Exploiting silver trifluoromethanesulfonate as efficient and reusable catalyst for the synthesis of dihydropyrimidine derivatives under different reaction environments

Article abstract of DOI:10.1002/jhet.3728

Different results were generated under different reaction conditions for the multicomponent reactions. Herein, an efficiently improved and mild protocol for the synthesis of dihydropyrimidine derivatives using cheap silver trifluoromethanesulfonate (CF

Full text of DOI:10.1002/jhet.3728

Received: 22 May 2019
DOI: 10.1002/jhet.3728
Revised: 19 August 2019
Accepted: 21 August 2019
A R T I C L E
Exploiting silver trifluoromethanesulfonate as efficient and
reusable catalyst for the synthesis of dihydropyrimidine
derivatives under different reaction environments
1
1,2
1,2
Dipak Kumar Roy | Kashyap Jyoti Tamuli
| Manobjyoti Bordoloi
1
Natural Products Chemistry Group,
Abstract
Chemical Sciences and Technology
Division, CSIR‐North East Institute of
Science and Technology, Jorhat, Assam,
India
Different results were generated under different reaction conditions for the
multicomponent reactions. Herein, an efficiently improved and mild protocol
for the synthesis of dihydropyrimidine derivatives using cheap silver
2
Academy of Scientific and Innovative
trifluoromethanesulfonate (CF SO Ag) as reusable catalyst is explained. With
Research, CSIR, New Delhi, India
3
3
conventional heating and microwave irradiation method, the synthesis of
Correspondence
substituted 3,4‐dihydropyrimidine‐2(1H)‐one and 3,4‐dihydropyrimidine‐
Manobjyoti Bordoloi, Natural Products
Chemistry Group, Chemical Sciences and
Technology Division, CSIR‐North East
Institute of Science and Technology,
Jorhat 785006, Assam, India.
2(1H)‐thione was achieved in different solvent environments like acetonitrile,
water, and under solvent free neat condition. Moreover, the solvents (CH CN
3
and H O) containing the CF SO Ag were reused for several times without loss
2
3
3
Email: mjb_rrljt@yahoo.co.in; m.j.
bordoloi.pub@gmail.com
of much catalytic activity after separation from the desired products. Thus, the
method provides much improved and efficient alternative pathway to the orig-
inal Biginelli reaction.
Funding information
CSIR New Delhi, India, Grant/Award
Numbers: OLP‐2020 and CSC‐0130
1
| INTRODUCTION
core moiety of this heterocycles has gained a tremendous
importance and several modified methodologies of the
[
11,12]
From the past few decades, we have witnessed that multi-
component reactions enjoy an outstanding status in
organic and pharmaceutical chemistry. In the field of
applications of diversity‐oriented cascade synthesis to form
active organic molecules from simple and easily available
synthons in a single‐reaction chamber has become a cen-
original Biginelli protocol.
The literature is enumer-
ated with numerous synthetic efforts concerning Biginelli
reaction, which were developed either by use of metal cat-
[
13]
alysts
like CaCl , FeCl or NiCl , RuCl , SnCl , and
2 3 2 3 2
[
14]
GaCl , metal triflates
like Bi (OTf) , Yb (OTf) , La
3
3
3
(OTf) , Ni (OTf) , In (OTf) , and Cu (OTf) , morpholinium
3
2
3
2
[1]
[15]
tral point in chemical research. 3,4‐dihydropyrimidine‐
(1H)‐one and 3,4‐dihydropyrimidine‐2(1H)‐thione
including 2‐imino analogues (dihydropyrimidinones
DHPM]) are important biologically active compounds of
acetate/polyphosphonate ester, or by various expensive
nano catalysts
[
16]
[17]
2
and ionic liquids.
Despite several of these reported procedures have lim-
itations such as use of expensive reagents, use of toxic sol-
vents or catalyst, use of concentrated acids, drastic
workup conditions, long reaction time give low to moder-
ate yields. Although many catalysts have been used in
Biginelli reaction, but little attention has been paid to
recover the used catalyst and reused for several cycles.
Moreover, from the point of green chemistry, in most of
the cases, it is not desirable that catalysts cannot be
[
[
2]
immense human health importance, such as, calcium
channel modulator, HIV gp120‐CD4 inhibition, anti-
cancer activity, inhibition of Walker carcinosarcoma,
blood platelet aggregation inhibition, antitumor, and
[3]
[4]
[5]
[6,7]
[
8]
[9]
[10]
antifungul.
Such compounds are also useful as α1‐
adrenoreceptorselective antagonists, inhibitor of benign
prostatic hyperplasia, orally active antihypertensive and
have antiviral activities. Thus, from over the years, the
[2]
[18]
reused.
J Heterocyclic Chem. 2019;1–11.
wileyonlinelibrary.com/journal/jhet
© 2019 Wiley Periodicals, Inc.
1

2
ROY ET AL.
In the recent past, silver trifluoromethanesulfonate has
been used with other substances as cocatalyst or copro-
TABLE 1 Effect of amount of the catalyst to optimize the syn-
thesis of dihydropyrimidinones (DHPM) under different conditions
[19]
moters for various organic transformations.
In addi-
tion to that, silver trifluoromethanesulfonate has also
been used to synthesize various nitrogen containing het-
[20]
erocycles recently.
Whereas, reports on microwave‐
assisted simple metal catalyzed cascade processes are very
rare. Therefore, we opted to explore the higher chances of
silver trifluoromethanesulfonate as catalyst for the syn-
thesis of dihydropyrimidine derivatives.
a
Entry
Urea, mmol
Catalyst, mmol
Yield, %
1
2
3
4
5
6
7
8
9
1
‐
0
65
73
75
82
79
50
85
94
93
Herein, we report a mild, cheap, environment
friendly, and feasible method for the synthesis of
dihydropyrimidine using silver trifluoromethanesulfonate
as catalyst alone in microwave irradiation (Scheme 1c).
Additionally, a comparative study has been performed
for the assessment of CF SO Ag using different solvents
1
0.1
1.1
1.2
1.7
2.0
1.5
1.2
1.2
1.2
1.2
0.1
0.1
0.1
0.1
3
3
such as CH CN and H O including under solvent free
3
2
0.05
0.15
0.20
0.25
0.20
conditions. After the completion of the reaction, the prod-
uct was separated out from the reaction mixture, and sol-
vent containing the catalyst can be reused for several
times.
1
1
0
1
b
97
Note. Reaction conditions: acetyl acetone 1a (1 mmol), urea 2a, 2‐
hydroxybenzaldehyde 3a (1 mmol); acetonitrile: 5 mL; time: 3 h for conven-
tional heating (CH); and 3 min for microwave (MW).
