Ylide rearrangements: a [3,2]-sigmatropic process in a phosphorus ylide

The thermal behaviour of 3-methylbut-2-enyl-diphenyl-(3-methylbut-2-enyl)phosphorane has been examined: unlike the carbon, nitrogen, oxygen, and sulphur analogues of this molecule only a small fraction of the rearrangement proceeds through the [3,2]-sigmatropic shift, the major pathway being a radical dissociation–recombination.