Aqueous-mediated DABCO and DABCO-ionic liquid catalysed synthesis of 3-acetylcoumarins: exploration by kinetic, electrochemical and spectroscopic studies

Abstract

A more efficient, green and user-friendly approach for the synthesis of a combinatorial library of 3-acetylcoumarins from easily available ethylacetoacetate (EAA) and o-hydroxyaldehydes in water at room temperature was developed with excellent yields by modifying novel methods. The experimental method is facile and more economical than traditional methods, requiring no further product purification. Furthermore, the experimental conditions were optimized at the gram scale. The catalyst was reusable, resulting in excellent yields in a shorter time. Additionally, the by-product ethanol formed in the reaction was distilled out. Interestingly, the use of DABCO, DABCO-ionic liquids and DABCO salts as catalysts yielded excellent results (95–98%) in a shorter time. All products were identified by comparing their physical and spectroscopic data. The versatility of the developed green approach encouraged us to investigate the kinetics of the slowest step in the reaction and arrive at a rate law for the reaction. The kinetic and thermodynamic experimental results prompted us to undertake spectroscopic studies, including IR and ¹H NMR, which demonstrated that the catalyst initiated the mechanism. Additionally, cyclic voltammetry (CV), a key electroanalytical tool, showed both the spontaneity of the reaction and the tautomerism of EAA.