Reusable catalysts for the asymmetric diels-alder reaction

Abstract

A new method for recycling chiral bis(oxazoline)-copper complexes is described based on the formation of charge-transfer complexes, their subsequent precipitation, and reuse after addition of new substrates. The conditions to perform this procedure were optimized in the presence of three bis-(oxazoline)-based ligands. When associated with copper salts, these ligands efficiently catalyzed the Diels-Alder reaction between cyclopentadiene and α,β-unsaturated acyloxazolidinones. These catalysts were successfully recycled up to ten times while maintaining their high activities and enantioselectivities. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.