Synthesis of 3-cyano-2-(1H-indol-3-yl)-6-(9-butylcarbazol-3-yl)pyridine derivatives by a multicomponent reaction under microwave irradiation

Article abstract of DOI:10.3184/174751913X13736278296459

Preparation of a series of 3-cyano-2-(1H-indol-3-yl)-6-(9-butylcarbazol-3- yl)pyridine derivatives through the one-pot four-component coupling of aromatic aldehydes, 1-(9-butylcarbazol-3-yl)ethanone, 3-(cyanoacetyl)indole and ammonium acetate is reported. All these compounds were obtained in good yield and their structures were confirmed by 1H NMR and IR spectroscopy and by elemental analysis.

Full text of DOI:10.3184/174751913X13736278296459

JOURNAL OF CHEMICAL RESEARCH 2013
RESEARCH PAPER 503
AUGUST, 503–505
Synthesis of 3-cyano-2-(1H-indol-3-yl)-6-(9-butylcarbazol-3-yl)pyridine
derivatives by a multicomponent reaction under microwave irradiation
Li-Jun Geng*, Guo-Liang Feng, Hong-Li Zhang and Yu-Mei Zhang
School of Science, Hebei University of Science andTechnology, Yuhua East Road, Shijiazhuang 050018, P. R. China
Preparation of a series of 3-cyano-2-(1H-indol-3-yl)-6-(9-butylcarbazol-3-yl)pyridine derivatives through the one-pot
four-component coupling of aromatic aldehydes, 1-(9-butylcarbazol-3-yl)ethanone, 3-(cyanoacetyl)indole and ammo-
nium acetate is reported. All these compounds were obtained in good yield and their structures were confirmed by
1H NMR and IR spectroscopy and by elemental analysis.
Keywords: multicomponent reaction, 3-cyanoacetylindole, 1-(9-butylcarbazol-3-yl)ethanone, pyridine derivatives, microwave
irradiation
During the past few years, the synthesis and application of
carbazole derivatives have been of great interest because of
their intrinsic photophysical and redox properties. They exhibit
relatively intense luminescence and undergo reversible oxida-
tion processes which make them suitable as hole carriers.1
Moreover, carbazole can be easily functionalised at its 3-, 6-,
or 9-positions and the carbazole moiety is beneficial for
raising the glass transition temperature and thermal stability.2
Carbazole derivatives are widely used as building blocks for
potential organic semiconductors3,4 and organic light-emitting
diodes.5,6 However, further progress in these fields requires an
intensification of the research effort focused on the design and
synthesis of new compounds with electrochemical, optical,
and electronic properties specifically tailored for each type of
application.
Since the publication of the Strecker reaction in 1850 con-
sidered to be the beginning of the multicomponent reaction
(MCR) story,7 there has been considerable interest in one-
pot MCRs due their diversity, efficiency and rapid access to
complex and highly functionalised organic molecules.8,9 In the
past decade, there have been many developments in three- and
four-component reactions10,11 and great efforts are being made
to find and develop new MCRs.12–14
efficient synthesis of 3-cyano-2-(1H-indol-3-yl)pyridine deriv-
atives by MCRs in good yields.17,18 In continuing our interest
in the multicomponent syntheses and in multi-functional
derivatives, we now report a simple and efficient protocol for
the preparation of a series of 3-cyano-2-(1H-indol-3-yl)-6-(9-
butylcarbazol-3-yl)pyridine derivatives. The target compounds
were synthesised by the four-component reaction of aromatic
aldehydes, 1-(9-butylcarbazol-3-yl)ethanone, 3-(cyanoacetyl)-
indole and ammonium acetate under microwave irradiation
(Scheme 1). To realise our objective, the starting compound
3-(cyanoacetyl)indole was prepared according to the proce-
dure described by Bergman et al.19 9-Butylcarbazole20 was
obtained by the reaction of carbazole with 1-bromobutane
in DMSO catalysed by KOH, subsequent acylation with acetyl
chloride in benzene provided 1-(9-butylcarbazol-3-yl) ethanone21
(Scheme 2).