2
| RESULTS AND DISCUSSION
a
The catalytic potential of silver trifluoromethanesulfonate
was first examined for one model reaction containing ace-
tyl acetone 1a, urea 2a, and 2‐hydroxybenzaldehyde 3a
under different catalytic conditions using acetonitrile as
solvent (Table 1). Initially, without using the catalyst, the
reaction does not yield any product (Table 1, entry 1).
Then, the reaction was observed with 0.1 mmol of silver
Isolated yield.
b
3
Using microwave irradiation in CH CN.
trifluoromethanesulfonate using different amount of urea
2a. In the model reaction, with acetonitrile (5 mL), it
stirred at refluxed temperature for 3 hours at 80°C. By
varying the amount of urea 2a, the reaction was carried
out till the formation of product in high yields. Excellent
yield was observed (based upon 2‐hydroxybenzaldehyde)
when loading of urea was increased from 1 to 1.2 mmol.
But the yield remained the same even after addition of
urea up to 2 mmol. Hence, 1.2 equivalent of urea 2a
was found to be optimum for the best yield of
dihydropyrimidines. Thereafter, keeping the reaction time
(
3 hours) constant, the reaction was appraised by changing
the concentrations of catalyst (0.5‐0.25 mmol) (Table 1,
entries 7‐10). In addition to that, use of 20 mmol of silver
trifluoromethanesulfonate is sufficient for the reaction to
accomplish with excellent yield up to 94% (Table 1, entry
9). Higher amount of the catalyst loading results almost
the same in terms of yield percentage. Therefore, an opti-
mum of 1.2 mmol of urea 2a and 0.20 mmol of silver
trifluoromethanesulfonate in the reaction mixture was
quintessential for attaining the best results. However, no
urea or thiourea is remaining in the solvents after the com-
pletion of the reactions, since we were using 1.2 mmol of
them. The dilution effects of other starting materials were
SCHEME 1 Processes for the synthesis of dihydropyrimidine
derivatives [Color figure can be viewed at wileyonlinelibrary.com]

ROY ET AL.
3
[
14]
explained and included in ESI (Table S1). With the all opti-
mum best results, we studied the model reaction with
microwave‐assisted method (Table 1, entry 11). Since to
our delight, the reaction was completed within 3 minutes
Biginelli type reactions,
we have chosen the same sol-
vent systems as they have used. All the examined metal
triflates showed good catalytic activity with our model
reaction, but CF SO Ag was particularly effective for this
3
3
with 97% of yield with CH CN.
transformation than other metal triflates. This method
also comprises of simple and easy purification process
for getting the products and enhances the scope of reus-
ability of the metal catalyst up to seven runs.
3
Again, to study the effects of different metal triflates
and solvents for the synthesis of DHPM derivatives, some
initial experiments were carried out by taking the same
model reaction (Table 2). At first, we took acetonitrile,
water, and neat conditions with our catalyst to evaluate
the solvent effects (Table 2, entries 1‐3). From the results,
it showed that acetonitrile works as better solvent (yield
With the established optimized reaction conditions, we
have extended all the possible methods to investigate the
flexibility of the catalytic environments in different reac-
tion conditions. The reactions were carried out by heating
mixture of substituted aldehydes (1 mmol), acetyl acetone
or ethylacetoacetate (1 mmol), and urea or thiourea
(1.2 mmol) with silver trifluoromethanesulfonate
(0.20 mmol) at 80°C (bath temperature) for appropriate
time (3 hours) for conventional heating method and at
35 W in 80°C (set at the programmer of the reactor) for
3 minutes for microwave‐irradiated methods. All results
were summarized in Table 3. At first, to study the solvent
effects, different solvents were also screened for this mul-
ticomponent reaction. To analyze the greener aspects in
organic synthesis, we studied the adaptability of the reac-
tion with solvent water and solvent free conditions,
although the resulting yields were reasonably low and
the rate of the reaction was slow while using water as sol-
vent. Therefore, we evoked of improving the method by
carrying out the reaction under solvent‐free neat condi-
tion, which is a new move in organic synthesis in recent
9
4% in CH and 97% in MW) than water (yield 68% in
CH and 72% in MW) or neat condition (yield 93% in
CH and 95% in MW). These all model reactions were
studied up to the production of maximum yield formation
in their respective reaction time. The same reaction was
performed in an oil bath (CH), the reaction proceed
lethargically and required 3 to 4 hours to completion of
the reaction, whereas in MW, heating method takes
3
minute to obtain the resulting products. In contrast,
various metal triflates were also screened to study the
in‐depth optimization condition (Table 2, entries 4‐9).
Following the pioneering works on metal triflates for
TABLE 2 Effect of different metal triflates and solvents for the
synthesis of dihydropyrimidinones (DHPM)
[
21]
times.
But no significant variations in yield percentage
were observed including the reaction time differed, as
compared with acetonitrile solvent‐mediated reactions.
Equipped with these encouraging preliminary results,
we explored the various prospects of improving the
method further by execute the reaction under solvent‐free
neat condition under microwave irradiation in a micro-
wave reactor. Here also, we observed that there is com-
pelling improvement in yield percentage as well as
DHPM were obtained within a short span of time
ac
Yield, (%)
Catalyst, Solvents,
Entry mmol mL
Time,
CH min
Time,
MW min
b
c
1
2
3
4
5
6
7
8
9
AgOTf
AgOTf
AgOTf
Bi (OTf)
CH
3
CN
94
68
93
182
240
45
97
72
95
90
88
81
83
94
87
3
10
5
2
H O
Neat
(
3 minutes) regardless of the nature of aldehydes. The
3
CH
CH
CH
CH
CH
3
3
3
3
3
CN[14d] 82
CN[14c] 83
CN[14c] 74
CN[14c] 77
CN[12j] 90
60
10
5
reaction takes place more efficiently in solvent‐free condi-
tion than those in solvents, since the catalysts or reagents
are organized more firmly when solvents were not used.
Under all these optimized condition, the substrates
consist of electron‐withdrawing or electron‐donating
groups on aromatic ring of aldehydes were well tolerated
in the reaction, affording the corresponding DHPM
adducts (4aa–4at) to give good to excellent yields (83%‐
97%). Hence, a series of functional groups on aromatic
aldehydes including methyl, methoxy, hydoxy, and
benzyloxy moieties were also well tolerated in this
reaction. Notably, aldehydes‐containing halogens as func-
tional groups on the aromatic ring are also compatible
Yb (OTf)
La (OTf)
Sc (OTf)
Cu (OTf)
In (OTf)
3
20
3
20
5
3
20
5
2
60
10
20
3
Ethanol[14e] 81
780
Note. Reaction conditions: acetyl acetone 1a (1 mmol), urea 2a (1.2 mmol), 2‐
hydroxybenzaldehyde 3a (1 mmol); catalysts (20 mmol); solvent 5 mL.
