Mechanistic insight on the Diels-Alder reaction catalyzed by a self-assembled molecular capsule.

We combined Monte Carlo simulations and density functional theory calculations to study the mechanism of the Diels-Alder reaction of p-quinone and cyclohexadiene catalyzed by a self-assembled molecular capsule. Our calculations show that the encapsulation of the reactants into the cage is driven by hydrogen-bonding interactions and π-π stacking interactions between two reactants and the capsule. The encapsulated Diels-Alder reaction at different locations inside the capsule may have quite different reactivity due to different guest-host interactions. A comparison of the free energy profiles of the Diels-Alder reaction in the capsule and in the bulk solution reveals that the Diels-Alder reaction in the capsule is accelerated because the host-guest interaction leads to a relatively smaller barrier for the cycloaddition step.