Because an appropriate solvent is of crucial importance for
the successful microwave-assisted synthesis, our initial studies
were carried out under various reaction conditions. Both
solvents and microwave power were tested in the one pot
four-component synthesis of the target compounds. We found
that AcOH and ethane-1,2-diol (glycol) (1:2) and irradiation at
300 W was optimal to maximise yields. Under these conditions,
a series of new 3-cyano-2-(1H-indol-3-yl)-6-(9-butylcarbazol-
3-yl)pyridine derivatives were synthesised in good yields. The
optimised results are summarised in Table 1.
Results and discussion
Other groups have described the synthesis of 3-cyano-2-(1H-
indole-3-yl)pyridines, for example the 4-aryl-6-(1H-indole-3-
yl)-2,2-bispyridine derivatives15 and 4-aryl-2,6-di(1H-indole-
3-yl)pyridine derivatives.16 Our group has reported a new and
As can been seen from Table 1, the reaction proceeded
smoothly with a series of substituted aromatic aldehydes.
In addition, we explored the synthesis of 5b under classical
Scheme 1
Scheme 2
* Correspondent. E-mail: genglijun@hebust.edu.cn

504 JOURNAL OF CHEMICAL RESEARCH 2013
Table 1 Synthesis of compounds 5a–k under microwave
through a one-pot four-component condensation reaction under
microwave irradiation. This method has several unique merits,
such as short reaction times, an easy workup procedure, and
efficient yields.
irradiation
Entry
Ar
Product Time/min Yielda/% M.p./°C
1
2
C6H5
5a
5b
5c
5d
5e
5f
5g
5h
5i
4
4
4
4
4
4
4
4
4
4
4
82
85
86
84
84
82
83
77
75
81
76
232.7–233.4
285.3–286.2
256.5–257.3
251.8–252.4
273.5–274.1
>300
4-CH3C6H4
Experimental
3
4-CH3OC6H4
3-CH3OC6H4
4-(CH3)2CHC6H4
4-(CH3)3CC6H4
4-(CH3)2NC6H4
4-HOC6H4
1-Naphthyl
4-ClC6H4
4-BrC6H4
Melting points were recorded on an Electrothermal digital melting
4
1
5
point apparatus and are uncorrected. H NMR spectra were deter-
6
mined on a Varian VXP-500s spectrometer using DMSO-d6 as solvent
and tetramethylsilane (TMS) as internal reference. The IR spectra
were obtained on a Nicolet 6700 spectrophotometer using KBr
pellets. Elemental analyses were performed by a Heraeus CHN-O-
RAPID analyser. Microwave reactions were carried out in a Xianghu
XH-100B microwave oven. All chemicals were purchased and used
without further purification.
7
250.9–251.7
281.5–282.2
272.0–273.2
>300
8
9
10
11
5j
5k
282.5–283.3
a Isolated yield.
General procedure
A mixture of aldehyde 1 (2 mmol), 1-(9-butylcarbazol-3-yl)ethanone
2 (2 mmol), 3-(cyanoacetyl)indole 3 (2 mmol), and ammonium
acetate 4 (8 mmol) in HOAc 2 mL and glycol 4 mL was irradiated at
300 W (flask equipped with a condenser). After completion of the
reaction (the reaction was followed by TLC), the mixture was allowed
to cool to room temperature and extracted with dichloromethane,
washed with H2O (3 × 10 mL) and the organic layer dried over MgSO4
and concentrated under reduced pressure. The crude product was
chromatographed on silica gel (200–300 mesh) using a mixture
of petroleum ether and dichloromethane as eluent to afford the pure
product (5a–k).
heating conditions. After refluxing for 2 h (AcOH-glycol, 1:2),
the desired product 5b was obtained in 56% yield. However,
under microwave irradiation, the yield of 5b was up to 85%
after just four minutes (entry 2). Therefore, microwave irradia-
tion exhibited several advantages over the conventional heat-
ing by significantly reducing the reaction times and improving
the product yield.
The structures of 5a–k were confirmed by spectral studies
and elemental analysis as exemplified for compound 5c as
follows: The IR spectrum of 5c showed an absorption at
2212 cm−1 for the CN group. The signals at δ 11.82 and δ 3.89
confirmed the presence of the indolyl NH and OCH3 groups
respectively in the 1H NMR spectrum.
3-Cyano-2-(1H-indol-3-yl)-4-phenyl-6-(9-butylcarbazol-3-yl)pyri-
dine (5a): Pale yellow powder; IR (KBr) νmax 3428, 3053, 2955, 2927,
2870, 2212 (CN), 1570, 1526, 1481, 1428, 1384, 1363, 1241, 1210,
1
1133, 1104, 746 cm−1; H NMR (500 MHz, DMSO-d6): δ 11.82 (s,
1H), 9.21 (s, 1H), 8.56 (dd, 1H, J = 1.5 Hz and J = 8.5 Hz), 8.53−8.51
(m, 1H), 8.39 (d, 1H, J = 3.0 Hz), 8.27 (d, 1H, J = 8.0 Hz), 8.12 (s,
1H), 7.85−7.80 (m, 3H), 7.66−7.57 (m, 5H), 7.50 (t, 1H, J = 7.5 Hz),
7.30−7.25 (m, 3H), 4.46 (t, 2H, J = 7.0 Hz), 1.82−1.77 (m, 2H),
1.37−1.30 (m, 2H), 0.90 (t, 3H, J = 7.5 Hz). Anal. Calcd for C36H28N4,
C, 83.69; H, 5.46; N, 10.84. Found: C, 83.62; H, 5.33; N, 10.98%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-methylphenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5b): Pale yellow powder; IR (KBr) νmax 3426, 3136,
3050, 2956, 2928, 2871, 2215 (CN), 1573, 1525, 1479, 1427, 1365,
Based on the above results, a possible mechanism was
proposed (Scheme 3). 3-(Cyanoacetyl)indole reacts with
ammonia from ammonium acetate to give intermediate 7,
which further reacts with the corresponding chalcones 6, to
yield 8. Michael addition product 8 was then cyclised to afford
the Hantzsch dihydropyridine derivative 9 with elimination of
water. Subsequent dehydrogenation of 9 leads to formation of
the highly substituted pyridine derivative 5.
1
1323, 1240, 1218, 1134, 1021, 811, 747 cm−1; H NMR (500 MHz,
In conclusion, a series of novel 3-cyano-2-(1H-indol-3-yl)-
6-(9-butylcarbazol-3-yl)pyridine compounds were synthesised
DMSO-d6): δ 11.82 (s, 1H), 9.20 (s, 1H), 8.55 (dd, 1H, J = 1.5 Hz and
Scheme 3

JOURNAL OF CHEMICAL RESEARCH 2013 505
J = 9.0 Hz), 8.51−8.50 (m, 1H), 8.38 (d, 1H, J = 3.0 Hz), 8.27 (d,
1H, J = 7.5 Hz), 8.09 (s, 1H), 7.82 (d, 1H, J = 9.0 Hz), 7.75 (d, 2H,
J = 8.0 Hz), 7.67 (d, 1H, J = 8.5 Hz), 7.59−7.57 (m, 1H), 7.51 (t, 1H,
J = 7.5 Hz), 7.45 (d, 2H, J = 8.0 Hz), 7.30−7.26 (m, 3H), 4.47 (t, 2H,
J = 7.0 Hz), 2.50 (t, 3H, J = 1.5 Hz), 1.84−1.78 (m, 2H), 1.38−1.31
(m, 2H), 0.91 (t, 3H, J = 7.5 Hz). Anal. Calcd for C37H30N4, C, 83.74;
H, 5.70; N, 10.56. Found: C, 83.72; H, 5.83; N, 10.68%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-methoxyphenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5c): Yellow powder; IR (KBr) νmax 3310, 3053,
2950, 2927, 2870, 2212 (CN), 1609, 1570, 1524, 1511, 1489, 1457,
1365, 1253, 1211, 1178, 1135, 1032, 834, 745 cm−1; 1H NMR
(500 MHz, DMSO-d6): δ 11.82 (s, 1H), 9.21 (s, 1H), 8.55 (dd, 1H,
J = 1.5 Hz and J = 8.5 Hz), 8.53−8.51 (m, 1H), 8.40 (d, 1H, J =
2.5 Hz), 8.28 (d, 1H, J = 8.0 Hz), 8.08 (s, 1H), 7.84−7.80 (m, 3H),
7.66 (d, 1H, J = 8.0 Hz), 7.60−7.58 (m, 1H), 7.51 (t, 1H, J = 8.0 Hz),
7.31−7.28 (m, 3H), 7.21−7.19 (m, 2H), 4.46 (t, 2H, J = 7.0 Hz), 3.89
(s, 3H), 1.83−1.77 (m, 2H), 1.38−1.31 (m, 2H), 0.91 (t, 3H, J =
7.5 Hz). Anal. Calcd for C37H30N4O, C, 81.29; H, 5.53; N, 10.25.
Found: C, 81.32; H, 5.42; N, 10.38%.
3-Cyano-2-(1H-indol-3-yl)-4-(3-methoxyphenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5d): Pale yellow powder; IR (KBr) νmax 3282, 3046,
2953, 2227 (CN), 1565, 1526, 1488, 1455, 1378, 1365, 1205, 1140,
1051, 815, 752, 742 cm−1; 1H NMR (500 MHz, DMSO-d6): δ 11.82 (s,
1H), 9.21 (s, 1H), 8.56 (d, 1H, J = 8.5 Hz), 8.51 (t, 1H, J = 5.0 Hz),
8.39 (d, 1H, J = 3.0 Hz), 8.28 (d, 1H, J = 8.0 Hz), 8.13 (s, 1H), 7.82
(d, 1H, J = 8.5 Hz), 7.67 (d, 1H, J = 8.0 Hz), 7.59−7.49 (m, 3H), 7.40
(d, 2H, J = 7.0 Hz), 7.29−7.27 (m, 3H), 7.18−7.16 (m, 1H), 4.47 (t,
2H, J = 7.0 Hz), 3.90 (s, 3H), 1.81 (t, 2H, J = 8.0 Hz), 1.37−1.32 (m,
2H), 0.91 (t, 3H, J = 7.5 Hz). Anal. Calcd for C37H30N4O, C, 81.29; H,
5.53; N, 10.25. Found: C, 81.25; H, 5.63; N, 10.18%.
3-Cyano-2-(1H-indol-3-yl)-4-(1-naphthyl)-6-(9-butylcarbazol-3-
yl)pyridine (5i): Pale yellow powder; IR (KBr) ν 3297, 3052, 2954,
2928, 2870, 2225 (CN), 1561, 1542, 1522, 1485, 1430, 1358, 1323,
1213, 1123, 777, 742 cm−1; 1H NMR (500 MHz, DMSO-d6): δ 11.83
(s, 1H), 9.21 (s, 1H), 8.63−8.60 (m, 2H), 8.38 (d, 1H, J = 3.0 Hz), 8.22
(d, 1H, J = 8.0 Hz), 8.19 (s, 1H), 8.17 (t, 1H, J = 6.0 Hz), 8.12 (d, 1H,
J = 8.5 Hz), 7.82 (d, 1H, J = 9.0 Hz), 7.75−7.73 (m, 3H), 7.67−7.57
(m, 4H), 7.49 (t, 1H, J = 7.5 Hz), 7.31 (t, 2H, J = 3.5 Hz), 7.23 (t, 1H,
J = 7.5 Hz), 4.47 (t, 2H, J = 7.0 Hz), 1.83−1.77 (m, 2H), 1.36−1.32
(m, 2H), 0.90 (t, 3H, J = 7.5 Hz). Anal. Calcd for C40H30N4, C, 84.78;
H, 5.34; N, 9.89. Found: C, 84.67; H, 5.41; N, 9.92%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-chlorophenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5j): Pale yellow powder; IR (KBr) νmax 3297, 3049,
