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NON-TRADITIONAL 'GREENER' ALTERNATIVES TO SYNTHETIC ORGANIC TRANSFORMATIONS
Citation:
Varma*, R S. NON-TRADITIONAL 'GREENER' ALTERNATIVES TO SYNTHETIC ORGANIC TRANSFORMATIONS. Presented at Sumitomo Chemical Research Lab, Osaka, JAPAN, November 10 - 20, 2002.
Impact/Purpose:
To inform the public.
Description:
Non-traditional 'Greener' Alternatives to Synthetic Organic Transformations
Rajender S. Varma
Synthetic organic transformations performed under non-traditional conditions are becoming popular primarily to circumvent the growing environmental concerns. A rapid and environmentally friendlier approach for organic synthesis and transformations is described which involves microwave (MW) exposure of neat reactants (undiluted) often in presence of inorganic oxides as recyclable catalysts such as alumina, silica, clay, or 'doped' surfaces. A variety of deprotection, condensation, cyclization, oxidation and reduction reactions will be presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and a-tosyloxyketones. Industrially significant compounds namely, enones, imines, enamines, nitroalkenes, oxidized sulfur species and heterocycles such as flavones, tetrahydroquinolones, 2-aroylbenzofurans, and thiazoles are easily obtainable by this methodology. The application of this solventless MW approach to multi-component reactions will be 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. The solvent-free preparation of ionic liquids, a newer class of solvents with barely measurable vapor pressure, is also described that proceeds nearly at room temperature. 'Greener' solvents such as supercritical (sc) carbon dioxide provide an attractive media for supported metallic catalysts such as Pd/alumina for industrially significant transformations namely selective hydrogenation of maleic anhydride to g-butyrolactone. The salient eco-friendly features of these processes namely the selectivity, experimental ease of manipulation, and the enhanced reaction rates will be described.