Bronsted acidic deep eutectic solvent catalysed the one-pot synthesis of 2H-indazolo[2,1-b]phthalazine-triones

Article abstract of DOI:10.3184/174751913X13787347508252

An efficient and facile protocol for the one-pot synthesis of 2H-indazolo[2,1-b]phthalazine-triones in the presence of a Bronsted acidic deep eutectic solvent has been developed. The Bronsted acidic deep eutectic solvent was readily prepared via heating t

Full text of DOI:10.3184/174751913X13787347508252

598 RESEARCH PAPER
OCTOBER, 598–600
JOURNAL OF CHEMICAL RESEARCH 2013
Brønsted acidic deep eutectic solvent catalysed the one-pot synthesis of
H-indazolo[2,1-b]phthalazine-triones
Liang Wang, Min Zhou, Qun Chen and Ming-Yang He*
2
Jiangsu Province Key Laboratory of Fine Petro-Chemical Technology, Changzhou University, Changzhou 213164, P.R. China
An efficient and facile protocol for the one-pot synthesis of 2H-indazolo[2,1-b]phthalazine-triones in the presence of a Brønsted
acidic deep eutectic solvent has been developed. The Brønsted acidic deep eutectic solvent was readily prepared via heating
the mixture of choline chloride and p-toluenesulfonic acid. In addition, the deep eutectic solvent is non-toxic, cost-effective and
recyclable.
Keywords: deep eutectic solvent, 2H-indazolo[2,1-b]phthalazine-triones, multicomponent reactions, p-toluene sulfonic acid
In the past few decades, the synthesis of new nitrogen
heterocycles containing a phthalazine moiety has been
a subject of great interest due to their biological and
pharmacological activities such as anticonvulsant, cardiotonic
and vasorelaxant. Therefore, a number of methods have
been reported for the synthesis of phthalazine derivatives.
Among them, multicomponent reactions of phthalhydrazide, an
aldehyde, and dimedone to give 2H-indazolo[2,1-b]phthalazine-
triones have recently attracted the interest of the synthetic
community because the formation of different condensation
products can be expected depending on the specific conditions
and structure of the building blocks. Thus, a series of catalysts
p-Toluenesulfonic acid is an important Brønsted acid catalyst
which is widely used in organic synthetic processes due to its
strong acidity as well as the ease of operation. However, it is
very deliquescent and difficult to recover. Recently, it was
reported that p-toluenesulfonic acid and choline chloride could
form a deep eutectic solvent via hydrogen bonding and such a
DES not only showed good catalytic activity but also could be
1–3
2
0
recovered and reused.
The DES ChCl/p-TsOH was readily prepared by mixing the
cholinechloride1(0.1 mol)withp-toluenesulfonicacid(0.1 mol)
at 100 °C until a clear solution was obtained (40 min) which
was used for reactions without any purification. The method
gave this DES with 100% atom economy since it completely
forms a eutectic mixture with no by-product formation.
With the DES in hand, we started to optimise the reaction
conditions via condensation of phthalhydrazide (1 mmol),
benzaldehyde (1 mmol) and dimedone (1 mmol) in different
catalytic systems (Table 1). The reaction medium played an
important role for the reaction. Good yields were obtained
when methanol and ethanol were used (86 and 82% yield,
respectively). Other organic solvents such ethyl acetate and
toluene gave much lower yields. When the reaction proceeded
in pure water, only trace amounts of product were detected.
However, good yields were obtained when ethanol/water and
4
5
6
such as p-TSA, Me SiCl, silica sulfuric acid, cyanuric
3
7
8
9
chloride, heteropolyacids, N-halosulfonamides have been
reported to catalyse such transformation. The direct four-
component condensations have also been achieved under
10
solvent-free conditions using Ce(SO ) .4H O and sulfuric
4
2
2
11
acid-modified PEG-6000 as catalysts. However, some of these
methods suffered with several drawbacks such as hazardous
organic solvents, high cost as well as use of stoichiometric
and excess amounts of acids. Therefore, the development of an
efficient and environment friendly procedure is in demand.