Abbreviations: CH, conventional heating; MW, microwave.
a
Isolated yield.
b
In conventional heating.
c
In microwave irradiation.

4
ROY ET AL.
TABLE 3 Synthesis of functionalized dihydropyrimidinones using silver trifluoromethanesulfonate as reusable catalyst
a
Yield
Acetonitrile
Water
Neat (Δ)
Microwave
EAA or
U or
Product
Code (4) min
Time, Yield, Time, Yield, Time, Yield, Time, Yield,
1
2
Entry AA (R ) T (X) RCHO (R )
%
min
%
min
%
min
%
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
AA
U
T
2‐(OH)‐C
3‐(OH)‐C
6
6
H
H
4
4
4aa
4bb
4ac
4ad
4ae
4af
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
94
93
94
91
87
88
82
85
86
83
80
91
92
90
87
85
81
84
80
82
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
240
68
69
70
65
63
65
60
62
65
64
61
66
64
61
60
59
61
60
57
61
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
45
93
91
93
90
88
90
81
87
89
85
82
87
88
86
85
82
83
82
81
83
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
97
96
97
93
90
91
86
89
90
87
85
95
96
91
90
87
86
85
83
85
AA
AA
U
U
U
U
T
4‐CH
4‐OH‐3‐CH
4‐(F)‐C
2,4‐(Cl)‐C
4‐(Br)‐C
4‐(benzyloxy)‐C
4‐(thiophenyl)‐C
4‐(pyridinyl)‐C
3
O‐C
6
H
4
AA
3
6 3
O‐C H
AA
6 4
H
AA
6 3
H
AA
6
H
4
4be
4ah
4ai
AA
U
U
U
U
U
U
T
6 4
H
AA
6
H
4
0
1
2
3
4
5
6
7
8
9
0
AA
6
H
4
4aj
AA
1H‐indolyl‐C
6
H
4
4ak
4al
EAA
EAA
EAA
EAA
EAA
EAA
EAA
EAA
EAA
3‐(OH)C
4‐(OH)C
4‐(OH)C
6
6
6
H
H
H
4
4
4am
4bn
4ao
4bp
4bq
4ar
4bs
4at
4
U
T
4‐CH
3
3
O‐C
O‐C
6
6
H
4
4
4‐CH
H
T
3 6 3
4‐OH‐3‐CH O‐C H
U
T
2,4‐(Cl)‐C
2,4‐(Cl)‐C
6
6
H
H
3
3
U
4‐(Br)‐C
6
H
4
180
3
1
2
Note. Reaction conditions: acetyl acetone (AA) or ethylacetoacetate (EAA) R (1 mmol), urea (U) or thiourea (T) X (1.2 mmol) with aldehydes R (1 mmol) and
3
Silver trifluoromethanesulfonate (0.20 mmol at 80°C Temperature; acetonitrile 5 mL; water 5 mL; time: 3 h in CH CN, 4 h in water, 45 min in neat (conven-
3
tional heating [CH]), and 3 min in CH CN (microwave [MW]).
a
Isolated yield.
under standard reaction conditions, producing the
desired products (Table 3, entries 1‐8). Moreover, it was
fascinating to identify that excellent amount of conver-
sion of dihydropyrimidine was observed when we used
heterocyclic aldehydes in the optimized reaction condi-
tion (Table 3, entries 9‐11). Additionally, by changing
the 1,3‐diketone source acetyl acetone by ethyl
acetoacetate and allowing to react with urea or thiourea
and utilized again for the transformation. Yield of the
obtained product was found to be similar to the reaction
did in water or acetonitrile. Since the silver
trifluoromethanesulfonate is soluble in water and some
−
organic solvents, even though CF SO3 is an extremely
3
stable anion. Due to strong solvation ability of the densely
occupied used solvents with the catalyst, here, silver
triflate incorporated with the reactants to results excellent
catalytic performance to afford desired products. Inclu-
sion of that, in water medium, triflates act as more acidic
by nature since triflate anion is an outstanding leaving
group. Conversely, in gas phase or other organic solvent
(
Table 3, entries 12‐20), the desired dihydropyrimidine
products were found in good to excellent yields by up to
3% to 96%. After separation of the precipitate obtained
8
on addition of ice cold water to the reaction mixture,
the water phase with the catalyst was distilled to dryness
[
22]
medium also, it serves as acidic in nature.

ROY ET AL.
5
As reusability of the catalyst after the completion of
the catalyst is stable and sustains for such catalytic
conditions.
the reaction are the main advantages of reactions. Since
triflates are active in accord with many Lewis bases hav-
ing oxygen, nitrogen, sulfur, etc. Thus, in common
organic solvents along with water, the triflate catalysts
can be recovered from the aqueous phase and reused
Since we have carried out many conventionally
heating and microwave‐assisted reactions under different
environments, so the energy consumed by the reactions
[24]
was calculated as we mentioned in our earlier report.
[23]
without attenuated activity.
So, we opted to improve
Herein, when the reaction reached its respective yield,
we examined the energy consumptions as well as energy
efficiency by the aforesaid reaction (Scheme 2). Appar-
ently, it has been observed that for this reaction, the
microwave‐irradiated method is far more energy efficient
and preferable than conventional heating method.
The most possible mechanism of the reaction is
depicted in Scheme 3. As described in the pathway, we
proposed that the reaction proceeds via the formation of
the N‐acylimine formed from aldehyde and urea (or
thiourea). The coordination of the lone pair of the nitro-
gen atom in the N‐acylimine with the salt (silver
trifluoromethanesulfonate) could lead to the in situ for-
mation of an N‐carbamoyliminium ion I. This possibly
a simple synthetic pathway, which allows to reuse
the catalyst for numerous time. Since the yield
getting after separation of the product by filtration is
relatively lower when water was used over acetonitrile
as solvents, the recovered solvent containing silver
trifluoromethanesulfonate was reused up to seven times
without any significant loss of catalytic activity
(
Table 4). Under the neat condition, recyclability of the
catalyst was not tested. But here in microwave mediated
reaction, we are using acetonitrile as solvent to reuse of
catalyst. These results clearly indicate the potent nature
and stability of the catalyst by maintaining the activity.
