Supramolecular Catalysis with Self-Assembled Capsules and Cages: What Happens in Confined Spaces

The confined space inside self-assembled capsules or cages provides a unique environment in which organic reactions can be efficiently catalyzed, thanks to the confinement effect of the substrates. In confined spaces the chemical reactions can show unusual mechanisms due to the conformational control of the substrates, steric constrictions, stabilization of species by secondary interactions, and solvent exclusion. Consequently, the classical rules of the organic reactivity are often broken. Thus, many examples reported to data in the literature confirm the paradigm stated by D. J. Cram in 1989: “These carceplexes represent a new state of matter whose interiors are new phase…”. The confined space inside the self-assembled capsules or cages represents a new phase for the chemical reactivity where there is still so much to explore. In this review we highlight the best-known cases of reactivity in confined spaces, focusing our attention on the driving forces that drive the encapsulated reactions toward uncommon outcomes. Literature examples that constitute the landmarks in the topic of supramolecular catalysis in confined spaces are also reviewed.