One-pot facile and mild construction of densely functionalized pyrimidines in water via consecutive C-C and C-S bonds formation

Article abstract of DOI:10.1039/C8RA04363A

Fused pyrimidines composed of alternating heteroatoms and a pyrimidine moiety were synthesized efficiently using readily available starting material 4-hydroxycoumarin, aromatic aldehydes, and urea/thiourea at room temperature. Acid, metal salts, and surfactants were screened for their influence on catalytic activity in three-component reactions and sodium lauryl sulphate (SLS) was used as the best catalyst with different concentrations. Screening results of catalyst loading from our investigation showed that good to excellent yields were obtained with 10 mol%. Our method efficiently synthesized heterocycles and avoided the use of hazardous solvents and conventional organic solvents. Our procedure which involves a surfactant is operationally simple, environmentally benign, has excellent yields, short reaction times, and synthetically is as efficient as conventional procedures using organic solvents.

Full text of DOI:10.1039/C8RA04363A

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One-pot facile and mild construction of densely
functionalized pyrimidines in water via consecutive
C–C and C–S bonds formation†
Cite this: RSC Adv., 2018, 8, 33952
ab
Praveen K. Sahu,b Manvendra S. Kaurav,a Mouslim Messali,c
*
Pramod K. Sahu,
Saud M. Almutairi,d Puran L. Sahue and Dau D. Agarwalab
Fused pyrimidines composed of alternating heteroatoms and a pyrimidine moiety were synthesized
efficiently using readily available starting material 4-hydroxycoumarin, aromatic aldehydes, and urea/
thiourea at room temperature. Acid, metal salts, and surfactants were screened for their influence on
catalytic activity in three-component reactions and sodium lauryl sulphate (SLS) was used as the best
catalyst with different concentrations. Screening results of catalyst loading from our investigation
showed that good to excellent yields were obtained with 10 mol%. Our method efficiently synthesized
heterocycles and avoided the use of hazardous solvents and conventional organic solvents. Our
procedure which involves a surfactant is operationally simple, environmentally benign, has excellent
yields, short reaction times, and synthetically is as efficient as conventional procedures using organic
solvents.
Received 22nd May 2018
Accepted 7th September 2018
DOI: 10.1039/c8ra04363a
rsc.li/rsc-advances
Coumarins and their derivatives (Fig. 1A) such as warfarin,
coumatetralyl, and difenacoum are used as anticoagulants
Introduction
whereas phenprocoumon and bromadiolone have antiviral and
potent rodenticide uses, respectively.29 Carbochromen30 is an
effective coronary vasodilator. In organic and medicinal chem-
The multicomponent reactions (MCRs) technique has been
explored for preparation of fused pyrimidines because of their
high efficiency one-pot construction instead of multi-step
synthesis. Worldwide, multicomponent reactions have been
explored as an efficient tool for synthesis of many active drugs.
MRCs offer several advantages such as one-pot rather than
multi steps for a target compound's synthesis and avoids
unnecessary expensive purication, toxic reagents, and
solvents.1–7 Chromenes are a promising class of heterocycles
that have been explored for antioxidant,8,9 anticancer,10–13 anti-
microbial,14–17 hypotensive,18 and local anesthetic activity.19
Apart from these, this class also has been explored for cognitive
enhancers,20,21 Alzheimer's disease,22 and schizophrenia.23
Many plant sources having coumarin derivatives24 also have
been extensively investigated as anticoagulation, antiviral,25
anti-inammatory,26 antibacterial,27 and anticancer agents.28
istry, 3,4-dihydropyrimidin-2(1H)-ones have
a great place
among other promising categories.31 Some drugs such as
monastrol (A),32 trimethoprim (B),33 and lamivudine (C)34 are
types of drugs with a pyrimidine core (Fig. 1B).
Finding an environmentally benign and greener approach
for biologically active heterocyclic derivatives in water is a diffi-
cult task because of the green nature of water35 but, in recent
years, water has been used as a diluent because of environ-
mental consciousness. Sometimes, water could not be used as
reaction medium due to insolubility of substances. But,
Kobayashi et al. discovered surfactants as an option which can
remove these problems36 and that's why some surfactants show
excellent catalytic activity and can be exploited as catalysts.
