Zn/CeCl3.7H2O-TBPB: A new and 'green' promoter system for rapid and regioselective thiolyzation of 1,2-epoxides with aryl disulfides

Article abstract of DOI:10.1246/cl.2004.1378

A new, efficient, clean, and regioselective 'one-pot' procedure for thiolyzation of epoxides with aryl disultides catalyzed by cerium(III) chloride heptahydrate immobilized on tetrabutyl phosphonium bromide as an ionic liquid is reported.

Full text of DOI:10.1246/cl.2004.1378

1378
Chemistry Letters Vol.33, No.10 (2004)
Zn/CeCl3.7H2O-TBPB: A New and ‘Green’ Promoter System for Rapid
and Regioselective Thiolyzation of 1,2-Epoxides with Aryl Disulfides
Ahmad R. Khosropour,ꢀ Mohammad M. Khodaei,ꢀ and Kazem Ghozati
Department of Chemistry, Faculty of Science, Razi University, Kermanshah 67149, Iran
(Received August 5, 2004; CL-040927)
A new, efficient, clean, and regioselective ‘one-pot’ proce-
and chemoselectivity in various chemical transformations, with
the additional advantages, that it is cheap, water-tolerant and
nontoxic.12
In order to investigate the influence of the catalyst in differ-
ent media, the thiolysis of styrene oxide with (PhS)2 was carried
out in CH3CN, diisopropyl ether, CH2Cl2, TBAB (tetrabutylam-
monium bromide), TBAF (tetrabutylammonium fluoride), TBAI
(tetrabutylammonium iodide), and under solvent-free condi-
tions. The results are summarized in Table 1.
dure for thiolyzation of epoxides with aryl disulfides catalyzed
by cerium(III) chloride heptahydrate immobilized on tetrabutyl
phosphonium bromide as an ionic liquid is reported.
The vicinal thioalcohols are a common structural compo-
nent in a vast group of natural products or synthetic molecules
with biological and pharmaceutical activities.1 One of the most
straightforward routes to synthesis of these compounds involves
the ring opening of epoxides with thiols.2 This reaction is gener-
ally carried out with large excess of the thiols with unpleasant
odor at elevated temperatures. The high temperature reaction
conditions are not only detrimentally to certain functional
groups, but also to the control of regioselectivity. Subsequently,
due to the harsh reaction conditions and long reaction times
some catalytic methods have recently been developed.3–7 How-
ever, in spite of their potential utility, many of these methods in-
volve expensive or stoichiometric amounts of reagents, strongly
acidic conditions, use of toxic solvents, poor selectivity, unsatis-
factory yields that entail undesirable side reactions such as poly-
merization or rearrangement and generation of a large amount of
toxic waste that leads this classic reaction to serious disadvan-
tages. In fact acid-catalyzed ring opening of epoxides with thiols
is requiring the careful control of the acidity to prevent side re-
actions. Since ꢀ-hydroxy sulfides have become increasingly use-
ful and important especially in pharmaceuticals, thus develop-
ment of simple, efficient, and environmentally friendly approach
for their synthesis is highly desirable.
Recently, ionic liquids have emerged as an alternative reac-
tion media for the immobilization of transition metal catalysts,
Lewis acids and enzymes.8,9 They are being used as green sol-
vents with unique properties such as good solvating ability, high
thermal stability, negligible vapor pressure, and ease of recycla-
bility. In continuation of our research on the ring opening reac-
tion of epoxides,10 recently we investigated the applicability of
Lewis acids immoblized on ionic liquid in aminolysis of epox-
ides with anilines.11 We report herein, for the first time, one-
pot region- and chemoselective ring opening reaction of 1,2-ep-
oxides with aryl disulfides by zinc powder in the presence of cat-
alytic amount of CeCl3. 7H2O immoblized on tetrabutylphos-
phonium bromide (TBPB) as an ionic liquid (Scheme 1).
Cerium(III) chloride heptahydrate was chosen because it has
emerged as potentially useful Lewis acid imparting high regio-
Table 1. Thiolysis of styrene oxide with (PhS)2 in the presence
of zinc powder and different catalytic conditions
Reaction
time / min
Yield
/ %
Entry
Catalytic conditions
1
2
3
4
3
4
5
6
7
none
CeCl3. 7H2O/CH3CNa
120
120
120
120
120
120
120
120
20
0
6
4
trace
0
53
64
48
92
CeCl3. 7H2O/Diisopropyl ethera
a
CeCl3. 7H2O/CH2Cl2
CeCl3. 7H2Ob
CeCl3. 7H2O/TBABc
CeCl3. 7H2O/TBAFc
CeCl3. 7H2O/TBAIc
CeCl3. 7H2O/TBPBc
aIn the presence of 0.2 mmol of CeCl3. 7H2O and 5 mL of the
b
c
solvent. Solvent free conditions. In the presence of 0.2 mmol
of CeCl3. 7H2O and 0.5 mmol of the ionic liquid.
Initially we studied the reactivity of symmetrical aliphatic
and aromatic disulfides using styrene oxide as a model substrate.
The reaction took place at 70 ꢁC with addition of 1 mmol of sty-
rene oxide, 1 mmol of the disulfide and 1 mmol of zinc powder in
the molten mixture of 0.2 mmol CeCl3. 7H2O and 0.5 mmol of
TBPB. Under these conditions, the epoxide was reacted only
with aryl disulfides and aliphatic disulfides remain intake. Con-
sequently, we focused our attention only on aryl disulfides with
various epoxides. All the experimental results are summarized in
Table 2.
In the method described here, a variety of epoxides with dif-
ferent 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 termi-
nal epoxides (Table 2, Entries 7–13), the products obtained by
the attack on the terminal carbon. This regioselectivity is prob-
ably due to the steric hinderance of nucleophile that attacks on
the less-hindered carbon of the epoxides. However, in the case
of reaction with styrene oxide we observed a reverse regioselec-
tivity in which the attack on the benzylic carbon was preferred.
The product obtained using cyclohexene oxide was shown to
posses a trans-configuration by 1H NMR spectroscopy. These
high reactivity and selectivity are similar to those observed in
ArS
OH
O
Zn / CeCl3. 7H2O-TBPB
OH
SAr
or
ArSSAr, 70 °C
R
R
R
Ar: Phenyl ; p-tolyl; 2-naphthyl
Scheme 1.
Copyright Ó 2004 The Chemical Society of Japan

