Can thiacalixarene surpass calixarene?

Heteroatom-bridged calixarenes have been confined into the unexplored frontier of the vast realm of the calixarene chemistry because of their synthetic difficulty. Since we found facile one-step synthesis of thiacalix[4]arene, in which four methylene bridges of calix[4]arene are replaced by four sulfides, we have been engaged in the study on this new molecular platform regarding the improvements for the synthetic procedures, structural analyses, chemical modifications, and functional developments. In this review are described the results of our own study to demonstrate the potentials over the limits of the conventional calixarenes, putting emphasis on the indispensable role of the bridging sulfur. Highlighted examples are (1) enlargement of the calix skeleton to provide larger cavity, (2) ready oxidizability to sulfoxide and sulfone for providing new members of S bridged calixarenes, and (3) coordination to specific metal ions controlled by the oxidation state of S. These indicate a hopeful future for the thiacalixarene platform in the forthcoming applications to functional molecular devices.