Yttrium triflate

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

Yttrium triflate catalyzes the reaction of lithium enolates with epoxides to form y-hydroxy ketones. 

There are few studies on the metal triflate-catalyzed addition of pyrroles to a, 1-unsaturated compounds <2001 AGE 160, 2001TL8063>. The Friedel-Crafts reaction of homochiral pyrrole derivatives 450 with a,P-unsatu-rated esters catalyzed by metal triflates furnished conjugated addition products 451 in good yields without racemiza-tion (Equation 107) <2004S2574>. The addition worked regioselectively at C-5 of pyrrole. The best yields were obtained by using yttrium triflate and methyl 4-phenyl-2-oxobut-3-enoate. The diastereoisomers were separated by column chromatography. 

A more remarkable elongation of the CS lifetime was attained by complex formation of yttrium triflate [Y(OTf)3] with the CS state in photoinduced ET of a ferrocene-anthraquinone (Ec AQ) dyad (53). Photoexcitation of the AQ moiety in Ec AQ in deaerated PhCN with femtosecond (150 fs width) laser light results in appearance of the absorption bands 420 and 600 run at 500 fs, as shown in Eig. 14(a) (53). The absorption bands 420 and 600 nm, which are assigned to AQ by comparison with the absorption spectrum of AQ produced by the chemical reduction of AQ with naphthalene radical anion (53). The decay process obeys first-order kinetics with the lifetime of 12 ps [Eig. um. 

The addition of a small concentration of yttrium triflate [Y(OTf)3] (10 M 10 M) to a deaerated PhCN solution of ZnP—CONH—Q results in a remarkable enhancement of the ZnP fluorescence intensity without change of spectral feamres, as shown in Pig. 20 (68). The enhancement of the fluorescence intensity results from the binding of Y " " to the Q moiety of ZnP—CONH—Q, which decelerate ET from ZnP to the Q-Y complex due to an increase in the reorganization energy of ET by the much stronger binding of Y to the one-electron reduced state (Q ). Prom the fluorescence titration of Y " " in ZnP CONH Q, the binding constant (K) between Y " " and ZnP—CONH—Q is estimated as 3900 in deaerated PhCN (68). 

Although Lewis add-catalyzed carbon-carbon bond-forming reactions are now of great interest in organic synthesis, these reactions must be conducted under strictly anhydrous conditions, because most Lewis adds react immediately with water rather than the substrates, and are decomposed or deactivated. Sc(OTf)3, however, was found to be stable in water, and effectively activated carbonyl and related compounds as a Lewis add in water. Although it had already been found that lanthanide triflates (Ln(OTf)3 Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) and yttrium triflate (Y(OTf)3) are stable in water and can act as Lewis acid catalysts in aqueous media [3], Sc(OTf)3 occasionally has even better properties even than Ln(OTf)3. Sc(OTf)3, moreover, worked well as a Lewis acid catalyst in several organic solvents, and chiral scandium triflates have also been developed. 

There are several examples of crown ether complexes where yttrium is not bound to the crown ether. [Y(H20)8]C13 (15-crown-5) has a [Y(H20)8]3+ cation (distorted dodecahedron) with the crown ether and chloride hydrogen bonded to the coordinated water molecules.58,225 An aqueous solution containing yttrium triflate and 18-crown-6 produces crystals of [Y(CF3-COO)2(H20)6](CF3COO),(18-crown-6) which have the crown ether hydrogen bonded to the coordinated water molecules.226 The complex [Y(N03)3(H20)3] (dibenzo-24-crown-8) has a nine-coordinate yttrium formed by bonding to three bidentate nitrate groups and three water molecules. The crown ether is hydrogen bonded to the water molecules.227... 

The polymerisation of PO initiated by hydroxyl groups and catalysed by aluminium triflate A1(CF3S03)3 [39, 44], or lanthanide triflates such as yttrium triflate Y(CF3(SOs)3 [40] are some variants of cationic polymerisations developed at higher temperatures. The hydroxyl numbers obtained are generally high (the MW of the resulting polyethers is low). 

The reactions of imines with silyl enolates were tested in the presence of 5 mol% of Ln(OTf)3, and selected examples are shown in Table 12 [41]. In most cases the reactions proceeded smoothly in the presence of 5 mol% of Yb(OTf)3 (a representative lanthanide triflate) to afford the corresponding b-amino ester 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 instead of Yb(OTf)3 as a catalyst. Not only silyl enolates derived from esters, but also that derived from a thioester, worked well to give the desired b-amino esters and thioester in high yields. In the reactions of the silyl enolate derived from benzyl propionate, anti adducts were obtained in good selectivities. In addition, the catalyst could be recovered after the reaction was completed and could be reused. 

It was also Karsch who reported the only yttrium and lanthanum complexes. Yttrium complex 138 was obtained by treatment of ligand 82 with yttrium triflate and lithium bromide in 75% yield (Chart 3). 

Ionic liquids in combination with supercritical fluids are a versatile tool for the immobilization and recycling of homogeneous catalysts, allowing continuous Friedel-Crafts acylation reactions to be realized. The acylation of anisole with acetic anhydride is carried out in a flow system using a metal triflate immobilized in the ionic liquid 1 -butyl-4-methylpyridinium bis(trifluoro-methylsulfonyl)imide as catalyst and scCO as continuous extraction phase [22]. Different metal triflates are utilized under continuous flow conditions using high pressure yttrium triflate possesses the best balance between sufficient acidity for catalytic activity and softness to release the product and so permits a good catalyst reuse (TONs up to 190). 

The large radius of lanthanide(lll) and the specific coordination number also attracted us, and we started to investigate the use of lanthanide triflates as Lewis-acid catalysts for the reaction of amines with nitriles under anhydrous conditions [7a]. After starting this study, we found that scandium triflate (ScfOTfls) and yttrium triflate (YfOTfla) are also excellent water-tolerant Lewis acids, and we have developed new synthetic reactions using these rare-earth triflates as catalysts. 

Preparative Method yttrium triflate is commercially available. However, it can be prepared by addition of yttrium(III) oxide (commercially available) to an aqueous solution of trifluo-romethanesulfonic acid (50% v/v) followed by heating to boiling for 0.5-1 h. The mixture is then purified by filtration and 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 or in a dry box. 

Friedel-Crafts Acylation. Yttrium triflate-catalyzed Friedel-Crafts acylation reactions have been seen in screening profiles along with other lanthanide triflates. In the acetylation of l-(phenylsulfonyl)pyrrole, it was reported that adduct A was preferentially obtained using 10 mol% Y(OTf)3 (eq 8). ... 

The yttrium triflate also promotes in an efficient way many other important reactions such as the addition of enolates to epoxides, leading to the corresponding hydroxyl ketones in almost quantitative yield (Equation (8.26)) [54], or the one-step synthesis of 1,2,4-oxadiazole from ketones, nitriles, and nitric acid (Equation (8.27)) [55]. 

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