A new class of ammonium ylid for [2,3]-sigmatropic rearrangement reactions: ene-endo-spiro ylids

The first examples of sigmatropic rearrangements of ene-endo-spirocyclic, tetrahydropyridine-derived ammonium ylids are reported. Thus, spiro6.7]-ylids rearrange primarily by a 2,3]-pathway, whereas the analogous 6.6]-ylids rearrange by 1,2]- and 2,3]-mechanisms in roughly equal proportions. This method serves as a rapid entry to the core of a range of alkaloids bearing a pyrrolo1,2-a]azepine or octahydroindolizidine nucleus.