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Rapid highly efficient and chemoselective trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) catalyzed by reusable electron-deficient tin(IV)porphyrin.

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Full Paper
Received: 7 March 2009
Revised: 5 July 2009
Accepted: 5 July 2009
Published online in Wiley Interscience 18 August 2009
(www.interscience.com) DOI 10.1002/aoc.1540
Rapid, highly efficient and chemoselective
trimethylsilylation of alcohols and phenols
with hexamethyldisilazane (HMDS) catalyzed
by reusable electron-deficient tin(IV)porphyrin
Majid Moghadam∗, Shahram Tangestaninejad, Valiollah Mirkhani,
Iraj Mohammadpoor-Baltork and Shadab Gharaati
In this paper, rapid and highly efficient trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS) in the
presence of catalytic amounts of high-valent [SnIV (TPP)(OTf)2 ] is reported. This catalytic system catalyzes trimethylsilylation of
primary, secondary and tertiary alcohols as well as phenols, and the corresponding TMS-ethers were obtained in high yields
and short reaction times at room temperature. It is noteworthy that this method can be used for chemoselective silylation of
primary alcohols in the presence of secondary and tertiary alcohols and phenols. The catalyst was reused several times without
c 2009 John Wiley & Sons, Ltd.
loss of its catalytic activity. Copyright Keywords: alcohol; phenol; trimethylsilyl ether; hexamethyldisilazane; high-valen tin(IV) porphyrin
Introduction
446
Protection of hydroxy functional groups by their conversion to
silyl ether groups is a common and often used method in
synthetic organic chemistry. The protection of such functional
groups is often necessary during the course of various transformations in a synthetic sequence, especially in the synthesis of fine
chemicals and natural products.[1 – 3] Commonly, silyl ethers are
prepared by treatment of hydroxyl compounds with silyl chlorides
or silyl triflates in the presence of bases such as imidazole,[4]
4-(N,N-dimethylamino)pyridine,[5] N,N-diisopropylethylamine[6]
and Li2 S.[7] However, some of these silylation methods suffer
from disadvantages such as the lack of reactivity or the difficulty in removal of amine salts derived from the reaction
of by-product acids and co-bases during the silylation reaction. 1,1,1,3,3,3-Hexamethyldisilazane (HMDS), which is a stable,
commercially available and cheap reagent can be used as an
alternative silylating agent for preparation of silyl ethers from
hydroxyl compounds. On the other hand, silylation with HMDS
is nearly neutral, does not need special precautions and produces ammonia as by-product. However, the main disadvantage
of HMDS is its poor silylating power in the absence of a suitable catalyst which needs forceful conditions and long reaction
times in many cases.[8] To solve this problem, a variety of catalysts including (CH3 )3 SiCl,[9] sulfonic acids,[10] ZnCl2 ,[11] K-10
montmorilonite,[12] LiClO4 ,[13] H3 PW12 O40 ,[14] iodine,[15] InBr3 ,[16]
zirconium sulfophenyl phosphonate,[17] CuSO4 .5H2 O,[18] sulfonic acid-functionalized nanoporous silica,[19] MgBr2 ÐOEt2 ,[20]
LaCl3 ,[21] poly(N-bromobenzene-1,3-disulfonamide) and N,N,N0 ,N0 tetrabromobenzene-1,3-disulfonamide,[22] Fe(TFA)3 ,[23] Fe3 O4 ,[24]
(n-Bu4 N)Br[25] and ZrO(OTf)2 [26] have been reported. Although
these procedures provide an improvement, many of these catalysts or activators need long reaction times, drastic reaction
conditions or tedious workups, are moisture sensitive or have
Appl. Organometal. Chem. 2009 , 23, 446–454
an expensive catalyst. Hence, introduction of new procedures to
circumvent these problems is still in demand.
