Synthesis of Thiiranes from Oxiranes Using Cross-Linked Polystyrene Supported Aluminium Chloride as a Catalyst

Article abstract of DOI:10.1081/SCC-120027239

A simple and efficient method for conversion of oxiranes to their corresponding thiiranes using thiourea catalyzed with cross-linked polystyrene supported aluminium chloride, (Ps-AlCl₃), under non-aqueous condition is described.

Full text of DOI:10.1081/SCC-120027239

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Synthesis of Thiiranes from Oxiranes Using
Cross‐Linked Polystyrene Supported Aluminium
Chloride as a Catalyst
B. Tamami a & K. Parvanak Borujeny a
a Department of Chemistry, College of Sciences, Shiraz University, Shiraz, 71454, Iran
Published online: 16 Aug 2006.
To cite this article: B. Tamami & K. Parvanak Borujeny (2004): Synthesis of Thiiranes from Oxiranes Using Cross‐Linked
Polystyrene Supported Aluminium Chloride as a Catalyst, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 34:1, 65-70
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 1, pp. 65–70, 2004
Synthesis of Thiiranes from Oxiranes Using
Cross-Linked Polystyrene Supported
Aluminium Chloride as a Catalyst
*
B. Tamami and K. Parvanak Borujeny
Department of Chemistry, College of Sciences, Shiraz University
Shiraz, Iran
ABSTRACT
A simple and efficient method for conversion of oxiranes to their
corresponding thiiranes using thiourea catalyzed with cross-linked
polystyrene supported aluminium chloride, (Ps-AlCl3), under non-
aqueous condition is described.
Key Words: Oxiranes; Thiirane; Aluminium chloride; Cross-linked
polystyrene.
*
Correspondence: B. Tamami, Department of Chemistry, College of Sciences, Shiraz
University, Shiraz 71454, Iran; Fax: 0098-711-2280926; E-mail: tamami@chem.susc.
ac.ir.
65
DOI: 10.1081/SCC-120027239
0039-7911 (Print); 1532-2432 (Online)
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Copyright # 2004 by Marcel Dekker, Inc.

66
Tamami and Parvanak Borujeny
INTRODUCTION
The generation of hybrid catalysts which combine the attributes of
homogeneous catalysts with the experimental ease of heterogeneous catalysts
has lured many workers into this area of research.[1,2] Among such hetero-
geneous catalysts, a large number of polymer supported polymeric Lewis
acids have been prepared by immobilization of the catalysts on polymers via
coordination or covalent bonds.[3] Such polymer catalysts are as active and
selective as their homogeneous counterparts while having the distinguishing
characteristics of being easily separable from reaction media, recyclability and
selectivity in various organic reactions. The most frequently used polymeric
support is polystyrene; its hydrophobic nature protects the water-sensitive
Lewis acids from hydrolysis by atmospheric moisture until it is placed in an
appropriate solvents where it can be used in a reaction medium.[4–10]
There are many methods reported in the literature for preparation of
thiirans,[11,12] and the most general one has been the conversion of oxiranes to
thiiranes. For this purpose several sulfured agents such as thiourea,[13,14]
inorganic thiocyanats,[15] phosphin sulfides,[16,17] silica gel-supported
KSCN,[18] dimethylthioformamide,[19] and low hydrate KSCN-liquid hetero-
geneous mediums,[20] have been used. Also, several different Lewis acids such
as, Ce(IV) as ceric ammonium nitrate (CAN),[21] Ru(III) as ruthenium
trichloride(RuCl3),[22] BiCl3,[23] TiO(CF3CO2)2,[24] and TiCl3(CF3SO3),[24]
have been used as catalysts for the conversion of epoxides to thiiranes.
However, some of these methods suffer from drawbacks such as, aqueous
and/or alcoholic medium has to be used, low yield, rapid increase of pH
during the reaction, reaction to be carried out in the presence of trifluroacetic
acid, difficulty in separation of the product from the original reactant and
catalysts, and formation of the polymeric by-products, and in some cases, use
of expensive and unreuseable catalysts. Thus, it seems that convenient and
general methods for this purpose especially by heterogeneous catalysts are
still being demanded.
Recently we reported,[25,26] polymer-supported thiocyanate as a reagent
and poly(vinylpyridine)-Ce(OTF)4 as a catalyst for synthesis of thiiranes from
oxiranes. Both these polymeric systems could overcome many drawbacks in
the synthesis of thiiranes. As part of our general program to investigate the
reactions of the polymer supported reagents and catalysts, herein we report
Scheme 1.

