Fe(III) substituted Wells-Dawson type polyoxometalate: An efficient catalyst for ring opening of epoxides with aromatic amines

Article abstract of DOI:10.1016/j.inoche.2012.11.005

Various β-aminoalcohols were prepared by the ring opening reaction of epoxides with aromatic amines in the presence of Fe(III) substituted Wells-Dawson type polyoxometalate, α₂-[(n-C₄H ₉)₄N]₇P₂

Full text of DOI:10.1016/j.inoche.2012.11.005

Inorganic Chemistry Communications 28 (2013) 37–40
Contents lists available at SciVerse ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Fe(III) substituted Wells–Dawson type polyoxometalate: An efficient catalyst for ring
opening of epoxides with aromatic amines
⁎
N. Aramesh, B. Yadollahi , V. Mirkhani
Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Various β-aminoalcohols were prepared by the ring opening reaction of epoxides with aromatic amines in
the presence of Fe(III) substituted Wells–Dawson type polyoxometalate, α2-[(n-C4H9)4N]7P2W17FeO61·3H2O,
as an efficient catalyst. The reaction was performed under neutral condition at room temperature and afforded
the corresponding products in high to excellent yields.
Received 2 September 2012
Accepted 15 November 2012
Available online 23 November 2012
© 2012 Elsevier B.V. All rights reserved.
Keywords:
Catalysis
Ring opening
Epoxides
Aromatic amines
Aminolysis
Introduction
several profitable promoters or catalysts for ring opening epoxides
have been reported such as: phosphomolybdic acid (PMA)-Al2O3 [9],
Polyoxometalate as an inorganic metal oxygen cluster anions, be-
cause of unique and intriguing properties including sizes, shapes, the
variety of compositions, redox potentials, acidity and solubility, has
attracted much attention in the recent decades. They have been cov-
ering a large area studied in the fields of chemistry, physics, biology
(TBA)4PFeW11O39·3H2O [10], silica and alumina/modified alumina
[11], zinc(II) and copper(II) [12], N,N-bis[3,5-bis(trifluoromethyl)
phenyl]-thiourea [13], [Ti(o-i-pr)4] [14], trifluoroethanol [15], metal
triflates such as Sn(OTf)2 [16], Cu(OTf)2 [17], Sm(OTf)3 [17], Al(OTf)3
[18], Er(OTf)3 [19], metal halides such as InCl3 [20], BiCl3 [21], SbCl3
[22], ZnCl2 [23], InBr3 [24], CoCl2 [25] and Y(NO3)3·6H2O [26]. In spite
of a broad set of available activators, because of the existence of
some defects in this methods such as high temperatures, low yields,
rearrangement of epoxides and by-products, long reaction times, and
high amount of catalysts, it is necessity to most study modification of
methods for the synthesis of β-aminoalcohols.
In this work, for the first time we were interested to investigate the
catalytic application of transition metal substituted Wells–Dawson type
polyoxometalate in the ring opening reaction of epoxides with amines
at room temperature. Thus, we report Fe(III) substituted polyoxometalate
α2-[(n-C4H9)4N]7P2W17FeO61·3H2O as an efficient, inexpensive and use-
ful catalyst for the synthesis of β-aminoalcohols.
and material science [1]. Up to the present, the Keggin {XM12O40
}
and Wells–Dawson {X2M18O62} (where M=W, Mo, less frequently
V and most common X=P, Si) structures have been most studied
[1,2]. Among diver applications of POMs, their catalytic activity is
the most important and much conspicuous. Various catalytic reac-
tions in the presence of Keggin type polyoxometalates as catalyst
have been reported [1]. However, the Wells–Dawson type heteropoly
compounds had a relatively poor study in the catalytic reactions. So,
in the context of our works [3] on the catalytic applications of
polyoxometalates, the transition metal substituted Wells–Dawson
type polyoxometalates were used as catalyst in the ring opening
of epoxides by amines.
