Microwave-enhanced bismuth triflate-catalyzed epoxide opening with aliphatic amines

Article abstract of DOI:10.1016/j.tetlet.2007.12.100

In the presence of a catalytic amount of Bi(OTf)₃·4H₂O and under microwave irradiation, neat mixtures of epoxides and amines afforded smoothly the corresponding 2-amino alcohols. A wide variety of aliphatic amines were reacted with cycloalkene oxide, styrene oxide, and stilbene oxide. The reaction proceeded rapidly and afforded the 2-amino alcohols in high up to quantitative yields. All products could be obtained without aqueous work-up by simple filtration.

Full text of DOI:10.1016/j.tetlet.2007.12.100

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 1546–1550
Microwave-enhanced bismuth triflate-catalyzed
epoxide opening with aliphatic amines
Thierry Ollevier *, Etienne Nadeau
De´partement de chimie, Universite´ Laval, Que´bec (Que´bec), Canada G1K 7P4
Received 6 November 2007; revised 16 December 2007; accepted 18 December 2007
Abstract
In the presence of a catalytic amount of Bi(OTf)3Á4H2O and under microwave irradiation, neat mixtures of epoxides and amines
afforded smoothly the corresponding 2-amino alcohols. A wide variety of aliphatic amines were reacted with cycloalkene oxide, styrene
oxide, and stilbene oxide. The reaction proceeded rapidly and afforded the 2-amino alcohols in high up to quantitative yields. All
products could be obtained without aqueous work-up by simple filtration.
Ó 2007 Published by Elsevier Ltd.
Keywords: Bismuth; Bismuth(III) triflate; Epoxide; Aliphatic amine; 2-Amino alcohol
1. Introduction
process) and toxic catalysts, and generate large amounts
of waste.
Nucleophilic opening of epoxide by amines is an impor-
tant reaction for synthetic, organic and medicinal chemists,
as the resultant 2-amino alcohols represent a broad range
of intermediates widely present in biologically active natu-
ral and synthetic products.1 The classical approach for the
synthesis of 2-amino alcohols from epoxides involves the
treatment of an epoxide with an amine under heating.
However, this procedure has drawbacks such as the need
of excess of amines and elevated temperature.2 Moreover,
poorly nucleophilic and sterically hindered amines do not
always lead to good yields of the expected amino alcohols.
Thus, there has been a lot of effort to develop methodolo-
gies for epoxide opening by amines as evidenced by numer-
ous recent reports.3 Still, some of these methods could not
overcome the requirement for long reaction times, mois-
ture/air sensitive, and costly catalysts. More importantly,
most of the above described methods could not avoid the
use of solvents (for both the reaction and the extraction
As a part of our ongoing interest in bismuth(III)-cata-
lyzed epoxide opening,4 we report herein our results in
the microwave-assisted bismuth(III) triflate-catalyzed
epoxide opening. In the last few years, bismuth compounds
have attracted attention due to their low toxicity, low cost,
and good stability.5 Bismuth salts have been reported as
catalysts for Mukaiyama-aldol reactions,6 Mannich-type
reactions,7 imine allylation,8 formation and deprotection
of acetals,9 Friedel–Crafts acylations,10 Diels–Alder reac-
tions,11 Fries rearrangement,12 and Claisen rearrange-
ment.13 Bi(OTf)3 is particularly attractive because it is
commercially available or can be easily prepared from
readily available starting materials.14 The BiX3-catalyzed
epoxide opening has already been reported with various
alkene oxides and various nucleophiles.15 In particular,
the BiCl3-catalyzed cyclohexene and cyclopentene oxide
opening has been disclosed by our group with various
substituted anilines.4a Bi(OTf)3 was then reported to be effi-
cient for the epoxide opening in aqueous conditions.4b
Recently, a very elegant asymmetric version of a Bi(OTf)3
catalyzed epoxide opening has been reported by Kobayashi
using a chiral bipyridine diol in aqueous conditions.15a
*
Corresponding author. Tel.: +1 418 656 5034; fax: +1 418 656 7916.
E-mail address: thierry.ollevier@chm.ulaval.ca (T. Ollevier).
0040-4039/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2007.12.100

