Silica-supported perchloric acid (HClO4-SiO2)

Abstract

(A) The Winkler reaction,4 the addition of cyanide to carbonyl, which allows the preparation of cyanohydrin, is one of the old carbon-carbon bond-forming reactions. Heydari et al. carried out the Winkler reaction by using HClO4-SiO2 to act as a highly effective catalyst. 5 [Chemical equation presented] (B) Xanthenes and benzoxanthenes are cited as active oxygen heterocycles possessing anti-bacterial, anti-inflammatory, and antiviral properties. They are also utilized in photodynamic therapy.6 Bigdeli et al. and Das et al. synthesised these molecules by using HClO4-SiO2 as catalyst. 7'8 [Chemical equation presented] (C) Quinolines are useful as drugs and pharmaceuticals. HClO4-SiO2 can be applied for the development of simple, convenient, and highyielding syntheses.9 [Chemical equation presented] (D) The Mannich reaction10 is an important cabon-carbon bond forming reaction and used for the synthesis of β-amino carbonyl compounds, which are important synthetic intermediates for various pharmaceuticals and natural products. Bigdeli et al. applied HClO 4SiO2 in a one-pot, three-component Mannich reaction. 11 [Chemical equation presented] (E) HClO4-SiO2 can be applied for the synthesis of 1, 4- dihydropyridines.12 [Chemical equation presented] (F) Carbamates (urethanes) are common components of agrochemicals, such as herbicides, fungicides, and pesticides as well as drug intermediates in the pharmaceuticals industry. Their ability to cyclize to heterocyclic compounds is widely exploited in organic synthesis. Modarresi-Alam et al. developed a novel and highly efficient method for the synthesis of various primary carbamates by using HClO4-SiO2 as an effective reagent.13 [Chemical equation presented] (G) One-pot Knoevenagel condensation, Michael addition, and cyclodehydration of dimedone and aldehydes in acetonitrile, aqueous and solvent free conditions was carried out by using this catalyst to give 1,8-dioxo-octahydroxanthenes.14 [Chemical equation presented] (H) 2,3-Unsaturated-O-glycosides are useful chiral intermediates in the synthesis of biologically active compounds, such as glycopeptide building blocks, oligosaccharides, and modified carbohydrates. HClO4-SiO2 allows the reaction of primary, secondary, and allylic alcohols, phenols, and thiophenols with 3,4,6-tri-O-acetyl-D-glucal to yield the corresponding 2,3-unsaturated-O-glycosides in good to excellent yields and in short reaction times with high a selectivity.15 [Chemical equation presented] (I) Nagarapu et al. applied HClO4-SiO2 for the synthesis of various homoallylic amines.16 [Chemical equation presented] (J) Recently, Shaterian et al. developed a new synthesis for amidoalkyl by the reaction of ary1 aldehyde, 2-naphthol, and acetonitrile or acetamide in the presence of HClO4-SiO2.17 [Chemical equation presented] (K) The conversion of cyclic diketones into keto enol ethers was previously carried out by treatment with alcohols in the presence of a catalyst, such as TiCl3, I2, B(C 6F5)3, (NH4)2Ce(NO 3)6, and Yb(OTf)3. However, the application of an improved heterogeneous catalyst in the preparation of keto enol ethers is felt to be highly useful and practical catalysts.18 [Chemical equation presented] (L) The Pechmann condensation19 is one of the most common procedures for the preparation of coumarin and its derivatives. This method involves the reactions between a phenol and a β-keto ester in the presence of an acidic catalyst. Maheswara et al. applied HClO 4-SiO2 under solvent-free conditions to carry out Pechmann condensation.20 [Chemical equation presented] © Georg Thieme Verlag Stuttgart.