Unanticipated synthesis of a C3 symmetrical tris-triazine under cyclization conditions of coumarinoyl thioureas with α-halo compounds

Abstract

A new highly symmetric 1,3,5-triazine-2,4,6-sulfanediyl species, was obtained by trimerization of ethyl (Z)-3-oxo-2-((N-(2-oxo-2H-chromene-3-carbonyl)-N´-phenylcarbamimidoyl)thio) butanoate derivatives under basic conditions. The compound has been characterized by FT-IR, Raman, NMR and X-ray diffraction analysis. Triethyl 2,2′,2″-((1,3,5-triazine-2,4,6-triyl)tris(sulfanediyl))tris(3-hydroxybutanoate) crystallizes in the trigonal system with space group R-3. The sulfur atom is located in the same plane of the triazine ring, leading to a planar synthon involving the whole 1,3,5-triazine-2,4,6-triyl-tris(sulfanediyl) core. Furthermore, the crystal structure was stabilized by π-stacking interactions favored by the heterocyclic aromatic triazine ring. Hirshfeld surface analyses for visually analyzing intermolecular interactions in crystal structure employing molecular surface contours and 2D fingerprint plots have been used to examine molecular shapes. The enol tautomeric form is observed in the crystal, favored by a strong O[sbnd]H···O = C intramolecular hydrogen bond. This form was also clearly observed in solution, with minor contribution of the keto tautomer, the relative contribution between the enol:keto forms is ca. 0.7:0.3. A thorough computational investigation of the conformational space of the triazine under study led to twelve different minima, the all-enol tautomer being the most stable form, in good agreement with the experimental findings. The solid phase infrared and Raman spectra were recorded, and the vibrational properties interpreted in terms of highly C3-symmetrical species.