The use of Nafion-H as an efficient catalyst for the deprotection of trimethylsilyl ethers to their corresponding alcohols under mild and heterogeneous conditions

Article abstract of DOI:10.1080/10426500490474996

Trimethylsilyl ethers were converted to their corresponding alcohols in the presence Nafion-H and wet SiO₂ with good-to-excellent yields under mild and heterogeneous conditions.

Full text of DOI:10.1080/10426500490474996

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Phosphorus, Sulfur, and Silicon
and the Related Elements
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THE USE OF NAFION-H® AS
AN EFFICIENT CATALYST
FOR THE DEPROTECTION OF
TRIMETHYLSILYL ETHERS
TO THEIR CORRESPONDING
ALCOHOLS UNDER MILD AND
HETEROGENEOUS CONDITIONS
a
Mohammad Ali Zolfigol , Iraj Mohammadpoor-
b
a
c
Baltork , Davood Habibi , BiBi Fatemeh Mirjalili
a
&
Abdolhamid Bamoniri
a
Chemistry Department, College of Science, Bu-Ali
Sina University, Hamadan, Iran
b
Department of Chemistry, Isfahan University,
Isfahan, Iran
c
Department of Chemistry, College of Science, Yazd
University, Yazd, Iran
Published online: 16 Aug 2010.
To cite this article: Mohammad Ali Zolfigol , Iraj Mohammadpoor-Baltork , Davood
Habibi , BiBi Fatemeh Mirjalili & Abdolhamid Bamoniri (2004) THE USE OF NAFION-H®
AS AN EFFICIENT CATALYST FOR THE DEPROTECTION OF TRIMETHYLSILYL ETHERS TO
THEIR CORRESPONDING ALCOHOLS UNDER MILD AND HETEROGENEOUS CONDITIONS,
Phosphorus, Sulfur, and Silicon and the Related Elements, 179:11, 2189-2193, DOI:
10.1080/10426500490474996
To link to this article: http://dx.doi.org/10.1080/10426500490474996

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Phosphorus, Sulfur, and Silicon, 179:2189–2193, 2004
Copyright ꢀC Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490474996
ꢀ
R
THE USE OF NAFION-H AS AN EFFICIENT
CATALYST FOR THE DEPROTECTION OF
TRIMETHYLSILYL ETHERS TO THEIR
CORRESPONDING ALCOHOLS UNDER MILD
AND HETEROGENEOUS CONDITIONS
a
b
Mohammad Ali Zolfigol, Iraj Mohammadpoor-Baltork,
a
c
Davood Habibi, BiBi Fatemeh Mirjalili,
a
and Abdolhamid Bamoniri
Chemistry Department, College of Science, Bu-Ali Sina
a
University, Hamadan, Iran; Department of Chemistry, Isfahan
b
University, Isfahan, Iran; and Department of Chemistry,
College of Science, Yazd University, Yazd, Iranc
(
Received March 23, 2004; accepted March 26, 2004)
Trimethylsilyl ethers were converted to their corresponding alcohols
ꢀ
R
in the presence Nafion-H and wet SiO with good-to-excellent yields
2
under mild and heterogeneous conditions.
ꢀ
R
Keywords: Heterogeneous conditions; Nafion-H ; trimethylsilyl ethers
Silyl protecting groups have played increasingly important roles in the
synthesis of complicated molecules, specially for the synthesis of bio-
logically significant products.1 Although there have been many new
–5
1
–17
reports for protection and deprotection of silyl groups,
the removal
of silyl group under mild conditions with easy workup procedure is
important.
The development of environmentally benign technologies is the most
challenging goal of contemporary chemistry and chemical engineer-
ing. Environmentally friendly chemical processes should be designed
to use environmentally benign feeds and solvents, and utilize efficient
Financial support for this work by the research affairs, Bu-Ali Sina University,
Hamadan, Iran, and also Isfahan University, Isfahan, Iran (as a common project) is
gratefully acknowledged.
Address correspondence to Mohammad Ali Zolfigol, Chemistry Department, Col-
lege of Science, Bu-Ali Sina University, P.O. Box 4135, Hamadan 65174, Iran. E-mail:
zolfi@basu.ac.ir
2
189

