Synthesis of vinyl sulfides under base-free conditions using selenium ionic liquid

Article abstract of DOI:10.1016/j.tetlet.2012.03.076

A very simple procedure is described for the efficient synthesis of vinyl sulfides by hydrothiolation of terminal alkynes using 1-n-butyl-3- methylimidazolium methylselenite, [bmim][SeO₂(OCH₃)]. The reaction proceeds cleanly under mi

Full text of DOI:10.1016/j.tetlet.2012.03.076

Tetrahedron Letters 53 (2012) 2651–2653
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Tetrahedron Letters
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Synthesis of vinyl sulfides under base-free conditions using selenium
ionic liquid
⇑
Samuel Thurow, Naiana T. Ostosi, Samuel R. Mendes, Raquel G. Jacob, Eder J. Lenardão
Laboratório de Síntese Orgânica Limpa (LASOL), CCQFA, Universidade Federal de Pelotas (UFPel), PO Box 354, 96010-900 Pelotas, RS, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
A very simple procedure is described for the efficient synthesis of vinyl sulfides by hydrothiolation of ter-
minal alkynes using 1-n-butyl-3-methylimidazolium methylselenite, [bmim][SeO2(OCH3)]. The reaction
proceeds cleanly under mild, base-free conditions and was performed with aromatic and aliphatic thiols.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 16 February 2012
Revised 8 March 2012
Accepted 20 March 2012
Available online 26 March 2012
Keywords:
Selenium ionic liquid
Vinyl sulfides
Hydrothiolation
Besides being very useful tools in organic reactions and acting
as key intermediates in organic synthesis,1 vinyl sulfides are pres-
ent in naturally occurring compounds, such as griseoviridin and
benzylthiocredillidone, which present important biological activi-
ties.2,3 Between the several methods described for the preparation
of vinyl sulfides, the most common and atom-economic protocols
involve the addition of thiol, or the respective anions, to terminal
or internal alkynes. These methods are of two major groups: those
involving transition-metals as catalyst4 and the base-promoted
ones.5 More recently, some improvements on selective preparation
of vinyl sulfides have been described.6–12 These comprise the use of
catalytic phenylselenenyl bromide,6 nickel,7 gold,8 or native silica
nanoparticle9 under solvent-free conditions, b-cyclodextrin in the
presence of water and acetone,10 KF/Al2O3 under solvent-free11
or under catalyst-free conditions.12
and alkynes under base-free conditions are limited.6–12 In this
sense, and due to our interest in new applications for selenium-
based ionic liquids, we decided to investigate the use of [bmim]
[SeO2(OCH3)] in the hydrothiolation of terminal alkynes to prepare
vinyl sulfides (Scheme 1).
SR1
+
R1 SH
selenite ionic liquid
60 °C, N2
R1S
(Z) and (E)-3a-o
+
R
H
R
R
4a-o
1a-f
2a-i
Scheme 1. General scheme of the reaction.
The use of ionic liquids (ILs) as catalyst has attracted great
attention in the last years. Because product isolation or catalyst
recycling is very easy in ILs and, in some cases, rate accelerations
and/or selectivity improvements are also observed, they are
regarded as environmentally friendly, green solvents.13 In this
context, recently we have reported the use of the new cationic
selenium-based acidic ionic liquid, phenyl butyl ethyl selenonium
tetrafluoroborate, [pbeSe][BF4], as an efficient catalyst in several
acid-catalyzed reactions.14 Besides, the application of the ionic
liquid containing anionic selenium-based [bmim][SeO2(OCH3)] in
the oxidative carbonylation of aniline15 and in the base-free oxida-
tion of thiols to disulfides were recently described.16 To the best of
our knowledge, the methods to access vinyl sulfides from thiols
⇑
Corresponding author. Tel./fax: +55 53 32757533.
E-mail address: lenardao@ufpel.edu.br (E.J. Lenardão).
Figure 1. Plot of conversion versus time for the reaction between propargyl alcohol
1a and benzenethiol 2a; determined by GC.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.03.076

