Efficient rearrangement of epoxides catalyzed by a mixed-valent iron trifluoroacetate [Fe3O(O2CCF3)6(H2O)3]

Article abstract of DOI:10.1016/j.tet.2010.01.102

The mixed-valent oxo-centered triiron(III, III, II) trifluoroacetate complex [Fe₂^IIIFe^IIO(O₂CCF₃)₆(H₂O)₃] was prepared by reacting anhydrous iron(III) chloride with boiling trifluoroacetic acid under nitrogen. The non-hygroscopic and readily available mixed-valent triiron trifluoroacetate complex was found to be an efficient catalyst for the regioselective rearrangement of epoxides. A number of carbonyl compounds formed via the rearrangement of epoxides could be obtained by a simple filtration of the reaction mixture through a short plug of silica gel.

Full text of DOI:10.1016/j.tet.2010.01.102

Tetrahedron 66 (2010) 2373–2377
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Efficient rearrangement of epoxides catalyzed by a mixed-valent iron
trifluoroacetate [Fe3O(O2CCF3)6(H2O)3]
,
b
b,
*
Erkan Ertu¨rk a , Mehmet Go¨llu¨ , Ayhan S. Demir
*
a Chemistry Institute, TUBITAK Marmara Research Center, 41470 Gebze, Kocaeli, Turkey
b Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
a r t i c l e i n f o
a b s t r a c t
The mixed-valent oxo-centered triiron(III, III, II) trifluoroacetate complex [FeI2IIFeIIO(O2CCF3)6(H2O)3] was
prepared by reacting anhydrous iron(III) chloride with boiling trifluoroacetic acid under nitrogen. The
non-hygroscopic and readily available mixed-valent triiron trifluoroacetate complex was found to be an
efficient catalyst for the regioselective rearrangement of epoxides. A number of carbonyl compounds
formed via the rearrangement of epoxides could be obtained by a simple filtration of the reaction
mixture through a short plug of silica gel.
Article history:
Received 14 October 2009
Received in revised form 17 December 2009
Accepted 27 January 2010
Available online 2 February 2010
Keywords:
Epoxide
Ó 2010 Elsevier Ltd. All rights reserved.
Rearrangement
Carbonyl
Iron
Catalysis
1. Introduction
rearrangement, in other words regioselectivity, is influenced by the
migration aptitude of the substituents that are attached to the
Epoxides are one of the most important and versatile precursors
in organic synthesis because they are readily available in racemic
and enantiomerically enriched forms and can be converted into
a variety of highly valuable products, usually in a stereoselective
manner.1 The rearrangement of epoxides (1) catalyzed by Lewis-
acids affords aldehydes (2) via alkyl migration (wR) and/or ketones
(3) via hydrogen migration (wH), easily and atom-economically
(Scheme 1). The product distribution (aldehyde or ketone) of the
oxirane ring, catalyst, and solvent.
After the pioneering work on the epoxide rearrangement to
carbonyl compounds from House,2a Filler and co-workers,2b
Meinwald and co-workers,2c and Rickborn and Gerkin2d,e using
stoichiometric amounts of Lewis- or Brønsted-acid catalysts, the
development of catalytic systems for the epoxide rearrangement
had been neglected for a long period of time until the 1990s. Then,
a number of Lewis-acid catalysts and palladium(0) catalysts were
identified for the rearrangement of epoxides with varying success
in terms of regioselectivity and the amount of catalyst.3–5 Indeed,
although a number of methods have been developed for this
rearrangement, only a few of them are regioselective and truly
catalytic. In this respect, while Pd(0)/PR3 (5 mol %),4b,c Bi(O-
Tf)3$xH2O (0.1 mol %),3k IrCl3$xH2O (1 mol %),3l and Er(OTf)3
(1 mol %)3m are noteworthy for the epoxide rearrangement via
hydrogen migration, chromium(III) tetraphenylporphyrin triflate
(CrTPP(OTf), 1 mol %)4d and chromium(III) phthalocyanine triflate
(CrTBPC(OTf), 1 mol %)4e give the corresponding aldehydes from
epoxides via alkyl migration in a stereoselective manner. The syn-
thetic efficiency of the epoxide rearrangement has also been uti-
lized many times in the literature.6,1b However, there remain
drawbacks and limitations that need to be improved in the existing
methods for the epoxide rearrangement, which include the use of
toxic or expensive metal catalysts, high catalyst loading, narrow
substrate scope, and moderate regioselectivity. Currently, the use of
O
R1
H
R2 R3
2
~R3
~H
R1
R2
H
R3
O
Lewis-acid
1
O
R1
R3
R2
3
Scheme 1. Lewis-acid catalyzed epoxide rearrangement.
