Mild and efficient silylation of alcohols and phenols with HMDS using Bi(OTf)3 under solvent-free condition

Article abstract of DOI:10.1016/j.jorganchem.2009.04.001

A very efficient and mild silylation of alcohols and phenols with hexamethyldisilazane (HMDS) at rt is developed using Bi(OTf)₃ as the catalyst. Primary, secondary and tertiary alcohols as well as phenols are excellently converted into correspo

Full text of DOI:10.1016/j.jorganchem.2009.04.001

Journal of Organometallic Chemistry 694 (2009) 2562–2566
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mild and efficient silylation of alcohols and phenols with HMDS using
Bi(OTf)3 under solvent-free condition
*
Santosh T. Kadam, Sung Soo Kim
Department of Chemistry, Inha University, Incheon 402-751, South Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A very efficient and mild silylation of alcohols and phenols with hexamethyldisilazane (HMDS) at rt is
developed using Bi(OTf)3 as the catalyst. Primary, secondary and tertiary alcohols as well as phenols
are excellently converted into corresponding TMS ethers in a very short reaction time. This procedure
can also be applied to large scale silylation for industrial application.
Received 30 January 2009
Received in revised form 3 April 2009
Accepted 3 April 2009
Available online 17 April 2009
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Alcohols
Phenols
HMDS
Silylation
Bi(OTf)3
1. Introduction
temperature [17] and excess amount of reagent [18]. The lack of
facile and general synthetic methodology under essentially mild
Functional group protection is the heart of multifunctional syn-
thesis of target molecules. Protection of alcohols and phenols rep-
resents one of the most ubiquitous steps [1]. Formation of silyl
ether from hydroxyl group is one of the most popular and widely
used method. Silylation of hydroxyl group is also used in analytical
chemistry to prepare volatile derivatives of alcohols and phenols
for GC and GC–MS analyses [2]. Silylation enhances solubility in
non-polar solvent and increases thermal stability as well. Many
silylating agents, such as chlorotrimethylsilane [3], hexame-
thyldisiloxane [4], and allylsilane [5], have been used for the intro-
duction of silyl group into a variety of alcohols. However, most of
the methods suffer from disadvantages such as long reaction time
and difficulties in the removal of amine salt formed as a by-prod-
uct. An alternative reagent for the silylation of hydroxyl compound
is 1,1,1,3,3,3-hexamethyldisilazane (HMDS) which is an inexpen-
sive, commercially available reagent and gives ammonia as the
only by-product. The weak silylation power of HMDS (it usually re-
quires relatively high catalyst loading) is the main drawback to its
application. Various catalysts have been developed such as InBr3
[6], I2 [7], LiClO4 [8], LaCl3 [9], K-10 montmorillionite [10], sulfonic
acid-functionalized nanoporous silica [11], zirconium sulfophenyl
phosphate [12] (CH3)3SiCl [13], zirconyl triflate [14] and iron (III)
trifluoroacetate [15] for the activation of HMDS. Even though these
catalytic systems enhance the ability of HMDS for the silylation,
still some of the catalysts require long reaction time [16], high
reaction condition has prompted us to develop an efficient, conve-
nient and practical procedure for the silylation of alcohols and phe-
nols under solvent-free conditions.
With increasing environmental concern the need for solvent-
free and environmentally benign method has become of significant
importance. According to the principle of green chemistry, syn-
thetic method should be designed to use substances that exhibit
little or no toxicity to human health and environment [19]. In this
regard, bismuth salts have recently attracted considerable atten-
tion because bismuth salts are remarkably non-toxic [20,21], stable
and cost less. Bi(OTf)3 has been a specially favourable candidate
because it is commercially available and can also be easily pre-
pared from commercially available compounds [22]. Accordingly
Bi(OTf)3 have been used as an effective catalyst for various organic
reactions such as benzylation of pentanediones [23], allylation of
aldehydes [24], synthesis of trisubstituted quinolines [25],
Friedel–Craft reaction [26] and Sakuri–Prins–Ritter reaction [27].
2. Results and discussion
In continuation of our interest on solvent-free catalytic method
[28,29], we herein report a simple, mild and efficient method for
the synthesis of trimethylsilyl ether of alcohols and phenols under
solvent-free condition (Scheme 1).
