An efficient three-component synthesis of hexahydroquinoline derivatives in ionic liquid

Article abstract of DOI:10.1002/jhet.703

A series of hexahydroquinoline derivatives were synthesized by the three-component reaction of 5,5-dimethyl-3-aminocyclohex-2-enone, aromatic aldehyde, and acyl acetonitrile in ionic liquid without using any catalyst. This protocol has the advantages of e

Full text of DOI:10.1002/jhet.703

September 2011
An Efficient Three-Component Synthesis of Hexahydroquinoline
Derivatives in Ionic Liquid
1145
Ju-Xian Wang,a Gao-Ling Shen,b and Da-Qing Shib*
aInstitute of Medical Biotechnology, Chinese Academy of Medical Sciences and Perking Union
Medical College, Beijing 100050, People’s Republic of China
bKey Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry,
Chemical Engineering and Materials Science, Soochow University, Suzhou 215123,
People’s Republic of China
*E-mail: dqshi@suda.edu.cn
Received July 15, 2010
DOI 10.1002/jhet.703
Published online 8 June 2011 in Wiley Online Library (wileyonlinelibrary.com).
A series of hexahydroquinoline derivatives were synthesized by the three-component reaction of 5,5-
dimethyl-3-aminocyclohex-2-enone, aromatic aldehyde, and acyl acetonitrile in ionic liquid without
using any catalyst. This protocol has the advantages of easier work-up, milder reaction conditions, high
yields, and environmentally benign procedure.
J. Heterocyclic Chem., 48, 1145 (2011).
INTRODUCTION
merization [13], hydrogenation [14], regioselective alkyl-
ation [15], Friedel-Crafts reactions [16], dimerization of
alkenes [17], Diels-Alder reactions [18], Michael reac-
tions [19], Cross-coupling reactions [20], and some enzy-
mic reactions [21] can be carried out in ionic liquid. As
part of our current studies on the development of new
routes to heterocyclic systems [22], we herein describe a
facile synthesis of hexahydroquinoline derivatives by the
three-component reaction of 5,5-dimethyl-3-aminocyclo-
hex-2-enone, aromatic aldehyde, and acyl acetonitrile in
ionic liquid without using any catalyst.
Quinolines are important as the scaffolds of bioactive
substances. The ring structure is one of the most popular
N-heteroaromatic moieties incorporated into the struc-
tures of pharmaceuticals. Many quinoline-containing
compounds exhibit a wide range of pharmacological
activities, such as antiplasmodial [1], intrinsic [2], cyto-
toxic [3], functional [4], antibacterial [5], antiprolifera-
tive [6], antimalarial [7], and anticancer activities [8].
Therefore, the synthesis of quinolines has become an
attractive research field.
Multicomponent reactions (MCRs) [9] are special
types of synthetically useful organic reactions in which
three or more different starting materials react to give a
final product in a one-pot procedure. Such reactions are
one of the best tools in modern organic synthesis to gen-
erate compound libraries for screening purposes because
of their productivity, simple procedures, convergence,
and facile execution [10]. This methodology allows mo-
lecular complexity and diversity to be created by the
facile formation of several new covalent bonds in a one-
pot transformation quite closely approaching the concept
of an ideal synthesis and is particularly well adapted for
combinatorial synthesis [11].
RESULTS AND DISCUSSION
The one-pot, three-component reaction of 5,5-di-
methyl-3-aminocyclohex-2-enone 1, aromatic aldehyde
2, and acyl acetonitrile 3 proceeded rapidly at 80ꢀC in
ionic liquid 1-butyl-3-methylimidazolium bromide
([bmim]Br) without using any catalyst and were complete
after 4–8 h to afford 1,4,5,6,7,8-hexahydroquinoline-3-car-
bonitrile derivatives 4 in good yields (Scheme 1). The
results are summarized in Table 1.
As shown in Table 1, this protocol can be applied not
only to the aromatic aldehyde with electron-withdrawing
groups (such as nitro and halide groups) and with elec-
tron-donating groups (such as methyl group) but also to
the heterocyclic aromatic aldehyde. Therefore, we con-
cluded that the electronic nature of the substituents of
aldehydes has no significant effect on this reaction.
The ionic liquids have been the subject of considerable
current interest as environmentally benign reaction media
in organic synthesis because of their unique properties of
nonvolatility, nonflammability, and recyclability, among
others [12]. Numerous chemical reaction, such as poly-
C
V
2011 HeteroCorporation