The oxygen-containing heterocycles are well-known carbon
electrophiles capable of reacting with several nucleophiles to provide
1,2-difunctional products [4]. Ring opening reaction of epoxides with
amines gave ß-aminoalcohols that are extensively used in the synthesis
of neutral products [5] and biologically active compounds [6], as
pharmaceuticals and medicine [7], as a powerful source of chirality and
also as insecticidal agents [8]. Due to the direct aminolysis of epoxides
perform with a large excess of amines at elevated temperatures,
Experimental.
General
The tetrabuthylammonium salts of Wells–Dawson type
polyoxometalates were prepared according to the literature [27]. All
catalysts were characterized by UV–vis and IR spectroscopy and TG
analysis. Infrared spectra were recorded on a Shimadzu IR-435 spectro-
photometer. The UV–vis spectra were recorded on a Variane Carey-5A
⁎
Corresponding author. Fax: +98 311 6689732.
E-mail addresses: yadollahi@chem.ui.ac.ir, yadollahi.b@gmail.com (B. Yadollahi).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.inoche.2012.11.005

38
N. Aramesh et al. / Inorganic Chemistry Communications 28 (2013) 37–40
Table 1
instrument. The GC analyses were performed on a Shimadzu GC-16A in-
strumentwith a flame-ionization detectorusing silicon DC-200 column.
1H NMR spectra were recorded on a Bruker AW 300 (300 MHz) spec-
trometer. Products were characterized by comparison of their spectral
and physical data with those of known samples. All yields refer to isolat-
ed products. Chemicals were purchased from Fluka and Merck chemical
companies. The chemical purities of all epoxides were checked by gas
Aminolysis of cyclohexane oxide catalyzed by transition metal Wells–Dawson
polyoxometalates.
Entry
Catalysta
Yieldb
1
2
3
4
5
6
7
8
α2-[K7P2W17O61(Fe3+·OH2)]·8H2O
α2-[K7P2W17O61(Mn3+·OH2)]·12H2O
α2-[K8P2W17O61(Co2+·OH2)]·16H2O
α2-[K8P2W17O61(Ni2+·OH2)]·17H2O
α2-[K8P2W17O61(Cu2+·OH2)]·16H2O
α2-[K8P2W17O61(Zn2+·OH2)]·8H2O
α2-[(n-C4H9)4N]7P2W17FeO61·3H2O
α2-[(n-C4H9)4N]7P2W17MnO61·3H2O
α2-[(n-C4H9)4N]8P2W17CoO61·3H2O
α2-[(n-C4H9)4N]8P2W17NiO61·3H2O
α2-[(n-C4H9)4N]8P2W17CuO61·3H2O
α2-[(n-C4H9)4N]8P2W17ZnO61·3H2O
4
14
13
7
5
3
96
15
13
8
4
3
chromatography and confirmed to be higher than 98%.
n−
Transition metal substituted polyoxometalates, [P2W17MO61
]
(M=Mn, Fe, Co, Cu, Ni, Zn), prepared according to the literature [27].
9
10
11
12
Aminolysis of epoxides
To a solution of epoxides (1 mmol) and amines (1.1 mmol) in ace-
tonitrile (3 mL) were added the α2-[(n-C4H9)4N]7P2W17FeO61·3H2O
(0.03 mmol). The reaction mixtures were stirred at room tempera-
ture for the appropriate time according to Table 2. TLC or GC indicated
progress and the completion of the reaction. Evaporation of the sol-
vent followed by plate chromatography on a plate of silica gel gave
the pure product (Table 2). All of the compounds were fully charac-
terized by IR, 1H NMR, and 13C NMR by comparison with the known
compounds.
a
3 mol% of catalyst was used.
Yields refer to isolated product.
b
of 1/1.1, in proper reaction times gave β-aminoalcohol with high to ex-
cellent yields.
Cyclohexene oxide (1 mmol) was treated with 1.1 mmol of aniline
and 0.03 mmol of catalyst at room temperature and after 40 min a quan-
titative yield of corresponding β-aminoalcohol was performed (Table 2,
entry 1). To show the scope of the reaction, we extended it to a variety
of aromatic amines and epoxides. In all cases, a very clean reaction was
observed and the aminoalcohols had trans stereochemistry. The trans-
configuration of aminoalcohols was assigned by 1H NMR spectrum.