Electron-deficient metalloporphyrins have been used as mild
Lewis acid catalysts.[27 – 32] Suda’s group has reported the use of
chromium and iron porphyrins in organic synthesis. They used
Cr(tpp)Cl for regioselective [3,3] rearrangement of aliphatic allyl
vinyl ethers and for Claisen rearrangement of simple aliphatic
allyl vinyl ethers, Fe(tpp)OTf for rearrangement of α,β-epoxy
ketones into 1,2-diketones and Cr(tpp)OTf for highly regio- and
stereoselective rearrangement of epoxides to aldehydes.[33 – 36]
Recently, we have reported the use of tin(IV)tetraphenylporphyrinato perchlorate,[37,38] tin(IV)tetraphenylporphyrinato trifluoromethanesulfonate[39,40] and tin(IV)tetraphenylporphyrinato tetraflouroborate[41,42] in organic transformations.
In this paper, a rapid and highly efficient method for trimethylsilylation of alcohols and phenols with hexamethyldisilazane catalyzed by high-valent [SnIV (TPP)(OTf)2 ] at room temperature is
reported (Scheme 1).
Experimental
Chemicals were purchased from Merck Chemical Company. 1 H
NMR spectra were recorded in CDCl3 solvent on a Bruker AM
80 MHz or a Bruker AC 500 MHz spectrometer using TMS as an
internal standard. Infrared spectra were run on a Philips PU9716 or
Ł
Correspondence to: Majid Moghadam, Department of Chemistry, Catalysis
Division, University of Isfahan, Isfahan 81746-73441, Iran.
E-mail: moghadamm@sci.ui.ac.ir
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan
81746-73441, Iran
c 2009 John Wiley & Sons, Ltd.
Copyright Rapid, highly efficient and chemoselective trimethylsilylation of alcohols and phenols
OTf
N
N
H
R
OH +
Me3Si
N
IV
N
Sn
N
OTf
SiMe3
R
CH3CN
OSiMe3 + NH3
Scheme 1. Trimethylsilylation of alcohols and phenols with HMDS catalyzed by SnIV (TPP)(OTf)2 .
Table 1. Optimization of catalyst and HMDS amounts in the
trimethylsilylation of benzyl alcohola
Entry
1
2
3
4
5
6
7
a
b
Catalyst
amount (mol%)
HMDS
(mmol)
Time
(min)
Yield
(%)b
1
1
1
0.25
0.5
0.75
2
1
0.7
0.5
0.5
0.5
0.5
0.5
0.5
1
1
1
1
1
0.5
100
100
100
32
67
88
100
Table 2. The effect of different solvents on trimethylsilylation of
benzyl alcohol with HMDS catalyzed by [SnIV (TPP)(OTf)2 ]a
Solvent
Time (min)
Yield (%)b
CH3 CN
CH3 COCH3
CH2 Cl2
CHCl3
n-Hexane
1
1
1
1
1
100
65
78
52
27
Entry
1
2
3
4
5
a Reaction conditions: benzyl alcohol (1 mmol), catalyst (1 mol%),
HMDS (0.5 mmol), solvent (1 ml).
b GC yield.
Reaction conditions: benzyl alcohol (1 mmol), CH3 CN (1 ml).
GC yield.
Shimadzu IR-435 spectrophotometer. All analyses were performed
on a Shimadzu GC-16A instrument with a flame ionization detector
using silicon DC-200 or Carbowax 20M columns and n-decane was
used as internal standard. The tetraphenylporphyrin was prepared
and metallated according to the literature.[43,44]
Preparation of the Catalyst
To a solution of [Sn(TPP)Cl2 ] (1.03 g, 1 mmol) in 100 ml of THF,
at 55 Ž C, AgCF3 SO3 (0.54 g, 2 mmol) was added. The solution
was stirred at 55 Ž C for 30 min. The AgCl precipitate was filtered
through a 0.45 µM filter. The resulting solution was evaporated at
room temperature. Then, the [SnIV (TPP)(OTf)2 ] was extracted with
CH2 Cl2 . The [SnIV (TPP)(OTf)2 ] crystals obtained by evaporation of
solvent at room temperature.[40]
General Procedure for the Silylation Reaction
A mixture of alcohol or phenol (1 mmol), [SnIV (TPP)(OTf)2 ] (10 mg,
0.01 mmol) and HMDS (0.5 mmol per OH group) in CH3 CN (1 ml)
was prepared and stirred at room temperature for the appropriate
time (Table 1). The progress of the reaction was monitored by
GC. After completion of the reaction, the solvent was evaporated,
n-hexane (10 ml) was added and the catalyst was filtered. The
filtrates were washed with brine and dried over Na2 SO4 then
concentrated under reduced pressure to afford the crude product,
which was confirmed by 1 H NMR and IR spectral data.