2954, 2930, 2870, 2214 (CN), 1592, 1570, 1524, 1467, 1441, 1243,
1211, 1137, 1011, 747 cm−1; 1H NMR (500 MHz, DMSO-d6): δ 11.84
(s, 1H), 9.21 (s, 1H), 8.57−8.55 (m, 1H), 8.52−8.50 (m, 1H), 8.39 (d,
1H, J = 3.0 Hz), 8.26 (d, 1H, J = 8.0 Hz), 8.13 (s, 1H), 7.87−7.81 (m,
5H), 7.67 (d, 1H, J = 8.5 Hz), 7.59−7.57 (m, 1H), 7.53−7.49 (m, 1H),
7.29−7.26 (m, 3H), 4.47 (t, 2H, J = 7.5 Hz), 1.84−1.78 (m, 2H),
1.38−1.31 (m, 2H), 0.91 (t, 3H, J = 7.0 Hz).Anal. Calcd for C36H27ClN4,
C, 78.46; H, 4.94; N, 10.17. Found: C, 78.52; H, 5.03; N, 10.29%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-bromophenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5k): Pale yellow powder; IR (KBr) νmax 3301, 3049,
2954, 2928, 2873, 2214 (CN), 1571, 1525, 1491, 1440, 1365, 1243,
1211, 1138, 1123, 1088, 799, 744 cm−1; 1H NMR (500 MHz, DMSO-
d6): δ 11.84 (s, 1H), 9.20 (s, 1H), 8.56−8.51 (m, 2H), 8.39 (d, 1H,
J = 3.0 Hz), 8.26 (d, 1H, J = 7.5 Hz), 8.12 (s, 1H), 7.88 (d, 2H, J =
8.5 Hz), 7.81 (d, 1H, J = 8.5 Hz), 7.72−7.66 (m, 2H), 7.59−7.58 (m,
1H), 7.52−7.49 (m, 2H), 7.29−7.26 (m, 3H), 4.46 (t, 2H, J = 7.0 Hz),
1.83−1.77 (m, 2H), 1.38−1.30 (m, 2H), 0.90 (t, 3H, J = 7.0 Hz). Anal.
Calcd for C36H27BrN4, C, 72.61; H, 4.57; N, 9.41. Found: C, 72.69; H,
4.43; N, 9.38%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-isopropylphenyl)-6-(9-butylcar-
bazol-3-yl)pyridine (5e): Pale yellow powder; IR (KBr) νmax 3300,
3051, 2952, 2869, 2220 (CN), 1562, 1524, 1494, 1442, 1379, 1320,
1
1247, 1201, 1140, 810, 741 cm−1; H NMR (500 MHz, DMSO-d6):
This work was partially supported by the Hebei Province
Science and Technology Support Plan Project (No. 12211406,
12211405) and Natural Science Foundation of Hebei Province
(No. B2012208051).
δ 11.82 (s, 1H), 9.21 (s, 1H), 8.57−8.55 (m, 1H), 8.51 (t, 1H, J =
4.5 Hz), 8.39 (d, 1H, J = 3.0 Hz), 8.27 (d, 1H, J = 8.0 Hz), 8.11 (s,
1H), 7.82−7.77 (m, 3H), 7.66 (d, 1H, J = 8.0 Hz), 7.59−7.58 (m, 1H),
7.52−7.49 (m, 3H), 7.29−7.25 (m, 3H), 4.46 (t, 2H, J = 7.0 Hz),
3.08−3.00 (m, 1H), 1.83−1.77 (m, 2H), 1.36−1.30 (m, 8H), 0.90 (t,
3H, J = 7.5 Hz). Anal. Calcd for C39H34N4, C, 83.84; H, 6.13; N, 10.03.