2
190
M. A. Zolfigol et al.
reagent or catalyst recycling systems.18 In the development of industrial
processes, separation is very important. Efficient separation of reagents
and catalysts to enable their reuse for subsequent cycles of reactions
are also key challenges. Especially in the stream of green chemistry,
separation protocols that allow for effective recovery of reagents and
1
9
catalysts have been increasingly appreciated. Perfluorinated solvents
are immiscible with conventional organic solvents at ambient temper-
◦
◦
20
ature (at 20 C) but become miscible at 36 C. Compounds functional-
ized with perfluorinated groups often dissolve preferentially in fluorous
2
1
solvents. Based on this fact, in the search for chemical transforma-
tions integrating innovative workup procedures fluorous techniques
(
fluorous biphasic chemistry18 and fluorous triphasic reactions ) are
22
becoming increasingly popular in organic synthesis for the separation
of temporarily fluorous labeled from fluorous non–labeled compounds.
Consequently, if one or more of the components of a reaction mixture,
e.g., homogeneous catalysts, reagents, or products, are equipped with
a perfluorinated auxiliary, the organic and the fluorous components
can be separated easily by either liquid–liquid extraction, solid–liquid
extraction, or fluorous chromatography.23
On the other hand, acids are widely used as catalysts in industry, pro-
8
ducing more than 1 × 10 mt/year of products. The most commonly used
acids are HF, H2SO4, HClO4, and H3PO4 (in liquid form or supported
on Kieselguhr). Solid acids have many advantages such as simplicity
in handling, decreased reactor and plant corrosion problems, and en-
vironmentally safe disposal.2
4–16
There is much current research and
general interest in heterogeneous systems27 because of the importance
that such systems have in industry and in developing technologies.
Among reported solid acids, Nafion-H has been used for a wide vari-
ety of reactions ranging from alkylation with olefins, reaction of alkyl
halides and alkyl esters, isomerization, transalkylation, acylation and
nitration reactions and ether and ester synthesis, and acetal forma-
tion and rearrangements. Very recently, we have reported the use of
Nafion-H as an excellent solid acid for the nitrosation of secondary
amines and also synthesis of ethers under mild and heterogeneous
conditions. Therefore, we decided to apply this perfluorinated catalyst
for the conversion of trimethylsilyl ethers to the corresponding alcohols
in the presence wet SiO2 at room temperature. Here we wish to report
an efficient procedure for the conversion of trimethylsilyl ethers into
alcohols with good-to-excellent yields under mild and heterogeneous
conditions (Scheme 1). This system can be combined with perfluori-
nated solvents and used for biphasic and triphasic fluorous systems for
different acid-catalyzed reactions.
2
8,29
ꢀ
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30
ꢀ
R
3
1

Deprotection of Silyl Ethers
2191
SCHEME 1
TABLE I The Direct Conversion of Trimethylsilyl Ethers 1 to the
ꢀ
R
Corresponding Alcohols 2 in the Presence of Nafion-H and Wet SiO
2
in
n-hexane at Room Temperaturea
Time Yieldc
Entry
Substrates
1
Productsb
2
(Min)
(%)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
4-CH3OC6H4CH2OTMS
C6H5CH(OTMS)CH2OTMS
4-(CH3)2CHC6H4CH2OTMS
4-(CH3)3CC6H4CH2OTMS
2-ClC6H4CH2OTMS
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
4-CH3OC6H4CH2OH
C6H5CH(OH)CH2OH
4-(CH3)2CHC6H4CH2OH
4-(CH3)3CC6H4CH2OH
2-ClC6H4CH2OH
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
15
30
20
20
40
30
45
40
40
40
30
30
25
25
25
40
98
95
98
98
95
90
90
90
90
90
90
98
95
90
90
95
4-ClC6H4CH2OTMS
4-ClC6H4CH2OH
2,4-Cl2C6H3CH2OTMS
2-BrC6H4CH2OTMS
2-O2NC6H4CH2OTMS
3-O2NC6H4CH2OTMS
4-O2NC6H4CH2OTMS
C6H5CHCH3CH2OTMS
C6H5CH CHCH2OTMS
n-C7H15OTMS
2,4-Cl2C6H3CH2OH
2-BrC6H4CH2OH
2-O2NC6H4CH2OH
3-O2NC6H4CH2OH
4-O2NC6H4CH2OH
C6H5CHCH3CH2OH
C6H5CH CHCH2OH
n-C7H15OH
1
1
1
1
1
1
1
n-C8H17OTMS
n-C8H17OH
1
7
q
q
30
95
1
1
8
9
r
s
r
s
30
30
95
90
2
2
0
1
t
t
20
25
90
90
u
u
ꢀ
R
a
Nafion-H /wet SiO2/trimethylsilyl ether (0.05 g: 0.05 g: 1 mmol).
All of the alcohols are known.
Isolated yields.
b
c

2
192
M. A. Zolfigol et al.
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A mixture of the substrate 1 (1 mmol), n-hexane (5 ml), Nafion-H
0.05 g), and wet SiO2 (0.2 g) was stirred at room temperature for the
(
specified time (Table I). The reaction was monitored by TLC. After com-
pletion of the reaction the mixture was filtered and the solid residue was
washed with n-hexane. Evaporation of the solvent gave pure ethers in
∗
good-to-excellent yields.
ꢀ
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In conclusion, Nafion-H can serve as an efficient catalyst for the
conversion trimethylsilyl ethers into the corresponding alcohols under
mild and heterogeneous conditions. The yields are good to excellent and
the procedure is simple and convenient. This system can be combined
with perfluorinated solvents and used for biphasic and triphasic fluo-
rous systems for any acid-catalyzed reactions. We believed that Nafion-
H can be recycled by applying fluorous biphasic system and then be
reused several times. Moreover, reaction is heterogeneous and may be
useful industrially.3
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4,35
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