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Greener Alternatives to Expedient Synthesis of Heterocycles and Nanomaterial
Citation:
VARMA, R. S. Greener Alternatives to Expedient Synthesis of Heterocycles and Nanomaterial. Presented at International Conference on Interface of Chemistry-Biology in Biomedical Researc, Beijing, CHINA, November 12, 2007.
Impact/Purpose:
To inform the public.
Description:
A brief account of reactions involving microwave (MW) exposure of neat reactants or catalyzed by mineral support surfaces, such as alumina, silica, clay, or their ‘doped’ versions, for the rapid one-pot assembly of heterocyclic compounds [1] from in situ generated reactive intermediates via enamines [2] or using hypervalent iodine reagents [3] will be described that can be adapted for parallel synthesis in multicomponent reactions (Biginelli and Ugi reactions) [4]. The eco-friendly nucleophilic substitution chemistry in water [5] can be manipulated using microwaves to generate cyclic amines via double N-alkylation of primary amines or hydrazines by dihalides or tosylates [6]. Greener protocols for the synthesis of pharmaceutically active heterocycles namely N-aryl azacycloalkanes, isoindoles, and dihydropyrazoles [6], 1,3,4-oxadiazoles, 1,3,4-thiadiazoles, 1,3-dioxanes [7a], pyrazoles, hydrazones [7b] and 3,4-dihydropyrimidin-2(1H)-ones [7c], catalyzed by basic water or polystyrene sulfonic acid (PSSA) in aqueous media or solid supported Nafion®NR50, or (P4S10/Al2O3) under solvent-free conditions will be described. Aqueous preparation of nanoparticles using vitamins B1 and B2 [8a], which can function both as reducing and capping agents and the bulk and shape-controlled synthesis of noble nanostructures via microwave (MW)-assisted spontaneous reduction of noble metal salts using -D-glucose, sucrose, and maltose [8b] will be presented. A general MW method has been developed that accomplishes the cross-linking reaction of poly (vinyl alcohol) (PVA) with metallic systems such as Pt, Cu, and In; bimetallic systems, namely Pt-In, Ag-Pt, Pt-Fe, Cu-Pd, Pt-Pd and Pd-Fe [9a]; and SWNT, MWNT, and C-60 [9b]. The strategy is extended to the formation of biodegradable carboxymethyl cellulose (CMC) composite films with noble nanometals [10]; such metal decoration and alignment of carbon nanotubes in CMC is possible using MW approach [11] which also enables the shape-controlled bulk synthesis of Ag and Fe nanorods in poly (ethylene glycol) [12]. The application of nano-sized MgO is demonstrated in the green synthesis of 2-amino-2-chromene derivatives in aqueous PEG [13].