Polymerisation vs. grafting in the preparation of polymer-supported aluminium catalysts for the Diels-Alder reaction: The role of the polymeric backbone.

Several polymers containing Al Lewis acids anchored to chiral prolinol moie ties have been prepared and studied as catalyst for the Diels-Alder reactio n of cyclopentadiene and methacrolein. The chiral fragment has been introdu ced by grafting and by polymerisation procedures using different crosslinki ng agents and ratios. All supported catalysts prepared show a good activity , but the polymeric network seems to play it very important role in the det ermining the selectivity observed. Best results, in terms of enantioselecti vity. are obtained when the chiral fragment is introduced through polymeris ation of the appropriate chiral monomer, but only when a high crosslinking degree (90% DVB) is used. It is shown that the presence of coordinating ato ms in the polymeric backbone is clearly detrimental for the selectivity obs erved. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.