* Corresponding authors.
E-mail address: erkan.erturk@mam.gov.tr (E. Ertu¨rk).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.01.102

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E. Ertu¨rk et al. / Tetrahedron 66 (2010) 2373–2377
Table 1
iron-based catalysts is attracting increasing attention, due to eco-
nomic and environmental concerns, since iron salts and complexes
are cost-effective and non-toxic compared to the other metal
counterparts.7 Because of the great abundance of iron in nature
(second most abundant metal in the earth’s crust, 4.7 wt %) and the
environmental concerns, iron salts and iron complexes become the
‘Rising Stars’ for the sustainable chemical industry.7b In the course
of our recent investigations on the addition reactions to epoxides
catalyzed by iron(III) trifluoroacetate [Fe(O2CCF3)3],8–10 we ob-
served that epoxides underwent high yielding reactions to produce
carbonyl products. Surprisingly, our brief literature survey revealed
that only more complex iron(III) tetraphenylporphyrin complex-
es3d,h,i have been utilized as the iron based catalysts for the epoxide
rearrangement so far. We would, therefore, like to report a readily
available mixed-valent oxo-centered trinuclear iron tri-
[FeI2IIFeII(m3-O)(O2CCF3)6(H2O)3] (4) catalyzed rearrangement of epoxidesa
Entry
1
Epoxide
Time (h)
Product
Yield (%)
O
H
3
92
O
1a
2a
O
H
2
3
3
3
88
82
O
1b
2b
O
H
1c
2c
2c
O
fluoroacetate complex, triiron(III, III, II) trifluoroacetate [FeI2IIFeII(m3
-
O)(O2CCF3)6(H2O)3] (4) that is a very efficient catalyst for the
rearrangement of epoxides to carbonyl compounds.
O
4
5
3
3
86
78
H
H
H
1d
O
O
2. Results and discussions
Triiron(III, III, II) trifluoroacetate complex 4 was easily prepared
in 94% yield by reacting anhydrous iron(III) chloride with boiling
trifluoroacetic acid under nitrogen (Scheme 2). The preparation of
mixed-valent iron complex 4 by reacting different iron sources (e.g.,
metalic iron, Fe2O3, Fe(NO3)3$9H2O) with trifluoroacetic acid was
reported in the literature and its structure was well determined by
X-ray analysis.10,11 However, we easily prepared the iron complex 4
from readily available FeCl3 and trifluoroacetic acid. The structure
of 4 was elucidated by means of induced coupled plasma atomic
emission spectroscopy (ICP-AES), elemental analysis (EA), and
O
1e
2d
2d
O
O
O
6b
1
3
74 (2d/2e¼27/73)
1f
2e
thermogravimetric analysis (TGA) and was proven to be [Fe2III
-
FeII(m3-O)(O2CCF3)6(H2O)3].11 The existence of the iron(II) species
was also empirically proven by titration against potassium di-
chromate. Compared to the other iron salts (e.g., FeCl3), the iron
trifluoroacetate complex 4 is remarkably non-hygroscopic and
bench-stable for long periods (longer than 6 months during our
studies) and has an enhanced Lewis-acid character.
7
H
88
72
1g
2f
O
O
H
8b
O
1
1
OH2
1h
1i
2g
O
O
O
O
F3C
F3C
CF3
CF3
Fe
O
O
O
9
Polymerization
No reaction
CF3CO2H
O
O
O
O
FeCl3
reflux, 48 h, N2
Fe
Fe
O
OH2
H2O
10b
24
O
O
1j
O
O
a
The reactions were carried out by employing 1.0 mmol of epoxide in the pres-
CF3
F3C
ence of 2 mol % 4 in dichloromethane at room temperature under nitrogen.
b
The reactions were carried out in 1,2-dichloroethane in an oil bath at 80 ꢀ
C
4, 94%
under nitrogen.
