Highly regioselective ring opening of epoxides with thiols catalyzed by SbCl3 under solvent-free conditions

Article abstract of DOI:10.1080/10426500802053201

The ring-opening reaction of epoxides with thiols by SbCl3 supported on Kieselguhr under solvent-free conditions, afforded high yields of β-hydroxy sulfides. Nucleophilic attack of the thiols occurs regioselectively at the less hindered side of the epoxid

Full text of DOI:10.1080/10426500802053201

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Phosphorus, Sulfur, and Silicon
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Highly Regioselective Ring
Opening of Epoxides with
Thiols Catalyzed by SbCl3
Under Solvent-Free Conditions
Dadkhoda Ghazanfari a , Mohammed M. Hashemi
b , Mohammad Reza Akhgar a , Mohammad Mehdi
Foroughi a & Fariba Najafi-Zadeh a
a Department of Chemistry, Islamic Azad University,
Kerman Branch, Kerman, Iran
b Department of Chemistry, Sharif University of
Technology, Tehran, Iran
Published online: 03 Nov 2008.
To cite this article: Dadkhoda Ghazanfari , Mohammed M. Hashemi , Mohammad
Reza Akhgar , Mohammad Mehdi Foroughi & Fariba Najafi-Zadeh (2008) Highly
Regioselective Ring Opening of Epoxides with Thiols Catalyzed by SbCl3 Under Solvent-
Free Conditions, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:12,
3018-3022
To link to this article: http://dx.doi.org/10.1080/10426500802053201
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Phosphorus, Sulfur, and Silicon, 183:3018–3022, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802053201
Highly Regioselective Ring Opening of Epoxides with
Thiols Catalyzed by SbCl3 Under Solvent-Free Conditions
Dadkhoda Ghazanfari,1 Mohammed M. Hashemi,2
Mohammad Reza Akhgar,1 Mohammad Mehdi Foroughi,1
and Fariba Najafi-Zadeh1
1Department of Chemistry, Kerman Branch, Islamic Azad University,
Kerman, Iran
2Department of Chemistry, Sharif University of Technology, Tehran,
Iran
The ring-opening reaction of epoxides with thiols by SbCl3 supported on Kieselguhr
under solvent-free conditions, afforded high yields of β-hydroxy sulfides. Nucle-
ophilic attack of the thiols occurs regioselectively at the less hindered side of the
epoxides.
Keywords β-hydroxysulfides; epoxides; ring opening; SbCl3; solvent-free reaction; thiols
INTRODUCTION
Ring opening of epoxides with thiols is an important part of organic
synthesis and has found much use in pharmaceutical1 and natural
product chemistry,2 particularly for the synthesis of leukotrienes.3
The classical approach for the synthesis of β-hydroxy sulfides in-
volves nucleophilic ring opening of epoxides with thiols catalyzed
by species such as InCl3,4,5 ZnCl2,6,7 B(C6F5)3,8 hexafluoroisopropyl
alcohol,9 lithium bistrifluoromethanesulfonamide,10,11 aluminal,12 gal-
lium complexes,13 NiCl2, 6H2O, 14CsF on celite,15 HBF4-SiO2 under
solvent-free conditions,16 etc.
In many of the these cases, the ring opening of epoxides is carried out
in a halogenated solvent normally requiring long time treatment un-
der refluxing temperatures or environmentally unfriendly conditions.
Received 6 January 2008; accepted 13 March 2008.
Financial support from the Research Council of Kerman Branch of Islamic Azad
University is gratefully acknowledged.
Address correspondence to Dadkhoda Ghazanfari, Department of Chemistry,
Kerman Branch, Islamic Azad University, P.O. Box 194, Kerman, Iran. E-mail:
dadkhodaghbk@yahoo.com
3018

