Green and efficient synthesis of acridine-1,8-diones and hexahydroquinolines via a KH2PO4 catalyzed Hantzsch-type reaction in aqueous ethanol

Article abstract of DOI:10.1007/s11164-016-2814-2

Abstract: A simple, clean, and economical methodology for the synthesis of acridine-1,8-dione and hexahydroquinoline derivatives via Hantzsch-type condensation has been described. This study highlights the development of a new green pathway for the prepar

Full text of DOI:10.1007/s11164-016-2814-2

Res Chem Intermed
DOI 10.1007/s11164-016-2814-2
Green and efficient synthesis of acridine-1,8-diones
and hexahydroquinolines via a KH2PO4 catalyzed
Hantzsch-type reaction in aqueous ethanol
Shi-Jun Yü1 Si Wu1 Xin-Min Zhao2
·
·
·
Cheng-Wei Lü1
Received: 15 September 2016 / Accepted: 12 November 2016
© Springer Science+Business Media Dordrecht 2016
Abstract A simple, clean, and economical methodology for the synthesis of acridine-1,8-
dione and hexahydroquinoline derivatives via Hantzsch-type condensation has been
described. This study highlights the development of a new green pathway for the preparation
of substituted 1,4-dihydropyridines derivatives. The mild, cheap, and nontoxic potassium
dihydrogen phosphate (KH2PO4) is proved to be an efficient catalyst for the above multi-
componentreactiontoget excellent yields. Widely available andmostlybenigncatalyst, eco-
friendly solvent, and easy purification are among the several attractive features.
Graphical Abstract
Electronic supplementary material The online version of this article (doi:10.1007/s11164-016-2814-2)
contains supplementary material, which is available to authorized users.
&
Cheng-Wei Lü
chengweilv@126.com
1
2
School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian 116029,
People’s Republic of China
Medical College of Jinzhou Medical University, Jinzhou 121000, People’s Republic of China
123

S.-J. Yü et al.
Keywords Hantzsch reaction · Acridine-1,8-dione · Hexahydroquinoline ·
Potassium dihydrogen phosphate · Aqueous ethanol
Introduction
Acridine-1,8-diones (1,8-dioxodecahydroacridines) are an important class of
nitrogen heterocyclic compounds containing a 1,4-dihydropyridine parent nucleus
[1]. They are the active pharmaceutical ingredients (APIs) and versatile reactive
intermediates in synthetic and medical chemistry [2]. There are many reports about
them possessing a wide range of pharmaceutical activities, such as antimicrobial
[3–5], antimalarial [6–8], antitumor [9], anticancer [10], antibacterial [11],
fungicidal [12, 13], and DNA binding properties [14], and they are prescribed as
calcium channel blockers [15]. Their derivatives have been used in chemotherapy
for the treatment of cancer [6–8] and cardiovascular diseases [14]. In addition,
acridinediones exhibit intense fluorescence efficiency allowing them to be used as
laser dyes [16–20], photo sensitizers, and initiators [21–23]. Moreover, they have
attracted much interest due to their unique photochemical and electrochemical
behavior [24, 25]. There are some reports about the application of acridinediones in
organic light-emitting diodes (OLED) [26]. Usual synthetic route for the synthesis
of acridinediones is Hantzsch type reaction between aldehydes, β-diketones, and
ammonium acetate or appropriate primary amines [27, 28] in the presence of
various catalysts, like Zn(OAc)2·2H2O [18], CeCl3·7H2O [25], 4-dodecylbenzene-
sulfonic acid (DBSA) [29], polyphosphoric acid [30], triethylbenzylammonium
chloride [31], proline [32], FeCl3-SiO2 [33], methanesulfonic acid [34], zeolite [35],
N-propylsulfamic acid [36], ceric ammonium nitrate (CAN) [7], silica-bonded
S-sulfonic acid [37], amberlyst-15 [38, 39], carbon-based solid acid [40], p-
toluenesulfonic acid [41], InCl3 [42], MCM-41-SO3H [43], silica-supported
preyssler nanoparticles [44], silica-supported polyphosphoric acid [45], In(OTf)3
[46], cetyltrimethylammonium bromide (CTAB) [47], FSG-Hf(NPf2)4 [48], tetra-
butylammonium hexatungstate [49], nano-Fe3O4 [50], nano-ZnO [51], amberlite IR-
120H [52], oxalic acid [53], sulfonic acid-functionalized silica [54, 55], [MIMPS]3-
PW12O40 [56], ionic liquids [57–63], and microwave irradiations [64–69]. Although
impressive successes have been achieved, there is still a great desire for more green,
general, efficient, feasible, high-yielding, and cost-effective methods using new and
cheap catalysts for the synthesis of this class of compounds [70–74]. Considering
the above facts, substantial investigations have been done to introduce novel
catalysts and chemical reagents in the last 2 years [1, 70–83]. The Hantzsch
condensation is also one of the most prominent methods to prepare polyhydro-
quinolines which also contain the 1,4-dihydropyridine moiety [84, 85]. Thus, the
development of a green, simple, and efficient method for the synthesis of
polyhydroquinoline derivatives is also an active area of research [86–90].
The green processes generally involve the use of efficient, cost-effective, and
biodegradable catalysts in combination with non-toxic and non-inflammable media
[79]. Recently, organic reactions conducted in the mixture of ethanol and water
123

