Sterically constrained spirocycles are common and privileged motifs in many bioactive natural products, as well as in pharmaceutical and agrochemical substances. In contrast to purely aromatic and usually flat molecules, spirocycles display a high level of three-dimensionality through their sp3 carbon atoms, which often give rise to high biological activity, as well as selectivity. Furthermore, spirocyclic motifs frequently open the door to novel and uncovered chemical space. Many examples of successfully marketed and investigational drugs based on spirocyclic scaffolds are described in the literature and highlights will be exemplified in this chapter.