In all cases, the reactions are performed at room temperature in
MeCN. In the reaction of cyclohexene oxide (Table 2, entry 1), except
2-nitroaniline, aminolysis was performed in a short time with quantita-
tive yields. The reaction of styrene oxide as an active epoxide (Table 2,
entry 2) has been completed with all of amines in 100–180 min. As
expected in the case of styrene oxide α-amino was obtained as the
major product (α/β=95/5) due to the formation of the stabilized ben-
zylic cation during the reaction. In order to see the effect of polar
electron-withdrawing groups adjacent to the epoxide's ring, the reaction
of chloromethyl oxirane with amines was studied (Table 2, entry 6). In
comparison with 1-hexene epoxide, which have an electron-donating
group adjacent to the epoxide's ring (Table 2, entry 4), longer times for
chloromethyl oxirane show the effect of polar electron-withdrawing
groups. Sterically more hindered anilines such as 2-methylaniline led
to the β-aminoalcohols still in excellent yields and not have any pro-
found effect on their reactivity toward ring opening of epoxide. As
shown in Table 2, the reaction was also efficient with the secondary
N-methylaniline.
Results and discussion
In this paper, the catalytic effects of transition metal substituted
n−
Wells–Dawson type polyoxometalates, [P2W17MO61
]
(M=Mn, Fe,
Co, Cu, Ni, Zn), in aminolysis of epoxides to β-aminoalcohols in acetoni-
trile have been reported (Scheme 1). These catalysts are readily available,
and the structure and composition of them confirmed by IR, UV–vis and
elemental analysis [27]. The results of thermal gravimetric analysis
(between 40 and 600 °C) on these catalysts indicated that the hydra-
tion numbers are about 3.
The best reaction conditions were found by study on cyclohexene
oxide as a model substrate. At first, to obtain the best catalyst, the
aminolysis of cyclohexene oxide in the presence of catalytic amounts
of various polyoxometalates [P2W17MO61]
n− (M=Mn, Fe, Co, Cu, Ni, Zn)
was performed. All of the reactions were carried out in acetonitrile at
room temperature with magnetic stirring. Although the reaction without
catalyst after 24 h gave a trace amount of product (below 5%), it was pre-
ceded catalytically upon addition of polyoxometalates. Among the cata-
7−
lysts tested, TBA salt of [P2W17FeO61
]
was found to be highly active
for this reaction (Table 1, entry 7). In this catalyst, Fe(III) acts as a good
Lewis acid and so it can play a very important role in catalytic perfor-
mance compared with the other metals. The catalytic activity for the
other catalysts appeared in Table 1.
In the next step various amounts of the catalyst (10, 5, 3, 2.5, and
2 mol%) were investigated and 3 mol% of the catalyst gave the best
result in the aminolysis of cyclohexene oxide. Among various solvents
tested, we chose the CH3CN as the best solvent for the ring opening of
epoxides. Lower catalytic activities were observed with other solvents
such as CH2Cl2, CH3Cl, THF, and n-C6H12. The optimum amount of
amine in this system was found 1.1 mmol and when the higher amount
of amine was employed, a significant increase in the β-aminoalcohol
was not observed. The catalytic reaction with substrate/amine ratios
Finally, in comparison between two types of polyoxometalates,
the Wells–Dawson type has larger molecular size than the Keggin
type polyoxometalates and shows higher potential for coordination
to transition metals. In literatures, a few works about the catalytic
effect of Wells–Dawson type polyoxometalates are reported. For this
reason and in comparison between catalytic effects of transition
metal substituted Keggin and Wells–Dawson type polyoxometalates,
the aminolysis of epoxides was performed. Our results showed that
Fe(III) substituted Wells–Dawson type polyoxometalate can act very
well and lesser catalytic amount of polyoxometalate is needed.
Conclusion
OH
O
In this report, we have developed an efficient approach for
the preparation of β- aminoalcohols. We have introduced α2-
[(n-C4H9)4N]7P2W17FeO61·3H2O as a efficient, non toxic, available,
and stable catalyst in the ring opening reaction of various epoxides
with aromatic amines. This method is also usable for deactivated and
sterically hindered amines in good yields.