Considering the signicance of catalytic systems and our
research interests to explore novel synthesis of heterocyclic
derivatives,37 we commenced our study with the synthesis of
fused pyrimidines using a surfactant (SLS) in aqueous micellar
form at room temperature (Scheme 1).
aSchool of Studies in Chemistry, Jiwaji University, Gwalior-474011, Madhya Pradesh,
India. E-mail: sahu.chemistry@gmail.com; researchdata6@gmail.com
bDepartment of Industrial Chemistry, Jiwaji University, Gwalior-474011, Madhya
Pradesh, India
cDepartment of Chemistry, Taibah University, 30002 Al-Madina Al-Mounawara, Saudi
Arabia
Results and discussion
dKing Abdulaziz City for Science and Technology, Riyadh 11442, P. O. Box 6086, Saudi
Arabia
In our initial study, we screened catalysts to nd an efficient one
for a model reaction of benzaldehyde, 4-hydroxy coumarin, and
urea in water at room temperature (Table 1). Due to today's
environmental consciousness, there is a need to develop eco-
eIndian Pharmacopoeia Commission Ministry of Health and Family Welfare, Sector-23,
Raj Nagar, Ghaziabad 201002, India
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c8ra04363a
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Fig. 1 Some drugs with coumarin and pyrimidine cores.
friendly processes for chemical entities. So, we have developed
p-TSA and metal salts did not afford good yields of the
a new system in water. But, organic substances oen have low desired product. An immiscible layer was formed with p-TSA
solubility in water which could be overcome by using surfactant while surfactants that possessed long alkyl chains formed
emulsions with them. Initial screenings showed that SLS ob- colloidal dispersions. However, yield and time to complete
tained an excellent yield (95%) over other surfactants, as shown a reaction was greatly affected by type of surfactant and cata-
in Table 1, entries 6 and 7. The other catalysts used in the lyst's loading. Due to this concern, the reaction underwent
reaction showed poor yields, comparatively (Table 1, entries exploration by altering the amount of catalyst (2, 5, 8, 10, and
8–11).
15 mol%) which afforded poor to excellent yields (33–95%) as
Scheme 1 Synthesis of fused pyrimidines.
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Table 1 Screening of catalystsa
Entry
Catalysts
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
SLS (2 mol%)
SLS (5 mol%)
SLS (8 mol%)
7.0
6.0
5.5
5.0
5.0
5.0
5.0
8.0
9.0
8.0
7.5
33
78
89
95
95
81
78
49
44
41
71
SLS (10 mol%)
SLS (15 mol%)
TBAB (10 mol%)
SDS (10 mol%)
KCl (10 mol%)
Mg(NO3)2 (10 mol%)
p-TSA (10 mol%)
LiBr (10 mol%)
9
10
11
a
Reaction was carried out with 4-hydroxy coumarin (5 mmol), urea (5 mmol), and benzaldehyde (5 mmol) at room temperature in water as solvent.
Isolated yield.
b
listed in Table 1. A signicant result with highest yield was hours duration was suitable for completing the reaction
obtained with 10 mol% which could not be increased further (Fig. 2).
with higher concentrations of catalyst. It can be concluded that
10% catalyst loading most efficiently catalyzed the reaction.
To select an appropriate solvent for the reaction, we turned
our attention to approaches of SLS with a number of solvents
An additional investigation was carried out further to (Table 2). Optimization was undergone in different protic and
evaluate reaction time on the yield. As time increased, yield aprotic solvents. As is shown in Table 2, the largest advance in
was also increased until it became constant aer 5 hours the synthesis was the speed up in water among solvents used
which could not be further increased with increasing the with signicant outcomes which are noted and acknowledged
reaction time. These studies showed that an optimized ve in Table 2, entry 1. Therefore, we have developed a new method
Fig. 2 Relationship between reaction time and yield.
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Table 2 Screening of solvents using SLS as catalysta
hazardous solvent (ACN), and higher temperatures. Many
studies have revealed that exposure to vanadium may cause
respiratory dysfunction,47 hematological and biochemical
alterations, renal toxicity,48 reproductive and developmental
toxicity, immunotoxicity, mutagenicity,49 and neurotoxicity.50 As
seen in Table 3, the present procedure is simpler, more effi-
cient, without the need for toxic solvents, uses low amounts of
the catalyst, and reacts at room temperature. It shows that SLS
is a powerful catalyst for the synthesis of 3,4-dihydro-1H-chro-
meno[4,3-d]pyrimidine-2,5-dione/thione derivatives, suggesting
that the present procedure is a clean and environmentally
friendly method.
On the basis of all aforementioned experimental optimiza-
tions, we took the best reaction conditions in hand with SLS as
catalyst and further explored the utility of the present meth-
odology for substrate scope which used derived benzaldehydes
to afford fused pyrimidines (4). As shown in Table 4, an electron
releasing moiety led to fused pyrimidines in good yield as
compared to ortho- and meta-moieties. With these reaction
conditions in hand, we explored the multicomponent reaction
with methyl derivatives of 4-hydroxycoumarin (4n–4q) and
found smoothness of reaction with good yields, plus there was
no impact of derivatization on 4-hydroxycoumarin on reaction
yield or time.
Entry
Solvents (10 mL)
Time (h)
Yieldb (%)
1
2
3
4
5
6
7
8
H2O
DCM
5.0
10
10
10
10
10
10
10
95
0
0
0
0
0
0
0
MeOH
EtOH
ACN
CHCl3
Toluene
Hexane
a
Reaction was carried out with 4-hydroxy coumarin (5 mmol), urea (5
mmol), and benzaldehyde (5 mmol) in the presence of SLS (10 mol%)
b
at room temperature. Isolated yield.
carried out in water which is free from problems like harsh
conditions and hazardous solvents.
A comparison of reported literature data and the novelty of
the present methodology is provided in Table 3. As shown in
Table 3, there are few reports in the literature for synthesis
of 3,4-dihydro-1H-chromeno[4,3-d]pyrimidine-2,5-dione/thione
derivatives using 4-hydroxycoumarin, aldehydes, and urea/
thiourea using homogeneous or heterogeneous catalysts. In
order to show the merit of the present protocol, SLS catalyst was
compared with other reported protocols for synthesis of
pyrimidines. In contrast with other existing methods, the
present methodology offers several advantages such as excellent
yields, a simple and easy synthetic procedure, simple work-up
rather than tedious methods, water used as a green solvent,
and room temperature conditions. The results clearly show that
researchers have used acids such as HCl38–40,42,43 and chloro
sulphonic acid38,41 which have drawbacks such as longer reac-
tion times,38–40,42 harsh reaction conditions such as microwave
and ultrasonication,39,41,43,44 higher temperatures (60 ꢀC, 110 ꢀC,
and reux), hazardous solvents (MeOH, EtOH, and
ACN),38–40,42–45 and oen have lower yields.40,42–44 Although
ultrasonication technology has been shown to be feasible on
a small scale, the commercialization of sonolysis is still a chal-
lenge due to its high energy requirements which makes ultra-
sonication an uneconomical technique.46 On the other hand,
vanadium chloride has been used as catalyst45 with lower yields,
To further explore the present methodology, we extended our
work with guanidine in place of urea/thiourea in a three
component reaction. But, the present investigation has shown
that this three component reaction could not be carried out
with guanidine. Biscoumarin compound 6 was observed with
poor yield as the target compound instead of targeted
compound 5 (Scheme 2). NMR spectra (1H and 13C) conrmed
the probable structure of compound 6 which is also supported
by literature.51
Catalytic activity of surfactant
Organic substrates have a hydrophobic nature which was solved
by attribution of a micellar solution of surfactant as catalyst
resulting in a form of emulsion droplets in water and substrate.
Spherical droplets, which act as hydrophobic reaction sites and
help to increase the effective accumulation of organic
substrates, are responsible for immediate reactions to afford
Table 3 Comparison of present methodology with other reported catalysts
Entry
Catalyst
Solvent
Conditions
Time (h minꢁ1
)
Yield (%)
Reference
1
2
3
4
5
6
HCl/chloro sulphonic acid
HCl
HCl
Chloro sulphonic acid
HCl
HCl/silica gel/acidic alumina/
montmorillonite-K10 clay
K2CO3
MeOH
EtOH
MeOH
—
EtOH
MeOH
60 ꢀC
8.0 h
12 h
Overnight
30 min
12 h
96
94
59
92
38
39
40
41
42
43
Reux/MWa
Reux
60 ꢀC/USb
Reux
74
110 ꢀC/MWa
4–6 min
60/83/90/85
7
8
8
EtOH/H2O
Acetonitrile
Water
Reux/MWa
Reux
7 h
2 h
4.5 h
53
82
95
44
45
VCl3
Sodium lauryl sulphate
RTc
Present work
a
b
Microwave conditions. Ultrasonication. c Room temperature.
