The meta-bridged calixarenes possess a rigidified and highly distorted cavity, where the additional single-bond bridge imposes an extreme internal strain on the whole system. As a consequence, these compounds exhibit a reasonably amended reactivity, compared with common calix[4]arene derivatives, which is governed by the release of internal strain. This can be documented by the reaction of the bridged calix[4]arene with P2O5 or Nafion-H, leading (apart from polymers) to a macrocyclic product with a rearranged basic skeleton. The methylene bridge next to the fluorene moiety is intramolecularly shifted from position 2 to position 4 of the phenolic subunit to minimize the tension. As revealed by single-crystal X-ray analysis and by application of the residual dipolar coupling method, the rearrangement occurs without altering the original conformation.

Department of Organic Chemistry University of Chemistry and Technology Prague Technická 5 166 28 Prague 6 Czech Republic

Institute of Physics AS CR v v i Na Slovance 2 182 21 Prague 8 Czech Republic

Laboratory of Nuclear Magnetic Resonance Spectroscopy UCTP 166 28 Prague 6 Czech Republic

References provided by Crossref.org

Enantiodiscrimination of Inherently Chiral Thiacalixarenes by Residual Dipolar Couplings

Upper rim-bridged calixarenes