Synthesis of Indolizines via Iodocyclization of Pyridine Allylic Acetates

Significance

Presented is a method for the synthesis of indolizines involving a 5-endo-trig iodo­cyclization of substituted pyridine allylic acetates. The work is a sequel of a previous report on a facile 5-endo-dig iodocyclization approach to highly substituted indolizines (I. Kim et al. Tetrahedron Lett. 2007, 48, 6863). The yields of products are moderate to good except for R³ = H, where the reaction failed or led to recovery of starting material. Furthermore, exposing 2-pyridyl propargylic acetate to the reported reaction conditions failed to give the expected product. The method is simple and efficient, but the starting pyridyl allylic acetates have to be prepared by metal-halogen exchange of substituted 2-bromo pyridines. The substrate scope was inadequately studied.