Synthesis of furan-2-ones and spiro[furan-2,3'-indoline] derivatives using polyether sulfone sulfamic acid catalysis

Polyether sulfone sulfamic acid (PES-NHSO₃H) was prepared by simple sulfonation of a modified polyether sulfone. The number of acidic sites (SO₃H) was determined to be 4.23 mmol H⁺/g by acid-base titration and 4.29 mmol H⁺/g by barium sulfate test. PES-NHSO₃H was used as an efficient acidic catalytic system for the preparation of functionalized furan-2-ones and 2',5-dioxo-5 H-spiro[furan-2,3 ' -indoline]-3-carboxylate derivatives via the three-component reaction of anilines, aldehydes/1-ethylindoline-2,3-dione, and diethyl acetylene dicarboxylate in high yields (85-97%). The effect of polar and non-polar solvents on the productivity of the reaction was investigated. The catalyst was recovered 11 times without losses in catalytic potential.