In many supramolecular catalytic systems designed to work with bimolecular addition reactions like the Diels-Alder, the product of the reaction binds more strongly to the supramolecular host than the two substrates do, consequently leading to inhibition by the product.  As a result, these catalysts has a turnover number of one and are not truly catalytic. A stoichiometric quantity of the catalysts is needed for a full conversion.