Results and Discussion
Silylation of Alcohols and Phenols with HMDS Catalyzed by
[SnIV (TPP)(OTf)2 ]
Appl. Organometal. Chem. 2009, 23, 446–454
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
447
First, in order to show the effect of OTf groups on the electron
deficiency of tin(IV) porphyrin, the silylation of benzyl alcohol
with HMDS was carried out in the presence of 1 mol% of
[SnIV (TPP)(OTf)2 ] and [SnIV (TPP)Cl2 ] catalysts at room temperature.
The results showed that the amount of the corresponding
silyl ether in the presence of [SnIV (TPP)Cl2 ] was 50% after
10 min, while the reaction was completed in the presence of
[SnIV (TPP)(OTf)2 ] in 1 min. Then, the amounts of catalyst and
HMDS were optimized in trimethylsilylation of benzyl alcohol. As
shown in Table 1, the best results were obtained with 1 mol% of
catalyst and 0.5 mmol of HMDS. In order to choose the reaction
media, different solvents such as dichloromethane, chloroform,
n-hexane, acetone and acetonitrile were used and the best
results were obtained in acetonitrile (Table 2). The optimized
conditions which obtained for silylation of benzyl alcohol were
alcohol, HMDS and catalyst in a molar ratio of 100 : 50:1. Under
the optimized reaction conditions, a wide variety of alcohols
were converted completely to their corresponding silyl ethers.
The obtained results for silylation of different primary, secondary
(including aliphatic and aromatic alcohols) and tertiary alcohols
showed that the reaction was immediately completed for all
alcohols at room temperature and no alcohol was detected
by TLC or GC (Table 3). The results showed that the nature
of substituents in benzylic alcohols (electron-withdrawing or
electron-releasing) has no significant effect on the yield of silyl
ethers. Blank experiments in the absence of catalyst showed that
only small amounts of the corresponding the silyl ethers were
produced.
In the case of bifunctional compounds bearing benzylic and
phenolic hydroxyl groups, both OH groups were silylated in the
presence of this catalyst with 1 mmol of HMDS (Table 3, entries 20
and 21).
In order to show the effectiveness of [SnIV (TPP)(OTf)2 ], different
catalysts such as (CH3 )3 SiCl,[9] ZnCl2 ,[11] K-10 montmorilonite,[12]
ž
H3 PW12 O40 ,[14] iodine,[15] InBr3 ,[16] CuSO4 5H2 O[18] and (n[25]
Bu4 N)Br were also used for trimethylsilylation of benzyl alcohol
using the same amounts of catalyst, solvent and HMDS which was
used with [SnIV (TPP)(OTf)2 ]. The results, which are summarized in
Table 4, showed that [SnIV (TPP)(OTf)2 ] is more efficient than the
others.