Recently, deep eutectic solvents (DES) have invoked
enormous interest as green potential solvents or catalysts in
12,13
organic reactions.
DES are similar to conventional ionic
liquids in terms of low vapour pressure and low flammability.
In addition, they are biodegradable, non-toxic, and inexpensive.
Generally, DES are mainly prepared by combining choline
chloride with different hydrogen bond donors, such as urea,
Optimisation of reaction conditionsa
Table 1
O
O
O
Ph
O
Cat.
N
N
O
NH
NH
+
+
PhCHO
Solvent
14
Lewis acids as well as Brønsted acids. It should be mentioned
that choline is a naturally occurring biocompatible compound
and choline chloride is commercially produced on a large scale
O
O
Yield/%b
Entry
1
2
3
4
5
6
7
8
Reaction medium
MeOH
DES catalyst/mol%
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
ChCl/p-TsOH (15)
–
10
as a chicken feed additive. However, their ability to serve as
catalysts as well as solvents has not been adequately explored
in the field of synthetic organic chemistry except for a few
86
82
trace
79
81
63
EtOH
H O
2
15–19
reported examples.
EtOH/H O(1:1)
2
We report here an efficient and reusable catalytic system for
one-pot synthesis of 2H-indazolo[2,1-b]phthalazine-triones
using deep eutectic solvents based on choline chloride and
p-toluenesulfonic acid (Scheme 1).
MeOH/H O(1:1)
2
CH CN
3
EtOAc
toluene
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
30
trace
trace
trace
52
37
44
28
49
67
88
9
10
11
O
O
Ar
ChCl (15)
p-TsOH (15)
ChCl/urea (15)
O
ChCl/p-TsOH
N
N
O
NH
NH
R
R
+
+
ArCHO
1
2
1
3
ChCl/malonic acid (15)
ChCl/glycerol (15)
ChCl/p-TsOH (5)
ChCl/p-TsOH (10)
ChCl/p-TsOH (20)
O
O
O
R
R
14
1
5
Scheme 1 ChCl/p-TsOH catalysed the one-pot synthesis of 2H-indazolo
2,1-b]phthalazine-triones.
16
[
17
aReaction conditions: phthalhydrazide (1 mmol), benzaldehyde (1 mmol),
dimedone (1 mmol), solvent (2 mL), reflux for 4 h.
Isolated yields.
*
Correspondent.
E-mail: lwcczu@126.com; hemingyangjpu@yahoo.com
b
JCR1302029_FINAL.indd 598
04/10/2013 09:09:28

JOURNAL OF CHEMICAL RESEARCH 2013 599
methanol/water were used as the reaction media. This can be
explained as DES shows excellent solubility in polar solvents
and the reaction proceeds in a homogeneous system. Various
deep eutectic mixtures as well as the catalyst amount were also
evaluated (Table 1, entries 9–17). A trace amount of product was
obtained in the absence of any catalyst. p-Toluenesulfonic acid,
when used alone, could also promote the reaction, albeit with a
moderate (52%) yield. Other deep eutectic mixtures generated
from urea, malonic acid and glycerol gave lower yields owing
to their lesser acidity than ChCl/p-TsOH. The optimisation of
the quantity of catalyst suggested 15 mol% of ChCl/p-TsOH
Experimental
All reagents were obtained from local commercial suppliers and used
without further purification. H and C NMR spectra were recorded
on a Bruker Avance III 500 analyser. All the products are known
compounds and were identified by comparing of their physical and
spectra data with those reported in the literature.
1
13
Synthesis of 2H-indazolo[2,1-b]-phthalazine-triones; typical procedure
In a 25 mL round-bottomed flask, phthalhydrazide (1 mmol), aromatic
aldehyde (1 mmol) and dimedone or 1,3-cyclohexandione (1 mmol)
were taken in the presence of 15 mol% (relative to phthalhydrazide)
of ChCl/p-TsOH in methanol (2 mL). Then the reaction mixture
was stirred at 65 °C for an appropriate time as monitored by TLC.
