Silica Chloride (SiO2-Cl) and Trimethylsilyl Chloride (TMSCl) Promote Facile and Efficient Dehydration of Tertiary Alcohols

Article abstract of DOI:10.1081/SCC-120025173

Silica chloride (SiO₂-Cl), as a heterogeneous reagent, has been used for the efficient dehydration of tertiary alcohols under mild reaction conditions. For comparison, we have also used trimethylsilyl chloride (TMSCl) as a homogeneous reagent for this purpose. We have found that silica chloride is a more efficient reagnet than trimethylsilyl chloride for this purpose. Handling of SiO₂-Cl is much safer and easier than TMSCl, especially for large-scale operation. The selectivity of the method is also demonstrated by several competitive reactions. Ether formation, rearranged products, and polymerization have not been observed in the reactions.

Full text of DOI:10.1081/SCC-120025173

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Silica Chloride (SiO -Cl) and Trimethylsilyl Chloride
2
(TMSCl) Promote Facile and Efficient Dehydration of
Tertiary Alcohols
a
a
a
a
Habib Firouzabadi , Naser Iranpoor , Hassan Hazarkhani & Babak Karimi
a
Chemistry Department, School of Sciences, Shiraz University, Shiraz, Iran
Version of record first published: 16 Aug 2006.
To cite this article: Habib Firouzabadi , Naser Iranpoor , Hassan Hazarkhani & Babak Karimi (2003): Silica Chloride (SiO -Cl)
2
and Trimethylsilyl Chloride (TMSCl) Promote Facile and Efficient Dehydration of Tertiary Alcohols, Synthetic Communications:
An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:21, 3653-3660
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 21, pp. 3653–3660, 2003
Silica Chloride (SiO -Cl) and Trimethylsilyl
2
Chloride (TMSCl) Promote Facile and Efficient
Dehydration of Tertiary Alcohols
Habib Firouzabadi,* Naser Iranpoor,*
Hassan Hazarkhani, and Babak Karimi
Chemistry Department, School of Sciences,
Shiraz University, Shiraz, Iran
ABSTRACT
2
Silica chloride (SiO -Cl), as a heterogeneous reagent, has been used
for the efficient dehydration of tertiary alcohols under mild reaction
conditions. For comparison, we have also used trimethylsilyl chloride
(
TMSCl) as a homogeneous reagent for this purpose. We have found
that silica chloride is a more efficient reagnet than trimethylsilyl
chloride for this purpose. Handling of SiO -Cl is much safer and
2
easier than TMSCl, especially for large-scale operation. The
selectivity of the method is also demonstrated by several competitive
reactions. Ether formation, rearranged products, and polymerization
have not been observed in the reactions.
*Correspondence: Habib Firouzabadi and Naser Iranpoor, Chemistry
Department, School of Sciences, Shiraz University, Shiraz 71454, Iran; Fax:
þ98-711-2286008; E-mail: firouzabadi@chem.susc.ac.ir; iranpoor@chem.susc.
ac.ir.
3
653
DOI: 10.1081/SCC-120025173
Copyright & 2003 by Marcel Dekker, Inc.
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3654
Firouzabadi et al.
Key Words: Silica chloride; Trimethylsilyl chloride; Dehydration;
Tertiary alcohols.
Solid supports have found wide applications in organic reactions from
They mostly facilitate the work-up of the reaction
[1,2]
different views.
mixtures and usually high selectivity accompanied with high yields of
the products is observed. Silica gel is one of the extensively used supports
[
3–6]
for different purposes in organic chemistry.
Modified silica supports
for functional group transformation is also of interest. Silica chloride has
been reported to be an efficient reagent for the transformation of sulfoxides
[7]
to thioethers. Recently, we have reported that silica chloride could also
[
be conveniently used for the conversion of acetals to thioacetals.
8]
Conversion of alcohols to olefins is an important reaction in organic
chemistry and a vast number of methods are documented in the literature
for this purpose. These methods include conventional protic acid catalysis
[
9]
(H SO , H PO ) in which the major drawback is the formation of rear-
ranged products and ether by products. Anhydrous CuSO , Al O ,
2
4
3
4
[
10]
[11]
4
[5b]
2
3
[
4]
[5a]
[12]
FeCl /silica gel, TosOH/silica gel,
3
H SO /silica gel,
2
BF ÁOEt ,
4
[15]
3
2
[13]
[14]
POCl /pyridine,
3
HMPA,
CF COCCl ,
Ph BiBr /I ,
3
metallic sulfates/silica
[18]
Triflates have found
2 2
[6]
[16]
[17]
gel, CH ReO ,
3
sulfuranes.
[
3
3
3
19]
useful applications in organic synthesis.
Copper(II) triflate has been
[
20]
used for dehydration of alcohols.
from one of the following drawbacks: (1) unavailability of the reagent,
2) sometimes elevated temperatures are required, (3) fairly large amount
These methods suffer more or less
(
of the catalyst or the reagent is needed, and (4) some of the reagents are
expensive. Therefore, introduction of a new mild and inexpensive method
for this aim could be a useful contribution in organic synthesis. In this
article we have demonstrated a new application of silica chloride (SiO -Cl)
2
as a cheap and an easily available reagent and trimethylsilyl chloride
(TMSCl) for efficient dehydration of tertiary benzylic alcohols.
[
21]
Preparation of silica chloride is reported in the literature. We have
modified this preparation in order to increase the capacity of the
[
8,22]
reagent.
by the reaction of thionyl chloride (SOCl ) and silica gel under reflux
According to this modification, the reagent can be prepared
2
conditions for 48 h in a quantitative yield. SiO -Cl is a grayish and stable
2
powder that should be stored in the absence of moisture.
Now in this article we report selective and efficient dehydration of
tertiary benzylic alcohols to their corresponding olefins in CHCl at room
3
temperature with excellent yields (Sch. 1, Table 1). Saturated tertiary
alcohols remained intact after prolonged reaction times. Surprisingly,
4
-hydroxy-4-methyl-2-pentanone (Table 1, Entry 1k) was dehydrated to

