Silica Sulfuric Acid: An Efficient Catalyst for the Direct Conversion of Primary and Secondary Trimethylsilyl Ethers to their Corresponding Ethers under Mild and Heterogeneous Conditions

Article abstract of DOI:10.1055/s-2003-41469

Primary and secondary trimethylsilyl ethers were converted to their corresponding ethers in the presence silica sulfuric acid with good to excellent yields under mild and heterogeneous conditions.

Full text of DOI:10.1055/s-2003-41469

LETTER
1877
Silica Sulfuric Acid: An Efficient Catalyst for the Direct Conversion of
Primary and Secondary Trimethylsilyl Ethers to their Corresponding Ethers
under Mild and Heterogeneous Conditions
a
b
c
a
A
M
n
E
fficient Catalyst
f
o
or the
D
irect
h
C
onversion
a
of Primar
y
m
and
S
econdary Trim
m
e
thylsilyl
E
thers ad Ali Zolfigol,* Iraj Mohammadpoor-Baltork, BiBi Fatemeh Mirjalili, Abdolhamid Bamoniri
a
Chemistry Department, College of Science, Bu-Ali Sina University, Hamadan, Zip Code 65174, Iran
Fax +98(811)8272404; E-mail: Zolfi@basu.ac.ir
b
c
Department of Chemistry, Isfahan University, Isfahan, Iran
Department of Chemistry, College of Science, Yazd University, Yazd. Iran
Received 18 July 2003
Abstract: Primary and secondary trimethylsilyl ethers were con-
verted to their corresponding ethers in the presence silica sulfuric
acid with good to excellent yields under mild and heterogeneous
conditions.
Scheme 1
Keywords: silica sulfuric acid, silyl ethers, ethers, heterogeneous
conditions
Symmetrical and unsymmetrical alkyl/aryl ether forma-
tion is an important reaction in organic synthesis and has
1
–8
generated significant interest in recent years. Methods
to effect this transformation include the classic William-
son procedure, the Mitsunobu reaction, and the Ullmann
condensation. Rearrangement and elimination of alkyl al-
cohols that are sterically hindered is the major disadvan-
tage of older reported procedures for ether synthesis. This
problem is amplified when the alcohols are immobilized
on solid supports and their activated species become the
Figure 1
A mixture of the substrate 1 (4 mmol), n-hexane (20 mL)
and silica sulfuric acid I (1 g) was stirred at room temper-
ature for the specified time (Table 1).1
1,12
The reaction
was monitored by TLC. After completion of the reaction
the mixture was filtered and the solid residue was washed
with n-hexane. Evaporation of the solvent followed by
column chromatography on silica gel gave highly pure
ethers with good to excellent yields. The solid residue is
silica sulfuric acid, which was recycled easily. Running
the reactions with recycled silica sulfuric acid for three
times show that no decrease in the yield was observed.
This means that silica sulfuric acid can be reused for sev-
eral times.1
4
limiting reagent. The alcohol-sulfuric acid reaction is
most often used for the conversion of simple primary
alcohols in to symmetrical ethers. Secondary and tertiary
alcohols undergo predominantly dehydration when sub-
jected to these conditions. Occasionally a small amount of
the symmetrical ether is formed as a by-product in the
9
case of secondary alcohols.
0g
Recently, we have reported the preparation of silica sulfu-
ric acid I (Figure 1) as a stable acidic reagent (solid acid)
and showed its catalytic activity in synthetic methodolo-
In conclusion, silica sulfuric acid can serve as an efficient
catalyst for the direct conversion of primary and second-
ary trimethylsilyl ethers into the corresponding ethers un-
der mild and heterogeneous conditions. The yields are
almost good to excellent and the procedure is simple and
convenient. Rearrangement, elimination and ether cleav-
age bond were not observed. Moreover, the new element
here is that the reaction is heterogeneous and this could be
worthwhile in an industrial setting for innovative green
chemical manufacturing in the future.14
1
0
gy. In continuation of our studies in this regard, we have
found that trimethylsilyl ethers can be converted to their
corresponding ethers in the presence silica sulfuric acid I.
Therefore, we decided to apply this reagent for ether syn-
thesis. Here we wish to report the first example of direct
conversion of primary and secondary trimethylsilyl ethers
into the related ethers with good to excellent yields under
mild and heterogeneous conditions (Scheme 1).
Acknowledgment
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) are gratefully acknowledged.
SYNLETT 2003, No. 12, pp 1877–1879
2
9
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9
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0
0
3
Advanced online publication: 19.09.2003
DOI: 10.1055/s-2003-41469; Art ID: G11603ST
©
Georg Thieme Verlag Stuttgart · New York

