Gold-Catalyzed Synthesis of Indolizin-7-ones from Enynyl β-Lactams

Significance

Described here is a gold-catalyzed synthesis of 5,6-dihydro-8H-indolizin-7-ones from tethered enynyl β-lactams. The now well recognized selective C-C triple bond activation by the gold catalyst is followed by a 5-exo-dig cyclization and heterolytic fragmentation of the amide functionality to form a highly nucleophilic acyl cation. This species is proposed, without evidence, to undergo cyclization to the enamine to give the indolizinone core. Application of the synthetic methodology to the construction of the naturally occurring indolizidine 167B is described.