Taking Up the Cudgels for Perchlorates: Uses and Applications in Organic Reactions under Mild Conditions

Abstract

Metal perchlorates are compounds of great chemical interest since they possess some unique properties, such as high electronegativity and relatively low charge density, poor complexing ability, high solubility in various organic solvents, and kinetic stability under mild conditions. Besides providing polar media when dissolved in solvents, metal perchlorates have recently found wide employment as Lewis acid promoters in various organic transformations, both in the development of new techniques for known and widely used reactions and in promotion of new kinds of reactivity. This paper presents a general overview of the more recent uses of lithium, magnesium, zinc, and nickel perchlorates, underlining the fact that such perchlorates are quite safe chemical products under mild conditions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Iron‐Catalyzed One‐Pot Oxidative Esterification of Aldehydes

“…As a result of its manipulation ease, low‐cost, and benign character, the new iron catalyst described appears promising for large‐scale applications. It must be pointed out that perchlorate salts are stable under ordinary conditions of use 18. Furthermore, the use of hydrogen peroxide as oxidant is quite attractive, because it generates water as the only byproduct.…”

Multicomponent Domino Reaction Promoted by Mg(ClO4)2: Highly Efficient Access to Functionalized 1,4‐Dihydropyridines

“…Concerning the reaction mechanism, a plausible explanation is depicted in Scheme 3. In the presence of magnesium perchlorate, which is known to be able to coordinate 1,3bidentate compounds, [10] carbonyl derivative 9 rapidly condensed with the amine eliminating water and forming enamino derivative 1. Compound 1 added to ethyl propiolate (4) to give Michael adduct 11, as an intermediate, which underwent a second conjugate addition from 1 to give 12.…”

“…, 3.14(d, J = 1.4 Hz, 1 H), 3.87 (ddd, J = 4.5, 10.5, 1.5 Hz, 1 H), 4.10-4.25 (m, 6 H),6.14 (br. q, J = 1.5 Hz, 1 H),6.50-6.60 (m, 3 H), 7.13 (t, J = 8.0 Hz, 1 H),10.30 (br. s, 1 H) ppm.…”

Magnesium perchlorate as efficient Lewis acid for the Knoevenagel condensation between β-diketones and aldehydes

“…On the other hand, perchlorate salts of alkaline and alkaline earth metals showed to be very active in promoting a large variety of reactions, 18 in some cases being more powerful than metal triflates. 16b,17c,19 Concerning the risk connected with the use of such salts, it has been demonstrated that such perchlorates are not dangerous chemicals if not employed under highly acidic conditions and not exposed to high temperatures (>300-500°C).…”