The reaction of vicinal triketones with cumulative phosphorus ylides. Synthesis of phosphoranylidenecyclobutanes

1,2,3‐Indantrione (1), diphenylpropanetrione(6), and alloxan (8) can be converted by reactions with ketenylidene‐(2a) and thioketenylidenetriphenylphosphorane (2b) into phosphoranylidenecyclobutanes (5, 7, and 9). The structures of the new cyclic compounds were confirmed on the basis of elemental analysis and spectral studies.