370 J. CHEM. RESEARCH (S), 1999
J. Chem. Research (S),
1999, 370^371y
Iron(III) 5,10,15,20-Tetrakis (pentafluorophenyl)-
porphyrin as an Efficient Catalyst for
Conversion of Epoxides to Thiiranesy
Shahram Tangestaninejad* and Valiollah Mirkhani
Department of Chemistry, Esfahan University, Esfahan 81744, Iran
Iron(III) 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, FeꢀTF5PPCl, is a new catalyst for the conversion of
epoxides to the corresponding thiiranes in the presence of ammonium thiocyanate in excellent yields.
Although metalloporphyrins are widely used as redox
Table
1 Conversion of epoxides to thiiranes with
6
catalysts1
there have been few studies on their catalytic
Fe(TF5PP)Cl/NH4SCN in refluxing MeCN
Entry
1
Substrate
Product
t/min Yield(%)a,b
activity as Lewis acids. The catalytic role of iron and
manganese tetraphenylporphyrins as mild Lewis acids have
been investigated in several reactions such as rearrangement
of oxaziridines,7;8 isomerization of epoxides9 and silylation
of hydroxyl groups.10;11 Recently the use of ruthenium
trichloride in the reaction of thiocyanate with epoxides
was reported.12 The catalytic activity is considered due to
the high electrophilic nature of the central ruthenium ion.
Here, we report that such catalytic activity can be observed
with an iron porphyrin if an electron de¢cient porphyrin
is used as the ligand.
As shown in Table 1, di¡erent aliphatic and cyclic epoxides
react rapidly with ammonium thiocyante in the presence of
0.02 molar equivalents of iron(iii) 5,10,15,20-tetrakis-
(penta£uorophenyl)porphyrin chloride, FeꢀTF5PPCl, in
re£uxing acetonitrile a¡ording the corresponding thiiranes
(Scheme 1).
O
S
15
95
O
S
C
H
CH2
C
H
CH2
2
3
20
25
92
95
O
S
ClCH2
C
H
CH2
O
ClCH2
C
H
CH2
S
4
5
OCH2CH
OCH2CH CH2
15
20
95
95
CH2
O
S
(CH3)2CHOCH2
O
C
H
CH2 (CH3)2CHOCH2
C
H
CH2
S
O
O
6
7
20
15
94
95
O
S
aAll products were identified by comparison of their physical and
spectral data with those of authentic samples. b Yields refer to
isolated products.
O
S
i
R
C
H
CH2
R
C
H
CH2
92–95%
Experimental
Scheme 1 Reagents and conditions: i, FeꢀTF5PPCl (0.02 mol
All chemicals used were of reagent grade. 5,10,15,20-Tetrakis
(penta£uorophenyl)porphyrin was prepared and metallated according
to the literature.14;15
General Procedure for Conversion of Epoxides to Thiiranes.öIn a
round-bottomed £ask (25 mL) equipped with
magnetic stirrer, a solution of epoxide (1mmol) in MeCN (5 mL)
was prepared. Ammonium thiocyanate (0.152 g, 2 mmol) and
Fe(TF5PP)Cl (0.021g, 0.02 mmol) were added to the resulting solution
and the reaction mixture stirred magnetically under re£ux. 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 quantitative
yield. Distillation of the product under reduced pressure resulted in
the corresponding thiirane in 92^95% yield, without any
polymerization by-products.
equiv.), NH4SCN, MeCN, reflux, 15^25 min.
The reaction of styrene oxide with ammonium thiocyanate
in the presence of Fe(TF5PP)Cl under re£ux was completed
in 20 min giving styrene sul¢de in 92% isolated yield, without
polymerization. By contrast, iron(iii) tetraphenylporphyrin
chloride, Fe(TPP)Cl was not e¤cient for this reaction and
only 7% yield was obtained under the same reaction con-
ditions. Therefore, the electron-withdrawing character of
the per£uorophenyl substituents of the ligand strongly raises
the electrophilic nature of the central iron ion.
The e¡ect of other solvents such as acetone, dichloro-
methane, chloroform and carbon tetrachloride was also
studied. Compared to acetonitrile, longer reaction times
and considerably lower yields were observed.
Control experiments carried out on the epoxides showed
that, in the absence of the catalyst, no conversion of epoxides
to thiirane compounds occurs over short reaction times.
Conversion of epoxides to thiiranes using thiourea as
another sulfur-introducing reagent has also been reported
under wet conditions (solvent free) or in aqueous ethanol
in the absence of catalyst.13 For example, the reaction of
styrene oxide with wet thiourea has been reported to a¡ord
styrene episul¢de in 45% yield after 10 h. The reaction of
cyclic epoxides with thiourea in aqueous ethanol su¡ers from
the drawback of long reaction times and low yields.13
a condenser and
Partial support of this work by Esfahan University
Research Council is gratefully acknowledged.
Received, 15th September 1998; Accepted, 24th February 1999
Paper E/8/07196I
References
1
2
3
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B. Meunier, Chem. Rev., 1992, 92, 1411.
M. Sono, M. P. Roach, E. D. Coulter and J. H. Dawson,
Chem. Rev., 1996, 96, 2841.
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A. J. Appleton, S. Evans and J. R. Lindsay Smith, J. Chem.
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A. Maldotti, C. Bartocci, G. Varani, A. Molinari, P. Battioni
and D. Mansuy, Inorg. Chem., 1996, 35, 1126.
D. Dolphin, T. G. Traylor and L. Y. Xie, Acc. Chem. Res.,
1997, 30, 251.
* To receive any correspondence.
y This is a Short Paper as de¢ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1999, Issue 1]; there is
therefore no corresponding material in J. Chem. Research (M).
Tangestaninejad, Shahram
