Confinement as a Tool in Chemistry: Accelerated Intracapsular Dimerization of Cyclopentadiene in Water

In this study, the occurrence of Diels–Alder reaction of cyclopentadiene yielding dicyclopentadiene within a confined closed space provided by octa acid (OA) in water at room temperature is established. The Diels–Alder reaction within the OA capsule occurs at least 2000 times faster than in water. Catalysis of Diels–Alder reaction by hosts such as cyclodextrin, cucurbituril, and Fujita's Pd nano–host occurs in water. Despite their similarity, these three hosts provide an open environment where the reactant molecules are exposed to aqueous environment. The only fully closed host known to catalyze the Diels–Alder reaction in water is OA. Although Rebek's host is established to catalyze Diels–Alder reaction it occurs in an organic solvent. The closed environment explored in this presentation provides an opportunity to better understand the origin of non–covalent catalysis in a restricted space and in water. Because the product binds stronger than the reactant, disappointingly, the capsule can't be recycled. We recognize that this aspect needs to be addressed for the OA capsule to become synthetically useful. We are in the process of understanding the origin of catalysis and finding ways to make reaction recyclable.