2 D "P, "N heteronuclear shift correlation, based on a non-refocused INEPT pulse sequence with "N detection, was applied to a "N NMR study of the azadiphosphiridines 1-5 which are formed by (2 + 11 cycloaddition of iminophosphines, RP=NR'. The pulse sequence used allowed consistent assignment of both the 31P and I5N NMR spectra in one experiment; by a slight modification, also the signs of numerous "P-"N coupling constants across one or two bonds could be determined. Comparison of the data with those of the azatriphosphetidine 6 (obtained from 1D 'H,"N and 3'P,'5N INEPT spectra) showed the influence of the ring size and conformational effects on the NMR parameters. 31P,13C shift-correlated 2 D spectra were further used to measure (including sign determination) and assign 31P-13C coupling constants across one to three bonds in 1-5. Based on the analysis of the coupling information and the known conformation of 4a, the relative stereochemistry of the diastereomers 4a and b could be derived; further, the comparison of the "P-''C coupling data of 1-3 with those of the 4a and b allowed the conformations of these derivatives, which were previously unknown, to be determined. The derived information of the constitution and stereochemistry of 1-5 gives insight into mechanistic details of the iminophosphine [ 2 + 11 cycloaddition.