A Novel, highly efficient, one-pot synthesis of 1,4-dihydroquinoline derivatives in the presence of a Pd(OAc)2/DABCO catalytic system

Article abstract of DOI:10.1002/ejoc.200900451

The Pd(OAc)₂/DABCO catalytic system was first found to be highly efficient for C-N cross-coupling reactions. With the aid of this transformation, a variety of new 1,4-dihydroquinoline derivatives were synthesized from o-halobenzaldehydes and va

Full text of DOI:10.1002/ejoc.200900451

FULL PAPER
DOI: 10.1002/ejoc.200900451
A Novel, Highly Efficient, One-Pot Synthesis of 1,4-Dihydroquinoline
Derivatives in the Presence of a Pd(OAc)2/DABCO Catalytic System
Xiao-Jin Wu,[a] Xiao-Ping Xu,[a] Xiao-Ming Su,[a] Gang Chen,[a] Yong Zhang,[a] and
Shun-Jun Ji*[a]
Keywords: Aldehydes / Enaminones / Nitrogen heterocycles / Cross-coupling / Synthetic methods
The Pd(OAc)2/DABCO catalytic system was first found to be
highly efficient for C–N cross-coupling reactions. With the
aid of this transformation, a variety of new 1,4-dihydroquinol-
ine derivatives were synthesized from o-halobenzaldehydes
and various β-enaminones in good to excellent yields.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
tionalities has been the most explored way (Mode A, Fig-
ure 1).[15] Rare examples were exhibited by the reaction of
bidonor with biacceptor (Mode B, Figure 1), which is rea-
sonably accessible. We have been interested in the synthesis
of heterocyclic compounds for years.[16] Recently, we found
that β-enaminone, as a popular candidate for a bidonor,
had been extensively applied to the construction of N-con-
taining heterocycles,[17] and o-halobenzaldehyde, as a com-
mercially available biacceptor, provided an active site (C–
X bond) for C–N bond formation by Buchwald–Hartwig
methodology; furthermore, another part of the acceptor,
the formyl group, can be attacked by the electron-rich β-C
atom in β-enaminones to fulfill the demand of cyclization
through the Baylis–Hillman reaction.[18] Meanwhile, it was
interesting to find that, in comparison to commonly used
PPh3, DABCO (triethylenediamine) is a cheap and stable
ligand, and it was confirmed to be the best choice in the
reaction. Herein, we report these results.
Introduction
The quinoline ring system occurs in various natural
products, especially in alkaloids. The quinoline skeleton is
widely used for the design of many important compounds
with pharmacological properties including antimalarial,[1]
anti-inflammatory,[2] and antibacterial activities.[3] Accord-
ingly, many methods for the assembly of the quinoline ring
system have been developed. The most well-recognized ones
should be those proposed by Skraup,[4] Doebner–Miller,[4]
Friedlander,[5] and Combes,[6] and all of these processes may
involve an initial intermolecular reaction of an aniline with
a carbonyl-containing compound or its precursor. The most
notable limitations in these procedures include the need to
employ strongly acidic conditions and sometimes the use of
refractory substrates such as o-aminobenzaldehydes.
The recent past has witnessed many successful methods
for the synthesis of quinolines mediated by transition met-
als.[7] The palladium-catalyzed C–C cross-coupling reac-
tion, due to its efficiency and wide substrate scope, is one
of the most useful approaches for the construction of quin-
oline derivatives. Some well-investigated examples include
the Heck,[8] Sonogashira,[9] Suzuki,[10] and Ullmann reac-
tions.[11] Although palladium-catalyzed C–N bond forma-
tion reactions have been pioneered and extensively investi-
gated by Buchwald[12] and Hartwig,[13] very few studies on
the synthesis of the quinoline ring have been reported.[14]
In addition, as for the cyclization process in quinoline
formation, interaction between two donor–acceptor bifunc-
Figure 1. Known and explored modes for the synthesis of the quin-
oline core.
Results and Discussion
Initial attempts focused on exploring the feasibility of the
proposed process. It is well known that an extra ligand plays
an important role in Pd-mediated C–N cross-coupling reac-
tions. Phosphane ligands are generally used to activate and
stabilize the palladium species, and excellent results have
been reported for the Buchwald–Hartwig reaction.[12,13,19]
However, phosphane ligands are air sensitive and poison-
[a] Key Laboratory of Organic Synthesis of Jiangsu Province, Col-
lege of Chemistry, Chemical Engineering and Materials Science,
Soochow University,
Suzhou 215123, P. R. China
Fax: +86-512-6588-0307
E-mail: chemjsj@suda.edu.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200900451.
