Solvent-free synthesis of 4-substituted coumarins catalyzed by novel brønsted acidic ionic liquids with perchlorate anion: a convenient and practical complementary method for pechmann condensation

Abstract

Herein, three novel sulfonic-functionalized Bronsted acidic ionic liquids containing perchlorate anion counterparts were prepared and well characterized using FTIR, 1H and 13C NMR, Electro-Spray Ionization Mass Spectrometry (ESI-MS), elemental analysis (CHNS) and TG techniques. These ionic liquid catalysts were prepared through simple and ecofriendly procedures and then applied as efficient catalysts with high yields under solvent-free conditions for the synthesis of 4-substituted coumarins through the Pechmann condensation of different phenols and β-ketoesters. Compared to previous works, the proposed method offers several benefits, such as cleaner reactions, decreased reaction times, high yields, and the lack of laborious workup or purification procedures. Particularly, these catalysts make the condensation of less activated phenols feasible. Besides the described benefits, this advanced protocol was applied successfully for the synthesis of coumarins from γ-lactones such as 3-acetyldihydrofuran-2(3H)-one. The simplicity in operation, applicability and feasibility of this protocol for diverse substrates make it an efficient alternative to conventional methods.