We have examined the potential of HMDS for silylation of alco-
hol in presence of various bismuth salts without using solvent at rt
as shown in Table 1.
* Corresponding author. Fax: +82 32 867 5604.
E-mail address: sungsoo@inha.ac.kr (S.S. Kim).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.04.001

S.T. Kadam, S.S. Kim / Journal of Organometallic Chemistry 694 (2009) 2562–2566
2563
Table 2
No Solvent
OH
OSiMe3
NH3
(Me3Si)2NH
Silylation of variety of alcohols and phenols with HMDS catalyzed by Bi(OTf)3 without
Bismuth salts
rt
solventa.
Entry
1
Product
Time (min)
Yield (%)b
Scheme 1. Silylation of benzyl alcohol with HMDS.
4
99
7c
92c
OTMS
Table 1
Silylation of benzyl alcohol with HMDS using bismuth salts at rt without solvent.
5d
5
91d
94
OTMS
Yield (%)a
2
3
4
5
6
Entry
Catalyst (mol%)
Time (min)
MeO
Me
1
2
2
4
5
Bismuth chloride (0.5)
Bismuth nitrate (0.5)
Bismuth triflate (0.5)
Bismuth oxide (0.5)
Bismuth bromide (0.5)
20
40
4
60
30
67
48
99
20
55
OTMS
6
95
91
90
99
OTMS
OTMS
8
Upon addition of bismuth triflate to the mixture of an alcohol
and HMDS, the silyl ether is formed in excellent yield in short reac-
tion time. Therefore, bismuth triflate is found to be an effective cat-
alyst for the silylation. The optimal molar ratio of alcohol, HMDS
and bismuth triflate is found to be 1.0 mmol: 1.0 mmol and
0.5 mol%, respectively. The efficiency of Bi(OTf)3 as the catalyst
for the silylation of aliphatic, aromatic, primary, secondary, hin-
dered alcohols is shown in Table 2.
Br
12
4
O2N
OTMS
MeO
O
Various benzyl alcohols having electron-donating and electron-
withdrawing substituents undergo smooth silylation with excel-
lent yield (entries 1–6). The catalyst may be equally applicable
for large scale (10.0 mmol and 0.1 mol) silylation of benzyl alcohol
and the reaction proceeds rapidly (entry 1). Isolation of larger scale
(0.1 mol) reaction was performed by distillation (bp: 206–210 °C).
Strongly electron-withdrawing nitro group affects the correspond-
ing silylation with quite high yield (entry 5). The ‘‘relatively” longer
reaction time (12 min) may indicate that slight substituent effects
are in operation for the reaction. trans-2-methyl-3-phenyl-2-pro-
pen-l-ol needs ‘‘relatively” prolonged reaction time (entry 7). The
catalytic system is also applicable to heterocyclic alcohol such as
furfuryl alcohol and gives corresponding silyl ether in high yield
(entry 8). Numerous secondary alcohols give corresponding silyl
ethers with remarkably high yield (entries 9–14). 1-(2-Methoxy-
phenyl)-1-propanol exhibits neither steric nor electronic effects
on reactivity (entry 13). Sterically hindered 4,-40-difluorobenzhy-
drol produces silyl ether in excellent yield with a very short
reaction time (entry 14). 3-Methyl-1-phenyl-1-propanol and 2-
adamantanol also underwent silylation under present conditions
(entries 15 and 16). The method tolerates the acid sensitive alco-
hols having double bond like geraniol (entries 18). The catalyst is
also able to convert the primary, secondary and neopentyl alcohol
into corresponding silyl ether in good yield (entries 19–22).
Interestingly, phenols too undergo the silylation in presence of
Bi(OTf)3 to produce silyl ether in considerably high yield (entries
23–26). Relative to 4-methoxyphenol, 3-methoxyphenol has lower
yield and longer reaction time (entries 24 and 25). This may sug-
gest that slight electronic effect could reduce the yield and length-
en the reaction time. Present catalytic system cannot produce any
silyl compounds from thiols and amines (entries 27 and 28). Ben-
zenethiol and benzylamine gave no silylation product at all even
by increasing the catalyst amount up to 2 mol% after 3 h. This is be-
cause oxophilicity of silicon atom towards alcoholic OH may be
strong enough to overcome the reactivities of HMDS with N–H
and S–H bonds of amines and thiols, respectively. The possible
chemoselective protection of alcohol in the presence of thiol and
amine is demonstrated as shown in Scheme 2.
