Imidazolium and pyridinium salts - Solvents influencing the rate and direction of the fries, beckmann, and claisen rearrangements

Article abstract of DOI:10.1007/s10593-010-0487-0

The Fries, Beckmann, and Claisen rearrangements have been investigated in ionic liquid media. The effect of the structural elements of the latter on the direction of these rearrangements and the product yields has been studied.

Full text of DOI:10.1007/s10593-010-0487-0

Chemistry of Heterocyclic Compounds, Vol. 46, No. 2, 2010
IMIDAZOLIUM AND PYRIDINIUM SALTS –
SOLVENTS INFLUENCING THE RATE AND
DIRECTION OF THE FRIES, BECKMANN,
AND CLAISEN REARRANGEMENTS
S. Katkevica1, A. Zicmanis1*, and P. Mekss1
The Fries, Beckmann, and Claisen rearrangements have been investigated in ionic liquid media. The
effect of the structural elements of the latter on the direction of these rearrangements and the product
yields has been studied.
Keywords: ionic liquids, imidazolium salts, pyridinium salts, Beckmann, Claisen, and Fries rearrangements.
Imidazolium and pyridinium salts are currently the most widely studied and used ionic liquids (IL) in
organic synthesis and they are often simultaneously used as solvent and catalyst in very varied reactions [1-7].
With careful choice of substituents in the heterocyclic cations and the type of anions in the IL it is possible to
change the rate, direction, and even mechanism of many organic reactions. The effect of heterocyclic salt IL on
molecular rearrangements is rarely represented in the chemical literature and that has prompted us to a
systematic investigation in this direction.
+
–
–
+
R2
N
R
X
N
N
X
Me
R1
2a–d
1a–j
1ae R1 = H, R2 = Bu [bmim]; a X = Br, b X = Cl, c X = I, d X = BF4, e X = PF6;
fh R1 = H, X = Br, f R2 = Et [emim], g R2 = C6H13 [hmim], h R2 = C8H15 [omim];
i R1 = Me, R2 = Bu, X = Br [bmmim]; j R1 = H, R2 = Et, X = OMs; 2ac R = C7H15 [C7Py];
a X = Br, b X = BF4, c X = PF6, d R = Me [mPy], X = OTs
_______
* To whom correspondence should be addressed, e-mail: zicmanis@latnet.lv.
1 Faculty of Chemistry, University of Latvia, Riga LV-1586, Latvia.
__________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 195-208, February, 2010, Original
article submitted May 30, 2008; revision submitted August 4, 2009.
158
0009-3122/10/4602-0158©2010 Springer Science+Business Media, Inc.

In this work we have studied the electrophilic Fries rearrangement, the nucleophilic Beckmann
rearrangement and the pericyclic Claisen rearrangement in IL media – the imidazolium 1 and pyridinium 2 salts.
Esters 3a-c, ketoximes 4a-c, and the allyl aryl ethers 5a-c respectively were used as substrates (see Scheme 1).
Scheme 1
OH
O
O
OH
+
O
Me
O
R
R
Me
3a–c
Me
O
6a–c
7a–c
OH
N
H
N
Me
Me
R
R
4a–c
8a–c
O
OH
O
+
R
R
Me
R
5a–c
10a–c
9a–c
3-10 a R = H, b R = OMe; 3,4,6-8 c R = Cl; 5,9,10 c R = NO2
The Fries and Beckmann rearrangements were carried out in the presence of AlCl3, TiCl4, SnCl4, and
BF3 (in the IL the molar fraction X of the Lewis acid was 0.67). It should be noted that only the use of AlCl3 in
IL has been reported in the literature [2, 8]. The Claisen rearrangement was studied without the use of a catalyst,
the substrate being held in the IL medium at a temperature of 200ºC. In this study the dependence of the reaction
rate and formation of products on the structural elements of the IL and the nature of the Lewis acid were
examined.
The effect of the nature of the heterocyclic cation of the IL on the Fries, Beckmann, and Claisen
rearrangements was examined through comparison of reactions in 1-butyl-3-methylimidazolium (1a) and 1-hep-
tylpyridinium (2a) bromides.
The IL cations can react with polar reaction partners, electron pair donors and hydrogen bond acceptors
while IL anions typically interact with electron pair acceptors and with hydrogen bond donors [9, 10].
