Aza-crown ether complex cation ionic liquids: Preparation and applications in organic reactions

Article abstract of DOI:10.1002/chem.201403118

Aza-crown ether complex cation ionic liquids (aCECILs) were devised, fabricated, and characterized by using NMR spectroscopy, MS, thermogravimetric differential thermal analysis (TG-DTA), elemental analysis and physical properties. These new and room-temperature ILs were utilized as catalysts in various organic reactions, such as the cycloaddition reaction of CO₂ to epoxides, esterification of acetic acid and alcohols, the condensation reaction of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes were investigated carefully. In these reactions, the ionic liquid exhibited cooperative catalytic activity between the anion and cation. In addition, the aza-[18-C-6HK][HSO₄]₂ was the best acidic catalyst in the reactions of esterification and Friedel-Crafts alkylation under mild reaction conditions. Jewel in the crown: Nine new and room-temperature aza-crown ether complex ionic liquids (aCECILs) composed of multiple cations and anions were fabricated through a convenient procedure (see scheme). Some of them were used as catalysts in various organic reactions, such as the cycloaddition reaction of CO₂ to propylene oxide, esterification of acetic acid and alcohols, the condensation of aniline and propylene carbonate, and Friedel-Crafts alkylation of indole with aldehydes.

Full text of DOI:10.1002/chem.201403118

DOI: 10.1002/chem.201403118
Full Paper
&
Ionic Liquids
Aza-Crown Ether Complex Cation Ionic Liquids: Preparation and
Applications in Organic Reactions
[
a]
Yingying Song, Chen Cheng, and Huanwang Jing*
Abstract: Aza-crown ether complex cation ionic liquids (aCE-
CILs) were devised, fabricated, and characterized by using
NMR spectroscopy, MS, thermogravimetric differential ther-
mal analysis (TG-DTA), elemental analysis and physical prop-
erties. These new and room-temperature ILs were utilized as
catalysts in various organic reactions, such as the cycloaddi-
pylene carbonate, and Friedel–Crafts alkylation of indole
with aldehydes were investigated carefully. In these reac-
tions, the ionic liquid exhibited cooperative catalytic activity
between the anion and cation. In addition, the aza-[18-C-
6HK][HSO ] was the best acidic catalyst in the reactions of
4
2
esterification and Friedel–Crafts alkylation under mild reac-
tion conditions.
tion reaction of CO to epoxides, esterification of acetic acid
2
and alcohols, the condensation reaction of aniline and pro-
Introduction
drogen bond donors and acceptors have been used in Michael
[8]
[9]
additions and Povarov reactions. Recently, Gao et al. applied
the cooperative catalyst of an ionic liquid, 1-butyl-3-methyl-
imidazolium, in reactions of aniline and ethylene carbonate
Ionic liquids (ILs) have attracted increased interest in the last
decades with a diversified range of applications. The types of
ionic liquids have also been extended to new families with
successfully. To our delight, the aza-[18-C-6HK][Br] (18-C-6=
2
[
1]
more specific and targeted properties. The large number of
cations and anions allows a wide range of physical and chemi-
cal characteristics to be achieved, including volatile and invola-
tile systems, thus the terms “designer” and “task-specific” ionic
[18]crown-6) also acts as cooperative catalyst in the reaction of
aniline and propylene carbonate and the cycloaddition of CO2
to epoxides.
[10]
Brønsted acidic ionic liquids possessing a proton in their
[
2]
À
À
liquids have been developed. Catalytic reactions in ionic liq-
uids have been examined for at least 20 years; for example,
the first report of the use of an ionic liquid as a catalyst in Frie-
counteranions, such as [HSO4] and [H PO ] , have attracted
2
4
attention due to their proton acidity and powerful catalytic
[11]
properties in the esterification reaction. Therefore, the aza-
[18-C-6HK][HSO ] was utilized as an efficient Brønsted acidic
[
3]
del–Crafts acylation was reported in 1986. However, there
has been an explosion in their usages of catalytic and stiochio-
4
2
catalyst in the esterification reaction of acetic acid and
alcohols.
[4]
metric reactions as well as in many other employments.
Pursuant to our own efforts toward the development of
highly efficient catalysts of crown ether complex ionic liquids
Bis(indolyl)methane derivatives are well known for their vari-
ous biological and pharmaceutical activities. In recent years,
many methods had been reported for the synthesis of bis-
(indolyl)methane catalyzed by Lewis acids, Brønsted acids, and
[
5]
(CECILs), in which the electrostatic interactions between large
cations and anions are relatively weak, versus the relatively
strong van der Waals forces that reduce the lattice energy and
[12]
ionic liquids. In 2004, Nagarajan and Perumal reported a nice
result for the synthesis of bis(indolyl)methane in the presence
[
6]
melting point of crystals. On the basis of these understand-
ings, we designed and fabricated a series of aza-crown ether
complex cation ionic liquids (aCECILs) that would be further
functionalized and employed in various organic reactions.
Cooperative catalysis is one of the most fundamental princi-
ples in enzymatic catalysis and has currently emerged for use
[13]
of potassium hydrogen sulfate.
Herein, the aza-[18-C-6HK]
[HSO ] was applied as a good homogenous catalyst in the
4
2
Friedel–Crafts alkylation reaction.
