Mild, efficient, and convenient conversion of oxiranes to thiiranes with ammonium thiocyanate and thiourea in the presence of cerium(IV) polyoxometallate

Article abstract of DOI:10.1081/SCC-120002409

Selective conversion of various oxiranes to the corresponding thiiranes in the presence of ammonium thiocyanate and thiourea can be effectively carried out by ammonium decatungestocerate(IV) icosahydrate, (NH₄)₈ [CeW₁₀O₃₆]·20H₂O.

Full text of DOI:10.1081/SCC-120002409

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MILD, EFFICIENT, AND CONVENIENT CONVERSION
OF OXIRANES TO THIIRANES WITH AMMONIUM
THIOCYANATE AND THIOUREA IN THE PRESENCE OF
CERIUM(IV) POLYOXOMETALLATE
V. Mirkhani a , S. Tangestaninejad a & L. Alipanah a
a Department of Chemistry , University of Isfahan , Isfahan, 81744, Iran
Published online: 16 Aug 2006.
To cite this article: V. Mirkhani , S. Tangestaninejad & L. Alipanah (2002) MILD, EFFICIENT, AND CONVENIENT
CONVERSION OF OXIRANES TO THIIRANES WITH AMMONIUM THIOCYANATE AND THIOUREA IN THE PRESENCE OF CERIUM(IV)
POLYOXOMETALLATE, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 32:4, 621-626, DOI: 10.1081/SCC-120002409
To link to this article: http://dx.doi.org/10.1081/SCC-120002409
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SYNTHETIC COMMUNICATIONS, 32(4), 621–626 (2002)
MILD, EFFICIENT, AND CONVENIENT
CONVERSION OF OXIRANES TO
THIIRANES WITH AMMONIUM
THIOCYANATE AND THIOUREA
IN THE PRESENCE OF CERIUM(IV)
POLYOXOMETALLATE
V. Mirkhani,* S. Tangestaninejad, and L. Alipanah
Department of Chemistry, University of Isfahan,
Isfahan 81744, Iran
ABSTRACT
Selective conversion of various oxiranes to the corresponding
thiiranes in the presence of ammonium thiocyanate and
thiourea can be effectively carried out by ammonium
decatungestocerate(IV) icosahydrate, (NH4)8[CeW10O36]Á20H2O.
Many methods have been already reported in the literature for the
preparation of thiiranes.1,2 The most general one is based on the conversion
of oxiranes to their corresponding thiiranes by an oxygen–sulfur exchange
reaction. Various sulfurating reagents such as inorganic thiocyanate,1–4
thiourea,4–6 phosphine sulfide,7,8 dimethylthioformamide,9 3-methylben-
zothiazole-2-thione,10 silica-gel supported KSCN,11 and polymer supported
*Corresponding author.
621
Copyright & 2002 by Marcel Dekker, Inc.
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MIRKHANI, TANGESTANINEJAD, AND ALIPANAH
thiocyanate12 have also been reported for this purpose. In general, all of
these reagents suffer from at least one of the following disadvantages: long
reaction times, low yields of the products, pH increase of the reaction
mixture, formation of polymeric by-products, tedious work-up, requirement
for aqueous reaction conditions, and presence of sulfuric and trifluoroacetic
acids. Therefore, there is a need to develop and introduce new methods
and reagents for the conversion of oxiranes to thiiranes. Recently, conver-
sion of oxiranes to thiiranes with ammonium thiocyanate or thiourea in
the presence of ruthenium(III) chloride,13 bismuth(III) chloride,14 iron(III)
tetrakis-(pentafluorophenyl)porphyrin15 and tin(IV) meso-tetraphenylpor-
phyrin16 as Lewis acids and ceric ammonium nitrate17 as a one-electron
transfer catalyst have been reported. The chemistry of Ce(IV) oxidation
of organic compounds is dominated by radical and radical cations.17–22
Since the fate of these radical intermediates and the nature of the oxidation
can affect the type of the organic products, new Ce(IV) reagents were
synthesized and applied for different types of transformations.18–23 The
application of some polyoxometallates as perfect outer-sphere one-electron
oxidizing agents for different functional group transformations have been
investigated.24–28
In this paper, we wish to report that (NH4)8[CeW10O36]Á20H2O can act
as a mild and highly effective one-electron transfer heterogeneous catalyst
for regio and stereoselective conversion of oxiranes to thiiranes with ammo-
nium thiocyanate and thiourea (Scheme 1).
Scheme 1.
At first, we examined the reaction of epichlorohydrin as a model
substrate with ammonium thiocyanate and thiourea in the presence of
(NH4)8[CeW10O36]Á20H2O (0.04 molar equivalents) as a catalyst in different
refluxing solvents such as dichloromethane, chloroform, carbon tetrachlor-
ide, n-hexane and acetonitrile. Compared to acetonitrile, longer reaction
times and lower yields were observed in all of the other solvents. The results
of our study are summarized in Table 1. It is worth mentioning that in cases
where an aqueous solvent is used, control of pH is important in order to
obtain high yields and to avoid polymerization of thiiranes. In this method,
no water is required and thiiranes are obtained in excellent yields without
any polymerization.