After completion of the reaction, the volume of the reaction mixture
was reduced, diluted with water and extracted with ethyl acetate.
The organic layer was dried over anhydrous magnesium sulfate and
then the solvent was removed under reduced pressure. The crude
product was washed with ethanol/water mixture (1: 3 v/v) (5 mL) and
recrystallised from ethanol to obtain the pure product.
(relative to phthalhydrazide) in methanol as the best choice.
The generality and functional group tolerance of this
protocol was examined by employing a number of substituted
aromatic aldehydes under the optimised conditions (Table 2).
It was obvious that this method showed good substrate
compatibility for aromatic aldehydes. Both aromatic aldehydes
bearing electron-donating groups and electron-withdrawing
groups gave the products in good to excellent yields (83–93%).
In the same way, the reactions of 1,3-cyclohexanedione for
the synthesis of 2H-indazolo[2,1-b]phthalazine-triones under
the optimum conditions were examined and the desired
products were obtained in high yields (Table 2, entries 9–11).
In addition, the product could be easily purified by washing
using an ethanol/water mixture (1: 3 v/v). Thus, this method
offers significant improvements with regard to the scope of the
transformation, simplicity, and green aspects.
One of the most important advantages employing DES
as solvent or catalyst is their recyclability. A batch reaction
between phthalhydrazide, benzaldehyde and dimedone was
scaled up to 10 mmol to examine the recycling process. The
recovery was very simple involving evaporation of the solvent
and water after isolation of product by extraction with ethyl
acetate. The deep eutectic solvent was reused without obvious
loss in activity in five consecutive runs (86, 87, 82, 82 and 80%
yield, respectively).
3,4-Dihydro-3,3-dimethyl-13-phenyl-2H-indazolo[2,1-b]phthalazine-
4
4
1
1,6,11(13H)-trione (a): M.p. 208–209 °C (lit. 204–206 °C) ; H NMR
(500 MHz, CDCl ) δ 1.24 (s, 6H), 2.35 (s, 2H), 3.25–3.43 (m, 2H), 6.46 (s,
3
1H), 7.32–7.40 (m, 3H), 7.44–7.46 (m, 2H), 7.76–7.86 (m, 2H), 8.30–8.37
13
(m, 2H); C NMR (125 MHz, CDCl ) δ 28.5, 28.7, 34.7, 38.1, 50.9, 64.9,
3
118.6, 127.1, 127.7, 127.9, 128.7, 128.9, 129.1, 133.6, 134.5, 136.4, 150.9,
+
154.3, 156.1, 192.2; MS (EI) m/z 372 (M ).
3,4-Dihydro-3,3-dimethyl-13-(4-methylphenyl)-2H-indazolo[2,1-b]
4
phthalazine-1,6,11(13H)-trione (b): M.p. 226–228 °C (lit. 227–229 °C);
1
H NMR (500 MHz, CDCl ) δ 1.23 (s, 6H), 2.30 (s, 3H), 2.36 (s, 2H),
3
3.23–3.42 (m, 2H), 6.42 (s, 1H), 7.12–7.14 (m, 2H), 7.30–7.38 (m, 2H),
13
7.84–7.87 (m, 2H), 8.28–8.38 (m, 2H); C NMR (125 MHz, CDCl3)
δ 21.3, 28.5, 28.8, 34.7, 38.1, 50.9, 64.9, 118.7, 127.1, 127.7, 127.9, 128.9,
129.2, 129.5, 133.4, 133.5, 134.5, 138.5, 150.8, 154.2, 156.1, 192.2; MS
+
(EI) m/z 386 (M ).
