The acidic ionic liquid [BSO3HMIm]HSO4: A novel and efficient catalyst for one-pot, three-component syntheses of substituted pyrroles

Article abstract of DOI:10.1515/znb-2014-0108

An acidic ionic liquid 3-methyl-2-(1-sulfobutyl)-1H-imidazolium hydrogensulfate, [BSO₃HMIm]HSO₄, was used as an efficient catalyst for the synthesis of a variety of pyrrole derivatives via a one-pot, three-component condensation of amines, nitroolefins, and 1,3-dicarbonyl compounds. Good to excellent yields of 72-96 % were obtained under reflux in ethanol. The catalyst could easily be recovered and recycled up to six times, resulting in good yields without prolonging the reaction time. This method was also efficient in large-scale preparation. The procedure could be easily expanded to a one-pot, four-component reaction. This ionic liquid-catalyzed reaction provided an environmentally friendly alternative to the synthesis of pyrrole derivatives.

Full text of DOI:10.1515/znb-2014-0108

Z. Naturforsch. 2015; 70(1)b: 29–38
YTuhaneLuao,cBaiod-QiicangioZhnanigc, Ylainq-HuonigdHe[*BanSd ZOhi3GHuaMn* Im]HSO4:
a novel and efficient catalyst for one-pot, three-
component syntheses of substituted pyrroles
Abstract: An acidic ionic liquid 3-methyl-2-(1-sulfobutyl)- of various natural products [7–10] as well as pharmaceu-
1H-imidazolium hydrogensulfate, [BSO3HMIm]HSO4, was ticals [11, 12] (Fig. 1). They exhibit a wide range of bio-
used as an efficient catalyst for the synthesis of a variety logical activities such as antitumor [13], antibacterial [14],
of pyrrole derivatives via a one-pot, three-component anticancer [15], antidiabetic [16], and anti-inflammatory
condensation of amines, nitroolefins, and 1,3-dicarbonyl properties [17]. Moreover, pyrroles have been extensively
compounds. Good to excellent yields of 72–96ꢀ% were used in material science [18, 19]. Thus, many useful strate-
obtained under reflux in ethanol. The catalyst could eas- gies have been developed for the synthesis of pyrroles and
ily be recovered and recycled up to six times, resulting in their derivatives. The most frequently used methods are
good yields without prolonging the reaction time. This Hantzsch reactions [20] (reaction of α-haloketones and
method was also efficient in large-scale preparation. The β-enaminones), Paal–Knorr reactions [21, 22] (the cyclo-
procedure could be easily expanded to a one-pot, four- condensation of primary amines with 1,4-diketones), and
component reaction. This ionic liquid-catalyzed reaction Knorr reactions [23–25] (condensation of α-aminoketone
provided an environmentally friendly alternative to the and active methylene group of ketones). Additionally,
synthesis of pyrrole derivatives.
in recent years, three-component reactions of amines,
nitroolefins and 1,3-dicarbonyl compounds, and four-
Keywords: ionic liquid; one-pot reaction; pyrrole deriva- component reactions of amines, aldehydes, nitroalkanes,
tives; recycle.
and 1,3-dicarbonyl compounds have been used to prepare
functionalized pyrroles. FeCl3 [26, 27], (diacetoxyiodo)
benzene (DIB) [28], NiCl2·6H2O [29], CeCl3·7H2O [30],
iodine [31], gluconic acid [32], and tungstic acid (STA) [33]
were used as catalysts, respectively. Moreover, Guan and
co-workers constructed pyrrole rings from enaminones or
enamino esters with nitroolefins via Michael-type addi-
tion and cyclization under purely thermal conditions [34].
In consideration of the great significance of pyrrole and
its derivatives, the development of new methods with
environmentally friendly, recoverable, and recyclable
catalysts to realize this important transformation is still
desirable.
In recent years, ionic liquids have been used as valu-
able alternatives to the common volatile organic solvents.
Besides, some ionic liquids have also been used as acid or
base catalysts with several advantages [35], such as more
environmentally benign, enhanced rate and activity, ease
of catalyst recovery [36]. For instance, a task-specific ionic
liquid, 1-butyl-3-methylimidazolium hydroxide, [bmIm]
OH, has been used as an efficient catalyst for Michael
reactions [37], Knoevenagel condensations [38], and
multi-component condensations [39]. Other task-specific
proline-tagged ionic liquids, based on 1,2,3-triazolium
salts, have also been used for Michael reactions [40].
More recently, a catalyst-free four-component protocol for
DOI 10.1515/znb-2014-0108
Received May 22, 2014; accepted August 29, 2014
1 Introduction
Multicomponent reactions (MCRs) offer a rapid and con-
vergent construction of complex molecules without the
need of isolation and purification of any intermediates,
resulting in substantial minimization of waste, time, and
cost [1–5]. Accordingly, MCRs have the advantage of sim-
plicity and synthetic efficiency over conventional chemi-
cal reactions [6].
