Friedel-crafts reactions catalyzed by rare earth metal trifluoromethanesulfonates

Article abstract of DOI:10.1246/bcsj.73.2325

Rare earth metal trifluoromethanesulfonates (rare earth metal trifiates, RE(OTf)₃) were found to be efficient catalysts for Friedel-Crafts acylation and alkylation. In the presence of a catalytic amount of RE(OTf)₃, acylation of aromatic compounds having electron-donating substituents such as anisole, thioanisole, and mesitylene with acid anhydrides proceeded smoothly to afford the corresponding aromatic ketones in high yields. Although RE(OTf)₃ alone is not effective for acylation of less reactive aromatics such as toluene, the combination of RE(OTf)₃ and lithium perchlorate (LiClO₄) enhanced the catalytic activity dramatically. Friedel-Crafts acylation reactions using rare earth metal perfluoroalkanesulfonates were also successfully performed in supercritical carbon dioxide (scCO₂). Moreover, in the presence of a catalytic amount of RE(OTf)₃, aromatic compounds reacted with benzyl chloride smoothly to afford the corresponding alkylation products in high yields. In these reactions, RE(OTf)₃ could be easily recovered after the reactions were completed and could be reused without loss of activity.