on the Diels-Alder reaction of n-butyl acrylate and cyclopentadiene (Scheme 7.7) showed that the endo exo ratio was again found to rise to a maximum and then decrease again as the pressure, and hence density, was increased (Figure 7.3) [19]. 

Non-chlorinated Lewis acids, such as scandium triflate, were found to be good catalysts for Friedel-Crafts alkylation reactions (167). Although no aromatic hydrocarbon alkylation occurred in CH2CI2, [BMIMJPFg, Sc(OTf)3 catalyzed the alkylation of benzene with high yields of the monoalkylated product. The lower acidity of the ionic liquid led to fewer byproducts and therefore higher yields. The products were separated by simple decantation and the catalyst was reused. 

Kobayashi reported an asymmetric Diels-Alder reaction catalyzed by a chiral lanthanide(III) complex 24, prepared from ytterbium or scandium triflate [ Yb(OTf)3 or Sc(OTf)3], (Zf)-BINOL and tertiary amine (ex. 1,2,6-trimethylpiperidine) [30], A highly enantioselective and endose-lective Diels-Alder reaction of 3-(2-butenoyl)-l,3-oxazolidin-2-one (23) with cyclopentadiene (Scheme 9.13) takes place in the presence of 24. When chiral Sc catalyst 24a was used, asymmetric amplification was observed with regard to the enantiopurity of (/ )-BINOL and that of the endoadduct [31 ]. On the other hand, in the case of chiral Yb catalyst 24b, NLE was affected by additives, that is, when 3-acetyl-l,3-oxazolidin-2-one was added, almost no deviation was observed from linearity, whereas a negative NLE was observed with the addition of 3-pheny-lacetylacetone. 

Ishihara, K. Kubota, M. Kurihara, H. Yamamoto, H. Scandium triflate as an extremely active Lewis acid catalyst in acylation of alcohols with acid anhydrides and mixed anhydrides./. Org. Chem. 1996, 61, 4560-4567. Zhao, H. Pendri, A. Greenwald, R. B. General procedure for acylation of tertiary alcohols Sc(OTf)3/DMAP reagent. /. Org. Chem. 1998, 63, 7559-7562. 

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... 

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... 

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