Thulium triflate

The use of Ln(OTf)3 in the activation of aldehydes other than formaldehyde was also investigated [18]. The model reaction of 1-trimethylsiloxycyclohexene (2) with benzaldehyde under the influence of a catalytic amount of Yb(OTf)3 (10 mol%) was examined. The reaction proceeded smoothly in H20-THF (1 4), but the yields were low when water or THF was used alone. Among several Ln(OTf)3 screened, neodymium triflate (Nd(OTf)3), gadolinium triflate (Gd(OTf)3), Yb(OTf)3, and lutetium triflate (Lu(OTf)3) were quite effective, while the yield of the desired aldol adduct was lower in the presence of lanthanum triflate (La(OTf)3), praseodymium triflate (Pr(OTf)3) or thulium triflate (Tm(OTf)3) (Table 2). 

The effect of other Ln(OTf)3 was also examined. As shown in table 31, the choice of lanthanide element strongly influenced the yields and selectivities. A slight difference between the two catalyst systems (catalysts A and B) on the effect of the lanthanide elements was also observed. In catalyst A, lutetium triflate (Lu(OTf)3) was also effective in generating the endo Diels-Alder adduct in 93% ee. The yields and selectivities diminished rapidly in accordance with the enlargement of the ionic radii. In catalyst B, on the other hand, the best results were obtained when thulium triflate (Tm(OTf)3) or erbium triflate (Er(OTf)3) was employed. Deviations to either larger or smaller ionic... 

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