Development of enantioselective reactions using novel chiral rare earth metal complex catalysts

Abstract

Some chiral rare earth metal complexes were prepared and used as efficient catalysts for various enantioselective reactions. Rare earth organophosphates effectively catalyzed the hetero-Diels-Alder reaction (up to 99% ee), the Michael addition of nitrogen-nucleophiles (up to 99% ee), and the electrophilic fluorination of β-keto esters (up to 88% ee). Epoxidation of conjugated enones using chiral lanthanum complexes prepared in situ from lanthanum triisopropoxide, (R)-BINOL, triarylphosphine oxide, and alkyl hydroperoxide, afforded the desired products in excellent chemical yields and enantioselectivities (up to >99% ee). Also, chiral and porous polymeric lanthanum complex (particle size: 50-200 nm) prepared by the self-organization of lanthanum ion, a chiral ligand containing two or three (R)-BINOL units linked with multi-ways spacer, and an achiral ligand, was found to work as an excellent reusable heterogeneous catalyst for the enantioselective epoxidation (99% ee in the third run using the recovered catalyst). The catalyst system could also be successfully applied to the flow reaction. Remarkably large positive nonlinear effects (asymmetric amplification) were observed in these reactions.