Conversion of Oxiranes
67
that polystyrene supported aluminium chloride can act as an efficient
polymeric catalyst for the conversion of various epoxides to thiranes using
thiourea under mild non-aqueous condition (Sch. 1).
RESULT AND DISCUSSION
Ps-AlCl3 was prepared by addition of anhydrous AlCl3 to polystyrene
[8% Divinylbenzene] in carbon disulfide under reflux condition.[4] Using this
polymeric catalyst, different kinds of epoxides were converted to their
corresponding thiiranes with thiourea as sulfurating agent (Table 1). Reactions
were carried out in refluxing acetonitrile which proved to be the solvent of
choice among other organic solvents. The reactions proceed in clean manner
and the conditions employed are both simple and convenient. The optimum
molar ratio of the polymeric catalyst to epoxide was found to be 0.3 : 1.
In conclusion, we believe that Ps-AlCl3 is an effective and convenient
catalyst for conversion of epoxides to thiranes with high yields, mild reaction
condition, and easy work-up procedure. The performance of reactions in non-
aqueous media can be ideal for substrates containing water sensitive groups.
The catalyst can be prepared easily with cheap starting materials and is
reusable.
EXPERIMENTAL
Starting materials were obtained from Fluka Company. Polystyrene (8%
divinylbenzene) was obtained from Iran Polymer Institute. Products were
characterized by comparison of their physical data with those of known
samples. Gas chromatography was recorded on Shimadzu GC. 14-A. IR
spectra recorded on Perkin–Elmer 781 spectrometer. 1H and 13C NMR spectra
were recorded on Bruker Advance DPX FT 250 MHz instrument.
Preparation of Ps-AlCl3
This catalyst was prepared using crosslinked polystyrene [8%
Divinylbenzene] as reported in the literature.[4] The chloride content of Ps-
AlCl3 was 5.28%.[29]

68
Tamami and Parvanak Borujeny
Table 1. Conversion of oxiranes to the corresponding thiiranes with thiourea
catalyzed by Ps-AlCl3.a
B.p(8C)/torr
Time Yield
Entry
Thiiraneb
(hr)
2.1
1.6
2.7
2
(%)c
Found
Reported
1
2
3
4
5
6
98
104.5–105.5/7 103–104/7[19]
93
80.5–81.5/5
77.5–78.7/8
48.7–51.5/1
59.7–60.5/30
85.5–86.7/5
83/5[27]
78–79/8[19]
43/0.16[28]
55/28[28]
93
95
2.5
1.5
90
85
85–86/5[21]
7
8
1.2
1.3
92
85
71.5–72/70
54.5–56.5/7
72–73/70[21]
55–56/7[23]
aThe molar ratio of epoxide/thiourea/Cat. is: 1 : 2 : 0.3.
bAll products were identified by comparison of their IR, 1H and 13C NMR spectra with
those of the authentic samples.[19]
cIsolated yield.
Conversion of Epoxides to Thiiranes: General Procedure
In a round-bottomed flask (25 mL) equipped with a condenser and a
magnetic stirrer a solution of epoxide (1 mmol) in acetonitrile (10 mL) was
prepared. Thiourea (2 mmol) and Ps-AlCl3 (0.3 mmol) were added to the
solution and the reaction mixture was stirred magnetically under reflux
condition. Progress of the reaction was followed by TLC and GC. On
completion of the reaction, solvent was evaporated and ether (2 Â 20 mL) was
added to the residue and filtered. The filtrate was washed with water
(2 Â 20 mL). The organic layer was passed through a short pad of silica gel
and dried with anhydrous Na2SO4 to obtain the pure products in 85–98%

Conversion of Oxiranes
69
yields after evaporation of solvent. The spent polymeric catalyst from
different experiments was washed with water, then with ether and dried
overnight in vacuum oven and reused.
ACKNOWLEDGMENT
We are thankful to Shiraz University Research Councial for partial
support of this work.
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Received in Poland March 24, 2003