NaH-promoted transformation of arylthioureas to aryl-isothioureas by S-allylation and S-benzylation reactions

Article abstract of DOI:10.3184/174751917X14878812592733

A series of 16 substituted aryl-isothioureas were prepared in excellent yields (80-97%) by reacting substituted arylthioureas with allyl bromide or substituted benzyl bromides in the presence of NaH in DMSO at room temperature. The substituent variations on the benzyl reactants had a larger effect on the yields than substituent variations on the allyl reactants. The method provides a facile and convenient preparation of some potentially biologically active compounds.

Full text of DOI:10.3184/174751917X14878812592733

JOURNAL OF CHEMICAL RESEARCH 2017
VOL. 41 MARCH, 165–167
RESEARCH PAPER 165
NaH-promoted transformation of arylthioureas to aryl-isothioureas by
S-allylation and S-benzylation reactions
a
a
a
a
a
a
c
Min Liu, Meng-Tian Zeng, Wan Xu, Cai-zhu Chang, Xing Liu, Hui Zhu, Yue-sheng Li and Zhi-
a
, b
Bing Dong *
a
School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430073, P.R. China
Key Laboratory of Green Chemical Process, Ministry of Education, Wuhan Institute of Technology, Wuhan 430074, P.R. China
Non-power Nuclear Technology Collaborative Innovation Center, Hubei University of Science and Technology, Hubei Xianning 437100, P.R. China
b
c
A series of 16 substituted aryl-isothioureas were prepared in excellent yields (80–97%) by reacting substituted arylthioureas with allyl
bromide or substituted benzyl bromides in the presence of NaH in DMSO at room temperature. The substituent variations on the benzyl
reactants had a larger effect on the yields than substituent variations on the allyl reactants. The method provides a facile and convenient
preparation of some potentially biologically active compounds.
Keywords: arylthioureas, aryl-isothioureas, S-allylation, S-benzylation, sodium hydride
Substituted aryl-isothioureas are one of the most important
classes of bioactive substances. They occur in some
agrochemicals and in numerous drugs, such as anti-infective
agents, ion channel blockers, cytoprotective agents and central
substituted arylthioureas reacting with primary amines, alkyl
18–24
halides or benzensulfonic acid.
However, these methods
suffer from the disadvantages of requiring high temperatures or
they give mixtures of products.
1–10
nervous system agents (Fig. 1), due to their anti-inflammatory
In this work, substituted arylthioroureas were converted
to aryl-isothioureas by base-catalysed S-allylation and
S-benzylation reactions (Scheme 1). The key grouping in the
product (boxed in Scheme 1) is known to be biologically active.
Thus, this protocol might pave the way to the synthesis of a
number of potentially pharmaceutically and biologically active
molecules.
11,12
and antibacterial activities.
As such, they have attracted
the attention of many biologists and chemists. Substituted
isothioureas can also be used as catalysts in synthetic
13
chemistry, due to their hydrogen-bonding interactions with
partially developing negatively charged atoms in the transition
state.
Several methods have been reported for the synthesis of
substituted aryl-isothioureas. For example, exchange reactions
Results and discussion
14
15
of isocyanates, the reaction of aromatic thiols with amines,
Our plan was to use allyl and benzyl bromides as alkylating
agents of arylthioroureas. The reaction conditions were
optimised using the arylthiourea lacking any substituent as the
16
sodium sulfide as a sulfur source, isocyanates reacting
17
with diazonium salts, but the most widely used method is
1
model compound (1a; R = H) in reaction with allyl bromide
(
Scheme 1). Various inorganic bases were evaluated, for
example, KOH, t-BuOK, t-BuONa, Cs CO , K CO , NaOCH
3
2
3
2
3
and NaH. NaH was found to be the most suitable base to
promote the transformation, and the base loading was chosen
to be 1 equiv. in relation to the thiourea (1a). The performance
of the reaction was also assessed by varying the substrate molar
ratio. The yield checking showed that the molar ratio of thiourea
to allyl bromide should be set as 1 : 1.
On the basis of these results we established the optimal
conditions, and then other substrates were evaluated. The results
are listed in Table 1. Various substituted aryl-isothioureas (3a–
p) were synthesised smoothly in excellent yields (80–97%).
