Flash‐Vacuum Pyrolysis of Stabilised Phosphorus Ylides, 9 . Preparation and pyrolysis of β,γ‐dioxo ylides, β,β′,γ,γ′‐Tetraoxo Ylides and Hexaoxo Bis(ylides)

Six examples of the β,β′,γ,γ′‐tetraoxo phosphorus ylides 6 have been prepared. While they are found, upon flash‐vacuum pyrolysis (FVP) at 500°C to decompose to give no useful products, conventional pyrolysis by distillation at 200°C gives the trioxo alkynes 12 and 13 where R 1 and R 2 are alkoxy groups. Three examples of the previously unknown hexaoxo bis(ylides) 7 have been obtained but, with eight contiguous C=X functions, these are too fragile to give any useful product upon FVP. The pyrolysis of the simpler β,γ‐dioxo ylides 9 used to prepare 6 and 7 has also been examined for the first time and at 600°C it gives the alkynes 11 in low yield for R 1 = OMe or OEt but not Ph. The fully assigned 13 C‐NMR spectra of all the ylides 6, 7 , and 9 are presented.