The hitchhiker’s guide to mechanical isomerism: fundamental motifs and their stereoselective synthesis Peter Gallagher a,b , Andrea Savoini a,b , Abed Saady a,b , John R. J. Maynard a , Patrick Butler a , Graham J. Tizzard a , Stephen M. Goldup b a Chemistry, University of Southampton, UK, b School of Chemistry, University of Birmingham, UK Upon mechanical bond formation, achiral sub-components can be desymmetrised to yield chiral and geometric isomers. 1 When considering the catenation of oriented and/or facially dissymmetric macrocycles ( I and II ) and rotaxane formation using the same with bilaterally symmetric axles ( III and IV ), seven distinct isomeric motifs can be formed ( V - XI ). 2 Of these, only mechanically planar chiral systems ( V and VIII ) have been studied significantly and axially chiral rotaxanes XI were only discovered in 2022. 3 Here we report a study of the factors controlling the selective synthesis of both of geometric and chiral mechanical isomers and the first direct enantioselective synthesis of a mechanically axially chiral rotaxane. All of the fundamental mechanical stereoisomers can now be synthesised stereoselectively. 4,5
Figure 1: Mechanical isomers of [2]catenanes and [2]rotaxanes through combination of oriented or facially dissymmetric macrocycles I and II and bilaterally symmetric axles III and IV . References 1. H. L. Frisch and E. Wasserman, J. Am. Chem. Soc. , 1961, 83 , 3789–3795. 2. E. M. G. Jamieson, F. Modicom, S. M. Goldup, Chem. Soc. Rev. , 2018, 47 , 5266-5311. 3. J. R. J. Maynard, P. Gallagher, D. Lozano, P. Butler S. M. Goldup, Nat. Chem. , 14 , 1038–1044 (2022).
4. P. Gallagher, A. Savoini, J. R. J Maynard, P. Butler S. M. Goldup, manuscript in preparation 5. A. Savoini, P. Gallagher, A. Saady, G. J. Tizzard S. M. Goldup, manuscript in preparation
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© The Author(s), 2023
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