A mild and efficient method for oxidative deprotection of trimethylsilyl ethers to the corresponding carbonyl compounds using [PhCH2NMe2Ph]2S2O8

Article abstract of DOI:10.1080/10426500701688214

Deprotection of trimethylsilyl ethers to the parent aldehydes and ketones in high yields has been carried out under mild conditions using N-benzyl N,N-dimethyl anilinium peroxodisulfate. Copyright Taylor & Francis Group, LLC.

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A Mild and Efficient Method
for Oxidative Deprotection
of Trimethylsilyl Ethers
to the Corresponding
Carbonyl Compounds Using
[PhCH2NMe2Ph]2S2O8
Hassan Ghasemnejad-Bosra a , Mahmood Tajbakhsh
b , Farhad Ramzanian-Lehmali c , Majid Shabani-
Mahali c & Mohammad A. Khalilzadeh b
a Islamic Azad University, Babol Branch Medicinal
and Basic of Science , Mazandaran, Babol, Iran
b Islamic Azad University, Ghaemshahr Branch ,
Mazandaran, Ghaemshahr, Iran
c Department of Chemistry, Faculty of Basic
Sciences , University of Mazandaran , Babolsar, Iran
Published online: 04 Jun 2008.
To cite this article: Hassan Ghasemnejad-Bosra , Mahmood Tajbakhsh , Farhad
Ramzanian-Lehmali , Majid Shabani-Mahali & Mohammad A. Khalilzadeh
(2008) A Mild and Efficient Method for Oxidative Deprotection of Trimethylsilyl
Ethers to the Corresponding Carbonyl Compounds Using [PhCH2NMe2Ph]2S2O8 ,
Phosphorus, Sulfur, and Silicon and the Related Elements, 183:6, 1496-1500, DOI:
10.1080/10426500701688214
To link to this article: http://dx.doi.org/10.1080/10426500701688214
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Phosphorus, Sulfur, and Silicon, 183:1496–1500, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701688214
A Mild and Efficient Method for Oxidative Deprotection
of Trimethylsilyl Ethers to the Corresponding Carbonyl
Compounds Using [PhCH2NMe2Ph]2S2O8
Hassan Ghasemnejad-Bosra,1 Mahmood Tajbakhsh,2
Farhad Ramzanian-Lehmali,3 Majid Shabani-Mahali,3
and Mohammad A. Khalilzadeh2
1Islamic Azad University, Babol Branch Medicinal and Basic of Science,
Mazandaran, Babol, Iran
2Islamic Azad University, Ghaemshahr Branch, Mazandaran,
Ghaemshahr, Iran
3Department of Chemistry, Faculty of Basic Sciences, University of
Mazandaran, Babolsar, Iran
Deprotection of trimethylsilyl ethers to the parent aldehydes and ketones in high
yields has been carried out under mild conditions using N-benzyl N,N-dimethyl
anilinium peroxodisulfate.
Keywords Deprotection; N-benzyl N,N-dimethyl anilinium peroxodisulfate; oxidation;
trimethylsilyl ethers
INTRODUCTION
The protection of certain functional groups and the deprotection of the
protected derivatives constitute important processes in the synthetic
organic chemistry of polyfunctional molecules, including the total syn-
thesis of natural products. Thus, a large number of protective groups
have been developed along with numerous method for their removal.1−4
Conversion of the hydroxy group to trimethylsilyl ether is one of the
most useful and convenient methods for the protection of this functional
group. Direct oxidation of trimethylsilyl ethers to the corresponding
carbonyl compounds has found considerable attention during recent
years.5−14
Received 6 August 2007; accepted 16 September 2007.
We are thankful to the Azad University of Medical Sciences of Babol and Mazandaran
University Research Council for partial support of this work.
Address correspondence to Hassan Ghasemnejad-Bosra, Islamic Azad University—
Babol Branch Medicinal and Basic of Science, Mazandaran, Babol, Iran. E-mail:
H ghasem2000@yahoo.it
1496