1
878
M. A. Zolfigol et al.
LETTER
Table 1 Direct Conversion Trimethylsilyl Ether 1 to their Corresponding Ethers 2 in the Presence of Silica Sulfuric Acid (I) in n-Hexane at
a
Room Temperature
Entry
Substrates
1
a
b
c
d
e
f
Productsb
2
a
b
c
d
e
f
Time (min)
Yield (%)c
1
2
3
4
5
6
7
8
9
4-CH °C H CH OTMS
4-CH OC H CH ) O
15
15
15
40
40
45
45
35
45
30
20
27
30
95
95
95
80
85
80
80
80
85
90
92
90
90
3
6
4
2
3
6
4
2 2
4-(CH ) CHC H CH OTMS
4-(CH ) CHC H CH ) O
3 2 6 4 2 2
3
2
6
4
2
4-(CH ) CC H CH OTMS
4-(CH ) CC H CH ) O
3 3 6 4 2 2
3
3
6
4
2
2-ClC H CH OTMS
(2-ClC H CH ) O
6 4 2 2
6
4
2
4-ClC H CH OTMS
(4-ClC H CH ) O
6 4 2 2
6
4
2
2,4-Cl C H CH OTMS
(2,4-Cl C H CH ) O
2 6 3 2 2
2
6
3
2
2-BrC H CH OTMS
g
h
i
(2-BrC H CH ) O
g
h
i
6
4
2
6
4
2 2
2-O NC H CH OTMS
(2-O NC H CH ) O
2 6 4 2 2
2
6
4
2
3-O NC H CH OTMS
(3-O NC H CH ) O
2 6 4 2 2
2
6
4
2
10
11
12
13
4-O NC H CH OTMS
j
(4-O NC H CH ) O
j
2
6
4
2
2
6
4
2 2
C H CHCH CH OTMS
k
l
(C H CHCH CH ) O
k
l
6
5
3
2
6
5
3
2 2
C H CH=CHCH OTMS
(C H CH=CHCH ) O
6 5 2 2
6
5
2
m
m
1
4
5
n
o
n
o
30
25
80
80
1
16
17
18
n-C H OTMS
p
q
r
n-(C H ) O
p
q
r
15
15
15
80
80
85
7
15
7
15 2
n-C H OTMS
n-(C H ) O
8 17 2
8
17
19
s
s
15
82
20
21
22
23
24
25
3-CH OC H CH OTMS
t
(3-CH OC H CH ) O
t
15
15
15
35
45
35
90
90
85
80
70
75
3
6
4
2
3
6
4
2 2
2-CH OC H CH OTMS
u
v
w
x
y
(2-CH OC H CH ) O
u
v
w
x
y
3
6
4
2
3
6
4
2 2
4-C H CH OC H CH OTMS
(4-C H CH OC H CH ) O
6 5 2 6 4 2 2
6
5
2
6
4
2
(C H ) CHOTMS
(C H ) CH) O
6 5 2 2
6
5
2
4-ClC H CHCH OTMS
(4-ClC H CHCH ) O
6 4 3 2
6
4
3
C H CH CHOTMS
(C H CH CH) O
6 5 3 2
6
5
3
a
b
c
Silica sulfuric acid/silyl ether (0.25 g:1 mmol).
All of the isolated products are known and their spectra and physical data have been reported in the literature.
Isolated yields.
Synlett 2003, No. 12, 1877–1879 © Thieme Stuttgart · New York

LETTER
An Efficient Catalyst for the Direct Conversion of Primary and Secondary Trimethylsilyl Ethers
1879
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(
(
(
13
the reported procedure.
1
(
12) Preparation of Silica Sulfuric Acid: A 500 mL suction
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2
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(
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10a
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(
(
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(
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Synlett 2003, No. 12, 1877–1879 © Thieme Stuttgart · New York