Enaminones as intermediates in the synthesis of indolizidine alkaloids

Abstract

The use of vinylogous urethanes as pivotal intermediates in the synthesis of indolizidine alkaloids is illustrated with reference to indolizidines 209B (1) and 167B (2), two simple alkaloids isolated from dendrobatid frogs. Methodology is optimized for the diastereoselective synthesis of the racemic alkaloids, after which modifications leading towards the enantioselective synthesis of (-)-indolizidine 209B are presented.