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Silica Chloride and Trimethylsilyl Chloride
3655
2
R
2
CHR
SiO -Cl (1g)
2
3
3
R
R
OH
CHCl , rt
3
1
R
1
R
1
2
3
R = Ph,Cyclohexyl, R = H, Me, n-Pr, R = H, Ph, Cl
Scheme 1.
Table 1. Dehydration of tertiary benzylic alcohols with SiO -Cl and TMSCl
2
in CHCl
3
.
a
Time (h)
b
Yield (%)
1
H-NMR
e
Entry
substrate
SiO -Cl,
2
TMSCl
SiO -Cl,
2
TMSCl
(olefinic H) ꢀ
(CDCl , ppm)
Product
3
OH
0.75, 1
95, 95
5.83
1
a
c
HO
1, 1.25
89, 88
5.82
1b
OH
0.66, 1.16
1.16, 1.1
94, 92
95, 94
93, 94
6.16
6.13
5.51
1
c
HO
1d
OH
OH
0.5, 0.75
C
CH
2
CH
3
1
e
0.75, 1
91, 90
89, 88
6.15
6.12
C
CHCH
3
CH CH
2
3
1f
OH
1.2, 1.33
C
CHPr
n-
Bu
1g
(
continued )

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3656
Firouzabadi et al.
Table 1. Continued.
a
Time (h)
b
Yield (%)
1
H-NMR
e
Entry
substrate
SiO -Cl,
2
SiO -Cl,
2
(olefinic H) ꢀ
(CDCl , ppm)
TMSCl
Product
TMSCl
3
CHPr 78.3, 79.2d
5.85
Ph
Ph
C
OH
CH
CH
3
n-
Bu
Ph
h
3, 4
1
f
f
CHPr
1
1.7, 8.7
5.85, 5.30
3
C
CH
3
d
31.5 , 25.4
d
CH
2
5.18, 5.42
5.70
Cl
C
OH
CH
n-Bu
n-
Bu
Cl
4, 5:4
CHPr
87.5, 52.6
1
i
3
Cl
C
CH
3
d
f
CH
2
50, 44.9
4.97, 5.08
—
C
OH
CH
3
1j
CH
3
37, 41.1
3, 4
C
d
78 , 25
d
OH
5, 5
5, 6
CH
6.02
2
CH
3
1k
CH
3
CH
3
d
87 , 80
d
f
OH O
O
5.07, 5.36
H C
3
H C
3
1
l
CH
CH
3
3
H C
CH
3
3
CH
12, 12
12, 12
N.R
N.R
—
—
—
—
3
1m
OH
H C OH
3
1
n
a
Substrate/SiO -Cl 1 mmol/1.0 g/1 h and substrate/TMSCl 1 mmol 1/2 mmol.
2
b
Isolated yields.
10% of the exo-isomer has also been formed.
c
d
Reactions were performed in refluxing CHCl3.
Some of the spectral data of the olefins produced in the reactions are given in
e
[
24]
Ref.
f
Two different olefinic protons.

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Silica Chloride and Trimethylsilyl Chloride
3657
its corresponding conjugated enone after a prolonged reaction time. We
believe the extension of conjugation by dehydration reaction provides the
driving force for this reaction to occur.
We have also used trimethylsilyl chloride (TMSCl) as a homogenous
reagent for this purpose in CH Cl . Dehydration of tertiary benzylic
2
2
alcohols proceeded with TMSCl at room temperature and in some
cases, refluxing of the reaciton mixture was obligatory for the completion
of the reaction. In general, SiO -Cl is more reactive reagent than TMSCl
2
for the dehydration of the tertiary alcohols in this study. Handling of
SiO -Cl is easy and is a suitable reagent for the heterogeneous large-scale
2
operation. The results are tabulated in Table 1.
In order to show the selectivity of SiO -Cl for the dehydration of
2
structurally different tertiary alcohols, several competitive reactions
proceeded (Sch. 2).
In conclusion, in this study we have shown new and useful applica-
tions of silica chloride (SiO -Cl) and trimethylsilyl chloride (TMSCl) for
2
dehydration of tertiary benzylic alcohols. Solid silica chloride is a cheap
reagent and its handling is much easier than highly reactive liquid
trimethylsilyl chloride (TMSCl). Laboratory large-scale operation, even
at elevated temperatures, can be conducted easily in the presence of solid
silica chloride. Reactions are not time-consuming and the yields of the
olefins are excellent.
OH
OH
OH
C
CH
2
CH
3
CH
Si-Cl (1g)
3
CH
3
+
+
0
.5 h
9
8%
89%
OH
OH
CH
OH
n-
Bu
Si-Cl (1g)
Cl
n-Bu
Cl
+
+
CH3
3
0
.5 h
9
8%
90%
OH
O
OH
CH
OH O
Si-Cl (1g)
H C
+
3
CH
+
H C
3
3
CH
3
3
CH
3
1
.16 h
9
8%
95%
Scheme 2.