The most important of the indicated reactions is likely the formation of hydrogen bonds between the IL
cations and the reaction substrates, mainly between the hydrogen atom of the H-2 bond of the imidazolium ion
and the hydrogen acceptor bonds of the reaction substrates. It is also important to take into account the
additional interaction of the heterocyclic cation with the conjugated systems and the polarized parts of the
reaction substrates (- interaction). It should be different in the IL with imidazolium 1 and pyridinium 2 series
cations. In turn, the reaction of the bromide anion with the rearranging substrates is likely virtually the same in
all IL used. For a quantitative discussion of the complex interactions an empirical scale of overall solvent
EN
polarity (the Reichardt constant T ) [9, 11] has more often been used and is employed in our work.
The results of comparative experiments in which the effect has been studied of the structure of the IL
cation 1a and 2a on the course of the Fries (substrates esters 3a-c) and Beckmann rearrangement (substrates
ketoximes 4a-c), catalyzed by Lewis acids, and the results are presented in Table 1.
159

TABLE 1. Product Conversion and Content in the Reaction Mixture upon
Fries and Beckmann Rearrangement in Ionic Liquids
Fries rearrangement
Experi- Convers-
Beckmann rearrangement
Lewis
acid
Ionic liquid
Experi-
Convers-
6, %* 7, %*
8, %*2
ment No. ion, %*
Substrate 3a
100 53
ment No. ion, %*2
Substrate 4a
[bmim][Br]
AlCl3
TiCl4
SnCl4
BF3
1
2
3
4
5
6
7
8
35
0
25
26
27
28
29
30
31
32
100
100
100
98
(1а)
100
98
28
8
0
68
88
82
0
0
78
88
[C7Py][Br]
AlCl3
TiCl4
SnCl4
BF3
95
52
25
15
0
31
0
100
100
100
88
(2а)
100
100
57
100
0
75
0
100
81
Substrate 3b
Substrate 4b
100
[bmim][Br]
AlCl3
TiCl4
SnCl4
BF3
9
100
100
68
66
33
34
35
36
37
38
39
40
100
100
100
97
(1а)
10
11
12
13
14
15
16
83
23
0
100
100
38
100
[C7Py][Br]
AlCl3
TiCl4
SnCl4
BF3
98
82
75
40
0
100
100
100
100
98
(2а)
100
50
100
100
48
100
Substrate 3c
Substrate 4c
100
[bmim][Br]
AlCl3
TiCl4
SnCl4
BF3
17
18
19
20
21
22
23
24
59
67
1
97
41
42
43
44
45
46
47
48
100
79
98
84
91
97
96
82
(1а)
100
100
0
34
96
18
94
81
10
62
32
[C7Py][Br]
AlCl3
TiCl4
SnCl4
BF3
98
62
100
0
80
(2а)
100
96
38
_______
* According to GLC data for the reaction mixture after being held for 3 h
at 120ºC.
*2 According to GLC data for the reaction mixture after being held for 3 h
at 80ºC (with the use of AlCl3 and TiCl4) or for 3 h at 120ºC (with the use
of SnCl4 and BF3).
High conversion of the starting material and selectivity of the reaction were found in almost all cases for
the Fries and Beckmann rearrangements catalyzed by AlCl3 and TiCl4 (Table 1). Somewhat lower yields were
attained using the ester 3c and oxime 4c (Table 1, experiments 17-24, 41-48). The Fries rearrangement of phenyl
acetate (3a) to form o-acetylphenol (6a) and the p-isomer 7a was seen only in reactions catalyzed by AlCl3.
With TiCl4 and SnCl4 catalysts only a small fraction of compound 3a is converted to the hydroxyaryl ketone 6a
(Table 1, experiments 2, 3, 6, 7) and the major part is hydrolyzed to form phenol. With use of BF3 the phenyl
acetate (3a) does not generally rearrange (Table 1, experiments 4, 8). A higher reaction selectivity was seen in
the Fries rearrangements of esters 3b and 3c in the presence of TiCl4 and SnCl4 but, as in the case of the phenyl
acetate (3a) this reaction cannot be achieved using BF3 as catalyst (Table 1, experiments 16, 24).