Eur. J. Org. Chem. 2009, 4963–4970
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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X.-J. Wu, X.-P. Xu, X.-M. Su, G. Chen, Y. Zhang, S.-J. Ji
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ous, which significantly limit their applications. Therefore,
the development of phosphane-free palladium catalysts for
C–N cross-coupling reactions comes to be the focus of at-
tention. Pd(OAc)2/DABCO, as a stable, inexpensive, and
highly efficient catalytic system, has been widely used in
C–C cross-coupling reactions such as Suzuki–Miyaura,[20]
Stille,[21] Sonogashira,[22] Hiyama,[23] and Heck reactions.[24]
However, to our best knowledge, the application of the
Pd(OAc)2/DABCO catalytic system in C–N cross-coupling
reactions has never been reported. Thus, a preliminary at-
tempt was carried out by using o-bromobenzaldehyde and
5,5-dimethyl-3-(p-tolylylamino)cyclohex-2-enone as sub-
strates in the presence of Pd(OAc)2 (5 mol-%), DABCO
(10 mol-%), and K2CO3 (3 equiv.) in refluxing toluene. As
expected, the cyclization was successfully accomplished, but
to our surprise, instead of the formation of expected target
product A, a more complex quinoline derivative B was ob-
tained [Scheme 1, Equation (2)].
Figure 2. The crystal structure for B.
Table 1. Influence of the catalysts for the reaction of 1b with 2a.[a]
Entry
Catalyst
Yield[b] [%]
1
2
3
Pd(OAc)2/DABCO
PdCl2/DABCO
Pd2(dba)3/DABCO
81
52
64
[a] Reaction conditions: 1b (0.25 mmol), 2a (0.5 mmol), palladium
catalyst (0.0125 mmol), DABCO (0.025 mmol), K2CO3 (3 equiv.),
toluene (3.0 mL), 110 °C, 12 h. [b] Isolated yield.
sired products in poor yields (Table 2, Entries 3–8). Cs2CO3
was found to be the most appropriate base. Then, the effect
of solvent was also evaluated: CH3CN, CH3NO2, and diox-
ane were not suitable solvents for the reaction (Table 2, En-
tries 10–12). To our surprise, commonly used solvents for
coupling reactions, such as THF, NMP, and DMSO, gave
disappointing results (Table 2, Entries 9, 13, and 14). Other-
wise toluene performed as the most-suitable solvent
(Table 2, Entry 2).
Scheme 1. Synthesis of 1,4-dihydroquinoline derivative B.
The definite structure of the final product was confirmed
by X-ray analysis (Figure 2).[25] Thus, the reaction was then
repeated with the use of o-bromobenzaldehyde (1 equiv.)
and
5,5-dimethyl-3-(p-tolylylamino)cyclohex-2-enone
(2 equiv.) in the presence of Pd(OAc)2/DABCO, and after
workup, a high yield of B was achieved.
Table 2. Optimization of conditions for the reaction of 1b with 2a.[a]
Subsequently, sets of experiments were performed to op-
timize the reaction conditions. Several other commonly
used palladium catalytic systems were tested for the cou-
pling reactions, and the results are shown in Table 1.
Among the various catalytic systems used, the Pd(OAc)2/
DABCO system proved superior and generated the desired
product in 81% yield (Table 1, Entry 1). Other combinatory
palladium catalytic systems only gave the product in lower
yields (52–64%; Table 1, Entries 2 and 3).
Furthermore, a brief study of the influence of base on
the reaction was carried out as well. As shown in Table 2,
according to their increasing basicities, K2CO3 and Cs2CO3
led to sharply ascending efficiencies in the synthesis of the
target product (Table 2, Entries 1 and 2), whereas, the use
of other inorganic and organic bases (such as K3PO4,
Entry
Base
Solvent
Yield[b] [%]
1
2
3
4
5
6
7
8
K2CO3
Cs2CO3
K3PO4
Na2CO3
NaOAc
NaOH
KOH
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
THF
CH3CN
CH3NO2
dioxane
NMP
81
92
60
21
40
11
34
27
21
trace
trace
trace
32
NEt3
9
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
10
11
12
13
14
DMSO
26
[a] Reaction conditions: 1b (0.25 mmol), 2a (0.5 mmol), Pd(OAc)2
(0.0125 mmol), DABCO (0.025 mmol), base (3 equiv.), solvent
Na2CO3, NaOAc, NaOH, KOH, and Et3N) gave the de- (3.0 mL), 110 °C, 12 h. [b] Isolated yield.
