Ionic liquid-mediated sustainable synthesis of mono-oxygen 3- and 5-membered heterocycles

Ionic liquids (ILs) have emerged as powerful enablers of sustainable chemistry, evolving beyond their initial role as low-volatility solvents to function as catalysts, mediators of reactivity, and recyclable platforms for diverse transformations. Their distinctive physicochemical properties, including negligible vapor pressure, tunable polarity, and high thermal stability, have positioned them as attractive alternatives in green synthetic methodologies when judiciously designed and applied. Among the many applications of ILs, the synthesis of oxygen-containing heterocycles represents a particularly dynamic and impactful area, given the central role of oxiranes and furans in pharmaceuticals, natural products, and biomass-derived value-added chemicals.This review highlights major advances reported over the past 25 years in ionic-liquid-mediated sustainable synthesis of mono-oxygen three- and five-membered oxygen heterocycles. The discussion is based on a curated selection of representative contributions that illustrate key methodological developments, mechanistic features, and context-dependent green chemistry benefits enabled by ionic liquids. Notably, ionic-liquid-mediated approaches to four-membered oxygen heterocycles remain largely unexplored, and only a single review (published in 2018) has addressed this field to date, underscoring the timeliness of the present work. By critically analyzing reaction design, mechanistic insights, sustainability considerations, and inherent limitations, this article highlights how ionic liquids can enable improved selectivity, reduced energy input, and efficient catalyst recycling under optimized conditions. The discussion further emphasizes emerging trends, including the use of functionalized and bio-derived ionic liquids, integration with renewable feedstocks, and hybrid systems that bridge homogeneous and heterogeneous catalysis. Collectively, this review demonstrates that ionic-liquid-mediated synthesis of small oxygen heterocycles extends beyond solvent replacement toward a broader paradigm of reaction engineering, offering valuable directions for future advances in green heterocyclic chemistry.