Results and Discussion
[
7]
with many organic syntheses. Following this concept, the hy-
Initially, following our previous procedure, the aza-crown ether
and potassium salt were mixed and dissolved in water; the de-
sired aza-crown ether complex cation ionic liquid could not be
obtained as a clear solution due to the poor solubility of aza-
crown ether. Strangely, when the solvent was changed to
a mixture of water/THF, it also formed a slurry due to the poor
coordination action of aza-crown ether to the potassium
cation. Considering the basicity of the aza-crown ether, anoth-
[
a] Dr. Y. Song, C. Cheng, Prof. H. Jing
State Key Laboratory of Applied Organic Chemistry
College of Chemistry and Chemical Engineering
2
22 South Tianshui Rd, Lanzhou (P.R. China)
Fax: (+86)0931-8912582
E-mail: hwjing@lzu.edu.cn
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201403118.
Chem. Eur. J. 2014, 20, 12894 – 12900
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Full Paper
Table 2. The coupling reaction of CO
2
and epoxides catalyzed by aCECIL.
[
a]
Entry
Catalyst
R
t
Yield
[%]
[
b]
[
h]
1
2
3
4
5
6
7
8
9
1a
2a
1a
2a
1a
2a
1a
2a
1a
2a
1a
2a
CH
CH
ClCH
ClCH
CH
CH
CH
CH
3
3
17
15
7
95.6
96.7
84.8
86.0
86.0
89.0
54.0
70.0
74.0
2
2
4
3
3
3
3
CH
CH
(CH
(CH
2
2
10
10
24
24
29
24
2
)
)
9
9
2
C
C
C
C
6
6
6
6
H
H
H
H
6
Figure 1. The structures of aza-crown ether complex cation ionic liquids.
10
6
>99
89.5
95.0
1
1
6
6
CH
CH
2
OCH
OCH
2
2
6.5
6.5
1
2
2
er portion of relevant acid was added into the mixture of aza-
crown ether and potassium salt in water/THF (1:1, v/v) solu-
tion. A clear solution was obtained. The existing excess aza-
crown ether with CH Cl was extracted then evaporated and
[
a] Reaction conditions: Epoxide: 100 mmol, catalyst: 0.5 g, initial pressure
of CO : 1.2 MPa, T=1008C. [b] Yield of the isolated product.
2
2
2
dried in vacuum to generate each aCECIL. All of the aza-crown
ether complex cation ionic liquids are pale yellow and very vis-
cous liquids. The structures of aCECILs are depicted in Figure 1.
They feature two positive charge centers in one cation: One in
the nitrogen and another in the potassium.
epichlorohydrin and phenyl glycidyl ether with CO are much
2
faster than other substrates (Table 2, entries 3, 4, 11, and 12).
The results also revealed that catalyst 2a showed higher activi-
ty than catalyst 1a due to its better solubility in epoxides.
Previous investigations reveal that the mechanism of cou-
The new aza-crown ether complex cation ionic liquids have
melting points below 08C (Table 1). They are thermally stable
up to 172–2668C measured by TG-DTA. The hydrogen connect-
ed with nitrogen in aCECILs can easily form hydrogen bonds
when it is used as a catalyst in catalytic reactions. Therefore,
these aza-crown ether complex cation ionic liquids can be ap-
plied to catalytic reactions, especially collaborative catalytic re-
actions.
pling reaction of epoxides and CO must involve two catalytic
2
[16]
centers: Lewis acid and Lewis base centers. Our aza-crown
ether complex cation ionic liquids is made up of two parts:
Cation (Lewis acid, electrophile) and anion (Lewis base, nucleo-
phile), with good catalytic activity for the coupling reaction of
CO and epoxides. The potassium in the cation acts as a Lewis
2
acid-activating epoxide and the proton also activates epoxide
through hydrogen bond (Scheme 1); simultaneously, the anion
Even though some ionic liquids have been used as catalysts
[
14]
À
in the coupling of CO and epoxides, few ionic liquids used
Br represents a nucleophile to attack the terminal carbon of
2
in this reaction as catalysts alone. On the basis of our previous
report that used a chiral ionic liquid as co-catalyst in the asym-
epoxide. These activations of epoxide promote the reactions
that can be carried out smoothly at 1008C.
[
6b,15]
metric cycloaddition of CO and epoxides,
these new aCE-
Ionic liquids have attracted great interest due to their plenti-
2
[17]
CILs were used alone to catalyze the coupling reaction of CO2
and epoxides in high yields within 24 h (Table 2). By utilizing
ionic liquid 1a and 2a as catalysts, the coupling reactions of
ful hydrogen bonds. They can provide both hydrogen bond
donors and acceptors, which gives them the chance to serve
as collaborative catalysts. Recent investigation of ionic liquids
reveals that the cations as hydrogen bond donors are effective
[18]
active sites for electrophiles in organic reactions. The cations
of our aza-crown ether complex cation ionic liquids also act as
hydrogen bond donors and the anions act as hydrogen bond
Table 1. The properties of aza-crown ether complex cation ionic liquids.
[
a]
Entry
Ionic
M.p.
T
d
liquid
[8C]
[8C]
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
2a
2b
2c
2d
À11
À18
À17
À10
À20
À10
À24
À16
À8
212
198
220
208
216
245
211
172
202
Scheme 1. The coupling reaction of CO
2
and epoxide catalyzed by aza-
À1
d
[a] T was determined by TG-DTA at 108C min under nitrogen.
crown ether complex cation ionic liquid.
Chem. Eur. J. 2014, 20, 12894 – 12900
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the environment. To overcome these drawbacks, ionic liquid
catalysts that are eco-friendly and have a high efficiency have
Table 3. The condensation reaction of aniline and propylene carbonate
catalyzed by aCECIL.