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3658
Firouzabadi et al.
EXPERIMENTAL
General
Silica chloride (SiO -Cl) was prepared according of the reported
2
[8]
procedure. IR spectra were recorded on a Perkin-Elmer 781 spectro-
1
13
photometer. H-NMR and C-NMR spectra were run on a Bruker
Avance DPX 250 MHz instrument.
Typical Procedure for Dehydration of Tertiary Alcohols
To a solution of 1,1-diphenylpropanol (Entry 1f, 5 mmol, 1.06 g), in
CHCl (25 mL), silica chloride (5 g) was added and the resulting hetero-
3
geneous mixture was stirred at room temperature. After completion of
the reaction (0.75 h, TLC, n-hexane/EtOAc, 10/1), silica gel (5 g) was
added to the reaction mixture and the solvent was evaporated under
reduced pressure. The resulting powder was applied on a silica gel pad
(5 cm thick) and washed with petroleum ether (100 mL). Evaporation of
the solvent afforded 1,1-diphenylpropene in excellent yields (0.88 g, 91%,
ꢀ
[23]
ꢀ
1
48–49 C, H-NMR
white crystals from methanol, m.p. 48–50 C, Lit.
(CDCl , 250 MHz) ꢀ: 1.77 (d, 3H), 6.18 (q, 1H), 7.16–7.36 (m, 10H),
3
1
3
C-NMR (CDCl , 62.89 MHz) ꢀ: 15.70, 124.14, 126.71, 126.82, 127.19,
3
1
28.05, 128.13, 130.05, 140.03, 142.43, 142.96 ppm.
ACKNOWLEDGMENT
The authors are grateful to the Shiraz University Research Council
for the partial support of this work.
REFERENCES
. McKillop, A.; Young, D.W. Synthesis 1979, 401.
. Cornelis, A.; Laszlo, P. Synthesis 1985, 909.
1
2
3
4
5
. Keinan, E.; Mazur, Y. J. Org. Chem. 1978, 43, 1020.
. Tal, D.M.; Keinan, E.; Mazur, Y. Tetrahedron 1981, 37, 4327.
. (a) Onofrio, F.D.; Scettri, A. Synthesis 1985, 1159; (b) Chavez, F.;
Suarez, S.; Diaz, M.A. Synthetic Commun. 1994, 24, 2325–2339.
. Nishiguchi, T.; Kamio, C. J. Chem. Soc. Perkin Trans. I 1989, 707.
6

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Silica Chloride and Trimethylsilyl Chloride
3659
7
8
9
. Mohanazadeh, F.; Momeni, A.R.; Ranjbar, Y. Tetrahedron Lett.
994, 6127.
. Firouzabadi, H.; Iranpoor, N.; Karimi, B.; Hazarkhani, H. Synlett
000, 263.
. March, J. Advanced Organic Chemistry, 3rd Ed.; Wiley Interscience:
New York, 1985; 344–345, 901–902.
1
2
1
0. Hoffman, R.V.; Bishop, R.D.; Fitch, P.M.; Hardenstein, R. J. Org.
Chem. 1980, 45, 917.
1
1
1. Knozinger, H. Synthesis 1968, 791.
2. Posner, G.H.; Shulman-Roskes, E.M.; Oh, C.h.; Carry, J.C.;
Green, J.V.; Clark, A.B.; Dai, H.; Anjeh, T.E.N. Tetrahedron
Lett. 1991, 6489.
1
3. Runk, C.S.; Haverty, S.M.; Klein, D.A.; McCrea, W.R.; Strobel,
E.D.; Klein, D.D. Tetrahedron Lett. 1992, 2665.
14. Monson, R.S.; Priest, D.N. J. Org. Chem. 1971, 36, 3826.
15. Dorta, R.L.; Suarez, E. Tetrahedron Lett. 1994, 5035.
16. Zhu, Z.; Espenson, J.H. J. Org. Chem. 1996, 61, 324.
17. Abdel-Baky, S.; Moussa, A. Synthetic Commun. 1988, 18, 1795.
18. Martin, J.C.; Arhart, R.J. J. Am. Chem. Soc. 1971, 93, 4327.
19. (a) Firouzabadi, H.; Karimi, B.; Eslami, S. Tetrahedron Lett. 1999,
58 and the references cited therein; (b) Corey, E.J.; Shimoji, K.
Tetrahedron Lett. 1983, 24, 169.
2
2
2
0. Laali, D.; Gerzina, R.J.; Flajnik, C.M.; Geric, C.M.; Dombroski,
A.M. Helv. Chem. Act. 1987, 70, 607 and the references cited therin.
1. Saunders, D.H.; Barford, R.A.; Magidman, P.; Olszewski, L.T.;
Rothbart, H.L. Anal. Chem. 1974, 46, 834–838.
2. (a) Firouzabadi, H.; Iranpoor, N.; Hazarkhani, H. Phosphorus,
Sulfur and Silicon 2002, 177, 2847–2858; (b) Firouzabadi, H.;
Iranpoor, N.; Hazarkhani, H. Phosphorus, Sulfur and Silicon
2
001, 176, 165; (c) Firouzabadi, H.; Iranpoor, N.; Hazarkhani, H.,
Tetrahedron Lett. 2002, 43, 7139; (d) Firouzabadi, H.; Iranpoor, N.;
Hazarkhani, H. Phosphorus, Sulfur and Silicon 2003, 178, 149–153;
(e) Firouzabadi, H.; Iranpoor, N.; Hazarkhani, H.; Karimi, B. J.
Org. Chem. 2002, 67, 2572.
2
2
3. Bruson, H.A.; Plant, H.L. J. Org. Chem. 1967, 32, 3356–3362.
4. Some spectral data of the isolated olefins:
1
1
ꢀ
a. IR (liquid film): 3080, 3040, 2950, 2900, 2840, 1500, 1460, 1380,
1
250, 1080, 1050, 820, 800, 760, 740. H-NMR (CDCl , 250 MHz):
2.05 (s, 3H), 2.27 (m, 2H), 2.71 (t, 2H), 5.83 (t, 1H), 7.09–7.16
3
(
1
7
m, 4H) ppm.
b. IR (liquid film): 3080, 3040, 2940, 2870, 1480, 1460, 1280, 1040,
1
70, 740. H-NMR (CDCl , 250 MHz): ꢀ 0.89 (t, 3H), 1.47–1.51
3

