Yb(OTf)3: An efficient catalyst for the synthesis of 3-arylbenzo [f]quinoline-1,2-dicarboxylate derivatives via imino-Diels-Alder reaction

Article abstract of DOI:10.1016/j.tetlet.2010.08.074

A mild and facile method for the synthesis of 3-arylbenzo[f]quinoline-1,2- dicarboxylate derivatives is reported by an imino-Diels-Alder reaction in high yields (76-92%). This procedure includes a novel three-component reaction of aromatic aldehyde, naphthalen-2-amine, and but-2-ynedioate catalyzed by Yb(OTf)₃ in toluene. The results are obviously different from those of the simple substituted aniline-involved reactions catalyzed by ZnCl ₂ or KOH in the literature.

Full text of DOI:10.1016/j.tetlet.2010.08.074

Tetrahedron Letters 51 (2010) 5721–5723
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Tetrahedron Letters
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Yb(OTf)3: an efficient catalyst for the synthesis of 3-arylbenzo [f]quinoline-
1,2-dicarboxylate derivatives via imino-Diels–Alder reaction
Xiang-Shan Wang a,b, , Jie Zhou a, Ke Yang a, Chang-Sheng Yao a
⇑
a School of Chemistry and Chemical Engineering, Xuzhou Normal University, Xuzhou Jiangsu 221116, PR China
b The Key Laboratory of Biotechnology for Medical Plant, Xuzhou, Jiangsu 221116, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A mild and facile method for the synthesis of 3-arylbenzo[f]quinoline-1,2-dicarboxylate derivatives is
reported by an imino-Diels–Alder reaction in high yields (76–92%). This procedure includes a novel
three-component reaction of aromatic aldehyde, naphthalen-2-amine, and but-2-ynedioate catalyzed
by Yb(OTf)3 in toluene. The results are obviously different from those of the simple substituted ani-
line-involved reactions catalyzed by ZnCl2 or KOH in the literature.
Received 25 May 2010
Revised 17 August 2010
Accepted 24 August 2010
Available online 27 August 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Benzo[f]quinoline-1,2-dicarboxylate
Yb(OTf)3
Imino-Diels–Alder reaction
But-2-ynedioate
Synthesis
Multi-component reactions (MCRs) play an important role in
modern synthetic organic chemistry since they generally occur in
a single pot and exhibit a high atom–economy and selectivity. They
also deliver fewer byproducts compared to the classical stepwise
synthetic routes. In addition, for multi-component reactions
involving the simultaneous molecular interaction of three or more
components, they always gave diverse compounds as well as small
and drug-like heterocycles through controlling of different reaction
parameters such as temperature, pressure, solvent, and catalyst
type.1
The synthesis of benzoquinoline derivatives has been the focus
of great interest, because it was reported that its derivatives pos-
sess a broad spectrum of biological properties, such as antibacterial
activity,2 UDP (Uridine diphosphate)-glucuronosyl transferase
activity,3 antimicrobial activity,4 antimalarial activity,5 agonistic
activity,6 and antipsychotic activity.7 Accordingly, novel strategies
for the synthesis of benzoquinolines continue to receive consider-
able attention in the field of synthetic organic chemistry in recent
years,8 and among which imino-Diels–Alder reaction provides an
easy access to the preparation of quinoline or benzoquinoline deriv-
atives. The imines derived from aromatic amines act as heterodienes
and undergo imino-Diels–Alder reaction with various dienophiles in
the presence of acid catalysts.9 The known reported dienophiles
included enol from aldehyde or ketone,9a–d 2,3-dihydrofuran or
3,4-dihydro-2H-pyran,9e–j vinyl ether,9l–n and 1-vinylpyrrolidin-2-
one.9n–r In view of the importance of the benzoquinoline and its
derivatives, searching for other dienophiles to construct novel
benzoquinoline moieties is of increasing interest.
As a part of our ongoing program to synthesize benzoquinoline
derivatives via imino-Diels–Alder reaction using various dieno-
philes,10 in this Letter, we would like to report the synthesis of
3-arylbenzo[f]quinoline-1,2-dicarboxylate derivatives using but-
2-ynedioate as dienophile via a one-pot imino-Diels–Alder reac-
tion catalyzed by Yb(OTf)3. Because over the past few years,
Yb(OTf)3 has emerged as a powerful catalyst for various organic
transformations to afford the products in good to excellent yields.
Owing to several advantages such as inexpensive, nontoxic, and
eco-friendly nature, Yb(OTf)3 has been used as a catalyst in the
investigation of different organic reactions.11
Treatment of aromatic aldehyde 1, naphthalen-2-amine 2, and
but-2-ynedioate 3 in toluene in the presence of 1 mol % Yb(OTf)3
at 80 °C resulted in the corresponding 3-arylbenzo[f] quinoline-
1,2-dicarboxylate derivatives 4a–o in high yields (Scheme 1).
Obviously, this structure 4 was different from that of the simple
substituted aniline-involved reactions reported by Zhang and
Jiang12 in 2008, which was carried out in refluxing toluene cata-
lyzed by ZnCl2, and in CH3CN in the presence of KOH reported by
the same team13 in 2007, respectively.
CO2R'
CO2R'
NH2
Yb(OTf)3
CO2R'
+
+
RCHO
CO2R'
N
R
4
1
2
3
⇑
Corresponding author. Tel.: +86 516 3403164.
E-mail address: xswang1974@yahoo.com (X.-S. Wang).
Scheme 1.
0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.08.074

5722
X.-S. Wang et al. / Tetrahedron Letters 51 (2010) 5721–5723
Table 1
Synthesis of 4a at different reaction conditionsa
Entry
T (°C)
Solvent
Cat. (mol %)
Yieldb (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
80
80
80
80
rt
50
110
80
80
80
80
80
65
80
80
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
I2/1
56
86
84
86
Trace
65
85
52
48
50
46
38
69
72
70
Yb(OTf)3/1
Yb(OTf)3/5
Yb(OTf)3/10
Yb(OTf)3/1
Yb(OTf)3/1
Yb(OTf)3/1
AgOTf/1
Cu(OTf)2/1
Zn(OTf)2/1
Ca(OTf)2/1
Fe(OTf)2/1
Yb(OTf)3/1
Yb(OTf)3/1
Yb(OTf)3/1
Benzene
DMF
a
Reaction condition: 10 mL solvent, 2 mmol 4-fluorobenzaldehyde, 2 mmol
naphthalen-2-amine, 2.1 mmol diethyl but-2-ynedioate.
b
Isolated yields.
In our initial study, dimethyl but-2-ynedioate was applied to this
imino-Diels–Alder reaction as dienophile to react with 4-fluoro-
benzaldehyde and naphthalen-2-amine catalyzed by iodine, with
expected 3-arylbenzo[f]quinoline-1,2-dicarboxylate derivatives
being obtained in lower yield (4a in 56% yield, Table 1, entry 1). In
order to further enhance the rate of conversion, screening higher
efficient Lewis acid catalyst is carried out in our lab; finally Yb(OTf)3
(4a in 86% yield, Table 1, entry 2) was selected as an efficient catalyst.
Subsequently, the above reaction was used as a model reaction to
optimize the conditions. A summary of the optimization experiment
was provided in Table 1. The results showed that at room tempera-
ture, trace amount of products was observed by TLC (Table 1, entry
1). To our delight, at 80 °C the reaction proceeded smoothly in high
yield. Similar reactions were then carried out in the presence of 1%,
5%, and 10 mol % of Yb(OTf)3. The results from Table 1 (entries 3–5)
showed that 1 mol % of Yb(OTf)3 at 80 °C is enough to give a high
yield (86%). Higher loading of the catalyst did not improve the
reaction condition to a great extent. Thus, the optimal reaction
temperature and catalyst amount are 80 °C and 1 mol % Yb(OTf)3,
respectively. Moreover, different solvents and various trifuloro-
methanesulfonates were further investigated as shown in Table 1,
Figure 1. The crystal structure of the product 4n.
we can conclude that the Yb(OTf)3/toluene was the best system for
this reaction.
In order to extend the above reaction (Scheme 1) to a library
system, various kinds of arylaldehydes 1 (Table 2) were subjected
to react with 2 and 3 to give the corresponding 3-arylbenzo[f]quin-
oline-1,2-dicarboxylate 4, and representative examples are shown
in Table 2. All of 1 gave the expected products at high yields, either
bearing electron-withdrawing groups (such as halide, nitro) or
electron-donating groups (such as alkyl group, or alkoxyl group)
under the same reaction condition. To further demonstrate the
scope and limitation of the substrates, aliphatic aldehydes, such
as phenylacetaldehyde, propionaldehyde, n-butyl aldehyde, and
n-heptaldehyde, were used as reactants to react with naphtha-
len-2-amine and dimethyl but-2-ynedioate. However, the desired
products were neither found nor obtained successfully. All of the
structures were characterized by 1H NMR, IR, and HRMS. The struc-
ture of the product 4n was additionally confirmed by an X-ray dif-
fraction analysis,14 and its crystal structure was shown in Figure 1.
According to the literatures,16 we think that Yb(OTf)3 catalyzes
the reaction as a mild Lewis acid. The mechanism was tentatively
proposed in Scheme 2. The Schiff base I may be formed by the reac-
tion of aromatic aldehyde and naphthalene-2-amine firstly. And
then imino-Diels–Alder reaction between the Yb(OTf)3-activated
Schiff base II and but-2-ynedioate takes place to form intermediate
III, followed by isomerization to give 3,4-dihydrobenzo[f]quino-
lines IV, which is further oxidized by air to afford the final aroma-
tized 3-arylbenzo[f]quinoline-1,2-dicarboxylate 4.
Table 2
Yb(OTf)3 catalyzed reactions of aromatic aldehyde, naphthalen-2-amine and but-2-
ynedioatea,15
Products
R
R0
Time (h)
Yieldsb (%)
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4-FC6H4
4-ClC6H4
3-ClC6H4
4-CH3C6H4
2,4-Cl2C6H3
3,4-Cl2C6H3
2-Thienyl
3-FC6H4
Me
Me
Me
Me
Me
Me
Me
Et
Et
Et
Et
Et
8
9
9
12
8
8
10
12
13
14
8
86
84
78
89
92
86
79
78
82
84
87
76
85
85
77
0c
R
NH2
N
Yb(OTf)3
+
RCHO
4-BrC6H4
4-CH3OC6H4
4-NO2C6H4
2,4-Cl2C6H3
3,4-OCH2OC6H3
3,4-Me2C6H3
2-Thienyl
PhCH2
I
9
Et
Et
Et
Me
12
12
13
15
CO2R'
CO2R'
CO2R'
CO2R'
CO2R'
CO2R'
N
(OTf)3Yb
4
N
a
Air
Reaction condition: 10 mL toluene, 2.0 mmol aromatic aldehyde, 2.0 mmol
N
R
R
naphthalen-2-amine, 2.1 mmol but-2-ynedioate and 0.02 mmol Yb(OTf)3.
H
R
III
b
Isolated yields.
IV
II
c
The expected products were not found using other aliphatic aldehydes, such as
propionaldehyde, n-butyl aldehyde, and n-heptaldehyde.
Scheme 2.

X.-S. Wang et al. / Tetrahedron Letters 51 (2010) 5721–5723
5723
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In conclusion, we have discovered an effective method for the
syntheses of 3-arylbenzo[f]quinoline-1,2-dicarboxylate derivatives
by an imino-Diels–Alder reaction of aromatic aldehyde, naphtha-
len-2-amine, and but-2-ynedioate in toluene using 1 mol % Yb(OTf)3
as catalyst. The note-worthy features of this procedure are mild
reaction conditions, economical steps, high yields, and operational
simplicity.
Acknowledgments
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The authors are grateful to the National Natural Science Foun-
dation of China (20802061), the Natural Science Foundation
(08KJD150019), and Qing Lan Project (08QLT001) of Jiangsu Educa-
tion Committee for the financial support.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2010.08.074.
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14. Crystal data for 4n: C27H25NO4; M = 427.48, colorless block crystals, 0.46 ꢀ
ꢀ
0.16 ꢀ 0.12 mm, Triclinic, space group P1, a = 7.6114(2), b = 10.7371(3), c =
14.9116(5) Å,
a = 101.774(2), b = 96.265(2), c
= 109.891(2)°, V = 1100.52(6)3,
Z = 2, Dc = 1.290 g cmꢁ3. F(0 0 0) = 452,
were collected on Rigaku Mercury diffractometer with graphite
monochromated MoK radiation (k = 0.71073 Å) using phi and omega scan
mode with 2.84° < h < 25.20°. Unique reflections (3937) were measured and
3154 reflections with I > 2 (I) were used in the refinement. The structure was
l(MoKa
) = 0.086 mmꢁ1. Intensity data
a
r
solved by direct methods and expanded using Fourier techniques. The final
cycle of full-matrix least squares technique to R = 0.0400 and wR = 0.0501.
15. General procedure for the syntheses of 3-arylbenzo[f]quinoline-1,2-dicarboxylate
derivatives 4a–o: A dry 50 mL flask was charged with aromatic aldehyde
(2.0 mmol), naphthalen-2-amine (0.286 g, 2.0 mmol), but-2-ynedioate
(2.1 mmol), Yb(OTf)3 (0.012 g, 0.02 mmol), and toluene (10 mL). The reaction
mixture was stirred at 80 °C for 8ꢁ14 h. After completion of the reaction as
indicated by TLC, another portion of toluene was added to the mixture until all
the yellow solid was dissolved when the mixture was cooled to room
temperature. The organic layer was washed with water, and then dried over
anhydrous MgSO4. The toluene was recovered by reduced pressure, and the
crude products were purified by recrystallization from 95% EtOH to give 4.
Selected data: dimethyl 3-(4-fluorophenyl)benzo[f]quinoline-1,2-dicarbox-
ylate 4a: mp: 165–167 °C. 1H NMR (DMSO-d6, 400 MHz): dH 3.74 (s, 3H,
CH3), 4.08 (s, 3H, CH3), 7.40 (t, J = 8.4 Hz, 2H, ArH), 7.69–7.73 (m, 2H, ArH),
7.81–7.84 (m, 2H, ArH), 8.04 (d, J = 9.2 Hz, 1H, ArH), 8.18–8.21 (m, 2H, ArH),
8.33 (d, J = 9.2 Hz, 1H, ArH). 13C NMR (CDCl3, 100 MHz): dC 169.5, 168.1, 164.7,
162.2, 154.8, 149.7, 138.5, 135.7, 135.6, 133.7, 132.9, 130.6, 130.5, 129.4, 128.2,
128.0, 127.5, 125.3, 124.1, 119.5, 115.7, 115.5, 53.4, 52.9. IR (KBr, m
, cmꢁ1):
2957, 1750, 1722, 1601, 1549, 1509, 1439, 1450, 1386, 1328, 1311, 1272, 1240,
1222, 1209, 1198, 1182, 1169, 1158, 1126, 1116, 1064, 1003, 840, 821, 809,
763. Diethyl 3-(3,4-dimethylphenyl)benzo[f]quinoline-1,2-dicarboxylate 4n:
mp: 153–155 °C. 1H NMR (DMSO-d6, 400 MHz): dH 1.09 (t, J = 7.2 Hz, 3H, CH3),
1.35 (t, J = 7.2 Hz, 3H, CH3), 2.32 (s, 6H, 2CH3), 4.19 (q, J = 7.2 Hz, 2H, CH2), 4.55
(q, J = 7.2 Hz, 2H, CH2), 7.30 (d, J = 7.6 Hz, 1H, ArH), 7.37 (d, J = 1.6 Hz, 1H, ArH),
7.45 (s, 1H, ArH), 7.79–7.83 (m, 2H, ArH), 8.04 (d, J = 8.8 Hz, 1H, ArH),m 8.18 (dd,
J = 6.0 Hz, J0 = 3.2 Hz, 1H, ArH), 8.27 (dd, J = 6.0 Hz, J0 = 3.2 Hz, 1H, ArH), 8.31 (d,
J = 9.2 Hz, 1H, ArH). 13C NMR (CDCl3, 100 MHz): dC 169.2, 167.9, 156.3, 149.6,
138.4, 137.3, 136.7, 133.1, 132.8, 129.8, 129.6, 129.2, 128.3, 127.7, 127.1, 126.0,
125.5, 124.6, 119.2, 77.3, 77.0, 76.7, 62.7, 62.0, 19.8, 19.6, 13.8, 13.6. IR (KBr, m,
cmꢁ1): 2977, 2939, 2920, 2902, 1739, 1717, 1608, 1504, 1476, 1450, 1411,
1384, 1371, 1348, 1325, 1308, 1294, 1269, 1238, 1201, 1181, 1148, 1139, 1107,
1066, 1023, 999, 859, 749. HRMS (ESI, m/z): calcd for C27H25NO4, (M+H+)
428.1862, found: 428.1889.
16. Kudale, A. A.; Kendall, J. K.; Miller, D. O.; Collins, J. L.; Bodwell, G. J. J. Org. Chem.
2008, 73, 8437–8447.