In this view of sustainable research, we studied the
change of size and morphology of the reused catalyst by
transmission electron microscopy (TEM) (Figure 1). From
Figure 1, we observed that the catalysts consist of
spherical particles with well distribution. Comparing
TEM images of fresh silver trifluoromethanesulfonate
formed a complex with silver trifluoromethanesulfonate
−
ion along with NO
one.
anion similar to the reported
3
[
25]
N‐carbamoyliminium ion I is sufficiently electro-
philic in the complex to react with the enol form of β‐
−
dicarbonyl II promoted by the NO3 ions. Thus, I and
(Figure 1A‐C) with TEM images of the catalyst after mul-
II afford an open chain intermediate III, which on
tiple reuses (Figure 1D‐F), there was no apparent change
in respect to size and morphology of the recovered
catalyst. With this type of alluring, results revealed that
further intra‐molecular cyclization, with loss of H O,
produces 3,4‐dihydropyrimidine‐2(1H)‐one (or 3,4‐
dihydropyrimidine‐2(1H)‐thione) IV.
2
TABLE 4 Reusabilty study on silver trifluoromethanesulfonate as catalyst for the synthesis of dihydropyrimidinones
a
Yield
Acetonitrile
Time, min
Water
Microwave
Time, min
Number
of cycles
Yield, %
Time, min
Yield, %
Yield, %
1
2
3
4
5
6
7
st run
nd run
rd run
th run
th run
th run
th run
180
180
180
180
180
180
180
94
94
93
92
91
90
85
240
240
240
240
240
240
240
68
68
67
65
65
63
63
3
3
3
3
3
3
3
97
95
94
94
91
90
87
Note. Reaction conditions: acetyl acetone 1a (1 mmol), urea 2a (1.2 mmol), 2‐hydroxybenzaldehyde 3a (1 mmol); acetonitrile 5 mL, water 5 mL; time: 3 h in
CH CN, 4 h in water for conventional heating (CH), and 3 min for microwave (MW) using CH CN.
3 3
a
Isolated yield.

6
ROY ET AL.
FIGURE 1 A to C, Transmission electron microscopy (TEM) images of fresh silver trifluoromethanesulfonate; D to F, TEM images of
reused silver trifluoromethanesulfonate after 7th run [Color figure can be viewed at wileyonlinelibrary.com]
SCHEME 2 Energy efficiency of the
reaction by microwave (MW) and
conventional heating (CH) methods
for three‐component condensation of substituted alde-
hydes, acetylacetone, or ethylacetoacetate with urea or
thiourea to produce 3,4‐dihydropyrimidine‐2(1H)‐one
and 3,4‐dihydropyrimidine‐2(1H)‐thione using silver
trifluoromethanesulfonate as reusable catalyst (seven
times) with or without microwave irradiation. The high
level of diversity is achievable in terms of employing dif-
ferent catalytic environments in one‐pot multicomponent
protocol without doing column chromatography. Thus,
with various salient features, this method provides much
improved and efficient alternative route to the existing
Biginelli methods for the synthesis of dihydropyrimidine
derivatives.
SCHEME
3
Plausible mechanism for the synthesis of
SO Ag
4
| EXPERIMENTAL SECTION
dihydropyrimidinones (DHPM) derivatives using CF
3
3
3
| CONCLUSIONS
All chemicals were purchased from commercially avail-
able sources and were used without further purification.
1
13
From our experiments, we have demonstrated a simple,
mild, economic, and environmental friendly protocol
H NMR spectra were recorded at 500 MHz, and
C
NMR spectra were 125 MHz in CDCl and/or DMSO‐d
3
6

ROY ET AL.
7
using tetramethylsilane (TMS, δ = 0.000 ppm) as an inter-
nal standard with Bruker Avance DPX. All chemical
shifts (δ) are reported in ppm and coupling constant (J)
in Hz. IR spectra were obtained from Elmer FT‐IR‐2000
spectrometer either on a thin film using chloroform or
by potassium bromide pellets. Mass spectra data were
recorded on Trace DSQ GC‐MS instrument. All
microwave‐irradiated experiments were carried out on a
Prolabo Synthwave Microwave reactor 402 in quartz reac-
tion vessels. In conventional heating method, reactions
were performed in Remi Magnetic Stirrers with Hotplate,
was reused for the next reaction after evaporated to the
dryness.
4
.1.3 | Procedure for solvent‐free synthe-
sis of 3,4‐dihydropyrimidine‐2(1H)‐one and
,4‐dihydropyrimidine‐2(1H)‐thione
3
A 10‐mL RB flask along with a magnetic stirring bar was
charged with aldehyde (1 mmol), acetyl acetone or ethyl
acetoacetate (1 mmol) and urea or thiourea (1.2 mmol)
with silver trifluoromethanesulfonate (0.20 mmol). The
flask was dipped in preheated oil bath at 80°C (bath tem-
perature). The contents were stirred till the solution mix-
ture turned to solid mass. Ice cold water (10 mL) was
added, and mixture was swirled with a glass rod. Thereaf-
ter, the solid product was separated by filtration, washed
with ice‐cold water (2 × 5 mL), and dried. The crude
product was purified by recrystallization from ethanol.
2
MLH. Melting points were determined in open capillary
tubes with a Buchi‐540 micro melting point apparatus.
TLC experiments were performed using pre‐coated Silica
gel 60 F254 sheets (Merck). Aqueous mother liquor was
concentrated using HETO lyophilizer working at −54°C
and 10 to 38 milibar pressure. High‐resolution transmis-
sion electron microscopy (HRTEM) was recorded on an
electron microscope JEM‐2100, 200 kV, JEOL.
4
.1.4 | Procedure for synthesis of
4
4
.1 | Experimental details
3,4‐dihydropyrimidine‐2(1H)‐one and
3
,4‐dihydropyrimidine‐2(1H)‐thione under
.1.1 | General experimental procedures
microwave irradiation
Syntheses of 3,4‐dihydropyrimidine‐2(1H)‐one and 3,4‐
dihydropyrimidine‐2(1H)‐thione (DHPM) were carried
out in four different conditions. Initially, the reaction
was carried out using acetonitrile as solvent. Then, the
process was extended using water as well as under
solvent‐free neat conditions under heating and micro-
wave irradiation using microwave reactor. While the
reaction was carried out using solvent such as water,
the solvent was reused after separating the product by fil-
tration. In case of second and subsequent runs, no extra
amount of catalyst were used.
