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Pure Appl. Chem., 2001, Vol. 73, No. 1, pp. 193-198

Solvent-free accelerated organic syntheses using microwaves

Rajender S. Varma

Clean Processes Branch, National Risk Management Research Laboratory, U.S. Environmental Protection Agency, MS 443, Cincinnati, Ohio 45268, USA

Abstract: A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure of neat reactants (undiluted) either in the presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces, namely, Fe(NO3)3-clay (clayfen), Cu(NO3)2-clay (claycop), NH2OH-clay, PhI(OAc)2-alumina, NaIO4-silica, MnO2-silica, and NaBH4-clay. A variety of deprotection, condensation, cyclization, oxidation, and reduction reactions are presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and a-tosyloxyketones. The application of this solvent-free MW approach to multicomponent reactions is highlighted that can be adapted for high-speed parallel synthesis of the library of dihydropyrimidine-2(1H)-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.