1146
J.-X. Wang, G.-L. Shen, and D.-Q. Shi
Vol 48
Scheme 1
standard TMS. HRMS data were obtained using TOF-MS
instrument.
In this study, all the structures of products 4 were char-
1
acterized by mp, IR, and H-NMR spectral data as well
General procedure for the synthesis of 1,4,5,6,7,8-hexa-
hydroquinoline-3-carbonitrile derivatives 4. A dry 50 mL
flask was charged with 5,5-dimethyl-3-aminocyclohex-2-enone
as HRMS analysis. The IR spectrum of 4 showed bands
at 3261–3485 cmꢁ1 due to NH, and strong absorption at
2195–2205 and 1637–1657 cmꢁ1 due to cyano and car-
bonyl group, respectively. The 1H-NMR specrtum of
compound 4 showed signals at 4.53–5.66 due to C4-H.
A possible mechanism for the formation of 4 is pro-
posed in Scheme 2. It is reasonable to assume that 4
results from initial formation of intermediate arylidene
acyl acetonitrile 5 by standard Knoevenagel condensa-
tion of the aldehyde 2 and acyl acetonitrile 3. Then, the
subsequent Michael-type addition of the 5,5-dimethyl-3-
aminocyclohex-2-enone 1 to the intermediate 5, fol-
lowed by tautomerization, cyclization, and dehydration,
affords the corresponding products 4 (Scheme 2).
In conclusion, we have developed an efficient, clean,
one-pot and three-component synthesis of new hexahy-
droquinoline derivatives in ionic liquid without any cata-
lyst. This protocol has the advantages of easier work-up,
milder reaction conditions, high yields, and environmen-
tally benign procedure.
1
(1 mmol), aldehyde 2 (1 mmol), acyl acetonitrile 3
(1 mmol), and ionic liquid [bmim]Br (2 mL). The mixture was
stirred at 80ꢀC for 4–8 h to complete the reaction (monitored
by TLC), then 50 mL H2O was added. The solid was filtered
off and washed with water. The crude product was purified by
recrystallization from ethanol to give 4.
2-(4-Chlorophenyl)-7,7-dimethyl-5-oxo-1,4-di(4-methylphenyl)-
1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4a). Mp: 212–
213ꢀC; IR (potassium bromide): 3035, 2953, 2886, 2198,
1641, 1580, 1512, 1373, 1245 cmꢁ1 1H-NMR (DMSO-d6) d:
;
0.74 (s, 3H, CH3), 0.90 (s, 3H, CH3), 1.79 (d, J ¼ 17.4 Hz,
1H, CH), 2.02 (d, J ¼ 16.2 Hz, 1H, CH), 2.20 (s, 3H, CH3),
2.26–2.32 (m, 5H, CH3þCH2), 4.64 (s, 1H, CH), 7.08–7.15
(m, 5H, ArH), 7.18–7.21 (m, 2H, ArH), 7.26–7.33 (m, 5H,
ArH). HRMS [Found: m/z: 492.1968 (Mþ); Calcd for
C32H2935ClN2O: M 492.1968].
2,4-Di(4-chlorophenyl)-7,7-dimethyl-5-oxo-1-(4-methylphenyl)-
1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4b). Mp: 239–
241ꢀC; IR (potassium bromide): 3035, 2953, 2885, 2199,
;
1640, 1579, 1512, 1371, 1247 cmꢁ1 1H-NMR (DMSO-d6) d:
0.75 (s, 3H, CH3), 0.92 (s, 3H, CH3), 1.82 (d, J ¼ 17.7 Hz,
1H, CH), 2.05 (d, J ¼ 16.2 Hz, 1H, CH), 2.23 (s, 3H, CH3),
2.26–2.33 (m, 2H, CH2), 4.74 (s, 1H, CH), 7.10–7.19 (m, 5H,
ArH), 7.29–7.32 (m, 3H, ArH), 7.46–7.51 (m, 4H, ArH).
HRMS [Found: m/z: 512.1426 (Mþ); Calcd for
C31H2635Cl2N2O: M 512.1422].
EXPERIMENTAL
Commercial solvents and reagents were used as received.
Melting points were uncorrected. IR spectra were recorded on
Varian F-1000 spectrometer in KBr with absorptions in cmꢁ1
.
4-(2-Chlorophenyl)-2-(4-chlorophenyl)-7,7-dimethyl-5-oxo-
1-(4-methylphenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carbon-
itrile (4c). Mp: 218–219ꢀC; IR (potassium bromide): 3056,
1H-NMR was determined on Varian-400 MHz or Varian-300
MHz spectrometer in DMSO-d6 solution. J values are in Hz.
Chemical shifts are expressed in ppm downfield from internal
2953, 2870, 2201, 1641, 1576, 1513, 1373, 1250 cmꢁ1 1H-
;
Table 1
Synthesis of hexahydroquinoline derivatives 4 in ionic liquid.
Entry
R1
Ar
R2
Time (h)
Isolated yield (%)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
4-CH3C6H4
n-But
4-CH3C6H4
4-ClC6H4
2-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
C6H5
8
4
5
4
7
5
5
5
7
92
95
96
95
90
95
95
96
91
3-ClC6H4
4-CH3C6H4
2-NO2C6H4
3-ClC6H4
C6H5
4-ClC6H4
4-ClC6H4
4-ClC6H4
H
H
4-CH3C6H4
Pyridin-3-yl
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