Pyrrole and its derivatives are an important class of
heterocyclic compounds, which constitute the key core
*Corresponding authors: Yan-Hong He and Zhi Guan, School
of Chemistry and Chemical Engineering, Southwest University,
Chongqing, 400715, PR China, Fax: +86-23-68254091,
E-mail: heyh@swu.edu.cn, guanzhi@swu.edu.cn
Yuan Luo and Bao-Qiang Zhang: School of Chemistry and Chemical
Engineering, Southwest University, Chongqing, 400715, PR China
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30ꢀ ꢀY. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4
HO
OH
O
NH
CH3
OMe
O
CH3
N
N
O
O
CH3
F
N
CH3
HO
OH
O
HOOC
OH
Atorvastatin
OH
Tolmetin
OMe
LamellarinP
Fig. 1ꢀTherapeutically active pyrroles.
the synthesis of substituted pyrroles was described using HSO4 was used, the highest yield of 90ꢀ% was achieved
the ionic liquid [Hbim]BF4 as the reaction medium. The after 10 h (Table 1, entry 6). The reactions with other
reaction conditions were mild; however, a large amount examined catalysts gave the product in low yields of
of ionic liquid was employed (5 mL of ionic liquid for 32–56ꢀ% after more than 20 h (Table 1, entries 2–5). There-
1-mmol scale of reaction) [41]. In this context, we report fore, we chose [BSO3HMIm]HSO4 as the catalyst for this
a simple and efficient method for the synthesis of pyrrole one-pot, three-component reaction. Furthermore,
a
derivatives, using the acidic ionic liquid [BSO3HMIm] solvent screening was performed to identify the optimal
HSO4 (3-methyl-2-(1-sulfobutyl)-1H-imidazolium hydro- conditions (Table 1, entries 6–12). The results revealed
gensulfate) (Fig. 2) (15 mol.%) as an easily available, that the solvent played an important role in the reaction.
economical, environmentally benign, and recoverable Among the tested solvents, the highest yield of 90ꢀ% was
catalyst. Furthermore, this strategy was efficient in large- obtained in EtOH at reflux temperature (Table 1, entry 6),
scale preparation, and could be expanded to a one-pot, while the reactions in PEG, toluene, CH3CN, and H2O pro-
four-component reaction.
vided the product in yields of 60–82ꢀ% (Table 1, entries
7–10), and the reactions in CH2Cl2 and EtOAc gave low
yields of 46ꢀ% and 40 %, respectively (Table 1, entries
11–12). Thus, EtOH was chosen as the optimum solvent for
further investigation.
2 Results and discussion
Then, a reaction temperature screening was per-
formed from 30ꢀ°C to reflux temperature in EtOH (Table 2,
entries 1–6). The best result was obtained at reflux temper-
ature (Table 2, entry 6), while the reactions at lower tem-
peratures took longer time and gave lower yields (Table 2,
entries 1–5). Thus, reflux temperature was selected as the
optimum temperature for the reaction. Subsequently, the
catalyst loading was investigated, and it was found that
15 mol.% of catalyst was sufficient to give the product
in an excellent yield of 94ꢀ% (Table 2, entry 7). Hence,
the catalyst loading was set as 15 mol.% for further
investigation.
In order to explore the scope and generality of this
ionic liquid-catalyzed three-component reaction for the
synthesis of pyrrole derivatives, various amines, 1,3-dicar-
bonyl compounds, and nitroolefins were tested under the
optimized conditions (Table 3, entries 1–22). A wide range
of substrates could effectively participate in the reaction.
Aromatic amines bearing either electron-donating (Me,
MeO) or electron-withdrawing (F, Cl, Br) groups were
Initially, the one-pot, three-component reaction of
aniline, β-nitrostyrene, and acetylacetone was used as a
model reaction for the synthesis of a substituted pyrrole.
A blank reaction was carried out in the absence of cat-
alyst in ethanol at reflux temperature for 25 h, and the
product was only obtained in a low yield of 15ꢀ% (Table 1,
entry 1). Then, several catalysts were evaluated including
DBU, l-proline, [BMIm]BF4, [Bpy]BF4, and [BSO3HMIm]
HSO4 (Table 1, entries 2–6). The reactions were carried
out under reflux in ethanol, and all the tested catalysts
showed catalytic effects in different degrees on the model
reaction to give the desired product. When [BSO3HMIm]
O
N
HO
S
O
NH
O
O
S
O
OH
Fig. 2ꢀChemical structure of the ionic liquid [BSO3HMIm]HSO4.
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Y. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4ꢀ
ꢀ31
Table 1ꢀThe screening of catalysts and solventsa.
O
Ph
catalyst (30 mol.%)
solvent, reflux
O
O
N
O2
Ph NH2
Ph
N
Ph
1a
2a
3a
4a
Entry
Catalyst
Solvent
Time (h)
Yield (%)b
1
2
none
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
PEG
toluene
CH3CN
H2O
25
25
25
22
21
10
10
10
10
10
10
10
15
32
35
54
56
90
82
70
62
60
46
40
DBU
3
l-proline
[BMIm]BF4
[Bpy]BF4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
[BSO3HMIm]HSO4
4
5
6
7c
8
9
10
11
12
CH2Cl2
EtOAc
aThe reaction conditions were as follows: aniline (0.5 mmol, 1 equiv.), β-nitrostyrene (0.5 mmol, 1 equiv.), acetylacetone (1.0 mmol, 2
equiv.), catalyst (30 mol.%) in solvent (1.0 mL) at reflux temperature. bIsolated yield after silica gel chromatography. cThe reaction was
carried out at 120 °C.
Table 2ꢀEffect of temperature on the ionic liquid-catalyzed three-component reactiona.
O
Ph
O
O
[BSO3HMIm]HSO4
EtOH
NO2
Ph NH2
Ph
N
Ph
1a
2a
3a
4a
Entry
Temp. (°C)
Time (h)
Yield (%)b
1
2
30
72
72
72
30
10
10
10
78
81
82
85
89
92
94
40
3
50
4
60
5
70
6
reflux
reflux
7c
aThe reaction conditions were as follows: aniline (0.5 mmol, 1 equiv.), β-nitrostyrene (0.5 mmol, 1 equiv.), acetylacetone (0.75 mmol, 1.5
equiv.) and [BSO3HMIm]HSO4 (30 mol.%) in EtOH (1.0 mL). bIsolated yield after silica gel chromatography. c[BSO3HMIm]HSO4 (15 mol.%).
tolerated as well (Table 3, entries 1–15). Benzylamine was electron-donating (MeO, Me) or electron-withdrawing
also applicable to the reaction with various 1,3-dicarbonyl (CN, Cl) substituents in the aromatic ring were examined
compounds and nitroolefins, giving desired products in with different amines and 1,3-dicarbonyl compounds,
good yields (Table 3, entries 16–22). Different 1,3-dicarbo- and the products were obtained in good yields (Table 3,
nyl compounds including acetylacetone, ethyl acetoace- entries 1–21). A heteroaromatic nitroolefin, 2-thienylnitro-
tate, and methyl acetoacetate could be used in the reaction ethylene, was also used in the reaction, giving an accept-
to generate the corresponding products in good to excel- able yield of 72ꢀ% with benzylamine and acetylacetone
lent yields. A series of nitrostyrenes containing either (Table 3, entry 22).
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ꢀY. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4
32ꢀ
Table 3ꢀInvestigation of the substrate scope for the ionic liquid-catalyzed three-component reactiona.
O
R3
R2
[BSO3HMIm]HSO4
O
O
R1 NH2
NO2
R3
(15 mol.%)
N
R1
R2
EtOH, reflux
1
4
2
3
Entry
R1
R2
R3
Product
Time (h)
Yield (%)b
1
2
Ph
Me
Ph
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
12
12
8
96
93
92
89
88
85
92
82
83
84
91
87
86
83
80
80
82
83
83
82
85
72
p-Me-C6H4
p-Me-C6H4
p-OMe-C6H4
p-OMe-C6H4
p-OMe-C6H4
p-OMe-C6H4
p-F-C6H4
p-F-C6H4
p-F-C6H4
p-Cl-C6H4
p-Br-C6H4
p-Br-C6H4
p-Br-C6H4
m-Br-C6H4
PhCH2
Me
p-OMe-C6H4
p-Me-C6H4
Ph
3
Me
4
Me
10
10
14
12
10
10
10
10
12
12
10
12
14
12
12
12
14
12
14
5
Me
p-Cl-C6H4
p-Cl-C6H4
p-OMe-C6H4
p-Cl-C6H4
p-OMe-C6H4
p-Me-C6H4
p-Me-C6H4
p-OMe-C6H4
p-Me-C6H4
p-Cl-C6H4
p-Me-C6H4
Ph
p-Cl-C6H4
p-Cl-C6H4
p-Me-C6H4
p-CN-C6H4
p-OMe-C6H4
2-thienyl
6
OEt
Me
7
8
Me
9
Me
10
11
12
13
14
15
16
17
18
19
20
21
22
Me
Me
Me
Me
Me
Me
OMe
OEt
OMe
OMe
OMe
OMe
Me
PhCH2
PhCH2
PhCH2
4s
4t
4u
4v
PhCH2
PhCH2
PhCH2
aReaction conditions: amine (0.5 mmol, 1 equiv.), nitroolefin (0.5 mmol, 1 equiv.), 1,3-dicarbonyl compound (0.75 mmol, 1.5 equiv.) and
[BSO3HMIm]HSO4 (15 mol.%) in EtOH (1.0 mL) at reflux temperature. bIsolated yield after silica gel chromatography.
A possible pathway for this ionic liquid-catalyzed
To verify that the ionic liquid catalyst [BSO3HMIm]
one-pot, three-component synthesis of pyrrole derivatives HSO4 could be recovered, a recycling study of the catalyst
is outlined in Scheme 1 (see also Refs. [20, 21]). The ionic was performed with the reaction of aniline, β-nitrostyrene,
liquid BSO3HMIm]HSO4 as a Brønsted acid catalyzes the and acetylacetone (Table 4). Upon completing the reaction
reaction sequence.
(monitored by TLC), the solvent was removed. The residue
O
R3
R2
[BSO3HMIm]HSO4
(15 mol.%)
O
O
1
NO2
R NH2
R3
R2
EtOH, reflux
N
R1
4
1
2
3
−
−H
HNO
2O
[BSO3HMIm]HSO4
R1
O
O
NH
O
R3
H
R3
R2
R2
R2
O
N
N+
O−
NH
R1
NH
R1
OH
N
O
O
R3
O
Scheme 1ꢀPossible pathway for the [BSO3HMIm]HSO4-catalyzed synthesis of pyrrole derivatives.
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Y. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4ꢀ
ꢀ33
Table 4ꢀRecycling and reuse of the catalysta.
O
Ph
[BSO3HMIm]HSO4
(15 mol.%)
O
O
NO2
Ph NH2
Ph
N
EtOH, reflux
Ph
1a
2a
3a
4a
Cycle
Time (h)
Yield (%)b
1
2
3
4
5
6
12
12
12
12
12
12
95
92
90
88
78
75
aReaction conditions: aniline (0.5 mmol, 1 equiv.), β-nitrostyrene (0.5 mmol, 1 equiv.), acetylacetone (0.75 mmol, 1.5 equiv.), and
[BSO3HMIm]HSO4 (15 mol.%) in EtOH (1.0 mL) at reflux temperature. bIsolated yield after silica gel chromatography.
was diluted with ethyl acetate, and water was added. The excess nitromethane as a solvent, and a yield of 74ꢀ% was
aqueous phase was washed with ethyl acetate. The organic obtained after 12 h (Scheme 3).
phase was combined for the isolation of the product. The
aqueous phase was evaporated in vacuo. The resulting
residue was directly used in the next reaction cycle without
adding more catalyst. Although the yield decreased gradu- 3 Conclusion
ally, a good yield was still obtained after 6 cycles without
prolonging the reaction time (Table 4).
