Breaking thiacalix[4]arene into pieces – a novel synthetic approach to higher calixarenes bearing mixed (–S–, –CH2–) bridges

Abstract

A novel approach to calix[5–7]arenes possessing mixed (S and CH₂) bridges within the skeleton is based on the reaction of thiacalix[4]arene monosulfoxide with BuLi leading to a linear phenolic tetramer in essentially quantitative yield. This key intermediate is then cyclized with suitable building blocks to give macrocyclic calixarene analogues. Compared to the traditional stepwise construction of similar systems, this procedure based on thiacalixarene cleavage represents a scalable, robust, and straightforward synthesis and enables the preparation of larger calixarenes on a gram scale. As shown by ¹H NMR and UV-vis titration experiments, the mixed-bridge calix[7]arene is able to recognize fullerenes C₆₀ and C₇₀, thus showing possible applications of such systems. The structures of the mixed bridge systems were confirmed by single crystal X-ray analysis, and the behavior of novel macrocyclic skeletons in solution was studied using dynamic NMR techniques.