Synthesis of 3-(quinolin-2-yl)-and 3,6-bis(quinolin-2-yl)-9H-carbazoles

Article abstract of DOI:10.3762/bjoc.6.108

A simple and efficient synthesis of novel 3-(quinolin-2-yl)-and 3,6-bis(quinolin-2-yl)-9H-carbazoles, utilizing sodium ethoxide as a catalyst via a Friedlaender condensation reaction between 3-acetyl-9-ethyl-9H- carbazole or 3,6-diacetyl-9-ethyl-9H-carbaz

Full text of DOI:10.3762/bjoc.6.108

Synthesis of 3-(quinolin-2-yl)- and
3,6-bis(quinolin-2-yl)-9H-carbazoles
Yang Li and Wentao Gao*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, 966–972.
Institute of Superfine Chemicals, Bohai University, Jinzhou 121000,
China
doi:10.3762/bjoc.6.108
Received: 17 August 2010
Accepted: 29 September 2010
Published: 08 October 2010
Email:
Wentao Gao* - bhuzh@163.com
* Corresponding author
Associate Editor: J. N. Johnston
Keywords:
© 2010 Li and Gao; licensee Beilstein-Institut.
License and terms: see end of document.
acetylcarbazole; β-aminoaldehyde; β-aminoketone; Friedländer
condensation; sodium ethoxide
Abstract
A simple and efficient synthesis of novel 3-(quinolin-2-yl)- and 3,6-bis(quinolin-2-yl)-9H-carbazoles, utilizing sodium ethoxide as
a catalyst via a Friedländer condensation reaction between 3-acetyl-9-ethyl-9H-carbazole or 3,6-diacetyl-9-ethyl-9H-carbazole and
β-aminoaldehydes or β-aminoketones is described. All of the title compounds were obtained in good yields of 52–72% and their
structures were confirmed by IR, 1H NMR, MS, and elemental analysis.
Introduction
Nitrogen-containing heterocycles are a very important group of especially in the area of medicinal chemistry, and moreover it is
organic compounds because of their wide application in medi- a ubiquitous sub-structure found in many biologically active
cine, agriculture, and technology. Among these, quinoline and natural products [4-8]. Carbazole-based compounds are also
carbazole derivatives are of significant synthetic interest due to embodied in many naturally occurring products and these too
their diverse range of biological activities. Compounds display a wide variety of biological effects such as anti-tumor
containing a quinoline framework have been found applications [9,10], anti-oxidative [11], anti-inflammatory, and anti-muta-
as pharmaceuticals and agrochemicals, as well as being general genic activities [12,13]. In addition, their derivatives are widely
synthetic building blocks [1-3]. Industrial, biological, and syn- used as building blocks for new organic materials and play a
thetic significance places this scaffold in a prestigious position. very important role in electroactive and photoactive materials.
Studies on new quinoline derivatives appear frequently in the They are also considered to be potential candidates for elec-
chemical literature. Therefore, significant effort continues to be tronic devices, such as color displays, organic semiconductor
directed toward the development of new quinolines . In particu- lasers, and solar cells because of their reversible electrochem-
lar, there is much current interest in the quinoline ring system ical oxidation [14-20]. Currently, there is a strong interest in the
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Beilstein J. Org. Chem. 2010, 6, 966–972.
synthesis of novel heteroarylcarbazole derivatives due to their Results and Discussion
intriguing structural features and promising biological activities In order to construct the desired quinolyl-substituted carbazoles,
[21-24]. Most heteroarylcarbazoles reported in the literature we devised a route that made use of a Friedländer condensation
contain a common heterocyclic ring moiety fused with a reaction between the readily available 3-acetyl-9-ethyl-9H-
carbazole such as pyridocarbazoles [25], thienocarbazole [26], carbazole (1) or 3,6-diacetyl-9-ethyl-9H-carbazole (4) and
quino and chromenocarbazoles [27], pyranocarbazoles, pyrrolo- β-aminoaldehydes or β-aminoketone (2a–c) as shown in
carbazoles [28], indolocarbazoles [29], and synthetic analogues Scheme 1.
thereof. However, to the best of our knowledge, there are very
few reports where the heteroaryl moiety is substituted with a The starting materials 1 and 4 of our study were readily
carbazole unit and hence the synthesis of such compounds is prepared according to the methods described in literature [35].
desirable. In this regard, Meesala et al. [30] recently described a For the construction of the quinoline ring, the Friedländer
short and facile route to the synthesis of new 3,6-bis(pyrazol-4- quinoline synthesis appears to be the most simple and straight-
yl)carbazoles from 3,6-diacetylcarbazoles through a Vilsmeier forward approach available to chemists, compared to other
reaction. Later, Chaitanya et al. [31] reported a new synthesis of possible methods such as the Skraup, Doebner–von Miller, and
3-(3-nitrochromenyl)carbazoles, 3,6-bis(3-nitrochromenyl)- Combes reactions [36-42]. Conventionally, the Friedländer
carbazoles under solvent-free conditions by the reaction of quinoline synthesis can be achieved by the use of a variety of
β-nitrovinylcarbazole or bis(β-nitrovinyl)carbazole with salicyl- Brønsted acid catalysts, such as hydrochloric acid, perchloric
aldehydes.
acid, sulfuric acid, p-toluene sulfonic acid, sulfamic acid, phos-
phoric acid, and trifluoroacetic acid [43-45]. However, many of
In light of these findings, and in view of the prominent role these procedures are not completely satisfactory with regard to
structural diversity plays in medicinal and combinatorial chem- operational simplicity, cost of the reagent, drastic reaction
istry, we felt that there was a real need for the synthesis of some conditions, and relatively low yields. Some recent protocols
new prototypes combining both the carbazole ring system and reported for the synthesis of quinolines involve the use of cata-
quinoline moiety in the same molecule. These could be vitally lysts such as SnCl2 [46], I2 [47], montmorillonite-KSF [48],
important for pharmacological studies or in creating new medic- ionic liquids [49], Bi(OTf)3 [50], Y(OTf)3 [51], silver dode-
inal properties. Therefore, in continuation of our studies on the catungstophosphate (Ag3POW12O40) [52], silica sulfuric acid
synthesis of novel and interesting quinolyl-substituted hetero- [53], sulfamic acid [54], neodymium nitrate [55], etc. However,
cycles [32-34], we report herein the synthesis of novel these methods suffer from the serious drawbacks of harsh reac-
3-(quinolin-2-yl)- and 3,6-bis(quinolin-2-yl)-9H-carbazoles. tion conditions, use of expensive catalysts, long reaction times,
Scheme 1: Synthetic route of the title compounds 3a–5c.
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Beilstein J. Org. Chem. 2010, 6, 966–972.
Table 1: Syntheses of 3-(quinolin-2-yl)- and 3,6-bis(quinolin-2-yl)-9H-carbazoles (3a–5c).
Yield
Entry
Substrate
Time (h)
Product
Mp (°C)
(%)a
116–117
Lit [57]: 116–117
1
4
3a
72
2
3
4
5
7
8
3b
3c
5a
65
59
66
170–172
210–211
208–209
5
11
5b
58
245–247
6
15
5c
52
260–262
aIsolated yield.
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Beilstein J. Org. Chem. 2010, 6, 966–972.
etc. Ionic liquids have emerged as effective solvents for green the literature data [57], further corroborating the assigned struc-
chemical processes. However, the high cost of most conven- ture. Compounds 3b–5c are novel and their structures were
tional ionic liquids and their toxicity has limited their use. established with the help of spectroscopic data and elemental
Recently, Yang et al. [56] reported a Friedländer condensation analysis. For example, the IR spectrum of 3b revealed no
reaction for the facile synthesis of various poly-substituted absorption for amino or carbonyl groups. Its 1H NMR spectrum
quinolines under mild conditions catalysed by sodium ethoxide. showed no signals attributable to an amino group but contained
In connection with our studies, we envisioned that the proce- signals for eleven aromatic protons between δ 7.07–8.86 ppm
dure could also be applied to the reaction of 3-acetyl-9-ethyl- and for two methylenedioxy protons at δ 6.11 ppm as well as
9H-carbazole or 3,6-diacetyl-9-ethyl-9H-carbazole with signals from the ethyl group, which is consistent with the
2-aminoaldehydes or 2-aminoketones, from which the quinoly- attachment of the nascent quinoline ring moiety to the carbazole
carbazoles 9-ethyl-3-(quinolin-2-yl)-9H-carbazoles and 9-ethyl- substrate. Finally, the structure was confirmed by its mass spec-
3,6-bis(quinolin-2-yl)-9H-carbazoles might be synthesized. trum through the appearance of a quasi-molecular ion peak at
Indeed, this was found to be the case as shown in Scheme 1. m/z 367.1 ([M+H]+). The obtained elemental analysis values are
The Friedländer condensation reaction of 3-acetyl-9-ethyl-9H- in agreement with theoretical values. The other synthesized
carbazole (1) with 1 molar equivalent of β-aminoaldehydes or compounds exhibited similar spectral characteristics.
β-aminoketone (2a–c) in the presence of 1 molar equivalent of
sodium ethoxide in anhydrous ethanol under reflux for 6–8 h Conclusion
afforded the corresponding products (3a–c) in good yields of A straightforward synthesis of 3-(quinolin-2-yl)- and 3,6-
59–72%. The ease of isolation of all the products was notable; bis(quinolin-2-yl)-9H-carbazoles (3a–5c) in good yields is
after aqueous work-up, the products were isolated as the main reported. These molecules should allow us, in the future, to
products. In addition, it is noteworthy that the use of 1 molar investigate structure-activity relationships in various biotests.
equivalent of the catalyst EtONa was sufficient to promote the
reaction and that there were no improvements in reaction rates Experimental
and yields by increasing the amount of EtONa or by the use of Melting points (uncorrected) were determined by using a WRS-
other bases such as NaOH or K2CO3. Similarly, 3,6-diacetyl-9- 1B melting point apparatus. The 1H NMR (400 MHz) spectra
ethyl-9H-carbazole (4) reacted with 2 molar equivalents of 2a–c were recorded on a Bruker AVANCE 400 NMR spectrometer at
in the presence of sodium ethoxide to yield the desired prod- 400 MHz with TMS as the internal standard. The mass spectra
ucts 5a–c in good yields (66%, 58%, and 52%, respectively). were determined using a MSD VL ESI1 spectrometer.
The yields and melting points of all the synthesized compounds Elemental analyses were performed with an Elementar Vario
3a–5c are listed in Table 1.
EL-III element analyzer. The progress of reactions was moni-
tored by thin-layer chromatography (TLC) on silica gel GF254
As shown in Table 1, both 9-ethyl-9H-carbazoles bearing acetyl using ethyl acetate/petroleum ether (1:4) as eluent.
and diacetyl substituents afforded the corresponding products in
good yields. Additionally, some reaction trends were also noted. General procedure for the synthesis of 9-ethyl-3-(quinolin-2-
Thus, the use of 3,6-diacetyl-9-ethyl-9H-carbazole led to yl)-9H-carbazole (3a–c). To a solution of 3-acetyl-9-ethyl-9H-
slightly lower yields of products when compared to 3-acetyl-9- carbazole (1) (0.24 g, 1 mmol) and the required β-amino car-
ethyl-9H-carbazole and required relatively longer reaction times bonyl compound, 2-aminobenzaldehyde, 2-aminobenzophe-
(Entries 4–6). On the other hand, in going from 2a to 2c with none or 2-amino-4,5-methylenedioxybenzaldehyde (2a–c),
either of the starting carbazoles, the yields of both sets of prod- (1 mmol) in 5 mL of absolute EtOH, was added sodium
ucts, i.e., 3a–c (Entries 1–3) and 5a–c (Entries 4–6) gradually ethoxide (0.07 g, 1 mmol). The resulting mixture was heated
decreased, whilst the corresponding reaction times gradually under reflux for 4–7 h. After the reaction was complete (TLC),
increased. This may be attributed to the reduced electrophilicity the mixture was cooled to room temperature, poured into water
of the carbonyl groups in 2b and 2c as a result of the electron- and filtered to give the crude product, which was then purified
rich nature of the methylenedioxy group or the phenyl ring. by silica gel column chromatography with ethyl acetate/petro-
This observation is consistent with the proposed mechanism leum ether (1:6) as eluent. The reaction times, yields and
which involves the enolate anion formed in the basic medium melting points are listed in Table 1.
attacking by the carbonyl carbon of the ortho-aminoarylalde-
hyde [56].
9-Ethyl-3-(quinolin-2-yl)-9H-carbazole (3a). This compound
was obtained as a yellow solid, IR (KBr) ν/cm−1: 3049, 2978,
It is worth noting here that only compound 3a is known and its 1596, 1551, 1493, 1473, 1452, 1437, 1379, 1237, 1141, 879,
melting point and proton NMR spectral data are identical with 808, 745; 1H NMR (CDCl3) δ (ppm): 8.93 (d, J = 1.5 Hz, 1H,
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Beilstein J. Org. Chem. 2010, 6, 966–972.
ArH), 8.35 (dd, J = 8.5, 2.0 Hz, 1H, ArH), 8.20–8.24 (m, 3H, 2974, 2929, 1592, 1552, 1488, 1434, 1381, 1329, 1286, 1242,
ArH), 8.03 (d, J = 8.5 Hz, 1H, ArH), 7.82 (dd, J = 8.5, 1.0 Hz, 1178, 1148, 1129, 1043, 973, 890, 786, 763; 1H NMR (CDCl3)
1H, ArH), 7.53 (d, J = 8.5 Hz, 1H, ArH), 7.48–7.52 (m, 2H, δ (ppm): 9.05 (d, J = 1.5 Hz, 2H, ArH), 8.39 (dd, J = 8.4,
ArH), 7.44 (d, J = 8.0 Hz, 1H, ArH), 7.35 (dd, J = 7.0, 1.5 Hz, 1.5 Hz, 2H, ArH), 8.17–8.25 (m, 4H, ArH), 8.06 (d, J = 8.7 Hz,
1H, ArH), 7.27 (dd, J = 8.0, 7.5 Hz, 1H, ArH), 4.42 (q, J = 2H, ArH), 7.80 (dd, J = 8.1, 1.8 Hz, 2H, ArH), 7.72 (dd, J = 8.4,
7.5 Hz, 2H, CH2), 1.47 (t, J = 7.5 Hz, 3H, CH3); MS (ESI, m/z): 1.5 Hz, 2H, ArH), 7.48–7.56 (m, 4H, ArH), 4.45 (q, J = 7.2 Hz,
323.1 [M+H]+; Anal. Calcd for C23H18N2: C, 85.68; H, 5.63; 2H, CH2), 1.49 (t, J = 7.2 Hz, 3H, CH3); MS (ESI, m/z): 450.4
N, 8.69. Found: C, 85.21; H, 5.68; N, 8.45.
[M+H]+; Anal. Calcd for C32H23N3: C, 85.50; H, 5.16; N, 9.35.
Found: C, 85.09; H, 5.21; N, 9.46.
9-Ethyl-3-(6,7-methylenedioxyquinolin-2-yl)-9H-carbazole
(3b). This compound was obtained as a yellow solid, IR (KBr) 3,6-Bis(6,7-methylenedioxyquinolin-2-yl)-9-ethyl-9H-
ν/cm−1: 3062, 2973, 2897, 1594, 1541, 1494, 1458, 1393, 1339, carbazole (5b). This compound was obtained as a yellow solid,
1252, 1235, 1173, 1142, 1125, 1039, 927, 853, 746; 1H NMR IR (KBr) ν/cm−1: 3052, 2958, 2925, 2853, 1595, 1521, 1492,
(CDCl3) δ (ppm): 8.86 (d, J = 1.32 Hz, 1H, ArH), 8.27 (dd, J = 1470, 1403, 1352, 1329, 1264, 1231, 1174, 1126, 1074, 1041,
8.5, 1.6 Hz, 1H, ArH), 8.22 (d, J = 7.7 Hz, 1H, ArH), 8.02 (d, 961, 934, 861, 811,777; 1H NMR (CDCl3) δ (ppm): 8.90 (d, J =
J = 8.5 Hz, 1H, ArH), 7.86 (d, J = 8.5 Hz, 1H, ArH), 7.45–7.52 1.5 Hz, 2H, ArH), 8.25 (dd, J = 7.0, 1.5 Hz, 2H, ArH), 7.98 (d,
(m, 4H, ArH), 7.26 (s, 1H, ArH), 7.07 (s, 1H, ArH), 6.11 (s, 2H, J = 7.0 Hz, 2H, ArH), 7.49 (d, J = 7.5 Hz, 2H, ArH), 7.38 (d,
OCH2O), 4.43 (q, J = 7.2 Hz, 2H, CH2), 1.47 (t, J = 7.2 Hz, 3H, J = 7.5 Hz, 2H, ArH), 7.19 (s, 2H, ArH), 7.02 (s, 2H, ArH),
CH3); MS (ESI, m/z): 367.1 [M+H]+; Anal. Calcd for 6.06 (s, 4H, OCH2O), 4.39 (q, J = 7.0 Hz, 2H, CH2), 1.41 (t, J =
C24H18N2O2: C, 78.67; H, 4.95; N, 7.65. Found: C, 78.35; H, 7.0 Hz, 3H, CH3); MS (ESI, m/z): 538.1 [M+H]+; Anal. Calcd
4.80; N, 7.53.
for C34H23N3O4: C, 75.97; H, 4.31; N, 7.82. Found: C, 76.19;
H, 4.17; N, 7.72.
9-Ethyl-3-(4-phenylquinolin-2-yl)-9H-carbazole (3c). This
compound was obtained as a yellow solid, IR (KBr) ν/cm−1: 3,6-Bis(4-phenylquinolin-2-yl)-9-ethyl-9H-carbazole (5c).
3057, 2925, 2854, 1589, 1542, 1495, 1473, 1457, 1442, 1385, This compound was obtained as a yellow solid, IR (KBr)
1232, 1160, 1133, 879, 771; 1H NMR (CDCl3) δ (ppm): 8.97 (s, ν/cm−1: 3049, 2976, 2932, 1587, 1544, 1488, 1446, 1409, 1367,
1H, ArH), 8.41 (d, J = 8.4 Hz, 1H, ArH), 8.29 (d, J = 8.7 Hz, 1346, 1275, 1231, 1174, 1127, 1074, 1022, 919, 878, 773;
1H, ArH), 8.23 (d, J = 7.8 Hz, 1H, ArH), 7.92 (d, J = 8.7 Hz, 1H NMR (CDCl3) δ (ppm): 9.05 (d, J = 1.2 Hz, 2H, ArH), 8.47
1H, ArH), 7.75 (dd, J = 8.1, 7.2 Hz, 1H, ArH), 7.64 (d, J = 8.1 (dd, J = 8.4, 1.5 Hz, 2H, ArH), 8.29 (d, J = 8.4 Hz, 2H, ArH),
Hz, 1H, ArH), 7.44–7.59 (m, 7H, ArH), 7.27–7.31 (m, 3H, 8.02 (s, 2H, ArH), 7.91 (d, J = 8.4 Hz, 2H, ArH), 7.71–7.77 (m,
ArH), 4.45 (q, J = 7.2 Hz, 2H, CH2), 1.49 (t, J = 7.2 Hz, 3H, 6H, ArH), 7.43–7.65 (m, 10H, ArH), 4.48 (q, J = 7.2 Hz, 2H,
CH3); MS (ESI, m/z): 399.1 [M+H]+; Anal. Calcd for CH2), 1.52 (t, J = 7.2 Hz, 3H, CH3); MS (ESI, m/z): 602.1
C29H22N2: C, 87.41; H, 5.56; N, 7.03. Found: C, 87.13; H, [M+H]+; Anal. Calc for C44H31N3: C, 87.82; H, 5.19; N, 6.98.
5.61, N, 6.79.
Found: C, 88.27; H, 5.07; N, 6.90.
General procedure for the synthesis of 3,6-bis(quinolin-2-
yl)-9-ethyl-9H-carbazole (5a–c). To a solution of 3,6-diacetyl-
9-ethyl-9H-carbazole (4) (0.28 g, 1 mmol) and the required
β-amino carbonyl compound, 2-aminobenzaldehyde,
2-aminobenzophenone or 2-amino-4,5-methylenedioxyben-
zaldehyde (2a–c), (2 mmol) in 5 mL of absolute EtOH was
added sodium ethoxide (0.14 g, 2 mmol). The resulting mixture
was heated under reflux for 8–15 h. After the reaction was
complete (TLC), the mixture was cooled to room temperature,
poured into water and filtered to give the crude product, which
was then purified by silica gel column chromatography with
ethyl acetate/petroleum ether (1:6) as eluent. The reaction times,
yields and melting points are listed in Table 1.
Supporting Information
Supporting Information features 1H NMR spectra of the
synthesized 3-(quinolin-2-yl)- and
3,6-bis(quinolin-2-yl)-9H-carbazoles.
Supporting Information File 1
1H NMR spectra of the title compounds 3a–5c.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-6-108-S1.pdf]
Acknowledgements
The authors would like to thank the Foundation of Liaoning
3,6-Bis(quinolin-2-yl)-9-ethyl-9H-carbazole (5a). This com- Province Key Laboratory of Applied Chemistry (Grant No.
pound was obtained as a white solid, IR (KBr) ν/cm−1: 3050, 2008s001) for financial support.
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