Computational and Experimental Study on Molecular Structure of Benzo[g]pyrimido[4,5-b]quinoline Derivatives: Preference of Linear over the Angular Isomer

A series of 5-aryl-2-methylthio-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-4,6,11(3H)-trione was synthesized through an environmental friendly multicomponent methodology and characterized with FT-IR (Fourier Transform infrared spectroscopy), 1H NMR (Nuclear Magnetic Resonance ), 13C NMR and GC-MS (gas chromatography-mass spectrometry). The 5-(4-methoxyphenyl)-2-methylthio-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-4,6,11(3H)-trione 4c compound was characterized by X-ray single crystal diffraction. The geometry of 4c has been fully optimized using DFT (Density functional theory), B3LYP functional and 6-31G(d,p) basis set, thus establishing the ground state energy and thermodynamic features for the mentioned compound, which are in accordance with the experimental data and the crystal structure. The experimental results reveal a strong preference for the regioselective formation of 4c linear four fused rings over the angular four fused and suggest a possible kinetic control in product formation.