Microwave-assisted Beckmann rearrangement of aryl ketoximes catalyzed by in(OTf)3 in ionic liquid

Article abstract of DOI:10.1080/00397911003707063

Beckmann rearrangement of aryl ketoximes catalyzed by In(OTf)3 gave amides in ionic liquid under microwave irradiation. Aryl ketoximes were converted to corresponding amides in good yield within very short times (10-270s). The catalyst and the ionic liquid were easily recovered and reused.

Full text of DOI:10.1080/00397911003707063

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Microwave-Assisted Beckmann
Rearrangement of Aryl Ketoximes
Catalyzed by In(OTf)3 in Ionic Liquid
Kazuhiro Sugamoto a , Yoh-ichi Matsushita a & Takanao Matsui a
a Department of Applied Chemistry, Faculty of Engineering ,
University of Miyazaki , Gakuen-Kibanadai , Miyazaki , Japan
Published online: 25 Feb 2011.
To cite this article: Kazuhiro Sugamoto , Yoh-ichi Matsushita & Takanao Matsui (2011) Microwave-
Assisted Beckmann Rearrangement of Aryl Ketoximes Catalyzed by In(OTf)3 in Ionic Liquid, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:6, 879-884, DOI: 10.1080/00397911003707063
To link to this article: http://dx.doi.org/10.1080/00397911003707063
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Synthetic Communications1, 41: 879–884, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003707063
MICROWAVE-ASSISTED BECKMANN
REARRANGEMENT OF ARYL KETOXIMES
CATALYZED BY In(OTf)3 IN IONIC LIQUID
Kazuhiro Sugamoto, Yoh-ichi Matsushita, and
Takanao Matsui
Department of Applied Chemistry, Faculty of Engineering, University of
Miyazaki, Gakuen-Kibanadai, Miyazaki, Japan
GRAPHICAL ABSTRACT
Abstract Beckmann rearrangement of aryl ketoximes catalyzed by In(OTf)3 gave amides
in ionic liquid under microwave irradiation. Aryl ketoximes were converted to corresponding
amides in good yield within very short times (10–270 s). The catalyst and the ionic liquid
were easily recovered and reused.
Keywords Beckmann rearrangement; In(OTf)3; ionic liquid; microwave
The rearrangement of ketoxime to the corresponding amide, known as the
Beckmann rearrangement, is a common method used in organic chemistry and is
a topic of current interest. It accomplishes both the cleavage of the carbon–carbon
bond and the formation of a carbon–nitrogen bond, and this reaction generally
requires high reaction temperatures and a large amount of a strong Brønsted acid
and dehydrating media, causing large numbers of by-products and serious corrosion
problems. In recent years, Beckmann rearrangements using catalysts such as InCl3,[1]
H2SO3H,[2] Nd(OTf)3,[3] RuCl3,[4] chlorosulfonic acid,[5] BOPCl-ZnCl2,[6] silica
sulfate,[7] PTSA-ZnCl2,[8] and 1,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-chloride[9]
in organic solvents have been carried out. Nevertheless, a relatively large amount of
organic solvent is generally needed. Consequently, there still exists a need for novel
and facile methods for efficient conversion of ketoximes into the corresponding
amides via Beckmann rearrangement. Room-temperature ionic liquids (RTILs)
Received July 6, 2009.
Address correspondence to Kazuhiro Sugamoto, Department of Applied Chemistry, Faculty of
Engineering, University of Miyazaki, Gakuen-Kibanadai, Miyazaki 889-2192, Japan. E-mail: sugamoto@
cc.miyazaki-u.ac.jp
879

880
K. SUGAMOTO, Y.-I. MATSUSHITA, AND T. MATSUI
Table 1. Effect of metal triflate in the Beckmann rearrangement of 1
Run 1
Run 2
Recov.
of 1 (%)
Run 3
Recov.
of 1 (%)
Run 4
Recov.
of 1 (%)
Recov.
Yield (%) of 1 (%)
Yield
(%)
Yield
(%)
Yield
(%)
Entry
M(OTf)n
1
2
3
4
5
Sc(OTf)3
In(OTf)3
Hf(OTf)4
Sm(OTf)3
Yb(OTf)3
89
89
79
89
88
1
4
1
0
3
82
86
80
81
89
11
7
78
87
83
64
77
17
4
52
86
79
48
4
41
6
1
13
29
10
11
37
94
4
15
are attracting increasing interest as green solvents in many organic transforma-
tions.[10] Efforts to use RTILs as reaction media for the Beckmann rearrangement
have been reported.[11–15] Moreover, using Brønsted acidic RTILs as catalyst has
been tried for the Beckmann rearrangement.[16–19] However, reusable catalytic
Table 2. Effect of ionic liquid in the Beckmann rearrangement of 1
Run 1
Recov. of 1 (%)
Run 2
Recov. of 1 (%)
34
Entry
Ionic liquida
Yield (%)
Yield (%)
60
1
2
3
4
4
5
[Bmim][PF6]
[Bmim][BF4]
[Bmim][OcSO4]
[Bmim][NTf2]
[Emim][PF6]
[Bdimim][PF6]
84
67
0
5
19
97
95
1
b
b
—
—
b
b
b
—
b
—
—
0
—
92
89
52
86
47
7
4
aAbbreviations: [Bmim][PF6], 1-butyl-3-methylimidazolium hexafluorophosphate; [Bmim][BF4],
1-butyl-3-methylimidazolium tetrafluoroborate; [Bmim][OcSO4], 1-butyl-3-methylmidazolium octylsulfate;
[Bmim][NTf2], 1-butyl-3-methylmidazolium bis(trifluoromethylsulfonyl)imide; [Emim][PF6], 1-ethyl-3-methyli-
midazolium hexafluorophosphate; and [Bdimim][PF6], 1-butyl-1,3-dimethylimidazolium hexafluorophosphate.
bNot examined.