T. Ollevier, E. Nadeau / Tetrahedron Letters 49 (2008) 1546–1550
1547
Microwave-assisted organic synthesis is currently gain-
ing importance in synthetic chemistry largely due to the
advancement in the technology that provides precision
controlled microwave equipments.16 Previous studies have
shown that epoxide opening reactions can be conducted
under microwave irradiation.15d,17 These methods usually
report the opening of aryloxymethyl epoxides with anilines
and sometimes involve the use of conventional kitchen
microwave ovens, often leading to modest and irreproduc-
ible yields. We wish to disclose our results in this area, that
is, the development of an efficient, microwave-assisted bis-
muth-catalyzed epoxide opening with aliphatic amines that
takes advantage of very mild reaction conditions. The reac-
tion is indeed run neat, with a catalyst loading as low as
1 mol %, and is completed within a few minutes under
microwave assistance.
With Bi(OTf)3Á4H2O identified as an effective catalyst
for the epoxide opening, cyclohexene oxide was treated
with various aliphatic amines (Scheme 2, n = 2). The reac-
tion gave the corresponding 2-amino alcohols in high yields
with all amines tested (Table 2, entries 1–5 and entry 7)
except with dipropylamine (Table 2, entry 6). The proce-
dure for these reactions is very simple as the pure product
is obtained without aqueous work-up and without purifica-
tion. In addition, the reaction could be substantially scaled
up without decreasing the yield (conditions: cyclohexene
oxide 30 mmol, morpholine 33 mmol, Bi(OTf)3Á4H2O
0.3 mmol, microwaves, 15 min, 99% yield of 2-
morpholinocyclohexanol).
The same method was also effective for the opening
reaction of cyclopentene oxide with the same amines giving
the corresponding 2-amino alcohols 5 (Scheme 2, Table 2,
n = 1). Cyclohexylamine, piperidine, morpholine, pyrroli-
dine, and n-hexylamine afforded the expected product in
high yields (Table 2, entries 1–5). Only dipropylamine pro-
duced the corresponding 2-amino alcohol in moderate yield
(Table 2, entry 6).
2. Results and discussion
Initial investigations in the epoxide opening with ali-
phatic amines involved the opening of cyclohexene oxide
with cyclohexylamine as a model reaction (Scheme 1, Table
1). These results were promising, as the corresponding 2-
amino alcohol could be obtained in excellent yield with
1 mol % of Bi(OTf)3Á4H2O as the catalyst (Table 1, entry
4). A lower loading of Bi(OTf)3Á4H2O (0.1 mol %) led to
a decreased yield (52% of 3a). While BiCl3 gave almost
no conversion (Table 1, entry 2), BiBr3 provided the prod-
uct in only moderate yield (Table 1, entry 3). Other metal
triflate catalysts, for example, Sc(OTf)3, Ga(OTf)3, and
Zn(OTf)2, appeared to be as efficient as Bi(OTf)3Á4H2O
(Table 1, entries 5–7). Triflic acid led to the expected prod-
uct in almost quantitative yield (Table 1, entry 8).
On the other hand, treatment of styrene oxide with dif-
ferent aliphatic amines gave a mixture of two regioisomers:
7a and 7b in high yields (Scheme 3, Table 3). Aminolysis of
NR1R2
Bi(OTf)3•4H2O (1 mol %)
+ R1R2NH
O
n
n
MW, 15 min.
OH
1 (n = 2)
4 (n = 1)
2
3 (n = 2)
5 (n = 1)
Scheme 2.
Table 2
Microwave-enhanced Bi(OTf)3Á4H2O-catalyzed opening of cyclohexene
and cyclopentene oxide with various aliphatic aminesa
H
NH2
N
cat. (1 mol %)
MW, 15 min.
Entry
Amine 2
Yield 3 (%)
(n = 2)
Yield 5 (%)
(n = 1)
+
O
OH
3a
NH2
1
2a
1
2
3
4
96
92
93
96
90
100
97
Scheme 1.
NH
Table 1
NH
Microwave-enhanced catalyzed opening of cyclohexene oxide by
cyclohexylaminea
O
Entry
Catalyst
Yield 3a (%)
NH
100
1
2
3
4
5
6
7
8
a
—
BiCl3
<5
5
BiBr3
47
96
97
94
95
99
5
6
93
48
96
48
NH2
Bi(OTf)3Á4H2O
Sc(OTf)3
Ga(OTf)3
Zn(OTf)2
HOTf
H
N
7
100b
—
Ph
NH2
a
Conditions: cyclohexene or cyclopentene oxide 1 or 4 (1 mmol), amine
2 (1.1 mmol), Bi(OTf)3Á4H2O (1 mol %), microwaves, 15 min.
Conditions: cyclohexene oxide
(1.1 mmol), catalyst (1 mol %), microwaves, 15 min.
1
(1 mmol), cyclohexylamine 2a
b
Epoxide/amine ratio = 1.1:1.