4964 Eur. J. Org. Chem. 2009, 4963–4970
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

One-Pot Synthesis of 1,4-Dihydroquinoline Derivatives
Further optimization of the reaction conditions by using Table 3. Scope for palladium-catalyzed synthesis of 1,4-dihydro-
quinoline derivatives.[a]
other commonly used ligands such as 8-hydroxyquinoline
(L1), -proline (L2), hexamethylenetetramine (L3), PPh3
(L4), 2,9-dimethyl-1,10-phenanthroline (L6), DBU (1,8-di-
azabicyclo[5.4.0]undec-7-ene, L7), and 1,10-phenanthroline
(L8) compared with DABCO (L5) was also examined under
the same conditions. As shown in Figure 3, the catalytic
activity strongly depended on the choice of ligands, and
dramatic changes in yields were observed. Fortunately,
DABCO was the best ligand among those tested. Besides,
without the use of DABCO, the reaction proceeded slug-
gishly to give the product in much lower yield (Figure 3,
L9), which also implied that the addition of ligand was criti-
Entry
Substrate
Product Time [h]
Yield[b]
[%]
cally necessary. Furthermore, the Pd(OAc)2/DABCO com-
plex has also been proved by Li.[26]
X
R
1
2
1a
1a
4-CH3 (2a)
3a
3b
12
12
98
97
4-OCH3
(2b)
3-CH3 (2c)
2-CH3 (2d)
H (2e)
4-Cl (2f)
3-Cl (2g)
4-Br (2h)
4-I (2i)
2a
3
4
5
6
7
8
9
1a
1a
1a
1a
1a
1a
1a
1b
1b
1b
1b
1b
1b
1b
1b
1b
1c
1c
1c
1c
1c
1c
1c
1c
1c
3c
3d
3e
3f
3g
3h
3i
3a
3b
3c
3d
3e
3f
3g
3h
3i
3a
3b
3c
3d
3e
3f
3g
3h
3i
24
24
12
12
24
24
24
12
12
24
24
12
12
24
24
24
16
16
30
30
24
12
30
24
24
71
75
95
81
75
78
76
92
88
61
65
81
76
66
70
72
81
85
65
61
74
70
60
73
71
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
2b
2c
2d
2e
2f
2g
2h
2i
2a
2b
2c
2d
2e
2f
2g
2h
2i
[a] Reaction conditions: 1 (0.25 mmol), 2 (0.5 mmol), Pd(OAc)2
(0.0125 mmol), DABCO (0.025 mmol), Cs2CO3 (0.75 mmol), tolu-
ene (3.0 mL). [b] Isolated yield.
To our delight, although electron-withdrawing groups on
the β-enaminones usually inhibited the efficiency of the re-
actions to a certain extent,[27] various electron-withdrawing
groups on the β-enaminones such as 4-I, 4-Br, and 4-Cl
Figure 3. Various ligands investigated in the reaction.
With the optimized conditions in hand, we continued to also afforded the desired products in good yields after 24 h
examine the substrate scope of the reaction by using a wide (Table 3, Entries 6, 8, and 9). In order to study the steric
variety of β-enaminones and o-halobenzaldehyde. As shown influence for the approach, we tested several β-enaminones
in Table 3, the representative examples illustrate the gener- with substituent groups in different positions. Noteworthy,
ality of this reaction. Various electron-donating groups on the reactions of enaminones including substituents in the
the β-enaminones such as 4-Me and 4-OMe were well toler- 2,3-positions are usually very sensitive,[27] yet our catalytic
ated by the catalytic system and gave the desired products system was very efficient for 2,3-substituted β-enaminones,
in excellent yields (Table 3, Entries 1 and 2). In addition, which reacted to furnish the corresponding products in 71,
the use of 5,5-methyl-3-(phenylamino)cyclohex-2-enone 75, and 75% yield, respectively (Table 3, Entries 3, 4, and
could also afford a satisfactory yield of the desired product 7). Unfortunately, this catalytic system was ineffective for
(Table 3, Entry 5).
2-chloro-substituted β-enaminone and the corresponding
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4965

X.-J. Wu, X.-P. Xu, X.-M. Su, G. Chen, Y. Zhang, S.-J. Ji
FULL PAPER
product was obtained only in 45% yield. We supposed it tory yields were also obtained after longer reaction times.
was the result of strong steric and electron-withdrawing in- The influence of steric and electronic effects was similar to
fluences. Encouraged by these results, the catalyst was then the reactions performed with the use of 2-iodobenzaldehyde
utilized for the reactions of 2-bromo- or 2-chlorobenzalde- as substrate. Furthermore, in the Pd(OAc)2/DABCO cata-
hyde with β-enaminones (Table 3, Entries 10–27). Satisfac- lytic system, some other enaminones containing alkylamine
Figure 4. Various enaminones investigated in the reaction.
Scheme 2.
Scheme 3.
Scheme 4. Possible mechanism for the formation of 1,4-dihydroquinoline derivatives.
4966
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Eur. J. Org. Chem. 2009, 4963–4970

One-Pot Synthesis of 1,4-Dihydroquinoline Derivatives
points were recorded with an electrothermal digital melting point
apparatus and are uncorrected. IR spectra were recorded with a
Varian FT-1000 spectrophotometer using KBr optics. NMR spec-
tra were recorded in CDCl3 with a Varian Inova-400 NMR spec-
or acyclic β-enone fragments were chosen as the substrates.
