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New heterocyclic compounds of diazaphosphorinanes, diazaphospholes, and oxazaphospholes were synthesized and characterized by 1 H, 13 C, 31 P, NMR, IR spectroscopy, and CHN elemental analysis. The 3D structure of compound (5) was determined by X-ray crystallography. Since benzo-or naphthodiazaphospholes/diazaphosphorinanes containing aromatic rings are usually unstable in the solution state, their single crystal structures are rarely reported and, to the best of our knowledge, this structure is the first occasion of naphthodiazaphosphorinanes obtained here. It is noticeable that the P=O and C=O bonds are closer to syn than anti configuration and the P=O bond is placed in a pseudoequatorial position. This structure produced a 3D polymeric chain via strong hydrogen bonds and electrostatic short contacts. Due to the ring strain of five-membered rings, for all diazaphospholes great 2 J(PNH endocyclic ) coupling constants (about 18.0 Hz), as well as high 2,3 J(P,C) coupling constants for the aromatic carbon atoms connected to the five-membered ring (about 14.5, 13.5 Hz, respectively) were measured. Replacement of one NH group in a diazaphosphole ring by an oxygen atom caused exceedingly decreased ring strain and hence highly diminished 2 J(PNH endocyclic ) coupling constant.Furthermore, 31 P NMR spectra of oxazaphospholes, like the spectra of diazaphosphorinanes, indicated highly shielded phosphorus atoms relative to those of their diazaphospholes analogs.

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