Triazolated calix[4]semitubes: assembling strategies towards long multicalixarene architectures

Abstract

Cone and 1,3-alternate calix[4]arenes bearing pairs of 2-azidoethyl or propargyl groups, and 1,3-alternate calix[4]arenes having four 2-azidoethyl and four propargyl groups or pairs of 2-azidoethyl and silylated propargyl groups were explored as the components for the CuAAC-syntheses of triazolated calix[4]semitubes having three calixarene cores in the structures. Though condition tuning for each of the calixarene combinations was performed, the four-fold CuAACs using the tetrafunctional calixarenes returned the respective tris(calixarenes) in good yields only in the syntheses involving the calixarene tetrakis(alkyne) and hydroxylated bis(azides). The stepwise approach towards the triazolated calix[4]semitubes by using the 2-azidoethylated/propargylated calix[4]arene as the key synthone and de-silylation as the intermediate step was found to be a good alternative, which allowed the preparation of the semitubes with different substituents in the terminal calixarene units and can also be used for further extension of the semi-tubular assemblies.