Treatment of the lithium 1-aza-allyl [Li{N(R)C( t Bu)CHR}] 2 1, abbreviated as [Li(LL′)] 2 , with PCl 3 gave in poor yields the trans-P,P′-dichlorodiazaphosphetidine ClPN(R′)P(Cl)NR′ 3 (R=SiMe 3 , R′=C( t Bu)C(H)SiMe 3 ). An improved route to 3 was based on [{Cu(μ−LL′)} 2 ] and PCl 3 . However, the method of choice involved conversion of 1 into successively the imine RNC( t Bu)CHR 2 4 (which upon heating gave the isomeric enamine 5) and Cl 2 PNC( t Bu)CHR 2 6 and thermolysis of 6. The imine RNC( t Bu)CH(R)PPh 2 7, obtained from [Li(LL′)] 2 1 and Ph 2 PCl, was isomerised into the Z-enamine R 2 NC( t Bu)C(H)PPh 2 8, which upon irradiation gave a mixture of 8 and its E-isomer 9. Treatment of 7 with R″PCl 2 or PCl 3 gave the cyclic phosphonium chlorides [Ph 2 PP(R″)N(H)C(tBu)CH]Cl (10 R″=Ph, or 11 R″=Et) or [Ph 2 PP(Cl)N(R)C(tBu)CH]Cl 12; 12 with AgOSO 2 CF 3 or Na[BPh 4 ] afforded [Ph 2 PP(Cl)N(R)C(tBu)CH]A (13 A=CF 3 SO 3 , or 14 A=BPh 4 ). The enamines RNC( t Bu)CH(X)R (15 X=Cl, or 16 X=I) were obtained from 1 and POCl 3 or ICl, respectively, and the enamine R 2 NC(Ph)CR 2 17 was obtained from the lithium 1-aza-allyl [Li{N(R)C(Ph)CR 2 }(THF)] and CF 3 SO 3 SiMe 3 . Compounds 3–17 were characterised by multinuclear NMR spectroscopy and (in most cases) MS, while single crystal X-ray diffraction data are provided for 3 and 10.