Microwave activated organic reactions

G. Bram, A. Loupy, D. Villemin, Microwave Activation of Reactions on Inorganic Solid Supports. In Solid Supports and Catalysts in Organic Synthesis, K. Smith (Ed.), Ellis Horwood Pretenice Hall, London, 1992. 

Westaway, K. and Gedye, R.N., The question of specific activation of organic reactions by microwaves, J. Microw. Power Electromagn. Energy., 1995, 30, 219. 

The use of domestic microwave and automated oven in organic synthesis is well established (Microwave activation has become a very popular and useful technology in organic and medicinal chemistry. For some recent examples, see [128-131]). This is particularly very noteworthy because of the unconventional set up necessary for conducting the reaction. Microwave irradiation of a solution of imines 21, 23, and 29 with acetoxyacetyl chloride in chlorobenzene using a domestic and... 

For the development of a sustainable chemistry based on clean technologies, the best solvent would be no solvent at all. For this reason, considerable efforts have recently been made to design reactions that proceed under solvent-free conditions, using modern techniques such as reactions on solid mineral supports (alumina, silica, clays), solid-state reactions without any solvent, support, or catalyst between neat reactants, solid-liquid phase-transfer catalysed and microwave-activated reactions, as well as gas-phase reactions [37-42]. However, not all organic reactions can be carried out in the absence of a solvent some organic reactions even proceed explosively in the solid state Therefore, solvents will still be useful in mediating and moderating chemical reactions and this book on solvent effects will certainly not become superfluous in the foreseeable future. 

A number of low-grade transition metal ores (for example, minerals containing nickel oxides) can be used as catalysts. Smuda has demonstrated that microwave or radiofrequency irradiation of a mixture of such ores with a carbon source initiates reduction of the oxide to metal. With this approach, poisoning the active sites of the catalyst will not be critical for the process since there will be a constant supply and generation of active catalyst with the feed material. In addition to well-known catalytic properties of nickel in organic reactions, it was also shown that Ni on carbon and other supports, catalyzes hydrodechlorination and dehydrochlorination of chlorinated organic waste streams [22-24],... 

Shiradkar et al. [19] reported the synthesis of clubbed thiazolyl triazole derivatives (vii) starting from ethyl acetoacetate, by microwave organic reaction enhanced method (MORE). The synthesized triazoles showed promising antimicrobial and antimycobacterial activities. 

Kniep R, Simon P (2007) Fluorapatite-Gelatine-Nanocomposites Self-Organized Morphogenesis, Real Structure and Relations to Natural Hard Materials. 270 73-125 Koenig BW (2007) Residual Dipolar Couplings Report on the Active Conformation of Rhodopsin-Bound Protein Fragments. 272 187-216 Komatsu K (2005) The Mechanochemical Solid-State Reaction of Fullerenes. 254 185-206 Kremsner JM, Stadler A, Kappe CO (2006) The Scale-Up of Microwave-Assisted Organic Synthesis. 266 233-278... 

Although phase-transfer catalysis has been most often used for nucleophilic substitutions, it is not confined to these reactions. Any reaction that needs an insoluble anion dissolved in an organic solvent can be accelerated by an appropriate phase-transfer catalyst. We will see some examples in later chapters. In fact, in principle, the method is not even limited to anions, and a small amount of work has been done in transferring cations," radicals, and molecules." The reverse type of phase-transfer catalysis has also been reported transport into the aqueous phase of a reactant that is soluble in organic solvents." Microwave activated phase-transfer catalysis has been reported." ... 

It is well known that a wide variety of organic reactions are accelerated substantially by microwave irradiation in sealed tubes. These rate enhancements can be attributed to superheating of the solvent, because of the increased pressure generated when the reactions are performed in the a.m. manner. Furthermore several reports have described increased reaction rates for reactions conducted under the action of microwave irradiation at atmospheric pressure, suggesting specific or nonthermal activation by microwaves. Some of these re-studied reactions occur at... 

The 2-pyridone core structure is present in a wide range of compounds with antibacterial, antifungal, and antitumor activity members of this family also play an important role in Alzheimer s disease. By employing microwave-assisted organic synthesis, efficient conditions have been established for introduction of ami-nomethylene substituents in highly substituted bicyclic 2-pyridones. To incorporate tertiary aminomethylene substituents in the 2-pyridone framework, a microwave-assisted Mannich reaction using preformed imminium salts proved to be effective. Primary amino methylene substituents were introduced via cyanodehalogenation then borane dimethyl sulfide reduction of the afforded nitrile (Scheme 10.36) [78]. Microwave irradiation proved superior to traditional conditions for these transformations. 

Microwave processing of zeolites and their application in the catalysis of synthetic organic reactions has recently been excellently reviewed by Cundy [25] and other authors [26], The microwave synthesis of zeolites and mesoporous materials was surveyed, with emphasis on those aspects which differ from conventional thermal methods. The observed rate enhancement of microwave-mediated organic synthesis achieved by use of these catalysts was caused by a variety of thermal effects, including very high rates of temperature increase, bulk superheating, and differential heating. Examples of microwave activation of chemical reactions catalyzed by zeolites will be presented in Section 13.3. 

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