3,4-Dihydro-3,3-dimethyl-13-(4-methyoxylphenyl)-2H-
indazolo[2,1-b]phthalazine-1,6,11(13H)-trione (c): M.p. 216–218 °C
21
1
In summary, we have developed a simple, green and efficient
catalytic system using deep eutectic mixtures for rapid synthesis
of 2H-indazolo[2,1-b]phthalazine-trione derivatives. The
reaction gave high yields in short reaction times. In addition,
the DES catalyst could also be easily recycled and reused at
least up to five runs without any considerable loss in yields.
(lit. 218–220 °C); H NMR (500 MHz, CDCl ) δ 1.21 (s, 6H), 2.34 (s,
3
2H), 3.23–3.42 (m, 2H), 3.76 (s, 3H), 6.42 (s, 1H), 6.84–6.86 (m, 2H),
13
7.35–7.37 (m, 2H), 7.82–7.86 (m, 2H), 8.26–8.35 (m, 2H); C NMR
(125 MHz, CDCl ) δ 28.5, 28.7, 34.6, 38.1, 51.0, 55.2, 64.6, 114.1, 118.6,
3
127.7, 127.9, 128.4, 128.5, 129.0, 129.2, 133.5, 134.5, 150.7, 154.2, 156.0,
+
1
59.7, 192.2; MS (EI) m/z 402 (M ).
3
,4-Dihydro-3,3-dimethyl-13-(4-fluorophenyl)-2H-indazolo[2,1-b]
4
phthalazine-1,6,11(13H)-trione (d): M.p. 220–222 °C (li. 217–219 °C);
H NMR (500 MHz, CDCl ) δ 1.21 (s, 6H), 2.33 (s, 2H), 3.22–3.40 (m,
1
Table 2 Synthesis of 2H-indazolo[2,1-b]phthalazine-trione derivativesa
3
2
H), 6.42 (s, 1H), 6.99–7.03 (m, 2H), 7.38–7.43 (m, 2H), 7.84–7.88 (m,
O
O
Ar
O
13
2H), 8.26–8.35 (m, 2H); C NMR (125 MHz, CDCl ) δ 28.5, 28.7, 34.7,
3
ChCl/p-TsOH
MeOH
N
N
O
NH
NH
R
R
+
+
ArCHO
38.0, 50.9, 64.3, 115.5, 115.9, 118.2, 127.7, 128.0, 128.9, 129.1, 132.2, 133.7,
+
134.6, 151.1, 154.4, 156.0, 192.2; MS (EI) m/z 390 (M ).
O
O
O
R
R
3,4-Dihydro-3,3-dimethyl-13-(4-chlorophenyl)-2H-indazolo[2,1-b]
4
Yield/%a
phthalazine-1,6,11(13H)-trione (e): M.p. 262–264 °C (lit. 262–264 °C);
Entry
Ar
C6H5
4-CH C H
4
R
CH3
Product
1
H NMR (500 MHz, CDCl ) δ 1.22 (s, 3H), 1.23 (s, 3H), 2.35 (s, 2H),
1
2
3
4
5
6
7
8
9
a
b
c
d
e
f
g
h
i
86
90
85
87
91
83
85
93
86
3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
3.25–3.43 (m, 2H), 6.43 (s, 1H), 7.31–7.33 (m, 2H), 7.37–7.41 (m, 2H),
7.85–7.88 (m, 2H), 8.26–8.39 (m, 2H); C NMR (125 MHz, CDCl ) δ
28.5, 28.7, 34.7, 38.0, 50.9, 64.3, 118.1, 127.7, 128.1, 128.5, 128.8, 128.9,
129.0, 133.7, 134.5, 134.6, 134.9, 151.1, 154.3, 156.0, 192.2; MS (EI) m/z
3
6
13
4-CH OC H
3
6
4
3
4-FC H
6
4
4-ClC H
6
4
4
2-ClC H
+
6
406 (M ).
4-BrC H
6
4
3
,4-Dihydro-3,3-dimethyl-13-(2-chlorophenyl)-2H-indazolo[2,1-b]
4-NO C H
2
6
4
4
phthalazine-1,6,11(13H)-trione (f): M.p. 268–270 °C (lit. 264–266 °C);
4-OHC H
6
4
1
H NMR (500 MHz, CDCl ) δ 1.22 (s, 3H), 1.23 (s, 3H), 2.33 (s, 2H),
1
11
0
2-Naphthyl
4-CH C H
H
H
j
k
89
88
3
3.24–3.42 (m, 2H), 6.69 (s, 1H), 7.25–7.34 (m, 2H), 7.49–7.50 (m, 2H),
3
6
4
13
7.84–7.89 (m, 2H), 8.25–8.40 (m, 2H); C NMR (125 MHz, CDCl ) δ
aReaction conditions: phthalhydrazide (1 mmol), aldehyde (1 mmol),
3
28.4, 28.8, 34.6, 38.0, 50.9, 64.0, 116.7, 127.2, 127.6, 128.0, 128.7, 129.0,
dimedone or 1,3-cyclohexanedione (1 mmol), ChCl/p-TsOH (15 mol%),
methanol (2 mL), reflux for 4 h.
129.9, 130.5, 132.6, 133.0, 133.6, 134.5, 151.9, 154.2, 156.2, 192.1; MS
(EI) m/z 406 (M ).
b
+
Isolated yields.
JCR1302029_FINAL.indd 599
04/10/2013 09:09:29

6
00 JOURNAL OF CHEMICAL RESEARCH 2013
3
,4-Dihydro-3,3-dimethyl-13-(4-bromophenyl)-2H-indazolo[2,1-b]
p-TsOH in methanol (20 mL) under reflux for an appropriate time as
monitored by TLC. After completion of the reaction, the mixture was
concentrated, diluted with water and extracted with ethyl acetate. The
recovery was very simple by evaporation of water.
4
phthalazine-1,6,11(13H)-trione (g): M.p. 264–266 °C (lit. 265–267 °C);
H NMR (500 MHz, CDCl ) δ 1.21 (s, 3H), 1.22 (s, 3H), 2.35 (s, 2H),
.24–3.41 (m, 2H), 6.41 (s, 1H), 7.29–7.31 (m, 2H), 7.35–7.38 (m, 2H),
.82–7.84 (m, 2H), 8.27–8.38 (m, 2H); C NMR (125 MHz, CDCl ) δ
1
3
3
7
13
3
2
8.5, 28.7, 34.7, 38.0, 50.9, 64.4, 118.0, 122.8, 127.8, 128.1, 128.8, 128.9,
Received 23 June 2013; accepted 24 July 2013
Paper 1302029 doi: 10.3184/174751913X13787347508252
Published online 7 October 2013
129.0, 131.9, 133.7, 134.7, 135.5, 151.1, 154.4, 156.0, 192.1; MS (EI) m/z
+
451 (M ).
3
,4-Dihydro-3,3-dimethyl-13-(4-nitrophenyl)-2H-indazolo[2,1-b]
4
phthalazine-1,6,11(13H)-trione (h): M.p. 220–222 °C (lit. 223–225 °C);
H NMR (500 MHz, CDCl ) δ 1.21 (s, 3H), 1.23 (s, 3H), 2.33–2.38 (m,
1
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1
1
(
(
8
6
,6,11(13H)-trione (i): M.p. 258–260 °C (lit. 265–266 °C); H NMR
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3
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26.2, 126.3, 126.7, 127.6, 127.7, 128.0, 128.2, 128.6, 129.0, 129.1, 133.2,
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13
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7
1
1
(
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11
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,4-Dihydro-13-(p-tolyl)-2H-indazolo[2,1-b]phthalazine-1,6,11(13H)-
14
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1
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(
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19
+
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Phthalhydrazide (10 mmol), benzaldehyde (10 mmol) and dimedone
21 G. Shukla, R.K. Verma, G.K. Verma and M.S. Singh, Tetrahedron Lett.,
2011, 52, 7195.
(10 mmol) were reacted in the presence of 15 mol% of a batch of ChCl/
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