Green and efficient synthesis of acridine-1,8-diones and…
have attracted a great deal of attentions. Because aqueous ethanol possesses the
charming properties of water such as non-toxic, inexpensive, safe, abundantly
available, and environmentally benign [91, 92] and could overcome the poor ability
of using pure water as a solvent to solubilize organic reactants [32]. Many organic
transformations can be carried out smoothly in a water–ethanol mixture [93–96],
including the preparation of acridinediones [1, 32, 48, 63, 79]. Potassium
dihydrogen phosphate (KH2PO4), a mild, cheap, non-toxic, and eco-friendly
inorganic salt, has been proved to be an effective catalyst in organic reactions
[97–100]. Being soluble in water, this catalyst gives the reaction an easy workup
and the commercial availability of this catalyst provides clean conversion [98]. As a
part of our program aimed at developing useful and environment-friendly synthetic
methods in the presence of KH2PO4 as catalyst [101, 102], here, we wish to extend
the synthetic applicability of this catalyst in the synthesis of acridine-1,8-diones and
hexahydroquinolines via a one-pot multi-component strategy of various substituted
aldehydes with 1,3-dicarbonyl compounds and ammonium acetate in aqueous
ethanol.
Experimental
General
Unless otherwise stated, all reagents were obtained from commercial sources and
were used without further purification. Melting points were determined on a Beijing
Tech X-5 melting point detector and were uncorrected. The IR spectra were
1
measured with a Bruker Shimadzu IR-460 spectrometer. H and 13C NMR spectra
were recorded on a Bruker Avance 500 MHz.
Typical experimental procedure for synthesis of 4
Aromatic aldehyde (0.5 mmol), dimedone (1 mmol), ammonium acetate
(0.85 mmol), KH2PO4 (0.025 mmol), and 1 mL aqueous ethanol (EtOH:H2O 3:1,
v/v) were added to a 10-mL pressure tube and this solution was stirred at 120 °C for
5 h. After completion of the reaction, 0.5 mL water was added and the mixture was
vigorously stirred for a moment at 120 °C. Then, the reaction mixture was cooled
and filtered on a Bu¨chner funnel. The precipitate was washed with 30% cold
aqueous ethanol without further purification to afford the desired acridine-1,8-dione,
except for 4n and 4p which were recrystallized from EtOH to give the pure product.
Typical experimental procedure for synthesis of 5
A similar procedure was followed for the preparation of hexahydroquinolines. A
mixture of aldehyde (0.5 mmol), ethyl acetoacetate (0.5 mmol), dimedone
(0.5 mmol), and ammonium acetate (1.0 mmol) in 1 mL aqueous ethanol (EtOH:
H2O 3:1 v/v) was stirred at 100 °C for 5 h. On completion of the reaction, the
mixture was added 0.7 mL water and vigorously stirred for a moment at 120 °C.
123