[19]
been reported. According to these reports, the presence of
an acidic proton on the anionic component of the IL plays an
important role in the activation of the reaction. Hence, great
efforts were made in exploring aza-[18-C-6KH][HSO ] in the
4
[
a]
esterification of acetic acid and fatty alcohol. It can be detect-
ed from Table 4 that the esterification of aliphatic acids with
primary alcohols was very satisfactory.
Entry
Catalyst
R
t
Yield
[%]
[
b]
[h]
1
2
3
4
5
6
7
8
9
1a
1b
2a
2b
1a
1b
2a
2b
1a
1b
2a
2b
H
H
H
H
7
5
7
5
35.0
51.0
50.0
72.7
60.7
63.2
70.8
90.0
trace
5.0
trace
8.1
Table 4. Esterification of acetic acid and alcohols catalyzed by aCECIL.
4-Cl
4-Cl
4-Cl
4-Cl
4-OCH
4-OCH
4-OCH
4-OCH
11
11
11
12
5
[
a]
3
3
3
3
Entry
Catalyst
Alcohol
t
[h]
Yield
[%]
[
b]
10
5
5
5
1
1
1
2
3
4
5
6
1e
1e
1e
1e
1e
1e
butan-1-ol
pentan-1-ol
3-methylbutan-1-ol
hexan-1-ol
cyclohexanol
2
2
2
2
2
2
99
96
87
99
85
12
[
a] Reaction conditions: Amine: 2 mmol, propylene carbonate: 10 mmol,
T=1308C; IL: 10 mol%. [b] Yield of the isolated product.
4-OCH
3
8.1
acceptors. The reaction of aniline and propylene carbonate
was investigated by using ionic liquids 1a, 1b, 2a, and 2b as
catalysts, respectively.
[a] Reaction conditions: Alcohol: 14 mmol, acetic acid: 2 mmol in cyclo-
hexane (2 mL), IL: 0.2 mmol, T=908C. [b] Yield was detected by GC with
a FID detector.
The condensation reactions of aniline derivatives and propyl-
ene carbonate were investigated by utilizing the aza-crown
ether complex cation ionic liquid as a catalyst. From Table 3,
we knew that aniline and its derivatives proceeded to this re-
action smoothly in moderate to high yields at 1308C. It is
worth mentioning that catalysts b have higher catalytic activity
Esterification is a reaction under equilibrium; the equilibrium
can be shifted towards the product by the removal of water or
an excess of one reactant. Therefore, with the aim of shifting
the equilibrium, we used cyclohexane as a dehydrating agent.
Furthermore, we have found that the best molar ratio of acid
to alcohols was 1:7 and the reaction would proceed smoothly
when being carried out at 908C. It is noteworthy that the
length of alkyl chains did not heavily affect the conversion
(Table 4, entries 1, 2, and 4) and the yield of the esterification
participated by branched alcohols (Table 4, entries 3 and 5) is
lower than those by unbranched ones.
À
than catalysts a, because the anion OAc of catalyst b is
a better hydrogen-bond acceptor compared with the anion
À
Br of catalyst a. The cations of ionic liquids formed hydrogen
bonds with ketonic oxygen, which activated the substrate pro-
pylene carbonate; the anion of ionic liquids formed hydrogen
bonds with amidogen to activate aniline simultaneously
(Scheme 2). The dual activation of propylene carbonate and
aniline by the cations and anions of ionic liquids is crucial to
promote the reaction.
Many synthetic routes to the bis-indolylmethanes comprise
the protic or Lewis acid-catalyzed condensation reaction of in-
doles or indolyl with aldehydes, ketones, imines, iminium salts,
Conventionally, the esterification of carboxylic acids and al-
cohols, particularly unbranched alcohols, was carried out in the
presence of catalyst, such as inorganic liquid acids, solid acids,
or bioenzymes. However, these catalysts reveal certain disad-
vantages, such as their low efficiency and negative effects on
[12,20]
or nitrones
Herein, we report a simple and efficient
method of synthesizing bis(indolyl)alkyane with indole and al-
dehyde, catalyzed by an acidic Brønsted ionic liquid, aza-[18-C-
6KH][HSO ] . The results are summarized in Table 5. In the ini-
4
2
tial catalytic activity experiments, different solvents were
screened (Table 5, entries 1–4) and the highest yield was
obtained with methanol.
Under the optimized reaction conditions, we examined the
Friedel–Crafts alkylation reaction with different substrates
(
Table 5). It can be seen that good yields were obtained from
a variety of substituted aldehydes. Evidently, both the elec-
tron-withdrawing groups and the electron-donating groups
that substitute aromatic aldehydes have no negative effects on
this reaction, but speed up the reaction process (Table 5, en-
tries 7–13) instead. The nitrobenzaldehyde and p-anisaldehyde
have the highest activity and give excellent yields (Table 5, en-
Scheme 2. The model of aza-crown ether complex cation ionic liquids to ac-
tivate substrates.
Chem. Eur. J. 2014, 20, 12894 – 12900
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Experimental Section
Table 5. Friedel–Crafts alkylation reaction of indoles with aldehydes by
aCECIL.
Materials and methods
All reagents were obtained from commercial resources and used
1
13
without further purification. H and C NMR spectra were recorded
on Varian 300 spectrometers, with TMS as internal reference (d =
H
7
.26 ppm for CDCl , d =77 ppm for CDCl ; d =4.80 ppm for D O,
3 C 3 H 2
d =2.50 for [D ]DMSO). Chemical shifts (d) are given in parts per
H
6
[
a]
million (ppm) and coupling contants (J) are given in Hertz (Hz).
