Green Knoevenagel condensation of indolin-2-one derivatives using undivided electrochemical cell

Electrochemical Knoevenagel condensation has emerged as an attractive alternative to conventional condensation methods because it avoids the use of stoichiometric oxidants and enables reactions under mild conditions. However, a general electrochemical methodology for the condensation of indolin-2-one derivatives has not been established. Herein, we describe a practical electrochemical method for the Knoevenagel condensation of indolin-2-one derivatives with aromatic aldehydes in an ethanol-water medium using a simple undivided cell. The reaction conditions were systematically optimized by evaluating the supporting electrolyte, solvent composition, and electrolysis parameters. The developed method proceeds at room temperature within a short reaction time and affords the desired products in good to excellent yields. The robustness and general applicability of the methodology were validated across a diverse range of aromatic and heteroaromatic aldehydes as well as indolin-2-one derivatives. The use of a green solvent system, operational simplicity, and broad substrate compatibility make this methodology readily applicable to the synthesis of 3-alkenylindolin-2-one derivatives for synthetic and medicinal chemistry studies. A practical electrochemical methodology for the Knoevenagel condensation of indolin-2-one derivatives in an ethanol-water medium. Validated across structurally diverse substrates with short reaction times under mild, room-temperature conditions using a simple undivided electrochemical cell.