September 2011
An Efficient Three-Component Synthesis of Hexahydroquinoline Derivatives
in Ionic Liquid
1147
Scheme 2
NMR (DMSO-d6) d: 0.90 (s, 3H, CH3), 0.98 (s, 3H, CH3),
1.91 (d, J ¼ 17.4 Hz, 1H, CH), 2.12 (d, J ¼ 17.7 Hz, 1H,
CH), 2.13 (d, J ¼ 16.5 Hz, 1H, CH), 2.23 (d, J ¼ 16.5 Hz,
1H, CH), 2.29 (s, 3H, CH3), 5.31 (s, 1H, CH), 6.87 (d, J ¼
8.1Hz, 2H, ArH), 6.99–7.15 (m, 6H, ArH), 7.18–7.23 (m, 1H,
ArH), 7.26–7.32 (m, 1H, ArH), 7.40 (d, J ¼ 7.8 Hz, 1H,
ArH), 7.50–7.53 (m, 1H, ArH). HRMS [Found: m/z: 512.1424
(Mþ); Calcd for C31H2635Cl2N2O: M 512.1422].
1H, CH), 2.04 (d, J ¼ 18.3 Hz, 1H, CH), 2.10–2.22 (m, 2H,
CH2), 2.27 (s, 3H, CH3), 5.66 (s, 1H, CH), 6.94–7.08 (m, 5H,
ArH), 7.13–7.20 (m, 4H, ArH), 7.36–7.41 (m, 1H, ArH), 7.59–
7.65 (m, 1H, ArH), 7.72–7.78 (m, 2H, ArH). HRMS [Found:
m/z: 489.2059 (Mþ); Calcd for C31H27N3O3: M 489.2052].
1-Butyl-4-(3-chlorophenyl)-2-(4-chlororphenyl)-7,7-dimethyl-
5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4g). Mp:
152–154ꢀC; IR (potassium bromide): 3035, 2956, 2872, 2196,
4-(3-Chlorophenyl)-2-(4-chlorophenyl)-7,7-dimethyl-5-oxo-1-
(4-methylphenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile
(4d). Mp: 194–196ꢀC; IR (potassium bromide): 3039, 2960,
1657, 1570, 1379, 1294 cmꢁ1 1H-NMR (DMSO-d6) d: 0.62
;
(t, J ¼ 7.2 Hz, 3H, CH3), 0.88–1.01 (m, 5H, CH3þCH2), 1.07
(s, 3H, CH3), 1.24–1.39 (m, 2H, CH2), 2.20 (d, J ¼ 16.2 Hz,
1H, CH), 2.27 (d, J ¼ 16.2 Hz, 1H, CH), 2.59 (d, J ¼ 17.4
Hz, 1H, CH), 2.72 (d, J ¼ 17.1 Hz, 1H, CH), 3.07–3.17 (m,
1H, CH), 3.56–3.65 (m,1H, CH), 4.68 (s, 1H, CH), 7.20–7.32
(m, 3H, ArH), 7.36–7.48 (m, 3H, ArH), 7.56–7.64 (m, 2H,
ArH). HRMS [Found: m/z: 478.1570 (Mþ); Calcd for
C28H2835Cl2N2O: M 478.1579].
2-(4-Chlorophenyl)-7,7-dimethyl-5-oxo-4-(4-methylphenyl)-
1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4h). Mp: 248–
250ꢀC; IR (potassium bromide): 3485, 3364, 3090, 2958,
2870, 2195, 1637, 1605, 1539, 1382, 1251 cmꢁ1 1H-NMR
;
2888, 2198, 1639, 1577, 1512, 1371, 1248 cmꢁ1 1H-NMR
;
(DMSO-d6) d: 0.87 (s, 3H, CH3), 1.01 (s, 3H, CH3), 1.95 (d, J
