Total synthesis of (-)-colchicine by an oxyallyl [4+3] cycloaddition

An enantioselective synthesis of (-)-colchicine, free from isocolchicine, is delineated and features tandem application of the intramolecular Diels-Alder reaction of acetylene-tethered oxazoles and the [4+3] cycloaddition of oxyallyls. This work underscores the synthetic utility of little explored oc-alkoxy substituted oxyallyls. (C) 2000 Elsevier Science Ltd. All rights reserved.