Green cyclic 1, 3-dicarbonyl compound using citric acid

Green protocol for the
synthesis of 1, 8-dioxodecahydroacridines using citric acid as organocatalyst

Monika Patil1, Shrikrishna
Karhale1, Ananda Kudale 1 Arjun Kumbhar2,
Sagar More2, Vasant Helavi*1

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1Department of Chemistry, Rajaram
College, Kolhapur 416004, Maharashtra, India.

2Department of Chemistry, P. D. V.
P. College, Tasgaon 416312, Maharashtra, India.

E-mail:
[email protected]

*Corresponding author: Tel.: +91
231 2537840; fax: +91 231 2531989.

 

Graphical Abstract:

 

 

 

 

 

 

 

 

 

 

 

Green protocol for the
synthesis of 1, 8-dioxodecahydroacridines using citric acid as organocatalyst

Monika Patil1,
Shrikrishna Karhale1, Ananda Kudale 1 Arjun Kumbhar2,
Sagar More2, Vasant Helavi*1

Abstract:
A simple, efficient and an environmentally benign route have been described for
synthesis of 1, 8-dioxodecahydroacridine via Hantzsch condensation of aldehydes
and ammonium acetate with cyclic 1, 3-dicarbonyl compound using citric acid as
an inexpensive green additive in ecological safe solvent. Utilization of cheap,
safe reagent and solvent, cleaner reaction profile, straightforward work-up
procedure and good to excellent yield are the remarkable features of this
method.

_____________________________________________________

M. Patil, S. Karhale,
A. Kudale,
A. Kumbhar, S. More, V. Helavi*

1Department of Chemistry, Rajaram College, Kolhapur,
416004, M.S., India

2Department of Chemistry, P. D. V. P. College, Tasgaon,
416312, M.S., India.

E-mail: [email protected]

*Corresponding
author. Tel.: +91 231 2537840; fax: +91 231 2531989.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Introduction:

                As our
environment is endowed by nature, needs to be protected from growing production
of large amount of waste and toxic by-products which sequentially leads to chemical
pollution. Therefore, synthetic chemists have earned tremendous interest to
develop relatively safe technologies which play a vital role in green chemistry.
By concerning above fact, establishing newer chemical transformations should satisfy
green principles such as non-toxicity, non-flammability, easy work-up, eco-friendly
medium, separation and recycling of the catalysts. Since, from the last decade more
efforts were devoted towards the design of an environment friendly chemical
synthesis with respect to reagents, environmentally benign solvents that could
be easily biodegradable 1, 2. Multi-component reaction (MCR) strategies which
have been widely used in the convergent synthesis of complex organic molecules
from simple and readily available starting materials with high atom economy and
high selectivity is one of the tool to achieve both economic and environmental
goals. Therefore, synthesis of heterocyclic compounds with significant
bioactivities with MCR support is an immensely important pursuit in organic
synthesis.

                Synthesis of
acridines
is an enormous area of interest due to polyfunctionalized group with wide range
of biological activities as well as an ecological point of view 3. Among
them, 1, 8-dioxodecahydroacridines is an important class of aza-heterocycles in
which a phenyl substituted pyridine ring is fused with two cyclohexanone rings.
These structure contains 1, 4-dihydropyridine (1,4-DHP) as a parent nucleus
which acts as fluorescent probes in bioanalytical chemistry 4 and also used as
potential drug candidates for the treatment of cardiovascular diseases. Some of
the representative compounds of this class are used in dye-sensitized solar
cells and also in the preparation of blue light-emitting devices 5-6. In
addition, the 9-aryl-decahydroacridine-1,8-dione derivatives have been widely
employed as DNA intercalator, SIRT1 inhibitors, calcium and potassium channel
modulators 7-8. Several studies reveal that these heterocycles exhibits copious
medicinal applications which include antitumor, calcium -blockers, antileukimic,
antifungal, anticancer, anti-atherosclerotic, and bronchodilator 9-13. These
are also used as, laser dyes, chemosensors and initiators in photo
polymerization process. These derivatives are important due to their structural
similarity with the coenzyme nicotinamide adenine dinucleotide (NADH), which
acts as coenzyme in biological systems.