An economical and environmentally benign ionic liquid
We further performed a larger-scale reaction with [BSO3HMIm]HSO4-catalyzed one-pot reaction of amines,
10 mmol of p-toluidine, 10 mmol of 4-methoxy-nitros- nitroolefins, and 1,3-dicarbonyl compounds for the prepa-
tyrene, and 15 mmol of acetylacetone. This experiment ration of polysubstituted pyrroles was developed. Good
could easily be carried out using the same procedure as to excellent yields (72–96ꢀ%) were obtained with different
for the experimental-scale reactions, and a good yield of types of substrates. The most notable advantages of this
90ꢀ% was obtained after 18 h (Scheme 2).
catalyst are in its high efficiency for a broad scope of sub-
Finally, this ionic liquid-catalyzed reaction could strates, easy recovery, and the ability to scale up. Moreo-
be easily expanded to a one-pot, four-component reac- ver, this procedure could easily be expanded to a one-pot,
tion. The reaction of benzaldehyde, aniline, acetylac- four-component reaction. This ionic liquid-catalyzed
etone, and nitromethane in the presence of [BSO3HMIm] reaction provides an environmentally friendly alternative
HSO4 proceeded smoothly at reflux temperature with to the synthesis of pyrrole derivatives.
OCH3
O
[BSO3HMIm]HSO4
NH2
O
O
NO2
N
(15 mol.%)
H
H
3C
3CO
10 mmol
EtOH, reflux, 18 h
10 mmol
15 mmol
CH3
Yield: 90 %
2.87 g
Scheme 2ꢀA large-scale reaction.
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34ꢀ
ꢀY. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4
O
[BSO3 HMIm]HSO4
(15 mol.%)
Ph
O
O
Ph
CHO
Ph NH2
Me NO2
0.5 mL
reflux,12 h
N
0.5 mmol
0.75 mmol
0.5 mmol
Ph
Yield: 74 %
Scheme 3ꢀThe ionic liquid-catalyzed one-pot, four-component reaction.
4 Experimental part
[BSO3HMIm]HSO4 (15 mol.%), and EtOH (1.0 mL) was
stirred at reflux temperature for 12 h. The solvent was
evaporated, and the residue was diluted with ethyl acetate
(8 mL), and water (3 mL) was added. The aqueous phase
was washed with ethyl acetate (2ꢀ×ꢀ8 mL). The combined
organic layer was concentrated, and purified by silica gel
column chromatography to give the product. The aqueous
phase was evaporated in vacuo, and the resulting residue
was directly used in the next reaction cycle without adding
more catalyst.
4.1 General information
The NMR spectra were recorded with TMS as the internal
standard in CDCl3 on a Bruker 300 MHz instrument at
room temperature. The chemical shifts (δ) were described
in parts per million (ppm), and J values are given in Hertz
(Hz). All reactions were monitored by thin-layer chroma-
tography (TLC) with Haiyang GF254 silica gel plates. Flash
column chromatography was carried out using 200–300
mesh silica gel at increased pressure. All chemical rea-
gents and solvents were purchased from commercial
vendors and used without any further purification. High-
resolution mass spectra (Varian QFT-ESI) were obtained
using ESI ion-ization sources. The purity of products was
determined by HPLC analysis on Chiralpak AD-H.
4.4 A typical procedure for reactions at a
larger scale
A 100-mL round-bottomed flask was charged with p-tolui-
dine (10 mmol), 4-methoxy-nitrostyrene (10 mmol), acety-
lacetone (15 mmol), [BSO3HMIm]HSO4 (15 mol.%), and
EtOH (20 mL). The mixture was stirred at reflux temper-
ature for 18 h. The solvent was removed under vacuum.
The resulting residue was treated with a small amount of
CH2Cl2 to dissolve the product, and the ionic liquid was left
at the bottom. The CH2Cl2 layer was directly loaded onto
the column of silica gel chromatography for purification,
eluted with petroleum ether and ethyl acetate to afford the
desired product as a colorless solid (2.87 g, 90ꢀ% yield).
4.2 General procedure for the ionic liquid-
catalyzed three-component reaction
A 10-mL round-bottomed flask was charged with amine
(0.5 mmol, 1 equiv.), nitroolefin (0.5 mmol, 1 equiv.),
1,3-dicarbonyl compounds (0.75 mmol, 1.5 equiv.),
[BSO3HMIm]HSO4 (15 mol.%), and EtOH (1.0 mL). The
mixture was stirred for a specified amount of time at reflux
temperature. Upon completing the reaction (monitored by
TLC), the solvent was removed under vacuum. The resulting
residue was treated with a small amount of CH2Cl2 to dissolve
the product, and the ionic liquid was left at the bottom. The
CH2Cl2 layer was directly loaded onto the column of silica
gel chromatography for purification, eluted with petroleum
ether and ethyl acetate to afford the desired product.
4.5 A typical procedure for the ionic liquid-
catalyzed four-component reaction
To a stirred mixture of benzaldehyde (0.5 mmol), aniline
(0.75 mmol), acetylacetone (0.5 mmol), and nitrometh-
ane (0.5 mL) was added [BSO3HMIm]HSO4 (15 mol.%).
The reaction mixture was heated to reflux for 12 h, and
then cooled to r.t. The excess nitromethane was removed
under vacuum. The resulting residue was treated with a
4.3 A typical procedure for catalyst recovery small amount of CH2Cl2 to dissolve the product, and the
ionic liquid was left at the bottom. The CH2Cl2 layer was
A mixture of aniline (0.5 mmol, 1 equiv.), β-nitrostyrene directly loaded onto the column of silica gel chromatog-
(0.5 mmol, 1 equiv.), acetylacetone (0.75 mmol, 1.5 equiv.), raphy for purification, eluted with petroleum ether and
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Y. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4ꢀ
ꢀ35
ethyl acetate to afford the desired product as a colorless 131.6(s), 129.3(s), 128.3(s), 127.5(s), 126.8(s), 126.0(s),
solid (103 mg, 74ꢀ% yield).