As shown in Figure 4, unfortunately no reaction occurred
even with the use of the most active 2-iodobenzaldehyde as
substrate.
1
trometer (400 MHz for H and 100 MHz for 13C) with TMS as an
Finally, we turned our attention to the mechanism of the
reaction. According to the literature,[28] a common mechan-
istic hypothesis involved first an intermolecular cross-cou-
pling reaction followed by an intramolecular cyclization. To
explore this possibility, we initially attempted the reaction
with the appropriately protected aldehyde aryl bromide as
substrate, under the Pd(OAc)2/DABCO catalytic condi-
tions, but the intermolecular reaction did not occur
(Scheme 2). This result clearly indicates that the synthetic
route may involve an intramolecular Buchwald–Hartwig re-
action. Next, without the palladium catalyst, a blank test
was done to attain expected intermediate C from o-bromo-
benzaldehyde and 3-(4-methoxyphenylamino)-5,5-dimeth-
ylcyclohex-2-enone; unfortunately, intermediate C was not
internal reference. High resolution mass spectra were obtained by
using a Microma GCT-TOF instrument. X-ray diffraction data
were recorded with a Rigaku Mercury CCD area detector with
graphite monochromated Mo-Kα radiation.
General Procedure for the Synthesis of Quinoline Derivatives 3: A
mixture of 1a (0.25 mmol), 2 (0.5 mmol), Pd(OAc)2 (2.8 mg,
0.0125 mmol), DABCO (2.9 mg, 0.025 mmol), Cs2CO3 (144.7 mg,
0.75 mmol), and toluene (3.0 mL) was stirred at 110 °C for the de-
sired time until complete consumption of the starting material as
monitored by TLC. The mixture was then poured into water and
extracted with ethyl acetate. The organic phase was dried with an-
hydrous MgSO4 and filtered, and the solvents were evaporated un-
der vacuum. The residue was purified by flash column chromatog-
raphy (ethyl acetate/petroleum ether, 1:6) to afford product 3.
trapped. In order to confirm our assumption, a further test 9-[2-(p-Tolylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-3,4-dihydro-
3,3-dimethyl-10-p-tolylacridin-1(2H,9H,10H)-one (3a): Yield:
was done with a similar substrate, benzaldehyde, which
could not participate in a C–N cross-coupling reaction
(Scheme 3). As expected, structure D, similar to possible
intermediate C, was afforded under the Pd(OAc)2/DABCO
catalytic conditions.
On the basis of these observations, it is reasonable to
generate product B instead of A in our initial reaction
(Scheme 1). Therefore, a possible reaction mechanism for
the formation of 1,4-dihydroquinoline derivatives from o-
133 mg (98%). Yellow solid. M.p. 246–248 °C. IR (KBr): ν = 3147,
˜
1
3029, 2954, 2871, 1634, 1589, 1512, 1458, 1389, 810, 756 cm–1. H
NMR (400 MHz, CDCl3): δ = 0.88 (d, J = 5.7 Hz, 6 H, 2 CH3),
0.99 (d, J = 8.4 Hz, 6 H, 2 CH3), 1.98–2.32 (m, 7 H), 2.36 (s, 3 H,
CH3), 2.46 (s, 3 H, CH3), 2.80 (d, J = 16.6 Hz, 1 H), 5.11 (s, 1 H,
CH), 6.10–6.14 (m, 1 H, ArH), 6.84–7.19 (m, 8 H, ArH), 7.32 (d,
J = 7.8 Hz, 1 H, ArH), 7.38 (d, J = 8.0 Hz, 1 H, ArH), 7.77 (d, J
= 7.3 Hz, 1 H, ArH), 10.15 (s, 1 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 196.8, 195.5, 156.5, 156.4, 141.1, 138.8,
halobenzaldehyde and a wide range of β-enaminones was 138.6, 138.5, 137.9, 137.8, 133.0, 131.8, 130.7, 130.2, 130.1, 129.9,
128.8, 127.7, 126.3, 123.2, 122.8, 120.6, 115.8, 107.5, 52.1, 50.1,
42.6, 40.7, 33.0, 32.5, 32.2, 30.1, 28.5, 27.9, 26.8, 21.6, 21.1 ppm.
HRMS: calcd. for C37H40N2O2 [M]+ 544.3090; found 544.3078.
proposed (Scheme 4). Firstly, expected intermediate C was
generated through a Baylis–Hillman-type reaction and nu-
cleophilic substitution of another β-enaminone. Then the
final product was afforded from an intramolecular Buch-
wald–Hartwig reaction of expected intermediate C.