                The
most common route for the synthesis of 1,8-dioxodecahydroacridines includes
condensation of diverse aldehydes, dimedone or cyclic 1, 3-dicarbonyl compounds
with various nitrogen source such as ammonium acetate, urea, ammonium
hydroxide, ammonium bicarbonate, and hydroxylamine 14-18. A variety of
catalysts such as sulfonated polyethylene glycol
(PEG-OSO3H), Silzic (SiO2-ZnCl2), silica
boron-sulfuric acid, Proline, Zn(OAc)2, nano nickel cobalt ferrite(Ni0.5Co0.5Fe2O4),
Carbon based solid acid, Bronsted acidic imidazolium salts, Ascorbic acid,
Acetic acid, Tris(pentafluorophenyl)borane/B(C6F5)3,
Silica-Supported polyphosphoric acid,
ammonium chloride, Silica-supported preyssler
nanoparticles 19-32 etc have been reported to accomplish this
transformation. However, most of these reported methodologies have certain drawbacks such
as use of toxic and corrosive solvent, use of expensive chemicals, tedious
preparation of catalyst, prolonged reaction times, tedious work-up, harsh
reaction conditions and low yields of the desired product. Therefore, a great demand
still exists for utilization of an efficient, simple and eco-friendly process
especially by using organocatalyst is highly desirable.

                Citric
acid (2-hydroxy-propane-1, 2, 3-tricarboxylic acid) is a weak organic acid with
the formula C6H8O7 and was first isolated and
crystallized from lemon juice in 1784. It is found as natural preservative and
antioxidant in variety of citrus fruits orange, lemon, pineapple, peach and
pear. This organic acid is a nearly universal intermediate product of
metabolism. Furthermore, citric acid is also used for the preparation of salt
and form complex with many metals such as magnesium, iron, manganese, calcium
and copper. Widespread presence, non-toxic nature and chemical stability of
this acid, it has been used as sequestering in industrial process, as softener
in detergent, as an anticoagulant blood preservative and as a complexing agent
in metal treatment. Other industrial and pharmaceutical applications of citric
acid include antioxidant in cosmetics, cleaning, buffering. Despite its huge
industrial and pharmaceutical importance, only a few reports exemplify its catalytic
application in organic synthesis.

                As part of our research work in the development of sustainable
methodologies for the synthesis of bioactive moiety 33-38, herein we report
green protocol for the synthesis of 1,8-dioxodecahydroacridines
from one pot multi-component reaction
of dimedone and NH4OAc with diverse aryl aldehydes in the presence
of inexpensive and highly efficient citric acid as organocatalyst (Scheme 1).

Scheme1: Citric acid
catalyzed multi-component synthesis of 1, 8-dioxodecahydroacridines.

 

 

Result and
discussion:

We optimized the reaction conditions such as effects
of solvents and catalyst. Initially to optimize the solvents efficacy, the
reaction of benzaldehyde (1 mmol), dimedone (2 mmol), and ammonium acetate (1.2
mmol) in presence of citric acid (2 mmol) was selected as a model reaction (Scheme
1). In pilot experiment, the reaction was carried out in a variety of solvents
water, ethanol, ethanol:water, methanol, acetonitrile, dichloroethane and toluene
as shown in Table 1. The
best result was obtained by the reaction using ethanol providing excellent
yield (89%) of the desired product (Table
1, entry 2). The reaction proceeded scarcely in water, ethanol:water,
methanol, acetonitrile, dichloroethane and toluene providing moderate yields of
anticipated products in comparatively prolonged reaction time (Table 1, entries 1, 3-7).

