A sustainable one-pot multi-component approach toward the synthesis of symmetric and unsymmetrical spiro heterocycles catalyzed by the Brønsted acidic ionic liquid [CMMIM][BF4]

Abstract

An efficient and sustainable one-pot protocol is developed for the synthesis of a broad range of isatin- and acenaphthoquinone-based spiroxanthene and spirochromenecarboxylate derivatives in aqueous ethanol. This approach involves the condensation of isatin- and acenaphthoquinone-based 1, 2 diketones with cyclic and acyclic active-methylene compounds, catalyzed by 5–6 mol% of the Brønsted acidic ionic liquid [CMMIM][BF₄]. The versatility of the protocol is demonstrated by the successful synthesis of 20 isatin- and acenaphthoquinone-derived spiroxanthene and spirochromenecarboxylate derivatives. This sustainable methodology offers a short reaction time and good to excellent yield (up to 97%), with easy product isolation, avoiding column chromatographic purification and providing valuable green chemistry metrics for symmetric 8a (E-factor: 0.15 and RME: 86.92%) and unsymmetrical 9a (E-factor: 0.08 and RME: 92.5%) derivatives. This study highlights the potential activity of Brønsted acidic ionic liquids [CMMIM][BF₄] as green and reusable catalysts for the atom-economical, environmentally benign construction of bioactive spiro-heterocycles.