9-[2-(4-Methoxyphenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-
3,4-dihydro-10-(4-methoxyphenyl)-3,3-dimethylacridin-
1(2H,9H,10H)-one (3b): Yield: 139 mg (97%). Yellow solid. M.p.
218–220 °C. IR (KBr): ν = 3218, 3063, 2955, 2871, 1613, 1589,
˜
1512, 1458, 1389, 833, 756 cm–1. 1H NMR (400 MHz, CDCl3): δ =
0.88 (d, J = 8.1 Hz, 6 H, 2 CH3), 0.98 (s, 6 H, 2 CH3), 2.00–2.31
(m, 7 H), 2.69 (d, J = 16.5 Hz, 1 H), 3.84 (s, 3 H, OCH3), 3.90 (s,
3 H, OCH3), 5.10 (s, 1 H, CH), 6.14–6.17 (m, 1 H, ArH), 6.85–
6.87 (m, 2 H, ArH), 6.92 (d, J = 8.6 Hz, 2 H, ArH), 6.99–7.17 (m,
6 H, ArH), 7.82 (d, J = 8.5 Hz, 1 H, ArH), 10.01 (s, 1 H, NH)
ppm. 13C NMR (100 MHz, CDCl3): δ = 196.9, 195.3, 159.8, 157.3,
156.6, 156.4, 141.5, 134.2, 133.3, 132.2, 131.5, 128.9, 127.9, 126.5,
125.1, 123.3, 119.8, 116.2, 115.9, 114.9, 114.8,107.7, 55.9, 52.0,
50.2, 42.8, 40.8, 32.9, 32.5, 32.4, 30.4, 30.2, 28.6, 28.4, 27.0 ppm.
HRMS: calcd. for C37H40N2O4 [M]+ 576.2988; found 576.3008.
Conclusions
In summary, we have developed a novel and efficient
method for the synthesis of various 1,4-dihydroquinoline
derivatives from o-halobenzaldehyde and a wide range of β-
enaminones. Noteworthy, the Pd(OAc)2/DABCO catalytic
system was employed in the C–N crossing coupling reaction
for the first time and showed outstanding performance.
Further study on the synthesis of some other heterocyclic
compounds with the use of the present approach is cur-
rently in progress.
9-[2-(m-Tolylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-3,4-dihydro-
3,3-dimethyl-10-m-tolylacridin-1(2H,9H,10H)-one (3c): Yield:
97 mg (71%). Yellow solid. M.p. 242–244 °C. IR (KBr): ν = 3129,
˜
3063, 3013, 2954, 2867, 1636, 1584, 1558, 1495, 1457, 1394, 889,
750, 727 cm–1 1H NMR (400 MHz, CDCl3): δ = 0.90 (d, J =
.
6.4 Hz, 6 H, 2 CH3), 1.00 (d, J = 12.3 Hz, 6 H, 2 CH3), 2.00–2.33
(m, 7 H), 2.39 (s, 3 H, CH3), 2.46 (s, 3 H, CH3), 2.86 (d, J =
15.2 Hz, 1 H), 5.12 (s, 1 H, CH), 6.08–6.13 (m, 1 H, ArH), 6.85–
6.87 (m, 2 H, ArH), 6.92 (d, J = 7.6 Hz, 1 H, ArH), 6.98–7.24 (m,
5 H, ArH), 7.27–7.31 (m, 1 H, ArH), 7.40–7.50 (m, 1 H, ArH),
7.68–7.72 (m, 1 H, ArH), 10.21 (s, 1 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 196.9, 195.8, 156.2, 155.9, 141.5, 141.1,
140.4, 140.3, 139.6, 139.4, 131.1, 129.8, 129.4, 129.1, 128.8, 127.6,
Experimental Section
General Experimental Methods: All reactions were carried out in
air. All o-halobenzaldehydes, Pd(OAc)2, and DABCO were pur-
chased from Aldrich or Alfa. β-Enaminones were prepared accord-
ing to known methods.[17] Analytical thin-layer chromatography
was performed using glass plates precoated with 200–400 mesh sil-
ica gel impregnated with a fluorescent indicator (254 nm). Melting
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127.4, 126.3, 124.0, 123.3, 121.2, 119.5, 115.8, 107.3, 52.1, 50.1,
42.6, 40.8, 33.2, 32.6, 32.3, 32.2, 30.2, 28.6, 27.8, 26.9, 21.7 ppm.
