Celite-Supported Reagents in Organic Synthesis: An Overview

V.      Pace; J.      V. Sinisterra; A.      R. Alcantara

doi:10.2174/138527210793358213

Abstract

The use of reagents supported on inorganic carriers is becoming increasingly more common due to their high efficiency, which is mainly caused by a combination of several factors: a) an increase in the effective surface area for reaction; b) the presence of pores which constrain both substrate and reactant, thus lowering the activation entropy of the reaction; c) a synergism (for displacement reactions) resulting from bringing electrophiles and nucleophiles into proximity. Thus, organic reactions can be carried out cleanly, rapidly and in high yield under mild conditions. In this context, the diatomaceous earth Celite has been successfully employed to support a plethora of reagents, ranging from alkali fluorides (which allow to attain high chemoselective (hetero) atom (N, O, S) functionalization protocols, as well as Michael additions, nucleophilic aromatic substitution or organotin waste product removal), to oxidant agents (such as silver carbonate or chromium trioxide, in order to promote mild oxidations), as well as dehydrating agents (such as DCC). The absence of any chemical reactivity of this support is compatible with high functionalized molecules, therefore constituting a suitable methodology to modulate the reactivity of the effective reagent. Furthermore, the application of Celite-supported enzymes is a well known strategy for performing regio and/or stereoselective biotransformations; in fact, this easy immobilization technique allows the preparation of highly stable and active biocatalysts for many synthetic applications. Thus, in this paper we will present an overview of the use of Celite-supported reagents, both organic molecules and biocatalysts, in organic chemistry and biotransformations.

Keywords: Celite, supported reagents, chemoselectivity, fluorides, biotransformations, functionalization protocols, oxidant agents, dehydrating agents, Celite-supported enzymes, diatomite, acetonitrile, Potassium Fluoride, α-bromo-γ-butyrolactone, electrophilic reagent, Nucleophilic Aromatic Substitutions, Intramolecular Michael Additions, Phosphoramidates Synthesis, Montmorillonite, kieselgel, Cesium Fluoride, tetraalkyammonium fluorides, nucleophilic oxygen atoms, nucleophile, heteroaromatic thiols, 3,4-dihydropyrimidin-2-(1H)ones, β-diketoester enolate, 1,3-thiazolidin-4-ones, Aquaphilicity, Porcine pancreas, Candida rugosa, C. Cylindracea, Thermomyces lanuginosus, Humicola lanuginosa, Penicillium camembertii, P.cyclopium, Rhizopus javanicus, Mucor javanicus, Rhizomucor miehei, Rhizopus oryzae, R. javanicus, R. delemar, R. niveus, Candida antarctica B, Pseudomonas cepacia, Burkhloderia cepacia, Pseudomonas fluorescens, Chromobacterium viscosum, Bacillus thermocatenolatus