Chemistry Letters Vol.33, No.10 (2004)
1379
Table 2. Thiolysis of 1,2-epoxides with aryl disulfides in the
presence of Zn/CeCl3. 7H2O-TBPB at 70 ꢁC
and reused in three runs without any loss of activity (Table 1,
Entries 1, 2).
In conclusion, a new, powerful, regioselective chemoselec-
tive and environmentally friendly method is described for thiol-
ysis of 1,2-epoxides with odorless aryl disulfides instead of the
thiols in good to high yields. In addition, short reaction times,
relatively mild reaction conditions and high yields with straight-
forward work-up, reusability, stability and non-toxicity of the
catalyst and ionic liquid make the present method efficient,
convenient and ‘green,’ which could be a very efficient alterna-
tive to the classic methodology.
Yield /%b/
Time /min
Entry R or Epoxide
Product a
HOCH2CHS
1
2
Ph
Ph
92/20(89)c
Ph
HOCH2CHS
Ph
CH3
90/20
HOCH2CHS
Ph
3
4
Ph
87/20
80/45
The authors thank to Razi University for financial
assistance.
S
O
O
O
References and Notes
OH
S
1
2
3
F. Viola, G. Balliano, P. Milla, L. Cattel, F. Rocco, and M.
Ceruti, Bioorg. Med. Chem., 8, 223 (2000).
M. E. Peach, ‘‘The Chemistry of the Thiol Group,’’ John
Wiley, New York (1974), Part 3, p 771.
a) D. Amantini, F. Fringuelli, F. Pizzo, S. Tortoioli, and L.
Vaccaro, Synlett, 2003, 2292. b) B. Movassagh, S. Sobhani,
F. Kheirdoush, and Z. Fadaei, Synth. Commun., 33, 3103
(2003). c) J. Downsland, F. Mckerlie, and D. J. Procter,
Tetrahedron Lett., 41, 4923 (2000).
CH3
5
6
80/55
78/50
OH
S
OH
4
F. Fringuelli, F. Pizzo, S. Tortoioli, and L. Vaccaro, J. Org.
Chem., 68, 8248 (2003).
7
8
9
PhOCH2
PhOCH2
90/30(87)c
89/35
PhOCH2CHCH2S-
OH
5
6
R. Fan and X.-L. Hou, J. Org. Chem., 68, 726 (2003).
S. Chanrasekar, C. R. Reddy, B. N. Babu, and G.
Chandrashekar, Tetrahedron Lett., 43, 3801 (2002).
a) F. Fringuelli, F. Pizzo, S. Tortoioli, and L. Vaccaro,
Adv. Synth. Catal., 344, 379 (2002). b) M. Romdhani Younes,
M. M. Chaabouni, and A. Baklouti, Tetrahedron Lett., 42,
3167 (2001).
a) J. S. Yadav, B. V. S. Reddy, A. K. Basak, and A. Venkat
Narsaiah, Tetrahedron Lett., 44, 1047 (2003).
a) R. Sheldon, Chem. Commun., 2001, 2399. b) P.
Wasserscheid and W. Keim, Angew. Chem., Int. Ed., 39,
3772 (2000).
PhOCH2CHCH2S-
OH
CH3
7
85/50
CH2CHCH2S
OH
O
O
8
9
O
10
11
80/55
85/30
CH2CHCH2S
OH
CH3
O
10 a) A. R. Khosropour, M. M. Khodaei, and K. Ghozati, Chem.
Lett., 34, 303 (2004). b) I. Mohammadpoor-Baltork and
A. R. Khosropour, Synth. Commun., 22, 3411 (2001).
CH3(CH2)4CH2
CH3(CH2)5 CH2CHCH2S
OH
11 M. M. Khodaei, A. R. Khosropour, and K. Ghozati,
Tetrahedron Lett., 45, 3525 (2004).
)
12
CH3(CH2 3OCH2
86/45
CH3(CH2)2CH2O CH2CHCH2S
OH
12 a) G. Bartoli, E. Marcantoni, and L. Sambri, Synlett, 2003,
2101. b) J. S. Yadav, B. V. S. Reddy, C. V. Rao, P. K. Chand,
and A. R. Prasad, Synlett, 2002, 137. c) J. S. Yadav, B. V. S.
Reddy, M. S. Reddy, and G. Sabitha, Synlett, 2001, 1134.
13 Typical procedure for preparation of trans-2-phenylthiocyclo-
hexanol (Table 2, Entry 4): To a molten mixture of (PhS)2
(1 mmol), CeCl3. 7H2O (0.2 mmol), and TBPB (0.5 mmol), cy-
clohexene oxide (1 mmol) and zinc powder (1 mmol) were
added. The reaction mixture was stirred at 70 ꢁC for 45 min
(monitored by TLC). After completion of the reaction, the mix-
ture was washed with Et2O (3 ꢂ 10 mL) and the organic layer
was evaporated. The residue was chromatographied on silica
gel (petroleum ether–EtOAc) to afford the pure product
Cl CH2CHCH2S
OH
82/60
13
ClCH2
aAll products were identified by comparison of their physical
and spectral data with those of authentic samples. bIsolated
yields. The yield achieved from the recycled promoter.
c
the case of strong Lewis acids with thiophenols.3–7
These results indicated that this reaction not only needs the
presence of the catalyst for proceeding, but also it is performed
only in the presence of the ionic liquids and among them TBPB
showed more effective in this transformation.
Another advantage of this method for this transformation is
recyclability of this promoter system. Since Zn–CeCl3.7H2O/
TBPB was weakly soluble in Et2O, this was separated by
washing with Et2O and dried at 80 ꢁC under reduced pressure
1
(80%). IR (KBr) ꢁmax 3620, 3200, 1580, 1435, 690. H NMR
(200 MHz, CDCl3): ꢂ 1.22–1.42 (m, 4H), 1.62–1.83 (m, 2H),
2.10–2.39 (m, 2H), 2.85 (ddd, 1H, J ¼ 11:6, 9.8, 4.5 Hz),
3.15 (br, 1H, OH), 3.42 (ddd, 1H, J ¼ 9:8, 9.8, 4.5 Hz),
7.25–7.42 (m, 5H). 13C NMR (50 MHz, CDCl3): ꢂ 24.7,
26.6, 33.1, 34.2, 56.9, 72.4, 128.2, 129.3, 133.0, 134.2. Anal.
Calcd. for C12H16OS (208.317): C, 69.19; H, 7.74; S,
15.39%. Found: C, 69.21; H, 7.76; S, 15.43%.
Published on the web (Advance View) September 25, 2004; DOI 10.1246/cl.2004.1378