Highly active polymer-supported (salen)Al catalysts for the enantioselective addition of cyanide to α,β-unsaturated imides

In this contribution, we describe polymer-supported (R,R)-(salen)AlCl complexes that were immobilized on poly(norbornene)s and display excellent activities and enantioselectivies as catalysts for the 1,4-conjugate addition of cyanide to alpha,beta-unsaturated imides. These supported catalysts could be recycled up to 5 times without compromising catalyst activities or selectivities. Furthermore, the catalyst loadings could be reduced from 10-15 mol%, the common catalyst loadings for non-supported (salen)Al catalysts, to 5 mol%, a decrease of metal content by 50-66%, without lowering product yields or enantioselectivities. Kinetic studies indicated that the polymer-supported catalysts are significantly more active than their corresponding unsupported analogues, which makes this catalyst system key to a successful implementation of this catalytic transformation into the fine chemical and pharmaceutical industries.