Oxidative Deprotection of Trimethylsilyl Ether
1497
However, some of the reported methods show limitations such as the
use of expensive reagents, long reaction times, low yields of the prod-
ucts, and tedious work-up. Therefore, the introduction of new methods
and inexpensiv reagents for the transformation of this functional group
is still in demand.
RESULTS AND DISCUSSION
As a part of our investigations to develop new oxidation methods, we
report here a new, simple, and general procedure that can be used for
the oxidative deprotection of trimethylsilyl ethers to the corresponding
carbonyl compounds under non-aqueous conditions.15 We have found
N-benzyl N, N-dimethyl anilinium peroxodisulfate to be a new, rapid
and efficient reagent for this purpose (Scheme 1).
SCHEME 1
N-Benzyl N, N-dimethyl anilinium peroxodisulfate ([PhCH2NMe2-
Ph2S2O8) is a mild, efficient, stable and cheap reagent, which was used
for our studies under non-aqueous conditions. This reagent is a white
powder and is prepared by dropwise addition of an aqueous solution
of K2S2O8 to an aqueous solution of N-benzyl N, N-dimethyl anilinium
bromide at room temperature. Filtration and drying of the precipitate
produced a white powder, which could be stored for months without los-
ing its oxidation ability. It was characterized by 1H MNR spectroscopy
and elemental analysis.
To find the optimum conditions for the oxidative deprotection of
trimethylsilyl ethers to the corresponding carbonyl compounds we have
chosen benzyl trimethylsilyl ether as a model compound.
The effect of the solvent in the oxidation reaction was evaluated by
carrying out the oxidation in a series of solvents with varying polarity.
Deprotection of benzyl trimethylsilyl ether with the aquimolar amount
of the peroxodisulfate was carried out in dichloromethane, chloroform,
tetrahydrofuran, n-hexane and acetonitrile at reflux temperature. The
results are presented in Table I.
As indicated in Table I a 1:1 molar ratio of the trimethylsilyl ether
and the oxidant in refluxing acetonitrile gives benzaldehyde in excellent
yield.

1498
H. Ghasemnejad-Bosra et al.
TABLE I Deprotection of Benzyl Trimethylsilyl Ether in Different
Solvents using [PhCH2NMe2Ph]2S2O8 at Reflux Temperature
Solvent
Reaction period (min)
Yield (%)a
CH3CN
CHCl3
CH2Cl2
n-C6H12
THF
5
90
96
100
95
99
70
74
15
35
aYields refer to isolated products.
In order to evaluate the general applicability of this method we have
oxidized benzylic, allylic and aliphatic trimethylsilyl ethers to the corre-
sponding carbonyl compounds with N-benzyl N, N-dimethyl anilinium
peroxodisulfate in acetonitrile. The results are shown in Table II. It
becomes clear from Table II that bezylic trimethylsilyl ethers are oxi-
dized in excellent yield under the reaction conditions. The strong elec-
tron withdrawing nitro group retards the reaction and also aliphatic
silylethers need longer reaction time for oxidation.
TABLE II Oxidative Deprotection of Trimethylsilyl Ethers with
[PhCH2NMe2Ph]2S2O8 in CH3CN at Reflux Temperature
Substrate
Time (min)
Producta
Yield (%) b,c
C6H5CH2OSiMe3
(C6H5)2CHOSiMe3
o-ClC6H4CH2OSiMe3
p-ClC6H4CH2OSiMe3
5
8
7
6
7
C6H5CHO
(C6H5)2CO
o-ClC6H4CHO
99
97
98
97
92
95
96
94
96
96
78
95
86
82
94
93
p-ClC6H4CHO
p-ClC6H4CO CH3
m-MeOC6H4CHO
p-MeOC6H4CHO
p-MeC6H4CHO
o-MeOC6H4CHO
p-MeC6H4C(CH3)O
p-NO2C6H4CHO
C6H5C(p-CIC6H4)O
C6H5CH2CH2CHO
CH3 (CH2)6CHO
A−tetralon
p-ClC6H4CH(CH3)OSiMe3
m-MeOC6H4CH2OSiMe3
p-MeOC6H4CH2OSiMe3
p-MeC6H4CH2OSiMe3
o-MeOC6H4CH2OSiMe3
p-MeC6H4CH(CH3)OSiMe3
p-NO2C6H4CH2OSiMe3
C6H5CH(p-CIC6H4)OSiMe3
C6H5CH2CH2CH2OSiMe3
CH3 (CH2)7OSiMe3
7
6
12
9
10
45
7
25
40
11
7
α−tetralol trimethylsilyl ether
C6H5CH=CHCH2OSiMe3
Cinnamaldehyde
aAll of the products were characterized by comparing their IR and 1H NMR data
with those of authentic samples; bYields refer to isolated products; and cEluent:
EtOAc/n-hexane (1:10).

