Additive-free thiolysis of epoxides in water: A green and efficient regioselective pathway to β-hydroxy sulfides

Article abstract of DOI:10.1080/00397910701749963

Room-temperature ring opening of various epoxides with aromatic thiols was carried out in water in the absence of any Lewis acid or additive. High yields of β-hydroxy sulfides with excellent regioselectivity were obtained under very environmentally friend

Full text of DOI:10.1080/00397910701749963

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Additive‐Free Thiolysis of Epoxides in Water:
A Green and Efficient Regioselective Pathway
to β‐Hydroxy Sulfides
a
a
a
Saeed M. Abaee , Mohammad M. Mojtahedi , Hassan Abbasi & Ensieh R.
b
Fatemi
a
Chemistry and Chemical Engineering Research Center of Iran , Tehran, Iran
b
Department of Chemistry , Islamic Azad University , Saveh, Iran
Published online: 18 Jan 2008.
To cite this article: Saeed M. Abaee , Mohammad M. Mojtahedi , Hassan Abbasi & Ensieh R. Fatemi (2008)
Additive‐Free Thiolysis of Epoxides in Water: A Green and Efficient Regioselective Pathway to β‐Hydroxy
Sulfides, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 38:2, 282-289, DOI: 10.1080/00397910701749963
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Synthetic Communications , 38: 282–289, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910701749963
Additive-Free Thiolysis of Epoxides in
Water: A Green and Efficient Regioselective
Pathway to b-Hydroxy Sulfides
1
M. Saeed Abaee, Mohammad M. Mojtahedi,
1
1
Hassan Abbasi, and Ensieh R. Fatemi
2
1
2
Chemistry and Chemical Engineering Research Center of Iran,
Tehran, Iran
Department of Chemistry, Islamic Azad University, Saveh, Iran
Abstract: Room-temperature ring opening of various epoxides with aromatic thiols
was carried out in water in the absence of any Lewis acid or additive. High yields of
b-hydroxy sulfides with excellent regioselectivity were obtained under very environ-
mentally friendly conditions.
Keywords: additive-free, aqueous conditions, epoxides, green chemistry, thiolysis
With increasing global environmental concerns, the design of green processes
using alternative media with fewer hazards has gained special attention from
[1]
synthetic organic chemists in recent years. In this context, many reactions
are found to proceed cleanly and efficiently in water,
[2]
a naturally
abundant, environmentally safe, and inexpensive medium. Although the
majority of organic compounds have limited solubility in water, there has
been a dramatic increase in the number of reactions carried out under
aqueous conditions due to rate and selectivity enhancements exhibited by
Received in the U.K. January 10, 2007
Address correspondence to Mohammad M. Mojtahedi, Chemistry and Chemical
Engineering Research Center of Iran, P. O. Box 14335-186, Tehran, Iran. E-mail:
mojtahedi@ccerci.ac.ir
2
82

Thiolysis of Epoxides in Water
283
[
3]
water. Thus, development of convenient procedures under mild aqueous
conditions is nowadays of prime importance in synthetic organic chemistry.
Ring opening of epoxides with thiols is an important class of organic
[4]
transformations and has found many uses in pharmaceutical and natural
[6]
[
5]
product chemistry,
Moreover, the resulting hydroxyl sulfide products are very convenient precur-
particularly for the synthesis of leukotrienes.
[
7]
[8]
sors to access allylic alcohols and a-substituted ketones. The classical
approaches for the synthesis of b-hydroxy derivatives of sulfides involve
thermal or Lewis acid–mediated nucleophilic ring opening of epoxides with
[
9]
thiols. In many cases, the process is carried out in a halogenated solvent
and normally requires a long treatment under refluxing temperatures or envir-
onmentally unfriendly conditions.
Recently, several reports were disclosed about thiolysis of epoxides under
aqueous conditions. However, in these procedures, use of water has been
[
10]
combined with simultaneous application of extra additives
11]
or microwave
In continuation of our studies on the development of environ-
[
irradiation.
mentally friendly processes,
[
12]
we herein report an efficient and selective
protocol for room-temperature thiolysis of epoxides in pure water, free from
any additive or external stimulant (Scheme 1). This is the most inexpensive
and environmentally friendly procedure offered so far for ring opening of
epoxides with thiols.
We evaluated this chemistry by stirring a 1:1 mixture of 2-(chloromethyl)
oxirane 1a and thiophenol 2a in pure water at room temperature. Thin-layer
chromatograpy (TLC) experiments showed complete disappearance of the
1
starting materials after 8 h. The H NMR spectrum of the crude mixture
showed the formation of b-hydroxy sulfide 3a as the sole product of the
reaction, indicating that the nucleophilic attack of the thiol occurred exclu-
sively at the less-hindered side of the epoxide. The product was easily
extracted with diethyl ether in a relatively pure form (Table 1, entry 1). Use
of aqueous conditions proved to be crucial for thiolysis to proceed efficiently.
A test reaction in the absence of water gave very low amounts of 3a after
several days, indicating the promoting effect of water.
Epoxide 1a also reacted with 4-chlorothiophenol (entry 2) and 2-thio-
naphthol (entry 3) under similar conditions in slightly longer reaction times,
Scheme 1.