OTMS
7
8
20
20
98
90
OTMS
OTMS
9
5
2
94
99
OTMS
Me
10
OTMS
11
4
98
Cl
OTMS
OTMS
OMe
12
13
2
2
96
99
OTMS
14
15
3
99
83
F
F
OTMS
The generality and the excellence of Bi(OTf)3 in terms of catalyst
loading, short reaction time and solvent-free condition can be eas-
ily understood from the comparison of the data with literature re-
sults as shown in Table 3.
45

2564
S.T. Kadam, S.S. Kim / Journal of Organometallic Chemistry 694 (2009) 2562–2566
Table 2 (continued)
ammonia and liberation of the catalyst. The evolution of ammonia
Entry
16
Product
Time (min)
15
Yield (%)b
90
was confirmed by its strong, pungent odor and using the red Lit-
mus paper which turns to blue. The silylation reaction using 2:1/
alcohol: HMDS molar ratio was performed and it produce corre-
sponding silyl compound with high yield (entry 29).
OTMS
In conclusion, we have demonstrated that Bi(OTf)3 is a highly
efficient chemoselective catalyst for silylation of alcohols and phe-
nols under solvent-free condition at rt. The catalyst is also capable
of large scale silylation. The major advantage of this method is
that: operational simplicity at rt within a short reaction time and
low catalyst loading (0.5 mol%). This reaction may require the low-
est catalyst quantity of all the previous studies in recent years (Ta-
ble 3). The use of relatively non-toxic and inexpensive catalyst add
to the versatility of this method.
OTMS
17
18
19
20
21
4
95
95
84
87
85
5
OTMS
Me
Me
Me
35
10
15
3. Experimental
OTMS
OTMS
In all cases the 1H NMR (200 MHz) spectra were recorded with
Varian Gemini 200. Chemical shifts were reported in ppm in CDCl3
with tetramethylsilane as the internal standard. 13C NMR data
were collected on a Varian Gemini 400 (100 MHz). Some com-
pounds were also identified by HRMS (EI) with Jeol DMX 303
and GCMS (EI 70 eV). Data were collected through 1200L Single
Quadrupole GC/MS system with 3800GC/Varian.
9
Me
Me
OTMS
Me
OTMS
3.1. Trimethylsilylation of alcohols and phenols
22
23
24
25
35
6
90
93
98
91
Me
Bi(OTf)3 (0.5 mol%) was added to the mixture of alcohol or phe-
nol (1.0 mmol) and HMDS (1.0 mmol). The reaction mixture was
stirred at rt for the appropriate time (see Table 2). The progress
of reaction was monitored by TLC. The reaction mixture was di-
luted with EtOAc. Concentration of the organic layer under vacuum
gave crude mass, which was purified by column chromatography
with silica gel.
OTMS
5
MeO
MeO
OTMS
1H and 13C NMR data for known products are the same with liter-
ature values [8,14,33–36]. Spectral data and HRMS values for new
products are given below (entries 6, 7, 9, 11, 13–15, 18–22 and 26).
Table 2, Entry 6: (4-Methoxyphenethoxy)trimehtylsilsne: 1H
NMR (200 MHz, CDCl3): d 0.28 (s, 9H), 2.78 (t, J = 16 Hz, 2H), 3.74
(t, J = 16 Hz, 2H), 3.78 (s, 3H), 6.84 (d, J = 8 Hz, 2H), 7.13 (d,
J = 8 Hz, 2H). 13C NMR (100 MHz, CDCl3): d 0.58, 38.53, 55.14,
64.07, 113.67, 129.91, 130.95, 158.04. HRMS-EI +: m/z Calcd for
C12H20O2Si: 224.1233; found: 224.1217.