M. Moghadam et al.
Table 3. Trimethylsilylation of alcohols with HMDS catalyzed by SnIV (TPP)(OTf)2 at room temperaturea
Entry
Hydroxy compound
TMS ether
1
CH2OH
CH2OSiMe3
CH2CH2OH
CH2CH2OSiMe3
CH2CH2CH2OH
CH2CH2CH2OSiMe3
2
3
4
CH2OH
Cl
CH2OH
CH2OH
100
[45]
1
100
[45]
1
100
[24]
1
100
[24]
2
100
[46]
2
100
[24]
2
100
[19]
1
100
[45]
1
100
New
1
100
[24]
1
100
New
1
100
[15]
1
100
New
1
100
[15]
1
100
[46]
1
100
[15]
CH2OSiMe3
O2N
7
CH2OSiMe3
CH2OH
NO2
NO2
8
CH2OH
MeO
CH2OSiMe3
MeO
9
CH2OSiMe3
CH2OH
OMe
OMe
10
CH2OH
t-Bu
CH2OSiMe3
t-Bu
11
CH2OSiMe3
CH2OH
F
F
Cl
Cl
CH2OSiMe3
CH2OH
Cl
Cl
CH2OSiMe3
CH2OH
14
CH2OH
Cl
CH2OSiMe3
Cl
Cl
Cl
15
CH2OSiMe3
CH2OH
Br
Br
16
448
Me
1
O2N
O2N
13
Reference
CH2OSiMe3
6
12
Yield (%)b
CH2OSiMe3
Cl
5
O2N
Time (min)
CH2OH
www.interscience.wiley.com/journal/aoc
Me
CH2OSiMe3
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 446–454
Rapid, highly efficient and chemoselective trimethylsilylation of alcohols and phenols
Table 3. (Continued)
Entry
Hydroxy compound
TMS ether
CH2OH
CH2OSiMe3
17
Me
Reference
1
100
[46]
1
100
New
1
100
[13]
1
100
[47]
1
100
New
1
98
[45]
1
96
[48]
2
97
[45]
1
100
[46]
1
100
[45]
1
100
[45]
2
90
[45]
2
100
[19]
1
100
New
CH2OSiMe3
CH2OH
Me
Me
19
OH
OSiMe3
20c
CH2OSiMe3
CH2OH
OSiMe3
OH
21c
CH2OH
HO
CH2OSiMe3
Me3SiO
MeO
MeO
22
OSiMe3
OH
23
OSiMe3
OH
24
OSiMe3
OH
Me
Me
OH
OSiMe3
26
27
Yield (%)b
Me
18
25
Time (min)
OH
OSiMe3
OH
OSiMe3
28
OSiMe3
OH
29
C OH
C OSiMe3
30
Me
Me
OH
Me
Me
OSiMe3
449
Appl. Organometal. Chem. 2009, 23, 446–454
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
M. Moghadam et al.
Table 3. (Continued)
Entry
Hydroxy compound
31
Me
TMS ether
Me
Me
OH
32
Reference
1
100
[23]
1
96
[45]
6
98
[45]
Me
CH3
H3C
C CH3
C
CH3
OSiMe3
OH
33
Yield (%)b
OSiMe3
CH3
H3C
Time (min)
OSiMe3
OH
a
Reaction conditions: alcohol (1 mmol), HMDS (0.5 mmol), catalyst (1 mol%), CH3 CN (1 ml).
GC yield.
c Reaction was performed with 1 mmol of HMDS.
b
Table 4. Trimethylsilylation of benzyl alcohol with HMDS catalyzed
by different catalystsa
Entry
1
2
3
4
5
6
7
8
9
Catalyst
Yield (%)b
Time (min)
Reference
(CH3 )3 SiCl
ZnCl2
K-10 montmorilonite
H3 PW12 O40
Iodine
InBr3
CuSO4 .5H2 O
(n-Bu4 N)Br
SnIV (TPP)(OTf)2
25
17
29
23
12
32
26
15
100
1
1
1
1
1
1
1
1
1
[9]
[11]
[12]
[14]
[15]
[16]
[18]
[25]
–
a
Reaction conditions: benzyl alcohol (1 mmol), HMDS (0.5 mmol),
catalyst (1 mol%), CH3 CN (1 ml).
b GC yield.