Catalyst
ArNH2
+
NHAr
CH3CN, rt
R
R
Scheme 1. Catalytic conversion of epoxides to β-aminoalcohols in the presence of tran-
sition metal substituted polyoxometalates.

N. Aramesh et al. / Inorganic Chemistry Communications 28 (2013) 37–40
39
(c) D. Sloboda-Rozner, K. Neimann, R. Neumann, Aerobic oxidation of alde-
hydes catalyzed by ε-Keggin type polyoxometalates [Mo1V2O39(μ2-OH)10H2
{XII(H2O)3}4] (X = Ni, Co, Mn and Cu) as heterogeneous catalysts, J. Mol.
Catal. A Chem. 262 (2007) 109–113;
Table 2
Aminolysis of various epoxides by aromatic amines in the presence of Fe(III) substituted
Wells–Dawson type polyoxometalatesa.
Entry Epoxide
1
ArNH2
Time (min) Yield (%)b,c
(d) E. Cadot, M.A. Pilette, J. Marrot, F. Sécheresse,
A supramolecular
tetra-Dawson polyoxothiometalate: [(α-H2P2W15O56)4{Mo2O2S2(H2O)2}4
{Mo4S4O4(OH)2(H2O)}2]28−, Angew. Chem. Int. Ed. 42 (2003) 2173–2176;
(e) K.T. Venkateswara Rao, P.S.N. Rao, P. Nagaraju, P.S. Sai Prasad, N. Lingaiah,
Room temperature selective oxidation of toluene over vanadium substituted
polyoxometalate catalysts, J. Mol. Catal. A Chem. 303 (2009) 84–89;
(f) M. Moghadam, V. Mirkhani, S. Tangestaninejad, I. Mohammadpoor-Baltork, M.
Moshref Javadi, Molybdenum Schiff base-polyoxometalate hybrid compound:
a heterogeneous catalyst for alkene epoxidation with tert-BuOOH, Polyhedron
29 (2010) 648–654.
PhNH2
40
80
98
85
80
80
85
90
80
85
95
87
90
90
90
87
85
88
80
85
86
80
82
85
80
85
81
67
80
70
80
75
70
80
90
85
86
80
82
85
80
85
89
70
60
80
70
60
70
70
70
70
75
80
70
72
60
70
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2
2-NO2PhNH2
PhNHCH3
50
40
40
40
180
50
120
140
100
100
120
[2] (a) J.F. Keggin, Structure of the molecule of 12-phosphotungstic acid, Nature 131
(1933) 908–909;
2d
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 120
2-NO2 PhNH2 180
PhNHCH3
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 130
2-NO2 PhNH2 300
PhNHCH3
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 120
2-NO2 PhNH2 300
PhNHCH3
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 130
2-NO2 PhNH2 300
PhNHCH3
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 170
2-NO2PhNH2
PhNHCH3
(b) B. Dawson, The structure of the 9(18)-heteropoly anion in potassium
9(18)-tungstophosphate, K6(P2W18O62)·14H2O, Acta Crystallogr. 6 (1953)
113–126.
[3] (a) V. Mirkhani, S. Tangestaninejad, B. Yadollahi, L. Alipanah, Efficient regio- and
stereoselective ring opening of epoxides with alcohols, acetic acid and water cata-
lyzed by ammonium decatungstocerate(IV), Tetrahedron 59 (2003) 8213–8218;
(b) V. Mirkhani, S. Tangestaninejad, B. Yadollahi, L. Alipanah, Ammonium
decatungstocerate (IV): an efficient catalyst for ring opening of epoxides with
aromatic amines, Catal. Lett. 101 (2005) 93–97;
100
120
160
140
100
120
3
(c) B. Yadollahi, F.K. Esfahani, Efficient preparation of vic-diacetates from epoxides
and acetic anhydride in the presence of iron(III)-substituted polyoxometalate as
catalyst, Chem. Lett. (2007) 676–677;
(d) B. Yadollahi, H. Danafar,
A facile synthesis of 1,2-azidoalcohols by
(TBA)4PFeW11O39·3H2O-catalyzed azidolysis of epoxides with NaN3, Catal.
Lett. 113 (2007) 120–123.
140
130
130
130
130
100
[4] J.G. Smith, Synthetically useful reactions of epoxides, Synthesis (1984) 629–656.
