2,4,6-Trichloro-1,3,5-triazine catalyzed synthesis of thiiranes from oxiranes under solvent-free and mild conditions

Article abstract of DOI:10.1016/j.tetlet.2006.03.171

A simple, mild and efficient method has been developed for the synthesis of thiiranes from epoxides using a catalytic amount of 2,4,6-trichloro-1,3,5-triazine under solvent-free conditions.

Full text of DOI:10.1016/j.tetlet.2006.03.171

Tetrahedron Letters 47 (2006) 4775–4777
2,4,6-Trichloro-1,3,5-triazine catalyzed synthesis of thiiranes from
oxiranes under solvent-free and mild conditions
B. P. Bandgar,* Neeta S. Joshi and V. T. Kamble
Organic Chemistry Research Laboratory, School of Chemical Sciences, Swami Ramanand Teerth Marathwada University,
Nanded 431 606, MS, India
Received 3 November 2005; revised 6 March 2006; accepted 30 March 2006
Abstract—A simple, mild and efficient method has been developed for the synthesis of thiiranes from epoxides using a catalytic
amount of 2,4,6-trichloro-1,3,5-triazine under solvent-free conditions.
ꢀ 2006 Published by Elsevier Ltd.
8
1. Introduction
(4-vinylpyridine)-Ce(OTf)4 and polymer supported
AlCl39 as well as polymeric co-solvents10 have been used
for this important transformation. More recently the
[bmim]PF6–H2O solvent system11 and MW12 irradiation
have been used for the conversion of oxiranes to thiir-
anes. However, long reaction times, high temperatures,
low yields of the products, use of organic solvents, the
use of acidic catalysts, difficulties in separation of the
product from the original reactant, formation of poly-
meric by-products, high catalyst loading and in most
of the cases, the use of expensive and unrecoverable
catalysts are all limitations.
Synthetic chemists continue to explore new methods to
carry out chemical transformations. One of these new
methods is to run reactions on the surface of solids.
Surfaces have properties that are not duplicated in the
solution or gas phase, hence entirely new chemistry
may occur. Even in the absence of new chemistry, a
surface reaction may be more desirable than a solution
counterpart, because the reaction can be more conve-
nient to run or a higher yield of the product is attained.
For these reasons, surface synthetic organic chemistry is
a rapidly growing field of study.
Over the last few years, there has been a considerable
growth in interest in the use of 2,4,6-trichloro-1,3,5-tri-
azine or its derivatives in organic synthesis.13 Recent
results from our laboratory showed that readily avail-
able 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride)
can assist some important organic reactions.13n–p This
prompted us to explore the catalytic activity of cyanuric
chloride for the synthesis of thiiranes. In this letter, we
report that thiiranes can be conveniently and efficiently
synthesized in high yields from the corresponding oxir-
anes with ammonium thiocyanate in the presence of
cyanuric chloride (2 mol %) at room temperature under
solvent-free conditions (Scheme 1).
Organic sulfur compounds are important and useful
building blocks in organic synthesis. Due to the
importance of thiiranes in the synthesis of polymers,
pharmaceuticals, pesticides and herbicides,1 various
methods have been developed for their synthesis. The
most common and important method is the transforma-
tion of oxiranes into thiiranes with thiourea, thioamides,
phosphine sulfide or dimethyl-thioformamide in the
presence of trifluoroacetic acid or using inorganic
thiocyanates, polymer-supported thiocyanates, silica-
supported KSCN or other related compounds.2 Usually,
with these sulfurated agents, Lewis acids such as ceric
ammonium nitrate (CAN),3 RuCl3,4 BiCl3,5 TiO(CF3-
CO2)26 and TiCl3(CF3SO3)7 have been used as catalysts.
Polymer-supported Lewis acid catalysts such as poly-
O
S
cyanuric chloride (2 mol%)
neat, r.t.
SCN
NH4
+
1
2
*
Corresponding author. Fax: +91 2462 229245; e-mail: bandgar_bp@
yahoo.com
Scheme 1.
0040-4039/$ - see front matter ꢀ 2006 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2006.03.171

4776
B. P. Bandgar et al. / Tetrahedron Letters 47 (2006) 4775–4777
2. Proposed mechanism
The likely role of cyanuric chloride is to act as a catalyst
for the activation of epoxide. Initially, a systematic
study was carried out for evaluation of cyanuric chloride
as a catalyst for the reaction of styrene oxide with
ammonium thiocyanate under various conditions (Table
1). The reaction was slow in the absence of catalyst
(Table 1, entry 1) and inferior results were obtained in
the presence of solvents (Table 1, entries 2–5). Next,
we optimized the quantity of catalyst at room tempera-
ture under solvent-free conditions (Table 1, entries 6–11)
and it was observed that the use of just 2 mol % was suf-
ficient to produce an excellent yield of the product
(Table 1, entry 9), whereas more than 2 mol % of the
catalyst did not improve the results (Table 1, entries
10–11).
Cl
Cl
N
O
N
N
N
S
N
+
NH SCN
4
Ph
O
Cl
N
C
Cl
Cl
..
O
Ph
C
N
S
S
N
Ph
O
C
H O
2
S
S
O
H
C N
Ph
Ph
Ph
Table 1. Reaction of styrene oxide with ammonium thiocyanate under
A variety of epoxides reacted smoothly with ammonium
thiocyanate in the presence of 2 mol % of cyanuric chlo-
ride at room temperature under solvent-free conditions
to furnish the corresponding thiiranes in high yields.
The reactions were rapid and in most cases thiirane for-
mation was complete in 5–20 min with excellent yields
due to the high concentration of substrate in the solid
state. The results shown in Table 2 clearly indicate the
scope and generality of this protocol as a variety of ali-
phatic, aromatic and allylic epoxides, including those
with electron-withdrawing and -donating substituents,
underwent smooth conversion into thiiranes. The pres-
ent procedure was efficient for the synthesis of thiiranes
from styrene oxide (Table 2, entry a), cyclohexene oxide
various conditions
Entry Solvent Catalyst (mol %)
(cyanuric chloride)
Time, min/[h] Yield (%)
1
2
3
Neat
CH2Cl2
THF
—
2
2
2
2
0.5
1.0
1.5
2
2.5
3.3
[20]
50
55
45
40
10
25
15
5
10
60
65
55
60
65
80
88
98
97
97
4
5
6
CH3CN
CHCl3
Neat
7
Neat
8
Neat
9
Neat
10
11
Neat
Neat
5
5
Table 2. 2,4,6-Trichloro-1,3,5-triazine catalyzed conversion of epoxides to thiiranes at room temperature
Entry
a
Epoxide
Product
Time (min)
5
Yielda,b (%)
9815
Ph
Ph
O
S
Cl
Cl
b
c
5
5
943
923
O
S
H3C
H3C
S
O
PhO
PhO
d
e
20
15
9015
903
O
S
O
S
9515
O
O
f
5
O
S
CH3(CH2)11
CH3(CH2)11
g
10
15
9212
O
S
Ph
Ph
h
9811
Ph
Ph
O
S

