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(NO 3 ) 3 -clay (clayfen), Cu(NO 3 ) 2 -clay (claycop), NH 2 OH-clay, PhI(OAc) 2 -alumina, NaIO 4 -silica, MnO 2 -silica, and NaBH 4 -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(1 H )-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.
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Rajender S. Varma (2001) studied this question.