The rearrangement of ketoximes 4a-c occurs readily in both IL 1a and 2a in the presence of AlCl3 and
TiCl4 the yields of the amides obtained 8a-c being almost quantitative (Table 1, experiments 25-48). By contrast
160

with aryl acetates, ketoximes rearrange in IL media even using SnCl4 and BF3. The reaction products show the
presence of the corresponding acetophenones as the result of hydrolysis. Hence the Lewis acids BF3 and SnCl4
show different catalytic activity in the Fries and Beckmann rearrangements.
Figures 1 and 2 show graphically the effect of IL 1a and 2a and also of the different Lewis acids on the
rate of reaction of the aryl acetates and ketoximes. The Fries rearrangements of phenyl acetate (3a) and
4-methoxyphenyl acetate (3b) occur rapidly (after 30-60 min) only with the most active of the catalysts TiCl4
and AlCl3 and the effect of both IL on the conversion of these esters can be considered as the same. An
analogous conversion of 4-chlorophenyl acetate (3c) with TiCl4 and AlCl3 and also acetates 3a,b with SnCl4 and
BF3 occurs much more slowly and, only in these cases, can the effect of structural elements of the IL on the rate
of the rearrangement be evaluated for now. The results of the majority of the experiments show a somewhat
greater rate of rearrangement in the IL 2a ([C7Py][Br]) while the 4-chlorophenyl acetate (3c) shows the greatest
substrate conversion for all four Lewis acids (Table 1, experiments 17-24). The rearrangement occurs at the
highest rate in the presence of TiCl4 (Fig. 1).
Fig. 1. TiCl4-catalyzed Fries rearrangement of esters 3a and 3c at 120ºC: 1 – 3a, [bmim][Br];
2 – 3a [C7Py][Br]: 3 – 3c [C7Py][Br]; 4 – 3c [bmim][Br].
Fig. 2. BF3- and SnCl4-catalyzed Beckmann rearrangement of ketoximes 4a and 4c at 120ºC: 1 – 4a,
[bmim][Br]/BF3; 2 – 4a, [C7Py][Br]/BF3; 3 – 4c, [C7Py][Br]/SnCl4; 4 – 4c, [bmim][Br]/SnCl4.
161

The Beckmann rearrangement of the ketoximes in the presence of TiCl4 and AlCl3 catalysts also occurs
readily and the conversion of the starting compound reaches almost 100% after 30 min. Ketoxime 4b contains a
methoxy group and also rearranges rapidly with SnCl4 and BF3 while reaction of these with ketoximes 4a,c takes
place more slowly, hence the effect of the structural features of the IL can be conveniently observed. Ketoximes
rearrange somewhat more rapidly in the IL 2a medium than in IL 1a (Fig. 2).
ENT
The polarities of the IL [C7Py][Br] and [bmim][Br] on the
(here and subsequently the starred values of
scale are 0.840* and 0.614* respectively
ENT
were evaluated by us using method [12]). In agreement with the
Hughes-Ingold law an increase in the polarity of the solvent raises the rate of the reaction in the case of
formation of a bipolar transition state [13]. Because the Fries and Beckmann rearrangements correspond to just
this requirement the results obtained are explained by the above difference in the overall polarity of the IL 1a
and 2a. This is most likely since the highest rearrangement rate is observed in the IL 2a.
For calculating the effect of a possible - interaction between the IL cation and the transition state for
the Fries and Beckmann rearrangements the latter were also carried out in IL with the aliphatic
ENT
tetrabutylammonium bromide cation [Bu4N][Br] for which
= 0.389 [9]. For comparison of the course of the
reaction in the IL medium and in general organic solvents the rearrangements were carried out in nitrobenzene
EN
(
= 0.324 [13]). It was found that the slowest of all of the Fries rearrangements occurs in the IL [Bu4N][Br]
T
(1a). By contrast, in this medium the Beckmann rearrangement occurs more rapidly than in other IL studied. The
rate of both reactions in nitrobenzene was markedly greater than in IL (Fig. 3).
Fig. 3. AlCl3-catalyzed Fries rearrangement of ester 3c and SnCl4-catalyzed Beckmann rearrangement of
ketoxime 4c in the ionic liquid [C7Py][Br] and nitrobenzene at 120ºC: 1 – 4-chloroacetophenone oxime,
[C7Py][Br]/SnCl4; 2 – 4-chloroacetophenone oxime, PhNO2/SnCl4; 3 – 4-chlorophenyl acetate,
PhNO2/AlCl3; 4 – 4-chlorophenyl acetate, [C7Py][Br]/AlCl3.
