Au-catalyzed synthesis of 5, 6-dihydro-8 H-indolizin-7-ones from readily available N-(pent-2- en-4-ynyl)-β-lactams is developed. In this reaction, a 5-exo-dig cyclization of the β-lactam nitrogen to the Au-activated C− C triple bond is followed by heterolytic fragmentation of the amide bond, forming a highly nucleophilic acyl cation. An expedient formal synthesis of indolizidine 167B was easily achieved using this new method.
