Sanchez-Blanco, A. I.; Gothelf, K. V.; Jørgensen, K. A.
Tetrahedron Lett. 1997, 38, 7923–7926, doi: 10.1016/S0040-4039(97)10048-X
Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark
The 1,3-dipolar cycloaddition reaction of alkenes with nitrones was catalyzed by Yb(OTf)3 or Sc(OTf)3 giving isoxazolidines in high yields and selectivities. The catalyst Yb(OTf)3 induce a high endo-selectivity in the reaction of up to 94% de, whereas Sc(OTf)3 show the highest rate accelerations. Both the conversion and endo-selectivity of the Yb(OTf)3 and Sc(OTf)3 catalyzed reactions proved to be dependent on the amount and type of molecular sieves added. The application of different chiral ligands in 1,3-dipolar cycloaddition reactions of a series of alkenes with nitrones catalyzed by Yb(OTf)3 or Sc(OTf)3 has been studied and it was found that high endo-selectivities and an ee’s of up to 73% could be obtained by the use of Yb(OTf)3 and 2,6-bis[4(S)-isopropyl-2-oxazolidin-2-yl]pyridine (PyBOX) as the chiral ligand.