8
OTMS
H
Me
Me
26
27
28
7
95
OTMS
SH
Table 2, Entry 7: (E)-Trimethyl-(2-methyl-3-phenylallyl-
oxy)silane: 1H NMR (200 MHz, CDCl3): d 0.12 (s, 9H), 1.80 (s, 3H),
4.11 (s, 2H), 6.47 (s, 1H), 7.24–7.27 (m, 5H). 13C NMR (100 MHz,
CDCl3): d 0.36, 15.09, 68.35, 124.42, 126.20, 128.05, 028.89,
137.23, 137.23, 37.91. HRMS-EI +: m/z Calcd for C13H20OSi:
220.1283; found: 220.1292.
Table 2, Entry 9: (Cyclopropyl(phenyl)methoxy)trimethylsi-
lane: 1H NMR (200 MHz, CDCl3): d 0.02 (s, 9H), 0.19–0.44 (m,
4H), 1.05 (d, J = 7.6 Hz, 1H), 3.99 (d, J = 6.8 Hz, 1H), 7.13–7.29 (m,
5H). 13C NMR (100 MHz, CDCl3): d 0.23, 2.80, 3.56, 80.25, 125.95,
127.00, 128.05, 15.18. HRMS-EI +: m/z Calcd for C13H20OSi:
220.1283; found: 220.1279.
3 h
3 h
6e
NR
NR
94e
NH2
OTMS
29
a
Reaction condition: alcohol (1.0 mmol), HMDS (1.0 mmol), Bi(OTf)3 (0.5 mol%).
Isolated yield.
10.00 mmol of benzyl alcohol, 10.00 mmol of HMDS.
Benzyl alcohol (0.1 mol): HMDS (0.1 mol).
b
c
Table 2, Entry 10:Trimethyl(1-phenylethoxy)silane: 1H NMR
(200 MHz, CDCl3): d 0.39 (s, 9H), 1.45 (d, J = 8 Hz, 3H) 4.87 (q,
J = 20 Hz, 1H), 7.30–7.35 (m, 5H). 13C NMR (100 MHz, CDCl3): d 0.06,
25.14, 26.83, 70.58, 125.33, 125.35, 126.81, 127.42, 128.11, 146.42.
HRMS-EI +: m/z Calcd for C11H18OSi: 194.1127; found: 194.1131.
Table 2, Entry 11: (1-(3-Chlorophenyl)ethoxy)trimethylsilane:
1H NMR (200 MHz, CDCl3): d 0.14 (s, 9H), 1.47 (d, J = 4 Hz, 3H),
4.86 (q, J = 8 Hz, 1H), 7.29–7.32 (m, 3H), 7.35–7.38 (m, 1H). 13C
NMR (100 MHz, CDCl3): d 0.04, 26.81, 69.98, 123.46, 125.56,
126.94, 129.44, 134.06, 148.70.HRMS-EI +: m/z Calcd for
C11H17ClOSi: 228.0737; found: 228.0729.
d
e
2.0 mmol of benzyl alcohol and 1.0 mmol of HMDS were used.
A plausible mechanism has been shown in Scheme 3. Lewis
acid–base interaction between the bismuth triflate and nitrogen
of HMDS polarizes the N–Si bond to produce the reactive silylating
agent (I), which rapidly reacts with alcohol to give the correspond-
ing silyl compounds and complex (II). This complex (II) reacts with
another molecule of alcohol to produce the corresponding silyl
derivative. Finally the complex (III) collapses to the formation of

S.T. Kadam, S.S. Kim / Journal of Organometallic Chemistry 694 (2009) 2562–2566
2565
Table 3
Bi(OTf)3 catalyzed silylation of alcohols in comparison with other literatures.a
No.
