Microwave-Assisted Synthesis and Dynamic Behaviour ofN2,N4,N6-Tris(1H-pyrazolyl)-1,3,5-triazine-2,4,6-triamines

Abstract

A series of N2,N4,N6-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.