450
Then, we investigated the ability of [SnIV (TPP)(OTf)2 ] in the
silylation of phenols with HMDS. The reaction of phenols was
carried out under the same conditions which were descried
for the silylation of alcohols with HMDS. The results showed
that all reactions were completed in 1–3 min for all phenols
and the desired silyl ethers were obtained in excellent yields
at room temperature (Table 5). The silylation of polyhydroxybenzenes such as hydroquinone, pyrocatechol, resorcinol and
pyrogallol was also performed. The results showed that all hydroxyl groups were silylated and the desired poly(trimethylsilyl
ether) were obtained in excellent yields (Table 5, entries
5–8).
A plausible mechanism has been shown in Scheme 2. Based
on this mechanism, the Lewis acid-base interaction between
porphyrin triflate and nitrogen in HMDS polarizes the N–Si bond
of HMDS and a reactive silylating agent (1) is produced, which
effectively silylates the hydroxyl compounds. The fast evolution of
ammonia gas is a good indication for the proposed mechanism.
www.interscience.wiley.com/journal/aoc
The selectivity of this method was also investigated. As shown
in Table 6, primary alcohols were completely converted to the
corresponding silyl ethers in the presence of secondary or tertiary
alcohols (Table 6, entries 1 and 2). Also, in a binary mixture of
benzyl alcohol and 1-octanol, the benzyl alcohol was converted
to the corresponding silyl ether in 90% yield, while only 10%
of the corresponding silyl ether was observed for the aliphatic
alcohol (Table 6, entry 3). Also, in an equimolar mixture of benzyl alcohol and phenol, only benzyl alcohol was transform to
its trimethylsilyl ether, while phenol remained intact in the reaction mixture (Table 6, entry 4). To stress such a selectivity,
trimethylsilylation of bifunctional compounds bearing both benzylic and phenolic hydroxyl groups such as 2-hydroxybenzyl
alcohol was also investigated. Using 0.5 mmol of HMDS, the
reaction progress was 75%; 2-hydroxybenzyltrimethylsilyl ether
and trimethysiloxybenzyltrimethysilyl ether were obtained in
50 and 25% yield, respectively (Table 6, entry 5). While in
the presence of 0.75 mmole of HMDS, the reaction was
completed and a 1 : 1 mixture of 2-hydroxybenzyltrimethylsilyl
ether:2-trimethylsilyloxybenzyltrimethysilyl ether was produced
(Table 6, entry 6). In order to determine the effect of trimethylsiloxy group on the reactivity of phenolic OH, a competitive reaction of 2-hydroxybenzyltrimethylsilyl ether with HMDS
in the presence PhOH was performed. Under these conditions, 80% of trimethysiloxybenzyltrimethysilyl ether and 20%
of phenyltrimethylsilyl ether were produced (Table 6, entry 7).
These results clearly indicate that, in 2-hydroxybenzyltrimethylsilyl
ether, the trimethylsilyl group can influence the trimethylsilylation
of 2-hydroxybenzyltrimethylsilyl ether with HMDS.
Reusability of Catalyst
The reusability of the catalyst was checked using multiple silylation
of 4-chlorobenzylalcohol with HMDS. At the end of the reaction,
the solvent was evaporated, n-hexane was added and the catalyst
was filtered and used in the next run. The results showed that
after reusing the catalyst several times (five consecutive runs
were checked), no change was observed in its catalytic activity.
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 446–454
Rapid, highly efficient and chemoselective trimethylsilylation of alcohols and phenols
Table 5. Trimethylsilylation of phenols with HMDS catalyzed by SnIV (TPP)(OTf)2 at room temperaturea
Entry
Phenol
TMS ether
Time (min)
Yield (%)b
Reference
1
100
[45]
1
100
[49]
2
100
[49]
2
100
New
1
100
[47]
1
100
New
1
100
New
1
100
New
3
100
[49]
2
100
[45]
2
100
[45]
1
100
[45]
1
OSiMe3
OH
2
OH
Cl
OSiMe3
Cl
3
OH
OSiMe3
Cl
Cl
4
OSiMe3
OH
Cl
Cl
5c
OH
HO
OSiMe3
Me3SiO
6c
OSiMe3
OH
OSiMe3
OH
7c
OSiMe3
OH
Me3SiO
HO
8c
OSiMe3
OH
HO
Me3SiO
OH
OSiMe3
9
O2N
OH
O2N
OSiMe3
H3C
OH
H3C
OSiMe3
10
11
12
OSiMe3
OH
OH
OSiMe3
a
Reaction conditions: phenol (1 mmol), HMDS (0.5 mmol), catalyst (1 mol%), CH3 CN (1 ml).