Table 1:
Optimization of solvent for synthesis of 1, 8-dioxodecahydroacridinea

Entry

Reaction
Condition

Time
(min)

Isolated
Yieldb (%)

1

Water/ Reflux

240

70

2

Ethanol/Reflux

150

89

3

Ethanol:Water/
Reflux

200

80

4

Methanol/
Reflux

300

72

5

Acetonitrile/
Reflux

360

68

6

Dichloroethane/
Reflux

400

55

7

Toulene/
Reflux

390

65

aReaction
conditions: Dimedone (2 mmol), benzaldehyde (1 mmol), NH4OAc (1.5
mmol) and citric acid monohydrate as green additive in various solvent at reflux.

bIsolated yields.

                Our
next task was to optimize the catalyst loading. For this, we have carried the model
reaction under optimized conditions by varying the quantity of citric acid as
summarized in Table 2. It was found
that the quantity of catalyst played crucial role on the product yield. When
the quantity of citric was increased, the yield of target product was elevated
significantly (Table 2, entries 1-3)
and maximum yield of the product obtained when 2 mmol of citric acid was used (Table 2, entry 4) Further increase in
quantity of citric acid did not influence on yield of the product (Table 2, entry 5).

                With this result in hand, we have
studied the effect of temperature on model reaction
condition by conducting model reaction at 100°C and at room temperature but the
reaction proceeded long time with unsatisfactory result.

Table
2 Optimization
of catalyst amount for the synthesis of 1, 8-dioxodecahydroacridinea

Entry

Citric Acid
(mmol)

Time (min)

Isolated Yield
(%)

1

150

2

1

150

68

3

1.5

150

78

4

2.0

150

89

5

3.0

150

89

aReaction
conditions: Dimedone (2 mmol), benzaldehyde (1 mmol), NH4OAc (1.5
mmol) and citric acid in ethanol at reflux.

Table
3:
synthesis of 1, 8-dioxo-decahydroacridine derivatives.a

Entry

Aldehydes
(2)

Product

Time(min)

Yield (%)

a

Benzaldehyde

4a

150

89

b

4-Nitrobenzaldehyde

4b

100

90

c

4-Chlorobenzaldehyde

4c

160

87

d

4-Bromobenzaldehyde

4d

180

85

e

4-Cyanobenzaldehyde

4e

200

74

f

4-Hydroxybenzaldehyde

4f

160

83

g

4-Methoxybenzaldehyd

4g

210

90

h

4-Methylbenzaldehyde

4h

130

79

i

3,4,5-Trimethoxybenzaldehyde

4i

230

80

j

Thiophene-2-carbaldehyde

4j

240

81

k

Isopropanaldehyde

4k

300

45

aReaction conditions:
Dimedone (2 mmol), aryl aldehyde (1 mmol), NH4OAc (1.5 mmol) and
citric acid in ethanol at reflux.

After
the optimization of reaction conditions, we evaluate the scope and generality
of protocol by reacting dimedone, NH4OAc with diverse aromatic aldehydes.
The results are shown in Table 3. The
reaction proceeded smoothly in all the cases to afford the desired 1,8-dioxodecahydroacridine
in good to excellent yields. It is worthy to note that both electron rich and
electron deficient aromatic aldehydes reacted efficiently with good chemical
reactivity. However, the reaction with aliphatic aldehyde, the time was
prolonged and the yield of the product was very low.

Fig 1:
Reusability of citric acid synthesis of 1, 8-dioxo-decahydroacridine

We have examined the reusability of citric acid for
the model reaction. After completion of the reaction, the product was separated
and resulting filtrate extracted by chloroform. The catalyst was separated from
aqueous layer and dried under vacuum. The recovered citric acid was used for
similar reaction and as it is shown in graph the catalyst could be reused
without significant loss of activity (Fig 1).

The plausible mechanism for 1,
8-dioxodecahydroacridines is depicted in scheme
2. First the citric acid promote for enolization of 1, 3-diketone molecule
and convert aldehydes into suitable electrophile by protonation and the
knoevengel adduct A formed by
reaction of enol form of 1, 3-diketone and the aldehydes. Then, A may undergo Michael addition with
another molecule of dimedone in its enol form influence by citric acid to yield
intermediate B. The resulting
intermediate reacts with ammonium acetate to yield imine which undergoes
an intramolecular cyclization and dehydration to yield the estimated product C.

