One-pot synthesis of 3,4-dihydropyrimidine-2(1H)-thione derivatives using DBU as green and recyclable catalyst

Article abstract of DOI:10.14233/ajchem.2018.21181

A short and simple one-pot synthesis of 3,4-dihydropyrimidine-2(1H)-thione derivatives was accomplished in excellent yields by reaction of aryl ketone, aryl aldehydes and thiourea in aqueous ethanol (50 %) using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a reusable catalyst.

Full text of DOI:10.14233/ajchem.2018.21181

Asian Journal of Chemistry; Vol. 30, No. 6 (2018), 1243-1246
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2018.21181
One-Pot Synthesis of 3,4-Dihydropyrimidine-2(1H)-thione
Derivatives Using DBU as Green and Recyclable Catalyst
*
T. SEKHAR, P. THRIVENI , M. HARIKRISHNA and K. MURALI
Department of Chemistry, Vikrama Simhapuri University, Nellore-524 003, India
*Corresponding author: E-mail: thriveni.vsu1@gmail.com
Received: 12 December 2017; Accepted: 2 January 2018;
Published online: 30 April 2018;
AJC-18873
A short and simple one-pot synthesis of 3,4-dihydropyrimidine-2(1H)-thione derivatives was accomplished in excellent yields by reaction
of aryl ketone, aryl aldehydes and thiourea in aqueous ethanol (50 %) using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a reusable
catalyst.
Keywords: Green synthesis, 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), Pyrimidine-2(1H)-thione, Multicomponent synthesis.
resources and reusable catalysts. Herein, we report a novel one-
pot synthesis of dihydropyrimidine-2(1H)-thiones from the
three component condensation of aldehyde, ketone, thiourea
in aqueous ethanol (50 %) using 1,8-diazabicyclo[5.4.0]undec-
7-ene (DBU) as a green and recyclable catalyst.
INTRODUCTION
Pyrimidine compounds till now been synthesized mainly
because of their wide range of pharmacological and biological
properties. These compounds have reported important appli-
cations in medicinal chemistry. Pyrimidine derivatives have
found applications such as antimicrobial [1], antitumor [2]
and antifungal [3]. In addition, pyrimidine compounds have
been considered to be significant for drugs and agricultural
intermediates [4]. This kind of important application of pyri-
midines encouraged the present synthesis of some pyrimidine
derivatives.
Various methods have been reported for the synthesis of
dihydropyrimidine-2(1H)-thione derivatives by cyclization of
chalcones with thiourea in the presence of ionic liquid [5],
potassium hydroxide in ethanol [6-10], potassium tert-butoxide
or sodium ethoxide in absolute ethanol [12]. It is also repor-
ted by reaction of 1,3-diphenyl-3-(phenylsulfonyl)propan-1-
one with thiourea in presence of potassium hydroxide [13].
Pyrimidine derivatives can also be prepared by the reaction of
certain aryl ketone, aryl aldehyde with thiourea in the presence
of sodium tert-butoxide in ethanol [14], 1-methylimidazolium
hydrogen sulfate [15], triphenyl phosphine [16] and neutral
alumina [17]. The main disadvantages of all these methods
are longer reaction times, tedious work up procedures. Some
of the catalysts are highly expensive and after workup cannot
be recovered and reused. These inadequacies surely show the
need for a safe, ecofriendly and efficient method to synthesize
these compounds. Recently the path of science and technology
has been shifting more towards environmental, natural product
EXPERIMENTAL
All the chemicals were purchased from Merck and Sigma
Aldrich. All the reactions were performed and monitored by
thin-layer chromatography (TLC) on Merck silica gel 60 F254
pre-coated plates (0.25 mm) and visualized by UV fluorescence
lamp. IR spectra were recorded on PerkinElmer 683(FT)-IR
spectrometer with KBr pellets. 1H and13C NMR spectra in dimethyl
sulfoxide (DMSO-d6) as solvent were recorded on Bruker 400
MHz and 100 MHz with tetramethylsilane (TMS) as internal
standard.