Multiplicity is indicated by one or more of the following: s (singlet);
d (doublet); t (triplet); q (quartet);m (multiplet); br (broad).Ther-
mogravimetric-differential thermal analysis (TG-DTA) was carried
out on a STA 449C (Netzsch, Germany). Elemental analyses were
carried out on Carioel elemental analyzer. Infrared spectra were
collected on a Nicolet NEXUS 670 FT-IR spectrometer using a KBr
pellet.
Entry
R
Solvent
t
Yield
[%]
[
b]
[h]
1
2
3
4
5
6
7
8
9
Ph
Ph
Ph
Ph
CH
CH
3
OH
Cl
OH
1
1
1
1
92
80
81
88
78
87
94
91
94
83
84
93
93
80
2
2
C
2
H
5
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CH
3
CN
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
2-NO
3-NO
4-NO
3-CH
4-CH
3-CH
4-CH
3-ClC
4-ClC
2 2 2
CH CH CH
2
2
2
C
C
C
OC
OC
6
6
6
H
H
H
4
4
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
2.5
4
3
6
H
4
4
General procedure for the synthesis of aza-crown ether
complex cation ionic liquids (aCECILs)
3
3
3
6
H
10
C
C
6
H
H
4
1
1
6
4
1
1
1
2
3
4
6 4
H
6
H
4
[a] Reaction conditions: Indole: 2.0 mmol, substituted benzaldehydes:
1.0 mmol in methanol (2 mL), RT, IL (1e): 0.1 mmol. [b] Yield of the isolat-
ed product.
N-Butyldiethanolamine: A mixture of n-butyl bromide (7.87 g,
5
7.5 mmol), diethanolamine (5.26 g, 50.0 mmol), and Na CO
2 3
(
1.3 equiv, 6.89 g, 65 mmol) were stirred at 808C in CH CN (1 mL)
3
tries 7 and 9). A decrease in the yield was observed when o-ni-
trobenzaldehyde was used, which could be attributed to the
steric effects (Table 5, entry 5). When aliphatic aldehydes were
used in this reaction, there was a slight decrease in the yield
under N2 for 24 h. After completion of the reaction, the mixture
was filtered and the filtrate was concentrated. Then, water (30 mL)
was added and the mixture was extracted by ethyl acetate (3ꢁ
2
0 mL). The combined organic layer was washed with water (3ꢁ
(
Table 5, entry 14).
10 mL) and dried by anhydrous Na SO . The solvent was removed
2
4
[21]
under vacuum to obtain the pale-yellow oily product (85.0%).
1
H NMR (CDCl , 300 MHz): d=0.90 (t, J=7.5, 7.2 Hz, 3H), 1.27 (m,
3
Conclusion
2
4
H), 1.41 (m, 2H), 2.51 (t, J=7.5 Hz, 2H), 2.64 (dd, J=3.0, 5.1 Hz,
H), 2.95 (br, 2H), 3.59 ppm (dd, J=5.4, 3.0 Hz, 4H).
We have designed and synthesized a series of aza-crown ether
complex cation ionic liquids. Compared with crown ether com-
plex cation ionic liquids, the new ionic liquids have protons en-
abling the catalytic activity of the cations. Then, we investigat-
ed their applications in several organic reactions, such as the
coupling reaction of CO and epoxides, the condensation reac-
2
tion of propylene carbonate and aniline, esterification of acetic
acid and alcohols, and Friedel–Crafts alkylation reaction. The
most attractive part of this work is that the cations and anions
of aza-crown ether complex cation ionic liquids simultaneously
participate in the catalytic reaction and show synergistic
effects.
N-benzyldiethanolamine: Benzyl bromide (7.14 g, 41.7 mmol) was
added to a solution of diethanolamine (4.82 g, 45.9 mmol) and
Na CO (4.42 g, 41.7 mmol) in acetone (30 mL) and stirred for 8 h
2
3
at 648C, then the resulting mixture was cooled down to room tem-
perature. Water (20 mL) was added after removing acetone. The
mixture was extracted with CH Cl (3ꢁ20 mL), The combined or-
2
2
ganic layer was washed with water (3ꢁ10 mL), dried over anhy-
drous sodium sulfate and concentrated under reduced pressure to
The advantages of this kind of aza-crown ether cation com-
plex ionic liquid over traditional ionic liquids could be due to
the nitrogen atom of the aza-crown, which gives them low
melting points and good catalytic activities in organic reac-
tions, and so on. To the best of our knowledge, this is the first
report of this type of IL and its application to catalyze organic
reactions. We hope this work can attract more and more scien-
tists to develop in this new field.
[22] 1
give the desired product (67.5).
H NMR (300 MHz, CDCl ): d=
3
2
7
.70 (dd, J=5.1 Hz, 4H), 3.06 (br, 2H), 3.62 (m, 4H), 3.69 (s, 2H),
.26 ppm (m, 5H).