122.2(s), 120.9(s), 114.5(s), 55.6(s), 31.1(s), 12.9(s) ppm. –
HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm, hexane-
i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ14.08 min.
4.6 Characterization
1-(4-(4-Chlorophenyl)-1-(4-methoxyphenyl)-2-methyl-
All the products are previously described compounds: 1H-pyrrol-3-yl)ethanone (4e)ꢀColorless solid; m.p.:
Refs. [27–30].
1
118–120ꢀ°C (117–119ꢀ°C [27]). – H NMR (300 MHz, CDCl3):
δꢀ=ꢀ7.36–7.21 (m, 6H, Ph), 6.99 (d, Jꢀ=ꢀ8.7 Hz, 2H, Ph), 6.61 (s,
1-(2-Methyl-1,4-diphenyl-1H-pyrrol-3-yl)ethanone 1H, CH), 3.86 (s, 1H, CH3), 2.37 (s, 3H, COCH3), 2.09 (s, 3H,
(4a)ꢁColorless solid; m.p.: 106–108ꢀ°C (105–107ꢀ°C [27]). – CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.1(s), 159.3(s),
1H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.51–7.42 (m, 3H, Ph), 7.39–7.32 135.9(s), 134.6(s), 132.6(s), 131.4(s), 130.5(s), 128.4, (s)
(m, 7H, Ph), 6.67 (s, 1H, CH), 2.41 (s, 3H, COCH3), 2.08 (s, 3H, 127.4(s), 124.7(s), 122.0(s), 121.0(s), 114.4(s), 55.4(s), 31.1(s),
CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.7(s), 138.7(s), 12.8(s) ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C,
136.0(s), 135.3(s), 129.4(s), 129.3(s), 128.3(s), 128.1(s), 254 nm, hexane-i-propanolꢀ=ꢀ85:15): tRꢀ=ꢀ30.07 min.
126.8(s), 126.3(s), 126.2(s), 122.5(s), 120.6(s), 31.1(s), 12.9(s)
ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ298.1205 (calcd. 298.1208 for Ethyl 4-(4-chlorophenyl)-1-(4-methoxyphenyl)-2-met-
C19H17NONa, [M+Na]+). – HPLC (Chiralpak AD-H column, hyl-1H-pyrrole-3-carboxylate (4f)ꢀOrange yellow liquid.
25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ8.73 min.
– 1H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.36–7.19 (m, 6H, Ph), 6.99–
6.96 (d, Jꢀ=ꢀ8.7 Hz, 2H, Ph), 6.64 (s, 1H, CH), 4.19 (q, Jꢀ=ꢀ7.1 Hz,
1-(4-(4-Methoxyphenyl)-2-methyl-1-(p-tolyl)-1H- 2H, CH2), 3.84 (s, 3H, CH3), 2.41 (s, 3H, CH3), 1.17 (t, Jꢀ=ꢀ7.1 Hz,
pyrrol-3-yl)ethanone (4b)ꢁBrown liquid. – 1H NMR 3H, CH2CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ165.6(s),
(300 MHz, CDCl3): δꢀ=ꢀ7.31–7.26 (m, 4H, Ph), 7.21–7.19 (m, 2H, 159.3(s), 137.2(s), 134.1(s), 132.0(s), 131.6(s), 130.5(s), 127.6(s),
Ph), 6.93 (d, Jꢀ=ꢀ8.7 Hz, 2H, Ph), 6.60 (s, 1H, CH), 3.83 (s, 3H, 127.5(s), 125.1(s), 121.2(s), 114.4(s), 111.0(s), 59.5(s), 55.5(s),
CH3), 2.41 (s, 3H, COCH3), 2.39 (s, 3H, Ar-CH3), 2.08 (s, 3H, 14.2(s), 12.6(s) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ392.1025 (calcd.
CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.6(s), 158.6(s), 392.1029 for C21H20ClNO3Na, [M+Na]+). – HPLC (Chiralpak
138.1(s), 136.2(s), 135.3(s), 130.4(s), 129.9(s), 128.4(s), AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ85:15):
126.0(s), 125.7(s), 122.4(s), 120.5(s), 113.7(s), 55.3(s), 31.1(s), tRꢀ=ꢀ20.28 min.
21.1(s), 12.9(s) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ320.1648
(calcd. 320.1651 for C21H22NO2, [M+H]+). – HPLC (Chiralpak 1-(1,4-Bis(4-methoxyphenyl)-2-methyl-1H-pyrrol-3-yl)
AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): ethanone (4g)ꢀColorless solid; m.p.: 134–136ꢀ°C (133–135ꢀ°C
1
tRꢀ=ꢀ17.56 min.
[27]). – H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.30–7.22 (m, 4H,
Ph), 6.99–6.59 (m, 4H, Ph), 3.84 (s, 3H, CH3), 3.82 (s, 3H,
1-(2-Methyl-1,4-di-p-tolyl-1H-pyrrol-3-yl)ethanone CH3), 2.38 (s, 3H, COCH3), 2.08 (s, 3H, CH3) ppm. – 13C NMR
1
(4c)ꢀColorless solid; m.p.: 95–97ꢀ°C (94–96ꢀ°C [30]). – H (75 MHz, CDCl3): δꢀ=ꢀ197.5(s), 159.2(s), 158.6(s), 135.5(s),
NMR (300 MHz, CDCl3): δꢀ=ꢀ7.28–7.25 (m, 4H, Ph), 7.21–7.17 131.6(s), 130.4(s), 128.4(s), 127.4(s), 126.6(s), 125.6(s), 122.2(s),
(m, 4H, Ph), 6.62 (s, 1H, CH), 2.41 (s, 3H, COCH3), 2.39 (s, 120.6(s), 114.4(s), 114.2(s), 113.7(s), 55.5(s), 55.2(s), 31.0(s),
3H, Ar-CH3), 2.38 (s, 3H, Ar-CH3), 2.08 (s, 3H, CH3) ppm. 12.8(s) ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm,
–
13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.7(s), 138.0(s), 136.4(s), hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ20.56 min.
