Polyvinylsulfonic acid as a novel Brønsted acid catalyst for Michael addition of indoles to α,β-unsaturated ketones

Ionic liquid coated sulfonated carbon/silica composites: novel heterogeneous catalysts for organic syntheses in water

“…Michael reaction of indoles to a,b-unsaturated carbonyl compounds provides easy access to 3-substituted indoles, which are important building blocks for the synthesis of important biologically active compounds and natural products. [37][38][39] Recently, catalysts such as polyvinyl sulfonic acid, 40 metal halide hydrates, 41 task-specic ionic liquids, 42 bimetallic iron-palladium catalysts, 43a and iron salts 43b have been reported for the Michael addition of indole to a,bunsaturated ketones. However, the acid-catalyzed conjugate addition of indoles requires careful control of acidity to prevent side reactions such as dimerization or polymerization.…”

Study of the catalytic activity of methylene-bridged dicationic –SO3H-functionalized imidazolium phosphomolybdate hybrids for the one-pot sequential synthesis of 3-substituted indoles

“…Conventionally, a,b-unsaturated ketones as substrates are utilized by many researchers for conjugate addition with indoles using various catalysts, such as SbCl 3 , GaI 3 , polyvinylsulfonic acid, ceric ammonium nitrate, p-toluene sulfonic acid, InCl 3 , and CeCl 3 Á7H 2 O-NaI supported on silica gel. [19][20][21][22][23][24][25] However, many of the above given procedures have shortcomings, such as a long reaction time, use of toxic reagents, formation of side products, or use of hazardous solvents. There are a few reports on the use of ionic liquids as catalysts for such reactions, with one such study performed by our group, in which a -SO 3 H-functionalized ionic liquid catalyst was used as a liquid catalyst for the synthesis of 3-substituted indoles.…”

Aminopropylated PEG as a novel, eco‐friendly and biodegradable basic catalyst for bis‐Michael addition to α,β‐unsaturated ketones under solvent‐free conditions

“…However, now a considerable improvement in terms of yield and time has been observed in the Michael addition reaction. In this context, a number of reagents have been developed which include silica nanoparticles, basic ionic liquid, tributylphosphine, poly( N ‐vinylimidazole), st‐DNA, tetraethylammonium superoxide, KF/CP, [C 4 dabco]OH ionic liquid, Rasta resin, immobilized lipase on Fe 3 O 4 /ZnO core/shell magnetic nanoparticles, polyvinyl sulfonic acid, silica sulfuric acid, KG‐60‐NEt 2 , KF/NP, NaHSO 4 .SiO 2 , 1 ‐Gd(OTf) 3 , Kf/basic alumina, Zn‐HAP and CSC‐Star‐SO 3 AlCl 2 . Moreover, most of the reactions are referred to mono‐Michael addition reaction, and very few reagents have been reported for the bis‐Michael addition reaction to date .…”