Highly Efficient Synthesis of Diverse Spirooxindoles Using DBU‐Based Ionic Liquid Catalyst

Abstract

1,8‐Diazabicyclo [5.4.0] undec‐7‐ene (DBU) supported ionic liquids (ILs) demonstrate potential catalytic performance and excellent basicity in organic reactions. Among diverse ionic liquids, DBU acetate (DBU[OAc]) stands out as an adaptable protic ionic liquid (PIL) and has been reported as a low‐volatile and stable catalyst. It promotes substrate activation by enhancing nucleophilicity and implements efficient organic transformations. In the present work, DBU[OAc] has been utilized for the one‐pot synthesis of spirooxindole derivatives from a comprehensive library of active methylene compounds, isatin derivatives, and malononitrile at room temperature (RT). The convergent spirooxindole synthesis was effectively accomplished by Knoevenagel‐Michael cyclo‐isomerization in EtOH at RT. The synthesis of thirteen spirooxindoles, including five unreported scaffolds have been successfully furnished in a short time span of 1–30 min with 77%–95% yields. This methodology offered operational simplicity, with an efficient and facile route. Being a metal‐free strategy, and utilizing ethanol as a solvent at RT with a recyclable catalyst demonstrates consistency with green chemistry principles. Moreover, the PIL revealed a low E‐factor 0.10–0.35, show atom economy 95.96%–96.11%, an excellent reaction mass efficiency 73.66%–90.62%, low process mass intensity 1.14–1.40, and a good eco score 72.6%5–81.95% for the synthesized spirooxindoles.