Assembling triazolated calix[4]semitubes by means of copper(i)-catalyzed azide-alkyne cycloaddition

Nine pairs of cone and 1,3-alternate calix[4]arenes having distal propargyl or 2-azidoethyl groups at their phenolic oxygen atoms were thoroughly studied during macrocyclization under copper(i) catalysis (CuAAC, copper(i)-catalyzed azide-alkyne cycloaddition). Though the formation of undesired polymeric species was not avoidable, the conditions for the preparation and purification of calix[4]semitubes comprising two calixarenes linked by two triazole units were found for all the bis(alkyne)/bis(azide) combinations, and the features of the reacting counterparts which affected the semitube/polymer ratio were analyzed. Formation of larger multi(macrocycles) was also observed in the interactions of sterically hindered bis(alkyne)/bis(azide) pairs under CuAAC conditions that was confirmed by mass spectrometry and diffusion NMR measurements. The molecular structures of the prepared triazolated multi(macrocycles) were confirmed using X-ray diffraction data in most cases. A preliminary complexation study demonstrated the ability of the triazolated calix[4]semitubes to bind Zn2+ or Ag+ cations, which was managed by the shape of the calixarene core (cone or 1,3-alternate) at the 'alkyne sides' of the semitubes and the steric hindrance in the molecules of the bis(calixarenes).

Automated summary

Nine pairs of cone and 1,3-alternate calix[4]arenes with propargyl or 2-azidoethyl groups at their phenolic oxygen atoms were studied for macrocyclization under copper(i) catalysis. Despite the formation of undesired polymeric species, conditions for preparing and purifying calix[4]semitubes were found for all bis(alkyne)/bis(azide) combinations, with larger macrocycles also observed under CuAAC conditions. X-ray diffraction confirmed the molecular structures of the prepared triazolated multi(macrocycles), while preliminary complexation studies showed the ability of triazolated calix[4]semitubes to bind Zn2+ or Ag+ cations.