Reactivity in a Self-assembled Organic Host

The interior of the hexameric resorcinarene capsule can emulate an enzyme pocket: there is enough space to host reagents and to favour bimolecular reactions. The overconcentration effect can lead to a rate acceleration with respect to reactions in the bulk medium. The reactions between molecules forced in the restricted space inside the resorcinarene capsule usually occur with unusual regiochemical and stereochemical outcomes. Consequently, the classic reactivity rules valid in the bulk medium are many times disregarded. Like a natural enzyme, the resorcinarene capsule can work in a selective way with respect to the structural features of reagents and products and can result in a regio-, enantio-, and diastereoselective reaction. Thanks to these properties, the hexameric capsule has been used as cyclase mimicking in order to catalyse terpene cyclisations. In these cases, the capsule pocket shields the carbocationic intermediates by chemical quenching and stabilise them through cation⋯π interactions. The capsular water molecules perform a double catalytic function: (1) they can act as hydrogen-bonding donor groups in catalysis, and (2) they can play a crucial role in Brønsted acid catalysis. Finally, as in natural systems, the catalytic activity of the hexameric capsule can be modulated in the presence of competitive inhibitors, which show high affinities for its internal cavity. All of these aspects are discussed in this chapter.