Synthesis and Conformation of New Azo-functionalized Calix[4]arenes^†

A new family of functionalized calix[4]arenes has been synthesized from calix[4]arene or azo-calix[4]arene by acylation with the corresponding ω-alkylmercapto acid chloride. Six new compounds 4a–4c and 5a–5c were isolated and characterised by MALDI, elemental analyses, ¹H NMR and ¹³C NMR. NMR spectral data showed that these azo-functionalized calix[4]arenes 5a–5c are all in 1,3-alternate conformation in solution at room temperature while calix[4]arenes 4a–4c are all in cone conformation. The IR and UV properties of calix[4]arenes 5a–5c were also investigated.