Synthesis of Thiacalix[4]arene Skeleton by the Conjugate Addition of Benzoquinone.

Macrocyclic systems having a thiacalix[4]arene-like structure with four bridging sulfur atoms can be easily constructed using benzoquinone and dithiol-based building blocks. The conjugate addition of benzene-1,3-dithiol with two equivalents of 2,6-dimethylbenzoquinone afforded the corresponding hydroquinone trimer, which, after oxidation to benzoquinone, undergoes a final macrocyclization with another benzene-1,3-dithiol molecule. The whole sequence represents a new strategy for the synthesis of macrocycles based on thiacalix[4]arenes. The conformational behavior of these macrocycles was studied using nuclear magnetic resonance and X-ray analyses, and their basic redox properties were investigated with electrochemical methods.