Cycloaddition reactions between the chiral 2-pyrone derivatives 9 and various dienophiles, catalysed by lanthanide shift reagents, afforded diastereomerically pure bicyclic lactones 3. A catalytic asymmetric version of these reactions, using optically active lanthanide catalysts, was successfully investigated.
Marko, I., Declercq, J.-P., & Evans, GR. (1994). Catalytic Asymmetric Diels-alder Reactions of 2-pyrone Derivatives. Tetrahedron, 50(15), 4557-4574. https://doi.org/10.1016/S0040-4020(01)89387-X (Original work published 1994)