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CONVERSION OF OXIRANES TO THIIRANES
623
Table 1. Conversion of Oxiranes to Thiiranes with Different Refluxing Solvents/
(NH4)SCN or NH2CSNH2
Yield%a,b (Time/h)
Entry
Solvents
Acetonitrile
Dichloromethane
Chloroform
NH4SCN
NH2CSNH2
1
2
3
4
5
98 (0.5)
31 (0.5)
17 (0.5)
46 (0.5)
38 (0.5)
95 (1)
27 (1)
15 (1)
40 (1)
36 (1)
Carbon tetrachloride
n-Hexane
aThe product was characterization by comparison with known sample.
bYields refer to product.
As shown in Table 2, different aliphatic and cyclic oxiranes react
rapidly with ammonium thiocyanate and thiourea in the presence of
0.04 molar equivalents of ammonium decatungestocerate(IV) icosahydrate,
(NH4)8[CeW10O36]Á20H2O, in refluxing acetonitrile affording the corre-
sponding thiiranes in excellent yields. It is important to note that in the
absence of catalyst, thiocyanate and thiourea were much less efficient in
conversion of oxiranes to thiiranes in refluxing acetonitrile.
In conclusion, we have shown that (NH4)8[CeW10O36]Á20H2O is a mild
and convenient catalyst for the efficient conversion of oxiranes to thiiranes
in the presence of ammonium thiocyanate and thiourea. In addition, high
yields, short reaction times and easy work-up make this method a useful and
important addition to the modern organic synthetic methodologies.
EXPERIMENTAL
All chemicals used were reagent grade. The ammonium decatun-
gestocerate(IV) icosahydrate was prepared according to the literature.29,30
Products were characterized by comparison of their physical data, IR and
NMR spectra with those of authentic samples.9,18,31,32
General Procedure for the Conversion of Epichlorohydrin
to Thiiranes in Different Refluxing Solvents
A mixture of epichlorohydrin (1 mmol), ammonium thiocyanate
(0.152 g, 2 mmol) or thiourea (0.152 g, 2 mmol) and (NH4)8[CeW10O36]Á
20H2O (0.04 mmol) in different solvents (5 ml) was stirred under reflux

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MIRKHANI, TANGESTANINEJAD, AND ALIPANAH
Table 2. Conversion of Oxiranes to Thiiranes with Ammonium Deca-
tungestocerate (IV)/(NH4)SCN or NH2CSNH2 in Refluxing CH3CN
conditions. The progress of the reaction was monitored by GLC. The catalyst
was removed by a silica-gel column (1 : 1 hexane–ethyl acetate). Evaporation
of the solvent, followed by chromatography on silica-gel gave the product in
15–98% yields (Table 1).
General Procedure for the Conversion of Oxiranes to
Thiiranes with Ammonium Thiocyanate
(NH4)8[CeW10O36]Á20H2O (0.04 mmol) was added to a solution of oxi-
rane (1 mmol) and ammonium thiocyanate (0.152 g, 2 mmol) in acetonitrile

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CONVERSION OF OXIRANES TO THIIRANES
625
(5 ml). The mixture was stirred for a specified time and reflux according
to Table 2. The progress of the reaction was monitored by GLC. After
completion of the reaction, the mixture was passed through a silica-gel
column (1 : 1 hexane–ethyl acetate) to remove the catalyst. The eluate was
concentrated under reduced pressure and chromatographed on a silica-gel
column to give a pure product in 88–98% yields, without any polymerization
by-products.
General Procedure for the Conversion of Oxiranes to
Thiiranes with Thiourea
In a round-bottomed flask (25 ml) equipped with a condenser
and magnetic stirrer, a solution of oxirane (1 mmol) in CH3CN (5 ml)
was prepared. Thiourea (0.152 g, 2 mmol) and (NH4)8[CeW10O36]Á20H2O
(0.04 mmol) were added to this solution and the mixture was stirred
magnetically under reflux conditions. After completion of the reaction
(monitored by GLC), the mixture was directly passed through a short
column of silica-gel (1 : 1 hexane–ethyl acetate) to remove the catalyst.
The eluate was evaporated under reduced pressure and the crude product
was obtained in a quantitative yield. Distillation of the product under
reduced pressure, afforded the corresponding thiirane in 81–98% yields,
without any polymerization by-products.
ACKNOWLEDGMENT
We thank the financial support for this work by the Isfahan University
Research Council and Prof. I. Mohammadpoor-Baltork for his expert
assistance.
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Received in Japan December 27, 2000

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