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The geometries allowed for formal transfers of oxygen to the phosphorus(III) of a phosphine from a nitrone, an O-acetylhydroxylamine, and a sulfoxide have been evaluated by the endocyclic restriction test. Investigations of the conversions of 1 to 2, 16 to 17, and 28 to 29, by isotopic labeling, substituent effect, and kinetic and spectroscopic experiments, reveal the operation of different mechanisms for each of these transfers. For 1, oxygen addition to phosphorus is the preferred mechanism. In the case of 16, the mechanism involves nucleophilic displacement of oxygen from nitrogen by phosphorus to give 26 followed by oxygen addition to phosphorus. In acetic acid, the oxygen is added to 26 from water in the workup whereas in toluene the oxygen is provided by the acetate produced by the displacement. For 28, either addition by oxygen of the sulfoxide to activated phosphorus or addition by phosphorus to sulfur of the sulfoxide precedes oxygen transfer.

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