The reactions of 2-(2-chloroethyl)amino-1,5-dimethyl-3-phenyl-1,3,5-triaza-2λ 3 -phosphorinan- 4,6-dione (1), 2-bis(2-chloroethyl)amino-1,5-dimethyl-3-phenyl-1,3,5-triaza-2A3-phosphorinan- 4,6-dione (2), 2-methoxy-1,3,5-trimethyl-1,3,5-triaza-2λ 3 -phosphorinan-4,6-dione (3) and 2-trimethylsiloxy-1,3,5-trimethyl-1,3,5-triaza-2λ 3 -phosphorinan-4,6-dione (5) with hexafluoracetone are described. In the case of 2 and 3 the reaction furnished the spirocyclic compounds 7 and 8. 2-Bis(2-chloroethyl)amino-1,3,5-triphenyl-1,3,5-triaza-2λ 3 -phosphorinan- 4,6-dione (4) did not react. In the case of 1 and 5 rearrangement reactions took place; the (2-chloroethyl)amino substituent of 1 reacted with one of two equivalents of hexafluoroacetone with formation of the spirocyclic phosphorane 6. The reaction of 5 with tetrabromoorthobenzoquinone gave the phosphoryl compound 9. Compounds 6 - 8 were characterized via their 1 H-, 13 C-, 19 F- and 31 P-NMR and mass spectra, compound 9 via its 1 H-, 13 C- and 31 P-NMR and mass spectra. An X-ray crystal structure determination of 8 was conducted; in the six-membered ring the phosphorus atom lies 73 pm out of the plane of the other atoms, and displays trigonal bipyramidal coordination.