Tetraethylnene glycol di-p-tosylate: Tetra(ethylene glycol) (5.00 g,
.40 mL, 25.7 mmol) and 4-methylbenzene-1-sulfonyl chloride
14.7 g, 77.2 mmol) were dissolved in THF (about 100 mL) and
4
(
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À1
cooled down to 08C in an ice-bath. Then, potassium hydroxide
10.1 g, 180.2 mmol) dissolved in water (25 mL) was added drop-
1295.8, 1249.4, 1105.6, 949.2, 834.8, 741.8, 702.1 cm ; elemental
(
analysis calcd (%):C 41.24, H 5.83, N 2.53; found: C 41.35, H 6.14,
N 2.16.
wise (ꢀ1 h) into the obtained THF solution. After additional 4 h of
stirring at room temperature the mixture was poured into water/
1
1
-Benzyl-1-aza-[18-C-6HK][OAc] ·1/4H O (1b): H NMR (300 MHz,
D O): d=1.91 (s, 6H), 3.26–3.40 (m, 4H), 3.66–3.92 (m, 20H), 4.37
m, 2H), 7.52 ppm (m, 5H); C NMR (75 MHz, D O): d=23.74,
3.58, 54.49, 54.82, 56.13, 64.01, 64.44, 69.06, 69.54, 69.85, 70.06,
0.26, 129.67, 130.35, 131.40, 131.86, 181.76 ppm. H NMR
300 MHz, [D ]DMSO): d=1.71 (s, 6H), 2.59 (m, 4H), 3.35–3.63 (m,
˜
22H), 5.85 (br, 1H), 7.31 ppm (m, 5H); IR: n=3382.0, 2880.0,
658.6, 1574.8, 1452.5, 1404.8, 1355.6, 1274.2, 1250.4, 1112.6, 952.0,
2
2
Et O (50/150 mL). The organic layer was separated and the aque-
2
2
ous layer was extracted three times with Et O. The combined or-
13
2
(
2
ganic layers were washed with saturated NH Cl solution and water
4
5
7
and were dried over MgSO before evaporating the solvent. Then,
1
4
[
23]
the clean product was obtained as a white solid in 95% yield.
(
6
1
H NMR (300 MHz, CDCl ): d=2.44 (s, 6H), 3.52–3.69 (m, 12H), 4.14
3
(
m, 4H), 7.34 (d, J=7.5 Hz, 2H), 7.79 ppm (d, J=8.1 Hz, 2H).
1
8
À1
34.8, 835.3, 774.6, 736.4, 703.3 cm ; elemental analysis calcd (%):
C 53.52, H 7.52, N 2.71; found: C 53.67, H 7.17, N 2.36.
1
1
-Benzyl-1-aza-[18-C-6HK][SO ]·(1c): H NMR (300 MHz, D O): d=
4
2
3
7
5
1
4
3
.37–3.44 (m, 4H), 3.64–3.93 (m, 20H), 4.45 (t, J=5.4, 6.3 Hz, 2H),
13
.51 ppm (s, 5H); C NMR (75 MHz, D O): d=53.93, 54.74, 54.98,
2
5.86, 63.93, 64.33, 69.29, 69.76, 70.09, 70.31, 70.52, 129.98, 130.82,
1
31.89, 132.13 ppm. H NMR (300 MHz, [D ]DMSO): d=2.85 (br,
6
H), 3.50–3.69 (m, 20H), 3.87 (br, 2H), 7.40 ppm (m, 5H); IR: n˜ =
405.1, 2878.5, 1706.5, 1645.5, 1456.2, 1356.5, 1248.9, 1223.2,
À1
1114.6, 951.9, 835.9, 742.1, 702.5 cm ; elemental analysis calcd
(
%):C 46.61, H 6.59, N 2.86; found: C 46.99, H 7.00, N 2.56.
-Benzyl-1-aza-[18-C-6HK][H PO ] ·1/4H O (1d):
300 MHz, D O) d=3.30–3.40 (m, 4H), 3.58–3.88 (m, 20H), 4.39 (t,
1
1
(
H NMR
2
4
2
2
2
13
The synthesis of aza-crown ether complex cation ionic liquid
a: NaH (40 mmol, 80%, 1.20 g) and dry THF (100 mL) were added
to a 500 mL round bottom flask and cooled to 08C in an ice-bath.
N-benzyldiethanolamine (10 mmol, 1.95 g) was dissolved in dry
THF (100 mL) and added dropwise to the cooled system during
J=8.7, 6.6 Hz, 2H), 7.45 ppm (s, 5H); C NMR (75 MHz, D O): d=
2
1
53.39, 54.22, 54.46, 55.31, 63.40, 63.80, 68.76, 69.25, 69.60, 69.80,
70.01, 129.52, 130.38, 131.36, 131.67 ppm. H NMR (300 MHz,
1
[D ]DMSO): d=2.70 (m, 4H), 3.45–3.58 (m, 20H), 3.70 (d, J=2.1 Hz,
6
2H), 5.82 (br, 1H), 7.33 ppm (m, 5H); IR: n˜ =3375.3, 2875.8, 1706.6,
1
h. The ice-bath was then removed and the mixture was heated
1600.6, 1457.2, 1355.2, 1295.1, 1248.5, 1111.1, 948.4, 740.2,
702.7 cm ; elemental analysis calcd (%): C 38.55, H 6.21, N 2.37;
found: C 38.54, H 6.08, N 2.36.
À1
to reflux for 2 h. This system was cooled to 08C in an ice-bath and
added the solution of THF (100 mL)-dissolved tetraethylnene glycol
ditosylate (10 mmol, 5.026 g). Then, the ice-bath was removed and
the mixture was stirred for 48 h under reflux. After completion of
the reaction, the mixture was concentrated and added water
1
1
-Benzyl-aza-[18-C-6HK][HSO ] ·H O (1e): H NMR (300 MHz,
4
2
2
D O): d=3.30–3.40 (m, 4H), 3.58–3.88 (m, 20H), 4.39 (t, J=8.7,
2
13
6
5
1
.6 Hz, 2H), 7.45 ppm (s, 5H); C NMR (75 MHz, D O): d=50.69,
2
(
100 mL). The mixture was extracted with CH Cl (3ꢁ70 mL). The
2 2
1.53,51.72, 52.62,55.48, 60.69, 61.10, 66.05, 66.54, 66.90, 67.06,
combined organic layer was washed with water (3ꢁ50 mL) and
dried by anhydrous MgSO . The yellow oily product was collected
by evaporating the solvent under vacuum and stored in a refrigera-
tor and was used in next reaction without further purification.
