Catalyst-free synthesis of coumarin-, quinolone- and pyridine-annulated oxazole derivatives

An efficient approach for the synthesis of coumarin-, quinolone- and pyridine-annulated oxazole derivatives has been achieved by direct base-mediated intramolecular carbon-oxygen bond formation in a transition metal catalyst-free protocol. Intramolecular cyclization of o-bromoamides in DMSO in the presence of Cs2CO3 at 130 degrees C affords heterocycle-annulated oxazole derivatives in high yields via a nucleophilic ;addition of amide to form the C-O bond. (C) 2012 Published by Elsevier Ltd.