S.-J. Yü et al.
Then, the reaction mixture was cooled and filtered on a Bu¨chner funnel. The
precipitate was washed with 30% cold aqueous ethanol without further purification
to afford the desired product.
Results and discussion
As a starting point for the development of our methodology, we commenced our
work to discover the best experimental conditions by choosing the three-component
condensation of benzaldehyde (0.5 mmol), dimedone (1 mmol), and ammonium
acetate (0.6 mmol) as a model reaction. The effects of various reaction parameters,
such as solvents, catalysts, and temperature, were evaluated to optimize the reaction
conditions (Table 1). The solvent screening studies revealed that aqueous ethanol is
truly the most suitable solvent. Although good yield was obtained when the reaction
took place in ethanol, water or acetonitrile, a higher yield was obtained using EtOH
and H2O (1:1, v/v) as the solvent (Table 1, entry 5). In order to improve the yield,
various volumes and ratios of EtOH and H2O were screened (Table 1, entries 6–12).
This reaction with 1 mL aqueous ethanol (EtOH:H2O 3:1, v/v) gave the best yield of
the desired product (Table 1, entry 10). On the basis of the above results, we
examined the effects of the type and amount of the catalyst (Table 1, entries 13–20).
As shown in Table 1, the reaction carried out under catalyst-free condition or with
other potassium salt such as KHSO4, K2HPO4, K3PO4, and K2CO3 gave inferior
results. Here, the yield could not be improved by increasing the amount of KH2PO4
(Table 1, entry 19), even while decreasing the amount of catalyst to 5 mol could
lead to a slightly higher yield of 83% (Table 1, entry 18). However, the product
yield dropped to 76% by further decreasing the catalyst to 2 mol% (Table 1, entry
20).
We also investigated the fate of varying the molar ratio of ammonium acetate,
which is summarized in Table 2. It is clear that when increasing the reagent’s
loading to 0.85 mmol (1.7 equiv. of benzaldehyde), a better outcome to afford the
desired product in 94% yield was observed (Table 2, entry 3). Finally, the reaction
temperature and time were tested (Table 2, entries 5–8). It was found that neither
decreasing nor increasing the reaction time/temperature could improve the yield.
Therefore, the reaction was optimized using a cheap, safe, and environmentally
benign reaction medium and catalyst.
To probe the generality as well as the effectiveness of our newly developed
protocol, a broad range of aromatic aldehydes were reacted with dimedone and
ammonium acetate under identical reaction conditions to furnish the corresponding
acridinediones (4a–4p) in moderate to excellent yields. As we can see in Table 3,
the presence of electron-withdrawing or electron-donating substituents in the same
position on the ring of various aromatic aldehydes had different influences on the
procedure to furnish the desired products. The electron-rich aromatic aldehydes
were transformed into the corresponding products in a slightly lower yield than that
of benzaldehyde (Table 3, entries 2–7). On the other hand, the introduction of
weakly electron-withdrawing substituent on the aromatic ring of aldehydes
accelerated the reaction rate and a similar or slightly higher yield was observed
123

Green and efficient synthesis of acridine-1,8-diones and…
Table 1 The screening of reaction conditions for the multi-component reaction of dimedone, ben-
zaldehyde, and ammonium acetate
Entrya
Catalyst (mol%)
Solvent
Volume (mL)
Yieldb (%)
1
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KH2PO4 10
KHSO4 10
K2HPO4 10
K3PO4 10
K2CO3 10
–
EtOH
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.0
3.0
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
73
58
70
70
76
77
82
81
82
59
80
69
79
80
79
77
83
82
76
2
MeOH
3
CH3CN
4
H2O
5
EtOH/H2O(1/1)
EtOH/H2O(2/1)
EtOH/H2O(3/1)
EtOH/H2O(6/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
EtOH/H2O(3/1)
6
8
9
10
11
12
13
14
15
16
17
18
19
20
a
KH2PO4
KH2PO4 15
KH2PO4
5
2
The reactions were carried out with 0.5 mmol benzaldehyde, 1.0 mmol dimedone, and 0.6 mmol
ammonium acetate at 120 °C for 5 h
b
Isolated yield
Table 2 The screening of reaction conditions
Entrya
Benzaldehyde/dimedone/ammonium acetate
Temp. (°C)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
a
0.5/1.0/0.6 mmol
0.5/1.0/0.75 mmol
0.5/1.0/0.85 mmol
0.5/1.0/1.0 mmol
0.5/1.0/0.85 mmol
0.5/1.0/0.85 mmol
0.5/1.0/0.85 mmol
0.5/1.0/0.85 mmol
120
120
120
120
110
130
120
120
5
5
5
5
5
5
4
6
83
87
94
85
87
89
89
94
The reactions were carried out in 1.0 mL EtOH/H2O (3/1) with 5 mol% KH2PO4 as catalyst
Isolated yield
b
(Table 3, entries 8–13). Unfortunately, introducing the strongly electron-withdraw-
ing group on the phenyl ring adversely affected the outcome of the reaction. Poor
yields were obtained when the nitryl was present in the ortho- or para-positions of
123