Catalyst (mol%)
Time (min)
Solvent
Reference
1
2
3
4
5
6
7
8
Bi(OTf)3 0.5
LiClO4 50
Fe(tpp)Cl 24
ZrCl4 20
Fe3O4 10
H3PW12O40 10
Barbituric acid 10
Cu(OTf)2 10
Iodine 10
Mostly less than 10
10–30
5–90
1–10
5
6–120
1–5 h
5–80
2–4
3–5 h
80–120
24–60
1–20 h
5 min–2 h
1–4
No
No
CH3CN
CH3CN
No
Present method
[8]
[30]
[33]
[31]
[17]
[16]
[32]
[7]
No
No
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
No
9
10
11
12
13
14
15
LaCl3 10
[9]
Sulfonic acid nanoporous silica 3
K-10 montmorillioni 100 mg
Zirconium sulfophenyl phosphonate 50 mg
Fe(F3CCO2)3
ZrO(OTf)2 0.5
[11]
[10]
[12]
[15]
[14]
5
CH3CN
a
All reactions were conducted at rt. The reaction of entry 6 was done at 60 °C.
(Me3Si)2NH
OSiMe3
NHSIMe3
NH2
OH
OH
Bi(OTf)3
rt, 5 min
88 %
0 %
SSiMe3
SH
(Me3Si)2NH
OSiMe3
Bi(OTf)3
rt, 5 min
90 %
0 %
Scheme 2. Chemoselectivity of benzyl alcohol in presence of benzyl amine and benzenethiol.
Me3SiNHSiMe3
Bi(OTf)3
19.26, 36.34, 80.42, 126.69, 126.80, 127.76, 144.48. HRMS-EI +:
m/z Calcd for C13H22OSi: 222.1440; found: 222.1438.
NH3
Table 2, Entry 18: (E)-(3,7-Dimethylocta-2,6-dienyloxy)tri-
methylsilane: d 0.06 (s, 9H), 1.59–1.67 (m, 9H), 2.00–2.10 (m,
4H), 4.15 (d, J = 3.6 Hz, 2H), 5.08 (t, J = 3 Hz, 1H), 5.32 (t, J = 3 Hz,
1H). 13C NMR (100 MHz, CDCl3): d 1.87, 16.19, 17.61, 25.60,
26.34, 39.49, 59.29, 123.31, 123.85, 131.67, 139.59. HRMS-EI +:
m/z Calcd for C13H26OSi: 226.1753; found: 226.1774.
Bi(OTf)3
HN
Me3Si
NH3-Bi(OTf)3
III
SiMe3
I
R-OH
Table 2, Entry 19: (Hexan-2-yloxy)trimethylsilane: 1H NMR
(200 MHz, CDCl3): d 0.10, (s, 9H), 0.85 (d, J = 5.8 Hz, 3H), 1.10 (t,
J = 11.4 Hz, 3H), 1.24–1.34 (m, 12H), 3.70–3.78 (m, 1H). 13C NMR
(100 MHz, CDCl3): d 0.18, 14.02, 22.61, 23.83, 29.29, 31.82, 39.60,
68.56. HRMS-EI+:m/zCalcdforC9H22OSi:174.1440;found:174.1458.
Table 2, Entry 20: Trimethyl(undecyloxy)silane: 1H NMR
(200 MHz, CDCl3): 0.28 (s, 9H), 0.88 (t, J = 5.8 Hz, 3H), 1.31-1.43
(m, 14H), 1.48-1.53 (m, 4H), 3.78 (t, J = 9.6 Hz, 2H). 13C NMR
(100 MHz, CDCl3): d 0.52, 14.07, 22.66, 25.81, 29.44, 29.63, 31.90,
32.73, 62.70. HRMS-EI +: m/z Calcd for C7H18OSi: 146.1127; found:
146.1145.
R-OSiMe3
R-OSiMe3
R-OH
Me3Si-NH2-Bi(OTf)3
II
Scheme 3. Plausible mechanism for silylation of an alcohol with HMDS.
Table 2, Entry 13: (1-(2-Methoxyphenyl)propoxy)trimethylsi-
lane: 1H NMR (200 MHz, CDCl3): d 0.46 (s, 9H), 1.33 (t, J = 14 Hz,
3H), 2.04 (m, 2H), 4.23 (s, 3H), 5.40 (t, J = 8 Hz, 1H), 7.24 (d,
J = 8 Hz, 1H), 7.38 (t, J = 13 Hz, 1H), 7.60 (t, J = 16 Hz, 1H), 7.86 (d,
J = 7.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): d 0.04, 10.40, 31.77,
55.17, 69.62, 109.85, 120.46, 126.79, 127.51, 133.98, 155.55.