HRMS: calcd. for C37H40N2O2 [M]+ 544.3090; found 544.3099.
one(3h): Yield: 131 mg (78%). Yellow solid. M.p. 241–243 °C. IR
(KBr): ν = 3156, 3056, 2955, 2871, 1613, 1589, 1566, 1489, 1389,
˜
825, 756 cm–1. 1H NMR (400 MHz, CDCl3): δ = 0.88 (s, 6 H, 2
CH3), 1.00 (d, J = 5.2 Hz, 6 H, 2 CH3), 1.94–2.33 (m, 7 H), 2.79
(d, J = 16.3 Hz, 1 H), 5.08 (s, 1 H, CH), 6.09–6.11 (m, 1 H, ArH),
6.87–6.98 (m, 3 H, ArH), 7.07 (d, J = 8.4 Hz, 2 H, ArH), 7.17 (d,
J = 6.6 Hz, 1 H, ArH), 7.47 (d, J = 8.5 Hz, 2 H, ArH), 7.71–7.85
(m, 3 H, ArH), 10.27 (s, 1 H, NH) ppm. 13C NMR (100 MHz,
CDCl3): δ = 197.1, 195.8, 155.5, 140.8, 140.5, 140.3, 139.6, 133.6,
132.9, 132.4, 129.2, 128.9, 127.4, 126.9, 126.5, 124.0, 123.8, 123.5,
123.0, 121.5, 115.8, 115.7, 111.7, 107.7, 60.6, 52.1, 49.9, 42.7, 41.8,
40.7, 36.6, 33.3, 32.2, 30.2, 27.6 ppm. HRMS: calcd. for
C35H34Br2N2O2 [M]+ 674.0967; found 674.0970.
9-[2-(o-Tolylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-3,4-dihydro-
3,3-dimethyl-10-o-tolylacridin-1(2H,9H,10H)-one (3d): Yield:
102 mg (75%). Yellow solid. M.p. 236–238 °C. IR (KBr): ν = 3142,
˜
1
3014, 2957, 2867, 1640, 1592, 1559, 1486, 1393, 750, 709 cm–1. H
NMR (400 MHz, CDCl3): δ = 0.91 (d, J = 10.1 Hz, 6 H, 2 CH3),
0.98 (d, J = 3.0 Hz, 6 H, 2 CH3), 2.03–2.12 (m, 4 H), 2.19 (s, 3 H,
CH3), 2.26 (s, 3 H, CH3), 2.53–2.62 (m, 4 H), 5.20 (s, 1 H, CH),
5.99–6.01 (m, 1 H, ArH), 6.86–6.88 (m, 2 H, ArH), 7.01–7.10 (m,
1 H, ArH), 7.13 (d, J = 7.1 Hz, 2 H, ArH), 7.23 (d, J = 7.3 Hz, 1
H, ArH), 7.28 (d, J = 7.3 Hz, 1 H, ArH), 7.34–7.43 (m, 3 H, ArH),
7.85–7.87 (m, 1 H, ArH), 9.63 (s, 1 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 191.8, 190.8, 152.5, 150.7, 135.0, 134.9,
134.7, 132.9, 128.0, 127.2, 126.4, 125.5, 124.4, 124.2, 124.1, 122.9,
122.0, 121.9, 120.1, 119.9, 118.4, 116.5, 110.2, 103.8, 47.1, 45.5,
36.7, 36.2, 27.9, 27.8, 27.5, 27.3, 24.7, 24.4, 23.1, 22.6, 14.0 ppm.
HRMS: calcd. for C37H40N2O2 [M]+ 544.3090; found 544.3089.
9-[2-(4-Iodophenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-3,4-di-
hydro-10-(4-iodophenyl)-3,3-dimethylacridin-1(2H,9H,10H)-one
(3i): Yield: 146 mg (76 %). Yellow solid. M.p. 264–266 °C. IR
(KBr): ν = 3143, 3058, 2953, 2864, 1609, 1583, 1566, 1483, 1389,
˜
824, 750 cm–1. 1H NMR (400 MHz, CDCl3): δ = 0.87 (s, 6 H, 2
CH3), 1.00 (d, J = 4.8 Hz, 6 H, 2 CH3), 1.94–2.32 (m, 7 H), 2.80
(d, J = 16.7 Hz, 1 H), 5.07 (s, 1 H, CH), 6.09–6.11 (m, 1 H, ArH),
6.87–6.89 (m, 2 H, ArH), 6.95 (d, J = 7.6 Hz, 4 H, ArH), 7.02–
7.04 (m, 1 H, ArH), 7.75 (d, J = 7.7 Hz, 2 H, ArH), 7.89–7.93 (m,
2 H, ArH), 10.29 (s, 1 H, NH) ppm. 13C NMR (100 MHz, CDCl3):
δ = 197.1, 195.9, 155.4, 155.2, 143.5, 141.1, 140.8, 140.7, 140.3,
138.9, 138.3, 133.1, 132.5, 128.9, 128.5, 127.7, 127.5, 127.3, 126.5,
124.0, 123.6, 121.7, 115.8, 107.7, 52.2, 50.0, 42.8, 41.9, 40.8, 40.3,
33.4, 32.2, 30.2, 28.9, 26.6 ppm. HRMS: calcd. for C35H34I2N2O2
[M]+ 768.0710; found 768.0721.
