Polymer immobilization of bis(oxazoline) ligands using dendrimers as cross-linkers

Homopolymers of bis(oxazoline) ligands can be used to prepare efficient catalysts for cyclopropanation reactions. However, the low accessibility to most bis(oxazoline) moieties leads to a low copper loading. As a consequence, the transmission of chiral information from the complexed polymer is not very efficient and only a few chiral cyclopropane molecules are obtained from each molecule of chiral ligand. The use of suitable dendrimers as cross-linkers in the polymerization process allows better copper functionalization. As a consequence the productivity of chiral cyclopropanes per molecule of chiral ligand greatly increases, which improves the ligand economy and the chirality transfer. (C) 2003 Elsevier Science Ltd. All rights reserved.