One pot imino Diels-Alder reaction for the synthesis of 3-aryl-3,4-dihydrobenzo[f]quinoline derivatives catalyzed by antimony trichloride

Article abstract of DOI:10.1016/j.tetlet.2013.03.093

An one pot simple and efficient approach toward the synthesis of dialkyl-3-aryl-3,4-dihydrobenzo[f]quinoline-1,2-dicarboxylate and its dehydro derivatives have been developed through the three-component reaction of aromatic aldehydes, 2-naphthylamine, and

Full text of DOI:10.1016/j.tetlet.2013.03.093

Tetrahedron Letters 54 (2013) 2920–2923
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One pot imino Diels–Alder reaction for the synthesis of 3-aryl-3,4-dihydro-
benzo[f]quinoline derivatives catalyzed by antimony trichloride
⇑
Gourhari Maiti , Rajiv Karmakar, Utpal Kayal
Department of Chemistry, Jadavpur University, Kolkata 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An one pot simple and efficient approach toward the synthesis of dialkyl-3-aryl-3,4-dihydro-
benzo[f]quinoline-1,2-dicarboxylate and its dehydro derivatives have been developed through the
three-component reaction of aromatic aldehydes, 2-naphthylamine, and but-2-ynedioate catalyzed by
SbCl3 under reflux in acetonitrile in good to excellent yields.
Received 1 October 2012
Revised 21 March 2013
Accepted 22 March 2013
Available online 3 April 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Naphthylamine
But-2-ynedioate
Imino Diels–Alder reaction
Multicomponent reaction
3-Aryl-3,4 dihydrobenzoquinoline-1,2-
dicarboxylate
Antimony trichloride
The current trends of synthetic organic chemistry are found to
involve wide applications of multicomponent reactions (MCRs) in
order to develop efficient and practical methods for the synthesis
of structurally diverse molecules.1 Metal catalyzed MCRs involving
cascade C–C and C–N bond formations have been greatly used in
the synthesis of a range of heterocycles. This powerful technique
has emerged as a greener approach for the preparation of bioactive
compounds in much shorter time with minimum waste production
and also to increase the synthetic efficiency by reducing the
number of steps.2
The quinoline and benzoquinoline nuclei are prominent struc-
tural motifs found in numerous natural products and synthetic
compounds with important pharmacological and biological activ-
ities. The quinoline and benzo[g]quinoline ring and their analogs
behave as agonists at the D2-site in schizophrenia.3 The benzo-
quinoline core structure is found in a wide variety of biologically
active natural products and pharmaceuticals with antimicrobial,4
antibacterial,5 antipsychotic,6 agonistic,7 antimalarial,8 antitu-
mor,9 and uridine diphosphate (UDP)-glucuronosyl transferase10
activities.
preparation of six-membered nitrogen heterocycles as well as
related fused ring heterocycles.12,13 In recent years, this reaction
has been found to have wide applications through the activation
of the imine systems for cycloadditions by increasing their
electron-deficient character.14 Although, several Lewis acid and
Brønsted acid catalyzed imino Diels–Alder reactions have been
developed15 as convenient routes for the construction of a wide
variety of nitrogen heterocycles, there is further scope for develop-
ment of this methodology.
Very recently, Wang et al.16 have reported a one-pot synthesis
of 3-arylbenzo[f]quinoline-1,2-dicarboxylate derivatives via an
imino Diels–Alder reaction catalyzed by Yb(OTf)3. To the best of
our knowledge, there is no report of the use of antimony trichloride
(SbCl3), a mild and inexpensive catalyst, for imino Diels–Alder
reaction using electron-deficient dienophiles like dialkyl acetylene
dicarboxylates. Recently, we have efficiently utilized this catalyst
for such reaction using electron rich dienophiles.17 Our recent suc-
cess in effective utilization of this catalyst for IDA reaction using
electron rich olefins coupled with our continuous effort toward
synthesis of bioactive heterocyclic compounds18 encouraged us
All the above aspects have attracted attention of organic
chemists to develop efficient synthetic routes to highly functional-
ized benzoquinoline derivatives for several decades.11 The
imino Diels–Alder (IDA) reaction provides an easy access for the
to study a three-component reaction using naphthylamines,
aromatic aldehydes, and dialkyl acetylene dicarboxylates. This
study resulted in the development of an efficient synthetic route
to 3-aryl-3,4-dihydrobenzo[f]quinoline-1,2-dicarboxylate and
3-arylbenzo[f]quinoline-1,2-dicarboxylate (dehydro derivative of
the former) via an imino Diels–Alder reaction. It may be mentioned
here that antimony(III) salts19 (chloride and sulfate) have been
⇑
Corresponding author.
E-mail address: ghmaiti123@yahoo.co.in (G. Maiti).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.03.093

G. Maiti et al. / Tetrahedron Letters 54 (2013) 2920–2923
2921
CO2Me
CO2Me
N
CO2Me
SbCl3 (10 mol %)
MeO2C
MeO2C
NH2
+
CHO
+
NH
+
CH3CN, 80 0
C
CO2Me
argon atm.
1a
4a
5a
2a
3a
Scheme 1. Synthesis of benzoquinoline derivative.
Table 1
Optimization of reaction conditionsa
MeO2C
MeO2C
MeO2C
MeO2C
CO2Me
CO2Me
CHO
+
NH2
+
Catalyst (10 mol %)
CH3CN,80 0C,
argon atm.
NH
N
+
1a
(1 equiv.)
2a
3a
(1.2 equiv.)
(1 equiv.)
4a
5a
Entry
Catalyst (mol %)
Solvent
T (°C)
Product ratio (4a:5a)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Sbcl3/1
Sbcl3/10
Sbcl3/5
CH3CN
CH3CN
CH3CN
CH3CN
Toluene
DMF
80
80
80
50
90
90
80
80
80
80
80
80
80
80
4:1
8:1
5:1
3:1
3:1
5:2
7:3
—
5:1
4:1
9:4
5:1
3:1
7:3
9
6
7
8
9
9
8
12
12
10
14
16
14
18
76
90
79
62
50
35
Sbcl3/10
Sbcl3/10
Sbcl3/10
Sbcl3/10
nil/10
lncl3/10
Fecl3/10
CAN/10
Sncl4/10
Agcl/10
Zncl2/10
THF
40
c
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
9
42
45
39
41
40
50
10
11
12
13
14
a
b
c
Reaction condition: benzaldehyde (1.0 mmol), naphthalen-2-amine (1.0 mmol), dimethyl but-2-ynedioate (1.2 mmol), catalyst, in 2 mL solvent.
Pure, isolated yield after column chromatography.
No product was isolated.
used by us as well as others as mild and efficient catalysts for var-
ious organic transformations.
however, yielded 3-arylbenzo[f]quinoline-1,2-dicarboxylate (fully
aromatized compound) as the sole product in open air. Therefore,
a special feature which needs mentioning here is that in our reac-
tion condition, we could isolate the dihydro derivatives as the ma-
jor product even without taking any precaution to exclude air.
To extend the applicability of the method, various aromatic
aldehydes 2b–n, 2-naphthylamine 1a, and acetylene diesters 3a–
b were subjected to similar reaction conditions and the results
are summarized in Table 2. All the aromatic aldehydes either bear-
ing electron-donating groups (such as methyl, methoxy, methyl-
enedioxy, etc.) or electron-withdrawing groups (such as fluoro,
chloro, bromo, nitro, etc.) gave the expected products in very good
yields under the reaction conditions.20 4-N,N-Dimethylaminobenz-
aldehyde (Table 2, entry 8) did not respond to the reaction most
probably due to the strong +R effect of dimethylamino group
which decreases the reactivity of the aldehyde group significantly.
In order to assess the scope of this reaction, 1-naphthylamine
1b was treated separately with the aromatic aldehydes 2f and 2n
and dimethyl but-2-ynoate 3a under similar reaction conditions.
This variation furnished mixtures of corresponding dimethyl
2-aryl-1,2-dihydrobenzo[h]quinoline-3,4-dicarboxylate 4o–p and
dimethyl 2-arylbenzo[h]quinoline-3,4-dicarboxylate 5o–p in very
good yield (Table 3).
In a preliminary study, the treatment of 2-naphthylamine 1a,
benzaldehyde 2a, and dimethyl but-2-ynedioate 3a in refluxing ace-
tonitrile in the presence of 10 mol % SbCl3 under argon atmosphere
for 8 h furnished a mixture of two compounds, dimethyl 3-phenyl-
3,4-dihydrobenzo[f]quinoline-1,2-dicarboxy-late 4a and dimethyl
3-phenylbenzo[f]quinoline-1,2-dicarboxy-late 5a (Scheme 1) in a
ratio of 8:1 in 90% overall yield. With this encouraging result, we ex-
plored to optimize the reaction conditions using SbCl3 and other Le-
wis acid catalysts, the results of which are summarized in Table 1. It
is apparent from Table 1 that among various Lewis acid catalysts
such as InCl3, FeCl3, SbCl3, ZnCl2, AgCl, ceric ammonium nitrate
(CAN), and SnCl4, SbCl3 (10 mol %) was the best one to give maxi-
mum yield of products.
By variation of the solvent used for this reaction (Table 1), ace-
tonitrile was found to be the most suitable one. In a separate
experiment, the reaction was carried out in open air for 24 h and
it was found that even under this condition compound 4a was
formed as a major product (4a:5a = 3:2) in good overall yield
(89%). It is noteworthy that when the reaction of 2-naphthylamine
1a, 4-chlorobenzaldehyde 2c, and dimethyl but-2-ynedioate 3a
was allowed to reflux in acetonitrile in the presence of 10 mol %
of SbCl3 for 24 h under the balloon pressure of air, compound 5c
was isolated in 87% yield along with compound 4c as minor prod-
uct (yield ca. 4%). The Yb(OTf)3 catalyzed version of this reaction,16
For further study in this area, aliphatic aldehydes such as but-
anal and octanal were used in place of aromatic aldehydes under
similar reaction conditions to react with 1a and 3a. However, such

2922
G. Maiti et al. / Tetrahedron Letters 54 (2013) 2920–2923
Table 2
a
One-pot synthesis of 3-aryl-3,4-dihydrobenzo[f]quinoline-1,2-dicarboxylate catalyzed by SbCl3
R2O2C
R2O2C
R2O2C
R2O2C
R1
R1
CHO
CO2R2
NH2
+
SbCl3 (10 mol %)
N
NH
+
+
R1
CH3CN, 80 0
argon atm.
C
CO2R2
3a-b
5a-p
4a-p
1a
2a-p
Entry
R1
H
R2
Product ratioc (4:5)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
Me
4a:5a = 8:1
4b:5b = 6:1
4c:5c = 7:2
4d:5d = 7:1
4e:5e = 5:1
4f:5f = 9:2
4g:5g = 5:1
—
4h:5h = 6:1
4i:5i = 4:1
4j:5j = 4:1
4k:5k = 4:1
4l:5l = 7:1
4m:5m = 6:1
4n:5n = 6:1
6
8
6
6
7
7
10
12
8
6
9
7
8
6
8
90
83
86
88
81
82
78
—
84
86
80
85
80
89
84
4-Methoxy
4-Chloro
4-Nitro
2,6-Dichloro
3-Niro
2,3,4-Trimethoxy
4-Dimethylamino
2,4-Dichloro
3-Bromo
3,4-Dimethoxy
2,3-Phenyl
3,4-Methylenedioxy
4-Fluoro
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Et
9
10
11
12
13
14
15
4-Methyl
Et
a
b
c
Reaction condition: benzaldehyde (1.0 mmol), naphthalen-2-amine (1.0 mmol), dimethyl but-2-ynedioate (1.2 mmol), catalyst (0.1 mmol) in 2 mL solvent.
Products were characterized by mp, IR, 1H NMR and 13C NMR, HRMS.
The product ratio was determined on the basis of the isolated pure compound.
Table 3
a
One-pot synthesis of dimethyl-2-phenyl-1,2-dihydrobenzo[h]quinoline-3,4-dicarboxylate catalyzed by SbCl3
R1
R1
CHO
NH2
CO2Me
CO2Me
CO2Me
SbCl3 (10 mol%)
CO2Me
CO2Me
HN
+
N
+
CH3CN, 80 0C
argon atm.
+
R1
CO2Me
1b
2
3a
4o-p
5o-p
Entry
R1
Product ratioc (4:5)
Time (h)
Yieldb (%)
1
2
3-Nitro (2f)
4-Methyl (2n)
4o:5o = 7:1
4p:5p = 5:2
7
6
80
77
a
b
c
Reaction condition: benzaldehyde (1.0 mmol), naphthalen-1-amine (1.0 mmol), dimethyl but-2-ynedioate (1.2 mmol), catalyst (0.1 mmol) in 2 mL solvent.
Products were characterized by mp, IR, 1H NMR and 13C NMR, HRMS.
The product ratio was determined on the basis of the isolated pure compound.
combinations furnished complex reaction mixtures from which
any desired product could not be isolated. Possibly, facile aldol
condensation involving aliphatic aldehydes is responsible for such
result.
In conclusion, we have developed a mild, simple, and efficient
methodology for one pot imino Diels–Alder reaction of N-aryl
imines with dimethyl but-2-ynedioate by use of SbCl3 as catalyst.
The reaction afforded a variety of novel 3-aryl-3,4-dihydro-benzo-
quinoline-1,2-dicarboxylate derivatives along with their dihydro
derivatives in good to excellent yield. The notable advantages of this
method are operational simplicity, use of inexpensive catalyst, ease
Supplementary data
Supplementary data (experimental procedures and spectral
data) associated with this article can be found, in the online ver-
sion, at http://dx.doi.org/10.1016/j.tetlet.2013.03.093.
References and notes
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20. Representative experimental procedure for the synthesis of dimethyl 3-phenyl-3,4-
dihydrobenzo[f]quinoline-1,2-dicarboxylate (4a): A magnetically stirred mixture
of benzaldehyde (100 mg, 1.0 mmol), naphthalene-2-amine (134 mg,
1.0 mmol), dimethyl acetylene dicarboxylate (159 mg, 1.2 mmol), and
anhydrous antimony trichloride (22 mg, 0.10 mmol) in dry acetonitrile
(3 mL) under argon was refluxed for 6 h (monitored by TLC). The solvent was
removed under reduced pressure and the residue obtained was purified by
column chromatography over silica gel (18% ethyl acetate in petroleum ether)
yielded 4a (315 mg, 80%) and 5a (39 mg, 10%). Compound 4a, mp 210 °C; IR
(KBr): 3342, 2950, 1718, 1702, 1619, 1604, 1561, 1431, 1237, 1205, 1097,
821,754 cmÀ1 1H NMR (300 MHz, CDCl3): d 3.79 (s, 3H), 3.95 (s, 3H), 5.64 (br s,
.
1H), 6.80 (d, J = 8.7 Hz, 1H), 7.20–7.26 (m, 4H), 7.37 (m, 3H), 7.61 (t, J = 9.0 Hz,
2H), 7.84 (d, J = 8.7 Hz, 1H). 13C NMR (CDCl3, 75 MHz): d 52.3, 52.5, 52.7, 109.8,
114.9, 116.9, 122.1, 122.9, 126.3, 127.7, 127.8, 128.3, 128.5, 129.2, 131.5, 134.0,
139.6, 141.8, 144.5, 165.0, 170.4. HRMS (ES+): calcd for [C23H19NO4] Na+:
396.1206; found: 396.1202. Compound 5a (39 mg, 10%), mp: 147–148 °C; IR
(KBr): 2956, 1747, 1718, 1548, 1443, 1435, 1241, 1005, 964, 842, 811, 766,
740 cmÀ1 1H NMR (300 MHz, CDCl3): d 3.71 (s, 3H), 4.10 (s, 3H), 7.48–7.51 (m,
.
3H), 7.64–7.68 (m, 2H), 7.70–7.73 (m, 2H), 7.94–7.97 (m, 1H), 8.06 (s, 2H),
8.27–8.30 (m, 1H). 13C NMR (CDCl3, 75 MHz): d 52.9, 53.5, 119.5, 124.2, 125.2,
127.4, 127.9, 128.2, 128.3, 128.5, 129.1, 129.4, 132.9, 133.5, 138.4, 139.6, 149.7,
156.0, 168.3, 169.6. HRMS (ES+): calcd for [C23H17NO4] Na+: 394.1050; found:
394.1053.