Abstract
Cyclodextrins (CDs) are cone-shaped molecular rings that have been widely employed in supramolecular/host–guest chemistry because of their low cost, high biocompatibility, stability, wide availability in multiple sizes, and their promiscuity for binding a range of molecular guests in water. Consequently, CD-based host–guest complexes are often employed as templates for the synthesis of mechanically bonded molecules (mechanomolecules) such as catenanes, rotaxanes, and polyrotaxanes in particular. The conical shape and cyclodirectionality of the CD “bead” gives rise to a symmetry-breaking effect when it is threaded onto a molecular “string”; even symmetrical guests are rendered asymmetric by the presence of an encircling CD host. This review focuses on the stereochemical implications of this symmetry-breaking effect in mechanomolecules, including orientational isomerism, mechanically planar chirality, and topological chirality, as well as how they support applications in regioselective and stereoselective chemical synthesis, the design of molecular machine prototypes, and the development of advanced materials.
Highlights
Cyclodextrins (CDs) [1] are a class of macrocyclic natural products that were first isolated in 1891 from cultures of starch-fermenting bacteria by Villiers [2]
It is clear that the symmetry-breaking effect of cyclodextrins, arising from their differentiated
It is clear that the symmetry-breaking effect of cyclodextrins, arising from their differentiated faces that lead to orientational isomerism, as well as their cyclodirectional constitutions that lead faces that lead to orientational isomerism, as well as their cyclodirectional constitutions that lead to to mechanically planar and topological chirality in mechanomolecules, has dramatic implications mechanically planar and topological chirality in mechanomolecules, has dramatic implications not on regio, stereo, and orientationally selective synthesis and stereochemical analysis only on regio, stereo, and orientationally selective synthesis and stereochemical analysis of of molecular structure, and on molecular dynamics such as biased molecular structure, and on molecular dynamics such as biased
Summary
Cyclodextrins (CDs) [1] are a class of macrocyclic natural products that were first isolated in 1891 from cultures of starch-fermenting bacteria by Villiers [2]. CD-based host–guest complexes are convenient templates for the synthesis of molecules with mechanical bonds [24,25,26,27,28,29], known [30] as mechanomolecules. The first successful template-directed synthesis of a [2]rotaxane was carried out by Ogino [33]. The first successful template-directed synthesis of a [2]rotaxane was carried out by Ogino [33] (Scheme (Scheme 1) using an amine-terminated dodecane (C12 ) guest with α-CD or β-CD hosts. Ogino’s seminal template-directed synthesis of [2]rotaxanes α-R1 and β-R14+ from diaminododecane and α-CD or β-CD, respectively. Useful in the generation of novel syntheses, molecular machines, and advanced materials
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