B. P. Bandgar et al. / Tetrahedron Letters 47 (2006) 4775–4777
4777
Table 2 (continued)
Entry
Epoxide
Product
Time (min)
Yielda,b (%)
95
4
4
ClC6H4
ClC6H4
i
15
Ph
Ph
O
S
O
O
O
O
j
5
5
9315
9711
O
S
k
Ph
Ph
Ph
Ph
O
S
a All products were identified by comparison of their physical and spectral data with those of authentic samples obtained.3,15
b Yields refer to isolated pure products.
Harvey, R. Synthesis 1972, 627–628; (e) Tamami, B.;
Kiasat, A. R. Synth. Commun. 1996, 26, 3953–3958; (f)
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Regen, S. L. J. Org. Chem. 1980, 45, 4254–4255.
3. Iranpoor, N.; Kazemi, F. Synthesis 1996, 821–822.
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Chem. 1991, 55, 63–65.
(Table 2, entry d) and stilbene oxides (Table 2, entries h
and i), which are otherwise difficult to prepare.14
In conclusion, the present work clearly demonstrates the
synthesis of thiiranes from oxiranes using a catalytic
amount of cyanuric chloride (2 mol %). It is a valid
alternative to the existing methods. The important
features of the present method are mild and solvent-free
reaction conditions, fast reaction rates, high yields of the
products, relatively clean reactions and an inexpensive
and easily available catalyst with low loading.
8. Iranpoor, N.; Tamami, B.; Shekarriz, M. Synth. Commun.
1999, 29, 3313–3321.
3. General procedure
9. Tamami, B.; Borujeny, K. P. Synth. Commun. 2004, 34,
65–70.
10. Tamami, B.; Kolahdoozan, M. Tetrahedron Lett. 2004, 45,
1535–1537.
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1283–1285.
A mixture of epoxide (5 mmol), ammonium thiocyanate
(5 mmol) and cyanuric chloride (2 mol %) was stirred at
room temperature for the specified time (Table 2). After
completion of the reaction (TLC), the reaction mixture
was diluted with water (2 · 10 mL) and extracted with
diethyl ether (3 · 15 mL). The combined organic layers
were dried over anhydrous Na2SO4, concentrated in
vacuo and, if required, purified by column chromato-
graphy (silica gel Merck; 60–120 mesh, petroleum
ether/ethyl acetate 9:1) to afford the pure product.
13. (a) Venkatraman, K.; Wagle, D. R. Tetrahedron Lett.
1979, 32, 3037–3040; (b) Kaminski, Z. J. Synthesis 1987,
917–920; (c) Kunishima, M.; Morita, J.; Kawachi, C.;
Iwasaki, F.; Terao, K.; Tani, S. Synlett 1999, 8, 1255–
1256; (d) Kaminska, J. E.; Kaminski, Z. J.; Gora, J.
Synthesis 1999, 4, 593–596; (e) Rayle, H. L.; Fellmeth, L.
Org. Process Res. Dev. 1999, 3, 172–176; (f) Falorni, M.;
Giacomelli, G.; Porcheddu, A.; Taddei, M. J. Org. Chem.
1999, 64, 8962–8964; (g) De Luca, L.; Giacomelli, G.;
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Lett. 2002, 43, 3413–3414; (o) Bandgar, B. P.; Pandit, S. S.
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3.1. Spectroscopic data for novel compound 2i
Liquid bp 75 ꢁC, IR (CHCl3) 710, 1260, 1305, 1450,
1715, 1805, 2920 cmÀ1 1H NMR (300 MHz, CDCl3)
;
d: 2.35 (d, 1H, J = 6.7 Hz), 2.60 (d, 1H, J = 6.7 Hz),
7.20 (m, 5H, Ar–H), 7.50 (d, 2H, J = 8.1 Ar–H), 7.62
(d, 2H, J = 8.1 Hz, Ar–H). Anal. Calcd for C14H11ClS
(246.5): C, 68.14; H, 4.49; S, 12.99. Found: C, 68.18;
H, 4.51; S, 12.93. EIMS: m/z 246.5 [M+].
References and notes
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779–780.