Thiamine hydrochloride (VB1) in aqueous media catalyzed the synthesis of polysubstituted quinolines via a one-pot strategy: a combined experimental and theoretical investigation

Abstract

In this work, an efficient one-pot three-component reaction of 2-cyano-N-methylacetamide, arylglyoxals, and arylamines in the presence of thiamine hydrochloride in H₂O under reflux conditions was designed for the synthesis of 4-amino-2-benzoylquinoline-3-carboxamide. In this protocol, various synthetic methods such as Knoevenagel/Michael/cyclization cascade reactions were used to introduce different functional groups, such as amino and carboxamide groups, on the quinoline ring system in a single step. In addition to operational simplicity and absence of tedious separation procedures, this method offered the advantages of catalyst reusability and high product yields. Characterization techniques such as nuclear magnetic resonance spectroscopy, infrared spectroscopy, and CHN analysis were used to confirm the structure and purity of the synthesized compounds. In addition to the experimental results, the influence of solvent on the stability of compounds was investigated using DFT calculations at the B3LYP/6-311++G(d,p) level. Compared with solvent-free conditions, the stability of compounds was amplified in the presence of solvents and increased in the order of H₂O > DMF > CH₃CN > EtOH > THF. This trend was also in agreement with the experimental results. Theoretical data confirmed that the reaction performed best in water medium. Moreover, some electronic properties of these compounds, such as band gap, first ionization energy, electron affinity, electronic chemical potential, electrophilicity index, hardness and softness, were theoretically estimated in the presence of various solvents.