Synthesis of symmetrical and unsymmetrical 3,3-di(indolyl)indolin-2-ones under controlled catalysis of ionic liquids.

Three ionic liquids, [BMIM][BF] doped with 60 mol % of LiCl ([BMIM][BF]-LiCl), ,,,-tetramethylguanidinium trifluoroacetate (TMGT), and ,,,-tetramethylguanidinium triflate (TMGT) were found useful as catalyst solvents for controlled 3-indolylation of isatins. Our investigation revealed that the reaction between isatin and indoles in [BMIM][BF]-LiCl or TMGT media stops at the step of addition of the two components providing 3-indolyl-3-hydroxyindolin-2-ones while the ionic liquid TMGT runs the reaction further through accompanying Friedel-Crafts substitution to afford symmetrical 3,3-di(indol-3-yl)indolin-2-ones. To take advantage of the difference between the effects of these ionic liquids on the reaction progress, we planned a two-step protocol for the efficient synthesis of unsymmetrical 3,3-di(indol-3-yl)indolin-2-ones.