[5] V. Alikhani, D. Beer, D. Bentley, I. Bruce, B.M. Cuenoud, R.A. Fairhurst, P. Gedeck, S.
Haberthuer, C. Hayden, D. Janus, L. Jordan, C. Lewis, K. Smithies, E. Wissler,
Long-chain formoterol analogues: an investigation into the effect of increasing
amino-substituent chain length on the β2-adrenoceptor activity, Bioorg. Med.
Chem. Lett. 14 (2004) 4705–4710.
[6] J. Cossy, D.G. Pardo, C. Dumas, O. Mirguet, I. Déchamps, T.-X. Métro, B. Burger, R.
Roudeau, J. Appenzeller, A. Cochi, Rearrangement of β-amino alcohols and applica-
tion to the synthesis of biologically active compounds, Chirality 21 (2009) 850–856.
[7] (a) E. Ruediger, A. Martel, N. Meanwell, C. Solomon, B. Turmel, Novel 3′-deoxy
analogs of the anti-HBV agent entecavir: synthesis of enantiomers from a
single chiral epoxide, Tetrahedron Lett. 45 (2004) 739–742;
4
160
130
160
120
100
120
5
(b) S. Zhu, L. Meng, Q. Zhang, L. Wei, Synthesis and evaluation of febrifugine an-
alogues as potential antimalarial agents, Bioorg. Med. Chem. Lett. 16 (2006)
1854–1858;
(c) W.J. Moore, F.A. Luzzio, Synthetic studies directed toward the liposidomycins:
preparation and reactions of serine-derived epoxides, Tetrahedron Lett. 36
(1995) 6599–6602;
(d) K.B. Lindsay, S.G. Pyne, Synthesis of (+)-(1R,2S,9S,9aR)-octahydro-1H-pyrrolo
[1,2-a]azepine-1,2,9-triol: a potential glycosidase inhibitor, Tetrahedron 60
(2004) 4173–4176.
140
175
200
200
180
190
6
[8] S. Wu, R. Takeya, M. Eto, C. Tomizawa, Insecticidal activity of optically active
1,3,2-oxazaphospholidine 2-sulfides and 1,3,2-benzodioxaphosphorin 2-sulfides, J.
Pestic. Sci. 12 (1987) 221–227.
[9] S.R. Kumar, P. Leelavathi, Phosphomolybdic acid-Al2O3: a mild, efficient, hetero-
geneous and reusable catalyst for regioselective opening of oxiranes with amines
to β-amino alcohols, J. Mol. Catal. A Chem. 266 (2007) 65–68.
[10] H. Danafar, B. Yadollahi, (TBA)4PFeW11O39·3H2O catalyzed efficient and facile
ring opening reaction of epoxides with aromatic amines, Catal. Commun. 10
(2009) 842–847.
[11] A.K. Chakraborti, S. Rudrawar, A. Kondaskar, An efficient synthesis of 2-amino alco-
hols by silica gel catalysed opening of epoxide rings by amines, Org. Biomol. Chem. 2
(2004) 1277–1280.
[12] M. Kokubo, T. Naito, S. Kobayashi, Chiral zinc(II) and copper(II)-catalyzed asym-
metric ring-opening reactions of meso-epoxides with aniline and indole deriva-
tives, Tetrahedron 66 (2010) 1111–1118.
[13] S.S. Chimni, N. Bala, V.A. Dixit, P.V. Bharatam, Thiourea catalyzed aminolysis of
epoxides under solvent free conditions. Electronic control of regioselective ring
opening, Tetrahedron 66 (2010) 3042–3049.
[14] S. Sagava, H. Abe, Y. Hase, T. Inaba, Catalytic asymmetric aminolysis of
3,5,8-trioxabicyclo[5.1.0]octane providing an optically pure 2-amino-1,3,4-butanetriol
equivalent, J. Org. Chem. 64 (1999) 4962–4965.
350
160
120
120
130
120
100
7
PhNH2
4-BrPhNH2
2-ClPhNH2
2-MePhNH2
4- MePhNH2
4-MeOPhNH2 120
2-NO2 PhNH2 230
PhNHCH3
110
a
3 mol% of catalyst was used.
