Highly efficient aminolysis of epoxides catalyzed by reusable zirconyl triflate, ZrO(OTf)2

Article abstract of DOI:10.1080/00397910802406729

Efficient ring opening of epoxides with aromatic amines catalyzed by ZrO(OTf)2 is reported, and the corresponding β amino (beta-amino acid) alcohols were obtained in high yields in CH3CN as solvent. The reactions were carried out at room temperature and in the presence of only 1.25 mol% of ZrO(OTf)2. This catalyst can be reused several times without loss of its activity. Copyright Taylor & Francis Group, LLC.

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Highly Efficient Aminolysis
of Epoxides Catalyzed by
Reusable Zirconyl Triflate,
ZrO(OTf)2
Majid Moghadam a , Shahram Tangestaninejad a ,
Valiollah Mirkhani a , Iraj Mohammadpoor-Baltork a ,
Saeedeh Gorjipoor a & Parvin Yazdani a
a Department of Chemistry, Catalysis Division,
University of Isfahan, Isfahan, Iran
Version of record first published: 08 Jan 2009.
To cite this article: Majid Moghadam, Shahram Tangestaninejad, Valiollah Mirkhani,
Iraj Mohammadpoor-Baltork, Saeedeh Gorjipoor & Parvin Yazdani (2009): Highly
Efficient Aminolysis of Epoxides Catalyzed by Reusable Zirconyl Triflate, ZrO(OTf)2
, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 39:3, 552-561
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Synthetic Communications1, 39: 552–561, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802406729
Highly Efficient Aminolysis of Epoxides
Catalyzed by Reusable Zirconyl
Triflate, ZrO(OTf)2
Majid Moghadam, Shahram Tangestaninejad, Valiollah Mirkhani,
Iraj Mohammadpoor-Baltork, Saeedeh Gorjipoor,
and Parvin Yazdani
Department of Chemistry, Catalysis Division, University of Isfahan,
Isfahan, Iran
Abstract: Efficient ring opening of epoxides with aromatic amines catalyzed by
ZrO(OTf)2 is reported, and the corresponding b amino (beta-amino acid) alcohols
were obtained in high yields in CH3CN as solvent. The reactions were carried out
at room temperature and in the presence of only 1.25 mol% of ZrO(OTf)2. This
catalyst can be reused several times without loss of its activity.
Keywords: Aminolysis, epoxide, ring-opening, zirconyl triflate
INTRODUCTION
b-Amino alcohols are useful synthetic intermediates for the preparation of
b-amino acids, natural products, and chiral auxiliaries. Therefore, synthesis
of these compounds from epoxides and amines is an important reaction in
medicinal and organic chemistry.[1,2] The classical and widely employed
strategy for the synthesis of b-amino alcohols is the direct aminolysis of
epoxides with an excess of amine at elevated temperature temperatures.[3]
However, under these conditions less reactive epoxides or sluggish amines
reacts slowly, and sensitive functional groups undergo undesirable side
Received July 21, 2008.
Address correspondence to Majid Moghadam, Department of Chemistry,
Catalysis Division, University of Isfahan, Isfahan, Iran. E-mail: moghadamm@
chem.ui.ac.ir
552