Hence for an understanding of the results of the rearrangements there should be borne in mind not only
the general polarity of the IL but also other possible interactions of the latter with the reaction substrates. For
example this may relate to the - interaction between aromatic groups of the substrate and the cation of IL 1a
or 2a which are also characteristic for nitrobenzene but not in the least typical of a [Bu4N] cation. However, the
nitrobenzene cannot take part in an ion-ion interaction with the transition state of the reaction which is possible
for all IL. It follows from the results obtained that the - interaction is advantageous for the Fries
rearrangement (increasing the reaction rate) but very undesirable for the Beckmann rearrangement (lowering the
reaction rate), an ion-ion interaction between the IL and the reaction substrates lowering the rate of both
rearrangements.
162

TABLE 2. Products Conversion and Content in the Reaction Mixture upon
Claisen Rearrangement in Ionic Liquids and without Solvent*
Experiment
Ionic liquid
Ether
Conversion, %
9, %
10, %
No.
1
2
[emim][OMs] (1j)
[bmim][Br] (1a)
[mPy][OTs] (2d)
[C7Py][Br] (2a)
Without solvent
[emim][OMs] (1j)
[bmim][Br] (1a)
[C7Py][Br] (2a)
Without solvent
[emim][OMs] (1j)
[bmim][Br] (1a)
[C7Py][Br] (2a)
Without solvent
5a
5a
5a
5a
5a
5b
5b
5b
5b
5c
5c
5c
5c
93
100
74
95
71
0
5
11
100
13
1
3
4
100
68
2
5
99
61
90
44
98
84
79
38
41
6
100
58
39
10
56
2
7
8
100
98
9
10
11
12
13
96
16
21
62
57
100
100
49
_______
* According to GLC data for the reaction mixture after 4 h at 200ºC.
Pericyclic reactions generally depend little on the nature of the solvent [13] hence in a Claisen
rearrangement in different IL there is no marked difference in reaction rates, even though some difference is
observed in the ratio of products (Table 2). Thus the allyl phenyl ethers 5a-c in the 1-alkyl-3-methylimidazolium
salts 1a,j media are principally converted to the allylphenols 9a-c but in the 1-alkylpyridinium salts 2a,d they form
more of the dihydrobenzo[b]furan derivatives 10a-c which are the products of further cyclization of compounds 9a-
c. In all experiments with the ethers 5a-c the phenol products of their hydrolysis are also observed.
In order to evaluate the effect of the hydrophobicity of the IL cation the Fries, Beckmann, and Claisen
rearrangements were carried out in the 1-alkyl-3-methylimidazolium bromides 1 with alkyl substituents R of
different lengths.
EN
Increase in the length of R led to a small decrease in the polarity of the IL. On the
scale this was reflected
T
in the following: [emim][Br] = 0.634*, [bmim][Br] = 0.614*, [hmim][Br] = 0.562*, and [omim][Br] = 0.549*. In IL
hydrophobic alkyl groups there is possible a further hydrophobic interaction with the lipophilic groups of the
reaction substrates and/or the transition states of the reaction. There is observed in the Fries rearrangement of
4-chlorophenyl acetate (3c) a lower yield of products with an increase in the length of R for the indicated
dialkylimidazolium bromides (Table 3, experiments 1-3) with the exclusion of IL with R = octyl (Table 3,
experiment 4). (Possibly in the latter case the octyl group is twisted into a shorter globular form). Thus the rate
of rearrangement of the 4-chlorophenyl acetate (3c) decreases in the following IL order:
[emim][Br] > [omim][Br] > [bmim][Br] > [hmim][Br].
At the same time, the length of R in the IL does not significantly influence the ratio of reaction products.
A lowering of the conversion with increase in the length of R in the IL is also observed in the Beckmann
rearrangement of the 4-chloroacetophenone oxime (4c) (Table 3, experiments 13-16) while, however, the
conversions of this oxime after 3 h in the IL [omim][Br] and [hmim][Br] were almost identical. The curves
characterizing the reaction rate graphically demonstrate its tendency to decrease in the IL series:
[emim][Br] > [bmim][Br] > [hmim][Br] ~ [omim][Br]
i.e. with an increase in the length of R in the IL cation (Fig. 4).
