Microwave-assisted efficient and convenient one-pot synthesis of novel 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins under solvent-free conditions

Article abstract of DOI:10.1007/s10593-018-2340-9

[Figure not available: see fulltext.] An efficient green synthesis of novel 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins has been developed. One-pot reaction of 3-acetylcoumarin, malononitrile, and elemental sulfur, catalyzed by L-proline, resulted in the formation of thiophene derivatives, which were used as precursors for the synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins. Target compounds were prepared by a one-pot method or stepwise, and NH₄OAc was exploited as a reagent and molten salt. Microwave irradiation method was successfully applied to afford the products in excellent yields.

Full text of DOI:10.1007/s10593-018-2340-9

DOI 10.1007/s10593-018-2340-9
Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
Microwave-assisted efficient and convenient one-pot synthesis
of novel 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins
under solvent-free conditions
1
1
Devulapally Srikrishna *, Pramod Kumar Dubey
1
Department of Chemistry,
Jawaharlal Nehru Technological University College of Engineering Hyderabad,
Kukatpally, Hyderabad-500085, Telangana, India;
e-mail: devulapallisrikrishna@gmail.com
Published in Khimiya Geterotsiklicheskikh Soedinenii,
Submitted March 17, 2018
Accepted after revision July 24, 2018
2
018, 54(7), 736–743
An efficient green synthesis of novel 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins has been developed. One-pot reaction of
-acetylcoumarin, malononitrile, and elemental sulfur, catalyzed by L-proline, resulted in the formation of thiophene derivatives, which
were used as precursors for the synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins. Target compounds were prepared by a
3
4
one-pot method or stepwise, and NH OAc was exploited as a reagent and molten salt. Microwave irradiation method was successfully
applied to afford the products in excellent yields.
Keywords: ammonium acetate, coumarin, thieno[2,3-d]pyrimidine, green synthesis, microwave irradiation, solvent-free.
Coumarins (2H-chromen-2-ones) are valuable hetero-
Among the pyrimidine derivatives containing annulated
cycles that have been incorporated in many natural
five-membered heteroaromatic rings, thienopyrimidines
occupy a special position. Thienopyrimidines are structural
analogs of biogenic purines and can be considered as
potential nucleic acid antimetabolites. Therefore, various
aspects of the synthesis as well as chemical and biological
1
products with diverse pharmacological activities, which
make them suitable as potential building blocks for
biologically active compounds containing coumarin–other
heterocycle scaffold. Coumarin derivatives have been
2
extensively utilized as therapeutic agents, active media for
properties of isomeric thienopyrimidines have been
3
4
18–21
tunable dye lasers, fluorescence quenching agents,
reviewed.
Keeping all the above considerations in
5
6
luminescent probes, and triplet sensitizers.
mind, it seemed interesting to prepare a thieno[2,3-d]-
pyrimidine ring with a coumarin motif in a single
framework, which is structurally related to a nucleobase
adenine (Fig. 1).
As another versatile heterocycle, pyrimidine is an important
motif that is commonly present in nucleic acids as nucleo-
bases cytosine (C), thymine (T), and uracil (U). Fused
pyrimidines continue to attract considerable attention of
researchers in different fields because of their great
practical utility, primarily, due to the wide spectrum of
7
biological activities. Accordingly, the pyrimidine ring has
been fused to various heterocycles to obtain structurally
8
diverse compounds, such as pyranopyrimidines, pyrido-
9
10
11
pyrimidines, triazolopyrimidines, pyrazolopyrimidines,
12
13
pyrimidoazepines,
coumarinopyrimidines, furopyrimi-
dines,14 pyrrolopyrimidines, thiazolopyrimidines, and
15 16
Figure 1. Structural similarity of nucleobase adenine and thieno-
[2,3-d]pyrimidines.
1
7
indolopyrimidines.
0
009-3122/18/54(7)-0736©2018 Springer Science+Business Media, LLC
736

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
Scheme 1
Method II
NC
CN, S8
R2
R2
R2
EtO
Me
L-Proline
(10 mol %)
L-Proline
O
O
O
O
O
O
(
25 mol %)
OH
CN
S
+
N(CH CH OH)
3
R1
O
PEG-600
100°C, 1–2 h
75–89%
R1
2
2
R1
NH2
CHO
rt, 30–40 min
Me
1a–e
8596%
2a–e
4a–e
NC
CN EtOH
L-Proline rt, 3–4 h
(
10 mol %) 78–88%
R2
O
O
Method I
CN
CN
S8, L-Proline (10 mol %)
1
2
1
2
a R = R = H; b R = Cl, R = H
1
2
1
2
R1
c R = Br, R = H; d R = NO , R = H
PEG-600
100°C, 30–45 min
88–94%
2
1
2
e R = H, R = OMe
Me
3a–e
Thienopyrimidines can be synthesized from either
concerns and hazardous waste management has promoted
development of greener synthetic methods. Obviously, an
advanced chemical process would be performed under
22
23
pyrimidine or thiophene derivatives. However, since
1
961, when the Gewald reaction was originally reported for
31
the synthesis of 2-aminothiophenes, they have become
solvent-free conditions. As an alternative, H
2
O, perfluori-
32
invaluable precursors for obtaining thieno[2,3-d]pyrimi-
nated hydrocarbons, and supercritical fluids, in particular
CO , have been used to replace the conventional organic
24
33
dines. Hussein reported the reaction of 3-acetyl-2H-benzo-
2
[
4,5]thiazolo[3,2-a]pyrimidin-2-one with malononitrile to
solvents that are often harmful and toxic. Molten salts and
ionic liquids have been also evaluated as environmentally
friendly solvents in both organic and organometallic
afford ylidenemalononitrile, which upon the reaction with
elemental sulfur provided the corresponding thiophene
derivative.25 The yield of product was increased by a
one-pot reaction of acetyl compound, malononitrile, and
elemental sulfur in refluxing EtOH containing triethyl-
amine (TEA). Baell presented the synthesis of different
thieno[2,3-d]pyrimidines by the reaction of 2-amino-
34
chemistry.
Based on the aforementioned information and in conti-
nuation of our earlier research on the synthesis of oxygen-
containing heterocycles with a special reference to
coumarins,3
5–38
we report here a convenient method for the
4
-(3,4-dimethoxyphenyl)-5-methylthiophene-3-carbonitrile
synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins
under solvent-free conditions. The application of L-proline as
2
6
39
and formamidine acetate at 160°C.
In addition,
Al-Mousawi and Elnagdi reported the construction of
pyrimidine ring in a reaction of ethyl 6-amino-5-cyano-
-phenyl-4H-pyran-3-carboxylate and N,N-dimethylform-
an environmentally benign catalyst for the synthesis of
differently substituted 2-amino-4-(2-oxo-2H-chromen-3-yl)-
thiophene-3-carbonitriles has been also demonstrated.
The synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)-
coumarins commenced with the reaction of commercially
available salicylaldehydes 1a–e and ethyl acetoacetate
using L-proline as a green catalyst and triethanolamine as a
4
amide dimethyl acetal (DMF-DMA) in refluxing DMF to
afford ethyl (E)-5-cyano-6-{[(dimethylamino)methylene]-
amino}-4-phenyl-4H-pyran-3-carboxylate, which upon the
cyclization with NH
4
OAc in AcOH under reflux provided
27
35
the corresponding pyrano[2,3-d]pyrimidine.
reaction media to give 3-acetylcoumarins 2a–e (Scheme 1).
Organocatalysis, as an approach for environmentally
friendly synthesis, has become a rapidly growing field of
chemistry. In this regard, L-proline has received much
L-Proline can act both as acid and base40 and thus facilitate
the chemical transformations in a concerted manner,
similar to enzymatic catalysis. The basic site of L-proline
may induce the formation of a carbanion of the methylene
compound, and the acidic site can activate the carbonyl
group of aldehyde to promote the Knoevenagel conden-
sation. Moreover, the acidic properties of the catalyst can
facilitate the formation of pyran-2-one ring by an intra-
molecular transesterification.
attention due to its dual role as a ligand2 and catalyst.
8
29
However, development of benign catalytic procedures for
the C=C and C–S bond formation reactions (Knoevenagel
condensation and Gewald reaction, respectively) with high
selectivity and yield of product is still desirable. Recently,
L-proline has been successfully exploited in the Gewald
reaction. Zeng et al. reported an efficient one-pot three-
component protocol for the preparation of 2-aminothio-
phenes via the Gewald reaction catalyzed by L-proline.30
Since most of the chemical transformations take place in
a solution, the role of solvents in organic synthesis is
crucial. In general, any liquid can be utilized as a solvent.
However, the ever-increasing awareness of environmental
The reaction of 3-acetylcoumarins 2a–e and malono-
nitrile in the presence of NH OAc in AcOH under reflux
4
conditions for 9 h resulted in formation of the desired
2-[1-(2-oxo-2H-chromen-3-yl)ethylidene]malononitriles 3a–e
and also the undesired products of self-condensation of the
starting materials 2a–e, i.e., (E)-3,3'-(1-oxobut-2-ene-1,3-
diyl)bis(2H-chromen-2-one) derivatives, some of which
7
37

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
Scheme 2
have been also reported by Bakeer.41 Exploitation of other
further extended to other 2-amino-4-(2-oxo-2H-chromen-
3-yl)thiophene-3-carbonitriles 4b–e, and the corresponding
imidamides 5b–e were successfully synthesized.
bases, such as piperidine, TEA, N,N-diisopropylethylamine
(
DIPEA), and 1,4-diazabicyclo[2.2.2]octane (DABCO),
leaded to the same dimeric impurities. Therefore, L-proline
was selected as a mild base and the reaction of 3-acetyl-
coumarins 2a–e and malononitrile was conducted in EtOH
to afford the corresponding 2-[1-(2-oxo-2H-chromen-3-yl)-
Further, reaction of imidamide 5a and NH OAc was
4
performed to obtain 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)-
coumarin (7a) (Scheme 3). To optimize the reaction
conditions and thereby ensure the highest yield of product
36
ethylidene]malononitriles 3a–e as the sole products.
7a, reaction of compound 5a and NH
in different solvents (Table 1). Protic solvents were
screened, as the solubility of NH OAc was taken into
4
OAc was examined
Further heating compounds 3a–e with elemental sulfur
using L-proline (10 mol %) as a catalyst and polyethylene
glycol 600 (PEG-600) as a solvent at 100°C provided the
respective thiophene derivatives 4a–e. Application of
L-proline in the Gewald reaction was further explored for
the possibility of a one-pot three-component synthesis of
4
consideration. In addition, solvent-free synthesis was also
performed. Interestingly, the latter method was superior
among the other tested conditions in terms of reaction time
and yield of product 7a.
2
-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles
4
a–e. Thus, equimolar amounts of starting material 2a–e,
Table 1. Optimization of the reaction conditions
for the synthesis of compound 7a*
malononitrile, and elemental sulfur in the presence of
L-proline were heated in PEG-600 at 100°C for 1–2 h. As
expected, the reaction was completed successfully to afford
the desired products 4a–e in high yields.
Solvent
AcOH
Temperature, °C
Time, h
Yield of product 7a, %
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
Reflux
114**
4
4.5
4
72
65
69
33
58
55
49
44
83
Subsequently, Vilsmeier–Haack formylation was per-
formed with compound 4a at room temperature for 7 h and
resulted in the formation of two imidamide products, which
were separated by column chromatography and identified
as N'-[3-cyano-4-(2-oxo-2H-chromen-3-yl)thiophen-2-yl]-
N,N-dimethylformimidamide (5a) and N'-[3-cyano-5-formyl-
2
EtCO H
2
HCO H
2
H O
15
6
MeOH
EtOH
i-PrOH
n-BuOH
–
6.5
7.5
12
2
4
-(2-oxo-2H-chromen-3-yl)thiophen-2-yl]-N,N-dimethylform-
imidamide (6) (Scheme 2). When the same chemical
transformation was conducted at 100°C for 3 h, compound
6
was obtained as the sole product, whereas the reaction of
DMF-DMA and thiophene 4a at room temperature for 3 h
exclusively provided the desired N,N-dimethylform-
imidamide 5a. Thus, generalization of this method was
*
3
4
Reaction conditions: imidamide 5a (3.23 g, 10 mmol), NH OAc (2.31 g,
0 mmol), solvent (30 ml).
** Melting point of NH
4
OAc.
Scheme 3
7
38

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
Table 2. Yields of compounds 7a–e synthesized
Table 3. Yields of compounds 7a–e synthesized
in a one-pot reaction from thiophenes 4a–e
by conventional and microwave methods
from imidamides 5a–e by conventional
and microwave methods
Conventional method*
Microwave method**
Conventional method*
Microwave method**
Product
Product
Time, h
Yield, %
Time, min
Yield, %
Time, h
Yield, %
Time, min
Yield, %
7
a
1
2
1.5
1.5
2
83
79
75
81
73
12
14
10
10
15
91
86
85
92
87
7a
7b
7c
7d
7e
2.5
2.5
2
2.5
3
83
80
79
83
85
16
18
15
17
20
89
90
86
87
91
7
b
7
c
7
d
7
e
*
3
*
3
Reaction conditions: imidamide 5a–e (10 mmol), NH
4
OAc (2.31 g,
* Reaction conditions: thiophene 4a–e (10 mmol), DMF-DMA (1.19 g,
10 mmol), NH OAc (2.31 g, 30 mmol), 115–120°C.
** Reaction conditions: thiophene 4a–e (10 mmol), DMF-DMA (1.19 g,
10 mmol), NH OAc (2.31 g, 30 mmol), MW, 114°C.
0 mmol), 115–120°C.
4
4
* Reaction conditions: imidamide 5a–e (10 mmol), NH OAc (2.31 g,
0 mmol), MW, 114°C.
4
The generality of this solvent-free reaction was studied
conventional and 1microwave-assisted methods, were
13
by changing substrates 5b–e which provided the respective
products 7b–e in high yields (Scheme 3, Table 2).
Furthermore, the scope of the reaction was also executed
under solvent-free conditions using microwave irradiation
confirmed by IR, H and C NMR spectroscopy and
HRMS data.
The role of NH OAc as a molten salt in the synthesis of
4
3-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins 7a–e has
been evaluated. According to Kennedy, a molten salt may
be one of the reactants or a catalyst and may also provide a
unique ionic environment for the reaction.42 Taking into
account these considerations, a plausible mechanism for the
formation of product 7a from imidamide 5a has been
(
MW). The results clearly indicate that both solvent-free
approaches using conventional and MW heating are
efficient. However, the remarkably shorter reaction times
and higher yields of products 7a–e make the microwave
method superior.
Alternatively, 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)-
coumarins 7a–e could be prepared in a one-pot three-
component reaction of thiophene derivatives 4a–e,
proposed (Scheme 4). At elevated temperatures, NH
4
OAc
may dissociate into AcOH and NH and thereby act as a
3
source of nitrogen for the construction of pyrimidine ring.
Compound 5a can abstract a proton from AcOH to
generate a positive charge on the nitrogen atom and thus
activate the imidamide moiety (intermediate A). The latter
DMF-DMA, and NH OAc at 115–120°C for 2–3 h (Scheme 3,
4
Table 3). As previously, microwave method was also
successfully applied to obtain products 7a–e in excellent
yields. Structures of all compounds, synthesized by
may then be attacked by NH in a nucleophilic addition
3
Scheme 4
7
39

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
manner to generate intermediate B, which loses a proton to
give compound C. The latter can undergo a cyclization
process and AcOH-facilitated subsequent loss of dimethyl-
amine molecule to afford the desired product 7a.
(2H, m, H Ar); 7.70–7.92 (2H, m, H Ar); 8.50 (1H, s, H-4).
3
1
C NMR spectrum, δ, ppm: 23.4; 87.8; 112.6; 112.7;
116.9; 118.3; 124.4; 125.8; 130.2; 134.7; 145.5; 154.2;
+
157.3; 172.6. Found, m/z: 237.1288 [M+H] . C14
Calculated, m/z: 237.1292.
H
9
N
2
O .
2
In summary, solvent-free one-pot synthesis of novel
3
-(4-aminothieno[2,3-d]pyrimidin-5-yl)coumarins has been
2-[1-(6-Chloro-2-oxo-2H-chromen-3-yl)ethylidene]-
malononitrile (3b). Yield 2.10 g (78%), white solid,
developed. For the first time, NH
molten salt and reagent to carry out the reaction of 2-amino-
-(2-oxo-2H-chromen-3-yl)thiophene-3-carbonitriles and
4
OAc has been used as a
36
mp 185–187°C (MeCN) (mp 185–187°C (MeCN) ).
–1
4
IR spectrum, ν, cm : 1724 (s, sh, C=O), 2213 (s, sh, C≡N),
1
DMF-DMA at elevated temperatures. Both conventional
and microwave methods allowed to obtain the desired
compounds. In comparison to the conventional heating
method, application of microwave irradiation proved to be
an environmentally benign and noticeably faster, safer, and
more efficient technique. Operational simplicity, solvent
and catalyst-free, mild reaction conditions, nonchromato-
graphic purification, and high yields of products are the
advantages of this synthetic protocol.
2376 (s, sh, C≡N). H NMR spectrum, δ, ppm: 2.56 (3H, s,
CH ); 7.50–7.75 (2H, m, H Ar); 8.06 (1H, s, H Ar); 8.59
3
13
(1H, s, H-4). C NMR spectrum, δ, ppm: 20.3; 82.8;
110.3; 114.7; 119.8; 120.3; 121.9; 125.2; 128.2; 131.8;
+
134.7; 150.8; 156.3; 169.9. Found, m/z: 271.0269 [M+H] .
C
14
H
8
ClN
2
O . Calculated, m/z: 271.0274.
2
2-[1-(6-Bromo-2-oxo-2H-chromen-3-yl)ethylidene]-
malononitrile (3c). Yield 2.75 g (88%), white solid,
36
mp 203–205°C (EtOH) (mp 203–205°C (EtOH) ). IR spect-
–1
rum, ν, cm : 1728 (s, sh, C=O), 2122 (s, sh, C≡N), 2284 (s,
Experimental
1
sh, C≡N). H NMR spectrum, δ, ppm: 2.55 (3H, s, CH );
3
IR spectra were recorded on a PerkinElmer 1600 FTIR
7.48–7.74 (2H, m, H Ar); 8.05 (1H, s, H Ar); 8.58 (1H, s,
1
13
13
spectrometer using KBr pellets. H and C NMR spectra
H-4). C NMR spectrum, δ, ppm: 22.5; 83.8; 110.8; 115.6;
(
400 and 100 MHz, respectively) were acquired on a
119.1; 121.2; 122.5; 125.0; 128.5; 132.3; 135.1; 151.8;
+
Varian 400 MHz spectrometer in DMSO-d using TMS as
6
158.2; 173.1. Found, m/z: 314.9767 [M+H] . C14
H
8
BrN
2
2
O .
internal standard. High-resolution mass spectra were
recorded on an Agilent 1100 LCMS instrument using ESI
method. Melting points were determined in open capillary
Calculated, m/z: 314.9769.
2-[1-(6-Nitro-2-oxo-2H-chromen-3-yl)ethylidene]malono-
nitrile (3d). Yield 2.27 g (81%), white solid, mp 138–140°C
36
–1
tubes using hot H
analyses were done on silica gel-G coated sheets supplied
by Merck, and visualization was done using UV lamp and I
2
SO
4
bath and are uncorrected. TLC
(MeOH) (mp 138–140°C (MeOH) ). IR spectrum, ν, cm :
1720 (s, sh, C=O), 2156 (s, sh, C≡N), 2283 (s, sh, C≡N).
1
2
.
H NMR spectrum, δ, ppm: 2.53 (3H, s, CH ); 7.45–7.75
3
Microwave-assisted reactions were carried out in a house-
hold microwave oven with a maximum power of 800 W.
All chemicals and solvents were obtained from commercial
suppliers and were used without any purification.
(2H, m, H Ar); 8.00 (1H, s, H Ar); 8.53 (1H, s, H-4).
13
C NMR spectrum, δ, ppm: 25.6; 84.4; 110.3; 116.5;
119.3; 121.8; 125.2; 125.5; 129.1; 132.0; 132.4; 153.0;
+
158.5; 172.1. Found, m/z: 282.0512 [M+H] . C14
Calculated, m/z: 282.0514.
H
8
N
3
O .
4
3
5
Synthesis of 3-acetylcoumarins 2a–e (General method).
A mixture of salicylaldehyde 1a–e (10 mmol), ethyl aceto-
acetate (1.56 g, 12 mmol), L-proline (288 mg, 25 mol %),
and triethanolamine (5 ml) was stirred at room temperature
for 30–40 min. Progress of the reaction was monitored by
TLC (eluent EtOAc–hexane, 3:7). After completion of the
2-[1-(8-Methoxy-2-oxo-2H-chromen-3-yl)ethylidene]-
malononitrile (3e). Yield 2.12 g (80%), white solid, mp 171–
36
173°C (MeOH) (mp 171–173°C (MeOH) ). IR spectrum,
–1
ν, cm : 1711 (s, sh, C=O), 2138 (s, sh, C≡N), 2238 (s, sh,
1
C≡N). H NMR spectrum, δ, ppm: 2.62 (3H, s, CH
(3H, s, OCH ); 7.36–7.52 (3H, m, H Ar); 8.56 (1H, s, H-4).
C NMR spectrum, δ, ppm: 19.8; 56.6; 82.5; 113.0; 113.3;
3
); 3.98
reaction, the mixture was poured into ice-cold H
The obtained solid was filtered off, washed with H
20 ml), and air-dried. Crude product 2a–e was
recrystallized from a suitable solvent.
2
O (50 ml).
3
13
2
O
(
113.8; 119.8; 120.3; 125.3; 125.7; 131.8; 142.5; 148.8;
+
158.9; 172.5. Found, m/z: 267.0769 [M+H] . C15
Calculated, m/z: 267.0769.
H
11
N
2
3
O .
Synthesis of 2-ethylidenemalononitriles 3a–e (General
method). A mixture of 3-acetylcoumarin 2a–e (10 mmol),
malononitrile (0.66 g, 10 mmol), L-proline (115 mg,
Synthesis of thiophene derivatives 4a–e from
2-ethylidenemalononitriles 3a–e. Method I. A mixture of
2-[1-(2-oxo-2H-chromen-3-yl)ethylidene]malononitrile 3a–e
(10 mmol), elemental sulfur (0.32 g, 10 mmol), L-proline
(115 mg, 10 mol %), and PEG-600 (30 ml) was stirred at
100°C for 30–45 min. Progress of the reaction was
1
0 mol %), and EtOH (50 ml) was stirred at room
temperature for 3–4 h. Progress of the reaction was
monitored by TLC (eluent CHCl ). After completion of the
3
reaction, the mixture was poured into ice-cold H
2
O
(
100 ml). The obtained solid was filtered off, washed with
monitored by TLC (eluent MeOH–CHCl
completion of the reaction, the mixture was poured into ice-
cold H O (50 ml). The obtained solid was filtered off,
washed with H O (2×20 ml), and air-dried. Crude product
3
, 5:95). After
H
2
O (2×50 ml), and air-dried. The crude product 3a–e was
recrystallized from a suitable solvent.
2
2-[1-(2-Oxo-2H-chromen-3-yl)ethylidene]malononitrile
2
(
3a). Yield 2.02 g (86%), white solid, mp 162–164°C
4a–e was recrystallized from a suitable solvent.
3
6
–1
(
MeOH) (mp 162–164°C (MeOH) ). IR spectrum, ν, cm :
728 (s, sh, C=O), 2238 (s, sh, C≡N), 2364 (s, sh, C≡N).
One-pot synthesis of thiophene derivatives 4a–e from
3-acetylcoumarins 2a–e. Method II. A mixture of 3-acetyl-
coumarin 2a–e (10 mmol), malononitrile (0.66 g, 10 mmol),
1
1
H NMR spectrum, δ, ppm: 2.62 (3H, s, CH ); 7.36–7.62
3
7
40

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
elemental sulfur (0.32 g, 10 mmol), L-proline (115 mg,
2.29 g (77%, method II), yellow solid, mp 147–149°C
36 –1
10 mol %), and PEG-600 (30 ml) was stirred at 100°C for
–2 h. Progress of the reaction was monitored by TLC
(EtOH) (mp 147–149°C (EtOH) ). IR spectrum, ν, cm :
1
1734 (s, sh, C=O), 2161 (s, sh, C≡N), 3150–3200 (m, br,
1
(
eluent MeOH–CHCl
3
, 1:19). After completion of the
NH
OCH
2
). H NMR spectrum, δ, ppm (J, Hz): 3.96 (3H, s,
reaction, the mixture was cooled to room temperature and
then poured into ice-cold H O (50 ml). The obtained solid
was filtered off, washed with H O (2×50 ml), and air-dried.
3
); 7.14 (2H, s, NH ); 7.37 (1H, d, J = 4.2, H Ar); 7.42
2
2
(1H, d, J = 4.6, H Ar); 7.48 (1H, d, J = 3.8, H Ar); 7.52
13
2
(1H, s, H thiophene); 8.62 (1H, s, H-4). C NMR
Crude product 4a–e was recrystallized from a suitable
solvent (see the characterization data of compounds 4a–e).
spectrum, δ, ppm: 56.6; 84.2; 110.3; 114.7; 116.5; 119.8;
120.3; 121.9; 125.2; 131.8; 141.0; 142.5; 146.8; 158.9;
+
2
-Amino-4-(2-oxo-2H-chromen-3-yl)thiophene-3-carbo-
165.9. Found, m/z: 299.0412 [M+H] . C15
Calculated, m/z: 299.0413.
H
11
N
2
O S.
3
nitrile (4a). Yield 2.51 (94%, method I), 2.38 g (89%,
method II), yellow solid, mp 240–242°C (EtOH) (mp 240–
Synthesis of imidamides 5a and 6. 2-Amino-4-(2-oxo-
2H-chromen-3-yl)thiophene-3-carbonitrile (4a) (2.68 g,
10 mmol) was added to a solution of DMF (20 ml) and
36
–1
2
2
42°C (EtOH) ). IR spectrum, ν, cm : 1720 (s, sh, C=O),
1
209 (s, sh, C≡N), 3290–3320 (m, br, NH
2
). H NMR
spectrum, δ, ppm (J, Hz): 7.18 (2H, s, NH
2
); 7.38 (1H, t,
POCl (10 ml) at 0–5°C. The reaction mixture was then
3
J = 4.8, H Ar); 7.45 (1H, d, J = 3.6, H Ar); 7.52 (1H, s,
H thiophene); 7.60 (1H, t, J = 4.0, H Ar); 7.83 (1H, d,
stirred at room temperature for 7 h. Progress of the reaction
was monitored by TLC (eluent EtOAc–hexane, 1:1). After
completion of the reaction, the mixture was poured into ice-
1
3
J = 8.0, H Ar); 8.50 (1H, s, H-4). C NMR spectrum,
δ, ppm: 81.8; 110.2; 116.5; 119.3; 121.8; 124.2; 126.5;
cold H
2
O (60 ml). The obtained solid was filtered off,
O (2×30 ml), and air-dried to obtain a
1
2
29.1; 132.0; 132.5; 145.8; 150.2; 153.2; 159.2. Found, m/z:
washed with H
2
+
69.0378 [M+H] . C14
H
9
N
O
2 2
S. Calculated, m/z: 269.0384.
mixture of products 5a and 6 that were separated by column
chromatography (silica gel, eluent EtOAc–hexane, 1:4).
(E)-N'-[3-Cyano-4-(2-oxo-2H-chromen-3-yl)thiophen-
2-yl]-N,N-dimethylformimidamide (5a). Yield 1.81 g
(56%), yellow solid, mp 228–230°C (EtOH). IR spectrum,
2
-Amino-4-(6-chloro-2-oxo-2H-chromen-3-yl)thiophene-
3
(
(
-carbonitrile (4b). Yield 2.70 g (90%, method I), 2.34 g
78%, method II), yellow solid, mp >250°C (MeCN)
36 –1
mp >250°C (MeCN) ). IR spectrum, ν, cm : 1702 (s, sh,
).
); 7.20
1H, d, J = 3.8, H Ar); 7.50 (1H, s, H thiophene); 7.83 (1H,
–
1
1
C=O), 2213 (s, sh, C≡N), 3295–3330 (m, br, NH
2
ν, cm : 1718 (s, sh, C=O), 2205 (s, sh, C≡N). H NMR
1
H NMR spectrum, δ, ppm (J, Hz): 6.98 (2H, s, NH
2
spectrum, δ, ppm: 3.08 (3H, s, CH
3
); 3.19 (3H, s, CH );
3
(
7.20 (1H, s, H thiophene); 7.36–7.56 (2H, m, H Ar); 7.60–
7.68 (1H, m, H Ar); 7.76–7.84 (1H, m, H Ar); 8.07 (1H, s,
d, J = 3.6, H Ar); 8.18 (1H, s, H Ar); 8.54 (1H, s, H-4).
1
3
13
C NMR spectrum, δ, ppm: 81.5; 113.5; 116.5; 119.1;
H-4); 8.27 (1H, s, N=CHN). C NMR spectrum, δ, ppm:
1
1
22.2; 122.5; 129.1; 129.5; 134.5; 140.8; 148.1; 151.0;
34.0; 35.2; 109.2; 114.3; 115.8; 119.2; 120.2; 124.6; 128.8;
+
51.5; 159.8. Found, m/z: 302.9992 [M+H] . C14
H
8
ClN
2
O
2
S.
131.5; 134.4; 138.4; 143.3; 154.3; 158.7; 163.2. Found, m/z:
+
Calculated, m/z: 302.9987.
324.0807 [M+H] . C17
H N
14 3
O S. Calculated, m/z: 324.0810.
2
2
-Amino-4-(6-bromo-2-oxo-2H-chromen-3-yl)thiophene-
(E)-N'-[3-Cyano-5-formyl-4-(2-oxo-2H-chromen-3-yl)-
thiophen-2-yl]-N,N-dimethylformimidamide (6). Yield
1.40 g (40%), yellow solid, mp 164–166°C (acetone).
3
(
(
-carbonitrile (4c). Yield 3.05 g (88%, method I), 2.76 g
80%, method II), yellow solid, mp 212–214°C (MeCN)
3
6
–1
–1
mp 212–214°C (MeCN) ). IR spectrum, ν, cm : 1705 (s,
).
H NMR spectrum, δ, ppm (J, Hz): 6.74 (1H, s,
H thiophene); 7.20 (2H, s, NH ); 7.56 (1H, d, J = 4.0,
H Ar); 7.82 (1H, d, J = 4.8, H Ar); 8.14 (1H, s, H Ar); 8.64
IR spectrum, ν, cm : 1720 (s, sh, C=O coumarin), 1738
1
sh, C=O), 2213 (s, sh, C≡N), 3280–3324 (m, br, NH
2
(s, sh, C=O aldehyde), 2228 (s, sh, C≡N). H NMR
1
spectrum, δ, ppm: 3.10 (3H, s, CH
3
); 3.21 (3H, s, CH );
3
2
7.38–7.84 (4H, m, H Ar); 8.30 (1H, s, H-4); 8.48 (1H, s,
N=CHN); 9.63 (1H, s, CHO). Found, m/z: 352.0755
1H, s, H-4). 13C NMR spectrum, δ, ppm: 83.3; 114.0;
[M+H] . C18
+
H
N
O S. Calculated, m/z: 352.0748.
(
14
3
3
1
1
16.3; 119.6; 121.8; 122.2; 128.4; 128.8; 134.9; 141.3;
Synthesis of imidamides 5a–e (General method).
A mixture of 2-amino-4-(2-oxo-2H-chromen-3-yl)thiophene-
3-carbonitrile 4a–e (10 mmol) and DMF-DMA (1.19 g,
10 mmol) was stirred at room temperature for 2–3 h.
Progress of the reaction was monitored by TLC (eluent
EtOAc–hexane, 3:7). After completion of the reaction, the
+
49.3; 152.4; 152.7; 158.9. Found, m/z: 346.9489 [M+H] .
C
14
2
H
8
BrN
2
O S. Calculated, m/z: 346.9478.
2
-Amino-4-(6-nitro-2-oxo-2H-chromen-3-yl)thiophene-
-carbonitrile (4d). Yield 2.78 g (89%, method I), 2.34 g
75%, method II), yellow solid, mp 128–130°C (MeOH)
3
(
(
3
6
–1
mp 128–130°C (MeOH) ). IR spectrum, ν, cm : 1738 (s,
).
); 7.46
1H, s, H thiophene); 7.61 (1H, d, J = 3.8, H Ar); 8.13 (1H,
mixture was poured into ice-cold H
2
O (50 ml). The
O (2×30 ml),
sh, C=O), 2248 (s, sh, C≡N), 3200–3265 (m, br, NH
2
obtained solid was filtered off, washed with H
2
1
H NMR spectrum, δ, ppm (J, Hz): 7.22 (2H, s, NH
2
and air-dried. Crude product 5a–e was recrystallized from a
suitable solvent.
(
d, J = 4.2, H Ar); 8.50 (1H, s, H Ar); 8.84 (1H, s, H-4).
(E)-N'-[3-Cyano-4-(2-oxo-2H-chromen-3-yl)thiophen-
2-yl]-N,N-dimethylformimidamide (5a). Yield 3.01 g (93%).
(E)-N'-[4-(6-Chloro-2-oxo-2H-chromen-3-yl)-3-cyano-
thiophen-2-yl]-N,N-dimethylformimidamide (5b). Yield
3.17 g (89%), yellow solid, mp 182–184°C (acetone).
1
3
C NMR spectrum, δ, ppm: 82.3; 110.6; 115.8; 118.3;
1
1
20.6; 120.9; 127.3; 127.7; 132.9; 140.6; 147.9; 151.4;
+
51.8; 157.9. Found, m/z: 314.0235 [M+H] . C14
H
8
N
3
O S.
4
Calculated, m/z: 314.0236.
–1
2
-Amino-4-(8-methoxy-2-oxo-2H-chromen-3-yl)thio-
IR spectrum, ν, cm : 1721 (s, sh, C=O), 2210 (s, sh, C≡N).
1
phene-3-carbonitrile (4e). Yield 2.68 g (90%, method I),
H NMR spectrum, δ, ppm: 3.09 (3H, s, CH ); 3.18 (3H, s,
3
7
41

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
CH
3
); 7.22 (1H, s, H thiophene); 7.38–7.48 (1H, m, H Ar);
(10 mmol), DMF-DMA (1.19 g, 10 mmol), and NH OAc
4
7
.57–7.65 (1H, m, H Ar); 7.71–7.79 (1H, m, H Ar); 8.05
(2.31 g, 30 mmol) was subjected to the conditions of
conventional (the reaction mixture heated at 115–120°C for
2–3 h) or microwave (the reaction mixture irradiated in a
microwave oven (800 W) at 114°C with 30% intensity for
15–20 min) method. Progress of the reaction was moni-
1
3
(
1H, s, H-4); 8.26 (1H, s, N=CHN). C NMR spectrum,
δ, ppm: 34.5; 35.3; 110.1; 113.9; 115.4; 119.7; 120.3;
1
1
25.7; 128.9; 129.3; 133.8; 137.1; 142.8; 153.8; 157.9;
62.6. Found, m/z: 358.0417 [M+H] . C17
+
H
13ClN
3
O S.
2
Calculated, m/z: 358.0412.
tored by TLC (eluent MeOH–CHCl
tion of the reaction, the mixture was poured into ice-cold
O (50 ml). The obtained solid was filtered off, washed
3
, 1:9). After comple-
(
E)-N'-[4-(6-Bromo-2-oxo-2H-chromen-3-yl)-3-cyano-
thiophen-2-yl]-N,N-dimethylformimidamide (5c). Yield
.44 g (86%), yellow solid, mp 168–170°C (MeCN).
H
2
3
with H O (2 30 ml), and air-dried. Crude product 7a–e was
2
–
1
IR spectrum, ν, cm : 1713 (s, sh, C=O), 2216 (s, sh, C≡N).
recrystallized from a suitable solvent. Yields of compounds
7a–e are given in Table 3.
1
H NMR spectrum, δ, ppm: 3.07 (3H, s, CH
CH ); 7.21 (1H, s, H thiophene); 7.37–7.45 (1H, m, H Ar);
.56–7.64 (1H, m, H Ar); 7.72–7.78 (1H, m, H Ar); 8.06
3
); 3.15 (3H, s,
3
3-(4-Aminothieno[2,3-d]pyrimidin-5-yl)-2H-chromen-
2-one (7a). Yellow solid, mp 193–195°C (MeOH).
7
1
3
–1
(
1H, s, H-4); 8.27 (1H, s, N=CHN). C NMR spectrum,
IR spectrum, ν, cm : 1720 (s, sh, C=O), 3400–3442 (m, br,
1
δ, ppm: 34.8; 35.1; 110.1; 113.9; 115.1; 119.6; 120.4;
NH
2
). H NMR spectrum, δ, ppm: 6.81 (1H, s, H thiophene);
1
1
23.0; 127.9; 130.9; 134.0; 137.9; 143.8; 153.1; 158.3;
62.5. Found, m/z: 402.2123 [M+H] . C17
7.30 (2H, s, NH
2
); 7.37–7.48 (3H, m, H Ar); 7.62–7.69
+
H
13BrN
3
O S.
2
(1H, m, H Ar); 7.76–7.80 (1H, m, H-2); 8.27 (1H, s, H-4).
1
3
Calculated, m/z: 402.2120.
C NMR spectrum, δ, ppm: 119.4; 125.1; 126.0; 126.1;
(
E)-N'-[3-Cyano-4-(6-nitro-2-oxo-2H-chromen-3-yl)-
thiophen-2-yl]-N,N-dimethylformimidamide (5d). Yield
.26 g (89%), yellow solid, mp 196–198°C (MeOH).
126.4; 128.0; 129.3; 129.5; 129.9; 134.7; 135.6; 138.9;
156.7; 160.6; 166.6. Found, m/z: 296.0493 [M+H] .
+
3
C
15
H
10
N
3
O S. Calculated, m/z: 296.0494.
2
–
1
IR spectrum, ν, cm : 1711 (s, sh, C=O), 2207 (s, sh, C≡N).
3-(4-Aminothieno[2,3-d]pyrimidin-5-yl)-6-chloro-2H-
chromen-2-one (7b). Yellow solid, mp 225–227°C
1
H NMR spectrum, δ, ppm: 3.08 (3H, s, CH
CH ); 7.20 (1H, s, H thiophene); 7.38–7.47 (1H, m, H Ar);
.56–7.63 (1H, m, H Ar); 7.73–7.78 (1H, m, H Ar); 8.07
3
); 3.16 (3H, s,
–
1
3
(EtOH). IR spectrum, ν, cm : 1725 (s, sh, C=O), 3376–
1
7
3432 (m, br, NH
2
). H NMR spectrum, δ, ppm: 6.84 (1H, s,
); 7.35–7.45 (2H, m, H Ar);
1
3
(
1H, s, H-4); 8.29 (1H, s, N=CHN). C NMR spectrum,
H thiophene); 7.35 (2H, s, NH
2
δ, ppm: 34.6; 35.0; 109.9; 113.6; 115.2; 119.2; 120.1;
7.59–7.66 (1H, m, H Ar); 7.74–7.79 (1H, m, H-2); 8.30
(1H, s, H-4). 13C NMR spectrum, δ, ppm: 119.2; 124.9;
125.8; 126.1; 126.3; 127.7; 129.1; 129.6; 129.8; 135.0;
1
1
23.9; 127.7; 131.6; 134.2; 137.7; 142.9; 153.1; 157.6;
62.7. Found, m/z: 369.0578 [M+H] . C17
+
H
13
N
4
O S.
4
Calculated, m/z: 369.0577.
135.3; 138.5; 156.1; 160.2; 165.7. Found, m/z: 330.0103
+
(
E)-N'-[3-Cyano-4-(8-methoxy-2-oxo-2H-chromen-
-yl)thiophen-2-yl]-N,N-dimethylformimidamide (5e).
Yield 3.17 g (90%), yellow solid, mp 205–207°C (MeOH).
[M+H] . C15
H
9
ClN
3
2
O S. Calculated, m/z: 330.0104.
3
3-(4-Aminothieno[2,3-d]pyrimidin-5-yl)-6-bromo-2H-
chromen-2-one (7c). Yellow solid, mp >250°C (CHCl ).
IR spectrum, ν, cm : 1721 (s, sh, C=O), 3405–3454 (m, br,
3
–
1
–1
IR spectrum, ν, cm : 1717 (s, sh, C=O), 2221 (s, sh, C≡N).
1
1
H NMR spectrum, δ, ppm: 3.09 (3H, s, CH
CH ); 3.84 (3H, s, OCH ); 7.22 (1H, s, H thiophene); 7.33–
.79 (3H, m, H Ar); 8.09 (1H, s, H-4); 8.28 (1H, s,
3
); 3.17 (3H, s,
NH
2
). H NMR spectrum, δ, ppm: 6.83 (1H, s, H thiophene);
3
3
7.36 (2H, s, NH ); 7.40–7.47 (2H, m, H Ar); 7.62–7.69
2
7
(1H, m, H Ar); 7.76–7.81 (1H, m, H-2); 8.28 (1H, s, H-4).
