PEG-400 has been used as a green and biodegradable polymeric solvent for the one-pot, two-step, multicomponent
synthesis of novel asymmetrical bis-spirooxindole derivatives by the reaction of N-alkyl isatin,
isatin derivatives, alkylmalonates and C–H activated carbonyl compounds in the presence of K2CO3 at room
temperature. Using this procedure, all the products were obtained in good to excellent yields.