3,4-Dihydro-3,3-dimethyl-9-[4,4-dimethyl-6-oxo-2-(phenylamino)-
cyclo-hex-1-enyl]-10-phenylacridin-1(2H,9H,10H)-one (3e): Yield:
123 mg (95%). Yellow solid. M.p. 152–154 °C. IR (KBr): ν = 3148,
˜
3033, 2955, 2871, 1736, 1589, 1559, 1489, 1458, 1389, 748,
1
702 cm–1. H NMR (400 MHz, CDCl3): δ = 0.89 (s, 6 H, 2 CH3),
0.98 (s, 3 H, CH3), 1.02 (s, 3 H, CH3), 1.96–2.33 (m, 7 H), 2.85 (d,
J = 16.4 Hz, 1 H), 5.14 (s, 1 H, CH), 6.09–6.11 (m, 1 H, ArH),
6.85–7.00 (m, 3 H, ArH), 7.10 (t, J = 7.0 Hz, 1 H, ArH), 7.20–7.62
(m, 8 H, ArH), 7.93 (d, J = 7.3 Hz, 1 H, ArH), 10.26 (s, 1 H, NH)
ppm. 13C NMR (100 MHz, CDCl3): δ = 197.1, 195.9, 156.1, 155.9,
141.1, 140.7, 131.4, 131.2, 130.6, 129.7, 129.5, 129.1, 129.0, 127.7,
126.5, 123.5, 123.3, 122.6, 121.3, 115.9, 107.6, 60.8, 52.3, 50.2, 42.8,
40.9, 33.3, 32.8, 32.4, 28.7, 28.0, 26.8 ppm. HRMS: calcd. for
C35H36N2O2 [M]+ 516.2777; found 516.2752.
9-[2-(2-Chlorophenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-10-
(2-chlorophenyl)-3,4-dihydro-3,3-dimethylacridin-1(2H,9H,10H)-one
(3j): Yield: 66 mg (45%). Yellow solid. M.p. 212–214 °C. IR (KBr):
1
ν = 3133, 3071, 2955, 2871, 1582, 1481, 1389, 756 cm–1. H NMR
˜
(400 MHz, CDCl3): δ = 0.91 (s, 6 H, 2 CH3), 1.00 (s, 6 H, 2 CH3),
1.97–2.34 (m, 7 H), 2.60 (d, J = 16.8 Hz, 1 H), 5.24 (s, 1 H, CH),
5.99–6.01 (m, 1 H, ArH), 6.88–7.13 (m, 4 H, ArH), 7.47–7.62 (m,
6 H, ArH), 8.05 (d, J = 8.0 Hz, 1 H, ArH), 9.87 (s, 1 H, NH) ppm.
13C NMR (100 MHz, CDCl3): δ = 197.4, 196.2, 155.6, 155.3, 142.8,
141.9, 140.9, 137.0, 135.2, 132.5, 131.4, 131.0, 130.8, 130.6, 129.7,
129.2, 127.4, 126.8, 123.8, 123.1, 122.0, 120.3, 115.9, 107.9, 52.4,
50.2, 42.9, 41.0, 33.6, 32.8, 32.4, 30.4, 29.0, 27.6, 26.8 ppm. HRMS:
calcd. for C35H34Cl2N2O2 [M]+ 584.1997; found 584.1974.
9-[2-(4-Chlorophenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-10-
(4-chlorophenyl)-3,4-dihydro-3,3-dimethylacridin-1(2H,9H,10H)-one
(3f): Yield: 118 mg (81 %). Yellow solid. M.p. 234–236 °C. IR
(KBr): ν = 3156, 3040, 2955, 2871, 1620, 1589, 1559, 1489, 1389,
˜
825, 756 cm–1. 1H NMR (400 MHz, CDCl3): δ = 0.88 (s, 6 H, 2
CH3), 1.00 (d, J = 5.4 Hz, 6 H, 2 CH3), 1.94–2.33 (m, 7 H), 2.78
(d, J = 16.3 Hz, 1 H), 5.09 (s, 1 H, CH), 6.09–6.12 (m, 1 H, ArH),
6.87–7.24 (m, 6 H, ArH), 7.33 (d, J = 8.5 Hz, 2 H, ArH), 7.52–
7.58 (m, 2 H, ArH), 7.90 (d, J = 6.4 Hz, 1 H, ArH), 10.27 (s, 1 H,
NH) ppm. 13C NMR (100 MHz, CDCl3): δ = 197.3, 195.9, 155.8,
155.7, 140.9, 140.0, 139.2, 135.1, 132.7, 132.1, 131.8, 130.1, 129.6,
129.1, 128.5, 127.6, 126.7, 123.7, 121.5, 115.9, 107.9, 52.3, 50.2,
42.9, 41.0, 40.9, 33.5, 32.7, 32.4, 30.5, 28.9, 27.9 ppm. HRMS:
calcd. for C35H34Cl2N2O2 [M]+ 584.1997; found 584.1967.