Synthesis of 3,4-dihydropyrimidine-2(1H)-thione deri-
vatives: Aryl ketone (1) (8 mmol), aryl aldehyde (2) (8 mmol)
and thiourea (3) (8 mmol) in 15ml of aqueous ethanol (50 %)
were mixed in 50 mL round bottom flask and DBU (20 mol %)
was added to the reaction mixture at room temperature. Then,
the resulting mixture was heated to 80 °C and stirred for 4 h. The
progress of the reaction was monitored by TLC. After compl-
etion of the reaction, the reaction mixture was allowed to cool
to 0 °C and compound was filtered and recrystallized from toluene
to afford desired product 3,4-dihydropyrimidine-2(1H)-thione
derivatives (4a-4n) (Table-1). The filtrate aqueous ethanol
(50 %) containing DBU was used as such for investigating the
recyclability of the catalyst. The product was identified by spectral
data.

1244 Sekhar et al.
Asian J. Chem.
Characterization data of synthesized compounds
8.11 (11H, m,Ar-H), 9.02(1H, bs, NH), 9.92(1H, bs, NH). 13C
NMR (100 MHz, DMSO-d6, δ, ppm): 56.1, 102.8, 124.29,
125.2, 126.9, 127.5, 127.8, 127.9, 128.9, 130.4, 130.7, 134.9,
138.4, 142.2, 176.8. MS m/z: 351 [M+1]+.
3,4-Dihydro-4,6-diphenylpyrimidine-2(1H)-thione
(4a): m.p. 182-184 ºC, FT-IR (KBr, νmax, cm-1): 3172 (NH),
1643 (C=N), 1558, 1479 (C=C), 1183 (C=S). 1H NMR (400
MHz, DMSO-d6, δ, ppm): 4.87 (1H, d, J = 5.0 Hz, 4-CH),
5.17 (1H, d, J = 5.0 Hz, 5-CH), 6.78-7.19 (10H, m, Ar-H),
8.87 (1H, bs, NH), 9.59 (1H, bs, NH). 13C NMR (100 MHz,
DMSO-d6, δ, ppm): 55.1, 101.6, 126.4, 126.8, 127.2, 128.86,
129.4, 129.4, 133.8, 134.8, 144.7, 175.9. MS m/z: 267 [M+1]+.
4-(4-Chlorophenyl)-6-phenyl-3,4-dihydropyrimidine-
2(1H)-thione (4b): m.p. 180-182 ºC, FT-IR (KBr, νmax, cm-1):
3153 (NH), 1648 (C=N), 1549, 1473 (C=C), 1185 (C=S). 1H
NMR (400 MHz, DMSO-d6, δ, ppm): 4.87 (1H, d, J = 5.0 Hz,
4-CH), 5.28 (1H, d, J = 5.0 Hz, 5-CH), 7.03-7.56 (9H, m, Ar-H),
8.77(1H, bs, NH), 9.70(1H, bs, NH). 13C NMR (100 MHz, DMSO-
d6, δ, ppm): 50.1, 56.3, 100.6, 111.3, 121.4, 126.2, 126.7, 128.5,
129.1, 129.4, 132.1, 133.6, 134.8, 155.7, 172.2. MS m/z: 301
[M+1]+.
3,4-Dihydro-6-(naphthalen-2-yl)-4-phenylpyrimidine-
2(1H)-thione (4c): m.p. 212-214 ºC, FT-IR (KBr, νmax, cm-1):
3190 (NH), 1675 (C=N), 1559, (C=C), 1184 (C=S). 1H NMR
(400 MHz, DMSO-d6, δ, ppm): 5.14 (1H, d, J = 5.0 Hz, 4-CH),
5.55-5.60 (1H, d, J = 5.0 Hz, 5-CH), 7.30-8.10 (12H, m, Ar-H),
9.07 (1H, bs, NH), 9.59 (1H, bs, NH). 13C NMR (100 MHz,
DMSO-d6, δ, ppm): 56.0, 102.8, 124.29, 125.2, 126.9, 127.5,
127.9, 127.9, 128.9, 130.4, 130.7, 134.9, 138.4, 142.2, 175.9.
MS m/z: 317 [M+1]+.
4-(4-Chlorophenyl)-3,4-dihydro-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4d): m.p. 214-216 ºC, FT-IR
(KBr, νmax, cm-1): 3190 (NH), 1673 (C=N), 1561, (C=C), 1182
(C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.21 (1H, d, J
= 5.0 Hz, 4-CH), 5.57 (1H, d, J = 5.0 Hz, 5-CH), 7.1-8.15 (11H,
m, Ar-H), 9.22 (1H, bs, NH), 10.07 (1H, bs, NH). 13C NMR (100
MHz, DMSO-d6, δ, ppm): 54.4, 101.9, 124.2, 125.3, 125.7, 127,
127.1, 127.9, 128.3, 128.6, 128.7, 129.1, 129.3, 130.7, 132.6,
132.9, 133.3, 134.8, 143.4, 175.7. MS m/z: 351 [M+1]+.