All products were identified by comparison of their physical and spectral data with
b
those of authentic samples.
c
Yields refer to crude product (isolated product).
2-Amino-2-phenyl ethanol was obtained as the major product (α/β=95/5).
d
[15] S. Khaksar, A. Heydari, M. Tajbakhsh, H.R. Bijanzadeh, A facile and efficient synthesis of
β-amino alcohols using 2,2,2-trifluoroethanol as a metal-free and reusable medium,
J. Fluor. Chem. 131 (2010) 106–110.
Acknowledgments
[16] G. Sekar, V.K. Sing, An efficient method for cleavage of epoxides with aromatic
amines, J. Org. Chem. 64 (1999) 287–289.
We are grateful to University of Isfahan for the financial support of
this work.
[17] J.S. Yadav, A.R. Reddy, A.V. Narsaiah, B.V.S. Reddy, An efficient protocol for
regioselective ring opening of epoxides using samarium triflate: synthesis of pro-
pranolol, atenolol and RO363, J. Mol. Catal. A Chem. 261 (2007) 207–212.
[18] D.B.G. Williams, M. Lawton, Aluminium triflate: an efficient recyclable Lewis acid
catalyst for the aminolysis of epoxides, Tetrahedron Lett. 47 (2006) 6557–6560.
[19] A. Procopio, M. Gaspari, M. Nardi, M. Oliverio, O. Rosati, Highly efficient and versatile
chemoselective addition of amines to epoxides in water catalyzed by erbium(III)
triflate, Tetrahedron Lett. 49 (2008) 2289–2293.
References
[1] (a) M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer-Verlag, Berlin,
1983.;
(b) Polyoxometalates, in: C.L. Hill (Ed.), Chem. Rev., 98, 1998, pp. 1–389;

40
N. Aramesh et al. / Inorganic Chemistry Communications 28 (2013) 37–40
[20] L.R. Reddy, M.A. Reddy, N. Bhanumathi, K.R. Rao, An efficient method for the ring
opening of epoxides with aromatic amines catalysed by indium trichloride, New
J. Chem. 25 (2001) 221–222.
[25] G. Sundararajan, K. Vijayakrishna, B. Varghese, Synthesis of β-amino alcohols by
regioselective ring opening of arylepoxides with anilines catalyzed by cobaltous
chloride, Tetrahedron Lett. 45 (2004) 8253–8256.
[21] T. Ollevier, G. Lavie-Compin, An efficient method for the ring opening of epoxides
with aromatic amines catalyzed by bismuth trichloride, Tetrahedron Lett. 43
(2002) 7891–7893.
[26] M.J. Bhanushali, N.S. Nandurkar, M.D. Bhor, B.M. Bhanage, Y(NO3)3·6H2O catalyzed
regioselective ring opening of epoxides with aliphatic, aromatic, and heteroaromatic
amines, Tetrahedron Lett. 49 (2008) 3672–3676.
[22] M.C. Singh, R.K. Peddinti, Antimony(III) chloride-catalyzed ring opening of epoxides
with anilines, Tetrahedron Lett. 48 (2007) 7354–7357.
[27] D.K. Lyon, W.K. Miller, Highly oxidation resistant inorganic-porphyrin analog
polyoxometalate oxidation catalysts. 1. The synthesis and characterization of
aqueous-soluble potassium salts of α2–W17O61(Mn+·OH2)(n-10) and organic
solvent soluble tetra-n-butylammonium salts of α2–W17O61 (Mn+·Br)(n-11)
(M = Mn3+, Fe3+, Co2+, Ni2+, Cu2+), J. Am. Chem. Soc. 113 (1991) 7209–7221.
[23] A.K. Chakraborti, A. Kondaskar, ZrCl4 as a new and efficient catalyst for the opening
of epoxide rings by amines, Tetrahedron Lett. 44 (2003) 8315–8319.
[24] J.R. Rodrı'guez, A. Navarro, Opening of epoxides with aromatic amines promoted
by indium tribromide: a mild and efficient method for the synthesis of β-amino
alcohols, Tetrahedron Lett. 45 (2004) 7495–7498.