T. Hanamoto et al., ASYMMETRIC HETERO-DIELS-ALDER REACTION CATALYZED BY CHIRAL YTTERBIUM(III) PHOSPHATE (YB[(R)-(-)-BNP](3)) - REMARKABLE LIGAND EFFECT ON THE ENANTIOSELECTIVITY, Synlett, (1), 1997, pp. 79
2,6-Lutidine was found to be an effective additive for the chiral ytte
rbium(III) phosphate {Yb[(R)-(-)-BNP](3)}-catalyzed asymmetric hetero
Diels-Alder reaction thus achieving high enantioselectivity (up to 93%
ee) at room temperature.