Acylation, ionic liquids acylated indoles

Acylated indoles are important building block for pharmaceutical synthesis. The chloroaluminate ionic liquids have been applied as the eco-friendly catalysts and reaction mediums to the acylation of indoles and substituted indoles. Yeung et al. have investigated the acylation of poor electron indole ring with acidic ionic liquid,... 

Yeung KS, Farkas ME, Qiu Z et al (2002) Fiiedel-Crafts acylation of indoles in acidic imida-zolium chloroaluminate ionic liquid at room temperature. Tetrahedron Lett 43 5793-5795... 

The aluminum chloride-promoted Friedel-Crafts acylation can also be successfully performed in ionic media. An easy-to-handle ionic liquid is that prepared from a mixture of one to two equivalents of aluminum chloride and l-ethyl-3-methylimidazolium chloride or iodide (EtMeimCl-AlCl3 and EtMeiml-AlCls, respectively). These solvent-catalysfs can be utilized in the easy and efficient acylation of unprotected indoles with a variety of acyl chlorides to give C-selective acylation at the 3-position in 38%-87% yield. ... 

Friedel-Crafts acylation can also be carried out in the absence of a catalyst. Seddon has described the synthesis of Pravadoline 70, a non-steroidal antiinflammatory drug starting from commercially available reagents, the indole 69 was prepared by a nucleophilic displacement in [bmimllPFe]. Friedel-Crafts acylation in the same solvent produced the desired product 70 (Scheme 25). The ionic liquid was reused after isolation of the product. " ... 

Wenkert, E., Moeller, P.D., Piettre, S.R. (1988). Five-membered aromatic heterocycles as dienophiles in Diels-Alder reactions. Furan, pyrrole and indole Journal of the American Chemical Society, 110, 21, 7188-7194, ISSN 0002-7863 Wenkert, E., Piettre, S.R. (1988). Reaction of a-and 3-acylated furans with conjugated dienes. Journal of Organic Chemistry, 53,5850-5853, ISSN 0022-3263 Wilkes, J.S. (2002). A short history of ionic liquids - From molten salts to neoteric solvents. Green Chemistry, 4, 73-80, ISSN 1463-9270... 

Acylated indoles that are commonly found in molecules of pharmaceutical interest are prepared in high yields using aluminum chloride in an ionic liquid (l-ethyl-3-methylimidazolium chloride) (eq 51). ... 

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