1548
T. Ollevier, E. Nadeau / Tetrahedron Letters 49 (2008) 1546–1550
NR1R2
OH
OH
O
Bi(OTf)3•4H2O (1 mol %)
R
R
R
+
R1R2NH
Ph
Ph
Ph
MW, 15 min.
NR1R2
6 (R = H)
8 (R = Ph)
2
7a
7 (R = H) 7b
9 (R = Ph)
Scheme 3.
Table 3
Table 4
Microwave-enhanced Bi(OTf)3Á4H2O-catalyzed opening of styrene oxide
Microwave-enhanced Bi(OTf)3Á4H2O-catalyzed opening of trans-stilbene
with various aliphatic aminesa
oxide with cyclohexylamine and piperidinea
Entry
Amine 2
Ratio 7a/7bb
Yield 7 (%)
Entry
Amine 2
Yield 9 (%)
NH2
NH2
1
68/32
96c
1
99
NH
NH
2
59/41
37/63
100
100
2
100
a
Conditions: trans-stilbene oxide 8 (1 mmol), amine 2 (1.1 mmol),
Bi(OTf)3Á4H2O (1 mol %), microwaves, 15 min.
NH
3
4
O
66/34
84c
NH2
In addition, the opening of trans-stilbene oxide 8 was
studied with both cyclohexylamine and piperidine (Scheme
3, Table 4). In both cases, the pure 2-amino alcohol 9 was
isolated in a quantitative yield using our standard condi-
tions (Table 4, entries 1 and 2). Finally, the opening of
the trisubstituted epoxide 10 with morpholine proceeded
smoothly with good regioselectivity and moderate yield
(Scheme 4).
H
5
60/40
100
N
a
Conditions: styrene oxide
6
(1 mmol), amine
2
(1.1 mmol),
Bi(OTf)3Á4H2O (1 mol %), microwaves, 15 min.
Determined by 1H NMR.
b
c
Traces (<10%) of the corresponding amino diol were also detected.
styrene oxide with cyclohexylamine, piperidine, and n-hex-
ylamine afforded 7a as the major regioisomer, by nucleo-
philic attack at the terminal carbon (Table 3, entries 1, 2,
and 4). In the case of morpholine, preferential attack
occurred at the benzylic position (Table 3, entry 3). The
opening of styrene oxide by n-hexylamine led to the corre-
sponding 2-amino alcohol in good yield (Table 3, entry 4).
In this particular case and in the case of cyclohexylamine,
traces of diol arising from the reaction of the amine with
2 equiv of styrene oxide were also detected (<10%) (Table
3, entries 1 and 4). Compared to the modest yields obtained
for the opening of cyclohexene and cyclopentene oxides
with dipropylamine (Table 2, entry 6), a quantitative yield
was obtained for the opening of styrene oxide with dipro-
pylamine (Table 3, entry 5).
Interestingly, for all these experiments, no side reaction
such as epoxide rearrangement was observed under these
conditions.18 Indeed, when cyclohexene oxide was heated
under microwave irradiation in the presence of
Bi(OTf)3Á4H2O and in the absence of amine, only trace
amount of the rearranged aldehyde was observed, the
major pathway being decomposition of starting material.
3. Conclusion
As an improvement over other catalyst systems,
Bi(OTf)3Á4H2O is a versatile catalyst for the epoxide open-
ing with amines. The reaction affords up to quantitative
yields in 2-amino alcohols in very short reaction times
O
N
OH
Bi(OTf)3•4H2O (1 mol %)
HN
+
+
O
MW, 15 min.
60%
O
N
OH
11b
O
10
2c
11a/11b = 85:15
11a
Scheme 4.

T. Ollevier, E. Nadeau / Tetrahedron Letters 49 (2008) 1546–1550
1549
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process, and no formation of by-products. The conditions
are suitable for a variety of aliphatic amines. Also, the
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environmentally benign Lewis acid. Moreover, our proto-
col does not require any solvent for the reaction to proceed.
The reaction is run neat. No aqueous work-up is needed for
the reaction: the 2-amino alcohol is directly obtained after
quick filtration of the catalyst. Because of its numerous
benefits, this method for the green and straightforward syn-
thesis of 2-amino alcohols using Bi(OTf)3Á4H2O catalysis
should find utility in the synthesis of biologically active
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Acknowledgments
This work was financially supported by the Natural
Sciences and Engineering Research Council of Canada
13. (a) Ollevier, T.; Mwene-Mbeja, T. M. Synthesis 2006, 3963; (b)
Ollevier, T.; Mwene-Mbeja, T. M. Tetrahedron Lett. 2006, 47, 4051.
´ ´
(NSERC), the Fonds Quebecois de la Recherche sur la
´
Nature et les Technologies (FQRNT, Quebec, Canada),
´
14. (a) Repichet, S.; Zwick, A.; Vendier, L.; Le Roux, C.; Dubac, J.
´
the Canada Foundation for Innovation, and Universite
`
Tetrahedron Lett. 2002, 43, 993; (b) Labrouillere, M.; Le Roux, C.;
Laval. E.N. thanks NSERC and FQRNT for postgraduate
scholarships. We thank R. Kadri from Biotage AB for his
help and support.
Gaspard, H.; Laporterie, A.; Dubac, J.; Desmurs, J. R. Tetrahedron
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(e) Bi(OTf)3Á4H2O has been prepared from Bi2O3 according to Ref.
14a.
Supplementary data
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Experimental procedure and spectral data for all new
compounds. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.tetlet.2007.12.100.
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T. Ollevier, E. Nadeau / Tetrahedron Letters 49 (2008) 1546–1550
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