2
84
M. S. Abaee et al.
Table 1. Aqueous thiolysis of 1,2-epoxides
Time
(h)
Yield
a
(%)
Entry
1
Epoxide
Thiol
Product
1a
2a
8
98
95
2
1a
2b
10
3
4
5
1a
1b
1b
2c
2a
2b
14
16
18
91
97
95
6
7
1c
1c
2a
2b
17
24
93
94
8
9
1c
1d
1d
2c
2a
2b
28
30
24
97
96
97
1
0
1
1
1
2
1e
1e
2a
2b
30
36
95
94
1
1
3
4
1f
1f
2a
2b
28
36
94
91
a
Isolated yields.

Thiolysis of Epoxides in Water
285
Scheme 2.
producing 95% and 91% of 3b and 3c, respectively. Applicability of this
procedure to other substrates was shown by subjecting epoxides 1b–e to
react with thiols. Consequently, 3d–3l were obtained in excellent yields
and within reasonable time periods (entries 4–12). In all instances,
exclusive formation of single isomeric products shown in Table 1 was
observed, illustrating the high regioselectivity of the ring-opening reactions.
Under the cited conditions, reactions of 1,2-epoxycyclohexane with thiols
2
(
a and b gave more than 90% of 3m and n with trans stereochemistry
entries 13 and 14).
When styrene oxide was treated under the same conditions, thiolysis
occurred with reversed and slightly lower regioselectivity. Therefore,
reactions of 1g with thiols 2a and b led to formation of 3o and p as regioiso-
meric mixtures, with the major isomers having regiochemistry opposite that
observed for cleavage of epoxides 1a–e (Scheme 2). The reversed selectivity
1
observed for the reactions of 1g was quantified by analysis of the H NMR
spectrum of the mixtures and was attributed to favorable electronic effects
associated with nucleophilic attack of the thiols on the benzylic carbon that
can eventually stabilize the developing positive charge on this carbon.
Because of importance of the selectivity issue in synthetic organic
chemistry, competitive reactions were carried out to evaluate the relative reac-
tivities of different epoxides toward thiophenol (Table 2). Under aqueous con-
ditions, 1a and 1c did not show any significant difference when reacting with
thiophenol (entry 1), while any of these two epoxides could selectively react
with the same thiol when they compete with 1g (entries 2 and 3).
The fact that these additive-free reactions proceed only in the presence of
water could be rationalized by proposing a favorable hydrogen-bonded
Table 2. Competitive thiolysis of epoxides with thiophenol in water
a
Entry
Epoxides
Products
Ratio
1
2
3
1a/1c
1a/1g
1c/1g
3a/3f
3a/3o
3f/3o
60:40
85:15
80:20
a
Ratios determined by GC-MS.

2
86
M. S. Abaee et al.
Scheme 3.
association of the reacting epoxides with water molecules. Such activation
[
13]
through hydrogen bonding,
as depicted in the Scheme 3, can stabilize the
transition state similar to stabilization in a Lewis acid–mediated epoxide
ring opening. This hypothesis can also be supported by a closer look at the
reactions of styrene oxide (Scheme 2), where 1g reacts with a regioselectivity
[9]
similar to that observed in Lewis acid–catalyzed thiolysis as opposed to
thermal or base-promoted ring openings,
cant regioselectivity.
[10e,11]
which proceed with no signifi-
In summary, the room-temperature ring opening of various epoxides with
aromatic thiols in water was carried out within a few hours in the absence of
any Lewis acid or additive. Reactions proceeded efficiently without the appli-
cation of harsh conditions and tedious workup procedures. High yields of the
products, excellent regioselectivity of the ring openings, and more important,
the environmental safety of the process are all advantages of this method-
ology, which make it an attractive addition to the existing literature.
EXPERIMENTAL
All reported yields are isolated yields. IR spectra were recorded on a FT-IR
Bruker Vector 22 infrared spectrophotometer. NMR spectra were recorded on
a FT-NMR Bruker Ultra ShieldTM (500 MHz) as CDCl solutions with TMS
3
as internal reference. Gas chromatography-mass spectra (GC-MS) spectra
were obtained on Fisons 8000 Trio instrument at an ionizationpotential of 70 eV.
Typical Procedure
A mixture of 3.0 mmol of epoxide and 3.0 mmol of thiophenol in distilled
water (2 mL) was stirred at room temperature for an appropriate length of
time until TLC showed completion of the reaction. The mixture was
extracted with 10 mL of diethyl ether. The ethereal phase was washed with
a saturated solution of NaHCO3 and filtered through a short Na SO
2
4
column. The solvent was removed under reduced pressure, and the product
was purified using bulb-to-bulb distillation or column chromatography over
silica gel, if necessary. The NMR, IR, and GC-MS spectra of the products
were obtained, and they matched perfectly those existing in the

