Organophosphorus chemistry. Part VIII. Four-membered phosphorus–nitrogen ring compounds
NN′-Dialkyl- or -diaryl-2,2,2,4,4,4-hexachloro-1,3,2,4-diazadiphosphetidines react with liquid sulphur dioxide to provide a convenient route to the corresponding 2,4-dichloro-1,3,2,4-diazadiphosphetidine 2,4-dioxides, which are readily converted into the 2,4-bisdimethylamino- or 2,4-bisthiomethyl derivatives. The n.m.r. spectra of these compounds are discussed in the light of dπ–pπ bonding, and virtual coupling.