Synthesis and Post-Assembly Modifications of Dynamic Covalent Boronic Ester [2]Rotaxanes

We report on the synthesis of [2]rotaxanes from vicinal diols through dynamic covalent boronic ester templates, as well as the use of the boronic ester for post-assembly modifications. A boronic acid pincer ligand with two alkene-appended arms was condensed with a linear diol-containing thread, and ring-closing metathesis then established a quasi[1]rotaxane architecture along with a non-entangled isomer. Advanced NMR spectroscopy and mass spectrometry unambiguously assigned the isomers and revealed that the quasi[1]rotaxane was in equilibrium with its hydrolyzed free [2]rotaxane form. The boronic ester handle in the quasi[1]rotaxane could also be synthetically addressed in a multitude of ways to obtain different [2]rotaxanes, including direct oxidation, protodeboronation, functional group interconversions and Pd-catalysed cross-couplings.