HRMS-EI +: m/z Calcd for C13H22O2Si: 138.1389; found: 138.1381.
Table 2, Entry 14: ((4-Fluorocyclohexa-2,4-dienyl)(4-fluoro-
phenyl)methoxy)trimethylsilane: 1H NMR (200 MHz, CDCl3): d
0.34 (s, 9H), 5.93 (s, 1H), 7.21–7.30 (m, 4H), 7.51–7.58 (m, 4H).
13C NMR (100 MHz, CDCl3): d 0.07, 75.26, 114.91, 115.34, 140.53,
140.58, 159.57, 164.45.
Table 2, Entry 21: Trimethyl(neopentyloxy)silane: 1H NMR
(200 MHz, CDCl3): d 0.08 (s, 9H), 0.85 (s, 9H), 3.19 (s, 2H). 13C
NMR (100 MHz, CDCl3): d 0.53, 26.27, 34.58, 72.71.
Table 2, Entry 22: (But-3-yn-2-yloxy)trimethylsilane: 1H NMR
(200 MHz, CDCl3): d 0.09 (s, 9H), 1.41 (d, J = 7.1 Hz, 3H), 2.34 (d,
J = 1.6 Hz, 1H), 4.7 (qd, J = 7.1, 1.6 Hz, 1H). 13C NMR (100 MHz,
CDCl3): d 0.07, 2.45, 25.29, 58.31, 71.45.
Table 2, Entry 25: (3-Methoxyphenoxy)trimethylsilane: 1H
NMR (200 MHz, CDCl3): 0.39 (s, 9H), 3.89 (s, 3H), 6.55-6.69 (m,
3H), 7.28 (t, J = 16 H z, 1H). 13C NMR (100 MHz, CDCl3): d 0.23,
55.18, 106.27, 107.05, 112.49, 129.77. HRMS-EI +: m/z Calcd for
C10H16O2Si: 196.0920; found: 196.0899.
Table 2, Entry 15: Trimethyl(2-methyl-1-phenylpropoxy)silane:
1H NMR (200 MHz, CDCl3): d 0.01 (s, 9H), 0.77 (q, J = 9.8 Hz, 3H),
0.91 (q, J = 9.8 Hz, 3H), 1.80–1.86 (m, 1H), 4.25–4.30 (m, 1H),
7.24–7.27 (m, 5H). 13C NMR (100 MHz, CDCl3): d 0.09, 18.14,
Table 2, Entry 26: (4-Isopropylphenoxy)trimethylsilane: 1H NMR
(200 MHz, CDCl3): d 0.26, 1.20 (d, J = 7 Hz, 6H), 2.77–2.91 (m, 1H),

2566
S.T. Kadam, S.S. Kim / Journal of Organometallic Chemistry 694 (2009) 2562–2566
6.74 (d, J = 8.4 Hz, 2H), 7.03 (d, J = 8.4 Hz, 2H). 13C NMR (100 MHz,
CDCl3): d 0.29, 24.24, 33.36, 119.74, 127.25, 141.70, 153.09. HRMS-
EI +: m/z Calcd for C12H20OSi: 208.1283; found: 208.1285.
[15] H. Firouzabadi, N. Iranpoor, A.A. Jafari, M.R. Jafari, J. Organomet. Chem. 693
(2008) 2711.
[16] A. Khazaei, M.A. Zolfigol, Z. Tanbakouchian, M. Shiri, K. Niknam, J. Saien, Catal.
Commun. 8 (2007) 917.
[17] H. Firouzabadi, N. Iranpoor, K. Amani, F. Nowrouzi, J. Chem. Soc., Perkin Trans.
1 (2002) 2601.
[18] N. Azizi, R. Yousefi, M.R. Saidi, J. Organomet. Chem. 691 (2006) 817.
[19] P. Anastas, J.C. Warner, in: Green Chemistry: Theory and Practice, Oxford
University Press, Oxford, 1998.
[20] H. Suzuki, Y. Matano (Eds.), Organobismuth Chemistry, Elsevier, Amsterdam,
2001.
