Diazo coupling: an alternative method for the upper rim amination of thiacalix[4]arenes

A common method for the introduction of amino groups into the upper rim of calix[n]arene—nitration and subsequent reduction of nitro derivatives—is not possible in the thiacalixarene series due to the easy oxidation of the sulphur bridges during the nitration step. Alternatively, thiacalix[4]arene reacts smoothly with diazonium salts to form the corresponding tetrasubstituted azo derivatives in high yields. These compounds can then be reduced to give upper rim amino substituted thiacalixarene derivatives.