Rings of rings: calixpyrrole cyclotrimers

Calixpyroles are a class of heteromacrocycles that have been a topic of considerable interest over the last two decades due to their rich host-guest chemistry as receptors for anions. A number of structures comprising more than one calixpyrrole unit have been reported as multitopic and multivalent receptors. Here we report the first syntheses of cyclotrimeric structures containing calixpyrrole rings (hence rings of rings) that can be obtained by the cyclo-oligomerization of either cis- or trans-1,3-meso-4-hydoxyphenyl-calix[4]pyrrole with 1,5-dichloro-2,4-dinitrobenzene via aromatic nucleophilic substitution reactions. The novel structures appear intriguing candidates for prospective molecular recognition studies.