Unusual reactivity of upper-rim bridged calix[4]arenes - Friedel-Crafts alkylation via cleavage of the macrocyclic skeleton

Upper-rim bridged derivatives of calix[4]arenes, prepared by the direct introduction of mercury into the meta position of the basic skeleton followed by Pd-catalyzed intramolecular bridging, represent a novel type of calixarenes bearing an additional single bond between the meta positions of neighboring aromatic units. Due to the presence of this short bridge, these compounds exhibit extremely distorted cavities when compared with common calix[4]arenes. As a consequence of highly enhanced inner strain, the bridged compounds can be cleaved under acidic conditions to form open oligomeric species (benzylic type carbocation) that can be used for the Friedel-Crafts alkylation of aromatic compounds. This behavior, never observed in common calix[4]arenes, demonstrates a reasonably amended reactivity invoked by the additional bridge. (C) 2018 Elsevier Ltd. All rights reserved.