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.
* Lectures presented at the International Symposium
on Green Chemistry, Delhi, India, 10-13 January 2001. Other presentations
are published in this issue, pp. 77-203.