4-(2-Chlorophenyl)-3,4-dihydro-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4e): m.p. 210-212 ºC, FT-IR
(KBr, νmax, cm-1): 3181 (NH), 1675 (C=N), 1562 (C=C), 1186
(C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.04 (1H, d, J
= 5.0 Hz, 4-CH), 5.54-5.62(1H, d, J = 5.0 Hz, 5-CH), 7.31-
3,4-Dihydro-6-(naphthalen-2-yl)-4-p-tolylpyrimidine-
2(1H)-thione (4f): m.p. 226-228 ºC, FT-IR (KBr, νmax, cm-1):
3181 (NH), 1672 (C=N), 1562, (C=C), 1188 (C=S). 1H NMR
(400 MHz, DMSO-d6, δ, ppm): 2.3 (3H, s, CH3), 5.1 (1H, d, J
= 5.0 Hz, 4-CH), 5.5 (1H, d, J = 5.0 Hz, 5-CH), 7.2-8.15
(11H, m,Ar-H), 9.15 (1H, bs, NH), 9.97 (1H, bs, NH). 13C NMR
(100 MHz, DMSO-d6, δ, ppm): 21.9, 54.9, 102.5, 124.2, 125.1,
126.8, 127, 127.05, 127.9, 128.3, 128.7, 129.6, 130.8, 133,
133.3, 134.4, 137.2, 141.6, 175.5. MS m/z: 331 [M+1]+.
4-(3-Bromophenyl)-3,4-dihydro-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4g): m.p. 232-234 ºC, FT-IR
(KBr, νmax, cm-1): 3174 (NH), 1679 (C=N), 1562, (C=C), 1182
(C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.12(1H, d, J =
5.0 Hz, 4-CH), 5.53-5.58 (1H, d, J = 5.0 Hz, 5-CH), 7.39-8.10
(11H, m, Ar-H), 9.17 (1H, bs, NH), 9.99 (1H, bs, NH). 13C NMR
(100 MHz, DMSO-d6, δ, ppm): 56.1, 102.8, 124.2, 125.2, 126.8,
127.5, 127.8, 127.9, 128.9, 130.4, 130.7, 134.9, 138.4, 142.2,
177.7. MS m/z: 396 [M+1]+.
4-(2,6-Dichlorophenyl)-3,4-dihydro-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4h): m.p. 218-220 ºC, FT-IR
(KBr, νmax, cm-1): 3190 (NH), 1676 (C=N), 1559, (C=C), 1184
(C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.12 (1H, d,
J = 5.0 Hz, 4-CH), 5.52-5.59 (1H, d, J = 5.0 Hz, 5-CH), 7.32-
8.11 (10H, m, Ar-H), 9.05 (1H, bs, NH), 9.93 (1H, bs, NH).
13C NMR (100 MHz, DMSO-d6, δ, ppm): 56.3, 102.8, 124.29,
125.2, 126.9, 127.5, 127.8, 127.9, 128.9, 129.6, 130.4, 130.6,
134.9, 138.4, 142.2, 177.6. MS m/z: 386 [M+1]+.
4-(3,4-Dichlorophenyl)-3,4-dihydro-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4i): m.p. 220-222 ºC, FT-IR
(KBr, νmax, cm-1): 3191 (NH), 1667 (C=N), 1553, (C=C), 1182
(C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.12 (1H, d, J =
5.0 Hz, 4-CH), 5.51-5.59 (1H, d, J = 5.0 Hz, 5-CH), 7.32-8.12
(10H, m,Ar-H), 9.06 (1H, bs, NH), 9.93 (1H, bs, NH). 13C NMR
(100 MHz, DMSO-d6, δ, ppm): 56.1, 102.7, 124.29, 125.2,
126.9, 127.6, 127.8, 127.9, 128.9, 129.6, 130.4, 130.6, 134.9,
139.4, 142.2, 177.7.385.31. MS m/z: 386 [M+1]+.
4-(4-Fluorophenyl)-3,4-dihydro-6-(naphthalen-2-yl)-
pyrimidine-2(1H)-thione (4j): m.p. 216-218 ºC, FT-IR (KBr,
TABLE-1
SYNTHESIS OF 3,4-DIHYDROPYRIMIDINE-2(1H)-THIONE DERIVATIVES
Entry
1
2
3
4
5
6
7
8
Ar1
Ar2
Time (h)
4.0
4.5
4.0
4.0
4.5
4.0
5.0
4.0
4.0
4.0
4.0
5.0
4.0
4.0
Product
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
Yield (%)
71
Phenyl
Phenyl
Phenyl
4-Chlorophenyl
Phenyl
76
74
76
82
81
87
86
81
82
79
83
81
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
4-Chlorophenyl
2-Chlorophenyl
4-Methylphenyl
3-Bromophenyl
2,6-Diclorophenyl
3,4-Dichlorophenyl
4-Flourophenyl
4-Methoxyphenyl
3,4,5-Trimethoxyphenyl
3,4-Dimethoxyphenyl
1-Naphthyl
9
10
11
12
13
14
4m
4n
82

Vol. 30, No. 6 (2018)
One-Pot Synthesis of 3,4-Dihydropyrimidine-2(1H)-thione Derivatives Using DBU 1245
S
ν
max, cm-1): 3191 (NH), 1674 (C=N), 1551, (C=C), 1181 (C=S).
O
4 hr, 80oC,DBU
Ethanol ,H2O
S
O
1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.01 (1H, d, J = 5.0
Hz, 4-CH), 5.59-5.63 (1H, d, J = 5.0 Hz, 5-CH), 7.39-8.16
(11H, m,Ar-H), 9.01 (1H, bs, NH), 9.99 (1H, bs, NH). 13C NMR
(100 MHz, DMSO-d6, δ, ppm): 56.1, 102.8, 124.29, 125.2,
126.8, 127.5, 127.8, 127.9, 128.5, 130.6, 130.7, 134.7, 138.4,
142.2, 177.9. MS m/z: 335 [M+1]+.
H
Ar2
HN
Ar1
NH
Ar2
+
+
Ar1
H2N
NH2
1
2
3
4
Ar1 = Naphthyl,Phenyl
Ar2= Phenyl
Scheme-I: One-pot three-component reaction of aryl ketone, aryl aldehyde
and thiourea
3,4-Dihydro-4-(4-methoxyphenyl)-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4k): m.p. 162-164 ºC, FT-IR
(KBr, νmax, cm-1): 3198 (NH), 1669 (C=N), 1565, 1186 (C=S).
1H NMR (400 MHz, DMSO-d6, δ, ppm): 3.77 (3H, s, OCH3),
4.87 (1H, d, J = 5.0 Hz, 4-CH), 5.17 (1H, d, J = 5.0 Hz, 5-CH),
6.79-7.19 (11H, m, Ar-H), 8.89 (1H, bs, NH), 9.97 (1H, bs, NH).
13C NMR (100 MHz, DMSO-d6, δ, ppm): 21.5, 54.6, 55.6, 102.5,
114.4, 124.2, 125.5, 125.7, 127, 127.9, 128.2, 128.6 128.7,
129, 130.9, 133, 133.3, 134.4, 136.6, 159.2, 175.5. MS m/z:
347 [M+1]+.
3,4-Dihydro-4-(3,4,5-trimethoxyphenyl)-6-(naphthalen-
2-yl)pyrimidine-2(1H)-thione (4l): m.p. 198-200 ºC, FT-IR
(KBr, νmax, cm-1): 3183 (NH), 1688 (C=N), 1558, 1186 (C=S).
1H NMR (400 MHz, DMSO-d6, δ, ppm): 3.35-3.78 (9H, s,
OCH3), 5.14 (1H, d, J = 5.0 Hz, 4-CH), 5.15 (1H, d, J = 5.0
Hz, 5-CH), 6.7-8.16 (9H, m, Ar-H), 9.13 (1H, bs, NH), 10.01
(1H, bs, NH). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 55.1,
56.3, 60.4, 102.2, 104.0, 124.2, 125.2, 127.4, 127.08, 127.9,
128.4, 128.7, 130.8, 133, 133.3, 134.6, 137.3, 140, 153.5, 175.7.
MS m/z: 407 [M+1]+.
3,4-Dihydro-4-(3,4-dimethoxyphenyl)-6-(naphthalen-
2-yl)pyrimidine-2(1H)-thione (4m): m.p. 192-194 ºC, FT-
IR (KBr, νmax, cm-1): 3198 (NH), 1680 (C=N), 1557, 1177 (C=S).
1H NMR (400 MHz, DMSO-d6, δ, ppm): 3.5-7 (6H, s, OCH3),
5.14 (1H, d, J = 5.0 Hz, 4-CH), 5.5 (1H, d, J = 5.0 Hz, 5-CH),
6.79-7.19 (10H, m, Ar-H), 8.89 (1H, bs, NH), 9.97 (1H, bs,
NH). 13C NMR (100 MHz, DMSO-d6, δ, ppm): 21.5, 54.65, 55.6,
102.5, 114.4, 124.2, 125.5, 125.7, 127, 127.9, 128.2, 128.3,
128.6 128.7, 129, 130.9, 133, 133.3, 134.4, 136.6, 159.2, 175.5.
MS m/z: 378 [M+1]+.
3,4-Dihydro-4-(naphthalen-1-yl)-6-(naphthalen-2-
yl)pyrimidine-2(1H)-thione (4n): m.p. 230-232 ºC, FT-IR
(KBr, νmax, cm-1): 3173 (NH), 1671 (C=N), 1549, 1465 (C=C),
1173 (C=S). 1H NMR (400 MHz, DMSO-d6, δ, ppm): 5.7 (1H,
d, J = 5.0 Hz, 4-CH), 6.01 (1H, d, J = 5.0 Hz, 5-CH), 7.5-8.33
(14H, m,Ar-H), 9.2 (1H, bs, NH), 10.15 (1H, bs, NH). 13C NMR
(100 MHz, DMSO-d6, δ, ppm): 52.5, 102.3, 123.7, 124.1, 124.4,
125.1, 126.3, 126.4, 126.9, 127, 127.8, 128.3, 128.7, 129.1, 129.7,
130.8, 132.9, 133.3, 134, 134.4, 139.9, 176.4. MS m/z: 367
[M+1] +.
the reaction. To the filtrate, aryl ketone (1a), aryl aldehyde (2a)
and thiourea (3a) were added in the same molar ratio without
additional load of DBU. The reaction mixture was stirred for
the specified time; marginal loss of the yield was observed.
Different dihydropyrimidine-2(1H)-thione and its deriva-
tives are confirmed by spectral parameters. The1H NMR spectrum
of 4a exhibited two broad singlet’s for NH of pyrimidine
protons at 8.8 and 9.6 ppm, a multiplet at 6.78-7.19 ppm was
assigned to aromatic protons. IR spectrum showed N-H stretc-
hing vibration at 3173 cm-1 corresponding to secondary amine
in pyrimidine. Weak intensity absorption band at 1643 cm-1
corresponds to C=N stretching vibration.A plausible mechanism
is proposed for the formation of product 4 (Scheme-II).
DBU-catalyzed condensation between 1 and 2 will give
an intermediate 5 which on reaction with 3 gave another inter-
mediate 6. The intermediate 6 formed in situ undergoes cycliz-
ation to give the final product 4.
Conclusion
In conclusion, a three-component synthetic method for
preparation of some dihydropyrimidine-2(1H)-thione derivatives
is carried out. This method has several advantages such as readily
available starting materials, easy workup, good yields of the
products and DBU as a green and recyclable catalyst.
ACKNOWLEDGEMENTS
One of the authors (P. Thriveni) thanks to BRNS, BARC,
Mumbai, India for providing the financial assistance of research
work. The authors also extended their gratitude towards IICT,
Hyderabad, S.V. University, Tirupati andV.S. University, Nellore,
India for providing facilities of IR spectra, 1H NMR, 13C NMR
and mass spectral characterization of compounds.
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Asian J. Chem.
O
N
O
Ar2
HN
N
O
N
O
O
O
O
Ar2
2
Ar1
CH2
Ar1
CH2
Ar1
CH2
OH
Ar1
1
O
O
O
HN
N
Ar2
Ar1
-H2O
H2O
Ar2
Ar1 +
Ar2
Ar1
H
N
N
5
N
N
HN
S
S
+
+
H2N
NH2
H2N
NH
N
(A)
3
S
S
S
O
NH2
H
1,4-Addition
N
N
N
HN
Ar1
NH
Ar2
Ar1
Ar2
(A)
+
Ar1
Ar2
Ar1
Ar2
H
H
6
4
Scheme-II: Mechanism of the reaction
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