2652
S. Thurow et al. / Tetrahedron Letters 53 (2012) 2651–2653
Table 1
Hydrothiolation of alkynes using [bmim][SeO2(OCH3)]—synthesis of vinyl sulfides
Entry
1
Alkyne 1
Thiol 2
Product 3 + 4
Time
16
Ratioa 3Z:3E:4
Yieldb (%)
80
SC6H5
OH
C6H5SH
2a
1a
OH
OH
C6H5S
48:2:50
3a
4a
SCH2C6H5
OH
C6H5CH2SH
2b
OH
2
3
4
5
1a
1a
1a
1a
16
10
9
53:3:44
60:8:32
56:13:31
31:12:57
63
78
62
70
C6H5CH2S
o-ClC6H4S
3b
4b
SC6H4-o-Cl
o-ClC6H4SH
2c
OH
OH
3c
4c
SCH2C6H4-m-Cl
m-ClC6H4SH
2d
OH
m-ClC6H4CH2S
p-Cl-C6H4CH2S
OH
3d
4d
4e
SCH2C6H4-p-Cl
p-ClC6H4SH
2e
OH
15
OH
3e
SC6H4-o-CH3
o-CH3C6H4SH
2f
OH
o-CH3C6H4S
6
7
8
1a
1a
1a
12
13
12
37:11:51
31:12:57
25:46:29
51
63
75
OH
3f
4f
SC6H4-m-CH3
m-CH3C6H4SH
2g
OH
m-CH3C6H4S
4g
OH
SC6H4-p-CH3
3g
p-CH3C6H4SH
2h
OH
p-CH3C6H4S
OH
3h
4h
SC12H25
CH3(CH2)11SH
2i
OH
C12H25
S
9
1a
8
44:2:54
45
78
OH
3i
4i
SC6H5
OH
1b
OH
10
2a
2a
C6H5S
C6H5S
10
14:29:57
3j
OH
4j
SC6H5
OH
11
12
17
23
19:7:74
97
60
OH
1c
OH
3k
4k
SC6H5
C6H5S
2a
53:20:27
HO
HO
OH
1d
4l
3l
SC6H5
1e
13
14
15
2a
2a
2e
21
2
80:20:0
42:4:53
61:24:15
30
98
93
C6H5S
C6H5S
C6H13
C6H13
3m
3n
4m
SC6H5
C6H5
C6H5
1f
C6H5
4n
SC6H4-p-Cl
C6H5
p-ClC6H4S
C6H5
1f
2
3o
4o
a
Determined by 1H NMR of the crude reaction mixture and confirmed after isolation of the mixture of formed isomers.
Yields of the mixture of isomers obtained by column chromatography eluting with hexanes (3m–3o) or with hexanes/ethyl acetate (98:2, 3a–3l).
b
A set of experiments were performed to find the best conditions
protocol in terms of energy efficiency, we made a study to establish
the minimum time associated with a good reaction rate under
optimized conditions, the results are summarized in Figure 1. As
can be seen in the Figure, the adducts can be detected after 1 h
of reaction and the highest yield was observed after 16 h (80%,
green line). The diphenyl disulfide observed in the chromatogram
(red line) probably was formed during the quenching process just
before the injection in the chromatograph, once this procedure was
performed in open atmosphere (air presence). We have already de-
scribed that [bmim][SeO2(OCH3)] is a good oxidant agent in the
presence of air.16 This assumption was confirmed when diphenyl
for the synthesis of vinyl sulfides using thiophenol and propargyl
alcohol as model starting materials. Careful analysis revealed that
the best yields were obtained when a mixture of alkyne 1a
(1.2 mmol), thiol 2a (1.0 mmol), and [bmim][SeO2(OCH3)] (15.8
mg, 5 mol %) was vigorously stirred at 60 °C under nitrogen
atmosphere. Under this condition, a mixture of the respective
adducts 3a and 4a was obtained in 80% overall yield after 16 h
(Table 1, entry 1).
The nitrogen atmosphere was crucial to minimize the formation
of disulfide by the oxidation of thiol. In order to obtain an efficient

