| Summary: | Two previously described Brønsted acidic ionic liquids, 3,3′-(1,6-hexanediyl)bis(1-methyl)-1<i>H</i>-imidazolium hydrogen sulfate (<b>Cat1</b>) and 1,1′-(1,6-hexanediyl)bis(pyridinium) hydrogen sulfate (<b>Cat2</b>), were used as catalysts for the preparation of spiro[furan-2,3′-indoline]-3-carboxylate derivatives via a three-component reaction of anilines, isatins (<i>N</i>-alkyl-indoline-2,3-diones), and diethyl acetylenedicarboxylate, in high yields. The use of ultrasonic (US) irradiation led to the targeted products (<b>1a</b>–<b>15a</b>) in high yields ranging from 80% to 98%. Under the same conditions, the use of sulfuric acid and acetic acid as a Brønstedt catalyst did not yield the desired benchmark product <b>1a</b>.
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