S.-J. Yü et al.
Table 3 Substrate scope for the
synthesis of product 4
Entrya
R
Product Yieldb (%) M.p. (°C) [Ref.]
1
H
4a
4b
4c
4d
94
88
90
85
90
90
86
90
95
94
97
93
95
24
90
39
274–276 (277–279) [55]
[300 (318–320) [25]
303–305
2
4-Me
3-Me
2-Me
3
4
299–302
5
4-MeO 4e
3-MeO 4f
2-MeO 4g
299–301 (278–280) [55]
[300
6
7
[300 ([300) [63]
[300 ([300) [63]
[300 (283–285) [63]
300–302 (263–264) [63]
[300 (312–315) [25]
[300 (294–297) [63]
[300 ([300) [25]
302–304 (320–322) [55]
293–295 (294–296) [25]
297–299 (286) [25]
8
4-Cl
3-Cl
2-Cl
4-Br
3-Br
2-Br
4h
4i
9
10
11
12
13
14
15
16
4j
4k
4l
a
The reactions were carried out
with aromatic aldehyde/
dimedone/ammonium acetate
(0.5/1.0/0.85 mmol) at 120 °C
for 5 h with 5 mol% KH2PO4 as
catalyst
4m
4-NO2 4n
3-NO2 4o
2-NO2 4p
b
Isolated yield
Scheme 1 The approach for the preparation of acridinedione and hexahydroquinoline derivatives
phenyl ring (Table 3, entries 14, 16). However, employing 3-nitrobenzaldehyde as
substrate gave a satisfactory result.
After successfully synthesizing a series of acridinediones derivatives in good
yields, we turned our attention to the synthesis of hexahydroquinoline derivatives
via Hantzsch-type reaction. Then, we found a paper reported online about the
synthesis of hexahydroquinoline employing CaHPO4 as a basic catalyst which could
promote the formation of nucleophilic anion [103]. As we know, KH2PO4 is a mild
acid salt and will catalyze this reaction in a different mechanism from CaHPO4.
Sure enough, this one-pot conversion can be efficiently catalyzed by KH2PO4 to
give the corresponding hexahydroquinolines 5a–5o in good yields (Scheme 1;
Table 4).
The plausible mechanism for the formation of acridine-1,8-dione is outlined in
Fig. 1. According to documents reported in the literature [41, 73, 75] and our
experience [102], we suggest that adding water can accelerate the dissociation of
dimedone to generate the nucleophilic species, due to water having a high dielectric
123

Green and efficient synthesis of acridine-1,8-diones and…
Table 4 Substrate scope for the
synthesis of product 5
Entrya Ar
Product Yieldb (%) M.p. (°C)
1
H
5a
5b
5c
5d
91
85
92
85
85
86
92
91
91
92
93
92
96
95
87
218–220 (210–211) [90]
254–256 (260–262) [88]
230–231
2
4-Me
3-Me
2-Me
3
4
203–205
5
4-MeO 5e
3-MeO 5f
2-MeO 5g
254–256 (255–257) [88]
199–201 (199–200) [86]
247–248 (250–253) [89]
241–243 (243–245) [86]
205–207 (192–194) [89]
203–204 (207–210) [86]
258–259 (252–254) [88]
196–198 (234–235) [89]
205–207 (192–194) [88]
182–184 (182–184) [87]
178–180 (207–209) [87]
6
7
8
4-Cl
3-Cl
2-Cl
4-Br
3-Br
2-Br
5h
5i
9
10
11
12
13
14
15
5j
a
The reactions were carried out
with aromatic aldehyde/
5k
5l
dimedone/ethyl acetoacetate/
ammonium acetate (0.5/0.5/0.5/
1.0 mmol) at 100 °C for 5 h with
5 mol% KH2PO4 as catalyst
5m
3-NO2 5n
2-NO2 5o
b
Isolated yield
Fig. 1 Plausible mechanistic pathway for the formation of acridinedione
constant [104]. On the other hand, the mild acid KH2PO4 can not only activate the
carbonyl group of aldehyde but also help to form the dehydration products 1, 3, and
4 [105].
Conclusions
In summary, we have demonstrated that KH2PO4 is an efficient catalyst and that
aqueous ethanol is the valid solvent for the synthesis of acridine-1,8-dione and
hexahydroquinoline derivatives via Hantzsch reaction of various aromatic aldehy-
des with ammonium acetate and 1,3-dicarbonyl compounds. This process does not
require the use of hazardous organic solvent, complicated and expensive catalysts,
or tedious experimental and isolation procedures.
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S.-J. Yü et al.
Acknowledgements We are grateful for financial support from the National Natural Science Foundation
of China (21403100) and Liaoning Province, the Doctoral Scientific Research Foundation (20141100).
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