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The title reaction between substituted phenyl azides 2 and diastereomeric diazaphospholenes 1 gives the corresponding cyclic phosphazenes 3 with different stereochemical results. Hydrolysis of some phosphazenes 3 yield the corresponding ring-opened compounds Z-4I together with small amounts of diazaphospholene-oxide 5 and anilines 6. The configuration of the compounds obtained are established by 1H n.m.r. spectroscopy. The results are explained invoking the formation of pentacoordinate phosphorus intermediates.

The reaction of phenylazostilbene (1) and methoxydichlorophosphine gives the formation of the title compound via an intramolecular “Arbuzov-like” reaction. The trans isomer is easily isolated in a pure form by simple filtration of the reaction mixture. This compound in dichloromethane solution at room temperature converts into 2,3-diphenylindole. In addition, the reaction of (1) with phosphorus trichloride gives a cycloadduct which easily decomposes to the same indole. These results are a further convincing evidence that diazaphosphole system can be an intermediate in the synthesis of aza-heterocycles.

The addition of phosphites to the azoalkene 1 gives mixtures of diazaphosphole derivatives 4 and related ring-opened compounds 3 in different proportions depending on the phosphite used. The compounds 3 have the Z-configuration, while cyclic compounds 4 are a mixture of isomers in which predominates the isomer bearing the C4-Ph and OR groups in a trans configuration. When P(OPh)3 is used in dry hexane with rigorous exclusion of moisture the new diazaphosphole derivative 5 is obtained. The results are explained in terms of the relative apicophilicities in the pentacoordinated intermediates.

Stable spirocyclic phosphoranes 2 have been prepared stereospecifically in high yields (90–95%) by reaction of o-azidophenol with cis and trans-diazaphosphole derivatives 1. Slow isomerization of pure diastereoisomer 2 was observed in acidic conditions.