Scandium trifluoromethane sulfonate

T. Akiyama, J. Iwai, Scandium Trifluoromethane-sulfonate-Catalyzed Chemoselective Allylation Reactions of Carbonyl Compounds with Tetraallylgermane in Aqueous Media Tetrahedron Lett. 1997,38, 853-856. 

Aggarwal VK, Vennall GP, Davey PN, Newman C (1998) Scandium trifluoromethane-sulfonate, an efficient catalyst for the intermolecular carbonyl-ene reaction and the intramolecular cyclization of citronellal. Tetrahedron Lett 39 1997-2000... 

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. 

Kobayashi, S., Moriwaki, M., and Hachiya, I. 1995. The catalytic Fries rearrangement of acyloxy naphthalenes using scandium trifluoromethane-sulfonate as catalyst. /. Chem, Soc., Chem. Commun. 1527-1528. 

The cyclization of a variety of substituted anilines 271 with ketones 274 in the presence of scandium trifluoromethane sulfonate under MWI at 150 oC produced 2,2,4-substituted 1,2-dihydroquinolines 275 within 50 min in 30-79% yields. Under conventional conditions at room temperature for about 2-6 h, the yields were 59-98% (Scheme 57) (02TL3907). 

Lim et al. used a palladium complex for the cationic polymerization of TH F and the ROMP of NB [10]. The same group also showed that even condensation and chain polymerization could be performed simultaneously in one step (Scheme 11.45). This was achieved by the use of unimolecular compounds which can simultaneously act both as an initiator for chain polymerization, and as an end-capper for condensation polymerization. The method provides a simple means of combining NMRP with a condensation polymerization to yield interesting and useful block copolymers [207]. Another interesting new system for the combination of chain (AROP of CL) and step (dehydration polycondensation) polymerizations for polyester-based new material, in which scandium trifluoromethane sulfonate catalyzed both polymerization modes, was reported by Takasu et al. (Scheme 11.46) [208]. 

Keimg et al. describes the optimization of 2-imino-piperazines using Lewis acids to catalyze the multicomponent a-amino amidine synthesis to make piperazines 39 (Scheme 6) [26]. A, Af -(jimethylethylenediamine 36 was used with an aldehyde 37 and isocyanide 38 in methanol with scandium (III) trifluoromethane sulfonate (Sc(OTf)3) as a catalyst to obtain the piperazine 39 in 57% yield. 

Kitazume and Zulfiqar have investigated the Claisen rearrangement of several aromatic allyl ethers in ionic Hquids, catalyzed by scandium(III) trifluoromethane-sulfonate [72]. The reaction initially gave the 2-aUylphenol but this reacted further to give 2-methyl-2,3-dihydrobenzo[b]furan (Scheme 5.1-41). The yields in this reaction were highly dependant on the ionic liquid chosen, with [EDBU][OTf giving the best yields (e.g., 91 % for R = 6-CH3). Reactions in [BMIMjlBFJ and [BMIM][PF j gave low yields (9-12 %). 

Against this background it is important that—quite fitting in this still new millennium— the first catalytic Friedel-Crafts acylations of (still relatively electron-rich) aromatic compounds were reported (Figure 5.35). Trifluoromethane sulfonates ( triflates ) of rare-earth metals, e. g., scandium(III)triflate, accomplish Friedel-Crafts acylations with amounts of as little as 1 mole percent. Something similar is true of the tris(trifluoromethanesulfonyl)-methides ( triflides ) of rare-earth metals. Unlike conventional Lewis acids, the cited rare-earth metal salts can form 1 1 complexes with the ketone produced, but these are so unstable that the Lewis acid can re-enter the reaction. Whether this works analogously for the third catalytic system of Figure 5.35 is unclear. 

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. 

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

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