Ytterbium trifluoromethanesulfonate

Ytterbium trifluoromethanesulfonate promoted a radical atom-transfer addition of chiral 3-bromoacetyl-2-oxazolidinones to norbornadiene, which afforded the corresponding 5-ex<9-3-bromo-5-nortricycleneacetic acid derivatives in good yields and with high diastereoselectivity (90-96% de, when using the chiral 4-isopropyl- and 4-benzyl-substituted 2-oxazolidinone auxiliaries).133... 

Readion of anisole (1) with acetic anhydride was chosen as a model, and ytterbium trifluoromethanesulfonate (ytterbium triflate, Yb(OTf)3) was the first RE(OTf)3 representative used. Several reaction conditions were examined the results are summarized in Table 1. When acetic anhydride, acetonitrile, or nitromethane was used as a solvent (entries 4—10), the reaction mixture became homogeneous and the acylation reaction proceeded smoothly. Nitromethane gave the highest yield of4-methoxyaceto-phenone (2) (entries 7-10). On the other hand, in carbon disulfide, dichloroethane, or nitrobenzene (entries 1-3), the reaction mixture was heterogeneous and the yield of 2 was low. It was noted that the acylation proceeded quantitatively when a catalytic amount of Yb(OTf)3 was used (0.2equiv., entry 9). Even when 0.05 equiv. of the catalyst was employed, 2 was obtained in 79 % yield (entry 10). 

A review of solvent properties of, and organic reactivity in, ionic liquids demonstrates the relatively small number of quantitative studies of electrophilic aromatic substitution in these media.3 Studies mentioned in the review indicate conventional polar mechanisms. 1-Methylpyrrole reacts with acyl chlorides in the ionic liquid 1-butylpyridinium tetrafluoroborate to form the corresponding 2-acylpyrrole in the presence of a catalytic amount of ytterbium(III) trifluoromethanesulfonate.4 The ionic liquid-catalyst system is recyclable. Chloroindate(III) ionic liquids5 are catalytic media for the acylation, using acid chlorides and anhydrides, of naphthalene, benzene, and various substituted benzenes at 80-120 °C. Again the ionic liquid is recyclable. 

Addition to carbonyls. Reaction of an alkyllithium or a Grignard reagent with tris(trifluoromethanesulfonate)ytterbium, Yb(OTf)3, provides a species of organo-... 

A -Butylpyridinium tetrafluoroborate, containing dissolved phosphorus pentachloride, allows catalytic Beckmann rearrangement of cyclohexanone oxime giving e-caprolactam with good conversion and selectivity <2001TL403>. The same ionic liquid containing dissolved ytterbium(m) trifluoromethanesulfonate was used to perform Friedel-Crafts acylation of furan and thiophene <2005JIG398>. 

Jayaprakash, KN, Radhakrishnan, K V, Fraser-Reid, B, Ytterbium(III) trifluoromethanesulfonate for specific activation of n-pentenyl orthoesters in the presence of acid sensitive functionahties. Tetrahedron Lett., 43, 6953-6955, 2002. 

Preparation of Ytterbium Triflate-. To 21 mL of a mixture of trifluoromethanesulfonic acid and H,0 (v/v = 1/1) 1 i.8 g (30 mmol) of Yb20, are added and the suspension is heated at 100 CC for 2 h. Al ter cooling, the unrcacted oxide is removed by filtration and the filtrate is concentrated under reduced pressure. The hydrate thus prepared is dried in vacuo at 200cC/0.5 Torr for 40 h to give an ytterbium triflate. Preparation of the Catalyst ... 

A proposed mechanism for this reaction involves the following three steps to generate the nitronium ion. The trifluoromethanesulfonate (triflate) ions act as spectators. The ytterbium cation is believed to be hydrated by the water present in the aqueous nitric acid solution. Nitric acid binds strongly to the hydrated ytterbium cation, as shown in equation 1. A proton is generated, as shown in equation 2, by the strong polarizing effect of the metal. Nitronium ion is then formed by the process shown in equation 3. Although the nitronium ion may serve as the active electrophilic species, it is more likely that a nitronium carrier, such as the... 

Place 0.375 g ytterbium (III) trifluoromethanesulfonate hydrate catalyst (ytterbium triflate) into a 25-mL round-bottom flask. Add 10 mL of 1,2-dichloroethane solvent followed by 0.400 mL of concentrated nitric acid (automatic pipette). Add two boiling stones to the flask. To fhis solution, weigh out and add approximately 6 millimoles of the aromatic substrate. Connect the round-bottom flask to a reflux condenser and clamp it into place on a ring stand. Use a very slow flow of water through the condenser. With a hot plate, heat the mixture to reflux for 1 hour. 

Catalytic amounts (5 mol%) of trityl chloride and tin(II) chloride, or antimony(V) chloride and tin(II) triflate, have also been used to promote the Michael additions, with stereoselectivity in favor of the anti isomers and slightly reduced ratios in comparison with the above results. No stereoselectivity was observed with catalytic amounts (10 mol %) of ytterbium(III) trifluoromethanesulfonate. ... 

Related Reagents. Ytterbium(III) trifluoromethanesulfonate ytterbium(in) trifluoromethanesulfonate hydrate cerium(ni) trifluoromethanesulfonate scandium trifluoromethanesulfonate. 

This triene was prepared via the silylation of ketone 166, and submitted without purification to a DA reaction with bis-activated dienophile 168. The transmitted diene generated from this reaction migrates upon addition of ytterbium(III) trifluoromethanesulfonate, yielding cross-conjugated enone 170. Upon heating in o-dichlorobenzene, an intramolecular DA reaction occurred, generating tricycle 171. Five steps were then required to access the amphilectene 172. 

The rare-earth salts of trifluoromethanesulfonic acid (triflic acid) are popular reagents for lanthanide-mediated organic reactions. Especially scandium(III) triflate, Sc(CF3S03)3, and ytterbium(lll) triflate, Yb(CF3S03)3, are often used as mild Lewis acids for reactions in water (Kobayashi et al., 2002). It is therefore surprising that only very few studies of cerium(IV)-mediated reactions describe the use of cerium(IV) triflate, Ce(CF3 803)4 or Ce(OTf)4, as a reagent. This salt was first reported by Kreh et al. (1987), who prepared a solution of cerium(lV) in aqueous triflic acid by electrochemical oxidation of a cerium(III) triflate solution. They illustrated the use of this reagent for oxidation of alkylaromatic and polycyclic aromatic compounds. Imamoto et al. (1990) prepared cerium(IV) triflate by reaction... 

---