13
13
N=CHN). C NMR spectrum, δ, ppm: 34.2; 34.8; 55.6;
10.2; 113.7; 115.2; 119.6; 120.3; 123.5; 127.6; 130.9; 133.8;
38.4; 143.3; 153.6; 157.2; 164.1. Found, m/z: 354.0911
C NMR spectrum, δ, ppm: 119.6; 123.7; 125.1; 125.8;
1
126.2; 127.2; 129.5; 129.8; 130.2; 135.1; 135.6; 137.1;
+
1
155.8; 160.4; 166.0. Found, m/z: 373.9598 [M+H] .
+
[
M+H] . C18
Synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-5-yl)-
coumarins 7a–e from imidamides 5a–e (General method).
A mixture of imidamide 5a–e (10 mmol) and NH OAc
2.31 g, 30 mmol) was subjected to the conditions of
conventional (the reaction mixture heated at 115–120°C for
–2 h) or microwave (the reaction mixture irradiated in a
microwave oven (800 W) at 114°C with 30% intensity for
0–15 min) method. Progress of the reaction was
monitored by TLC (eluent MeOH–CHCl , 1:9). After
completion of the reaction, the mixture was poured into ice-
cold H O (50 ml). The obtained solid was filtered off,
washed with H O (2×30 ml), and air-dried. Crude product
H
16
N
3
O
3
S. Calculated, m/z: 354.0912.
C
15
H
9
BrN
3
O S. Calculated, m/z: 373.9599.
2
3-(4-Aminothieno[2,3-d]pyrimidin-5-yl)-6-nitro-2H-
chromen-2-one (7d). Yellow solid, mp 208–210°C
–1
4
(EtOH). IR spectrum, ν, cm : 1717 (s, sh, C=O), 3394–
1
(
3445 (m, br, NH
2
). H NMR spectrum, δ, ppm: 6.81 (1H, s,
); 7.38–7.47 (2H, m, H Ar);
H thiophene); 7.33 (2H, s, NH
2
1
7.58–7.66 (1H, m, H Ar); 7.74–7.79 (1H, m, H-2); 8.27
(1H, s, H-4). 13C NMR spectrum, δ, ppm: 119.3; 124.2;
125.2; 126.4; 126.7; 127.5; 128.7; 129.5; 129.9; 134.7;
1
3
135.2; 138.7; 155.6; 161.1; 166.6. Found, m/z: 341.0344
+
[M+H] . C15
H
9
N
4
O S. Calculated, m/z: 341.0344.
4
2
3-(4-Aminothieno[2,3-d]pyrimidin-5-yl)-8-methoxy-2H-
chromen-2-one (7e). Yellow solid, mp 196–198°C (MeCN).
2
–1
7
a–e was recrystallized from a suitable solvent. Yields of
IR spectrum, ν, cm : 1728 (s, sh, C=O), 3426–3485 (m, br,
1
compounds 7a–e are given in Table 2.
NH
(1H, s, H thiophene); 7.29 (2H, s, NH
H Ar); 7.75–7.78 (1H, m, H-2); 8.31 (1H, s, H-4).
2
). H NMR spectrum, δ, ppm: 3.85 (3H, s, OCH
3
); 6.85
One-pot synthesis of 3-(4-aminothieno[2,3-d]pyrimidin-
2
); 7.37–7.66 (3H, m,
5
-yl)coumarins 7a–e from thiophene derivatives 4a–e
13
(
General method). A mixture of thiophene derivative 4a–e
C NMR spectrum, δ, ppm: 55.6; 113.5; 119.3; 121.2;
7
42

Chemistry of Heterocyclic Compounds 2018, 54(7), 736–743
1
1
23.5; 125.2; 125.7; 126.8; 128.1; 128.5; 129.1; 135.0;
17. Tawari, N. R.; Bag, S.; Degani, M. S. J. Mol. Model. 2008,
+
1
4, 911.
38.5; 156.3; 160.2; 165.1. Found, m/z: 326.0599 [M+H] .
1
8. Litvinov, V. P. Adv. Heterocycl. Chem. 2006, 92, 83.
9. Abdel-Fattah, B.; Kandeel, M. M.; Abdel-Hakeem, M.;
Fahmy, Z. M. J. Chin. Chem. Soc. 2006, 53, 403.
0. Elrazaz, E. Z.; Serya, R. A. T.; Ismail, N. S. M.; Abou El Ella, D. A.;
Abouzid, K. A. M. Future Journal of Pharmaceutical
Sciences 2015, 1, 33.
16
C H
12
N
3
O S. Calculated, m/z: 326.0599.
3
1
1
A Supplementary information file containing IR, Н and
С NMR spectra and HRMS of compounds 2–5, 7 a is
2
2
1
3
available at the journal website at http://link.springer.com/
journal/10593.
1. Litvinov, V. P. Russ. Chem. Bull., Int. Ed. 2004, 53, 487. [Izv.
Akad. Nauk, Ser. Khim. 2004, 463.]
The authors are thankful to the authorities of Jawaharlal
Nehru Technological University, Hyderabad for providing
laboratory facilities.
Devulapally Srikrishna is also grateful to the
Department of Science and Technology, Government of
India, New Delhi for the financial support as INSPIRE
Fellowship.
22. Sakamoto, T.; Kondo, Y.; Watanabe, R.; Yamanaka, H. Chem.
Pharm. Bull. 1986, 34, 2719.
2
2
3. Arya, V. P. Indian J. Chem. 1972, 10, 1141.
4. Bugge, S.; Skjønsfjell, E. M.; Willumsen, F. B.; Sundby, E.;
Hoff, B. H. Chem. Heterocycl. Compd. 2014, 50, 1177.
[
Khim. Geterotsikl. Soedin. 2014, 1275.]
25. Hussein, A. H. M.; El-Gaby, M. S.; Abu-Shanab, F.; Abdel-
Raheim, M. A. M. Org. Commun. 2009, 2, 66.
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