163

164

For the pericyclic Claisen rearrangement a clear effect of the length of the alkyl group on the conversion
of the starting material 5a in the alkylimidazolium salts was not observed (Table 3, experiments 25-28). A
marked difference was also not observed in the ratio of products, the 2-allylphenol (9a) always being formed in
excess.
Fig. 4. SnCl4-catalyzed Beckmann rearrangement of ketoxime 4c at 120ºC in ionic liquids with different
hydrophilicity: 1 – [hmim][Br]; 2 – [omim][Br]; 3 – [bmim][Br]; 4 – [emim][Br].
For reckoning the effect of the acid H-2 atom in the imidazolium ion on the rearrangements discussed
they were carried out in the IL [bmim][Br] (1a), able to form a hydrogen bond with the reaction substrates
ENT
(having H-2;
= 0.614*), and in the IL [bmmim][Br] (1i), having a methyl group in place of H-2 (with
ENT
ENT
= 0.486*) and so not possible in this case. The
values for the IL [bmim] series were significantly higher
than for the [bmmim][Br]. This, inter alia, means that the acidity of the H-2 atom markedly augments the
polarity of the IL.
For the Fries rearrangement, the conversion of the 4-chlorophenyl acetate (3c) in the IL [bmim][Br] is
somewhat greater than in the IL [bmmim][Br] (Table 3, experiments 2, 5). An opposing tendency is seen in the
Beckmann rearrangement of ketoxime 4c in the [bmim][Br] and [bmmim][Br] media (Table 3, experiments
14, 17). This means that there is the undesirable formation in the Beckmann rearrangement of an additional
hydrogen bond between the reaction substrates and the IL. Formation of such (an additional) bond in the
pericyclic Claisen rearrangement of the allyl phenyl ether 5a markedly increases the reaction rate (cf.
experiments 26 and 29).
The type of anion in the IL markedly affects the rate of the Fries and Beckmann rearrangements but with
the Claisen rearrangement this effect appears only in the product ratios. A less basic and/or more bulky anion
binds more weakly with the IL cation thus increasing the possibility of a tighter interaction of this cation with
the reaction substrates. The effect of halide anions on the Fries and Beckmann rearrangements corresponds to
their nucleophilicity in polar protonic solvents: [bmim][I] > [bmim][Br] > [bmim][Cl] (Table 3). In the Fries
rearrangement of ester 3c and the Beckmann rearrangement of oxime 4c the highest yield is seen in the
–
–
[bmim][I] medium (Table 3, experiments 7, 19). In IL with the complex anions BF4 and PF6 the Fries
rearrangement of ester 3c does not occur at all (Table 3, experiments 8, 9, 11, 12). Independently of the nature of
the cation the Beckmann rearrangement of ketoxime 4c in IL was accompanied by a lowering of the rate in the
series of anions: PF6 > Br– > BF4 (Table 3, experiments 22-24). It should be noted that ketoxime 4c rearranges
–
–
rapidly over the course of 5 min in the IL media [bmim][PF6] and [C7Py][PF6] (Table 3, experiments 21 and 24).
-
However, it has to be borne in mind that the literature reports the ready hydrolysis of the PF6 anion to form HF
[7, 14] and the latter may be the real rearrangement catalyst. The results discussed confirm the opposing effects
noted above for the nature of the IL anions on the rate of the Fries and Beckmann rearrangements.
165

In the Claisen rearrangement of the allyl phenyl ether 5a the highest yields of 2-allylphenol (9a) are
achieved in IL containing a halide anion (Table 3, experiments 25-30) with the exclusion of the IL [C7Py][Br] and
[bmim][I] (Table 3, experiments 31, 34). All of the allyl aryl ethers 5a-c were readily converted to the corresponding
2-allylphenols in the IL with an alkanesulfonate anion [emim][OMs] (Table 2, experiments 1, 6, 10). In the IL
[bmim][BF4] the ether 5a forms the allylphenol 9a and dihydrobenzofuran 10a (approximately 1:1 ratio) but in
-
an IL containing the PF6 anion this ether is fully converted to product 10a after 4 h (Table 3, experiments
33, 36).