[21] J. Reglinski, in: C.N. Norman (Ed.), Chemistry of Arsenic, Antimony and
Bismuth, Blackie Academic and Professional, New York, 1998, pp. 403–440.
[22] S. Repichet, A. Zwick, L. Vendier, C. Le Roux, J. Dubac, Tetrahedron Lett. 43
(2002) 993.
Acknowledgments
Authors thank the Centre for Biological Modulators from KRICT
for the financial assistance. This work also has been supported by
BK 21 of Korea Research Council.
References
[23] M. Rueping, B.J. Nachtsheim, A. Kuenkel, Org. Lett. 9 (2007) 825.
[24] T. Ollevier, Z. Li, Eur. J. Org. Chem. 34 (2007) 5665.
[25] J.S. Yadav, B.V.S. Reddy, K. Premalatha, Synlett (2004) 963.
[26] Y. Matsushita, K. Sugamoto, T. Maysui, Tetrahedron Lett. 45 (2004) 4723.
[27] G. Sabitha, M. Bhikshapathi, S. Nayak, J.S. Yadav, R. Ravi, A.C. Kunwar,
Tetrahedron Lett. 49 (2008) 5727.
[1] T.W. Green, P.G.M. Wuts, in: Protective Groups in Organic Synthesis, 3rd ed.,
John Wile & Sons, New York, 1999, pp. 150–160.
[2] G. Van Look, G. Simchen, J. Heberle, Silylation Agents, Fluka, Buchs,
Switzerland, 1995.
[3] B.P. Bandgar, S.N. Chavare, S.S. Pandit, J. Chin. Chem. Soc. 52 (1) (2005) 125.
[4] B.E. Cooper, Chem. Ind. 107 (1978) 794.
[28] S.T. Kadam, S.S. Kim, Synthesis (2008) 267.
[29] S.T. Kadam, S.S. Kim, Synthesis (2008) 3307.
[30] H. Firouzabadi, A.R. Sardarian, Z. Khayat, B. Karimi, S. Tangestaninejad, Synth.
Commun. 27 (1997) 2709.
[5] T. Morita, Y. Okamoto, H. Sakurai, Tetrahedron Lett. 21 (1980) 835.
[6] J.S. Yadav, B.V.S. Reddy, A.K. Basak, G. Baishya, A. Vankat Narsaiah, Synthesis
(2006) 3831.
[31] M.M. Mojtahedi, M.S. Abaee, M. Eghtedari, Appl. Organomet. Chem. 22 (2008)
529.
[32] H. Firouzabadi, N. Ranpoor, S. Sobhani, S. Ghassamipour, Z. Amoozgar,
Tetrahedron Lett. 44 (2003) 891.
[33] F. Shirini, E. Mollarazi, Catal. Commun. 8 (2007) 1393.
[34] M.S. Khalili, H. Ghafuri, S.M. Jahromi, M.M. Hashemi, Phosphorus Sulfur Relat.
Elements 182 (2007) 175.
[7] B. Karimi, B. Golshani, J. Org. Chem. 65 (2000) 7228.
[8] M.R. Saidi, N. Azizi, Organometallics 23 (2004) 1457.
[9] A.V. Narsaiah, J. Organomet. Chem. 692 (2007) 3614.
[10] Z.H. Zang, T.S. Li, F. Yang, C.G. Fu, Synth. Commun. 28 (1998) 3105.
[11] D. Zareyeea, B. Karimi, Tetrahedron Lett. 48 (2007) 1277.
[12] M. Curini, F. Epifano, M.C. Marcotullio, O. Rosati, Synth. Commun. 29 (1999)
541.
[35] A. Khazaei, M.A. Zolfigol, A. Rostami, A.G. Choghamarani, Catal. Commun. 8
(2007) 543.
[13] P. Gauuret, S. El-Ghamarli, A. Legrand, D. Couirier, B. Rigo, Synth. Commun. 26
(1996) 707.
[36] F. Shirini, K. Marjani, H.T. Nahzomi, M.A. Zolfigol, Phosphorus Sulfur Relat.
Elements 183 (2007) 168.
[14] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, S.
Chahardahcheric, Z. Tavakoli, J. Organomet. Chem. 693 (2008) 2041.