136.2(s), 135.3(s), 133.0(s), 129.7(s), 129.2(s), 129.0(s),
126.1(s), 126.0(s), 122.4(s), 120.5(s), 31.1(s), 21.2(s), 21.1(s), 1-(4-(4-Chlorophenyl)-1-(4-fluorophenyl)-2-methyl-
1
12.9(s) ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 1H-pyrrol-3-yl)ethanone (4h)ꢀBrown oily liquid. – H
254 nm, hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ14.14 min.
NMR (300 MHz, CDCl3): δꢀ=ꢀ7.37–7.27 (m, 6H, Ph), 7.22–7.16
(m, 2H, Ph), 6.63 (s, 1H, CH), 2.37 (s, 3H, COCH3), 2.09
1-(1-(4-Methoxyphenyl)-2-methyl-4-phenyl-1H-pyrrol- (s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.2(s),
3-yl)ethanone (4d)ꢀYellowish solid; m.p.: 93–95ꢀ°C (90– 163.7(s), 160.4(s), 135.6(s), 134.3(s), 132.8(s), 130.4(s),
91ꢀ°C [27]). – H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.38–7.36 (m, 128.5(s), 128.1(s), 127.9(s), 125.0(s), 122.4(s), 120.7(s),
1
4H, Ph), 7.32–7.29 (m, 1H, Ph), 7.23 (d, Jꢀ=ꢀ8.8 Hz, 2H, Ph), 116.5(s), 116.2(s), 31.1(s), 12.8(s) ppm. – HRMS ((+)-
6.98 (d, Jꢀ=ꢀ8.8 Hz, 2H, Ph), 6.62 (s, 1H, CH), 3.84 (s, 3H, ESI): m/zꢀ=ꢀ350.0722 (calcd. 350.0724 for C19H15ClFNONa,
CH3), 2.38 (s, 3H, COCH3), 2.07 (s, 3H, CH3) ppm. – 13C NMR [M+Na]+). – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm,
(75 MHz, CDCl3): δꢀ=ꢀ197.6(s), 159.3(s), 136.1(s), 135.7(s), hexane-i-propanolꢀ=ꢀ85:15): tRꢀ=ꢀ18.08 min.
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ꢀY. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4
36ꢀ
1-(1-(4-Fluorophenyl)-4-(4-methoxyphenyl)-2-methyl- 7.27–7.18 (m, 6H, Ph), 6.61 (s, 1H, CH), 2.39 (s, 3H, COCH3),
1H-pyrrol-3-yl)ethanone (4i)ꢀBrown solid; m.p.: 76–79ꢀ°C 2.38 (s, 3H, Ph-CH3), 2.07 (s, 3H, CH3) ppm. – 13C NMR
(78–80ꢀ°C [27]). – 1H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.31–7.27 (m, (75 MHz, CDCl3): δꢀ=ꢀ197.7(s), 137.7(s), 136.6(s), 134.9(s),
4H, Ph), 7.16 (t, Jꢀ=ꢀ8.4 Hz, 2H, Ph), 6.91 (d, Jꢀ=ꢀ8.4 Hz, 2H, Ph), 132.7(s), 132.5(s), 129.1(s), 129.0(s), 127.7(s), 126.5(s),
6.58 (s, 1H, CH), 3.82 (s, 3H, CH3), 2.37 (s, 3H, COCH3), 2.06 122.9(s), 121.9(s), 120.2(s), 31.1(s), 21.2(s), 12.9(s) ppm. –
(s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.6(s), HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm, hexane-
163.6(s), 160.3(s), 158.7(s), 135.2(s), 130.3(s), 128.1(s), i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ18.45 min.
128.0(s), 127.9(s), 125.9(s), 122.5(s), 120.4(s), 116.4(s), 116.1(s),
113.7(s), 55.2(s), 31.0(s), 12.8(s) ppm. – HPLC (Chiralpak 1-(1-(4-Bromophenyl)-4-(4-chlorophenyl)-2-methyl-
1
AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): 1H-pyrrol-3-yl)ethanone (4n)ꢀYellow liquid. – H NMR
tRꢀ=ꢀ17.75 min.
(300 MHz, CDCl3): δꢀ=ꢀ7.62–7.60 (d, Jꢀ=ꢀ8.4 Hz, 2H, Ph), 7.36–7.27
(m, 4H, Ph), 7.21–7.18 (d, Jꢀ=ꢀ8.4 Hz, 2H, Ph), 6.62 (s, 1H, CH),
1-(1-(4-Fluorophenyl)-2-methyl-4-(p-tolyl)-1H-pyr- 2.38 (s, 3H, COCH3), 2.07(s, 3H, CH3) ppm. – 13C NMR (75 MHz,
rol-3-yl)ethanone (4j)ꢀColorless oily liquid. – H NMR CDCl3): δꢀ=ꢀ197.1(s), 137.5(s), 135.3(s), 134.2(s), 132.9(s), 132.6(s),
1
(300 MHz, CDCl3): δꢀ=ꢀ7.33–7.24 (m, 4H, Ph), 7.20–7.14 (m, 130.41(s), 128.5(s), 127.7(s), 125.3(s), 122.7(s), 122.1(s), 120.4(s),
4H, Ph), 6.61 (s, 1H, CH), 2.38 (s, 6H, COCH3, Ph-CH3), 2.08 31.1(s), 12.8(s) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ411.9902 (calcd.