Hence for the Fries and Beckmann rearrangements there is observed a small increase in the rate in the 1-
heptylpyridinium bromide (2a) when compared with the 1-butyl-3-methylimidazolium bromide (1a). IL
containing aromatic cations increase the rate of the Fries rearrangement but the rate of the Beckmann
rearrangement increases with aliphatic cations. Both of these reactions take place more rapidly in the molecular
liquid nitrobenzene than in IL. An increase in the hydrophobicity of the IL lowers the rate of the Fries and
Beckmann rearrangements but the formation of a hydrogen bond between the H-2 atom of the imidazolium ion
in the IL and electron donor groups of the reaction substrates affects their rates differently, increasing the former
and slowing the latter. The rate of these rearrangements is greater in IL with the more nucleophilic anion 1c than
in IL with the less nucleophilic anion 1b. The effect of complex anions on both reactions is opposed. IL with a
–
PF6 anion lower the rate of the Fries rearrangement but speed up the Beckmann rearrangement. The products of
the Claisen rearrangement of the allyl aryl ethers (2-allylphenols 9) in IL frequently cyclize to
dihydrobenzo[b]furans 10 and this cyclization is assisted by IL containing the more polar pyridinium cation
-
and/or the PF6 anion.
EXPERIMENTAL
GLC analysis was carried out on a Hewlett Packard 5890 instrument with an A DB-5MS column
(30 m×0.25 mm) and flame ionization detector (rates of H2 30, air 300, and helium 25 ml/min). The evaporator
temperature was 250ºC. GC/MS analysis was performed on a Shimadzu GC 2010 instrument with QP 2010
mass spectrometric detector (electron ionization energy 70 eV) and OAC 20i evaporator (ratio of separation of
gas carried in the evaporator 1:30). The sample volume for analysis was 1l.
1H NMR spectra were taken on a Varian Mercury BB spectrometer (200 MHz) in CDCl3 (compounds
6a-c, 7a, 8a-c, 9a-c, 10a-c) or DMSO-d6 (IL 1a-i, 2a-d) with TMS as internal standard.
Ionic liquids: 1-butyl-3-methylimidazolium bromide, chloride, iodide, tetrafluoroborate, and hexa-
fluorophosphate (1a-e), 1-alkyl(ethyl, hexyl, octyl)-3-methylimidazolium bromides (1f-h), 1-butyl-2,3-di-
methylimidazolium bromide (1i), 1-heptylpyridinium bromide, tetrafluoroborate, and hexafluorophosphate (2a-
c), and 1-methylpyridinium p-tolylsulfonate (2d) were prepared by a known methods [15-19]. The
tetrabutylammonium bromide was obtained from the Aldrich company and the 3-ethyl-1-methylimidazolium
methanesulfonate (1j) from Solvent-Innovation. The aryl acetates 3a-c, ketoximes 4a-c, and allyl aryl ethers 5a-
c were prepared by methods [20, 21].
Fries Rearrangement of 4-Chlorophenyl acetate (3c) in the medium [bmim][Br] in the Presence of
TiCl4 Catalyst. TiCl4 (1.15 ml, 1.99 g, 10.5 mmol) was added to [bmim][Br] (1.15 g, 5.25 mmol). The mixture
was held at 120ºC for 30 min under an argon atmosphere. Compound 1c (0.75 g, 4.38 mmol) was added to the
mixture and the product was held for 3 h at 120ºC. After 5, 15, 30, 60, 120, and 180 min samples (~ 1 mg) were
removed for analysis. HCl (6M, 2 ml) was added to the sample which was thoroughly mixed and extracted with
ether (2×3 ml). The combined extract was analyzed using GLC.
Fries rearrangement with other IL, aryl acetates, and Lewis acids was carried out similarly. The results
obtained are correlated in Tables 1 and 3 and shown in Figs. 1 and 3.
166

Beckmann Rearrangement of 4-Chloroacetophenone Oxime (4c) in the Medium [Bu4N][Br] in the
.
