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3-Methyl-1-sulfonic acid imidazolium hydrogen sulfate ([MSIm][HSO4]) catalyzed the condensation of 5-aminobenzotriazole and 5,5-dimethyl-cyclohexane-1,3-dione (dimedone) with aromatic aldehydes under microwave irradiation. This method is efficient to synthesize 11-aryl-8,8-dimethyl-6,7,9,11-tetrahydro[1,2,3]triazolo[4,5-a]acridine-10(1H)-one derivatives as a series of tetrahydroacridines in good to excellent yields, while the catalyst can be recovered and reused up to six times without significant loss of activity. This one-pot three-component reaction provided an efficient method for the synthesis of aromatic heterocycles.

N-Methylimidazolium perchlorate ([MIm]ClO4) was synthesized and some of its physico-chemical properties, such as density, surface tension were investigated. A thermo gravimetric analysis (TGA) and solvent performance were also studied. The results show that this ionic liquid is an excellent catalyst for the synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ol) derivatives under solvent-free conditions. This method has the advantages of high yield, clean transformation, simple operation and short reaction time. The ionic liquid can be recycled without significant loss of activity.

Poly(4-vinylpyridinium) perchlorate is found to be an excellent catalyst for the chemoselective N-Boc protection of various amines under neat reaction conditions.

via multicomponent reaction of 4-hydroxypyran-2-one with aromatic aldehydes and malononitrile

Poly(N-vinylimidazole) is able to promote instantaneous quantitative acetylation of a variety of functionalized alcohols, phenols, thiols and amines with acetic anhydride at room temperature under solvent-free conditions. This new method consistently has excellent yields and the catalyst can be reused and recovered several times. Furthermore, the reaction can even be carried out on a larger scale.

The reaction of 2-naphthol with aromatic aldehydes is catalyzed by DBH in the presence of kaolin as an additive to give dibenzoxanthene derivatives in high yields.

Acidic ionic liquid [Msim]HSO4 is used as an efficient catalyst for Pechmann condensation reaction.

Succinimide sulfonic acid (SuSA) as a stable reagent is easily prepared by the reaction of succinimide with neat chlorosulfonic acid. This compound is able to catalyze the chemoselective conversion of amines to their corresponding N-Boc protected derivatives with (Boc)2O. All reactions were performed under mild conditions, giving the desired products in good to high yields.

A novel method for the synthesis of polycyclic triones of type (IV) includes a three-component condensation in the presence of a recycable heterogeneous catalyst.