Scheme 2. Preparation of triiron(III, III, II) trifluoroacetate complex [FeI2IIFeII(m3-O)-
(O2CCF3)6(H2O)3] (4).
smoothly gave phenylacetaldehyde (2a) in the same yield in-
dicating [FeI2IIFeII(m3-O)(O2CCF3)6(H2O)3] (4) is the Lewis-acid cat-
alyst for the rearrangement of epoxides. In a similar manner to
styrene oxide (1a), 2-(2-naphthyl)oxirane (1b) could be trans-
formed into the corresponding aldehyde 2b (2-(2-naph-
thyl)acetaldehyde) in 88% yield within 3 h at room temperature in
the presence of 2 mol % 4 (entry 2). The rearrangement of 2,2-
diphenyl oxirane (1c) furnished diphenylacetaldehyde (2c) in 82%
yield (entry 3). The rearrangement of trans-stilbene oxide (1d)
proceeded to give diphenylacetaldehyde (2c) in 86% yield under
full-regioselectivity with exclusive aryl migration (entry 4).
Styrene oxide (1a) was first employed as the model substrate
for the epoxide rearrangement. After the simple optimization of
the rearrangement of styrene oxide (1a) in terms of the catalyst
loading and the yield of the product, 2 mol % 4 in dichloromethane
was found to be optimum. By stirring styrene oxide (1a) in the
presence of 2 mol % 4 at room temperature for 3 h under nitrogen,
phenylacetaldehyde (2a) was obtained in 92% yield (Table 1,
entry 1). It could be speculated that trifluoroacetic acid is the
actual catalyst formed by the partial hydrolysis of 4 with moisture
present in the reaction mixture, if the rearrangement had not
proceeded in the presence of dry K2CO3. Even in the presence of
K2CO3, the rearrangement of styrene oxide (1a) using 2 mol % of 4
a
-Methylstyrene oxide (1e) rearranged into 2-phenylpropanal
(2e) in 78% yield (entry 5). The mixed-valent iron trifluoroacetate

E. Ertu¨rk et al. / Tetrahedron 66 (2010) 2373–2377
2375
complex 4 could not effect the rearrangement of trans-
ylstyrene oxide (1f) at room temperature. By heating the reaction
mixture at 80 ꢀC for 1 h in 1,2-dichloroethane, the rearrangement
b
-meth-
4. Experimental
4.1. General
of trans-b-methylstyrene oxide (1f) proceeded to give 2-phenyl-
propanal (2d) and phenylacetone (2e) in 74% total yield and under
low regioselectivity (2d/2e¼27:73) in favor of phenylacetone (2e)
via the preferential hydrogen migration (entry 6). The rear-
rangement of 1-phenyl-1,2-epoxycyclohexane (1g) led to the ring
contracted product 2f (1-phenyl-1-cyclopentane carboxaldehyde)
All reactions were carried out in oven-dried Schlenk tubes with
magnetic stirring under a positive pressure of nitrogen. Dichloro-
methane and 1,2-dichloroethane were freshly distilled from calcium
hydride prior to use under a nitrogen atmosphere. Epoxides 1a, 1h,
1i, 1j, anhydrous iron(III) chloride, and trifluoroacetic acid were
purchased from Aldrich and used as received. Epoxides 1b, 1d, 1f, 1g
were prepared by the epoxidation of the corresponding olefins with
m-chloroperbenzoic acid.13 Epoxides 1c and 1e were synthesized by
the Corey–Chaykovsky epoxidation of corresponding ketones with
trimethylsulfoxonium iodide. Thin layer chromatography (TLC) was
conducted on aluminum sheets that were pre-coated with silica gel
SIL G/UV254 from MN GmbH & Co., in which the spots were visualized
in 88% yield via alkyl migration (entry 7). a-Pinene oxide (1h), as
a representative for the trisubstituted aliphatic epoxides, had to
be heated at 80 ꢀC for 1 h in 1,2-dichloroethane in the presence of
2 mol % 4 to give the rearranged product 2g (campholenic alde-
hyde) in 72% yield (entry 8). Cyclohexene oxide (1i) underwent
rapid polymerization in the presence of 2 mol % 4 to give poly(-
cyclohexene oxide) (entry 9). However, 1,2-epoxyhexane (1j) was
found to be unreactive toward rearrangement in the presence of
2 mol % 4, even by heating at 80 ꢀC in 1,2-dichloroethane (entry
10). The purity of the products was determined by 1H NMR
spectroscopy. The products 2a, 2c, 2d, and 2f were isolated in
satisfactory NMR purities by simple filtration of the reaction
mixtures through a short plug of silica gel using ca. 100 mL
dichloromethane as the eluent.