Presence of BF3 OEt2 Catalyst. BF3·OEt2 (0.37 ml, 0.41 g, 2.92 mmol) was added to [Bu4N][Br] (0.47 g,
1.46 mmol). The mixture obtained was held at 120ºC for 30 min under an argon atmosphere. Oxime 4c (0.26 g,
1.46 mmol) was added and the reaction mixture was held for a further 3 h at 120ºC. After 5, 15, 30, 60, 120, and
180 min samples (~1 mg) were removed for analysis. Water (2 ml) was added to the sample which was
thoroughly mixed and extracted with ether (2 x 3 ml). The combined extract was analyzed using GLC.
The Beckmann rearrangement with other IL, ketoximes, and Lewis acids was carried out similarly. The
results obtained are correlated in Tables 1 and 3 and shown in Figures 2 and 4.
Claisen Rearrangement of Allyl Phenyl Ether (5a) in the Medium [bmim][Br]. Ether 5a (0.30 g,
2.23 mmol) was added to [bmim][Br] (0.49 g, 2.23 mmol). The mixture obtained was held at 200ºC for 4 h
under an argon atmosphere. After 5, 15, 30, 60, 120, 180, and 240 min samples (~1 mg) were removed for
analysis. After treatment as reported above the samples were analyzed by GLC.
The Claisen rearrangements with other IL and with allylphenyl ethers were carried out similarly. The
results obtained are collated in Tables 2 and 3.
Rearrangement Products 6-10. At the end of the rearrangement the reaction mixture was extracted
three times with ether. The extract was evaporated and the residue was distilled under reduced pressure or
recrystallized from dilute ethanol. In the case of a mixture (6a and 7a, 9b and 10b, 9c and 10c) it was separated
on a silica gel column using ethyl acetate and hexane (3:1) as eluent.
1
2-Hydroxyacetophenone (6a), colorless liquid, bp 76ºC (3 mm Hg) (bp 218ºC [22]). H NMR
spectrum, , ppm (J, Hz): 11.99 (1H, s, OH); 7.85 (1H, dd, J = 8.4 and 1.7, H-6); 7.49 (1H, dt, J = 8.4, J = 1.7,
H-4); 6.90 (2H, m, H-3,5); 2.54 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 136 [M]+ (38).
4-Hydroxyacetophenone (7a), white crystals, mp 108ºC (dilute ethanol) (mp 108-109ºC [23]).
1H NMR spectrum, , ppm (J, Hz): 8.26 (1H, s, OH); 7.86 (2H, d, J = 8.3, H-2,6); 6.9 (2H, d, J = 8.3, H-3,5);
2.54 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 136 [M]+ (30).
2-Hydroxy-5-methoxyacetophenone (6b), white crystals, mp 49ºC (dilute ethanol) (mp 52ºC [24]).
1H NMR spectrum, , ppm (J, Hz): 11.45 (1H, s, OH); 7.29 (1H, d, J = 3.1, H-6); 7.16 (1H, dd, J = 8.9, J = 3.1,
H-4); 6.88 (1H, d, J = 8.9, H-3); 4.25 (3H, s, CH3); 3.08 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 166 [M]+ (87).
5-Chloro-2-hydroxyacetophenone (6c), white crystals, mp 53ºC (dilute ethanol). 1H NMR spectrum, ,
ppm (J, Hz): 11.72 (1H, s, OH); 7.83 (1H, d, J = 2.7, H-6); 7.53 (1H, dd, J = 8.9, J = 2.7, H-4); 6.83 (1H, d, J =
8.9, H-3); 2.62 (3H, s, CH3); Mass spectrum, m/z (Irel, %): 170 [M]+ (38).
N-Phenylethaneamide (8a), white crystals, mp 115ºC (dilute ethanol) (mp 113-115ºC [25, p. 1252].
1H NMR spectrum, , ppm (J, Hz): 9.90 (1H, s, NH); 7.50 (2H, d, J = 8.1, H-2,6); 7.31 (2H, t, J = 8.1, J = 7.7,
H-3,5); 6.99 (1H, t, J = 8.1, J = 7.7, H-4); 2.02 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 135 [M]+ (24).
N-(4-Methoxyphenyl)ethaneamide (8b), white crystals, mp 127ºC (dilute ethanol) (mp 128-130ºC [25,
p. 10]). 1H NMR spectrum, , ppm (J, Hz): 9.76 (1H, s, NH); 7.45 (2H, d, J = 8.8, H-2,6); 6.83 (2H, d, J = 8.8,
H-3,5); 3.69 (3H, s, OCH3); 1.98 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 165 [M]+ (26).