(s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.7(s), 411.9903 for C19H15BrClNONa, [M+Na]+). – HPLC (Chiralpak
163.6(s), 160.3(s), 136.6(s), 135.3(s), 134.8(s), 134.7(s), AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20):
132.8(s), 129.1(s), 129.0(s), 128.0(s), 127.9(s), 126.3(s), tRꢀ=ꢀ19.52 min.
122.5(s), 120.5(s), 116.4(s), 116.1(s), 31.1(s), 21.1(s), 12.8(s)
ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm, 1-(1-(3-Bromophenyl)-2-methyl-4-(p-tolyl)-1H-pyrrol-
hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ14.05 min.
3-yl)ethanone (4o)ꢀColorless oily liquid. – 1H NMR
(300 MHz, CDCl3): δꢀ=ꢀ7.57–7.52 (m, 2H, Ph), 7.39–7.33 (m,
1-(1-(4-Chlorophenyl)-2-methyl-4-(p-tolyl)-1H-pyrrol- 1H, Ph), 7.29–7.18 (m, 5H, Ph), 6.62 (s, 1H, CH), 2.41 (s,
3-yl)ethanone (4k)ꢀColorless solid; m.p.: 124–126ꢀ°C 3H, COCH3), 2.38 (s, 3H, Ph-CH3), 2.07 (s, 3H, CH3) ppm.
1
(127–129ꢀ°C [27]). – H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.4 6 –7.43
–
13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.7(s), 139.9(s), 136.6(s),
(m, 2H, Ph), 7.28–7.25 (m, 4H, Ph), 7.20–7.17 (m, 2H, Ph), 6.61 135.0(s), 132.6(s), 131.2(s), 130.6(s), 129.3(s), 129.1(s),
(s, 1H, CH), 2.39 (s, 3H, COCH3), 2.38 (s, 3H, Ph-CH3), 2.08 129.0(s), 126.6(s), 124.9(s), 122.9(s), 122.7(s), 120.2(s), 31.1(s),
(s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.6(s), 21.2(s), 12.9(s) ppm. – HPLC (Chiralpak AD-H column,
137.2(s), 136.6(s), 135.0(s), 133.9(s), 132.7(s), 129.5(s), 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ9.39 min.
129.1(s), 127.4(s), 126.5(s), 122.8(s), 120.2(s), 31.1(s), 21.1(s),
12.8(s) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ346.0972 (calcd. Methyl 1-benzyl-2-methyl-4-phenyl-1H-pyrrole-3-car-
346.0975 for C20H18ClNONa, [M+Na]+). – HPLC (Chiralpak boxylate (4p)ꢀColorless oily liquid. – 1H NMR (300 MHz,
AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ85:15): CDCl3): δꢀ=ꢀ7.39–7.23 (m, 8H, Ph), 7.06 (d, Jꢀ=ꢀ6.9 Hz, 2H, Ph),
tRꢀ=ꢀ20.09 min.
6.58 (s, 1H, CH), 5.04 (s, 2H, CH2), 3.66 (s, 3H, COOCH3), 2.46
(s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ166.3(s),
1-(1-(4-Bromophenyl)-4-(4-methoxyphenyl)-2-methyl- 136.7(s), 136.6(s), 135.7(s), 129.0(s), 128.9(s), 128.8(s),
1H-pyrrol-3-yl)ethanone (4l)ꢀColorless solid; m.p.: 127.8(s), 127.3(s), 126.7(s), 126.5(s), 126.1(s), 120.5(s), 110.7(s),
1
123–125ꢀ°C (119–121ꢀ°C [27]). – H NMR (300 MHz, CDCl3): 50.5(s), 11.5(s) ppm. – HRMS ((+)-ESI): m/zꢀ=ꢀ306.1493
δꢀ=ꢀ7.61 (d, Jꢀ=ꢀ8.5 Hz, 2H, Ph), 7.27 (d, Jꢀ=ꢀ8.5 Hz, 2H, Ph), 7.21 (calcd. 306.1494 for C20H19NO2H [M+H]+). – HPLC (Chiralpak
(d, Jꢀ=ꢀ8.5 Hz, 2H, Ph), 6.93 (d, Jꢀ=ꢀ8.5 Hz, 2H, Ph), 6.60 (s, AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ85:15):
1H, CH), 3.83 (s, 3H, CH3), 2.40 (s, 3H, COCH3), 2.07 (s, 3H, tRꢀ=ꢀ7.89 min.
CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.6(s), 158.7(s),
137.7(s), 134.9(s), 132.5(s), 130.3(s), 128.0(s), 127.7(s), 126.2(s), Ethyl 1-benzyl-4-(4-chlorophenyl)-2-methyl-1H-pyr-
1
122.9(s), 121.8(s), 120.1(s), 113.7(s), 55.2(s), 31.0(s), 12.9(s) role-3-carboxylate (4q)ꢀColorless oily liquid. – H NMR
ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm, hex- (300 MHz, CDCl3): δꢀ=ꢀ7.31–7.24 (m, 7H, Ph), 7.05 (d, Jꢀ=ꢀ6.8
ane-i-propanolꢀ=ꢀ85:15): tRꢀ=ꢀ27.86 min.