Ring Opening of Epoxides with Thiols
3019
SR2
O
Kieselghur, SbCl3
+R2-SH
R1
R1
RT
OH
3a-3r
2
1
SCHEME 1
Stringent environmental protection laws in recent years prompted an
increasing emphasis on the use and design of eco-friendly reagents,
solid state procedures, and solvent–free reactions.17 Dry procedures
have recently attracted much attention because they can be carried
on in open vessels, and the use of expensive and hazardous organic
solvents can be avoided.18 We extended our previous experience on
solid supported reagents.19−24 Here, we wish to report the results of
using a simple procedure for efficient thiolysis of epoxides using SbC13
supported on Kieselguhr, as a non toxic and convenient heterogeneous
catalyst surface under solvent- free conditions at room temperature.
The SbC13 was used as a convenient catalyst for ring opening of epox-
ides with aniline and its derivatives at room temperature to afford the
corresponding β-amino alcohols.25
RESULTS AND DISCUSSION
Our approach to a clean and simple procedure for efficient thioly-
sis of epoxides, makes use of SbCl3 supported on Kieselguhr. This
heterogeneous catalyst was used in ring opening of various epox-
ide in thiolysis reaction under solvent-free conditions. Initially, 2-
(chloromethyl)oxirane was treated with an equimolar amount of p-
methoxythiophenol in the presence of SbCl3 impregnated on Kiesel-
guhr under solvent-free conditions. The experiments were complete
within 8 h, as monitored by TLC showing the disappearance of the
1
starting epoxide. The IR and H NMR spectrum of the crude reaction
mixture revealed the formation of the β-hydroxysulfide 3a indicating
that the nucleophilic attack of the p-methoxythiophenol occurred at the
less hindered side of the epoxide (Scheme 1). Moreover, in the crude
mixture the other regioisomer was detected in a very small amount
(about 3%) proving the high regioselectivity of the reaction. Purifica-
tion of product by column chromatography (silica gel 60, petroleum
ether/ EtOAc; 6 : 1) gave 96% of the desired product 3a (Table I, en-
try 1).Control experiments confirmed the combined promoting effect of

3020
D. Ghazanfari et al.
TABLE I Synthesis of β–Hydroxysulfides 3
Epoxides 1
R1
Thiols 2
R2
Time
(h)
Yield
[%]b
Entry
3a
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Cl
Cl
Cl
OPh
OPh
OPh
O-allyl
O-allyl
O-allyl
Ph
4-OCH3C6H4
Ph
4-CH3C6H4
4-OCH3C6H4
Ph
4-CH3C6H4
4-OCH3C6H4
Ph
4-CH3C6H4
4-OCH3C6H4
Ph
4-CH3C6H4
4-OCH3C6H4
Ph
4-CH3C6H4
4-OCH3C6H4
Ph
8
8
8
8
8
8
9
9
10
9
9
8
10
10
12
8
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
96
94
92
96
95
94
90
91
88
94
92
92
88
88
80
89
90
85
Ph
Ph
O-n-butyl
O-n-butyl
O-n-butyl
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
8
10
4-CH3C6H4
aAll compounds were characterized by IR and1H NMR and compared
with authentic samples.; and bisolated yields.
catalyst and solid support. When a mixture of 2-(chloromethyl)oxirane
and p-methoxythiophenol was reacted in a similar conditions without
the SbCl3 for more than 20 h, only about 15% of the product was de-
tected. An alternative reaction without Kieselguhr led to formation
only 45% of 3a after 14 hours, at room temperature. To asses the gen-
erality of the method, a variety of epoxides (1) and thiols (2) reacted in
a similar manner, producing 3b–3r (Table I, entries 2–18).
CONCLUSION
In summary, we have achieved an efficient protocol for the highly regios-
electivity ring opening reaction of epoxides with thiols, by use of SbCl3
supported on Kieselguhr under solvent-free conditions. Compared to

Ring Opening of Epoxides with Thiols
3021
previous methods, this simple procedure uses more friendly reaction
conditions at room temperature and generally gives high yields.
EXPERIMENTAL
General
All chemicals were purchased from Merck, Aldrich, and Riedel Haen
AG, and were used without further purification. IR and NMR spectra
were recorded on a FT–IR Unicam Mattson 1000 using KBr disks or
as neat samples and Bruker AC (80-MHz) with CDCl3 as solvent and
TMS as internal reference, respectively.
Ring Opening of Epoxides with Thiols—General Procedure
A mixture of epoxide (1; 10 mmol), thiol (2; 10 mmol), was added
to SbCl3 (0.112 g, 1 mmol) that was impregnated on Kieselguhr
(0.1 g, 12%, w/w). The mixture was magnetically stirred initially under
solvent-free conditions at 15◦C, which was gradually raised to room
temperature (30◦C) at specified time (cf. Table I). The course of the
reaction was monitored by TLC until complete disappearance of the
starting material was observed. Chloroform (15 ml) was added then
filtered through a celite column and catalyst filtered off. The solvent
was removed at reduced pressure and the respective product (3) was
purified by column chromatography over a short silica gel pad (petere-
1
lium ether/EtOAc; 6: 1) or by bulb to bulb distillation. The H NMR
and IR spectra of pure products were obtained and compared with the
literature value as well as with authentic samples.26,27
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