Abstract
Molecular chirality provides a key challenge in host–guest recognition and other related chemical applications such as asymmetric catalysis. For a molecule to act as an efficient enantioselective receptor, it requires multi‐point interactions between host and chiral guest, which may be achieved by an appropriate chiral 3D scaffold. As a consequence of their interlocked structure, catenanes and rotaxanes may present such a 3D scaffold, and can be chiral by inclusion of a classical chiral element and/or as a consequence of the mechanical bond. This Minireview presents illustrative examples of chiral [2]catenanes and [2]rotaxanes, and discusses where these molecules have been used in chemical applications such as chiral host–guest recognition and asymmetric catalysis.
Highlights
Any undergraduate chemistry student will be familiar with the concept of chirality, and that chiral molecules are non-superimposable on their mirror image
A straightforward way to create a chiral catenane or rotaxane is by incorporating a classical chiral element, such as a chiral centre, axis or plane into at least one of the components that make up the interlocked molecule
Mechanical chirality originates in [2]rotaxanes from both the axle and the macrocycle being directional (Figure 9c) or when a macrocycle is trapped on one side of what would be a prochiral centre of the non-interlocked axle component - in a manner with parallels to atroposiomerism (Figure 9d)
Summary
Any undergraduate chemistry student will be familiar with the concept of chirality, and that chiral molecules are non-superimposable on their mirror image. Many processes in the natural world rely on the ability to recognize chiral molecules, and this, in part at least, inspires chemists to study chiral hostguest recognition and related themes such as asymmetric catalysis.[1] It is generally accepted that a 3D arrangement of at least three interactions (one of which needs to be stereochemically dependent) must exist between a chiral host and its chiral guest to achieve chiral recognition.[2] As a consequence of their interlocked structures, catenanes[3, 4] (molecules consisting of two or more interlocked macrocyclic rings, Figure 1a) and rotaxanes[5] (molecules consisting of stoppered axle(s) components threaded through one or more macrocyclic rings, Figure 1b) could form the basis of useful 3D scaffolds for chiral hosts It is well-established that template synthesis provides a versatile route to interlocked molecules,[6] relying on the preorganization of components prior to final covalent bond formation to trap the interlocked species.[7] Classical templating strategies using metal cations,[8] π-π stacking[9] and hydrogen bonding[10] have been supplemented by more recent work on anionic,[11] radical-radical[12] and halogen bond[13] templation. His current research interests are in the area of functional supramolecular chemistry, including the synthesis and study of chiral interlocked host molecules for enantioselective guest recognition
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