N-(4-Chlorophenyl)ethaneamide (8c), white crystals, mp 173ºC (dilute ethanol) (mp 172-180ºC [25, p.
1
352]. H NMR spectrum, , ppm (J, Hz): 10.04 (1H, s, NH); 7.58 (2H, d, J = 8.9, H-3,5); 7.30 (2H, d, J = 8.9,
H-2,6); 2.02 (3H, s, CH3). Mass spectrum, m/z (Irel, %): 154 [M]+ (100).
1
2-Allylphenol (9a), colorless liquid, bp 56ºC (3 mm Hg) (bp 103-106ºC (19 mm Hg) [20]). H NMR
spectrum, , ppm (J, Hz): 9.28 (1H, s, OH); 7.13-6.65 (4H, m, H-2,3,4,5); 5.93 (1H, ddt, J = 16.8, J = 9.9,
J = 6.6, CH=CH2); 5.01 (2H, m, CH=CH2); 3.26 (2H, d, J = 6.6, ArCH2). Mass spectrum, m/z (Irel, %): 134 [M]+
(100).
1
2-Methyl-2,3-dihydrobenzo[b]furan (10a), colorless liquid. H NMR Spectrum, , ppm (J, Hz):
7.22-6.81 (4H, m, H-4 to H-7); 4.98 (1H, m, H-2); 3.36 (1H, dd, J = 15.5, J = 8.5, H-3); 2.86 (1H, dd, J = 15.5,
J = 7.9, H-3); 1.52 (3H, d, J = 6.8, CH3). The spectrum was identical to that reported in the literature [26]. Mass
spectrum, m/z (Irel, %): 134 [M]+ (100).
167

1
2-Allyl-4-methoxyphenol (9b), colorless liquid, bp 74ºC (3 mm Hg) (bp 102ºC (10-1 mbar) [27]). H
NMR spectrum, , ppm (J, Hz): 8.82 (1H, s, OH); 6.74-6.54 (3H, m, H-2,4,5); 5.92 (1H, ddt, J = 17.0, J = 10.1,
J = 6.6, CH=CH2); 5.99 (2H, d, CH=CH2); 3.62 (3H, s, OCH3); 3.23 (2H, d, J = 6.7, ArCH2). Mass spectrum,
m/z (Irel, %): 164 [M]+ (100).
1
5-Methoxy-2-methyl-2,3-dihydrobenzo[b]furan (10b), colorless liquid. H NMR spectrum, , ppm
(J, Hz): 7.70-6.60 (3H, m, H-4,6,7); 4.84 (1H, m, H-2); 3.69 (3H, s, OCH3); 3.20 (1H, dd, J = 15.9, J = 8.6,
H-3); 2.75 (1H, dd, J = 15.9, J = 7.2, H-3); 1.40 (3H, d, J = 6.2, CH3). The spectrum was identical to that
reported in the literature [28]. Mass spectrum, m/z (Irel, %): 164 [M]+ (100).
1
2-Allyl-4-nitrophenol (9c), yellowish crystals, mp 75ºC (dilute ethanol) (mp 70-72ºC [29]). H NMR
spectrum, , ppm (J, Hz): 9.57 (1H, s, OH); 7.85-7.14 (3H, m, H-3,5,6); 5.95 (1H, ddt, J = 16.1, J = 10.1,
J = 5.0, (CH=CH2); 4.95 (2H, m, CH=CH2); 3.70 (2H, d, J = 5.9, ArCH2). Mass spectrum, m/z (Irel, %): 179
[M]+ (94).
1
2-Methyl-5-nitro-2,3-dihydrobenzo[b]furan (10c), yellowish liquid. H NMR spectrum, , ppm
(J, Hz): 7.85-7.07 (3H, m, H-4,6,7); 5.07 (1H, m, H-2); 3.55 (1H, dd, J = 15.6, J = 9.3, H-3); 3.18 (1H, dd,
J = 15.6, J = 7.5, H-3); 1.82 (3H, d, J = 6.2, CH3). Mass spectrum, m/z (Irel, %): 179 [M]+ (100).
The authors express their sincere thanks to the European Social Fund for financial support of this
research.
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