MICROWAVE-ASSISTED BACKMANN REARRANGEMENT
881
systems are few.[19] Herein, we report our results for the microwave-assisted
Beckmann rearrangement of aryl ketoximes catalyzed by In(OTf)3 in ionic liquid.
The ionic liquid and the catalyst were easily recovered and reused.
The activity and recyclability of various metal triflate were initially evaluated
with Beckmann rearrangement of acetophenone oxime (1) as shown in Table 1.
The reaction was performed in the presence of 0.1 equiv. of various metal triflate
and 300 mg of 1-butyl-2,3-dimethylimidazolium hexafluorophosphate ([Bdmim][PF6])
under microwave irradiation for 10s. Importantly, isolation of the product and
Table 3. Beckmann rearrangement of various ketoximes by In(OTf)3 and [Bdmim][PF6] under microwave
irradiation
Entry
Substrate
Time
30
Product
Yield (%)
1
84
2
30 Â 2
73
70
3
4
20 Â 4
20
92
54
5
6
90 Â 3
60
Complex mixture

882
K. SUGAMOTO, Y.-I. MATSUSHITA, AND T. MATSUI
substrate was easily accomplished by extraction with diisopropyl ether, and the
[Bdmim][PF]6 layer containing metal triflate was reused with a new loading substrate.
In every case, the reaction proceeded smoothly to give acetanilide (2) on the first run.
However, the activity of the recovered catalysts, such as Sc(OTf)3, Sm(OTf)3, and
Yb(OTf)3, decreased as repeated runs increased (entries 1, 4, and 5). In contrast,
the recovered ionic liquid phase containing the catalyst, such as In(OTf)3 and
Hf(OTf)4, was reused for four runs without any loss of activity (entries 2 and 3). As
shown in entry 2, a better result was obtained using In(OTf)3.
The recycling performance of various RTILs was investigated in the Beckmann
rearrangement of 1 in the presence of a catalytic amount of In(OTf)3 under micro-
wave irradiation for 10 s, as shown in Table 2. The reaction proceeded smoothly
to give 2 in the case of 1-butyl-3-methylimidazolium hexafluorophosphate
([Bmim][PF6]), 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF6]),
and [Bdmim][PF6] on the first run (entries 1, 5, and 6). However, the activity of
the recovered ionic liquid and catalyst were low in the case of [Bmim][PF6] and
[Emim][PF6]. In the case of [Bmim][PF6] and [Emim][PF6], the poor yield was
presumably caused by the formation of a hydrogen bond between C2-H in imidazo-
lium cation and oxygen in the oxime as reported in the literature.[19] When 1-butyl-3-
methylimidazolium tetrafluoroborate ([Bmim][BF4]) was used as solvent, the
reaction of 1 gave 2 in only 67% yield (entry 2). On the other hand, no reaction took
place in the presence of 1-butyl-3-methylmidazolium octylsulfate ([Bmim][OcSO4])
and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2])
(entries 3 and 4). The combined use of [Bdmim][PF6] and In(OTf)3 was the most suit-
able for the Beckmann rearrangement under microwave irradiation.
Next, we tried the Beckmann rearrangement of some ketoximes in the presence
of 0.1 equiv. of In(OTf)3 and 300 mg of [Bdmim][PF6] under microwave irradiation
(Table 3). Aryl ketoximes were converted into the corresponding amides in good
yields within very short times (entries 1–4). The cyclic ketoxime, such as a-tetralone
oxime, gave the amide in 54% yield (entry 5). However, cyclohexanone oxime gave
complex mixtures (entry 6).
In conclusion, the Beckmann rearrangement of aryl ketoximes was successfully
carried out using In(OTf)3 as the catalyst in ionic liquid [Bdmim][PF6] under micro-
wave irradiation. In this reaction, the catalyst and ionic liquid are reasily recovered
and reused.
EXPERIMENTAL
General
All starting materials were purchased form Wako Pure Chemical Industries,
Ltd. (Japan) and used without further purification. All yields refer to isolated
products after purification. Products were characterized by comparison with auth-
entic samples. Melting points were determined on a Yanaco MP-500P micromelt-
ing-point apparatus (Japan). Infrared (IR) spectra were measured on a Hitachi IR
1
270–30 spectrometer (Japan). H and 13C nuclear magnetic resonance (NMR) spec-
tra were recorded using tetramethylsilane as an internal reference on a Bruker
AC-250P instrument. High-resolution mass spectrometry (HRMS) was performed

MICROWAVE-ASSISTED BACKMANN REARRANGEMENT
883
on a Hitachi M-2000 AM mass spectrometer (Japan) in electron impact (EI) mode at
70 eV.
Typical Procedure
A mixture of acetophenone oxime 1 (135 mg, 1.0 mmol), In(OTf)3(56 mg,
0.1 mmol), and [Bdmim][PF6] (300 mg) in a glass tube was irradiated in a domestic
microwave oven (Elabitax Eor-17, Yoshii Electric Co., Ltd., Japan, 2450 MHz,
350 W) for 10 s. After 5 mL of diisopropyl ether were added to reaction mixture,
the resulting biphasic solution was treated with ultrasonic cleaner bath (200 W)
for 1 min. The upper diisopropyl ether containing the expected products was sepa-
rated by decantation. This extraction process was repeated three times. The diiso-
propyl ether was evaporated under reduced pressure to afford the crude product.
The product was purified by flash-column chromatography on silica gel to give
acetanilide 2 (120 mg) in 89% yield along with 1 (1 mg) in 4% yield. The other
hand, the bottom phase of the [Bdmim][PF6] containing In(OTf)3 was reused on
the next run.
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