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ENVIRONMENTALLY FRIENDLIER ALTERNATIVES TO ORGANIC SYNTHESIS USING MICROWAVES
Citation:
Varma*, R S. ENVIRONMENTALLY FRIENDLIER ALTERNATIVES TO ORGANIC SYNTHESIS USING MICROWAVES. Presented at Presentation Chemistry Department, Clemson University, Clemson, SC, 9/27/2001.
Description:
Microwave irradiation has been used for a variety of organic transformations wherein chemical reactions are expedited because of selective adsorption of microwave (MW) energy by polar molecules, non-polar molecules being inert to the MW dielectric loss. The MW application under solventless conditions enables rapid synthetic transformations at ambient pressure thus providing unique chemical processes with special attributes such as ease of manipulation, enhanced reaction rates and higher yields. Recent results from our laboratory on this MW-expedited approach will be described for the synthesis of a variety of industrially significant compounds and intemediates namely, enones, imines, enamines, nitroalkenes, oxidized sulfur compounds and ionic liquids. This solvent-free synthetic methodology involves microwave exposure of reactants in neat form or their reaction in presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports namely silica, alumina, clay, or 'doped' surfaces, such as clayfen, claycop, NH2OH-clay, PhI(OAc)2-alumina, NaIO4-silica and NaBH4-clay. A variety of condensation, cyclization, oxidation and reduction rections will be presented including the convergent one-pot assembly of heterocyclic molecules from in situ generated intermediates such as a-tosyloxyketones and enamines. The application of this solventless MW approach to multi-component reactions will be highlighted which can be adapted for high-seed parallel synthesis of the library of biologically active molecules. The distinct advantages of this strategy, that reduces or prevents pollution 'at-source,' will be exemplified by efficient functional group transformations involving non-metallic hypervalent iodine oxidants nd substitution of conventonal metal-based reducing agents as demonstrated in crossed Cannizzaro reaction using paraformaldehyde and solid state synthesis of heterocyclic hydrazones under catalyst-free conditions.