Chemistry. 2023 Nov 20:e202303501. doi: 10.1002/chem.202303501. Online ahead of print.
Detailed investigations on the stepwise bis-functionalization of a pillararene-containing rotaxane building block have been carried out. Upon a first stopper exchange, the pillararene moiety of the mono-acylated product is preferentially located close to its reactive pentafluorophenyl ester stopper, thus limiting the accessibility of the reactive carbonyl group by the nucleophilic reagents. Selective mono-functionalization is thus very efficient. Introduction of a second stopper is then possible to generate dissymmetrical rotaxanes with different amide stoppers. Moreover, when dethreading is possible upon the second acylation, the pillararene plays the role of a protecting group allowing the synthesis of dissymmetrical axles particularly difficult to prepare under statistical conditions. Finally, detailed conformational analysis of the rotaxanes revealed that the position of the pillararene moiety on its axle subunit is mainly governed by polar interactions in nonpolar organic solvents while solvophobic effects are playing a major role in polar solvents.