Admicellar catalysis

Sarkar and Mukhopadhyay have developed a three-component green methodology to synthesize ethyl/methyl 4-hydroxy-5-oxo-l,2-diaryl-2,5-dihydro-lH-pyrrole-3-carboxylates under admicellar catalysis by Ti02 nanoparticles at room temperature [59]. The catalyst in aqueous CTAB solution promotes the formation of admicelles, and the reaction occurs in admicellar environment. A number of aromatic aldehydes 51, amines 9, and diethyl/dimethyl acetylene dicarboxylate (DEAD/DMAD, 70) react to give the products 71 in good yields (Scheme 23). In this reaction, aldehydes have also been replaced with isatin 55 to give spiro-fused products. 

SCHEME 23 Synthesis of ethyl/methyl 4-hydroxy5-oxo-l,2-diaryl-2,5-dihydro-lH-pyrrole-3-carboxylates under admicellar catalysis. CTAB, cetyltrimethylammonium bromide. 

The coexistence of hydrophilic and hydrophobic nano-domains separated in space, with a local order and fluidity typical of liquids, confer to supramolecular surfactant structures remarkable properties, which are advantageous in applications involving molecular confinement within nanoscopic regions and reactivity in micro-heterogeneous media. Micelle-mediated reactions constitute the basis of the so-called micellar catalysis [62, 116], admicellar catalysis [117] or admicellar polymerisation [118] in which reaction mechanisms may be controlled at a molecular level to save energy and raw materials, as well as to avoid lengthy post-reaction purification and analytical steps. 

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