L. Gao et al. / Journal of Organometallic Chemistry 735 (2013) 26e31
27
2.3. Procedure for the synthesis of N-substituted pyrroles
To a mixture of amine (7 mmol) and 2,5-hexanedione (8.4 mmol,
3 40
1.2 equiv) in 5 ml acetonitrile was added 5 mol% [MIMBS] PW12O .
The mixture was stirred at set temperature for the appropriate time.
The progress of the reaction was monitored by thin layer chroma-
tography (TLC). After reaction, the mixture was filtered. The filtrate
was evaporated and the residue was purified on silica gel with ether/
ethyl acetate as eluent. All N-substituted pyrroles are known com-
pounds and were characterized by NMR spectroscopy.
Scheme 1. Synthesis of N-substituted pyrroles via PaaleKnorr reaction.
organic cations and heteropolyacids-based anions can cause the
formation of special ILs, which is also called organiceinorganic
hybrid materials [33]. Unlike common ILs, heteropolyacids-based
ILs always have high melting point, and there are insoluble in
common organic solvents. Recently, the design and application of
heteropolyacids-based hybrids have been proposed as a catalyst
upgrade for organic syntheses, and some thermal/solvent-
responsive HPA-based IL hybrids have been reported [34,35]. The
advantages of heteropolyacids-based solid catalyst lie in not only
low corrosiveness to equipment but also low energy consumption
during the separation process. Therefore, the use of recoverable
HPA-based IL hybrids solid catalyst in organic transformations has
economical and environmental benefits. Herein, in this paper, we
describe here a simple method of synthesis of N-substituted pyr-
roles in excellent yields by the reaction of 2,5-hexanedione and
various amines in the presence of catalytic amount (w5 mol%)
2.3.1. 1-(4-Phenyl)-2,5-dimethyl-1H-pyrrole (compound 1 in
Table 2)
1H NMR (400 MHz, CDCl3)
d (ppm): 7.42, 7.27 (m, 3H), 7.07e7.15
13
(m, 2H), 5.82 (s, 2H), 2.02 (s, 6H); C NMR (100 MHz, CDCl3)
12.3, 104.9, 123.5, 125.6, 127.5, 129.6, 143.1.
dC:
2.3.2. 1-(4-Methoxyphenyl)-2,5-dimethyl-1H-pyrrole (compound 2
in Table 2)
1H NMR (400 MHz, CDCl3)
3
d (ppm): 2.07 (s, 6H, 2CH ), 5.98 (s,
3H, eOCH ) 5.94 (s, 2H, pyrrole), 7.00e7.02 (d, 2H, J ¼ 8.0 Hz, m,
3
0
0
13
m eArH), 7.16e7.18 (d, 2H, J ¼ 8.0 Hz, o,o eArH). C NMR
(100 MHz, CDCl ) : 12.9, 58.7,105.2, 114.1,128.9, 129.1, 131.6, 158.7.
3
d
C
[
MIMBS]
3
PW12
O
40
.
2.3.3. 1-(4-Nitrophenyl)-2,5-dimethyl-1H-pyrrole (compound 3 in
Table 2)
1H NMR (400 MHz, CDCl
)
d
(ppm): 2.11 (s, 6H, 2CH
), 5.98 (s,
2
. Experimental sections
3
3
0
2
2
1
H, pyrrole), 7.40e7.20 (d, 2H, J ¼ 8.0 Hz, o,o eArH), 8.36e8.38 (d,
0
13
H, J ¼ 8.0 Hz, m,m eArH). C NMR (100 MHz, CDCl
3 C
) d : 13.1,
2.1. Materials and methods
05.9, 124.5, 128.5, 128.7, 144.7, 146.6.
