Enantioselective catalysis of Diels-Alder reactions by heterogeneous chiral bis(oxazoline) catalysts

We report here two heterogenization methods of a chiral bis(oxazoline) (BOX) ligand: (a) by grafting onto an inorganic (silica) surface, and (b) by its polymerization as a polyurethane chain polymer. The activity and enantioselectivity of both polymers as catalysts for the Diels-Alder reaction were checked, and it was shown that under certain conditions enantioselectivities similar to those of the homogeneous catalyst are reached. It has also been shown that under the same conditions the catalyst can be recycled without loss of activity or selectivity. (C) 2002 Elsevier Science B.V. All rights reserved.