1
26.81, 127.66, 128.74, 128.94 ppm. H NMR (300 MHz, [D ]DMSO):
6
4
d=2.94 (m, 4H), 3.50–3.65 (m, 20H), 3.97 (d, J=2.1 Hz, 2H),4.11
br, 1H), 7.40 ppm (m, 5H). IR: n˜ = 3394.5, 2885.9, 1741.0, 1648.5,
(
[24]
1
454.9, 1353.4, 1248.7, 1215.5, 1107.5, 1047.8, 945.0, 880.3,
À1
Hydrobromic acid (3 mmol, 174 mL) was then added to a solution
of the yellow oily product obtained previously, and water (40 mL),
THF (40 mL), and KBr (3 mmol, 0.357 g) were then added and
stirred for 24 h at room temperature. Then, the THF and existing
excess aza-crown ether were extracted off with CH Cl (5ꢁ20 mL).
The excess water was evaporated under reduced pressure. The de-
sired product 1a was obtained by drying under vacuum for 12 h
at 808C (75%) and stored in a desiccator.
740.0 cm ; elemental analysis calcd (%): C 37.67, H 5.99, N2.31;
found: C 37.66, H 6.34, N 2.26.
1
1
-Butyl-1-aza-[18-C-6HK][Br]2 (2a): H NMR (300 MHz, D O): d=
2
0
4
1
6
8
3
1
7
.99 (m, 3H), 1.44 (m, 2H), 1.7 (m, 2H), 3.30 (m, 2H), 3.43–3.51 (m,
2
2
13
H), 3.75–3.93 ppm (m, 20H); C NMR (75 MHz, D O): d=13.19,
2
9.59, 25.01, 53.60, 53.75, 54.62, 64.28, 68.78, 69.33, 69.69, 69.77,
1
9.91, 70.05 ppm. H NMR (300 MHz, [D ]DMSO): d=0.90 (t, J=6.0,
6
.7 Hz, 3H), 1.32 (m, 2H), 1.64 (m, 2H), 3.22 (br, 2H), 3.38 (br, 4H),
.52 (br, 16H), 3.81 ppm (br, 4H); IR n˜ =3394.0, 2921.3, 2876.1,
632.7, 1386.1, 1300.9, 1251.6, 1104.8, 948.6, 828.6, 835.3,
The synthesis methods of other aza-crown ether complex cation
ionic liquids (1b–2d) are similar to aza-crown ether complex
cation ionic liquid 1a.
À1
39.3 cm ; elemental analysis calcd (%):C 37.00, H 6.60, N 2.70;
The NMR spectral data, elemental analysis data, IR data, and mass
found: C 37.32, H 6.91, N 2.51.
spectra of aza-crown ether complex cation ionic liquids are de-
scribed as follows:
1
1
0
-Butyl-aza-[18-C-6HK][OAc]2 (2b): H NMR (300 MHz, D O): d=
2
.90 (m, 3H), 1.35 (m, 2H), 1.60 (m, 2H), 1.86 (s, 6H), 3.12 (m, 2H),
3.34 (br, 4H), 3.66 (m, 16H), 3.78 ppm (m, 4H); C NMR (75 MHz,
1
13
1
-Benzyl-1-aza-[18-C-6HK][Br] (1a): H NMR (300 MHz, D O): d=
2
2
3
7
5
1
4
7
.30–3.40 (m, 4H), 3.57–3.88 (m, 20H), 4.39 (t, J=6.6, 8.7 Hz, 2H),
D O): d=13.19, 19.63, 23.60, 24.98, 53.66, 53.84, 54.68, 64.15, 68.67,
69.41, 69.68, 69.72, 69.77, 70.00, 70.16, 181.61 ppm; H NMR
2
1
3
1
.45 ppm (s, 5H); C NMR (75 MHz, D O): d=53.39, 54.22, 54.46,
2
5.31, 63.40, 63.80, 68.77, 69.25, 69.59, 68.80, 70.01, 129.52, 130.38,
(300 MHz, [D ]DMSO): d=0.88 (dd, J=7.5, 6.6 Hz, 3H), 1.26 (m,
6
1
31.36, 131.67 ppm. H NMR (300 MHz, [D ]DMSO): d=3.32 (br,
4H), 1.75 (s, 6H), 2.42 (m, 2H), 2,58 (t, J=5.7 Hz, 4H), 3.43–
3.56 ppm (m, 20H); IR: n˜ =3405.4, 2954.7, 2924.7, 2874.0, 1709.6,
1576.8, 1456.9, 1356.5, 1251.6, 1108.0, 952.9, 877.2, 835.2,
6
H), 3.42–3.57 (br, 16H), 3.85 (m, 4H), 4.48 (br, 2H), 7.45 (m, 3H),
.60 ppm (m, 2H); IR: n˜ =3402.7, 2911.4, 1634.6, 1456.0, 1353.9,
Chem. Eur. J. 2014, 20, 12894 – 12900
www.chemeurj.org
12898
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
À1
1
7
35.4 cm ; elemental analysis calcd (%): C 50.29, H 8.44, N 2.93;
found: C 50.67, H 8.17, N 2.72.