Keggin-type phosphotungstic acid was purchased from Tianjin
2
.3.4. 1-Propyl-2,5-dimethyl-1H-pyrrole (compound 4 in Table 2)
Damao Chemical Reagent Factory (Tianjin, China). N-methyl-
imidazole (99%) were obtained from Sinopharm Chemical Reagent
Co., Ltd (Shanghai China), and were freshly distilled before use. 1,4-
Butane sultone (99%) was supplied by Wuhan Fengfan Chemical
Co., Ltd (Wuhan, China). 2,5-Hexanedione and all the amines were
purchased from Aladdin-reagent. Co., Ltd (Shanghai, China). HY-
zeolite (Si/Al ¼ 5) supplied by Nankai University Catalyst Co., Ltd
1
H NMR (400 MHz, CDCl
.70e1.74 (m, 2 H, eCH e), 2.28 (s, 6H, 2CH
J ¼ 8.0 Hz, 2 H), 5.84 (s, 2H, pyrrole). C NMR (100 MHz, CDCl
1.3, 24.2, 45.1, 104.8, 127.3.
3
)
d
(ppm): 1.00e1.04 (t, J ¼ 8.0 Hz, 3 H),
1
2
3
), 3.74e3.78 (t,
1
3
3 C
) d :
1
2
.3.5. 1-Cyclohexyl-2,5-dimethyl-1H-pyrrole (compound 5 in
Table 2)
1H NMR (400 MHz, CDCl
.62 (m, 2 H), 1.49e1.47 (m, 1 H), 1.87e1.85 (m, 4 H), 2.24 (s, 6H,
(
Tianjin, China). All other reagents and solvents were obtained from
3
) d (ppm): 1.08e0.96 (m, 3 H), 1.68e
commercial suppliers (Wuhan Guoyao Chemical Reagent Co., Ltd.,)
with reagent grade quality. NMR spectra were measured with a
Bruker DRX-400 spectrometer at 298 K.
1
13
2
CH
3
), 3.84e3.88 (m, 1 H), 5.88 (s, 2H, pyrrole). C NMR
: 12.8, 23.8, 28.2, 36.2, 47.5, 104.6, 128.5.
(125.75 MHz, CDCl ) d
3 C
2
.2. Preparation of the catalyst
2
1
.3.6. 2,5-Dimethyl-1-(3-(2,5-dimethyl-1H-pyrrol-1-yl)propyl)-
H-pyrrole (compound 6 in Table 2)
The catalyst was prepared according to the known procedure
1
H NMR (400 MHz, CDCl
3 2
) d (ppm): 1.28e1.32 (m, 2H, eCH e)
without any modifications (Scheme 2), as described in our previous
work [36]. Briefly, N-methylimidazole and 1,4-butane sultone were
reacted at 50 C for 24 h. After reaction, the slurry mixture was
filtered and washed with ethyl acetate for three times, then dried in
vacuum. Then an aqueous solution of H
1.74e1.78 (m, 4H, 2 eCH
2
e), 3.72e3.76 (t, J ¼ 8.0 Hz, 4H, 2 eNe
ꢀ
Table 1
The cyclocondensation reaction of 2,5-hexanedione with aniline under different
reaction conditions.
a
3
PW12
O40 was added, and
the mixture was stirred at room temperature for 24 h. Water was
removed in vacuum, and the final product was obtained as a white
Yield (%)b
Entry
Solvent
THF
Reaction conditions
Time (h)
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
2
3
4
5
6
7
8
9
80 C, 5 mol% catalyst
12
2
2
2
2
2
6
24
1
5
14
77
83
69
48
93
95
94
91
93
solid, which was named as [MIMBS]
3
PW12O
40
.
CH
CHCl
CCl
2
Cl
2
80 C, 5 mol% catalyst
3
80 C, 5 mol% catalyst
4
80 C, 5 mol% catalyst
CH
CH
CH
CH
CH
CH
3
CH
CN
CN
CN
CN
CN
2
OH
80 C, 5 mol% catalyst
3
3
3
3
3
80 C, 5 mol% catalyst
50 C, 5 mol% catalyst
25 C, 5 mol% catalyst
ꢀ
ꢀ
80 C, 10 mol% catalyst
10
80 C, 2.5 mol% catalyst
a
Reaction conditions: 7 mmol amine, 8.4 mmol 2,5-hexanedione and a set
PW12 40 were added into 5 ml solvent, and the reaction were
amount of [MIMBS]
3
O
carried out at a set temperature for the desired time.
b
Scheme 2. Illustration of the catalyst preparation.
Isolated yield.