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3660
Firouzabadi et al.
(m, 4H), 2.24 (m, 2H), 2.39 (m, 2H), 2.68 (t, 2H), 5.82 (t, 1H),
7
1
1
2
.11–7.25 (m, 4H) ppm.
c. IR (liquid film): 3060, 3020, 2980, 2940, 2900, 1620, 1460, 1440,
1
400, 1380, 1290, 1110, 1000, 950, 770, 720. H-NMR (CDCl ,
50 MHz): ꢀ 2.14 (t, 3H), 3.28 (t, 2H), 6.16 (t, 1H), 7.20–7.43
3
(
m, 4H) ppm.
d. IR (liquid film): 3060, 3030, 2960, 2940, 2880, 1610, 1490, 1460,
1
1
(
1
290, 1030, 940, 760, 740. H-NMR (CDCl , 250 MHz): ꢀ 0.98
t, 3H), 1.43 (m, 2H), 1.66 (m, 2H), 2.52 (t, 2H), 3.26 (d, 2H),
3
1
.13 (t, 1H), 7.12–7.36 (m, 4H). C-NMR (CDCl , 62.89 MHz):
3
6
ꢀ
1
1
1
3
13.51, 22.63, 27.34, 30.09, 37.41, 118.73, 123.46, 124.26, 125.57,
27.07, 144.16, 144.51, 145.35 ppm.
e. IR (liquid film): 3080, 3060, 3040, 1610, 1580, 1490, 1450, 1330,
1
070, 1030, 900, 780, 700. H-NMR (CDCl , 250 MHz): ꢀ 5.51
3
(
1
s, 2H), 7.26 (m, 5H) ppm.
k. IR (liquid film): 3020, 2980, 2920, 1690, 1620, 1450, 1360, 1220,
1
170, 970, 760. H-NMR (CDCl , 250 MHz): ꢀ 1.87 (s, 3H), 2.17
1
(
3
1
d, 6H), 6.02 (m, 1H). C-NMR (CDCl , 62.89 MHz) ꢀ: 27.47,
3
3
3
1
1
ꢀ
1.33, 123.98, 154.17, 197.11 ppm.
l. IR (liquid film): 3100, 3080, 3040, 3000, 2940, 1610, 1500, 1450,
1
380, 1270, 1080, 900, 790, 770, 710. H-NMR (CDCl , 250 MHz):
2.14 (d, 3H), 5.07 (m, 1H), 5.36 (m, 1H), 7.28–7.47 (m, 5H) ppm.
3
Received in the UK September 25, 2001