An Auxiliary Approach for the Stereoselective Synthesis of Topologically Chiral Catenanes

Catenanes, molecules in which two rings are threaded through one another like links in a chain, can form as two structures related like an object and its mirror image but otherwise identical if the individual rings lack bilateral symmetry. These structures are described as “topologically chiral” because, unlike most chiral molecules, it is not possible to convert one mirror-image form to the other under the rules of mathematical topology. Although intriguing and discussed as early as 1961, to date all methods of accessing molecules containing only this topological stereogenic element require the separation of the mirror-image forms via chiral stationary phase high-performance liquid chromatography, which has limited their investigation to date. Here, we present a simple method that uses a readily available source of chiral information to allow the stereoselective synthesis of topologically chiral catenanes. [Display omitted] •First stereoselective synthesis of a topologically chiral catenane•First absolute stereochemical assignment of a topologically chiral catenane•First example of an auxiliary approach to topologically chiral catenanes Chiral molecules have occupied a special place in chemistry since Pasteur reported the painstaking separation of mirror-image crystals of tartaric acid salts in 1848. In the 21st century, chiral molecules remain a major scientific focus because of their importance in biology and their emerging applications in materials science. However, topologically chiral molecules, such as the catenanes described here, have received little attention because they are hard to make; preparative chiral stationary phase high-performance liquid chromatography allows the separation of their mirror-image forms but only on a very small scale. Here, we demonstrate the synthesis of topologically chiral catenanes by using standard synthetic techniques, marking their transition from “inaccessible curiosities” to valid synthetic targets for investigation in catalysis, sensing, medicinal chemistry, and materials science. Furthermore, this work will inspire efforts to access other neglected classes of chiral interlocked molecules. Catenanes, molecules comprising two rings held together like links in a chain, can exist as two mirror-image forms if the rings lack bilateral symmetry. These “topological enantiomers” are unusual because they cannot be interconverted by stretching or bending chemical bonds. To date, their synthesis has required the separatio