Microwave-induced organic reaction enhancement (more) chemistry: Techniques for rapid, safe and inexpensive synthesis

Research on Chemical Intermediates (Impact Factor: 1.22). 06/2010; 20(1):1-11. DOI: 10.1163/156856794X00027


Synthetic organic reactions have been conducted under microwave irradiation in open vessels in unaltered domestic microwave
ovens. Reaction times vary from a few seconds for sub-milligram reactions to about 15 minutes for reactions carried out on
a scale of hundreds of grams. Promising results have been obtained for several condensations, as well as the Bischler-Napieralski
reaction, the Wolff-Kishner reduction, free radical dehalogenation reactions, and other standard synthetic operations. Rapid
catalytic transfer hydrogenation using ammonium formate as the source of hydrogen has been conducted at about 100-130 °C under
microwave irradiation.

Meaningful, safe and inexpensive synthetic experiments for undergraduate and pre-college students have been developed and
tested. The MORE chemistry techniques make it possible to use simple apparatus and very short reaction times.

Commercial microwave ovens are now essential equipment in our research and teaching laboratories [1-3]. These ovens are relatively
inexpensive, easy to move from one laboratory and set up in another, and safe to operate. Glass, plastics, and ceramics are
essentially transparent to microwaves whereas many organic compounds are dipolar in nature and absorb microwave energy readily.
We have found that untraditional experimental arrangements are possible for conducting a wide variety of organic reactions
in open vessels inside domestic microwave ovens. Depending on the quantity of reactants, most reactions (on a scale of milligrams
to several grams) can be completed in minutes instead of hours. One important element of our “Microwave-induced Organic Reaction
Enhancement” (MORE) chemistry is the proper choice of a microwave energy transfer agent as the reaction medium.

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    • "Similarly, Kumar and Joshi reported the reaction of several substituted β-diketones/β-ketoesters of pyrazolo[4,3-d]pyrimidin-7-one with 34 under microwave power at 300W without solvent using silica to yield several pyrazolo[4,3-d]pyrimidin-7-one based 3H-1,5-benzodiaze- pines [72]. Jiang et al. reported an efficient tandem methodology for the synthesis of highly functionalized pentacyclic isoindolefused benzo[b,e][1] [4]diazepine derivatives (57) in aqueous "
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    ABSTRACT: Microwave irradiation has been applied with success to cycloaddition reactions. The special characteristics of such irradiation entails the use of new methodologies, including equipment, glassware, solvents, and solid supports. All of these aspects are described in this review. Under classical heating conditions, these reactions usually require long reaction times, high temperatures, and/or Lewis acid catalysts, resulting in partial or total decomposition of sensitive compounds. This is a particularly significant problem in the synthesis of natural products. These problems have been conveniently overcome by the use of microwave irradiation. The short reaction time associated with microwave activation avoids decomposition of reagents and products, and prevents polymerization of the diene or dienophile. Heterocyclic compounds have been synthesized by cycloaddition reactions, or have been observed to react as dienes and dipoles under microwave irradiation conditions. Even those heterocyclic systems that are very reluctant to participate in cycloaddition reactions, such as pyrazoles, can be induced to react under microwave irradiation conditions. The application of this method to the chemistry of [60]fullerene has permitted derivatization of this system while avoiding the problems of polycycloaddition and cycloreversion. In most cases, spectacular accelerations and great improvements in yields and reaction conditions are observed. Finally, in some cases, changes in the chemo-, regio-, or stereoselectivity have been observed. These changes have been connected with the absolute hardness of the transition state, with the harder state being favored under microwave irradiation conditions. Microwave chemistry thus opens new possibilities for modifying the result of competitive reactions by considering the relative hardness of the transition states.
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