Thiolysis of Epoxides in Water
287
[
9a,9k,12a]
literature.
Finnigan Flash EA 1112 instrument.
Elemental analysis for 3e was performed using a Thermo
Selected Spectral Data
[
9j] 1
1
0
1
-Butoxy-3-phenylthiopropan-2-ol (3d).
H NMR (500 MHz, CDCl ): d
3
.95 (t, J ¼ 7.5, 3H), 1.35–1.42 (m, 2H), 1.55–1.60 (m, 2H), 2.82 (br s,
H), 3.03 (dd, J ¼ 7, 14 Hz, 1H), 3.11 (dd, J ¼ 6, 14 Hz, 1H), 3.43–3.54
1
m, 4H), 3.87–3.94 (m, 1H), 7.21–7.42 (m, 5H); C NMR (125 MHz,
3
(
CDCl ): d 14.3, 19.7, 32.1, 37.8, 69.4, 71.7, 73.3, 126.6, 129.4, 129.9,
3
þ
1
36.2; MS: m/z, 240 [M ], 222, 135, 113, 57; IR (KBr): n˜ 3442, 1480,
2
1
1
119 cm
.
1
-Butoxy-3-(4-chlorophenylthio)propan-2-ol (3e). H NMR (500 MHz,
1
CDCl ): d 0.95 (t, J ¼ 7.5, 3H), 1.35–1.43 (m, 2H), 1.55–1.61 (m, 2H),
3
2
.82 (br s, 1H), 3.04 (dd, J ¼ 7, 14 Hz, 1H), 3.11 (dd, J ¼ 6, 14 Hz, 1H),
.44–3.56 (m, 4H), 3.87–3.94 (m, 1H), 7.28 (d, J ¼ 8.5 Hz, 2H), 7.34
3
1
3
(
d, J ¼ 8.5 Hz, 2H); C NMR (125 MHz, CDCl ): d 14.3, 19.7, 32.1, 38.1,
3
þ
6
1
5
9.4, 71.8, 73.3, 129.5, 131.3, 132.8, 134.8; MS: m/z, 274 [M ], 257, 183,
2
1
13; IR (KBr): n˜ 3433, 1462, 1109 cm . Calcd. for C H ClO S: C,
1
3
19
2
6.82; H, 6.97. Found: C, 56.88; H, 6.82.
[12b] 1
-(Naphthalen-2-ylthio)-3-phenoxypropan-2-ol (3h).
1
H NMR (500 MHz,
CDCl ): d 2.79 (br s, 1H), d 3.31 (dd, J ¼ 7, 14 Hz, 1H), 3.41 (dd, J ¼ 5.5,
3
1
2
7
6
1
1
4 Hz, 1H), 4.10–4.14 (m, 2H), 4.15–4.21 (m, 1H), 6.93 (d, J ¼ 7.5 Hz,
H), 7.00 (t, J ¼ 7.5 Hz, 1H), 7.28–7.32 (m, 2H), 7.47–7.53 (m, 3H),
1
.75–7.84 (m, 3H), 7.89 (s, 1H); C NMR (125 MHz, CDCl ): d 38.2,
3
3
9.0, 70.3, 114.9, 115.0, 121.8, 129.7, 129.8, 130.0, 130.1, 131.5, 133.1,
þ
34.2, 158.7; MS: m/z, 310 [M ], 217, 173, 160, 115; IR (KBr): n˜ 3437,
2
1
595, 1087, 745 cm
.
[12b]
1
1
-(4-Chlorophenylthio)-3-isopropoxypropan-2-ol (3l).
H
NMR
(
500 MHz, CDCl ): d 1.18 (d, J ¼ 6.5 Hz, 6H), 2.70 (br s, 1H), 3.05 (dd,
3
J ¼ 7, 14 Hz, 1H), 3.11 (dd, J ¼ 6, 14 Hz, 1H), 3.48 (dd, J ¼ 6, 9.5 Hz,
1
H), 3.55 (dd, J ¼ 9.5, 14 Hz, 1H), 3.60–3.65 (m, 1H), 3.85–3.90 (m, 1H),
1
3
7
.28 (d, J ¼ 8.5 Hz, 2H), 7.35 (d, J ¼ 8.5 Hz, 2H); C NMR (125 MHz,
CDCl ): 22.4, 37.9, 69.5, 70.6, 72.8, 129.5, 131.2, 132.7, 134.8; MS: m/z,
2
3
þ
21
60 [M ], 157, 143, 99, 43. IR (neat): n˜ 3443, 1575, 1093, 747 cm
.
ACKNOWLEDGMENT
The Ministry of Science, Research, and Technology of Iran is gratefully
acknowledged for partial financial support of this work.

2
88
M. S. Abaee et al.
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