in UV-light (
l
¼254 nm) and/or by staining with phosphomolybdic
acid. Chromatographic separations were performed using silica gel
(MN-silicagel 60, 230–400 mesh). 1H and 13C NMR spectra were
recorded on a Bruker DPX400 NMR spectrometer. Chemical shifts
d
are reported in parts per million (ppm) relative to the residual
protons in the NMR solvent (CHCl3: 7.24) and carbon resonance of
the solvent (CDCl3: 77.0). NMR peak multiplicities were given as
d
d
The chiral version of the epoxide rearrangement that was cata-
lyzed by the triiron trifluoroacetate complex 4 was tested by
follows: s¼singlet, d¼doublet, t¼triplet, q¼quartet, m¼multiplet,
br¼broad. Elemental analyses (EA) were performed using a Ther-
moFinnigan FLASH 1112 SERIES EA instrument. ICP-AES was recor-
ded on a Thermo Jarrel Ash AtomScan 25 instrument.
employing enantiomerically enriched (R)-(ꢁ)-
a
a
-methylstyrene ox-
-methylstyrene by
ide (1e, 54% ee), which was prepared from
enantioselective epoxidation with
a Jacobsen catalyst ((R,R)-
(ꢁ)-N,N0-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamino-
manganese(III) chloride). The enantiomeric excess of 1e was
determined by HPLC (Chiralpak OD; n-hexane/iPrOH (99:1);
0.5 mL/min; tR¼12.3 min (ent-1e), tR¼13.5 (1e)). The primary
product of the rearrangement (2-phenylpropanal, 2d) was then
transformed into the corresponding alcohol 5 by sodium borohy-
dride reduction since a better enantiomeric separation for 5 and
ent-5 could be performed by HPLC. However, the enantiopurity of
1e was predominantly lost after the rearrangement and the sub-
sequent sodium borohydride reduction (5, 7% ee, Scheme 3). During
the rearrangement of 1e, we are expecting the preferential migra-
tion of the hydride syn to the less hindered site of the epoxide ring
(Me vs Ph) resulting in the selective formation of 2d accompanied
by the partial inversion of the starting epoxide 1e. The favored
migration of hydride syn to the less hindered site of the epoxide
ring has been already observed in the MABR catalyzed rearrange-
4.1.1. Preparation of the iron trifluoroacetate complex [FeI2IIFeII(m3-O)-
(O2CCF3)6(H2O)3] (4). Anhydrous iron(III) chloride (1.62 g,
10.0 mmol) and 16 mL of trifluoroacetic acid were added into
a 100 mL one-necked round bottomed flask. The mixture was then
refluxed under a nitrogen atmosphere for 48 h. After the removal of
theexcessivetrifluoroaceticacidbyrotaryevaporationunderreduced
pressure, the residue was filtered off using a sintered glass funnel and
washed with a plenty of n-hexane. The light orange solid was dried
under vacuum (approx. 10ꢁ3 mbar) at 80 ꢀC for 12 h. The iron tri-
fluoroacetate complex 4 was obtained as a light orange powder
(2.87 g, 3.13 mmol, 94%). Mp: 151–173 ꢀC (decomposition). EA: Anal.
Calcd for C12H6F18Fe3O16: C, 15.74; H, 0.66. Found: C, 16.12; H, 0.95.
ICP-AES: Anal. Calcd for C12H6F18Fe3O16: Fe, 18.30. Found: Fe, 18.20.
4.1.2. Phenylacetaldehyde3o (2a, typical procedure for the re-
arrangement of the epoxides). The iron trifluoroacetae complex 4
(18 mg, 20 mmol, 2 mol %) was placed in an oven-dried Schlenk tube
ment of
a,
a
-disubstituted epoxides by Yamamoto et al.12
and then the tube was capped with a glass stopper. The tube was
evacuated for 15 min and back-filled with nitrogen. The glass
stopper was replaced with a rubber septum under positive pressure
of nitrogen. After addition of dry dichloromethane (5 mL) as the
solvent, styrene oxide (1a, 120 mg, 1.0 mmol) was dropwise added
to the suspension at room temperature. Upon addition of the ep-
oxide, a homogenous solution formed instantaneously. The re-
action progress was monitored by TLC. After completion of the
reaction (room temperature, 3 h), the reaction mixture was filtered
through a short plug of silica gel using dichloromethane (100 mL)
as the eluent. After removing the solvent by rotary evaporation
under reduced pressure, phenylacetaldehyde (2a, 110 mg,
0.92 mmol, 92%) was obtained as a colorless oil. Rf¼0.23 (silica gel,
O
4 (2 mol%)
H
NaBH4
MeOH
CH2Cl2
O
OH
rt, 3 h, N2
1e
2d
5
54% ee
78%
94%, 7% ee
a-methylstyrene oxide (1e).
Scheme 3. Rearrangement of chiral
3. Conclusions
In conclusion, we have shown that 2 mol % of the readily
-
available mixed-valent iron trifluoroacetate complex 4 [Fe2III
FeII(m3-O)(O2CCF3)6(H2O)3] can catalyze the regioselective rear-
rangement of a wide variety epoxides to carbonyl compounds. In
general, the products were able to be isolated in high yields by the
simple filtration of the reaction mixtures through a short plug of
silica gel. The non-toxicity, ready availability of the iron tri-
fluoroacetate complex 4 along with the great abundance of iron in
nature make this catalytic system rather attractive for large scale
applications.
n-hexane/EtOAc 10:0.4). 1H NMR (400 MHz, CDCl3):
d
¼3.61 (d, 3JH–
¼2.0 Hz, 2H, CH2), 7.14–7.16 (m, 2H, Haryl), 7.24–7.32 (m, 3H, Haryl),
H
9.67 (t, 3JH–H¼2.0 Hz, 1H, CHO). 13C NMR (100 MHz, CDCl3):
¼50.5,
d
127.3, 128.9, 129.5, 131.8, 199.2.
4.1.3. 2-(2-Naphthyl)acetaldehyde3c (2b). After stirring 2-(2-naph-
thyl)oxirane (1b, 170 mg, 1.0 mmol) in the presence of 2 mol % 4 in
dichloromethane (5 mL) at room temperature for 3 h under

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E. Ertu¨rk et al. / Tetrahedron 66 (2010) 2373–2377
nitrogen, the rearranged product 2b was obtained as a colorless oil
(150 mg, 0.88 mmol, 88%) via column chromatographic purifica-
tion. Rf¼0.21 (silica gel, n-hexane/EtOAc 10:0.5). 1H NMR (400 MHz,
methylstyene oxide (1e, 54% ee) in the presence of 2 mol % 4 was
reduced to 2-phenyl-1-propanol (5) with sodium borohydride in
methanol. The alcohol product 5 (94%) was purified by flash chro-
matography. Rf¼0.42 (silica gel, n-hexane/EtOAc 5:1). 1H NMR
3
3
CDCl3):
d
¼3.69 (d, JH–H¼2.4 Hz, 2H, CH2), 7.18 (dd, JH–H¼8.4 Hz,
4JH–H¼1.6 Hz, 1H, Haryl), 7.35–7.38 (m, 2H, Haryl), 7.54 (s, 1H, Haryl),
(400 MHz, CDCl3):
d
¼1.28 (d, 3JH–H¼8.0 Hz, 3H, CH3), 2.94 (q, 3JH–H
¼
3
7.67–7.73 (m, 3H, Haryl), 9.67 (t, JH–H¼2.4 Hz, 1H, CHO). 13C NMR
8.0 Hz, 1H, CH), 3.69 (d, 3JH–H¼8.0 Hz, 2H,CH2OH), 7.22–7.25 (m, 3H,
Haryl), 7.30–7.34 (m, 2H, Haryl). HPLC: Chiralpak AD-H; n-hex-
ane/iPrOH (99.5:0.5); 1 mL/min; tR¼86.5 min (5), tR¼107.8 min
(ent-5).