Scheme 2: Proposed
reaction mechanism for synthesis of 1,8-dioxodecahydroacridines

Table
4:
Effect of various catalysts on synthesis of 1, 8-dioxodecahydroacridines

Entry

Catalyst

Reaction
Condition

Time
(min)

Yield
(%)

References

1

Citric
acid (2 mmol)

Ethanol/Reflux

150

89

This
work

2

Ni0.5Co0.5Fe2O4
(20 mol %)

EtOH:H2O
(1:1),Reflux

40

92

24

3

SiO2-ZnCl2
(0.2 g mol %)

100°
C

30

70

20

4

B
(C6F5)3 (3 mol %)

RT

168

80

29

5

PPA-SiO2
(0.02
gm)

100°C

10

93

30

6

Ammonium
chloride

120°C

60

87

31

7

SPNP
(0.03 mmol)

H2O,
reflux

120

91

32

In
order to show the efficiency and advantages of citric acid with the reported
catalysts, we have tabulated several results for the synthesis of 1,8-dioxodecahydroacridines in Table 4. It is clear that, citric acid is effective in terms of
yield and reaction times than reported catalysts.

Experimental:

All chemicals were purchase from local supplier and
used without further purification. Melting points were determined by the open
capillary method and are uncorrected. The IR spectra were measured on Bruker
ALPHA FT-IR spectrometer in between the frequency range 500-4000 cm-1.
The NMR spectra were recorded on Bruker AC (400 MHz for 1H NMR and
75 MHz for 13C NMR) spectrometer using TMS as an internal standard.
Chemical shifts (d)
are expressed in ppm.

General
procedure for the synthesis of 1, 8-dioxodecahydroacridine derivatives (4a-k):

A mixture of dimedone (2 mmol), aldehyde (1 mmol),
ammonium acetate (1.2 mmol) and citric acid (2 mmol) in ethanol (4 mL) was
stirred at reflux for appropriate time (Table 3). After complete conversion as
indicated by TLC, the reaction mixture was allowed to cool at room temperature,
poured onto ice-cold water (20 ml) and stirred continuously for 10 minutes. The
formed solid filtered, washed with cold water and then dried. The solid was recrystallized
by in ethanol. All the resulting products were purified and characterized by
spectroscopic techniques.

Selected
spectral data of representative compounds

3, 3, 6, 6-Tetramethyl-9-(phenyl)-1, 8-dioxo-decahydroacridine
(Table 3, entry a):

Mp:
193-195°C, 1H NMR (400 MHz, CDCl3) ? (ppm): 7.45 (s, 1H,
NH), 7.65-7.10 (m, 5H, Ar-H), 5.15 (s, 1H, CH), 2.42-2.17 (m, 8H, CH2),
1.12 (s, 6H, CH3), 0.98 (s, 6H, CH3); 13C NMR
(75 MHZ, CDCl3) ?: 193.8, 148.3, 136.4, 126.8, 128.1, 1256.8, 114.3,
51.1, 41.3, 34.2, 33.6, 29.9, 27.6; IR (KBr, cm-1) ? : 3275, 2959,
1631, 1368.

3, 3, 6, 6-Tetramethyl-9-(4-chlorophenyl)-1, 8-dioxo-decahydroacridine
(Table 3, entry c):

Mp:
295-297 °C, 1H NMR (400 MHz, CDCl3) ? (ppm): 7.66 (s, 1H, NH), 7.48 (d, J = 9, 2H), 7.38 (d, J = 9, 2H), 5.16 (s, 1H, CH), 2.30-2.13 (m, 8H, CH2), 1.17 (s, 6H, CH3), 0.95 (s, 6H, CH3);
13C
NMR (75 MHZ, CDCl3) ?: 196.1, 150.1, 144.9, 132.0, 130.1, 127.9, 113.2,
51.5, 41.1, 34.4, 33.6, 30.5, 26.8; IR (KBr, cm-1): 3436, 2954, 1647, 1612, 1365.