-Butyl-1-aza-[18-C-6HK][SO ]·(2c): H NMR (300 MHz, D O): d=
3-(4-Chlorophenyl)-5-methyloxazolidin-2-one: H NMR (300 MHz,
CDCl ): d=1.52 (d, J=6.3 Hz, 3H), 3.58 (t, J=7.5, 7.2 Hz, 1H), 4.08
(t, J=8.4, 8.7 Hz, 1H), 4.78 (m, 1H), 7.30 (m, 2H), 7.47 ppm (m,
H); C NMR (300 MHz, CDCl ): d=20.56, 51.63, 69.53, 119.16,
3
3
1
1
4
2
13
2
0
4
1
6
0
3
2
8
3
.96 (m, 3H), 1.41 (m, 2H), 1.72 (m, 2H), 3.24 (m, 2H), 3.42–3.49 (m,
H), 3.69 (m, 16H), 3.85 ppm (m, 4H); C NMR (75 MHz, D O): d=
3.27, 19.65, 24.87, 53.87, 54.03, 54.72, 63.89, 64.05, 68.99, 69.52,
9.86, 69.94, 70.14, 70.31 ppm; H NMR (300 MHz, [D ]DMSO): d=
.89 (m, 3H), 1.29 (m, 2H), 1.48 (m, 2H), 2.79 (m, 2H), 3.00 (m, 4H),
.17–3.67 (m, 20H), 4.26 ppm (br, 1H). IR: n˜ =3393.7, 2873.6,
500.1, 1654.8, 1463.5, 1380.9, 1354.0, 1297.8, 1250.5, 1111.0, 952.5,
37.9, 737.9 cm ; elemental analysis calcd (%):C 42.18, H 7.52, N
.07; found: C 42.56, H 7.46, N 3.12.
13
128.88, 136.89, 154.62 ppm.
2
1
6
General procedure for esterification reaction
Taking the esterification of acetic acid with n-butanol as an exam-
ple: 1-Butanol (1.29 mL, 14 mmol), acetic acid (0.11 mL, 2 mmol),
cyclohexane (1 mL), and aza-[18-C-6K][HSO ] (117 mg, 0.2 mmol)
À1
4
were added in a flask with a reflux condenser, a water segregator,
and a magnetic stirrer. The reaction mixture was stirred for 2 h
with the oil bath at 1108C. All resulting products were analyzed by
a gas chromatograph equipped with an FID detector capillary
column (30 mꢁ0.25 mmꢁ0.3 mm).
1
1
-Butyl-aza-[18-C-6HK][H PO ] ·1/4H O (2d): H NMR (300 MHz,
2
4
2
2
D O): d=0.95 (m, 3H), 1.41 (m, 2H), 1.71 (m, 2H), 3.23 (m, 2H),
.38–3.47 (m, 4H), 3.67 (m, 16H, H-aza crown), 3.87 ppm (m, 4H,
H-aza crown); C NMR (75 MHz, D O): d=13.22, 19.65, 24.87,
3.87, 54.03, 54.72, 63.88, 64.05, 68.99, 69.52, 69.88, 69.94, 70.14,
2
3
1
3
2
5
7
1
0.31 ppm; H NMR (300 MHz, [D ]DMSO): d=0.88 (m, 3H), 1.26
6
(
(
1
m, 2H), 1.39 (m, 2H), 2.56 (m, 2H), 2.68–3.46 (m, 20H), 7.78 ppm
Typical procedure for the tandem acetylation-Friedel–Crafts
synthesis of bis-indolylmethanes
br, 1H); IR: n˜ =3452.4, 2873.1, 2375.1, 1707.6, 1644.4, 1464.4,
À1
356.5, 1294.5, 1249.5, 1225.5, 1107.8, 948.0, 837.0 cm ; elemental
analysis calcd (%): C 34.44, H 6.95, N 2.51; found: C 34.56, H 6.97,
N 2.56.
Indole (2.0 mmol) and the substituted benzaldehyde (1.0 mmol)
were added to a round-bottomed flask charged with aza-[18-C-
6K][HSO ] (0.1 mmol) in methanol (2 mL) under stirring at 308C for
+
1
3
-Benzyl-1-aza-[18-C-6HK]: MS (ESI): m/z calcd for C H NO
:
1
9
32
5
4
2
+
+
54.2 [MÀK] ; found: 354.4; calcd: 392.2 [MÀH] ; found: 392.3;
calcd: 196.6 [M] ; found: 196.3.
-Butyl-1-aza-[18-C-6HK]: MS (ESI): m/z calcd for C H NO : 320.2
the appropriate time (monitored by TLC). When the reaction was
complete, water (10 mL) was added to the mixture and extracted
with CH Cl (3ꢁ10 mL). The combined organic layers were dried
2
+
+
1
16
34
5
2
2
+
+
[MÀK] ; found: 320.4; calcd: 358.2 [MÀH] ; found: 358.3.
over anhydrous Na SO , filtered and concentrated under vacuum
2 4
to give the desired product, which was then purified by flash
column chromatography (petroleum ether/ethyl acetate).
General procedure for the coupling reaction of CO and ep-
2
oxides
All coupling reactions were performed in a 100 mL stainless auto-
clave equipped with a magnetic stir bar and pressurized with CO2
to 1.2 MPa at 1008C. The autoclave was charged with epoxide
The NMR spectral data of products
1
3
,3’-Bis(indolyl)-phenylmethane: H NMR (300 MHz, CDCl ): d=
3
5
.88 (s, 1H, Ar-CH), 6.63 (dd, J=2.4, 2.1 Hz, 2H, pyrrole), 6.97–7.40
m, 13H), 7.86 ppm (br, 2H, NH).
