Perchloric Acid Impregnated on Silica Gel (HClO₄/SiO₂): A Versatile Catalyst for Michael Addition of Thiols to the Electron‐Deficient Alkenes

Abstract

Perchloric acid adsorbed on silica gel (HClO4/SiO2) has been found to be a highly efficient and versatile catalyst for the Michael addition of thiols to a wide variety of conjugated alkenes such as α,β‐unsaturated ketones, carboxylic esters, nitriles, amides and chalcones in dichloromethane or methanol at room temperature. The reactions are completed within 2–20 min in high yields. Some of the additional advantages are: no aqueous work‐up is necessary, and the catalyst is also reusable. Moreover, the solid product can be obtained without chromatographic separation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Preparation, Characterization and First Application of Alumina Supported Polyphosphoric Acid (PPA/Al2O3) as a Reusable Catalyst for the Synthesis of 14-Aryl-14H-dibenzo[a, j]xanthenes

“…, respectively, increased the yield of the product 3d, whereas further increase in both catalyst amount and temperature was found to have an inhibitory effect on formation of the product (entries 5,8,11,14).…”

Alumina Supported Acidic Ionic Liquid: Preparation, Characterization, and Its Application as Catalyst in the Synthesis of 1,8-dioxo-octahydroxanthenes

“…Among the various supported catalysts, particularly, alumina and silica supported reagents have advantages of low cost, ease of preparation, and catalyst recycling. [15][16][17][18] Xanthenes have received great attention because of their wide range of therapeutic and biological properties, such as antibacterial, [19] antiviral, [20] and anti-inflammatory activities. [21] Apart from their use as valuable synthetic precursors for many organic compounds [22] and dyes [23] they also found uses in laser technologies, [24] and fluorescent materials for visualization of biomolecules.…”

A One-Pot synthesis of 1,2-Dihydro-1-arylnaphtho[1,2-e][1,3]oxazine-3-one Derivatives catalyzed by Perchloric Acid Supported on Silica (HClO4/SiO2) in the absence of solvent

“…The use of silica-supported reagents in one-pot multi-component construction of heterocycles has received considerable attention in organic synthesis [10]. In particular, perchloric acid adsorbed on silica gel (HClO 4 /SiO 2 ) [11] has emerged as an extremely useful catalyst in various organic transformations including acylation of alcohols [11], acylation of aldehydes [12], 1,3-dithiolane/dithiane formation [13], tetrahydropyranylation [14], thio-acetalization [14], Ferrier rearrangement [15], Michael addition [16], cleavage of ketals and benzylidene acetals [17], the Hantzsch condensation [18], synthesis of bis-indolylmethanes [19], glycosylation of sugars [20] N-tert-butoxycarbonylation of amines [21], synthesis of tetrasubstituted imidazoles [22], synthesis of polysubstituted quinolines [23] and synthesis of benzoxanthenes [24].…”