3, 3, 6, 6-Tetramethyl-9-(4-cynophenyl)-1, 8-dioxo-decahydroacridine
(Table 3, entry e):

Mp:
324-326°C, 1H NMR (400 MHz, CDCl3)
? (ppm): 0.96 (s, 6H, CH3), 1.13 (s, 6H, CH3), 2.19 (d, J?16.5 Hz, 2H), 2.28 (d, J?16.5 Hz, 2H), 2.26(d, J?16.5 Hz, 2H), 2.43 (d, J?16.5 Hz, 2H), 5.11 (s, 1H, CH), 5.91 (s, 1H, NH),
7.46 (d, J?8.3
Hz, 2H, Ar-H), 7.52 (d, J?8.3
Hz, 2H, Ar-H); 13C NMR (75 MHZ, CDCl3) ?: 194.8, 148.7, 146.1, 130.2,
129.5, 120.7, 112.9, 50.4, 32.9, 32.0, 30.5, 29.1, 26.6; ); IR (KBr): 3321, 2955, 2233, 1631, 1491 cm-1

3, 3, 6, 6-Tetramethyl-9-(4-methoxyphenyl)-1, 8-dioxo-decahydroacridine
(Table 3, entry g):

Mp:
270-272°C, 1H NMR (400 MHz, CDCl3)
? (ppm): 8.82 (s, 1H, NH), 7.12 (d, J = 8.6 Hz, 2H), 6.64 (d, J = 8.6 Hz, 2H), 4.83(s, 1H, CH), 3.65 (s, 3H,
O-CH3), 2.35 (d, J
= 17.0 Hz, 1H), 2.24 (d, J = 16.3 Hz, 1H), 2.10 (d, J =15.9, 1H), 1.98 (d, J = 16.2 Hz, 1H), 1.01 (s, 6H, CH3),
0.98 (s, 6H, CH3);
13C
NMR (75 MHZ, CDCl3)
?:
192.4, 154.6, 149.1, 138.9, 128.6, 112.8, 111.8, 54.6, 51.8, 32.2, 30.3, 28.9,
26.5.; IR (KBr, cm-1): 3448, 2954, 1643, 1612, 1365, 1141.

3, 3, 6, 6-Tetramethyl-9-(4-methylphenyl)-1, 8-dioxo-decahydroacridine
(Table 3, entry 1):

Mp: 271-273°C, 1H NMR (400 MHz, CDCl3)
? (ppm): 11.9 (s, 1H, NH), 7.09 (d, J = 9, 2H), 6.98 (d, J = 9, 2H), 5.50 (s,
1H, CH), 2.29 (s, 3H, CH3), 2.19-2.47 (m, 8H, CH2), 1.22 (s, 6H, CH3),
1.09 (s, 6H, CH3); 13C NMR (75 MHZ, CDCl3) ?:
190.6, 135.5, 135.1, 129.3, 128.9, 126.5, 117.7, 47.2, 46.6, 32.5, 31.3, 29.8,
27.4; 20.9; IR (KBr, cm-1) : 2958, 2877, 1569, 1369.

Conclusion:

In this work,
the reported method offers simple, and economically viable one-pot method for synthesis
of decahydroacridine-1, 8-diones derivatives via Hantzsch condensation
of various aldehydes, ammonium acetate with cyclic 1, 3-dicarbonyl compound using commercially available, inexpensive
citric acid as a green additive. Some important superiorities of this method
are use of inexpensive reagents, absence of toxic effluents, use of green
solvent, easy workup and operational simplicity In addition, employment of
green, inexpensive, eco-friendly and commercially available additive make this
procedure very attractive in modern synthetic methodologies. 

 

 

 

 

 

 

 

 

 

 

 

 

 

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