Tri-/eAt-butylcyclotriphosphane Monoxide, 1,2,3-Tri-terr-butyl-l-oxocyclotriphosphane, Tetrarm-butylcyclotetraphosphane Monoxide, Tetra-/m-butylcyclotetraphosphane Dioxide, 1,2,3,4-Tetra-te/-f-butyl-l,2-dioxocyclotetraphosphaneThe partially oxidized cyclotriphosphane (PB u')30 (1,2,3-tri-rm-butyl-l-oxocyclotriphosphane) (1) has been obtained by [2 + 1] cyclocondensation of K (B u')P -P (B u')K with Bu'P(0)C12 in toluene at -7 8 °C. The cyclophosphanes (PBu% and (PBuf)3 as well as small amounts of the open-chain triphosphane [B u'P(0)C l]2P (0 )B u ' are also formed. In contrast to the unoxidized com pound (PBu')3, compound 1 is not stable at room tem perature, but decomposes above -3 0 °C undergoing rearrangement into the cyclotetraphosphanes (P B u % 0 (2), (PBur)402 (3), and (PBu')4. The 31P NMR parameters of 1 and 3 are reported and discussed.