Scandium triflate aromatics acylation

Matsushita, Y.-L, Sugamoto, K., and Matsui, T. 2004. The Eriedel-Crafts acylation of aromatic compounds with carboxylic acids by the combined use of perfluoroalkanoic anhydride and bismuth or scandium triflate. Tetrahedron Lett. 45 4723-4727. 

Table 5.3 Scandium-triflate-catalyzed acylation of aromatics with acyl chlorides...

In addition to the works previously reported [50] Bi(0Tf)3 x H20 proved to be as active as scandium triflate in the EC acylation of aromatic compounds with carboxylic acids in the presence of perfluoroalkanoic anhydrides using solvent-free conditions (Equation 31) [60]. Under these conditions no reactions were reported with aromatics less activated than benzene. As previously reported [21], Bi(0Tf)3 xH20 was shown to be recoverable in good yields with no loss of activity. In addition, Bi(NTf2)3 [61] is proved to be an excellent catalyst for the intramolecular EC cyclization of 4-arylbutyric acids [62]. 

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. 

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