Recent Advances in KF/alumina Promoted Organic Reactions

Abstract

Organic reactions promoted on a solid heterogeneous phase attract widespread interest within synthetic chemists from industries and academia. Potassium fluoride impregnated over aluminum oxide (KF/alumina) has been recognized as remarkably useful heterogeneous surface to promote many base-catalyzed organic transformations. The basic sites on KF/alumina may be associated to a very hard anion (F -anion), which possibly augments the surface to be active as a potential base and differentiates from other alkaline earth metal oxides as base catalysts. The source of the basicity has, however, been the subject of some debate in the literature. Besides classical organic reactions, such as alkylation, condensation and elimination reactions, KF/alumina has been successfully utilized as heterogeneous basic surface in several metal-catalyzed coupling reactions. Palladium-catalyzed C-C bond-forming reactions (e.g. Heck, Stille, Suzuki, Trost-Tsuji reactions), C-N bond-forming Buchwald-Hartwig reactions, and C-O bond-forming Baylis-Hillman type reactions have been reported with the aid of KF/alumina as the heterogeneous base. The KF/alumina catalyzed reactions are in many cases carried out without using any solvent, thus providing a clean and "green" reaction set up followed by easy product isolation. The solid surface has also been employed for preparing combinatorial libraries of different small molecules. In many cases, application of microwave irradiation has shown dramatic acceleration of the rate of transformations. This article will review the applications of KF/alumina in various organic reactions focusing on achievements during the period from 2001 to 2005.

Solvent-free and time-efficient Suzuki–Miyaura reaction in a ball mill: the solid reagent system KF–Al2O3under inspection

“…Over the last two decades, a major trend in the field of organic chemistry has been evident: environmentally friendly processes using safer reagents, generating fewer side products and requiring less use of solvents are in vogue [ 1 – 2 ]. This trend has led to an explosive growth in the fields of solvent-free synthesis [ 3 – 13 ] and solid-supported reagents [ 14 – 18 ] such as potassium fluoride on alumina (KF–Al 2 O 3 ) [ 19 – 20 ]. This versatile reagent was originally introduced in 1979 by Ando et al as a useful agent for inducing alkylation reactions [ 21 ].…”

“…This versatile reagent was originally introduced in 1979 by Ando et al as a useful agent for inducing alkylation reactions [ 21 ]. Additional benefits have been derived by taking advantage of the strongly basic nature of KF–Al 2 O 3 , which can replace organic bases in a number of reactions including, but not limited to, alkylations or epoxidations [ 18 – 20 22 – 29 ]. Apart from the plethora of synthetic applications, there is one major issue that has not been addressed in the literature so far.…”

KF/Al2O3 Mediated Multicomponent Reactions for the Efficient Synthesis of Highly Substituted Dihydropyridines

“…Interestingly, the same reaction provided 80% yield in the presence of KF/Al 2 O 3. The exact explanation for the better efficacy of KF/Al 2 O 3 in base catalyzed reactions is still a subject of debate in the literature . As per Ando et al, the better catalytic activity of KF/Al 2 O 3 may be due to the presence of three basic species (i) co‐ordinately unsaturated active fluoride; (ii) the presence of [Al–O ‾ ] ion which generates OH ‾ when water is added; and (iii) the cooperation of F ‾ and [Al–OH] .…”

Modification of bio-based β-diketone from wheat straw wax: synthesis of polydentate lipophilic super-chelators for enhanced metal recovery

“…14 Several heterogeneous bases have been found to be excellent catalysts for promoting Michael addition reactions. 15,16 KF/ alumina in particular has attracted widespread interest due to the simplicity of its use and environmentally-benign production. 17,18 It has been shown to be effective at a low loading of 5 mmol g À1 KF on alumina in the reaction of acetylacetone with methyl acrylate.…”