Synthesis of amino and ammonium resorcin[4]arenes as potential receptors

Starting from the tetrabromide la (cone conformation) a number of resorcin[4]arene derivatives (3a, 4a, 5a, 6a) containing an amino function in the side chains have been prepared. Preliminary investigations, including UV, NMR, and NIS analyses, of mixtures of the resorcinarene and its potential guests, such as metal cations or amino acids, evidenced promising new properties, depending on the nature of the substituents. Notably, treatment of 1a with pyridine gave readily the corresponding pyridinium salt 7a, capable of interacting with Ga(III) salts in aqueous solution. The same results have been obtained starting from the tetrabromide 1b (1,2alternate conformation) for two of the above reactions, giving derivatives 3b and 7b.