Chapter 186 Triflates

Abstract

Publisher Summary Rare-earth triflates mean group-3 metal triflates. While actinides are not commonly used, the term lanthanide triflates (Ln(OTf)3) has often been used to include Sc, Y, La-Lu triflates. Ln(OTf)3 are classified into hard Lewis acids. The trifluoromethanesulfonyl group (OTf) is one of the strongest electron-withdrawing groups and thus, the Ln(OTf)3 compounds are expected to be stronger Lewis acids compared to LnCl3 or LnBr3. While continuous use of Ln(OTf)3 is possible, it is also easy to recover the Ln(OTf)3 themselves. The Ln(OTf)3 are more soluble in water than in organic solvents such as dichloromethane. Almost 100% of the Ln(OTf)3 was quite easily recovered from the aqueous layer after the reaction was completed, and it could be reused. Scandium triflate (Sc(OTf)3) was found to be an effective catalyst in the aldol reactions. Several examples of the Sc(OTf)3-catalyzed aldol reactions of silyl enolates with aldehydes were examined and it was found that silyl enolates derived from ketones, thioesters, and esters reacted smoothly with aldehydes in the presence of 5 mol% Sc(OTf)3 to afford the aldol adducts in high yields. Sc(OTf)3 was also found to be an effective catalyst in the aldol-type reaction of silyl enolates with acetals. The reactions proceeded smoothly at –78°C or room temperature to give the corresponding aldol-type adducts in high yields without side reaction products.