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CHEMICAL TRANSFORMATIONS USING NON-TRADITIONAL APPROACHES: MICROWAVE-ASSISTED GREENER SYNTHESES IN AQUEOUS MEDIA OR UNDER SOLVENT-FREE CONDITIONS
Citation:
VARMA, R. S. CHEMICAL TRANSFORMATIONS USING NON-TRADITIONAL APPROACHES: MICROWAVE-ASSISTED GREENER SYNTHESES IN AQUEOUS MEDIA OR UNDER SOLVENT-FREE CONDITIONS. Presented at Cambridge Healthtech Institute Process R&D Summit, Philadelphia, PA, October 03 - 06, 2006.
Impact/Purpose:
To inform the public
Description:
Microwave (MW) irradiation in conjunction with water as reaction media has proven to be a 'greener' chemical approach for expeditious N-alkylation reactions of amines and hydrazines wherein the reactions under mildly basic conditions afford tertiary amines and double N-alkylation to assemble a series of heterocyclic moieties such as N-azacycloalkanes, 4,5-dihydropyrazoles and pyrazolidines etc. Nucleophilic substitution reactions in water using microwaves lead to cleaner syntheses of alkyl azides, thiocynates, sulfones and β-ketosulfones with considerable reduction in reaction times, and improved tolerance for functional groups such as carbonyl, hydroxyl and esters. Another eco-friendly solvent-free strategy will be discussed that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of recyclable mineral supports such as alumina, silica, clay, or 'doped' surfaces which is applicable to a wide range of cleavage, condensation, cyclization, rearrangement, oxidation and reduction reactions including rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermediates.