Citation:

Varma*, R S. AND Ju**,Y. ‘GREENER’ CHEMICAL SYNTHESES USING MICROWAVES. Presented at AIChE Annual Meeting 4th World Congress on Microwaves and Radio Frequency Applications, Austin, TX, November 07 - 12, 2004.

Impact/Purpose:

To inform the public.

Description:

The diverse nature of chemical entities requires various green strategic pathways in our quest towards attaining sustainability. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports such as alumina, silica, clay, or ‘doped’ surfaces is presented 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. Recent results on MW-assisted solventless preparation of ionic liquids and the application of microwave heating in aqueous medium rapid preparation of cyclic amines and tertiary amines is described. The synthesis of cyclic amines, important building blocks for pharmaceuticals, is accelerated via double N-alkylation of primary amines thus shortening the reaction time significantly. The protocol utilizes readily available primary amine and alkyl dihalides to assemble two C-N bond in a simple SN2 cyclization experimental protocol and avoids the conventional multi-step approach that involves expensive metal catalysts. A three-component solventless coupling of aldehyde, alkyne and amine (A3 coupling) has also been optimized that uses only CuBr as a catalyst. The potential application of this reaction in the enantioselective construction of a new chiral center by utilizing an effective chiral ligand such as 2,6-bis-[(4S)-(-)-isopropyl-4,5-dihydro-oxazol-2-yl]-pyridine will be described.

Record Details: