One-pot synthesis of benzofuryl-substituted semicarbazides under microwave irradiation

Article abstract of DOI:10.1080/15459620500408835

A series of asymmetric semicarbazides was synthesized by reactions of 2-benzofuran isocyanate, which was prepared by Curtius rearrangement from 2-benzofuroyl azide with acid hydrazide under microwave irradiation using a one-pot procedure. Comparing to the conventional method, this method has the advantages of mild conditions, easy handling, and high yield. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15459620500408835

This article was downloaded by: [Moskow State Univ Bibliote]
On: 23 October 2013, At: 06:28
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office:
Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An International
Journal for Rapid Communication of
Synthetic Organic Chemistry
Publication details, including instructions for authors and subscription
information:
http://www.tandfonline.com/loi/lsyc20
One‐Pot Synthesis of Benzofuryl‐ Substituted
Semicarbazides Under Microwave Irradiation
a
a b
a
a
Xi‐Cun Wang , Lan‐Qin Chai , Man‐Gang Wang , Zheng‐Qun Quan
&
a
Zheng Li
a
Gansu Key Laboratory of Polymer Materials , College of Chemistry and
Chemical Engineering, Northwest Normal University , Lanzhou, Gansu, China
b
College of Chemistry and Biological Engineering , Lanzhou Jiaotong
University , Lanzhou, Gansu, China
Published online: 16 Aug 2006.
To cite this article: Xi‐Cun Wang , Lan‐Qin Chai , Man‐Gang Wang , Zheng‐Qun Quan & Zheng Li (2006)
One‐Pot Synthesis of Benzofuryl‐ Substituted Semicarbazides Under Microwave Irradiation, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:5,
645-652
To link to this article: http://dx.doi.org/10.1080/15459620500408835
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)
contained in the publications on our platform. However, Taylor & Francis, our agents, and our
licensors make no representations or warranties whatsoever as to the accuracy, completeness, or
suitability for any purpose of the Content. Any opinions and views expressed in this publication
are the opinions and views of the authors, and are not the views of or endorsed by Taylor &
Francis. The accuracy of the Content should not be relied upon and should be independently
verified with primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities
whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or
arising out of the use of the Content.
This article may be used for research, teaching, and private study purposes. Any substantial
or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or
distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use
can be found at http://www.tandfonline.com/page/terms-and-conditions

w
Synthetic Communications , 36: 645–652, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/15459620500408835
One-Pot Synthesis of Benzofuryl-
Substituted Semicarbazides Under
Microwave Irradiation
Xi-Cun Wang
Gansu Key Laboratory of Polymer Materials, College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou,
Gansu, China
Lan-Qin Chai
Gansu Key Laboratory of Polymer Materials, College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou,
Gansu, China and College of Chemistry and Biological Engineering,
Lanzhou Jiaotong University, Lanzhou, Gansu, China
Man-Gang Wang, Zheng-Qun Quan, and Zheng Li
Gansu Key Laboratory of Polymer Materials, College of Chemistry and
Chemical Engineering, Northwest Normal University, Lanzhou,
Gansu, China
Abstract: A series of asymmetric semicarbazides was synthesized by reactions of
2-benzofuran isocyanate, which was prepared by Curtius rearrangement from 2-benzo-
furoyl azide with acid hydrazide under microwave irradiation using a one-pot
procedure. Comparing to the conventional method, this method has the advantages
of mild conditions, easy handling, and high yield.
Keywords: Curtius rearrangement, isocyanate, microwave irradiation (MWI),
semicarbazides
Received in Japan July 31, 2005
Address correspondence to Xi-Cun Wang, Gansu Key Laboratory of Polymer
Materials, College of Chemistry and Chemical Engineering, Northwest Normal
University, Lanzhou, Gansu 730070, China. Fax: þ086-931-7971971; E-mail:
wangxicun@nwnu.edu.cn
6
45

6
46
X.-C. Wang et al.
INTRODUCTION
The rapid heating effect of microwave irradiation has caught the attention
of synthetic chemists in recent years because of the remarkable reduction
[1]
of reaction time and enhancement of reaction yield. Semicarbazide deriva-
tives are widely used as medicines and agrochemicals because of their
[2–5]
anticonvulsive, herbicidal, antineoplastic, and hypotensive activities.
The synthetic protocols of semicarbazides generally utilize phosgene or
[6]
phosgene-based isocyanates as starting materials,
both of which are
toxic or unstable. These methods also need long periods. Therefore, it is
necessary to develop some phosgene-free and shorter-period routes for
semicarbazides.
Recently we reported the synthesis of some 1,4-diacyl semicarbazides
using easily made 1,4-diacyl thiosemicarbazides in water suspension and
[7–9]
under solvent-free conditions, respectively.
We herein report an expeditious, one-pot, efficient method for the prep-
aration of a series of asymmetric semicarbazides by addition of acid hydra-
zides to 2-benzofuran isocyanate irradiated by microwave.
As described in Scheme 1, 1-benzoyl-4-(2-benzofuran)semicarbazides
and 1-aryloxyacetyl-4-(benzofuran-2-yl)semicarbazides were synthesized by
reactions of 2-benzofuran isocyanate, which were prepared by treating
benzofuran-2-carboxylic acid with sodium azide and ethyl chlorocarbamate
[10]
in the presence of triethylamine followed by Curtius rearrangement,
with
various aryl carboxylic acid hydrazides or aryloxyacetic acid hydrazides,
respectively, under microwave irradiation (Scheme 1).
The experiment discussed here constitutes a large improvement when
compared to those of the literature, which need long reaction times. In
summary, excellent yields can be obtained in the synthesis of asymmetrical
semicarbazides under microwave irradiation. The reaction times are shorter
and rates can be as higher as 35–60 times than those obtained with conven-
tional heating.
Scheme 1.

Benzofuryl-Substituted Semicarbazides
647
To check the effects of microwave irradiation, all the reactions were
performed in an oil bath at 120 8C. When compared to the classical heating,
rates of microwave irradiation are multiplied by at least 32 times with high
yields. The results are given in Table 1.
Meanwhile, we selected the synthesis of compound 1a as the typically
reaction, studying the effects of irradiation power and time on the yields.
The best yields are 81% after 15 min of irradiation with 490 W using
toluene as solvent. A greater power or longer irradiation induces a decrease
in yield (only 73% with 700 W or 78% after 16 min) due to the decomposition
of 2-benzofuran isocyanate.
In summary, the reactions for 2-benzofuran-substituted asymmetric
semicarbazides have been accomplished by employing the Curtius
rearrangement reaction of 2-benzofuroyl azide followed by nucleophile
addition, under microwave irradiation. Compared to conventional thermal
heating, microwave irradiation decreased the reaction time from 8–14 h to
1
4–24 min with high yields. The main advantages of this method are
rapid reaction rate, high yield, fewer by-products, and convenient
manipulation.
Table 1. Preparation of compounds 4a–p under microwave irradiation
Yield (%)
Reaction time
MWI
(min)
Reflux
b
(h)
a
b
a
Entry
R
MWI
Reflux
Mp (8C)
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
a
b
c
d
e
f
C
6
H
5
81
88
85
72
70
76
74
84
83
82
81
84
86
73
70
76
75
81
80
66
64
70
69
78
80
79
78
81
82
69
65
72
15
14
14
18
18
16
16
16
20
20
20
18
18
24
24
22
8
8
192–193
.300
4-CH
3
OC
6
H
4
3-CH C H
3
8
292–294
208–209
230–232
200–202
.300
184–186
208–209
200–201
215–216
198–200
194–195
178–180
208–210
274–276
6
4
3-NO
4-NO
2-ClC H
2
C
6
H
4
4
9
2
C
6
H
9
9
6
4
g
h
i
4-ClC
2-IC
6
H
4
9
6
H
4
10
10
11
12
8
6 5 2
C H CH O
j
2-CH C H OCH
3
3
3
6
6
6
4
4
4
2
2
2
k
l
3-CH
4-CH
C
C
H
H
OCH
OCH
m
n
o
p
4-CH OC H OCH
3
12
13
10
12
6
4
2
3-NO
4-NO
2
C
C
6
H
4
OCH
2
2
2
6
H
4
OCH
4-ClC H OCH
2
6
4
a
b
Irradiated by microwave at less than 490 W.
Heated at 1208C.

6
48
X.-C. Wang et al.
EXPERIMENTAL
IR spectra were recorded using KBr pellets on a Nicolet Avatar 360 FT-IR
1
spectrophotometer and H NMR spectra on Avanci-D2X-200 instrument
using DMSO-d6 as solvent and TMS as internal standard. Elemental
analyses were performed on a Vario E-1 Elemental Analysis instrument.
Melting points were determined with a XT-4 thermal apparatus and are
uncorrected.
[
11]
[12]
Benzofuran-2-carboxylic acid, aryl carboxylic acid hydrazides, and
13]
[
aryloxyacetic acid hydrazides
were prepared according to literature pro-
cedures. Aryloxyacetic acids were commercially available and used as
received.
Preparation of 2-Benzofuroylazide 2
The mixture of benzofuran-2-carboxylic acid (1) (1 mmol), triethylamine
(
1.1 mmol), and ethyl chlorocarbamate (1.1 mmol) in dry acetone (30 mL)
was stirred at 08C for 1 h. Then sodium azide (1.1 mmol) with 15 mL water
was added to the mixture and it was kept at 08C for 7 h. After the reaction
completed (monitored by TLC), the mixture was poured onto ice. Then the
suspension was filtered and the product was obtained. Yield: 96.3%, white
2
1
crystal. Mp 110–1118C. IR (KBr, n/cm ): 2162 (N ;; N), 1703 (C 55 O),
1
1
333 (N 55 N). H NMR (200 MHz, DMSO-d ) d ¼ 6.90–7.36 (m, 5H). MS:
6
m/z ¼ 187. Anal. calcd. for C H N O : C, 57.76; H, 2.69; N, 22.45. Found:
9
5 3 2
C, 57.83; H, 2.71; N, 22.52.
General Procedure for the Synthesis of Compounds 4a–p
The solution of 2-benzofuroyl azide (2) (0.5 mmol) in toluene was heated at
1208C for 4 h to give benzofuran-2-yl isocyanate 3, which does not need to
be isolated, and which was treated with acid hydrazide under microwave
irradiation at 490 W for the time according to Table 1. After the completion
of the reaction [monitored by TLC using ethyl acetate and petroleum ether
(2 : 3) as eluent], the mixture was distilled under reduced pressure,
removing excess solvent, and the residue was purified by recrystallization
from DMF–EtOH to give product 4.
2
-Benzoyl-4-(benzofuran-2-yl)semicarbazide (4a). IR (KBr, n/cm ):
1
1
3
1
296, 3277 (N-H), 1684, 1652 (C 55 O); H NMR (200 MHz, DMSO-d )
6
d ¼ 11.08 (s, 1H, NH), 10.76 (s, 1H, NH), 10.23 (s, 1H, NH), 8.77–6.46
m, 10H, ArH & benzofuran H). MS: m/z ¼ 295. Anal. calcd. for
C H N O : C, 65.08; H, 4.44; N, 14.23. Found: C, 64.99; H, 4.49; N, 14.30.
(
1
6 13 3 3

Benzofuryl-Substituted Semicarbazides
649
1
-(4-Methoxybenzoyl)-4-(benzofuran-2-yl)semicarbazide (4b). IR (KBr,
2
1
1
n/cm ): 3310, 3274 (N-H), 1680, 1647 (C 55 O); H NMR (200 MHz,
DMSO-d ) d ¼ 11.06 (s, 1H, NH), 10.72 (s, 1H, NH), 10.18 (s, 1H, NH),
6
8
.73–6.41 (m, 9H, ArH & benzofuran H), 3.78 (s, 3H,CH O). MS:
3
m/z ¼ 325. Anal. calcd. for C H N O : C, 62.76; H, 4.65; N, 12.92.
1
7 15 3 4
Found: C, 62.59; H, 4.62; N, 12.88.
1
n/cm ): 3298, 3276 (N-H), 1681, 1650 (C 55 O); H NMR (200 MHz,
-(3-Methylbenzoyl)-4-(benzofuran-2-yl)semicarbazide (4c). IR (KBr,
2
1
1
DMSO-d ) d ¼ 11.03 (s, 1H, NH), 10.74 (s, 1H, NH), 10.16 (s, 1H, NH),
6
8
.71–6.43 (m, 9H, ArH & benzofuran H), 2.23 (s, 3H, CH ). MS:
3
m/z ¼ 301. Anal. calcd. for C H N O : C, 66.01; H, 4.89; N, 13.58.
1
7 15 3 3
Found: C, 65.92; H, 4.82; N, 13.64.
1
n/cm ): 3314, 3297 (N-H), 1678, 1648 (C 55 O); H NMR (200 MHz,
-(3-Nitrobenzoyl)-4-(benzofuran-2-yl)semicarbazide (4d). IR (KBr,
1
2
1
DMSO-d ) d ¼ 11.10 (s, 1H, NH), 10.79 (s, 1H, NH), 10.25 (s, 1H, NH),
6
8
C H N O : C, 56.47; H, 3.55; N, 16.46. Found: C, 56.41; H, 3.50; N, 16.62.
.78–6.48 (m, 9H, ArH & benzofuran H). MS: m/z ¼ 340. Anal. calcd. for
16 12 4 5
1
n/cm ): 3291, 3289 (N-H), 1680, 1645 (C 55 O); H NMR (200 MHz,
-(4-Nitrobenzoyl)-4-(benzofuran-2-yl)semicarbazide (4e). IR (KBr,
1
2
1
DMSO-d ) d ¼ 11.04 (s, 1H, NH), 10.80 (s, 1H, NH), 10.21 (s, 1H, NH),
6
8
C H N O : C, 56.47; H, 3.55; N, 16.46. Found: C, 56.53; H, 3.49; N, 16.51.
.81–6.50 (m, 9H, ArH & benzofuran H). MS: m/z ¼ 340. Anal. calcd. for
16 12 4 5
1
n/cm ): 3308, 3292 (N-H), 1674, 1653 (C 55 O); H NMR (200MHz,
-(2-Chlorobenzoyl)-4-(benzofuran-2-yl)semicarbazide (4f). IR (KBr,
1
21
DMSO-d ) d ¼ 11.08 (s, 1H, NH), 10.76 (s, 1H, NH), 10.23 (s, 1H, NH),
6
8
C H ClN O : C, 58.28; H, 3.67; N, 12.74. Found: C, 58.30; H, 3.62; N, 12.49.
.76–6.45 (m, 9H, ArH & benzofuran H). MS: m/z ¼ 329. Anal. calcd. for
16 12 3 3
1
n/cm ): 3304, 3286 (N-H), 1683, 1650 (C 55 O); H NMR (200 MHz,
-(4-Chlorobenzoyl)-4-(benzofuran-2-yl)semicarbazide (4g). IR (KBr,
1
2
1
DMSO-d ) d ¼ 11.09 (s, 1H, NH), 10.79 (s, 1H, NH), 10.26 (s, 1H, NH),
6
8
C H ClN O : C, 58.28; H, 3.67; N, 12.74. Found: C, 58.43; H, 3.89; N,
.79–6.47 (m, 9H, ArH & benzofuran H). MS: m/z ¼ 329. Anal. calcd. for
16 12 3 3
1
2.52.
1
n/cm ): 3312, 3294 (N-H), 1685, 1656 (C 55 O); H NMR (200 MHz,
-(2-Iodobenzoyl)-4-(benzofuran-2-yl)semicarbazide (4 h). IR (KBr,
2
1
1
DMSO-d ) d ¼ 11.10 (s, 1H, NH), 10.75 (s, 1H, NH), 10.24 (s, 1H, NH),
6
8
for C H IN O : C, 45.63; H, 2.87; N, 9.98. Found: C, 45.52; H, 3.10;
.77–6.44 (m, 9H, ArH & benzofuran H). MS: m/z ¼ 421 Anal. calcd.
16 12 3 3
N, 9.65.