Aminolysis of Epoxides
553
reactions. To overcome these problems, a variety of catalysts have been
reported for the ring opening of epoxides with amines. These include
Sn(OTf)2,[4] Cu(OTf)2,[4] Bi(OTf)3,[5,6] Al(OTf)3,[7] TaCl5,[8] InCl3,[9] BiCl3,[10]
VCl3,[11] ZrCl4,[12] InBr3,[13] CoCl2,[14] SmI2,[15] Sc(OTf)3,[16] montmorillonite
K-10 and KSF,[17] LiOTf,[18] Yb(OTf)3,[19] Ln(OTf)3,[20] cyclodextrine,21
Al(DS)3 ꢀ 3H2O,[22] Cu(BF4)2,23 Zn(ClO4)2,[24] heteropoly acids,[25–27] ionic
liquids,[28] mesoporous aluminosilicate,[29] silica nanoparticles,[30]
MgBr2 ꢀ Oet2,[31] SbCl3,[32] sulfated zirconia,[33] zirconium sulfophenylphos-
phonate,[34] and Er(OTf)3.[35]
Some of these methods suffer from disadvantages such as the use of
expensive or air-sensitive reagents, extended reaction times, the tedious
workup procedures, or limited range of amines. Therefore, the introduc-
tion of new and efficient methods is still in demand.
Zirconium(IV) salts have recently attracted much attention because of
their low cost, high catalytic activity, easy availability, and low toxicity. A
variety of Zr(IV) salts have been used for several organic transformations.[36]
Here, we introduce an efficient room-temperature procedure for
regioselective ring opening of various epoxides with aromatic amines
catalyzed by reusable ZrO(OTf)2 catalyst (Scheme 1).
EXPERIMENTAL
Chemicals were purchased from Fluka and Merck chemical companies.
1H NMR spectra were recorded in CDCl3 solvent on a Bruker AM
80-MHz or a Bruker AC 500-MHz spectrometer using TMS as an inter-
nal standard. Infrared spectra were run on a Philips PU9716 or Shimadzu
IR-435 spectrophotometer. All analyses were performed on a Shimadzu
GC-16A instrument with a flame ionization detector using silicon
DC-200 or Carbowax 20M columns. ZrO(OTf)2 was prepared according
to the reported procedure.[37]
General Procedure for Aminolysis of Epoxides
ZrO(OTf)2 (5 mg, 1.25 mol%) was added to a mixture of epoxide
(1 mmol) and amine (2 mmol) in CH3CN (2 mL) at room temperature,
Scheme 1. Aminolysis of epoxides with amines catalyzed by ZrO(OTf)2.

554
M. Moghadam et al.
a
Table 1. Aminolysis of various epoxides catalyzed by ZrO(OTf)2
Entry
Epoxide
R-NH2
Product=conversion (%)b,c
1
2
3
4
5
6
7
8
9
R ¼ C6H5
92
93
91
90
72
85
84
82
82
R ¼ 2-Cl C6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
10
11
12
13
14
15
16
17
18
R ¼ C6H5
81
83
95
92
91
86
91
78
82
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
19
20
21
22
23
24
25
26
27
R ¼ C6H5
81
90
73
96
87
84
81
76
96
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
(Continued )

Aminolysis of Epoxides
555
Table 1. Continued
Entry
Epoxide
R-NH2
Product=conversion (%)b,c
28
29
30
31
32
33
34
35
36
R ¼ C6H5
90
92
92
87
98
85
97
97
89
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
37
38
39
40
41
42
43
44
45
R ¼ C6H5
91
90
88
92
93
88
91
93
84
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
46
47
48
49
50
51
52
R ¼ C6H5
90
92
84
83
92
91
87
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
(Continued )

556
M. Moghadam et al.
Table 1. Continued
Entry
Epoxide
R-NH2
Product=conversion (%)b,c
53
54
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
84
91
55
56
57
58
59
60
61
62
63
R ¼ C6H5
93
97
98
87
92
88
86
95
80
R ¼ 2-ClC6H4
R ¼ 2-NO2C6H4
R ¼ 4-NO2C6H4
R ¼ 4-MeC6H4
R ¼ 2-MeC6H4
R ¼ 3-MeOC6H4
R ¼ 4-MeOC6H4
R ¼ 2-MeOC6H4
aReaction conditions: epoxide, 1 mmol; amine, 2 mL; catalyst, 5 mg, 1.25 mol%;
and reaction time, 1 h.
bAll products were identified by comparison of their physical and spectral data
with those of authentic samples.[1–20]
cYields refer to isolated products.
and the reaction mixture were stirred for 1 h. The reaction progress was
monitored by thin-layer chromatography (TLC) or gas chromatography
(GC). After the reaction was completed, the solvent was evaporated,
Et2O (20 mL) was added, and the catalyst was filtered. After that, the
organic solution was dried (MgSO4), concentrated, and chromato-
graphed on a silica-gel column to furnish the pure b-amino alcohol.
RESULTS AND DISCUSSION
First, the ability of ZrO(OTf)2 was investigated in the ring opening of
cyclohexene oxide with aniline. The results showed that in the presence
of catalytic amounts of ZrO(OTf)2 (1.25 mol%) and at room temperature,
1
90% of amino alcohol (with trans-configuration, indicated by H NMR)
was obtained after 1 h in CH3CN as solvent. The reaction was generalized
to various aromatic amines. As shown in Table 1, the reaction was also
efficient with other epoxides such as styrene oxide, 1,2-epoxyoctane,
phenylglycidyl ether, and epichlorohydrine. In all cases, only one product
was observed in the reaction mixture. Because of the predominant attack