GC yield.
c Reaction was performed with 0.5 mmole of HMDS per OH group.
b
In another experiment, at the end of the reaction, fresh alcohol
and HMDS were added to the reaction mixture. Execution of the
reaction showed that the alcohol was completely converted to its
corresponding TMS-ether.
1H, Ar), 4.82 (s, 2H, CH2 ), 3.87 (s, 3H, OCH3 ), 0.25 [s, 9H, Si(CH3 )3 ]
ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 156.4 (Ar), 129.3 (Ar), 128.4
(Ar), 127.5 (Ar), 120.8 (Ar), 110.3(Ar), 61.5 (CH2 ), 55.2 (OCH3 ), 0.28
(Si(CH3 )3 ) ppm; IR (CCl4 ): 2999. 2959, 2901, 1597, 1498, 1459, 1264,
1081, 1052, 870, 840, 751 cm1 .
Spectral Data for New Compounds
2-Methyl-1-phenyl-2-propyltrimethylsilyl ether (entry 30, Table 3)
1H
1H
NMR (CDHCl3 , 400 MHz): δ D 7.51 (d, J D 8 Hz, 1H, Ar), 7.29
(t, J D 8 Hz, 1H, Ar), 7.03 (t, J D 8 Hz, 1H, Ar), 6.89 (d, J D 8 Hz,
Appl. Organometal. Chem. 2009, 23, 446–454
NMR (CDHCl3 , 400 MHz): δ D 7.32-7.26 (m, 5H, Ar), 2.79 (s, 2H,
CH2 ), 1.28 (s, 6H, 2 ð CH3 ), 0.13 [s, 9H, Si(CH3 )3 ] ppm; 13 C NMR
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
451
2-Methoxybenzyltrimethylsilyl ether (entry 9, Table 3)
M. Moghadam et al.
H
N
Me3Si
SiMe3
H
+N
Me3Si
OTf
SiMe3
_
Sn IV
OTf
Sn IV
OTf
1
OTf
ROH
NH3 + R-O-SiMe3
Me3Si
+
NH2 _
Sn
ROH
OTf
IV
R-O-SiMe3
OTf
Scheme 2. Proposed mechanism for trimethylsilylation of alcohols and phenols with HMDS catalyzed by SnIV (TPP)(OTf)2 .
(CDCl3 , 100 MHz): δ D 138.9 (Ar), 130.8 (Ar), 128.1 (Ar), 126.5 (Ar),
74.1 (CH2 ), 51.3 (2 ð CH3 ), 30.0 (C–OSi), 2.9 (Si(CH3 )3 ) ppm; IR
(CCl4 ): 3102, 3028, 2955, 1604, 1489, 1423, 1382, 1352, 1262, 1212,
1046, 838, 750, 690 cm1 .
9-Anthracenylmethyltrimethylsilyl ether (entry 13, Table 3)
1
2-Fluorobenzyltrimethylsilyl ether (entry 11, Table 3)
1H
NMR (CDHCl3 , 400 MHz): δ D 7.51–7.01 (m, 4H, Ar), 4.80 (s,
2H, CH2 ), 0.18 [s, 9H, Si(CH3 )3 ] ppm; 13 C NMR (CDCl3 , 100 MHz):
δ D 161.3 (Ar), 158.8 (Ar), 128.4 (Ar), 124.0 (Ar), 115.4 (Ar), 114.9
(Ar), 58.4 (CH2 ), 0.5 [Si(CH3 )3 ] ppm; IR (CCl4 ): 3120, 2998, 1610,
1582, 1480, 1260, 1182, 1110, 1073, 870, 820, 775 cm1 .