3,3’-Bis(indolyl)-2-nitrophenylmethane:
CDCl ): d=6.66 (m, 3H, Ar-CH+pyrrole), 6.99–7.41 (m, 11H), 7.86
(d, J=6.6 Hz, 1H), 7.95 ppm (br, 2H, NH).
3’-Bis(indolyl)-3-nitrophenylmethane:
CDCl ): d=6.00 (s, 1H, Ar-CH), 6.68 (s, 2H, pyrrole), 6.99–7.47 (m,
(
(
100 mmol) and aza-crown ether complex cation ionic liquid
(
0.5 g). After an appropriate reaction time, CO was released to ter-
2
1
minate the reaction. The remaining mixture was fractionally dis-
tilled under reduced pressure or recrystallized in ethanol to obtain
a pure chiral cyclic carbonate.
H NMR
(300 MHz,
3
1
3
,
H NMR (300 MHz,
General Procedure for the reaction of aniline and propylene
carbonate
3
9
1
H), 7.70 (d, J=7.5 Hz, 1H), 8.00 (br, 2H, NH), 8.10 (d, J=1.2 Hz,
H), 8.21 ppm (s, 1H).
The reaction of aniline and propylene carbonate was carried out in
a 10 mL round-bottomed flask equipped with a magnetic stirrer.
Aniline (2 mmol), propylene carbonate (10 mmol), and the aza-
crown ether complex cation ionic liquid (10 mol%) were mixed to-
gether and heated at 1308C. After completion of the reaction, the
reactor was cooled to room temperature and the mixture was
added to water (20 mL). The mixture was extracted by ethyl ace-
tate (3ꢁ20 mL). The combined organic layer was dried with anhy-
1
3
,3’-Bis(indolyl)-4-nitrophenylmethane:
H NMR
(300 MHz,
CDCl ): d=6.00 (s, 1H, Ar-CH), 6.69 (d, J=2.4 Hz, 2H, pyrrole),
.00–7.52 (m, 9H), 7.70 (d, J=8.4 Hz, 1H), 8.02 (br, 2H, NH),
3
7
8
.14 ppm (d, J=8.1 Hz, 2H).
1
3
,3’-Bis(indolyl)-3-methoxylphenylmethane: H NMR (300 MHz,
CDCl ): d=3.72 (s, 3H, OCH ), 5.85 (s, 1H, Ar-CH), 6.65 (dd, J=
.1 Hz, 2H, pyrrole), 6.75 (m, 1H), 6.90–7.41 (m, 11H), 7.89 ppm (br,
3
3
8
2
H, NH).
drous MgSO , filtered and concentrated under reduced pressure to
4
1
3
,3’-Bis(indolyl)-4-methoxylphenylmethane: H NMR (300 MHz,
CDCl ): d=3.78 (s, 3H, OCH ), 5.84 (s, 1H, Ar-CH), 6.66 (d, J=
.2 Hz, 2H, pyrrole), 6.82 (m, 2H), 6.90–7.40 (m, 10H), 7.91 ppm (br,
give the desired product that was then purified by flash column
chromatography using petroleum ether/ethyl acetate as eluent.
3
3
1
2
H, NH).
The NMR spectral data of selected products
1
3
,3’-Bis(indolyl)-3-methylphenylmethane:
H NMR (300 MHz,
1
CDCl ): d=2.28 (s, 3H, CH ), 5.84 (s, 1H, Ar-CH), 6.63 (dd, J=2.1 Hz,
3 3
H, pyrrole), 6.97–7.41 (m, 12H), 7.86 ppm (br, 2H, NH).
5
-Methyl-3-phenyloxazolidin-2-one: H NMR (300 MHz, CDCl3):
2
d=1.50 (d, J=6.0 Hz, 3H), 3.59 (t, J=7.2, 6.9 Hz, 1H), 4.08 (t, J=
.7, 8.4 Hz, 1H), 4.76 (m, 1H), 7.11 (m, 1H), 7.36 (m, 2H), 7.50 ppm
1
8
3,3’-Bis(indolyl)-4-methylphenylmethane: H NMR
CDCl ): d=2.17 (s, 3H, CH ), 5.85 (s, 1H, Ar-CH), 6.66 (s, 2H, pyr-
3 3
(300 MHz,
1
3
(
m, 2H); C NMR (300 MHz, CDCl ): d=20.53, 51.66, 69.44, 117.99,
3
1
23.75, 128.87, 138.24, 154.77 ppm.
role), 6.97–7.41 (m, 12H), 7.89 ppm (br, 2H, NH).
12899 ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2014, 20, 12894 – 12900
www.chemeurj.org

Full Paper
1
3
,3’-Bis(indolyl)-3-chlorophenylmethane:
H NMR
(300 MHz,
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3
[
6
.97–7.39 (m, 12H), 7.89 ppm (br, 2H, NH).
,3’-Bis(indolyl)-4-chlorophenylmethane:
CDCl ): d=5.86 (s, 1H, Ar-CH), 6.65 (t, J=1.2 Hz, 2H, pyrrole), 6.99–
1
3
H NMR
(300 MHz,
3
7
.38 (m, 13H), 7.93 ppm (br, 2H, NH).
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[
[
Acknowledgements
We are grateful to the financial support of National Natural Sci-
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Keywords: alkylation
compounds · esterification · ionic liquids · synthetic methods
·
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·
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