BiCl3 catalyzed thiolyzation reaction of 1,2-epoxides with diaryl disulfides in the presence of zinc powder and ionic liquid

Article abstract of DOI:10.1080/104265090929931

A new and efficient method has been developed for the regio- and chemoselective synthesis of β-hydroxysulfides with the ring-opening reaction of 1,2-epoxides by diaryl disulfides and zinc powder in the presence of a catalytic amount of BiCl₃ in

Full text of DOI:10.1080/104265090929931

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Phosphorus, Sulfur, and Silicon
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BiCl3 Catalyzed Thiolyzation
Reaction of 1,2-Epoxides
with Diaryl Disulfides in the
Presence of Zinc Powder and
Ionic Liquid
A. R. Khosropour a , M. M. Khodaei a & K. Ghozati a
a Department of Chemistry , Razi University ,
Kermanshah, Iran
Published online: 16 Aug 2006.
To cite this article: A. R. Khosropour , M. M. Khodaei & K. Ghozati (2005) BiCl3
Catalyzed Thiolyzation Reaction of 1,2-Epoxides with Diaryl Disulfides in the Presence
of Zinc Powder and Ionic Liquid, Phosphorus, Sulfur, and Silicon and the Related
Elements, 180:11, 2525-2531, DOI: 10.1080/104265090929931
To link to this article: http://dx.doi.org/10.1080/104265090929931
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Phosphorus, Sulfur, and Silicon, 180:2525–2531, 2005
Copyright © Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/104265090929931
BiCl3 Catalyzed Thiolyzation Reaction of 1,2-Epoxides
with Diaryl Disulfides in the Presence of Zinc Powder
and Ionic Liquid
A. R. Khosropour
M. M. Khodaei
K. Ghozati
Department of Chemistry, Razi University, Kermanshah, Iran
A new and efficient method has been developed for the regio- and chemoselective
synthesis of β-hydroxysulfides with the ring-opening reaction of 1,2-epoxides by
diaryl disulfides and zinc powder in the presence of a catalytic amount of BiCl in
3
molten tetrabutyl phosphonium bromide as an ionic liquid.
Keywords β-hydroxysulfides; aryl disulfides; BiCl3; epoxides; ionic liquid; ring opening
reaction
INTRODUCTION
In recent years, β-hydroxysulfide derivatives have attracted con-
siderable interest due to their wide utilization in organic synthe-
sis for the preparation of benzoxathiepines,1 benzotiazepines,2 β-
hydroxysulfoxides,3 or α-thioketones,4 which are versatile in the realm
of pharmaceutical, biological, or organic chemistry. Thus, the synthesis
of this heterochemical system is of much interest. One of the classical
synthetic methods for the preparation of β-hydroxysulfides consists of
a ring opening of an epoxide with an excess of thiol.5 Because some
functional groups may be sensitive to high temperature, some modified
methods have been developed.6 However, many of these procedures are
associated with one or more disadvantages, such as involving toxic and
expensive catalysts or hazardous and carcinogenic organic solvents for
reactions. In addition, low yields, long reaction times, and the utiliza-
tion of large amounts of catalyst or solvent limit these synthetic scopes
Received September 14, 2004; accepted December 1, 2004.
The authors are grateful to the Razi University Research Council for partial support
of this work.
Address correspondence to A. R. Khosropour, Razi University, Department of Chem-
istry, Faculty of Science, Kermanshah 67149, Iran. E-mail: arkhosropour@razi.ac.ir
2525

2526
A. R. Khosropour et al.
to small scales. Hence, a simple, green, and efficient procedure avoiding
these drawbacks that leads to convenient procedures and better yields
is recommended.
RESULTS AND DISCUSSION
The toxic and volatile nature of many organic solvents have posed a se-
rious threat to the environment. Consequently, methods that minimize
their use are the focus of much attention. In this respect, ionic liquids
are attracting a growing interest as an alternative reaction media for
various chemicals and biotransformations.7 These compounds offer an
alternative and ecologically friendly media that, in contrast to organic
solvents, are nonvolatile and non-explosive.8 On the other hand, the
catalysts that have polar or ionic character can be immobilized without
additional structural modification, and thus, the ionic solutions con-
taining the catalyst easily can be separated from products. Thus, ionic
liquids have proven to be excellent solvents for many organic reactions.9
Most bismuth (III) salts are relatively nontoxic, easy to handle,
and can tolerate small amounts of moisture.10 With increasing envi-
ronmental concerns and the need for green reagents, the interest in
bismuth (III) salts has increased tremendously in the last decade.11
In continuation of our studies using Bi(III) salts for various organic
transformations,12 we wish to present a new and convenient method
for the synthesis of β-hydroxysulfides toward the ring opening of epox-
ides with diaryl disulfides and zinc powder catalyzed by BiCl3 that is
immobilized on molten tetrabutylphosphonium bromide (TBPB) as an
ionic liquid (Scheme 1).
SCHEME 1
The experimental procedure is very simple. To the mixture of molten
TBPB and BiCl3, zinc powder, diaryl disulfide and 1,2-epoxide were

BiCl Catalyzed Thiolyzation Reaction
2527
3
TABLE I Ring Opening of 1,2-Epoxides With ArSSAr in the Presence
of Zinc Powder and 10 mol% of BiCl3 in the Presence of Molten TBPB
Yield (%)a/
Entry
Epoxide
Ar
Time(min)
Product
OHCH2CH SAr
|
1
2
Ph
92/20
92/20
Ph
OHCH2CH SAr
|
P-CH3C6H4
Ph
OHCH2CH SAr
|
3
4
2-Naphthyl
Ph
88/25
Ph
80/60b
5
6
P-CH3C6H4
80/45b
78/65b
2-Naphthyl
7
8
Ph
89/40
90/45
80/65
80/65
86/30
PhOCH2CH(OH)CH2 SAr
P-CH3C6H4
Ph
PhOCH2CH(OH)CH2 SAr
9
CH2 CHCH2OCH2CH(OH)CH2 SAr
CH2 CHCH2OCH2CH(OH)CH2 SAr
CH3(CH2)5CH(OH)CH2 SAr
10
11
P-CH3C6H4
Ph
12
13
Ph
Ph
90/60
86/55
CH3(CH2)2CH2OCH2CH(OH)CH2 SAr
ClCH2CH(OH)CH2 SAr
aIsolated yields.
bIn the presence of 20 mol% of BiCl3.
added and the system was stirred at 65◦C and the product was iso-
lated by usual work-up. The results are summarized in Table I. In the
method described here, a variety of epoxides with different functional
−
groups such as PhO-, RO-, ClCH2 , and allyl ether were converted to
the products with high efficiency and chemoselectivity. It is important
to note that in the case of terminal epoxides (Table I, entries 7–13), the
products were obtained by the attack of nucleophiles on the terminal
carbon. This regioselectivity is probably due to the steric hinderance of
nucleophile that attacks on the less-hindered carbon of the epoxides.

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A. R. Khosropour et al.
TABLE II Competetive Ring Opening Reaction of 1,2-Epoxides With
Diaryl Dosulfides in the Presence of Zinc Powder and BiCl3 in the
Presence of Molten TBPB
However, in the case of the reaction with styrene oxide, we observed
a reverse regioselectivity in which the attack on the benzylic carbon
(which may be due to the formation of more stable carbocation on ben-
zylic carbon) was preferred (Table I, entries 1–3). The products that
were obtained using cyclohexene oxide posses a trans-configuration by
1H NMR spectroscopy (Table I, entries 4–6). This high reactivity and
selectivity is similar to those observed in the case of strong Lewis acids
with thiophenols.6 On the other hand, we found that aliphatic disulfides
such as dibenzyl disulfide or dicyclohexyl disulfide are quite resistant
to the reaction conditions and completely recovered.
In order to evaluate the intermolecular chemoselectivity of the
reagents, we also examined the competitive reactions (Table II). It is
noteworthy that high chemoselectivity was exhibited with styrene ox-
ide and the corresponding β-hydroxysulfide that was obtained in the
presence of the other epoxides. In this competitive reaction, other acid-
sensitive epoxides such as cyclohexane oxide in the presence of styrene
oxide were stable.
CONCLUSIONS
In conclusion, we have demonstrated a new, efficient, and green cat-
alytic procedure for the regio- and chemoselective thiolysation of 1,2-
epoxides with diaryl disulfides in the ionic liquid media. In addition,

BiCl Catalyzed Thiolyzation Reaction
2529
3
the ease of availability and low toxicity of the catalyst and the ionic
liquid make this procedure environmentally acceptable. Furthermore,
the low cost of the catalyst and ionic liquid, the high catalytic nature
of the Lewis acid, and fast reaction rates make the present procedure
a practical protocol for the β-hydroxysulfide synthesis.
EXPERIMENTAL
All yields refer to isolated products. The products were characterized
by comparison with authentic samples.6 All 1H and 13C NMR spec-
tra were recorded on a Bruker Avance 200 MHz spectrophotometer in
CDCl3 as a solvent. Diaryl disulfides were prepared according to the
literature.13BiCl3-TBPB was prepared by mixing BiCl3 (0.1–0.2 mmol)
and molten tetrabutylphosphonium bromide (0.5 mmol), which heated
to 120◦C, then this mixture cooled to 65◦C.
General Procedure for the Ring Opening Reaction of
1,2-Epoxides With Diaryl Disulfides in the Presence of Zinc
Powder Catalyzed by BiCl3-TBPB
In a 50 mL round bottom, 1,2-epoxide (1 mmol), diaryl disulfide
(1 mmol), and zinc powder (1 mmol) were added to a molten mix-
ture of tetrabutylphosphonium bromide (0.5 mmol) and BiCl3 (0.1–
0.2 mmol), then the reaction mixture stirred at 65◦C for the appro-
priate times (Table I). The progress of the reaction was followed by
TLC (n-heptane/ethyl acetate: 3/1). After completion of the reaction,
Et2O (20 mL) was added and the mixture was filtered. The evapora-
tion of the organic layer gave the corresponding crude products, which
were purified by chromatography on a silica-gel plate to afford the pure
β-hydroxythioethers in 78–92% yields. Spectroscopy data: Product of
entry 1. IRνmax cm−1: 3370, 3005, 2895, 2860, 1585, 1465, 1050, 740,
1
695 (neat). H NMR (200 MHz, CDCl3) δ 7.15–7.55 (m, 10H), 4.35 (t,
J 6.8 Hz, 1H), 3.95 (d, J 6.8 Hz, 2H), 2.10 (s, 1H).13C NMR (50 MHz,
CDCl3) δ 139.40, 134.20, 132.90, 129.40, 129.20, 128.50, 128.20, 128.00,
65.70, 56.50. Product of entry 2. IR νmax cm−1: 3430, 3015, 2905, 2880,
1590, 1495, 1440, 1060, 850, 735, 690 (neat). 1H NMR (200 MHz, CDCl3)
δ 7.50–7.90 (m, 9H), 4.75 (t, J 6.9 Hz, 1H), 4.35 (d, J 6.9 Hz, 2H), 2.80 (s,
4H).13C NMR (50 MHz, CDCl3) δ 139.60, 138.30, 133.70, 130.30, 130.20,
129.10, 128.60, 128.20, 65.50, 56.80, 21.60. Product of entry 3. IR νmax
cm−1: 3520, 3030, 2905, 2890, 1595, 1490, 1450, 1090, 850, 730, 695
(neat). 1H NMR (200 MHz, CDCl3) δ 7.30–7.95 (m, 12H,), 4.52 (t, J 8.0
Hz, 1H), 4.05 (d, J 7.0 Hz, 2H), 2.25 (s, 1H).13C NMR (50 MHz, CDCl3) δ
139.30, 133.90, 132.80, 131.80, 131.50, 130.10, 129.20, 128.90, 128.60,

2530
A. R. Khosropour et al.
128.30, 128.10, 127.90, 127.00, 126.80, 65.70, 56.40. Product of entry 4.
IR νmax cm−1: 3650, 3015, 2905, 2885, 1590, 1495, 1440, 1065, 840, 735,
690 (neat). 1H NMR (200 MHz, CDCl3) δ 7.25–7.60 (m, 5H), 3.30–3.50
(m, 1H), 2.90 (s, 1H), 2.70–2.85 (m, 1H), 2.05–2.25 (m, 2H), 1.62–1.83
(m, 2H), 1.20–1.50 (m, 4H).13C NMR (50 MHz, CDCl3) δ 134.20, 133.00,
129.30, 128.20, 72.40, 56.90, 34.20, 33.10, 26.60, 24.70. Product of entry
5. IR νmax cm−1: 3450, 3010, 2900, 2880, 1590, 1495, 1450, 1060, 820
(neat). 1H NMR (200 MHz, CDCl3) δ 7.85 (d, J 10.0 Hz, 2H), 7.55 (d, J
10.0 Hz, 2H), 3.70–3.85 (m, 1H), 3.55 (s, 1H), 3.10–3.25 (m, 1H), 2.8 (s,
3H), 2.50–2.65 (m, 2H), 2.05–2.20 (m, 2H), 1.10–1.60 (m, 4H).13C NMR
(50 MHz, CDCl3) δ 138.50, 134.90, 130.10, 128.90, 72.20, 56.90, 34.20,
32.90, 26.60, 24.70, 21.60. Product of entry 6. IR νmax cm−1: 3440, 3020,
1
2905, 2885, 1595, 1490, 1440, 1085, 810 (neat). H NMR (200 MHz,
CDCl3) δ 7.50–8.10 (m, 7H), 3.40–3.60 (m, 1H), 2.90–3.05 (m, 2H), 2.10–
2.25 (m, 2H), 1.70–1.90 (m, 2H), 1.15–1.60 (m, 4H).13C NMR (50 MHz,
CDCl3) δ 133.90, 133.30, 132.90, 131.50, 130.30, 128.90, 128.10, 127.90,
127.00, 126.90, 72.50, 57.00, 34.30, 33.20, 26.60, 24.70. Product of entry
7. IR νmax cm−1: 3400, 3010, 2900, 2880, 1590, 1480, 1245, 1050, 730,
695 (neat). 1H NMR (200 MHz, CDCl3) δ 7.85–7.70 (m, 10H), 3.95–4.25
(m, 3H), 3.10–3.40 (m, 2H), 2.75 (s, 1H).13C NMR (50 MHz, CDCl3) δ
158.80, 135.60, 130.25, 130.00, 129.60, 127.10, 121.70, 115.00, 70.50,
69.00, 38.00. Product of entry 9. IR νmax cm−1: 3350, 3020, 2905, 2880,
1
1600, 1490, 1380, 1060, 735, 690 (neat). H NMR (200 MHz, CDCl3) δ
7.15–7.50 (m, 5H), 5.80–6.05 (m, 1H), 5.15–5.35 (m, 2H), 4.00 (d, J =
6.8 Hz, 2H), 3.80–3.95 (m, 1H), 3.45–3.65 (m, 2H), 3.00–3.25 (m, 2H),
2.70 (s, 1H).13C NMR (50 MHz, CDCl3) δ 135.90, 134.80, 130.10, 129.50,
126.90, 117.80, 72.80, 72.70, 69.40, 37.90. Product of entry 10. IR νmax
1
cm−1: 3700, 3015, 2905, 2885, 1590, 1495, 1440, 1080, 790 (neat). H
NMR (200 MHz, CDCl3) 7.75 (d, J = 8.0 Hz, 2H), δ 7.55 (d, J 8.0 Hz,
2H), 6.20–6.45 (m, 1H), 5.60–5.80 (m, 2H), 4.40 (d, 2H), 4.25–4.35 (m,
1H), 3.90–4.10 (m, 2H), 3.35–3.65 (m, 2H), 3.20 (s, 1H), 2.80 (s, 3H).13C
NMR (50 MHz, CDCl3) δ 137.10, 134.80, 132.10, 130.90, 130.20, 117.70,
72.80, 72.70, 69.30, 38.70, 21.40. Product of entry 11. IR νmax cm−1
:
3405, 3015, 2905, 2880, 1585, 1490, 1435, 735, 690 (neat). 1H NMR (200
MHz, CDCl3) δ 7.15–7.50 (m, 5H), 3.50–3.80 (m, 1H), 3.10–3.25 (dd, J
4.5 Hz, J 4.5 Hz, 2H), 2.80–2.95 (dd, J 9.5 Hz, J 9.5 Hz, 2H), 2.70(s, 1H),
1.15–1.70 (m, 8H), 0.95 (t, J 7.0 Hz, 3H).13C NMR (50 MHz, CDCl3) δ
136.00, 130.30, 130.00, 126.90, 69.90, 42.50, 36.60, 32.20, 29.60, 26.10,
23.00, 14.50. Product of entry 12. IR νmax cm−1: 3410, 3025, 2900, 2890,
1
1590, 1490, 1430, 735, 690 (neat). H NMR (200 MHz, CDCl3) δ 7.15–
7.50 (m, 5H), 3.85–4.00 (m, 1H), 3.40–3.65 (m, 4H), 3.00–3.25 (m, 2H),
2.80 (s, 1H), 1.55–1.70 (m, 2H), 1.30–1.50 (m, 2H), 0.95 (t, J 8.3 Hz,
3H).13C NMR (50 MHz, CDCl3) δ 136.10, 129.90, 129.40, 126.70, 73.70,

BiCl Catalyzed Thiolyzation Reaction
2531
3
71.70, 69.40, 37.80, 32.10, 19.70, 14.30. Product of entry 13. IR νmax
cm−1: 3425, 3010, 2920, 2830, 1600, 1490, 1430, 1365, 1110, 740, 690
1
(neat). H NMR (200 MHz, CDCl3) δ 7.20–7.50 (m, 5H), 3.90–4.10 (m,
1H), 3.72 (d, J = 8.0 Hz, 2H), 3.05–3.18 (m, 2H), 2.88 (s, 1H).13C NMR
(50 MHz, CDCl3) δ 135.10, 130.50, 129.70, 127.30, 69.90, 48.40, 38.60.
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