¼ 17.7 Hz, 1H, CH), 2.15–2.26 (m, 3H, CH2þCH), 2.30 (s,
3H, CH3), 4.90 (s, 1H, CH), 6.86 (d, J ¼ 8.1 Hz, 2H, ArH),
7.05–7.08 (m, 3H, ArH), 7.14–7.17 (m, 2H, ArH), 7.23–7.27
(m, 1H, ArH), 7.29–7.44 (m, 4H, ArH). HRMS [Found: m/z:
512.1425 (Mþ); Calcd for C31H2635Cl2N2O: M 512.1422].
7,7-Dimethyl-5-oxo-2-phenyl-1,4-di(4-methylphenyl)-1,4,5,6,
7,8-hexahydroquinoline-3-carbonitrile (4e). Mp: 189–191ꢀC;
IR (potassium bromide): 3057, 2961, 2870, 2197, 1642, 1584,
1
1512, 1373, 1248 cmꢁ1; H-NMR (DMSO-d6) d: 0.80 (s, 3H,
(DMSO-d6) d: 0.92 (s, 3H, CH3), 1.05 (s, 3H, CH3), 2.05 (d, J
¼ 16.4 Hz, 1H, CH), 2.24 (d, J ¼ 16.4 Hz, 1H, CH), 2.41 (d,
J ¼ 17.2 Hz, 1H, CH), 2.52 (d, J ¼ 17.2 Hz, 1H, CH), 4.53
(s, 1H, CH), 7.13 (d, J ¼ 8.0 Hz, 2H, ArH), 7.17 (d, J ¼ 8.4
Hz, 2H, ArH), 7.56 (d, J ¼ 8.8 Hz, 2H, ArH), 7.60 (d, J ¼
8.8 Hz, 2H, ArH), 9.64 (s, 1H, NH). HRMS [Found: m/z:
402.1502 (Mþ); Calcd for C25H2335ClN2O: M 402.1499].
2-(4-Chlorophenyl)-7,7-dimethyl-5-oxo-4-(pyridin-3-yl)-1,4,5,
6,7,8-hexahydroquinoline-3-carbonitrile (4i) Mp: 290–292ꢀC;
IR (potassium bromide): 3485, 3261, 3015, 2952, 2873, 2200,
CH3), 0.96 (s, 3H, CH3), 1.87 (d, J ¼ 17.2 Hz, 1H, CH), 2.08
(d, J ¼ 16.4 Hz, 1H, CH), 2.24 (s, 3H, CH3), 2.30 (d, J ¼
16.4 Hz, 1H, CH), 2.35 (s, 3H, CH3), 2.36 (d, J ¼ 17.2 Hz,
1H, CH), 4.71 (s, 1H, CH), 7.10–7.17 (m, 5H, ArH), 7.23–
7.30 (m, 6H, ArH), 7.36–7.41 (m, 2H, ArH). HRMS [Found:
m/z: 458.2380 (Mþ); Calcd for C32H30N2O: M 458.2358].
7,7-Dimethyl-4-(2-nitrophenyl)-5-oxo-2-phenyl-1-(4-methyl-
phenyl)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4f). Mp:
246–248ꢀC; IR (potassium bromide): 3061, 2962, 2870, 2205,
1639, 1603, 1528, 1375, 1251 cmꢁ1
;
1H-NMR (DMSO-d6) d:
1637, 1605, 1592, 1380, 1260 cmꢁ1
;
1H-NMR (DMSO-d6) d:
0.84 (s, 3H, CH3), 0.96 (s, 3H, CH3), 1.93 (d, J ¼ 18.0 Hz,
0.88 (s, 3H, CH3), 1.02 (s, 3H, CH3), 2.03 (d, J ¼ 16.2 Hz,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

1148
J.-X. Wang, G.-L. Shen, and D.-Q. Shi
Vol 48
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet