Polyethylene glycol (PEG-400): An efficient green reaction medium for the synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones under catalyst-free conditions

Article abstract of DOI:10.1016/j.tetlet.2014.09.135

A simple and an efficient eco-friendly methodology has been developed for the synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones in excellent yields under catalyst-free-conditions using inexpensive and non-toxic polyethylene glycol (PEG-400) medium. This new protocol offers an environmental acceptability, shorter reaction time, room temperature, low cost, high yields, and recyclability of the PEG-400 medium are the important features. This method provides a green and much improved protocol over the existing methods.

Full text of DOI:10.1016/j.tetlet.2014.09.135

Accepted Manuscript
Polyethylene glycol (PEG-400): an efficient green reaction medium for the syn-
thesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones un-
der catalyst-free conditions
Mudumala Veeranarayana Reddy, Jong Su Kim, Know Taek Lim, Yeon Tae
Jeong
PII:
S0040-4039(14)01671-2
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.09.135
TETL 45229
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
4 August 2014
25 September 2014
30 September 2014
Please cite this article as: Reddy, M.V., Kim, J.S., Lim, K.T., Jeong, Y.T., Polyethylene glycol (PEG-400): an
efficient green reaction medium for the synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-
ones under catalyst-free conditions, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.2014.09.135
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Polyethylene glycol (PEG-400): an efficient green
reaction medium for the synthesis of benzo[4,5]imidazo
[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones under
catalyst-free conditions
Mudumala Veeranarayana Reddy, Jong Su Kim, Know Taek Lim and Yeon Tae Jeong*
O
NH
NH
R
R
O
N
N
PEG-400
C
NH2
2
+
R CHO
(2a-r)
N
N
+
H2N
RT
N
H
NH
(1)
(4a-r)
(3)

2
Tetrahedron Letters
jo u rn al h ome p ag e : w ww .e lse vie r .c om
Polyethylene glycol (PEG-400): an efficient green reaction medium for the synthesis
of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones under catalyst-
free conditions.
Mudumala Veeranarayana Reddy, Jong Su Kim, Know Taek Lim and Yeon Tae Jeong*
Department of Image Science and Engineering, Pukyong National University, Busan, Korea, 608-737
ARTICLE INFO
ABSTRACT
Article history:
Received
A simple and an efficient eco-friendly methodology has been developed for the synthesis of
benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones in excellent yields under
catalyst-free-conditions using inexpensive and non-toxic polyethylene glycol (PEG-400)
medium. This new protocol offers an environmental acceptability, shorter reaction time, room
temperature, low cost, high yields and recyclability of the PEG-400 medium are the important
features. This method provides a green and much improved protocol over the existing methods.
Received in revised form
Accepted
Available online
Keywords:
Polyethylene glycol (PEG-400)
Benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-
4(1H)-ones
2009 Elsevier Ltd. All rights reserved.
1H-benzo[d]imidazol-2-amine
Catalyst-free conditions
Several organic transformations are widely recognized and
evidenced as ‘green’ solvent medium in modern organic
1. Introduction
synthesis7 and developed new methodologies for syntheses of
various kinds of heterocycles8.
Many natural products and molecules containing
heterocyclic units have been identified as potential drug
candidates with a wide range of biological activities.1 Therefore,
the interest for development of a new, versatile and an efficient
synthesis of heterocycles has always been a crucial thread in the
synthetic community2 of diversity oriented synthesis (DOS),
combinatorial chemistry and medicinal chemistry. In which,
heterocycles containing benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-
d]pyrimidin-4(1H)-one derivatives are important core motifs in a
broad range of biologically active compounds that are frequently
used in pharmaceutical and drug research, agricultural science
and dye industry.3
To the best of our knowledge there is only Lihong et al., have
been reported for the preparation of benzo[4,5]imidazo[1,2-a]-
pyrimido[4,5-d]pyrimidin-4(1H)-one derivatives.9 However, this
methodology still has some more disadvantages such as long
reaction time, and high reaction temperature. But so farther are
no reports for the synthesis of these benzo[4,5]imidazo[1,2-a]-
pyrimido[4,5-d]pyrimidin-4(1H)-ones by using PEG-400 as a
reaction medium under catalyst-free conditions at room
temperature was found.
This inspired us to continuation of our work on the multi-
component synthesis of heterocyclic compounds with
environmentally begin PEG-400 as a reaction medium.10 Herein
we report the results of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-
d]pyrimidin-4(1H)-one derivatives(4a–r) in one-pot synthesis by
coupling of 1H-benzo[d]imidazol-2-amine (1, 1 mmol),various
aldehydes (2a-r, 2 mmol) and 2-cyanoacetamide (3, 1 mmol) by
using PEG-400 as a recyclable medium without adding any
organic solvent and catalyst at room temperature (RT) (Scheme
1).
In recent years there has been an emergent interest in
the development of efficient methodologies for the
environmentally benign modern organic synthesis both in
academia and industrial research. In this context, traditional
volatile organic solvents as reaction media are continuously
being replaced either by the use of solvent-free techniques,4 or
environmentally benign solvents such as water5 and ionic liquids
(ILs).6 In them each has its own advantages and is dependent on
external factors like lipophilicity, pressure, and viscosity.
Polyethylene
glycol
(PEG)
and
modified
polyethyleneglycol derivatives have become more popular
alternate reaction media, due to their interesting properties like
non-toxicity, bio-compatibility, and bio-degradability. Moreover,
PEG is considered as a cheap, safe, natural, non-flammable, low
cost, reduced flammability, recyclability, facile degradability,
environmentally benign and abundantly available green solvent.
O
NH
R
R
O
N
N
PEG-400
NH
C
NH2
2
+
R
CHO
N
N
+
H2N
RT
N
H
NH
(2a-r)
(1)
(4a-r)
(3)
Scheme 1: Catalyst-free synthesis of benzo[4,5]imidazo[1,2-a]-
pyrimido[4,5-d]pyrimidin-4(1H)-ones (4a-r) using PEG-400
medium.
------------
∗ Corresponding author.
e-mail: ytjeong@pknu.ac.kr
∗ Tel.: +82-51-629-6411; fax: +82-51-629- 6408;

2. Result and Discussions
Entry
Catalyst
FeCl3
PTSA
InF3
Solvent
Neat
Temp.
90
Time
90
Yieldb
35
1
2
3
We have carried out a series of experiments to
Neat
90
90
25
standardize the reaction conditions for the efficient formation of
benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones
via a one-pot, three-component reaction and results are presented
in Table 1. In order to optimize the reaction conditions, firstly,
we investigated the effect of different temperature, solvents and
catalysts on the reaction rate and as well as yields of the product.
As a model reaction, the reaction between 1H-benzo[d]imidazol-
2-amine (1, 1 mmol), 3-fluorobenzaldehyde (2a, 2 mmol) and 2-
cyanoacetamide (3, 1 mmol) was carried out at different
temperature under neat condition in the presence of different
catalysts such as FeCl3, PTSA, InF3 and FeF3 and was not
obtained satisfactorily results (Table 2, entries 1-4). Further
attempts were made to carry out the same reaction in different
solvents such as H2O, Toluene, THF, ethanol and1-Butyl-3-
methylimidazolium chloride at different temperatures in the
absence of catalyst (Table 2, entries 5–9). The reaction can also
be progressed in H2O but at an elevated temperature and
prolonged reaction time (Table 2, entry 5). The results showed
that the reaction can proceed successfully even without a catalyst.
With this view to determine the optimized conditions of the
reaction further we have carried out the same experiment in PEG-
400 medium using different catalyst and temperatures (Table 2,
entries 10–16). PEG-400 was found to be the best reaction
medium in terms of short reaction time and excellent yield
(Table 2, entry 10) at room temperature. However, no more
increments were found when the reaction temperature was raised
from RT to 100 °C (Table 2, entries 10-12). Therefore, RT was
chosen as the reaction temperature for all other reactions.
Neat
90
90
20
4
5
FeF3
Neat
H2O
90
100
120
60
90
150
200
220
200
220
60
20
-
80
60
6
-
Toluene
THF
Ethanol
7
-
46
65
8
-
90
9
-
-
[bmim][HCl]
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
PEG 400
110
RT
60
100
RT
RT
RT
RT
70
94, 92, 90, 89
c10
11
12
13
14
15
16
-
-
60
60
94
94
85
88
87
88
FeCl3
PTSA
InF3
FeF3
60
60
60
60
aReaction
of 1H-benzo[d]imidazol-2-amine
(1,
1
mmol), 3-
1 mmol).
fluorobenzaldehyde (2a, 2 mmol), and 2-cyanoacetamide (3,
bObtained yield, cReused PEG-400.
Formation of the final products should be postulated in
a stepwise manner as shown in Scheme 2. At first Knoevenagel
condensation between 2-cyanoacetamide (3) and various
aldehydes (2a-r) to form the intermediate 5 on the acidic activity
of PEG-400, which suffers immediate Michael addition of 1H-
benzo[d]imidazol-2-amine (1) to the C=C bond of 5 forms
iminomethylene derivative intermediate
6
followed by
intramolecular cyclization to forms the intermediate 7.
Condensation of 7 with second mole of 2 in acidic of PEG-400
formed the imino comopound 8 and it could be undergo further
intramolecular cyclisation and gave the titled compounds (4a–r).
O
H
H
O
O
O
OH
H
N
OH
O
N
N
In order to show that the use of PEG-400 as solvent
medium was also accomplished and it could be expediently
recycled with minimal loss of activity and decomposition. Since
PEG-400 is immiscible with solvent ether the preferred product
was extracted with it and the retained PEG-400 phase can be
reused. In this recycling the medium activity was decreased for
three cycles and something like 5% weight loss of PEG-400 was
observed from cycle to cycle (Table 2 entry 10). Therefore, the
reaction in PEG-400 going more smoothly than that in standard
solvent (Table 2, entries 5-8). In the standard solvent medium
most probably solvation is common phenomenon and resulting
lower yields. In addition, PEG-400 acting as catalyst, since mild
acidic nature, and enhance the rate of reaction to complete
conversion of reactants even at room temperature (RT).
N
n
R
O
(2a-r)
C
H2N
C
NH2
H2
N
H2
N
- H2O
H
HO
OH
n
H
R
(3)
R
O
OH
(5)
n
N
NH2
N
H
(1)
O
O
NH2
NH
O
NH2
NH2
R
O
R
NH2
N
R
NH
R
R
N
N
(2a-r)
R
N
NH
NH
NH
N
N
NH
(8)
NH
N
H
N
N
(7)
(6)
(4a-r)
Scheme 2. Mechanistically formation of the titled compounds.
3. Conclusion
In summary, we have demonstrated a green and
efficient method for the synthesis of series of
a
benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones
(4a–r) in excellent yields via one-pot multi-component reaction
by using recyclable PEG-400 as a reaction medium from easily
available starting materials without any catalyst. Environmental
acceptability, economic viability, less reaction time, high yields,
purification of products by non-chromatographic method, cleaner
reaction profiles, and recyclability of PEG-40 are the important
features of this protocol. We believe that this would be suitable
for the generation of a library of relevant natural products
synthesis.
Under these optimized set of experimental reaction
conditions the condensation of 2-cyanoacetamide (3) with
different aromatic aldehydes (2a-r) and 1H-benzo[d]imidazol-2-
amine (1) was carried out and obtained benzo[4,5]imidazo[1,2-
a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones (4a-r) in good to
excellent yields without the formation of any side products. This
reaction medium worked excellently for aromatic aldehydes
bearing both electron-donating and electron-withdrawing
substituents. 2-pyridinecarboxaldehyde also participated in the
reaction and gave higher product yields.
4. Experimental section
Table 2. Effect of catalyst, temp, solvent and time on the
yield
4.1. 2,5-Bis(3-fluorophenyl)-2,3,5,12-tetrahydrobenzo
[4,5]imidazo-[1,2-a]pyrimido[4,5-d]pyrimidin-4(1H)-one (4a).
of
2,5-Bis(3-fluorophenyl)-2,3,5,12-
tetrahydrobenzo[4,5]imidazo-[1,2-a]pyrimido[4,5-
d]pyrimidin-4(1H)-one (4a).a
A
mixture of 1H-benzo[d]imidazol-2-amine (1
2
1
mmol), 3-fluorobenzaldehyde (2a, mmol), and 2-
F
O
F
CHO
NH
NH
cyanoacetamide (3, 1 mmol) was taken in 5 mL of polyethylene
glycol, and stirred at RT for 60 min. After completion of the
reaction (TLC), the reaction mass was extracted into diethyl ether
and the organic layer was removed under reduced pressure. The
O
N
N
C
NH2
+
+
N
N
2
H2N
N
H
NH
F

4
Tetrahedron Letters
obtained crude product was recrystallized from ethanol to
130.4, 124.5, 121.3, 118.5, 115.8, 115.2, 114.8, 110.4, 61.2, 59.8,
58.5; HRMS (ESI, m/z): calcd for C24H17F2N5O (M+H+)
429.1401, found: 429.1399.
afford the pure product 4a in 93% of product yield. The
recovered PEG-400 can be reused for further cycles without any
significant loss of activity. Yield 93%; White solid; mp 238-240
1
°C. H-NMR (400 MHz, DMSO-d6): 8.53 (s, 1H), 7.86 (s, 1H),
7.55-7.49 (m, 2H), 7.46 (s, 1H), 7.41-7.37 (m, 3H), 7.33-7.28 (m,
1H), 7.17 (d, J = 7.6 Hz, 2H), 7.05 (s, 1H), 6.96 (t, J = 7.7 Hz,
1H), 6.67 (t, J = 7.6 Hz, 1H), 6.13 (s, 1H), 5.81 (d, J = 8.0 Hz,
1H), 5.32 (s, 1H); 13C NMR (100. MHz, DMSO-d6) δ:163.4,
161.7 (d, J = 251.8 Hz), 152.7, 142.6, 137.5, 135.2, 132.6, 130.7,
Table 1. Synthesis of benzo[4,5]imidazo[1,2-a]-pyrimido[4,5-d]pyrimidin-4(1H)-ones (4a-r)a.
mp (°C)
Entry
Product
R
Time (min)
Yieldb(%)
Found
Reported
1
2
3
4
5
4a
4b
4c
4d
4e
4f
3- F-C6H4
2- F-C6H4
60
60
65
71
70
62
73
70
79
65
70
73
60
60
65
60
62
69
93
94
90
92
91
93
90
90
88
89
88
90
90
89
90
91
90
89
238-240
228-230
222-224
230-232
236-238
234-236
229-231
223-225
232-234
194-196
201-203
228-230
231-233
228-230
230-232
229-231
223-225
237-239
-
-
4- Br-C6H4
3- NO2-C6H4
3- Br-C6H4
-
-
-
6
4-OMe-C6H4
4-Cl-C6H4
2-Pyridyl
(236)9
(229)9
-
7
4g
4h
4i
8
9
4- OEt-C6H4
2- 4-F2-C6H3
2- 3-F2-C6H3
3- 4-F2-C6H3
4- F-C6H4
4-Me-C6H4
3-Me-C6H4
4-Pyridyl
-
10
11
12
13
14
15
16
17
18
4j
-
4k
4l
-
-
4n
4m
4n
4o
4q
4r
(230)9
(231)9
(232)9
(232)9
(224)9
(236)9
C6H5
3-Cl-C6H4
aReaction of 1H-benzo[d]imidazol-2-amine (1, 1 mmol), aldehyde (2a-r, 2 mmol), and 2-cyanoacetamide (3, 1 mmol) in PEG-400 at room temperature. bIsolated
yield.
Supporting Information
All new compounds data and NMR spectra were provided as Supplementary data.
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