Multi-Component Syntheses of Spiro[furan-2,3'-indoline]-3-carboxylate Derivatives Using Ionic Liquid Catalysts.

Two previously described Brønsted acidic ionic liquids, 3,3'-(1,6-hexanediyl)bis(1-methyl)-1 H -imidazolium hydrogen sulfate ( Cat1 ) and 1,1'-(1,6-hexanediyl)bis(pyridinium) hydrogen sulfate ( Cat2 ), were used as catalysts for the preparation of spiro[furan-2,3'-indoline]-3-carboxylate derivatives via a three-component reaction of anilines, isatins ( N -alkyl-indoline-2,3-diones), and diethyl acetylenedicarboxylate, in high yields. The use of ultrasonic (US) irradiation led to the targeted products ( 1a - 15a ) 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 1a .