Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 5. Selective extrusion of Ph₃PO from β,γ,β′-trioxo ylides to give diacylalkynes

Sixteen examples of the previously unknown trioxo ylides 7 have been prepared by acylation of stabilised phosphorus ylides 8 with alpha-oxo acid chlorides 9. Extrusion of Ph(3)PO from these is readily achieved using FVP at 500 degrees C in most cases, to afford the diacylalkynes 10 in moderate yield. Three examples failed to give the expected alkynes and the nature of the processes involved in these cases is uncertain. Fully assigned C-13 NMR spectra are presented for the ylides and an unexpected pattern is observed in the value of J(p-c) for the three carbonyl carbons depending on the nature of the substituents present. There is some correlation between the value of (2)J(p-c) for the central carbonyl carbon and the success of the pyrolysis although this is not complete. The method has been used to prepare a specifically C-13 labelled acetylenic diester 14.