Hz, 2H, Ph), 6.56 (s, 1H, CH), 5.04 (s, 2H, Ph-CH2), 4.15 (q,
Jꢀ=ꢀ7.1 Hz, 2H, COOCH2), 2.46 (s, 3H, CH3), 1.15 (t, Jꢀ=ꢀ7.1 Hz,
1-(1-(4-Bromophenyl)-2-methyl-4-(p-tolyl)-1H-pyr- 3H, CH2CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ165.6(s),
1
rol-3-yl)ethanone (4m)ꢀYellow oily liquid. – H NMR 136.7(s), 136.6(s), 134.3(s), 131.9(s), 130.5(s), 128.9(s),
(300 MHz, CDCl3): δꢀ=ꢀ7.62–7.59 (d, Jꢀ=ꢀ8.5 Hz, 2H, Ph), 127.8(s), 127.6(s), 126.5(s), 125.0(s), 120.5(s), 110.8(s),
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Y. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4ꢀ
ꢀ37
59.4(s), 50.5(s), 14.0(s), 11.5(s) ppm. – HPLC (Chiralpak 1-(1-Benzyl-2-methyl-4-(thiophen-2-yl)-1H-pyrrol-3-yl)
AD-H column, 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): ethanone (4v)ꢁGray solid; m.p.: 137–139ꢀ°C (136–138ꢀ°C
1
tRꢀ=ꢀ7.97 min.
[27]). – H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.37–7.29 (m, 3H,
Ar-H), 7.26–7.25 (m, 1H, Ar-H), 7.10–7.07 (m, 2H, Ar-H), 7.05–
Methyl 1-benzyl-4-(4-chlorophenyl)-2-methyl-1H-pyr- 7.02 (m, 1H, Ar-H), 6.96 (d, Jꢀ=ꢀ2.8 Hz, 1H, Ar-H), 6.63 (s, 1H,
role-3-carboxylate (4r)ꢀOff-white solid; m.p.: 77–79ꢀ°C CH), 5.05 (s, 2H, Ph-CH2), 2.43 (s, 3H, COCH3), 2.15 (s, 3H,
1
(79–80ꢀ°C [27]). – H NMR (300 MHz, CDCl3): δꢀ=ꢀ7.34–7.25 CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ197.1(s), 137.1(s),
(m, 7H, Ph), 7.06 (d, Jꢀ=ꢀ7.0 Hz, 2H, Ph), 6.57 (s, 1H, CH), 5.05 136.2(s), 135.5(s), 129.0(s), 128.9(s), 128.1(s), 127.9(s),
(s, 2H, Ph-CH2), 3.67 (s, 3H, COOCH3), 2.46 (s, 3H, CH3) ppm. 127.1(s), 126.9(s), 126.6(s), 124.8(s), 121.5(s), 117.2(s), 50.3(s),
–
13C NMR (75 MHz, CDCl3): δꢀ=ꢀ166.0(s), 136.8(s), 136.5(s), 30.5(s), 11.7(s) ppm. – HPLC (Chiralpak AD-H column,
134.2(s), 131.9(s), 130.4(s), 128.9(s), 127.8(s), 127.7(s), 25ꢀ°C, 254 nm, hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ7.00 min.
126.5(s), 125.0(s), 120.6(s), 111.4(s), 50.6(s), 50.5(s), 11.5(s)
ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm,
hexane-i-propanolꢀ=ꢀ85:15): tRꢀ=ꢀ9.67 min.
5 Supporting information
Methyl 1-benzyl-2-methyl-4-(p-tolyl)-1H-pyrrole-3-car-
The spectra and chromatograms of 4a–4v are given as
boxylate (4s)ꢀColorless oil. – 1H NMR (300 MHz, CDCl3):
Supporting Information.
δꢀ=ꢀ7.24–7.14 (m, 5H, Ph), 7.06–7.03 (m, 2H, Ph), 6.98–6.95
(d, Jꢀ=ꢀ6.9 Hz, 2H, Ph), 6.47 (s, 1H, CH), 4.95 (s, 2H, Ph-CH2),
Acknowledgments: This work was financially supported
3.59 (s, 3H, COOCH3), 2.36 (s, 3H, Ph-CH3), 2.27 (s, 3H, CH3)
by the National Natural Science Foundation of China (no.
ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ166.3(s), 136.7(s),
21276211).
136.4(s), 135.7(s), 132.7(s), 128.9(s), 128.9(s), 128.8(s),
128.4(s), 127.7(s), 127.3(s), 126.7(s), 126.5(s), 126.1(s),
120.4(s), 110.6(s), 82.7(s), 50.5(s), 50.4(s), 21.2(s), 11.5(s)
References
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ppm. – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm,
hexane-i-propanolꢀ=ꢀ85:15): tRꢀ=ꢀ9.58 min.
Methyl 1-benzyl-4-(4-cyanophenyl)-2-methyl-1H-pyr-
role-3-carboxylate (4t)ꢀOrange yellow liquid. – 1H NMR
(300 MHz, CDCl3): δꢀ=ꢀ7.60–7.57 (m, 2H, Ph), 7.48–7.45 (m,
2H, Ph), 7.35–7.30 (m, 3H, Ph), 7.08–7.05 (m, 2H, Ph), 6.65
(s, 1H, CH), 5.08 (s, 2H, Ph-CH2), 3.69 (s, 3H, COOCH3), 2.47
(s, 3H, CH3) ppm. – 13C NMR (75 MHz, CDCl3): δꢀ=ꢀ165.7(s),
140.7(s), 137.4(s), 136.2(s), 131.5(s), 131.4(s), 130.5(s),
129.6(s), 129.0(s), 128.3(s), 128.0(s), 127.5(s), 126.6(s),
126.4(s), 121.2(s), 119.4(s), 109.4(s), 50.7(s), 11.6(s) ppm.
– HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm, hexane-
i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ14.03 min.
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((+)-ESI): m/zꢀ=ꢀ358.1417 (calcd. 358.1419 for C21H21NO3Na
[M+Na]+). – HPLC (Chiralpak AD-H column, 25ꢀ°C, 254 nm,
hexane-i-propanolꢀ=ꢀ80:20): tRꢀ=ꢀ8.40 min.
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ꢁꢁꢁꢂ
ꢀY. Luo et al.: The acidic ionic liquid [BSO3HMIm]HSO4
38ꢀ
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