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Table 4 Synthesis of 3,4-dihydro-1H-chromeno[4,3-d]pyrimidine-2,5-dione/thione derivatives using SLS (10 mol%) in watera
a
Reaction was carried out with 4-hydroxycoumarin derivatives (5 mmol), urea/thiourea (5 mmol), and aromatic aldehyde (5 mmol) at room
temperature in water using SLS (10 mol%) as catalyst.
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Scheme 2 Optimization with guanidine.
the target products in a micellar solution. It can be concluded
that a micelle solution induces collision between organic
substrates by pressing them together. This mechanistic
pathway of a surfactant enhances catalytic activity and the
resultant reaction proceeds rapidly and increases the reaction
rate.36,52
Fig. 3 Light microscopic detected micelles (scale bar ¼ 5 mm).
Mechanistic pathway
A plausible mechanism for fused pyrimidines synthesis (4) is
shown in Scheme 4. Initially, 4-hydroxycoumarin (1) and alde-
hyde (2) interacted each other by Knoevenagel condensation to
produce an intermediate which was pursued by Michael addi-
tion of urea/thiourea (3) on the double bond of the intermediate
(A) to form intermediate (B). Furthermore, the carbonyl and
amino corner of the Michael adduct B was condensed through
intramolecular cyclization to give the desired target (4).
Relation between action of SLS and aqueous medium
It is believed that molecules of a surfactant generate stable
colloidal particles which capture the organic substrates and
surfactants attracted to the surface of the particles due to
counter cations. However, substrate-replaced water molecules
readily covered the sodium cation portion of surfactants.53
Equilibrium of a reaction may be shied towards the product
because water molecules, which are generated during a reac-
Conclusion
tion, are easily excluded by the hydrophobic interior and result We have explored a facile construction of biologically signi-
in an increase of reaction yields.54,55 Details of this phenomena cant fused pyrimidine-2,5-dione/thione in water as green
are schematically represented in Scheme 3.
solvent at room temperature. SLS was successfully synthesized
It is noticeable that the reaction mass, which was initially and suitable for use as a micellar catalyst and removed the
oating, was converted to a homogeneous mixture by addition problem of using an organic solvent, thus generating a green
of SLS, which further became a white turbid emulsion result- platform for future synthesis of novel molecules in water. The
ing in colloidal particles. Overall examination showed the protocol for the synthesis of fused pyrimidine-2,5-dione/thione
arrangement of micelles which was conrmed by optical with different aromatic aldehydes over the present catalytic
microscopy (Fig. 3). Literature also suggested our observation system was successfully applied with excellent yields. This
of the formation of spherical particles.52,56–58
method has described for the rst time use of SLS as a catalyst
Scheme 3 Schematic diagram representing the role of SLS.
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Scheme 4 A proposed mechanistic pathway for the synthesis of derivatives (4).
in the transformation of fused pyrimidines-2,5-dione/thione. As
far as reactivity and selectivity are concerned, water as an
inexpensive green solvent also played a vital role. Taking
9 T. Symeonidis, M. Chamilos, J. Hadjipavlou-Litina,
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´
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Typical procedure. A three neck round-bottomed ask was
charged with aldehydes (2 mmol), 4-hydroxy coumarin (2
mmol), and urea/thiourea (2 mmol) in water (10 mL). Catalyst
sodium lauryl sulphate (10 mol%) was charged in the reaction
mixture. Reaction was conducted at RT for a desired period of
time. The reaction was monitored by TLC analysis and
conrmed by spectroscopic analysis.
3276.
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Conflicts of interest
17 R. R. Kumar, S. Perumal, P. Senthilkumar, P. Yogeeswari and
D. Sriramm, Bioorg. Med. Chem. Lett., 2007, 17, 6459.
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There are no conicts to declare.
Acknowledgements
We acknowledgements and humble thanks to Dr P. L. Sahu, IPC
Ghaziabad, India for their valuable suggestion and spectral
analytical data.
20 H. Bedair, A. El-Hady, S. Abd El-Latif, H. Fakery and M. El-
Agrody, Farmaco, 2000, 55, 708.
21 M. M. Heravi, K. Bakhtiari, V. Zadsirjan and F. Bamoharram,
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