The atropisomeric dynamic behaviour of symmetrical N-acylated amine-bridged calix[4]arenes

The amine-bridged calix[4]arene is available via the introduction of an azide group into the meta position of the macrocyclic skeleton followed by thermal decomposition. While further modification of the amine bridge by the alkylation reactions was proved to be problematic, the acylation reactions led smoothly to the expected N-acyl products. As shown by NMR spectroscopy, unusual dynamic behaviour of these compounds can be attributed to their restricted rotation around the amide C-N bond, leading finally to the desymmetrization of the whole molecule in the H-1 NMR spectra at low temperatures (slow exchange conditions). Further substitution of the proximal aromatic units of acylated amine-bridged calix[4]arene with bromine atoms leads to inherently chiral systems with hindered rotation at room temperature.

Automated summary

The amine-bridged calix[4]arene can be synthesized by introducing an azide group into the macrocyclic skeleton and then undergoing thermal decomposition. Alkylation reactions for further modification of the amine bridge were problematic, but acylation reactions proceeded smoothly. The compounds displayed unusual dynamic behavior due to restricted rotation around the amide C-N bond, which led to desymmetrization in the H-1 NMR spectra at low temperatures. Substituting the proximal aromatic units of the acylated amine-bridged calix[4]arene with bromine atoms resulted in inherently chiral systems with hindered rotation at room temperature.