Introduction
The title compound is one of the most important oxygen transfer
reagents for selective stoichiometric or catalytic oxy-functionalization.
[1]
The involvement of PhIO
in numerous reactions such as the asymmetric alkene epoxidation,
[2]
[3]
the
asymmetric oxidation of sulfides
[3]
[4]
and enol ether derivatives,
[3a]
[5]
allylic
[6]
and asymmetric benzylic C-H
oxidation,
[3a]
[7]
the chemoselective oxidation of
alcohols and aldehydes to carbonyl compounds,
[8]
the
oxidation of amines
[9]
and hydrochinons,
[10]
among others, convincingly proves
the versatility of this oxidizing agent.
PhIO is not only employed as a terminal oxidant, it may also
serve as a mediator in aziridinations and cyclopropanations of alkenes,
[3a]
[11]
in
amidoglycosylations
[12]
and α-functionalizations
of carbonyl compounds.
[13]
PhIO is insoluble in most organic solvents due to its polymeric
structure, therefore reactions with PhIO are usually carried out
in water or methanol. The active monomeric species is also generated
in the presence of Lewis acids like BF3
·Et2O
or various transition metals, such as Fe(IV),
[2c]
[7a]
[4b]
Mn(III),
[2b]
[3]
[14]
Cr(III),
[2a]
[3]
[6]
Rh(II)/(III),
[12]
[14b]
Ru(II)/(III),
[8a]
[15]
Cu(I)/(II),
[11]
[12]
Yb(III),
[8b]
Co(II),
[16]
Ni(II),
[17]
which serve as excellent
catalysts for a wide range of oxidative transformations. Nevertheless,
non-catalytic oxidations in aprotic solvents
[9a]
[18]
and solid-state reactions
of polymeric PhIO
[19]
have
also been reported. In most cases the oxidative properties of PhIO
are related to the electrophilic reactivity of the hypervalent iodine
centre. In transition metal complex-catalyzed oxygenations with
PhIO an intermediate high-valent oxo complex is responsible for
the final oxygen transfer. Additionally, PhIO serves as a precursor
to various other iodine(III) compounds like iodosyl dihalides, dicarboxylates
and disubstituted derivatives of strong acids.
[20]
Imidoiodanes,
the formal analogs of iodosobenzene and azido-iodanes can also be
conveniently synthesized from PhIO.
[21]
Preparation of PhIO: Commercially available
iodosobenzene diacetate is treated with aqueous sodium
hydroxide to give pure PhIO as a yellowish amorphous powder after
filtration and air-drying.
[22]
Precautions: PhIO explodes if heated
to 210 °C due to disproportion into PhI and colorless,
explosive iodylbenzene PhIO2.
