An unusual reaction of hexafluoroacetone with methylenediphosphanes: Facile synthesis of carbodiphosphoranes

The oxidation of the methylenediphosphanes 3a,b with hexafluoroacetone does not lead to the expected dioxaphospholane heterocycles, but yields quantit atively the carbodiphosphoranes 5a,b. Compounds 5a,b easily add HCl, HF or Cl-2 to the ylidic bonds. The chloro derivative 14b, and its analogue 17 we re used for the synthesis of phosphonium substituted carbenes.