Aminolysis of Epoxides
557
of amine on the less substituted carbon of epoxide, all terminal epoxides
furnished highly regioselective b-amino alcohol in quantitative yields.
In the aminolysis of styrene oxide, as a result of the formation of the
stabilized benzylic cation, a-amino alcohol was produced. In the case
of epichlorohydrine, in which an electron-deficient substituent is present
in the epoxide structure, the aminolysis was performed efficiently, and the
corresponding b-amino alcohol was obtained in excellent yield.
The actual mechanism of these reactions is not clear at present.
However, a plausible explanation is that epoxide is first activated by
the catalyst to afford 1. This happens via coordination of Zr4þ with
the oxygen of epoxide. This makes the epoxide susceptible to nucleophilic
attack by the amine to give 2, which in turn converts to the final product
and releases the catalyst for the next catalytic cycle (Scheme 2). This
probable mechanism was also reported previously.[12]
To show the applicability and efficiency of this method further, the
results of the aminolysis of cyclohexane oxide with this catalyst has been
compared with some of those recently reported. As can be seen in Table 2,
Scheme 2. Proposed mechanism for aminolysis of epoxides with amines catalyzed
by ZrO(OTf)2.

558
M. Moghadam et al.
Table 2. Comparison of the obtained results for the aminolysis of cyclohexene
oxide catalyzed by ZrO(OTf)2 with those obtained by the recently reported
catalysts
Catalyst
amount
(mol%)
Time Conversion TOF
(hꢁ1
Entry
Catalyst
ZrO(OTf)2
Sn(OTf)2
Cu(OTf)2
Bi(OTf)3
TaCl5
InCl3
BiCl3
ZrCl4
InBr3
SmI2
(h)
(%)
)
Ref.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
1.25
5
5
10
10
2
10
5
1
20
30
7
92
94
95
83
85
90
84
100
84
75
93
100
82
97
100
93
93
85
88
91
85
73.6
0.94
0.63
1.19
8.5
—
4
4
5, 6
8
9
1
12
—
0.25
12
18
3
3.75
—
80
1.4
0.42
—
10
12
13
15
17
17
21
23
25
26
27
29
30
31
33
5
10
Montmorillonite K-10 10% w=w
Montmorillonite KSF 10% w=w
24
24
1=12
0.5
3
—
Cyclodextrine
Cu(BF4)2
(NH4)8[CeW12O36]
K5[CoW12O40]
H3PW12O40
Aluminosilicate
Silica nanoparticle
MgBr2 ꢀ OEt2
SbCl3
25
10
4
5
0.14
116.4
50
6.2
2
2
6
0.25
0.25
7
23.25
—
—
36.4
1.22
120 mg
40 mg
10
10
all methods give 100% of the desired amino alcohol. Our method is
superior to the most of the previously reported methods in terms of turn-
over frequency (TOF) and reusability.
The reusability of ZrO(OTf)2 was also investigated in the aminolysis
of cyclohexene oxide (5 mmol) with aniline. After the reaction was
completed, Et2O was added, and the catalyst was filtered and reused in
another reaction. The results showed that the catalyst can be reused
several times (four consecutive times were checked) without loss of its
activity. (The amount of product was 89% at the end of fourth run with
100% selectivity.) The nature of the recovered catalyst was followed by
Fourier transform infrared (FT-IR) spectroscopy. The results showed that
after reusing the catalyst several times, no change was observed in its IR
spectrum. To check the catalyst leaching, fresh epoxide and amine were
added to the filtrates. The results showed that the amount of produced
amino alcohol is comparable to the blank experiments (less than 5%).

Aminolysis of Epoxides
559
In conclusion, we have found that ZrO(OTf)2 is an efficient and reu-
sable catalyst for ring opening of epoxides with a wide range of aromatic
amines at room temperature in CH3CN as solvent, and the corresponding
b-amino alcohols were obtained in high to excellent yields.
ACKNOWLEDGMENT
We are thankful to the Center of Excellence in Chemistry of the Univer-
sity of Isfahan (CECUI) and University of Isfahan Research Council
(Project No. 861237) for financial support of this work.
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