DIELS-ALDER REACTIONS THROUGH REVERSIBLE ENCAPSULATION

Experimental details are given for the preparation of large self-compl ementary molecules capable of assembly into pseudospherical capsules. These structures exist as hydrogen bended diners in organic solvents, and they form and dissipate on a time scale that permits direct NMR ob servation of the reversible encapsulation of smaller molecules. The ca vity is roomy enough to accommodate more than one molecule, and two so lvent molecules such as benzene appear to occupy the resting state of the capsules. Liberation of these solvent molecules is responsible for the unexpected thermodynamic parameters of the encapsulation process. A bimolecular reaction-the Diels-Alder reaction-is shown to be accele rated by the capsule as both reactants can occupy the capsule concurre ntly. Size selectivity, saturation kinetics, and product inhibition st udies point to a reaction that takes place within the capsule.