In a typical reaction, a mixture of 1 mmol of an aldehyde,
1.2 mmol of thiourea (or urea), and 1 mmol of
acetylacetone (or ethyl acetoacetate) was mixed thor-
oughly with 0.20 mmol of silver trifluoromethanesulfonate
and acetonitrile (5 mL) in a quartz reaction vessel of
Prolabo Synthwave Microwave reactor 402 and allowed
to react under microwave irradiation at a temperature of
80°C for 3 minutes in 35 W. During the reaction, the tem-
perature was not allowed to rise above 80°C by setting the
programmer. Then, ice cold water was added to the reac-
tion mixture, and precipitated solid was separated by filtra-
tion, washed with ice‐cold water (2 × 5 mL), and then
recrystallized from ethanol to get 3,4‐dihydropyrimidine‐
2(1H)‐one and 3,4‐dihydropyrimidine‐2(1H)‐thione. The
solvent containing the catalyst was lyophilized to remove
the solvents, and resulting substance was reused further
for catalysis.
4
3
3
.1.2 | Procedure for synthesis of
,4‐dihydropyrimidine‐2(1H)‐one and
,4‐dihydropyrimidine‐2(1H)‐thione in ace-
tonitrile or water
Aldehydes (1 mmol), acetyl acetone or ethyl acetoacetate
5‐acetyl‐4‐(2‐hydroxyphenyl)‐6‐methyl‐3,4‐
dihydropyrimidin‐2(1H)‐one (4aa)
(1 mmol) and urea or thiourea (1.2 mmol) with silver
trifluoromethanesulfonate (0.20 mmol) were mixed with
acetonitrile or water (5 mL) in a 25‐mL round bottom
Using the general experimental procedure to afford 4aa as
white solid, (239 mg, 97% yield), M. P.: 208°C, H NMR
1
(
RB) flask and refluxed for appropriate time. The reaction
(DMSO, 500 MHz): δ 7.18 (s, 1H), 7.51 (s, 1H), 6.90‐6.88
(m, 2H), 5.70 (d, 1H, J = 3.0 Hz), 2.28 (s, 3H), 1.69
mixture was cooled in ice, and the precipitated solid was
filtered through a sintered funnel. The crude product
was further purified by recrystallization from ethanol to
afford pure 3,4‐dihydropyrimidine‐2(1H)‐one and 3,4‐
dihydropyrimidine‐2(1H)‐thione. The filtrate obtained
13
(s, 3H); C NMR (DMSO, 125 MHz): 203.11, 154.69,
150.76, 129.66, 128.84, 125.98, 120.22, 116.47, 83.22,
−
1
49.74, 28.90, 23.51; FT‐IR (KBR, cm ): 3247, 3003,
+
2939, 1706, 1695, 1441, 1239, 902; MS (m/z): 246.1 [M ].

8
ROY ET AL.
5
‐acetyl‐4‐(3‐hydroxyphenyl)‐6‐methyl‐3,4‐
(DMSO, 500 MHz) δ 9.30 (s, 1H), 8.30 (s, 1H), 7.78 (q,
1H, J = 15 Hz), 7.25‐7.41 (m, 3H), 5.62 (d, 1H,
dihydropyrimidin‐2(1H)‐one (4bb)
Using the general experimental procedure to afford 4bb as
white solid, (254 mg, 96% yield), M. P.: 211°C, H NMR
13
J = 3.5 Hz), 2.33 (s, 3H), 2.08 (s, 3H); C NMR (DMSO,
125 MHz): 194.54, 152.06, 149.72, 140.72, 133.49, 133.43,
130.58, 129.62, 128.65, 109.06, 51.82, 30.93, 19.18; FT‐IR
1
(DMSO, 500 MHz): δ 8.88 (s, 1H), 8.41 (s, 1H), 7.41
−
1
(t, 3H, J = 10 Hz, 10 Hz), 6.76 (t, 1H, J = 7 Hz, 5 Hz),
(KBR, cm ): 3429, 1712, 1668, 1620, 1466, 1384, 1230,
13
+
5
.30 (d, 1H, J = 2.5 Hz), 2.35 (s, 3H), 2.09 (s, 3H);
C
1102, 1046, 825; MS (m/z): 302.0 [M ].
NMR (DMSO, 125 MHz): 195.23, 157.52, 152.31, 146.97,
1
3
1
44.78, 129.62, 117.46, 115.00, 113.61, 109.38, 55.49,
5‐acetyl‐4‐(4‐bromophenyl)‐6‐methyl‐3,4‐
dihydropyrimidin‐2(1H)‐one (4ag)
Using the general experimental procedure to afford 4ag as
−
1
0.00, 19.35; FT‐IR (KBR, cm ): 3243, 3103, 2931, 1708,
+
664, 1456, 1241, 768; MS (m/z): 262.1 [M ].
1
white solid, (266 mg, 86% yield), M. P.: 216°C, H NMR
5
‐acetyl‐4‐(4‐methoxyphenyl)‐6‐methyl‐3,4‐
(CDCl , 500 MHz,) δ 8.98 (s, 1H), 7.55 (s, 1H), 7.85 (d,
3
dihydropyrimidin‐2(1H)‐one (4ac)
Using the general experimental procedure to afford 4ac as
yellow solid, (253 mg, 97% yield), M. P.: 171°C, H NMR
1H, J = 10 Hz), 7.04 (d, 1H, J = 10 Hz), 5.85 (d, 1H,
J = 5 Hz), 2.44 (s, 3H), 2.21 (s, 3H); C NMR (CDCl3,
13
1
125 MHz): 196.54, 164.70, 154.77, 149.88, 138.99, 129.54,
−
1
(DMSO, 500 MHz): δ 9.90 (s, 1H), 7.83 (s, 1H),7.21(d,
116.42, 111.86, 55.32, 31.29, 18.62; FT‐IR (KBR, cm ):
2
3
1
1
H, J = 6.0 Hz), 6.85 (d, 2H, J = 6.0 Hz), 5.39 (s, 1H),
3289, 1718, 1622, 1599, 1512, 1349, 1207, 1124, 809; MS
(m/z): 308.0 [M ].
13
+
.78 (s, 3H), 2.34 (s, 3H), 2.11 (s, 3H),; C NMR (DMSO,
25 MHz): 195.47, 159.52, 153.42, 145.57, 135.25, 127.90,
14.39, 110.69, 55.24, 55.29, 30.74, 19.59; FT‐IR (KBR,
5‐acetyl‐4‐(4‐(benzyloxy)phenyl)‐6‐methyl‐3,4‐
dihydropyrimidin‐2(1H)‐one (4ah)
−
1
cm ): 3306, 1698, 1614, 1466, 1364, 1235, 1178, 832; MS
+
(
m/z): 260.88 [M ].
‐acetyl‐4‐(4‐hydroxy‐3‐methoxyphenyl)‐6‐methyl‐3,4‐
Using the general experimental procedure to afford 4ah
1
as white solid, (294 mg, 89% yield), M. P.: 221°C, H
5
NMR (DMSO, 500 MHz): δ 9.08 (s, 1H), 7.76 (s, 1H),
6.91‐7.40 (m, 4H), 5.19 (d, 1H, J = 5 Hz), 2.25 (s, 3H),
dihydropyrimidin‐2(1H)‐one (4ad)
Using the general experimental procedure to afford 4ad
as yellow solid, (258 mg, 93% yield), M. P.: 215°C, H
NMR (DMSO, 500 MHz): δ 9.11 (s, 1H), 8.96 (s, 1H),
13
2.06 (s, 3H); C NMR (DMSO, 125 MHz): 196.04,
158.21, 152.93,148.82, 137.54, 136.89, 129.15,128.56,
128.26, 115.44, 110.46, 69.81, 53.83, 30.74, 19.44; FT‐IR
1
−
1
7
5
.70 (q, 1H), 6.85 (d, 2H, J = 2 Hz), 6.58–6.71 (m, 1H),
.16 (d, 1H), 3.73 (s, 3H), 2.27 (s, 3H), 2.06 (s, 3H);
(KBR, cm ): 3295, 1699, 1608, 1509, 1453, 1383, 1236,
13
+
C
1173, 830; MS (m/z): 329.1 [M ].
NMR (CDCl3 and DMSO, 125 MHz): 195.29, 152.75,
1
1
3
48.46, 148.12, 146.55, 135.70, 119.08, 115.93, 111.82,
09.88, 56.69, 54.36, 30.71, 19.19; FT‐IR (KBR, cm ):
5‐acetyl‐6‐methyl‐4‐(thiophen‐2‐yl)‐3,4‐
dihydropyrimidin‐2(1H)‐one (4ai)
Using the general experimental procedure to afford 4ai as
−
1
388, 1659, 1555, 1425, 1119, 1022, 729; MS (m/z): 276.0
+
1
[
M ].
brown solid, (213 mg, 90% yield), M. P.: 212°C, H NMR
(
CDCl , 500 MHz): δ 7.48 (s, 1H), 7.20 (s, 1H), 7.09 (s,
3
5
‐acetyl‐4‐(4‐fluorophenyl)‐6‐methyl‐3,4‐
1H), 6.45 (s, 1H),, 6.44 (d, 1H, J = 5.0 Hz), 5.43 (d, 1H,
13
dihydropyrimidin‐2(1H)‐one (4be)
Using the general experimental procedure to afford 4be as
white solid, (224 mg, 90% yield), M. P.: 220°C, H NMR
J = 2.5 Hz), 2.37 (s, 3H), 2.30 (s, 3H); C NMR (CDCl3,
125 MHz): 194.90, 147.79, 145.57, 137.28, 123.96, 117.35,
111.96, 119.41, 105.59, 48.10, 30.49, 25.13; FT‐IR (KBR,
1
−
1
(CDCl , 500 MHz,) δ 8.86 (s, 1H), 7.42 (s, 1H), 7.32 (d,
cm ): 3268, 1788, 1674, 1588, 1322, 1177, 899; MS
3
+
1
H, J = 3.0 Hz), 6.94 (d, 1H, J = 10 Hz), 5.40 (d, 1H,
(m/z): 236.1 [M ].
13
J = 3 Hz), 2.31 (s, 3H), 2.10 (s, 3H); C NMR (CDCl3,
1
1
3
25 MHz): 195.04, 163.72, 152.92, 147.26, 139.44, 128.40,
15.30, 110.22, 54.56, 30.27, 19.42; FT‐IR (KBR, cm ):
5‐acetyl‐6‐methyl‐4‐(pyridin‐4‐yl)‐3,4‐
dihydropyrimidin‐2(1H)‐one (4aj)
Using the general experimental procedure to afford 4aj as
−
1
294, 1708, 1677, 1614, 1509, 1331, 1236, 1157, 839; MS
+
(
m/z): 248.0 [M ].
yellow solid, (202 mg, 87% yield), M. P.: greater than
1
3
00°C, H NMR (CDCl and DMSO, 500 MHz): δ 9.50
3
5
‐acetyl‐4‐(2,4‐dichlorophenyl)‐6‐methyl‐3,4‐
(s, 1H), 8.97 (s, 1H), 6.67‐6.88 (m, 1H), 5.31 (s, 1H), 2.37
(s, 3H), 2.10 (s, 3H); C NMR (CDCl3 and DMSO,
13
dihydropyrimidin‐2(1H)‐one (4af)
Using the general experimental procedure to afford 4af as
white solid, (275 mg, 91% yield), M. P.: 225°C, H NMR
125 MHz): 195.67, 147.32, 146.02, 133.69, 119.27, 115.06,
110.33, 55.66, 29.86, 18.59; FT‐IR (KBR, cm ): 3293,
1
−1

ROY ET AL.
9
3
183, 2990, 1630, 1583, 1449, 1367, 1274, 1191, 949; MS
ethyl
4‐(4‐methoxyphenyl)‐6‐methyl‐2‐oxo‐1,2,3,4‐
+
(
m/z): 231.1 [M ].
tetrahydropyrimidine‐5‐carboxylate (4ao)
Using the general experimental procedure to afford 4ao
1
5
‐acetyl‐4‐(1H‐indol‐3‐yl)‐6‐methyl‐3,4‐
as white solid, (262 mg, 90% yield), M. P.: 208°C, H
dihydropyrimidin‐2(1H)‐one (4ak)
NMR (CDCl and DMSO, 500 MHz): δ 7.49 (s, 1H), 7.24
3
Using the general experimental procedure to afford 4ak
as white solid, (228 mg, 85% yield), M. P.: 222°C, H
(s, 1H), 7.23 (d, 1H, J = 5 Hz), 6.83 (d, 1H, J = 10 Hz),
5.35 (d, 1H, J = 15 Hz), 4.07 (q, 2H, J = 7.5 Hz), 3.78 (s,
3H), 2.34 (s, 3H), 1.17 (t, 3H, J = 5 Hz); C NMR (CDCl
3
1
13
NMR (CDCl , 500 MHz): δ 9.83 (s, 1H), 8.31 (s, 1H),
3
7
7
.56 (d, 1H, J = 10 Hz), 7.35 (d, 1H, J = 10 Hz), 6.88‐
and DMSO, 125 MHz): 165.55, 159.14, 152.67, 145.48,
135.90, 127.72, 113.87, 101.69, 59.96, 55.17, 18.73, 14.06;
FT‐IR (KBR, cm ): 3230, 3121, 1722, 1628, 1543, 1380,
1230, 1040, 799; MS (m/z): 290.1 [M+].