Oxidative Deprotection of Trimethylsilyl Ether
1499
It is noteworthy that, unlike other oxidative hydrolytic methods, the
major drawback of overoxidation of the resulting aldehydes is not ob-
served under the reaction conditions. α,β-Unsaturated derivatives are
oxidized very efficiently without affecting the olefinic bond and the re-
action is essentially chemoselective. Furthermore, functional groups
such as chloro, methoxy, nitro, and alkyl groups were also inert to this
reagent and no byproduct formation was observed (Table II).
In conclusion, N-benzyl N, N-dimethyl anilinium peroxodisulfate is
a mild, efficient, and inexpensive reagent for the one-pot oxidative de-
protection of trimethylsilyl ethers to the corresponding carbonyl com-
pounds in non-aqueous conditions.
EXPERIMENTAL
All products were isolated and identified by comparison of their physical
data with those of authentic samples. 1H NMR spectra were measured
at 90 MHz with a JEOL JNM-EX 90 spectrometer with tetramethyl-
silane as an internal reference and DMSO-d6 as solvent. IR spectra
were recorded with a Pye-unicam SP 1100 spectrophotometer. Elemen-
tal analyses were performed on a LECO 250 instrument. Melting points
were determined with an Electro Thermal 9100 apparatus. All solvent
were freshly distilled before use. The trimethylsilyl ethers were pre-
pared according to a published procedure.10
Preparation of N-Benzyl, N,N-Dimethyl Anilinium
Peroxodisulfate [PhCH2NMe2Ph]2S2O8
To a solution of N, N-dimethyl anilinium bromide (14.60 g, 50 mmol)
in water (100 mL) was added dropwise K2S2O8 (13.51 g, 50 mmol) in
water (100 mL) and the reaction mixture was stirred for 0.5 h at room
temperature. The precipitate formed was filtered, washed with cooled
distilled water (50 mL), and dried in a desiccator under vacuum over
calcium chloride to afford a white powder (92%), which decomposes
at 181–183◦C to a dark brown material.1H NMR (DMSO): δ 8.2–6.9
(m, 10H, C6H5), 5.80 (s. 2H, CH2), 3.95 (s. 6H, CH3). Analysis: for
C30H36N2O8S2 Calcd. C, 58.43%; H, 5.87%; N, 4.54%, Found: C, 58.46%;
H, 5.89%; N, 4.56%.
General Procedure for the Oxidative Deprotection of
Trimethylsilyl Ethers with N-Benzyl, N,N-Dimethyl Anilinium
Peroxodisulfate
In a round bottomed flask (50 mL) equipped with a magnetic stirrer
a mixture of the substrate (1 mmol) in CH3CN (5 mL) and N-benzyl

1500
H. Ghasemnejad-Bosra et al.
N, N-dimethyl anilinium peroxodisulfate (1 mmol) was placed. The re-
action mixture was stirred at reflux temperature for the specified time
(Table II). The progress of the reaction was monitored by TLC. After
the reaction was completed, the mixture was filtered and the solid ma-
terial was washed with diethyl ether (2 × 10 mL). From the combined
filtrates, the solvent was evaporated under reduced pressure to afford
pure carbonyl compound in 78–99%. If necessary, the products were
further purified by column chromatography on a silica gel using an
appropriate eluent (EtOAc/n-hexane, 15:85).
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