Our model compound, 1,1-dimethyl-3-phenyl-thiourea (1a),
reacted with allyl bromide (2a) in NaH suspension in 2 h at
room temperature to give 1,1-dimethyl-2-(2-allyl)-3-phenyl-
isothiourea (3a) in 89% isolated yield (entry 1). The next
compound, 1,1-dimethyl-3-(4-methylphenyl)-thiourea (1b)
reacted with allyl bromide (2a) in 2 h to give 1,1-dimethyl-2-
Fig. 1 Isothioureas with biological activity.
Scheme 1 NaH-promoted transformation of arylthioureas to aryl-isothioureas by S-allylation and S-benzylation reactions.
*
Correspondent. E-mail: dzb04982@wit.edu.cn

166 JOURNAL OF CHEMICAL RESEARCH 2017
Table 1 Yields of aryl-isothioureas 3a–p prepared from the reaction of
refer to isolated compounds estimated to be > 95% pure, as determined
by H NMR and capillary GC analysis.
various arylthioureas 1a–g with a series of allyl and benzyl bromides
1
a
2
a–e
Synthesis of 1,1-dimethyl-2-(2-allyl)-3-phenyl-isothiourea (3a);
general procedure
H
N
N
N
N
NaH / DMSO
r.t.
C
S
Br
R2
1,1-Dimethyl-3-phenyl-thiourea (1a, 0.182 g, 1 mmol), allyl bromide
(2a, 0.08 mL, 1 mmol) and NaH (0.0358 g, 67%, 1 mmol) were
added to a tube equipped with a rubber septum, dissolved in DMSO
S
R
1
R
1
R2
1
2
3
(
2 mL). The reaction was performed at room temperature within 2 h,
b
Entry
R1
R2
Product
Yield (%)
then quenched with NH Cl solution and extracted with ethyl acetate.
4
1
2
3
4
5
6
7
8
9
1a: H
1b: 4-Me
1a: H
1b: 4-Me
1a: H
1a: H
2a: CH=CH2
2a: CH=CH2
2b: Ph
2c:4-Br-Ph
2c:4-Br-Ph
2d: 2-I-Ph
2e: 4-MeO-Ph
2e: 4-MeO-Ph
2b: Ph
2b: Ph
2b: Ph
2b: Ph
2b: Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
89
90
90
80
83
80
90
88
95
95
96
97
88
87
95
85
The combined organic phases were dried with Na SO . The crude
residue obtained after evaporation of the solvent was purified by
flash chromatography (petroleum ether/ethyl acetate 3 : 1) to yield
2
4
1
(
,1-dimethyl-2-(2-allyl)-3-phenyl-isothiourea (3a) as a light yellow oil
0.0197 g, 89%).
,1-Dimethyl-2-(2-allyl)-3-phenyl-isothiourea (3a): Light yellow
1
1
oil; H NMR: δ 7.28 (t, J = 8 Hz, 2H), 6.99 (t, J = 7.2 Hz, 1H), 6.92 (d,
1a: H
J = 7.2 Hz, 3H), 5.73–5.62 (m, 1H), 5.04 (t, J = 9.2 Hz, 2H), 3.15(s, 6H),
1b: 4-Me
1c: 2-Br
1d: 3-Br
1e: 4-Br
1f:2-Cl
1b: 4-Me
1g: 2,4,6-Trimethyl 2b: Ph
1c: 2-Br
1f:2-Cl
13
3
.06 (d, J = 7.2 Hz, 2H); C NMR: δ 155.1, 149.4, 133.5, 128.7, 122.2,
1
22.1, 117.8, 40.2, 35.4; HRMS m/z for C H N S: calcd: 220.1032;
12
16
2
1
0
found: 220.1057.
1
1
1,1-Dimethyl-2-(2-allyl)-3-(4-methylphenyl)-isothiourea
Light yellow oil; H NMR: δ 7.28–6.76 (m, 8H), 5.01 (t, J = 7.4 Hz, 1H),
(3b):
1
1
2
3
.79 (s, 3H), 3.20–2.92 (m, 3H), 1.82 (m, 2H), 0.98 (s, 9H), 0.21 (s, 6H);
C NMR: δ 154.2, 147.5, 133.8, 131.2, 129.3, 121.8, 117.5, 34.0, 35.4,
0.9; HRMS m/z for C H N S: calcd: 234.1191; found: 234.1209.
1
3
1
3
1
4
2
1
5
2e: 4-MeO-Ph
2e: 4-MeO-Ph
13 18
2
1
,1-Dimethyl-2-benzyl-3-phenyl-isothiourea (3c): Light yellow oil;
1
6
1
H NMR: δ 7.23–7.20 (m, 5H), 7.10 (d, J = 6.8 Hz, 2H), 6.98 (t, 1H),
.84 (d, J = 8 Hz, 2H), 3.617 (s, 2H), 3.055 (s, 6H); C NMR: δ 155.6,
a
Reaction conditions: an arylthiourea 1 (1 mmol) was reacted with an allyl or a benzyl
bromide 2 (1 mmol) in the presence of NaH (1 mmol) in dry DMSO (2 mL) at room
temperature for 2 h.
Isolated yield of analytically pure product.
13
6
149.0, 137.4, 128.8, 128.7, 128.5, 127.4, 40.2, 36.9; HRMS m/z for
C H N S: calcd: 270.1191; found: 270.1232.
b
16 18
2
1
,1-Dimethyl-2-(4-bromobenzyl)-3-(4-methylphenyl)-isothiourea
1
(
3d): Light yellow oil; H NMR: δ 7.37 (d, J = 8Hz, 2H), 7.26 (s, 2H),
.04–6.98 (m, 3H), 6.91 (d, J = 8Hz, 2H), 3.63 (s, 3H), 3.09 (s, 6H);
C NMR: δ 153.80, 149.93, 136.94, 131.58, 130.55, 128.78, 122.10,
22.06, 121.22, 39.96, 36.05; HRMS m/z for C H BrN S: calcd:
7
(2-allyl)-3-(4-methylphenyl)-isothiourea (3b) in 90% isolated
13
yield (entry 2). 1,1-Dimethyl-3-phenyl-thiourea (1a) reacted
with benzyl bromide (2b) within 2 h at room temperature to
give 1,1-dimethyl-2-benzyl-3-phenyl-isothiourea (3c) in 90%
isolated yield (entry 3).
1
1
6
17
2
348.0296; found: 348.0318.
1,1-Dimethyl-2-(4-bromobenzyl)-3-phenyl-isothiourea (3e): Light
1
yellow oil; H NMR: δ 7.30 (d, J = 8 Hz, 2H), 6.98 (d, J = 8 Hz, 2H),
Arylthioureas bearing electron-withdrawing groups (o-Br,
m-Br, p-Br and o-Cl) could be transformed to the products
in higher yields (95–99%) (entries 9–12), whereas electron-
donating groups (p-CH3, 2,4,6-trimethyl) attached to
arylthioureas slightly reduced the yields (entries 13–14). An
6.92 (d, J = 8 Hz, 2H), 6.68 (d, J = 8 Hz, 2H), 3.53 (s, 3H), 2.98 (s,
13
6H), 2.23 (s, 3H); C NMR: δ 136.48, 132.22, 131.22, 130.52, 129.43,
121.91, 40.46, 36.29, 20.91; HRMS m/z for C H BrN S: calcd:
17
19
2
362.0452; found: 362.0552.
1
,1-Dimethyl-2-(2-iodobenzyl)-3-phenyl-isothiourea (3f): Light
1
yellow oil; H NMR: δ 7.79 (d, J = 8 Hz, 1H), 7.31–7.21 (m, 3H), 7.12
electron-donating substituent (p-OCH ) on the allyl reagents
3
(
3
1
d, J = 8 Hz, 1H), 7.01 (t, J = 8 Hz, 1H), 6.92–6.88 (m, 3H), 3.75 (s, 3H),
.07 (s, 6H); C NMR: δ 154.19, 150.05, 140.25, 139.73, 130.07, 129.13,
28.83, 128.43, 122.21, 122.07, 100.07, 42.21, 40.05; HRMS m/z for
promoted the yield (entry 7), whereas electron-withdrawing
groups caused a slight decrease (p-Br, o-I, entries 4–6).
Electron-withdrawing groups (o-Br, o-Cl) on arylthioureas
13
C H IN S: calcd: 396.0157; found: 396.0212.
16
17
2
and electron-donating substituents (p-OCH ) on benzylating
3
1
,1-Dimethyl-2-(4-methoxybenzyl)-3-phenyl-isothiourea (3g): Light
reagents gave good yields (entries 15–16). These results showed
that substituent variations on arylthioureas had a larger effect
than substituent variations on the allyl reagents.
In summary, substituted aryl-isothioureas were obtained
smoothly in excellent yields (80–97%) at room temperature
in the presence of NaH. The arylthioroureas were converted
to aryl-isothiourea anions by NaH and then quenched with an
electrophile (an allyl bromide or a substituted benzyl bromide)
to give the allylation/benzylation products in excellent yields.
1
yellow oil; H NMR: δ 7.39 (t, J = 8 Hz, 2H), 7.30 (t, J = 8 Hz, 1H), 7.12 (t,
J = 8 Hz, 1H), 6.93 (d, 2H), 6.90 (d, 1H), 6.85 (d, 1H), 6.79 (s, 1H), 3.89 (s,
13
3
H), 3.75 (s, 2H), 3.21 (s, 6H); C NMR: δ 159.67, 154.94, 149.98, 139.02,
129.47, 128.68, 122.14, 121.13, 114.17, 113.18, 55.25, 40.05, 36.92; HRMS
m/z for C H N OS: calcd: 300.1296; found: 300.1357.
17
20
2
1
,1-Dimethyl-2-(4-methoxybenzyl)-3-(4-methylphenyl)-isothiourea
1
(
3h): Light yellow oil; H NMR: δ 7.28–6.76 (m, 8H), 5.01 (t,
J = 7.4 Hz, 1H), 3.79 (s, 3H), 3.20–2.92 (m, 3H), 2.10–1.54 (m, 2H),
13
0.98 (s, 9H), 0.21 (s, 6H); C NMR: δ 159.66, 154.92, 146.91, 139.14,
31.52, 129.45, 129.29, 121.94, 121.13, 114.16, 113.15, 55.22, 40.07,
1
Experimental
3
6.95, 20.91; HRMS m/z for C H N OS: calcd: 314.1453; found:
18 22 2
NMR spectra were obtained on a Bruker AC 400 MHz spectrometer
314.1578.
1
13
(
H NMR at 400 Hz, C NMR at 100 Hz) in CDCl using TMS as
1,1-Dimethyl-2-benzyl-3-(2-bromophenyl)-isothiourea (3i): Light
yellow oil; H NMR: δ 7.60–7.57(m, 1H), 7.32–7.26 (m, 3H), 7.22–7.19
(m, 3H), 6.90–6.86 (m, 2H), 3.78 (s, 2H), 3.14 (s, 6H); C NMR: δ
155.87, 148.74, 137.31, 132.54, 129.00, 128.61, 127.76, 127.48, 123.48,
123.21, 117.68, 40.06, 37.35; HRMS m/z for C H BrN S: calcd:
3
1
internal standard. Chemical shifts are given in ppm and coupling
constants (J) are given in Hz. High-resolution mass spectra (HRMS-
ESI) were determined on an Ion Spec (7.0 T) spectrometer.
All starting materials were purchased from commercial suppliers and
were used without further purification unless otherwise stated. Yields
13
16
17
2
348.0296; found: 348.0376.

JOURNAL OF CHEMICAL RESEARCH 2017 167
1
,1-Dimethyl-2-benzyl-3-(3-bromophenyl)-isothiourea (3j): Light
Distinguished Fellows from Hubei Provincial Department
of Education and the Foundation of the High-end Talent
Cultivation Program of Wuhan Institute of Technology for
financial support. We also thank Prof. Aiwen Lei at Wuhan
University for his generous support in the NMR analysis.
1
yellow oil; H NMR: δ 7.33–7.27 (m, 3H), 7.16–7.11 (m, 4H), 6.98 (s,
13
1
1
3
3
H), 6.79 (d, 1H), 3.69 (s, 2H), 3.08 (s, 6H); C NMR: δ 155.11, 151.44,
37.39, 129.91, 128.89, 128.63, 127.53, 125.01, 124.74, 122.26, 120.97,
9.95, 37.15; HRMS m/z for C H BrN S: calcd: 348.0296; found:
16
17
2
48.0386.
,1-Dimethyl-2-benzyl-3-(4-bromophenyl)-isothiourea (3k): Light
1
Electronic Supplementary Information
1
yellow oil; H NMR: δ 7.35 (d, J = 7.8 Hz, 2H), 7.28 (d, J = 9.6 Hz,
H), 7.13 (d, J = 8 Hz, 2H), 6.70 (d, J = 8 Hz, 2H), 3.66 (s, 2H), 3.07 (s,
H); C NMR: δ 155.16, 148.75, 137.42, 131.60, 128.77, 128.59, 127.50,
23.92, 114.86, 40.02, 37.11; HRMS m/z for C H BrN S: calcd:
The ESI are available from:
stl.publisher.ingentaconnect.com/content/stl/jcr/supp-data
3
6
1
3
13
16
17
2
Received 11 January 2016; accepted 10 February 2017
Paper 1704526 DOI: 10.3184/174751917X14878812592733
Published online: 8 March 2017
48.0296; found: 348.0362.
,1-Dimethyl-2-benzyl-3-(2-chlorophenyl)-isothiourea (3l): Light
1
1
yellow oil; H NMR: δ 7.38 (d, J = 8 Hz, 1H), 7.30–7.25 (m, 3H), 7.17
t, J = 8 Hz, 3H), 6.95 (t, J = 8 Hz, 1H), 6.85 (d, J = 7.6 Hz, 1H), 3.76 (s,
H), 3.12 (s, 6H); C NMR: δ 155.92, 147.63, 137.39, 129.48, 128.98,
28.61, 127.48, 127.08, 126.68, 123.60, 122.88, 39.98, 37.29; HRMS
(
2
1
13
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8
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16
17
2
1,1-Dimethyl-2-benzyl-3-(4-methylphenyl)-isothiourea (3m): Light
1
yellow oil; H NMR: δ 7.28–7.22 (m, J = 7.2 Hz, 3H), 7.13 (d, J = 6.8 Hz,
H), 6.73 (d, J = 8 Hz, 2H), 3.64 (s, 2H), 3.04 (s, 6H), 2.31 (s, 3H);
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2
13
1
2
17
20
2
84.1347; found: 284.1398.
,1-Dimethyl-2-benzyl-3-(2,4,6-trimethylphenyl)-isothiourea (3n):
1
1
Light yellow oil; H NMR: δ 7.39–7.27 (m, 3H), 7.23 (d, J = 7.6 Hz,
2
H), 6.89 (s, 2H), 3.91 (s, 3H), 3.13 (s, 6H), 2.34 (s, 3H), 2.08 (s, 6H);
C NMR: δ 155.46, 144.69, 137.51, 131.35, 131.35, 129.98, 128.96,
28.53, 128.45, 128.30, 127.70, 127.34, 40.42, 37.12, 20.93, 18.15;
13
1
HRMS m/z for C H N S: calcd: 312.1660; found: 312.1754.
19
24
2
1,1-Dimethyl-2-(4-methoxybenzyl)-3-(2-bromophenyl)-isothiourea
1
(
(
5
1
4
3
3o): Light yellow oil; H NMR: δ 7.68 (d, J = 7.6 Hz, 1H), 7.34–7.28
m, 2H), 6.97 (t, J = 8.8 Hz, 2H), 6.90 (t, J = 6.8 Hz, 3H), 3.86 (s,
H), 3.23 (s, 6H); C NMR: δ 159.74, 155.63, 148.93, 138.88, 132.49,
29.57, 127.72, 123.44, 123.12, 121.27, 117.62, 114.26, 113.34, 55.29,
0.00, 37.32; HRMS m/z for C H BrN OS: calcd: 378.0401; found:
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13
11
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17
19
2
12
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,1-Dimethyl-2-(4-methoxybenzyl)-3-(2-chlorophenyl)-isothiourea
1
20, 9867.
1
13 G. Stark, T.J.C. O’Riordan and A.D. Smith, Org. Lett., 2014, 16, 6496.
1
(
(
3
1
1
3
3p): Light yellow oil; H NMR: δ 7.36 (d, J = 8 Hz, 1H), 7.19–7.12
m, 2H), 6.92 (t, J = 8 Hz, 1H), 6.82 (d, J = 8 Hz, 1H), 6.77–6.72 (m,
H), 3.74 (s, 3H), 3.71 (s, 2H), 3.10 (s, 6H); C NMR: δ 159.68, 156.22,
38.76, 129.54, 129.43, 127.03, 126.66, 123.66, 122.96, 121.22, 114.18,
13.32, 55.26, 40.05, 37.30; HRMS m/z for C H ClN OS: calcd:
34.0907; found: 334.1087.
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Acknowledgements
We thank the National Natural Science Foundation of China
21302150, 11405050), Hubei Provincial Department of
2
21
0
(
Education (D20131501), the Scientific Research Foundation for
the Returned Overseas Chinese Scholars, the State Education
Ministry [2012] 1707, the President’s Foundation of Wuhan
Institute of Technology (2014038), the Foundation of Chutian
2
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