A Sulfonic Acid Polyvinyl Pyridinium Ionic Liquid Catalyzes the Multi-Component Synthesis of Spiro-indoline-3,5′-pyrano[2,3-d]-pyrimidines and -Pyrazines

Abstract

A sulfonated poly-4-vinyl pyridinium (PVPy-IL-B-SO3H) containing an acidic pyridinium/HSO3− ionic liquid moiety was prepared and used as a catalyst for the three-component reaction of malononitrile with 1-alkylindoline-2,3-diones and 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione or methyl 5-hydroxy-1H-pyrazole-3-carboxylate, leading to methyl 6′-amino-5′-cyano-2-oxo-2′H-spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylates or -3,4′-pyrano[2,3-d]pyrimidine]-6′-carbonitrile derivatives under ultrasonic irradiation conditions. The solid catalyst allows easy separation, is cheap, produces high yields under mild conditions, and does not require column chromatography for product isolation and purification.

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

“…p.a., absolute, ≥99.8% (GC)), diethyl ether (Fisher Scientific, Schwerte, Germany, ExtraPure, BHT stabilized), and DMSO-d 6 (Thermo Fisher, Schwerte, Germany, 99.5%) were commercially available and used without further purification. The catalysts Cat1 and Cat2 were synthesized from 1,6-dichlorohexane and N -methyl imidazole or pyridine, adopting reported methods (see Supplementary Materials ) [ 38 , 39 , 40 , 41 ]. Analytic data were consistent with reported values.…”

“…In continuation of our recent work using a heterogeneous sulfonic acid polyvinyl pyridinium IL catalyst for multi-component synthesis of spiroindole-3,5-pyrano[2,3-d]pyrimidines and pyrazines [ 41 ], we report herein the synthesis of spiro[furan-2,3′-indoline]-3-carboxylate derivatives using the two easy-to-make and versatile homogeneous Brønsted-acidic IL catalysts Cat1 and Cat2 in three-component reactions using isatin ( N -alkyl-indoline-2,3-dione) derivatives, anilines, and diethyl acetylenedicarboxylate ( Scheme 2 ). The use of ultrasonic irradiation was motivated by our own experience with such multi-component reactions suffering from limited miscibility of the components due to their different hydrophilic/hydrophobic properties and the wish to use only one solvent.…”