Microwave-assisted synthesis and dynamic behaviour of N2,N4,N6-tris(1H-pyrazolyl)-1,3,5-triazine-2,4,6-triamines

A series of N-2,N-4,N-6-tris(1H-pyrazolyl)-1,3,5-triazine-2,4,6-triamines has been synthesised under microwave irradiation in solvent-free conditions. By reaction of pyrazolylamines with cyanuric chloride and 2-chloro-4,6-diamino-1,3,5-triazines under microwave irradiation, 1,3,5-triazine-2,4,6-triamies with symmetrical and asymmetrical substitution, respectively, can be obtained. In the latter case, the procedure can be easily adapted by addition of a small amount of Dimethyl Sulfoxide (DMSO) for the preparation of polymer-supported triazines, with application in supramolecular combinatorial synthesis. At low temperature, the presence of two or four conformers has been detected for symmetrically and asymmetrically substituted derivatives respectively. 1D- and 2D-exchange spectroscopy studies in various solvents and at different temperatures have been used to determine the equilibrium constants and the activation free energies of the restricted rotation about the amino-triazine bond. A plot of the activation free energy versus temperature shows a good linear correlation and confirms that the same process is present in all of the compounds under investigation.