Single crystal XRD, spectroscopic, DFT studies and synthesis of [1,2,4]triazolo[4,3-a]pyrimidines

Abstract

• Regioselective oxidative cyclization of unsymmetrical substituted pyrimidines hydrazones. • Spectroscopic ( 1 H & 13 C-NMR, IR) characterization of [1,2,4]triazolo[4,3-a]pyrimidines. • Single crystal XRD structure of four [1,2,4]triazolo[4,3-a]pyrimidines have been developed to confirm the exact regioisomeric structure. • FMOs, MEPs and HFs were investigated to study the surface characteristics. The current research investigation demonstrates about the regioselective synthesis of halogen-containing scarcely explored [1,2,4]triazolo[4,3-a]pyrimidine heterocyclic system by facile dehydrogenation of four different 2-(2-(4-halobenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidines. The exact regiochemistry of the final skeleton has been confirmed by their spectral data along with a single crystal XRD structure. The single crystal-XRD analysis exposed that, crystals of 2a, 2a׳, 2b, and 2c are in monoclinic, triclinic, orthorhombic, and monoclinic systems with P21/c, P-1, Pbca, C12/c1 space groups respectively. The molecular electrostatic potential (MEP) and hirshfeld surface analysis disclosed that [1,2,4]triazolo[4,3-a]pyrimidines stabilized by H•••N/N•••H interactions. HOMO, LUMO energies, Frontier molecular orbitals (FMO) analysis, and molecular electrostatic potentials (MEP) are also reported by using DFT methods. Graphical Abstract .