13
.12 (m, 2H), 4.21 (s, 1H), 2.48 (s, 3H), 2.22 (s, 3H);
C
−
1
NMR (CDCl , 125 MHz): 206.42, 157.57, 151.52, 136.33,
3
1
1
1
27.43, 122.41, 122.11, 121.76, 119.11, 119.03, 115.52,
−
1
10.94, 32.11, 22.20, 18.74; FT‐IR (KBR, cm ): 3400,
+
608, 1439, 1239, 1015, 745; MS (m/z): 269.1 [M ].
ethyl
4‐(4‐methoxyphenyl)‐6‐methyl‐2‐thioxo‐1,2,3,4‐
tetrahydropyrimidine‐5‐carboxylate (4bp)
ethyl
4‐(3‐hydroxyphenyl)‐6‐methyl‐2‐oxo‐1,2,3,4‐
Using the general experimental procedure to afford 4bp
as white solid, (2767 mg, 87% yield), M. P.: 218°C, H
1
tetrahydropyrimidine‐5‐carboxylate (4al)
Using the general experimental procedure to afford 4al as
white solid, (263 mg, 95% yield), M. P.: 166°C, H NMR
NMR (CDCl and DMSO, 500 MHz): δ 9.57 (s, 1H),
3
1
8.88 (s, 1H), 7.49 (d, 1H, J = 5 Hz), 6.81 (d, 1H,
J = 10 Hz), 5.29 (d, 1H, J = 3 Hz), 4.07 (q, 2H,
J = 7.5 Hz), 3.82 (s, 3H), 2.92 (s, 3H), 1.18 (t, 3H,
(
CDCl and DMSO, 500 MHz): δ 8.87 (s, 1H), 8.62 (s,
3
1
5
3
1
1
H), 7.09 (d, 1H, J = 10 Hz), 6.88 (d, 1H, J = 10 Hz),
13
.28 (d, 1H, J = 3 Hz), 4.07 (q, 2H, J = 4 Hz), 2.33 (s,
J = 5 Hz); C NMR (CDCl and DMSO, 125 MHz):
3
13
H), 1.19 (t, 3H, J = 5 Hz); C NMR (CDCl and DMSO,
179.11, 170.36, 163.71, 148.90, 140.57, 132.76, 118.41,
3
25 MHz): 165.71, 157.26, 152.68, 152.27, 146.73, 129.31,
106.63, 64.55, 59.86, 59.26, 22.45, 18.78; FT‐IR (KBR,
−
1
17.52, 114.80, 113.56, 55.19, 18.43, 14.01; FT‐IR (KBR,
cm ): 3246, 3115, 1706, 1652, 1514, 1384, 1225, 1089,
−
1
cm ): 3245, 1725, 1643, 1454, 1221, 1091, 777; MS
791; MS (m/z): 306.0 [M+].
+
(
m/z): 276.0 [M ].
ethyl 4‐(4‐hydroxy‐3‐methoxyphenyl)‐6‐methyl‐2‐oxo‐
1,2,3,4‐tetrahydropyrimidine‐5‐carboxylate (4bq)
Using the general experimental procedure to afford 4bq
as yellow solid, (278 mg, 86% yield), M. P.: 238°C, H
NMR (CDCl and DMSO, 500 MHz): δ 9.43 (s, 1H), 8.74
3
ethyl 4‐(4‐hydroxyphenyl)‐6‐methyl‐2‐oxo‐1,2,3,4‐
tetrahydropyrimidine‐5‐carboxylate (4am)
1
Using the general experimental procedure to afford 4am
1
as white solid, (266 mg, 96% yield), M. P.: 193°C, H
NMR (CDCl and DMSO, 500 MHz): δ 8.80 (s, 1H), 8.58
(s, 1H), 6.82 (d, 1H, J = 8 Hz), 6.74‐6.79 (m, 2H), 5.27
(d, 1H, J = 3 Hz), 4.07 (q, 2H, J = 2.0 Hz), 3.84 (s, 3H),
3
(s, 1H), 7.41 (s, 1H), 7.13 (d, 1H, J = 5 Hz), 6.75 (d, 1H,
13
J = 5 Hz), 5.26 (d, 1H, J = 2.5 Hz), 4.05 (q, 2H,
2.35 (s, 3H), 1.18 (t, 3H, J = 1.5 Hz, 1.5 Hz); C NMR
(CDCl and DMSO, 125 MHz): 184.63, 174.28, 165.58,
146.93, 145.73, 134.83, 119.29, 114.81, 110.00, 102.01,
13
J = 5 Hz), 2.32 (s, 3H), 1.16 (t, 3H, J = 5 Hz, 5 Hz);
C
3
NMR (CDCl3 and DMSO, 125 MHz): 165.74, 156.43,
−
1
1
5
1
53.11, 146.62, 135.22, 127.55, 115.07, 100.76, 59.36,
59.80, 55.70, 54.99, 17.74, 13.96; FT‐IR (KBR, cm ):
−
1
4.38, 18.05, 13.92; FT‐IR (KBR, cm ): 3199, 1709,
3246, 3118, 1698, 1645, 1516, 1453, 1222, 1092, 799; MS
+
+
589, 1470, 1310, 1196, 1047, 813; MS (m/z): 276.1 [M ].
(m/z): 322.1 [M ].
ethyl
4‐(4‐hydroxyphenyl)‐6‐methyl‐2‐thioxo‐1,2,3,4‐
ethyl
4‐(2,4‐dichlorophenyl)‐6‐methyl‐2‐oxo‐1,2,3,4‐
tetrahydropyrimidine‐5‐carboxylate (4bn)
tetrahydropyrimidine‐5‐carboxylate (4ar)
Using the general experimental procedure to afford 4bn
as white solid, (263 mg, 91% yield), M. P.: 195°C, H
Using the general experimental procedure to afford 4ar as
white solid, (280 mg, 85% yield), M. P.: 229°C, H NMR
1
1
NMR (CDCl and DMSO, 500 MHz): δ 8.80 (s, 1H), 8.78
(CDCl and DMSO, 500 MHz): δ 8.98 (s, 1H), 7.10‐7.45
3
3
(
1
s, 1H), 8.58 (s, 1H), 7.13 (d, 1H, J = 10 Hz), 6.75 (d,
H, J = 10.0 Hz), 5.26 (d, 1H, J = 2.5 Hz), 4.05 (q, 2H,
J = 4.0 Hz), 2.32 (s, 3H), 1.16 (t, 3H, J = 5 Hz, 5 Hz);
(m, 2H), 6.10 (d, 1H, J = 10 Hz), 5.72 (d, 1H,
J = 10 Hz), 4.10 (q, 2H, J = 5 Hz), 2.21 (s, 3H), 1.28 (t,
13
3H, J = 1.5 Hz);
C NMR (CDCl and DMSO,
3
1
3
C NMR (CDCl and DMSO, 125 MHz): 174.33, 165.73,
125 MHz): 168.69, 153.54, 150.24, 139.51, 133.71, 130.78,
3
1
5
1
57.00, 143.68, 134.37, 128.12, 115.45, 102.41, 59.94,
128.64, 98.92, 58.74, 52.23, 18.72, 11.95; FT‐IR (KBR,
−
1
−1
4.97, 17.87, 14.10; FT‐IR (KBR, cm ): 3207, 1716,
cm ): 3359, 1750, 1454, 1390, 1219, 1110, 809; MS
+
+
585, 1476, 1315, 1189, 1084, 834; MS (m/z): 291.9 [M ].
(m/z): 328.0 [M ].

10
ROY ET AL.
ethyl 4‐(2,4‐dichlorophenyl)‐6‐methyl‐2‐thioxo‐1,2,3,4‐
tetrahydropyrimidine‐5‐carboxylate (4bs)
[3] G. C. Rovnyak, K. S. Atwal, A. Hedberg, S. D. Kimball, S.
Moreland, J. Z. Gougoutas, B. C. O'Reilly, J. Schwartz, M. F.
Malley, J. Med. Chem. 1992, 35, 3254.
Using the general experimental procedure to afford 4bs as
1
[4] A. D. Patil, N. V. Kumar, W. C. Kokke, M. F. Bean, A. J. Freyer,
C. Debrose, S. Mai, A. Trunch, D. J. Falkner, B. Carte, A. L.
Breen, R. P. Hertzberg, R. K. Johnston, J. W. Westley, B. C.
M. Ports, J. Org. Chem. 1995, 6, 1182.
white solid, (283 mg, 83% yield), M. P.: 236°C, H NMR
(
CDCl and DMSO, 500 MHz): δ 8.66 (s, 1H), 7.19‐7.39
3
(m, 1H), 6.04 (d, 1H, J = 6.0 Hz), 5.79 (d, 1H,
J = 6.0 Hz), 4.01 (q, 2H, J = 4.0 Hz), 2.17 (s, 3H), 1.10
[
[
[
[
5] K. Rana, A. Arora, S. Bansal, R. Chawla, Indian J. Pharm. Sci.
13
(
t, 3H, J = 1.5 Hz); C NMR (CDCl3 and DMSO,
2014, 76, 339.
1
1
25 MHz): 165.19, 152.00, 149.19, 138.95, 132.98, 129.13,
6] A. Ziderman, G. Dubers, A. Zilbere, R. Verpele, J. Uldrikis, K.
Kumasars, Latv. PSR Zinat Akad Vestis. 1971, 75, 77.
27.51, 97.97, 59.65, 51.47, 18.12, 13.85; FT‐IR (KBR,
−
1
cm ): 3361, 1704, 1466, 1384, 1227, 1100, 817; MS
7] K. Kumasars, A. Valena, G. Dubers, J. Uldrikis, A. Ziderman,
Biokhimiya 1971, 36, 1201.
+
(
m/z): 344.8 [M ].
8] a) B. Tozkoparan, H. Akgun, M. Ertan, Y. Sara, N. Ertekin,
Arch. Pharm. 1995, 328, 169; b) K. Cooper, PCT Int Appl
1990, n/a, WO 11281.
ethyl 4‐(4‐bromophenyl)‐6‐methyl‐2‐oxo‐1,2,3,4‐
tetrahydropyrimidine‐5‐carboxylate (4at)
Using the general experimental procedure to afford 4at
[9] N. Y. M. Abdo, Acta Chim. Slov. 2015, 62, 168.
as pale yellow solid, (288 mg, 85% yield), M. P.: 215°C,
[
[
10] a) C. Rami, L. Patel, C. N. Patel, J. P. Parmar, J. Pharm.
Bioallied Sci. 2013, 5, 277; b) M. M. Ghorab, Y. A. Mohamad,
S. A. Mohamad, Y. A. Ammar, Phosph Sulf Silic Relat Elem.
1
H NMR (CDCl and DMSO, 500 MHz): δ 8.75 (s, 1H);
3
7
7
2
5
1
9
3
3
.85 (d, 1H, J = 10 Hz), 7.65 (d, 1H, J = 10 Hz),
.12‐7.40 (m, 1H), 5.81 (d, 1H, J = 3.0 Hz), 4.01 (q,
H, J = 2.0 Hz), 2.44 (s, 3H), 1.06 (t, 3H, J = 3 Hz,
1996, 108, 249.
11] P. Biginelli, Gazz. Chim. Ind. 1893, 23, 360.
13
Hz);
C NMR (CDCl3 and DMSO, 125 MHz):
[12] a) P. Chen, M. Tu, Tetrahedron Lett. 2018, 59, 987; b) N.
Ahmed, J. E. van Lier, Tetrahedron Lett. 2007, 48, 5407; c) H.
Yu, P. Xu, H. He, J. Zhu, H. Lin, S. Han, Tetrahedron: Asymme-
try 2017, 28, 257; d) J. Safari, S. G. Ravandi, New J. Chem. 2014,
65.26, 152.15, 148.88, 141.65, 132.88, 129.12, 122.55,
−
1
8.46, 59.47, 54.25, 17.94, 13.79; FT‐IR (KBR, cm ):
346, 2978, 1693, 1440, 1227, 1097, 744; MS (m/z):
38, 3514; e) H. E. Badaoui, R. Bazi, R. Tahir, H. B. Lazrek, S.
+
38.0 [M ].
Sebti, Cat. Com. 2005, 6, 455; f) M. M. Heravi, F. Derikvand,
F. F. Bamoharram, J. Mol. Cat. A Chemical. 2005, 242, 173; g)
M. Gohain, D. Prajapati, J. S. Sandhu, Synlett 2004, 2, 235; h)
B. C. Ranu, A. Hajra, U. Jana, J. Org. Chem. 2000, 65, 6270; i)
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ACKNOWLEDGMENTS
We would like to thank CSIR New Delhi, India for pro-
viding financial support for conducting this research
work under the grant of CSC‐0130 and OLP‐2020 project.
Also, we would like to offer our sincere thanks to the
Director, CSIR‐North East Institute of Science and Tech-
nology, Jorhat, Assam for providing all the needed
facilities.
2018, 1160, 161; o) S. K. Dey, R. A. Gibbs, Synthesis 2005, 11,
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ORCID
Synlett 2018, 29, 1047; q) D. Ding, C. G. Zhao, Eur. J. Org.
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Kashyap Jyoti Tamuli
644
Manobjyoti Bordoloi
824
https://orcid.org/0000-0002-3110-
https://orcid.org/0000-0003-0478-
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Bordoloi M. Exploiting silver
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