(100 MHz, CDCl3):
128.7, 129.4, 132.5, 133.5, 199.2.
d
¼50.6, 126.0, 126.4, 127.4, 127.5, 127.7, 128.4,
4.1.4. Diphenylacetaldehyde3c (2c). After stirring 2,2-diphenyl oxir-
ane (1c, 196 mg, 1.0 mmol) in the presence of 2 mol % 4 in
dichloromethane (5 mL) at room temperature for 3 h under nitro-
gen, the rearranged product 2c was obtained as a colorless oil
(161 mg, 0.82 mmol, 82%) via simple filtration through a short plug
of silica gel using dichloromethane (100 mL) as the eluent. Rf¼0.20
Acknowledgements
This work was supported by the Scientific and Technological
Research Council of Turkey (TUBITAK), the Turkish Academy of
Science, and the Middle East Technical University (METU). We
thank Mr. Murat Koral (Chemistry Institute, TUBITAK Marmara
Research Center) for performing ICP-AES analysis.
(silica gel, n-hexane/EtOAc 10:0.5). 1H NMR (400 MHz, CDCl3):
3
d
¼4.81 (d, JH–H¼2.4 Hz, 1H, CH), 7.14–7.32 (m, 10H, Haryl), 9.87
(d, 3JH–H¼2.4 Hz, 1H, CHO).
References and notes
4.1.5. 2-Phenylpropanal3n (2d). After stirring
a-methylstyrene oxide
(1e, 134 mg, 1.0 mmol) in the presence of 2 mol % 4 in dichloro-
methane (5 mL) at room temperature for 3 h under nitrogen, the
rearranged product 2d was obtained as a colorless oil (105 mg,
0.78 mmol, 78%) via simple filtration through a short plug of silica
gel using dichloromethane (100 mL) as the eluent. Rf¼0.32 (silica gel,
1. (a) Smith, J. G. Synthesis 1984, 629–656; (b) Crotti, P.; Pineshi, M. In Aziridines
and Epoxides in Organic Synthesis; Yudin, A. K., Ed.; Wiley-VCH: Weinheim,
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2. For the epoxide rearrangement catalyzed by excessive BF3$OEt2, see: (a) House,
H. O. J. Am. Chem. Soc. 1955, 77, 3070–3075 catalyzed by 1.00 equiv MgBr2$OEt2,
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d
¼1.37 (d, 3JH–H
¼
4.0 Hz, 3H, CH3), 3.54 (dq, 3JH–H¼1.2 Hz, 3JH–H¼7.6 Hz, 1H, CH), 7.06–
7.31 (m, 5H, Haryl), 9.60 (d, 3JH–H¼1.4 Hz, 1H, CHO).
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C.; Pillinger, K. S.; Graham, A. E. Tetrahedron Lett. 2006, 47, 5919–5921 catalyzed
by mesoporous aluminosilicates, see: (o) Robinson, M. W. C.; Davies, A. M.;
Buckle, R.; Mabbet, I.; Taylor, S. H.; Graham, A. E. Org. Biomol. Chem. 2009, 7,
2559–2564.
4.1.6. 2-Phenylpropanal3n (2d) and phenylacetone14 (2e). After stir-
ring trans-b-methylstyrene oxide (1f, 134 mg, 1.0 mmol) in the
presence of 2 mol % 4 in 1,2-dichloroethane (5 mL) in an oil bath at
80 ꢀC for 1 h under nitrogen, 2-phenylpropanal (2d) and phenyl-
acetone (2e) were obtained in 74% total yield (99 mg, 0.74 mmol) via
simple filtration through a short plug of silica gel using dichloro-
methane (100 mL) as the eluent. The regioisomeric ratio was found
to be 2d/2e¼27:73 by means of 1H NMR. Compound 2e: Rf¼0.20
(silica gel, n-hexane/EtOAc 10:0.5). 1H NMR (400 MHz, CDCl3):
d¼2.08 (s, 3H, CH3), 3.63 (s, 2H, CH2), 7.13–7.31 (m, 5H, Haryl).
4.1.7. 1-Phenyl-1-cyclopentane carboxaldehyde4d (2f). After stirring
1-phenyl-1,2-epoxycyclohexane (1g, 174 mg, 1.0 mmol) in the
presence of 2 mol % 4 in dichloromethane (5 mL) at room temper-
ature for 3 h under nitrogen, the ring-contracted product 2f was
isolated as a colorless oil (153 mg, 0.88 mmol, 88%) via simple fil-
tration through a short plug of silica gel using dichloromethane
(100 mL) as the eluent. Rf¼0.46 (silica gel, n-hexane/EtOAc 10:0.5).
