asc.wiley-vch.de
0.2 mm  25 m capillary column (OV-17). Mass spectra were
determined at an ionizing voltage of 70 eV. All starting mate-
rials, catalysts, and initiators were purchased from commer-
cial sources and used without further treatment. The yields
of products were estimated from the peak areas based on the
internal standard technique.
ether reacts with PPh3 to lead to aldehyde and alcohol
through the formation of a hemiacetal (D). On the
other hand, the treatment of hydroperoxide C with
acid gives rise to a formate and an aldehyde as prod-
ucts. It seems likely that the attack of a proton to the
hydroperoxide C occurs via two different pathways
to form two pairs of products, i.e., alcohol and for-
mate from the path a, and aldehyde and H2O2 from
path b. The rearrangement of the R1 group of the C
to the oxygen part followed by the attack of H2O to a
carbocation formed gave alcohol and formate
(path a), while the addition of a proton to alcoholic
oxygen and subsequent removal of alcohol from an
intermediate G followed by addition of H2O gave a ꢀ-
hydroxyhydroperoxide (I) which eventually trans-
formed to aldehyde and H2O2 (path b).
General Procedure for the Oxidation of Various
Substrates to the Phenol Derivatives
An acetonitrile (3 mL) solution of substrate (3 mmol), NHPI
(10 mol %), and AIBN (3 mol %) was placed in a two-necked
flask equipped with a balloon filled with O2. Caution: A bal-
loon filled with oxygen can be hazardous, even with a small-
scale reaction. The mixture was stirred at 75 °C for 20 h. The
reaction mixture was treated with various acidic solutions
[0.15 M H2SO4 in CH3CN (2 mL) or InCl3 (10 mol %) in
CH3CN (1 mL)] at 75 °C or 25 °C for 6 h, respectively. Re-
moval of the solvent under reduced pressure afforded a
cloudy solution, which was purified by column chromato-
graphy on silica gel (n-hexane/AcOEt = 3/2) to give the cor-
responding product. The products were characterized by 1H
and 13C NMR, IR, and GC-MS, respectively.
Procedure for the Oxidation of Various Substrates
to Aldehyde Derivatives
To the solution of substrate (3 mmol) in acetonitrile (3 mL)
in a two-necked flask were added NHPI (10 mol %) and
AIBN (3 mol %), and the flask was equipped with a balloon
filled with O2. Caution: A balloon filled with oxygen can be
hazardous, even with a small-scale reaction. The solution
was stirred at 75 °C for 20 h. The reaction mixture was treat-
ed with an excess amount of PPh3. The work-up was per-
formed by the same method as described above. All products
except for 13[6]and 24[7] were commercially available, and
were identified through comparison of the isolated product
with an authentic sample.
Acknowledgements
Scheme 2. A possible reaction path for aerobic oxidation of
ethers catalyzed by NHPI followed by treatment with PPh3
or acid.
This work was partially supported by Daicel Chemical Indus-
tries Ltd. and
a Grant-in-Aid for Scientific Research
(No. 13853008) from Japan Society for the Promotion of
Science (JSPS).
In conclusion, we have achieved the selective pro-
duction of alkyl hydroperoxides in high yields by
aerobic oxidation of alkylbenzenes by NHPI under
mild conditions, and demonstrate its potential appli-
cation to organic synthesis.
References
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1979, 602.
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K.-Boymann, J. Ullrich, in Ullmann's Encyclopedia of
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[3] (a) Y. Yoshino, Y. Hayashi, T. Iwahama, S. Sakaguchi,
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Experimental Section
General Procedures
1H and 13C NMR spectra were measured at 270 and
67.5 MHz, respectively, in CDCl3 with TMS as the internal
standard. Infrared (IR) spectra were measured as thin films
on NaCl plates or as KBr pressed disks. The GLC analysis
was performed with a flame ionization detector using a
812
Adv. Synth. Catal. 2001, 343, 809±813