Endocyclic Restriction Test: Applications to Transfers of Oxygen from Nitrogen and from Sulfur to Phosphorus(III)

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.