S. Thurow et al. / Tetrahedron Letters 53 (2012) 2651–2653
2653
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disulfide was used instead of benzenethiol; no product was veri-
fied even after 24 h of stirring at 60 °C.
With this optimized condition in hand,17 a detailed study was
performed with aliphatic and aromatic thiols and several alkynes,
as propargyl alcohols, phenylacetylene, and octyne, showing the
generality of the method. The results depicted in Table 1 show that
[bmim][SeO2(OCH3)] was an excellent catalyst, affording a wide
range of vinyl sulfides. Concerning the stereochemistry of prod-
ucts, for all the hydroxylated alkynes 1a–1d, a mixture of Mark-
ovnikov and anti-Markovnikov adducts was obtained (Table 1,
entries 1–12). Despite the low selectivity, a good yield was
achieved in most of the tested examples. An exception was the
reaction between octyne 1e with benzenethiol 2a, which afford
the respective anti-Markovnikov adduct 3n in 30% yield and a Z/E
ratio = 80:20 (entry 13). Under our conditions, phenyl acetylene
1f reacted with 2a to afford a 1:1 mixture of isomers 3n and 4n
in excellent yield (Table 1, entry 14). The best selectivity was ob-
tained when p-chlorobenzenethiol 2e was used, in preference to
the anti-Markovnikov adduct, (Z)-3o (entry 15).
To speculate if a radical mechanism could be involved, the reac-
tion was also performed in the presence of hydroquinone. Thus,
when a mixture of 1a, 2a, and the ionic liquid reacted in the pres-
ence of hydroquinone (10 mol %), the respective adducts were ob-
tained in same yields and isomeric relation as described above
(Table 1, entry 1).
In conclusion, we have described a new application for the sele-
nium-based ionic liquid [bmim][SeO2(OCH3)], which was an effi-
cient catalyst for the synthesis of a range of vinyl sulfides via
hydrothiolation of alkynes. This is a useful alternative to the exist-
ing methodologies, once no strong bases are involved.
13. (a) Tadesse, H.; Luque, R. Energy Environ. Sci. 2011, 4, 3913; (b) Welton, T. Chem.
Rev. 1999, 99, 2071; (c) Dupont, J.; Souza, R. F.; Suarez, P. A. Z. Chem. Rev. 2002,
102, 3667; (d)Wasserscheid, P., Welton, P., Eds.Ionic Liquids in Synthesis;
Wiley-VCH: Weinheim, 2003; (e) Rantwijk, F.; Sheldon, R. A. Chem. Rev. 2007,
107, 2757; (f) Martins, M. A. P.; Frizzo, C. P.; Moreira, D. N.; Zanatta, N.;
Bonacorso, H. G. Chem. Rev. 2008, 108, 2015.
14. (a) Lenardão, E. J.; Feijó, J. O.; Thurow, S.; Perin, G.; Jacob, R. G.; Silveira, C. C.
Tetrahedron Lett. 2009, 50, 5215; (b) Lenardão, E. J.; Borges, E. L.; Mendes, S. R.;
Perin, G.; Jacob, R. G. Tetrahedron Lett. 2008, 49, 1919; (c) Lenardão, E. J.;
Mendes, S. R.; Ferreira, P. C.; Perin, G.; Silveira, C. C.; Jacob, R. G. Tetrahedron
Lett. 2006, 47, 7439.
15. For the synthesis of [bmim][SeO2(OCH3)] see: Kim, H. S.; Kim, Y. J.; Lee, H.;
Park, K. Y.; Lee, C.; Chin, C. S. Angew. Chem., Int. Ed. 2002, 41, 4300.
16. Thurow, S.; Pereira, V. A.; Martinez, D. M.; Alves, D.; Perin, G.; Jacob, R. G.;
Lenardão, E. J. Tetrahedron Lett. 2011, 52, 640.
Acknowledgments
The authors thank FAPERGS (PRONEX 10/0005-1, PRONEM 11/
2026-4 and PqG 11/0881-2), CNPq, and CAPES for financial
support.
17. General procedure for the synthesis of vinyl sulfides with [bmim][SeO2(OCH3)]: In a
Schlenk tube under nitrogen atmosphere and at 60 °C, propargyl alcohol (1a;
0.067 g; 1.2 mmol) and benzenethiol (2a; 0.110 g; 1 mmol) were added to
[bmim][SeO2(OCH3)]15 (0.0158 g, 0.05 mmol). The reaction mixture was
allowed to stir at 60 °C for the time indicated in Table 1. The progress of the
reaction was monitored by TLC or GC. After the reaction was complete, water
(15 mL) was added and the organic phase was extracted with EtOAc
(3 Â 5 mL), dried over MgSO4, and concentrated under vacuum. The residue
was purified by column chromatography on silica gel using hexanes/ethyl
acetate (90:10) as eluent, yielding a mixture of 3a and 4a (0.133 g, 80%). 1H
NMR (400 MHz, CDCl3)11b d Z isomer: 7.21–7.42 (m, 5H); 6.35 (dt, J 9.2 and 1.2,
1H); 5.96 (dt, J 9.2 and 6.6, 1H); 4.37 (dd, J 6.6 and 1.2, 2H); 1.92 (br s, 1H); E
isomer: 7.21–7.42 (m, 5H); 6.46 (dt, J 15.6 and 1.2, 1H); 5.95 (dt, J 15.6 and 6.8,
1H); 4.20 (dd, J 6.8 and 1.2, 2H); 1.92 (br s, 1H); Markovnikov adduct: 7.21–
7.42 (m, 5H); 5.57 (s, 1H); 5.24 (s, 1H); 4.16 (s, 2H); 1.92 (br s, 1H).
References and notes
1. For the synthetic utility of vinyl sulfides see, for example: (a) Aucagne, V.;
Lorin, C.; Tatibouët, A.; Rollin, P. Tetrahedron Lett. 2005, 46, 4349; (b) Muraoka,
N.; Mineno, M.; Itami, K.; Yoshida, J.-I. J. Org. Chem. 2005, 70, 6933; (c)
Woodland, C. A.; Crawley, G. C.; Hartley, R. C. Tetrahedron Lett. 2004, 45, 1227;
(d) McReynolds, M. D.; Dougherty, J. M.; Hanson, P. R. Chem. Rev. 2004, 104,
2239; (e) Oae, S. Organic Sulfur Chemistry: Structure and Mechanism; CRC Press:
Boca Raton, FL, 1991; (f) Cremlyn, R. J. An Introduction to Organosulfur
Chemistry; Wiley & Sons: New York, 1996.