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CHEMISTRY UNDER NON-TRADITIONAL CONDITIONS: SOLVENT-FREE SYNTHESIS USING MICROWAVE IRRADIATION
Citation:
VARMA, R. S. CHEMISTRY UNDER NON-TRADITIONAL CONDITIONS: SOLVENT-FREE SYNTHESIS USING MICROWAVE IRRADIATION. Presented at 2nd International Conference on Green & Sustainable Chemistry, Washington, DC, June 20 - 24, 2005.
Impact/Purpose:
To inform the public.
Description:
A solvent-free approach that involves microwave (MW) irradiation of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces is presented which is applicable to a wide range of cleavage, condensation, cyclization, oxidation and reduction reactions including rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermediates. The strategy is adaptable to multi-component reactions e.g. Ugi and Biginelli reactions for rapid assembly of a library of compounds. Synthesis of a wide variety of significant precursors and intermediates namely, enones, imines, enamines, nitroalkenes, and oxidized sulfur species is depicted and their value in concise synthesis of flavones, tetrahydroquinolones, 2-aroylbenzofurans, and thiazole derivatives is illustrated including the solventless preparation of ionic liquids. In this historical account, the rationalization of microwave effects and mechanistic considerations possibly involving the intermediacy of polar transition states will be discussed.