Found: C, 83.68; H, 6.26; N, 10.11%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-tert-butylphenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5f): Pale yellow powder; IR (KBr) νmax 3308, 3048,
2959, 2869, 2221 (CN), 1565, 1537, 1470, 1379, 1245, 1212, 1140,
1122, 838, 809, 739 cm−1; 1H NMR (500 MHz, DMSO-d6): δ 11.82 (s,
1H), 9.22 (s, 1H), 8.57−8.52 (m, 2H), 8.40 (d, 1H, J = 3.0 Hz), 8.27
(d, 1H, J = 8.0 Hz), 8.11 (s, 1H), 7.80−7.77 (m, 3H), 7.66−7.63 (m,
3H), 7.60−7.58 (m, 1H), 7.50 (t, 1H, J = 8.0 Hz), 7.29−7.25 (m, 3H),
4.45 (t, 2H, J = 7.0 Hz), 1.82−1.76 (m, 2H), 1.38 (s, 9H), 1.36−1.31
(m, 2H), 0.90 (t, 3H, J = 7.5 Hz). Anal. Calcd for C40H36N4, C, 83.88;
H, 6.34; N, 9.78. Found: C, 83.71; H, 6.47; N, 9.69%.
3-Cyano-2-(1H-indol-3-yl)-4-(4-dimethylaminophenyl)-6-(9-butyl-
carbazol-3-yl)pyridine (5g): Yellow powder; IR (KBr) νmax 3408,
3297, 3052, 2924, 2214 (CN), 1609, 1568, 1526, 1517, 1493, 1440,
1360, 1211, 1136, 1123, 813, 744 cm−1; 1H NMR (500 MHz, DMSO-
d6): δ 11.79 (s, 1H), 9.18 (s, 1H), 8.54−8.52 (m, 1H), 8.50−8.48 (m,
1H), 8.37 (d, 1H, J = 3.0 Hz), 8.28 (d, 1H, J = 7.5 Hz), 8.04 (s, 1H),
7.80 (d, 1H, J = 9.0 Hz), 7.75 (d, 2H, J = 8.5 Hz), 7.66 (d, 1H, J =
8.5 Hz), 7.58−7.56 (m, 1H), 7.52−7.49 (m, 1H), 7.29−7.26 (m, 3H),
6.92 (d, 2H, J = 9.0 Hz), 4.47 (t, 2H, J = 7.0 Hz), 3.04 (s, 6H),
1.83−1.77 (m, 2H), 1.38−1.30 (m, 2H), 0.90 (t, 3H, J = 7.5 Hz). Anal.
Calcd for C38H33N5, C, 81.54; H, 5.94; N, 12.51. Found: C, 81.60; H,
5.83; N, 12.68%.
Received 5 May 2013; accepted 9 June 2013
Paper 1301932 doi: 10.3184/174751913X13736278296459
Published online: 9 August 2013
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3-Cyano-2-(1H-indol-3-yl)-4-(4-hydroxyphenyl)-6-(9-butylcarba-
zol-3-yl)pyridine (5h): Yellow powder; IR (KBr) νmax 3405, 3378,
3322, 3059, 2955, 2873, 2218 (CN), 1569, 1515, 1435, 1355, 1238,
1
1211, 1130, 1113, 837, 745 cm−1; H NMR (500 MHz, DMSO-d6):
δ 11.81 (s, 1H), 10.00 (s, 1H), 9.19 (s, 1H), 8.55−8.49 (m, 2H), 8.38
(d, 1H, J = 2.5 Hz), 8.28 (d, 1H, J = 7.5 Hz), 8.06 (s, 1H), 7.80 (d, 1H,
J = 8.5 Hz), 7.72 (d, 2H, J = 8.5 Hz), 7.66 (d, 1H, J = 8.5 Hz),
7.59−7.57 (m, 1H), 7.51 (t, 1H, J = 7.0 Hz), 7.29−7.26 (m, 3H), 7.01
(d, 2H, J = 8.5 Hz), 4.46 (t, 2H, J = 7.0 Hz), 1.83−1.77 (m, 2H),
1.38−1.30 (m, 2H), 0.90 (t, 3H, J = 7.0 Hz).Anal. Calcd for C36H28N4O,
C, 81.18; H, 5.30; N, 10.52. Found: C, 81.09; H, 5.43; N, 10.48%.
19 J. Slatt, I. Romero and J. Bergman, Synthesis, 2004, 2760.
20 H.Y. Wang, G. Chen, X.P. Xu, H. Chen and S.J. Ji, Dyes Pigm., 2010, 86,
238.
21 D. Philippe and D. Fanny, U.S. Pat. 20120039804, 2012.

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