H NMR (CDHCl3 , 400 MHz): δ D 8.56 (s, 1H, Ar), 8.40 (d, J D 8 Hz,
2H, Ar), 8.02 (d, 8 Hz, 2H, Ar), 7.56 (dd, J1 D 8 Hz, J2 D 8 Hz, 2H, Ar),
7.50 (dd, J1 D 8 Hz, J2 D 8 Hz, 2H, Ar), 5.66 (s, 2H, CH2 ), 0.21 (s, 9H,
Si(CH3 )3 ) ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 131.7 (Ar), 131.1
(Ar), 130.6 (Ar), 129.3 (Ar), 128.8 (Ar), 126.0 (Ar), 125.0 (Ar), 124.4
(Ar), 57.3 (CH2 ), 0.1 (Si(CH3 )3 ) ppm; IR (KBr): 3063, 2989, 2863,
1622, 1492, 1392, 1354, 1252, 1089, 1038, 882, 842, 740 cm1 .
3-Chlorobenzyltrimethylsilyl ether (entry 4, Table 5)
4-Trimethylsiloxy-3-methoxybenzyltrimethylsilyl ether (entry 21,
Table 3)
1H
1H
NMR (CDHCl3 , 400 MHz): δ D 7.17–6.89 (m, 3H, Ar), 6.77 (dd,
J1 D 4 Hz, J2 D 8 Hz, 1H, Ar), 0.31 (s, 9H, Si(CH3 )3 ) ppm; 13 C NMR
(CDCl3 , 100 MHz): δ D 156.15 (Ar), 134.4 (Ar), 130.9 (Ar), 121.5 (Ar),
120.4 (Ar), 118.3 (Ar), 0.2 (Si(CH3 )3 ) ppm; IR (CCl4 ): 3115, 2989, 1593,
1480, 1260, 1091, 1050, 930, 840, 775 cm1 .
1,2-Bis(trimethylsiloxy)benzene (entry 6, Table 5)
1H
NMR (CDHCl3 , 400 MHz): δ D 6.88-6.78 (m, 3H, Ar), 4.63 (s, 2H,
CH2 ), 3.82 (s, 3H, OCH3 ), 0.25 [s, 9H, CH2 OSi(CH3 )3 ], 0.15 [s, 9H,
Si(CH3 )3 ] ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 150.8 (Ar), 144.5
(Ar), 133.6 (Ar), 120.6 (Ar), 119.2 (Ar), 111.0 (Ar), 64.8 (CH2 ), 55.3
(OCH3 ), 0.29 [CH2 OSi(CH3 )3 ], 0.33 [Si(CH3 )3 ] ppm; IR (CCl4 ): 2980,
2840, 1599, 1582, 1506, 1454, 1404, 1262, 1150, 1030, 899, 820,
775, 698 cm1 .
NMR (CDHCl3 , 400 MHz): δ D 6.88 (s, 4H, Ar), 0.29 (s, 18H, 2 ð
Si(CH3 )3 ) ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 146.70 (Ar), 121.96
(Ar), 121.26 (Ar), 0.38 [Si(CH3 )3 ] ppm; IR (CCl4 ): 2973, 1592, 1493,
1260, 1060, 920, 852, 746 cm1 .
1,3-Bis(trimethylsiloxy)benzene (entry 7, Table 5)
1 H NMR (CDHCl
3 , 400 MHz): δ D 7.09 (t, J D 8 Hz, 1H, Ar), 6.52 (dd,
J1 D 8, J2 D 4 Hz, 2H, Ar), 6.39 (t, J D 4 Hz, 1H, Ar), 0.29 [s, 18H, 2 ð
Si(CH3 )3 ] ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 156.24 (Ar), 129.69
(Ar), 113.52 (Ar), 112.31(Ar), 0.23 (Si(CH3 )3 ) ppm; IR (CCl4 ): 2974,
1589, 1483, 1270, 1130,1160, 1060, 979, 832, 752 cm1 .
3-Methylbenzyltrimethylsilyl ether (entry 18, Table 3)
1H
452
NMR (CDHCl3 , 400 MHz): δ D 7.50–7.48 (m, 1H, Ar), 7.31–7.32
(m, 3H, Ar), 4.79 (s, 2H, CH2 ), 2.41 (s, 3H, CH3 ), 0.28 [s, 9H, Si(CH3 )3 ]
ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 138.9 (Ar), 135.6 (Ar), 129.9
(Ar), 126.7 (Ar), 127.2 (Ar), 126.4 (Ar), 63.1 (CH2 ), 18.7 (CH3 ), 0.1
[Si(CH3 )3 ] ppm; IR (CCl4 ): 3063, 2981, 2721, 1482, 1351, 1264, 1106,
1027, 983, 923, 735 cm1 .
www.interscience.wiley.com/journal/aoc
1,2,3-Tris(trimethylsiloxy)benzene (entry 8, Table 5)
1
H NMR (CDHCl3 , 400 MHz): δ D 6.69 (t, J D 8 Hz, 1H, Ar), 6.50 (d,
J D 8 Hz, 2H, Ar), 0.27 [s, 18H, 2 ð Si(CH3 )3 ], 0.23 [s, 9H, Si(CH3 )3 ]
ppm; 13 C NMR (CDCl3 , 100 MHz): δ D 148.11 (Ar), 138.89 (Ar),
120.52 (Ar), 114.11 (Ar), 0.69 [Si(CH3 )3 ], 0.33 [Si(CH3 )3 ] ppm; IR
(CCl4 ): 2960, 1620, 1482, 1262, 1069, 915, 846, 754 cm1 .
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 446–454
Rapid, highly efficient and chemoselective trimethylsilylation of alcohols and phenols
Table 6. Selective silylation of alcohols and phenols catalyzed by SnIV (TPP)(OTf)2 in CH3 CNa
Row
ROH
Silyl ether
CH2OH
CH2OSiMe3
1
OH
Time (min)
Yield (%)b
1
100
0
OSiMe3
1
2
CH2OH
Me
100
CH2OSiMe3
Me
Me
0
Me
OSiMe3
OH
3
1
CH2OH
90
CH2OSiMe3
OH
10
OSiMe3
1
4
CH2OH
CH2OSiMe3
OH
OSiMe3
CH2OH
CH2OSiMe3
100
0
5c
1
50
OH
OH
25
CH2OSiMe3
OSiMe3
6d
1
50
CH2OSiMe3
CH2OH
OH
OH
50
CH2OSiMe3
OSiMe3
7
1
CH2OSiMe3
80
CH2OSiMe3
OSiMe3
OH
20
OH
OSiMe3
a
Reaction conditions for a binary mixture: 1 mmol of each alcohol or phenol, HMDS (0.5 mmol), catalyst (1 mol%), CH3 CN (1 ml).
GC yield.
c
The amount of HMDS is 0.5 mmol.
d The amount of HMDS is 0.75 mmol.
b
453
Appl. Organometal. Chem. 2009, 23, 446–454
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
M. Moghadam et al.
Conclusion
In this paper, a rapid, efficient and chemoselective method for
the silylation of primary, secondary and tertiary alcohols and
phenols with 1,1,1,3,3,3-hexamethyldisilazane (HMDS) catalyzed
by an electron-deficient tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate, [SnIV (TPP)(OTf)2 ], which is a stable Sn(IV)
compound, is reported. Short reaction times, excellent yields, easy
work-up and stability and reusability of the catalyst are noteworthy
advantages of this method. Other applications of this catalyst in
organic transformations are under investigation.
Acknowledegment
We are thankful to the Center of Excellence of Chemistry of
University of Isfahan for financial support of this work.
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rapid, chemoselective, porphyrio, electro, phenols, alcohol, catalyzed, efficiency, tin, trimethylsilylation, deficiency, reusable, highly, hmds, hexamethyldisilazane
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