1H NMR (400 MHz, CDCl3):
d
¼1.54–1.60 (m, 2H), 1.64–1.68 (m, 2H),
4. For the regioselective epoxide rearrangement affording aldehydes via alkyl
migration catalyzed by methylaluminum bis(4-bromo-2,6-di-tert-butylphen-
oxide) (MABR), see: (a) Maruoka, K.; Ooi, T.; Yamamoto, H. J. Am. Chem. Soc.
1989, 111, 6431–6432; (b) Ref. 3a; catalyzed by B(C6F5)3, see: (c) Ishihara, K.;
Hanaki, N.; Yamamoto, H. Synlett 1995, 721–722 catalyzed by chromium(III)
tetraphenylporphyrin triflate (CrTPP(OTf)), see: (d) Suda, K.; Kikkawa, T.; Na-
kajima, S.; Takanami, T. J. Am. Chem. Soc. 2004, 126, 9554–9555 catalyzed by
a chromium(III) phthalocyanine complex (CrTBPC(OTf)), see: (e) Suda, K.; Na-
kajima, S.; Satoh, Y.; Takanami, T. Chem. Commun. 2009, 1255–1257.
1.76–1.83 (m, 2H), 2.41–2.47 (m, 2H), 7.15–7.19 (m, 3H, Haryl), 7.24–
7.28 (m, 2H, Haryl), 9.31 (s, 1H, CHO). 13C NMR (100 MHz, CDCl3):
d¼24.2, 32.3, 63.6, 127.1, 127.6, 128.7, 140.3, 200.6.
4.1.8. Campholenic aldehyde15 (2g). After stirring
a-pinene oxide
(1g, 152 mg, 1.0 mmol) in the presence of 2 mol % 4 in 1,2-di-
chloroethane (5 mL) in an oil bath at 80 ꢀC for 1 h under nitrogen,
campholenic aldehyde (2 g) was obtained as a colorless oil (109 mg,
0.72 mmol, 72%) via column chromatographic purification. Rf¼0.37
(silica gel, n-hexane/EtOAc 10:0.5). 1H NMR (400 MHz, CDCl3):
5. For the stereoselective rearrangement of
a,b-epoxy acylates catalyzed by
BF3$OEt2, see: (a) Kita, Y.; Kitagaki, S.; Yoshida, Y.; Mihara, S.; Fang, D.-F.; Kondo,
M.; Okamoto, S.; Imai, R.; Akai, S.; Fujioka, H. J. Org. Chem. 1997, 62, 4991–4997
for the kinetic resolution of enol ester epoxides catalyzed by [(R)-BINOL]2/
Ti(OiPr)4, see: (b) Feng, X.; Shu, L.; Shi, Y. J. Org. Chem. 2002, 67, 2831–2836 for
the rearrangement of disubstituted vinyl epoxides catalyzed by Ga(OTf)3, see:
(c) Deng, X.-M.; Sun, X.-L.; Tang, Y. J. Org. Chem. 2005, 70, 6537–6540 for the
stereoselective rearrangement of chiral 2,3-epoxy alcohols catalyzed by SnCl4,
see: (d) Kita, Y.; Matsuda, S.; Inoguchi, R.; Ganesh, J. K.; Fujioka, H. Tetrahedron
Lett. 2005, 46, 89–91; (e) Kita, Y.; Matsuda, S.; Inoguchi, R.; Ganesh, J. K.; Fu-
jioka, H. J. Org. Chem. 2006, 71, 5191–5197 for the stereoselective rearrangement
of chiral spiro oxiranes catalyzed by Et2AlCl or LiI, see: (f) Shen, Y.-M.; Wang, B.;
Shi, Y. Angew. Chem., Int. Ed. 2006, 45, 1429–1432.
d
¼0.79 (s, 3H, CH3), 1.00 (s, 3H, CH3), 1.61–1.62 (m, 3H, CH3), 1.85–
1.93 (m,1H), 2.25–2.31 (m,1H), 2.34–2.42 (m, 2H), 2.52 (ddd, 3JH–H
¼
3
3
2.0 Hz, JH–H¼4.4 Hz, JH–H¼15.6 Hz, 1H), 5.23 (m, 1H), 9.80 (t,
3JH–H¼2.4 Hz, 1H, CHO). 13C NMR (100 MHz, CDCl3):
¼12.5, 20.0,
d
25.6, 35.5, 44.2, 45.0, 46.9, 121.5, 147.9, 202.8.
4.1.9. 2-Phenyl-1-propanol16 (5). 2-Phenylpropanal (2d) prepared
by the rearrangement of enantiomerically enriched (R)-(ꢁ)-
6. For the representative synthetic applications of the epoxide rearrangement,
see: (a) Kita, Y.; Furukawa, A.; Futamura, J.; Ueda, K.; Sawama, Y.; Hamamoto,
a
-

E. Ertu¨rk et al. / Tetrahedron 66 (2010) 2373–2377
2377
H.; Fujioka, H. J. Org. Chem. 2001, 66, 8779–8786; (b) Kita, Y.; Futamura, J.; Ohba,
Y.; Sawama, Y.; Ganesh, J. K.; Fujioka, H. J. Org. Chem. 2003, 68, 5917–5924; (c)
Islas-Gonza´les, G.; Benet-Buchholz, J.; Maestro, M. A.; Riera, A.; Perica`s, M. A. J.
Org. Chem. 2006, 71, 1537–1544.
7. (a) Bolm, C.; Legros, J.; Paih, J. L.; Zani, L. Chem. Rev. 2004, 104, 6217–6254; (b)
Enthaler, S.; Junge, K.; Beller, M. Angew. Chem., Int. Ed. 2008, 47, 3317–3321.
8. Ertu¨rk, E.; Demir, A. S. ARKIVOC 2008, ii, 160–171.
9. For the other catalytic applications of Fe(O2CCF3)3, see: (a) Iranpoor, N.; Adibi,
H. Bull. Chem. Soc. Jpn. 2000, 73, 675–680; (b) Adibi, H.; Jafari, H. J. Fluorine
Chem. 2007, 128, 679–682; (c) Adibi, H.; Samimi, H. A.; Beygzadeh, M. Catal.
Commun. 2007, 8, 2119–2124; (d) Firouzabadi, H.; Iranpoor, N.; Jafari, A. A.;
Jafari, M. R. J. Organomet. Chem. 2008, 693, 2711–2714.
However, such a structure Fe(O2CCF3)3 doesn’t exist. The actual structure of the
iron trifluoroacetate complex obtained by reacting FeCl3 with boiling CF3CO2H
is [FeI2IIFeII(m3-O)(O2CCF3)6(H2O)3]. For an excellent review on iron carboxylate
complexes and their properties in biology and chemistry, see: (b) Lippard, S. J.
Angew. Chem., Int. Ed. Engl. 1988, 27, 344–361.
11. (a) Ponomarev, V. I.; Filipenko, O. S.; Atovmyan, L. O.; Bobkova, S. A.; Turte, K. I.
Sov. Phys. Dokl. 1982, 27, 6–9; (b) Tapper, A. E.; Long, J. R.; Staples, R. J.; Stav-
ropoulos, P. Angew. Chem., Int. Ed. 2000, 39, 2343–2346; (c) Glazunova, T. Y.;
Boltalin, A. I.; Troyanov, S. I. Mendeleev Commun. 2004, 14, 141–143.
12. Maruoka, K.; Ooi, T.; Yamamoto, H. Tetrahedron 1992, 48, 3303–3312.
13. Page, P. C. B.; Buckley, B. R.; Barros, D.; Blacker, A. J.; Heaney, H.; Marples, B. A.
Tetrahedron 2006, 62, 6607–6613.
10. In our previous publication (Ref. 8) and in Refs. 9a–d, it was reported that
iron(III) trifluoroacetate [Fe(O2CCF3)3] was formed by reacting FeCl3 with
boiling CF3CO2H under nitrogen based on the results reported in: (a) Baillie, M.
J.; Brown, D. H.; Moss, K. C.; Sharp, D. W. A. J. Chem. Soc. A 1968, 3110–3114
14. Li, L.; Guo, Q.; Xue, S. J. Org. Chem. 2008, 73, 3516–3522.
´
15. Constantino, M. G.; Junior, V. L.; Inverzina, P. R.; Filho, L. C. S.; Silva, G. V. J. Synth.
Commun. 2007, 37, 3529–3539.
´
´
16. Gomez, C.; Macia, B.; Lillo, V. J.; Yus, M. Tetrahedron 2006, 62, 9832–9839.