2,2Ј-(Phenylmethylene)bis[3-(4-methoxyphenylamino)-5,5-dimethyl-
cyclohex-2-enone] (D): Yield: 97 mg (67%). White solid. IR (KBr):
ν = 3438, 2954, 2928, 2836, 1737, 1617, 1569, 1510, 1408, 832 cm–1.
˜
1H NMR (400 MHz, CDCl3): δ = 1.09 (s, 12 H, 4 CH3), 2.05–2.44
(m, 8 H), 3.79 (s, 6 H, 2 OCH3), 6.03 (s, 1 H, CH), 6.83–7.22 (m,
13 H, ArH), 10.53 (d, J = 9.7 Hz, 2 H, NH) ppm. 13C NMR
(100 MHz, CDCl3): δ = 195.4, 157.7, 141.0, 132.4, 127.8, 127.4,
126.9, 125.0, 114.5, 55.7, 41.5, 34.8, 32.4, 28.6 ppm. HRMS: calcd.
for C37H42N2O4 [M]+ 578.3145; found 578.3147.
9-[2-(3-Chlorophenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-10-
(3-chlorophenyl)-3,4-dihydro-3,3-dimethylacridin-1(2H,9H,10H)-one
(3g): Yield: 110 mg (75 %). Yellow solid. M.p. 202–204 °C. IR
(KBr): ν = 3156, 3063, 2955, 2871, 1628, 1582, 1489, 1389, 887,
˜
Supporting Information (see footnote on the first page of this arti-
748, 725 cm–1. 1H NMR (400 MHz, CDCl3): δ = 0.89 (s, 6 H, 2
CH3), 1.02 (d, J = 8.3 Hz, 6 H, 2 CH3), 1.94–2.34 (m, 7 H), 2.84
(d, J = 16.4 Hz, 1 H), 5.08 (s, 1 H, CH), 6.01 (s, 1 H, ArH), 6.89–
7.07 (m, 5 H, ArH), 7.19–7.98 (m, 6 H, ArH), 10.33 (s, 1 H, NH)
ppm. 13C NMR (100 MHz, CDCl3): δ = 197.3, 196.1, 155.5, 142.8,
141.9, 140.9, 136.9, 135.2, 132.5, 131.4, 130.9, 130.7, 130.6, 129.7,
129.6, 129.1, 127.4, 126.8, 123.8, 123.1, 122.0, 120.3, 115.8, 107.9,
52.4, 50.2, 49.0, 42.9, 41.0, 33.6, 32.8, 32.5, 29.1, 27.8, 27.0 ppm.
HRMS: calcd. for C35H34Cl2N2O2 [M]+ 584.1997; found 584.1968.
1
cle): Copies of the H NMR, 13C NMR, and mass spectra; crystal
data and structure refinement details for B.
Acknowledgments
The work was partially supported by the National Natural Science
Foundation of China (No. 20672079), Natural Science Foundation
of Jiangsu Province (No. BK2006048), Nature Science of Jiangsu
Province for Higher Education (No. 05KJB150116), Nature Sci-
9-[2-(4-Bromophenylamino)-4,4-dimethyl-6-oxocyclohex-1-enyl]-10-
(4-bromophenyl)-3,4-dihydro-3,3-dimethylacridin-1(2H,9H,10H)-
4968
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2009, 4963–4970

One-Pot Synthesis of 1,4-Dihydroquinoline Derivatives
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CCDC-670335 (for 3a) contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Structural parameters
for 3a: data collection: Rigaku Mercury CCD area detector;
crystal size: 0.72ϫ0.40ϫ0.20 mm3. C37H40N2O2, Mr = 544.71,
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¯
Triclinic, space group P1,
a
=
11.9357(11) Å,
b
=
15.1588(13) Å, c = 18.9987(14) Å, α = 111.618(9) °, β =
100.972(12) °, γ = 98.956(14)°, V = 3039.7(4) Å3, Z = 4, Dcalcd.
= 1.190 mgcm–3, R[IϾ2σ(I)] = 0.1032, wR[IϾ2σ(I)] = 0.2455.
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Eur. J. Org. Chem. 2009, 4963–4970
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4969

X.-J. Wu, X.-P. Xu, X.-M. Su, G. Chen, Y. Zhang, S.-J. Ji
FULL PAPER
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Received: April 24, 2009
Published Online: August 31, 2009
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Eur. J. Org. Chem. 2009, 4963–4970