6
50
X.-C. Wang et al.
1
-Phenyloxyacetyl-4-(benzofuran-2-yl)semicarbazide (4i). IR (KBr,
2
1
1
n/cm ): 3300, 3264 (N-H), 1678, 1663 (C 55 O); H NMR (200 MHz,
DMSO-d ) d ¼ 10.10 (s, 1H, NH), 10.04 (s, 1H, NH), 8.50 (s, 1H, NH),
6
7
.95–6.44 (m, 10H, ArH & benzofuran H), 4.71 (s, 2H, CH O). MS:
2
m/z ¼ 325. Anal. calcd. for C H N O : C, 62.76; H, 4.65; N, 12.92.
1
7 15 3 4
Found: C, 62.34; H, 4.59; N, 12.61.
1
-(2-Methylphenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4j). IR
2
KBr, n/cm ): 3295, 3258 (N-H), 1670, 1658 (C 55 O); H NMR
1
1
(
(
(
200 MHz, DMSO-d ) d ¼ 10.07 (s, 1H, NH), 10.01 (s, 1H, NH), 8.48
6
s, 1H, NH), 7.92–6.42 (m, 9H, ArH & benzofuran H), 4.68 (s, 2H, CH O),
2
2
.22 (s, 3H, CH ). MS: m/z ¼ 339. Anal. calcd. for C H N O : C, 63.71;
3
18 17 3 4
H, 5.05; N, 12.38. Found: C, 63.52; H, 5.33; N, 12.35.
1
-(3-Methylphenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4k). IR
2
KBr, n/cm ): 3298, 3260 (N-H), 1673, 1653 (C 55 O); H NMR
1
1
(
(
(
200 MHz, DMSO-d ) d ¼ 10.04 (s, 1H, NH), 9.98 (s, 1H, NH), 8.45
6
s, 1H, NH), 7.94–6.43 (m, 9H, ArH & benzofuran H), 4.70 (s, 2H, CH O),
2
2
.24 (s, 3H, CH ). MS: m/z ¼ 339. Anal. calcd. for C H N O : C, 63.71;
3
18 17 3 4
H, 5.05; N, 12.38. Found: C, 63.64; H, 5.37; N, 12.51.
1
-(4-Methylphenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4l). IR
2
1
1
KBr, n/cm ): 3300, 3262 (N-H), 1680, 1651 (C 55 O); H NMR
(
(
(
200 MHz, DMSO-d ) d ¼ 10.08 (s, 1H, NH), 10.02 (s, 1H, NH), 8.49
6
s, 1H, NH), 7.96–6.42 (m, 9H, ArH & benzofuran H), 4.67 (s, 2H, CH O),
2
2
.20 (s, 3H, CH ). MS: m/z ¼ 339. Anal. calcd. for C H N O : C, 63.71;
3
18 17 3 4
H, 5.05; N, 12.38. Found: C, 63.93; H, 5.29; N, 12.62.
1-(4-Methoxyphenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4m).
IR (KBr, n/cm ): 3293, 3264 (N-H), 1685, 1665 (C 55 O); H NMR
2
1
1
(
(
200 MHz, DMSO-d ) d ¼ 10.05 (s, 1H, NH), 10.01 (s, 1H, NH), 8.48
6
s, 1H, NH), 7.93–6.40 (m, 9H, ArH & benzofuran H), 4.72 (s, 2H, CH O),
2
3
.77 (s, 3H, CH O). MS: m/z ¼ 355. Anal. calcd. for C H N O : C,
3
18 17 3 5
6
0.84; H, 4.82; N, 11.82. Found: C, 60.67; H, 5.09; N, 11.79.
1
-(3-Nitrophenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4n). IR
2
KBr, n/cm ): 3296, 3256 (N-H), 1688, 1654 (C 55 O); H NMR
1
1
(
(
(
200 MHz, DMSO-d ) d ¼ 10.11 (s, 1H, NH), 10.05 (s, 1H, NH), 8.52
6
s, 1H, NH), 7.96–6.44 (m, 9H, ArH & benzofuran H), 4.77 (s, 2H, CH O).
2
MS: m/z ¼ 370. Anal. calcd. for C H N O : C, 55.14; H, 3.81; N, 15.13.
1
7 14 4 6
Found: C, 54.93; H, 4.07; N, 15.09.
1
-(4-Nitrophenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4o). IR
2
KBr, n/cm ): 3294, 3253 (N-H), 1683, 1652 (C 55 O); H NMR
1
1
(
(
200 MHz, DMSO-d ) d ¼ 10.13 (s, 1H, NH), 10.06 (s, 1H, NH), 8.54
6

Benzofuryl-Substituted Semicarbazides
651
(s, 1H, NH), 7.97–6.46 (m, 9H, ArH & benzofuran H), 4.79 (s, 2H, CH O).
2
MS: m/z ¼ 370. Anal. calcd. for C H N O : C, 55.14; H, 3.81; N, 15.13.
1
7 14 4 6
Found: C, 54.87; H, 4.12; N, 15.36.
1
-(4-Chlorophenyloxyacetyl)-4-(benzofuran-2-yl)semicarbazide (4p). IR
2
1
1
(
(
(
KBr, n/cm ): 3298, 3257 (N-H), 1686, 1660 (C 55 O); H NMR
200 MHz, DMSO-d ) d ¼ 10.12 (s, 1H, NH), 10.07 (s, 1H, NH), 8.50
6
s, 1H, NH), 7.94–6.45 (m, 9H, ArH & benzofuran H), 4.78 (s, 2H, CH O).
2
MS: m/z ¼ 359. Anal. calcd. for C H ClN O : C, 56.76; H, 3.92; N,
17
14
3 4
1
1.68. Found: C, 56.60; H, 4.19; N, 11.85.
ACKNOWLEDGMENT
We are thankful for the financial support from the Natural Science Foundation
of Gansu Province (ZS021-A25-006-Z) and the Scientific and Technological
Innovation Engineering Program of Northwest Normal University (NWNU-
KJCXGC-02-08).
REFERENCES
1
. Bose, A. K.; Manhas, M. S.; Ghosh, M.; Shah, M.; Raju, V. S.; Bari, S. S.;
Newaz, S. N.; Banik, B. K.; Chaudhary, A. G.; Barakat, K. J. Microwave-
induced organic reaction enhancement chemistry. 2. Simplified techniques.
J. Org. Chem. 1991, 56 (25), 6968–6970.
2
3
4
. Takumi, M.; Takanobu, K.; Takatoshi, I.; Toshiyuki, M. Synthesis of aromatic
urea herbicides by the selenium-assisted carbonylation using carbon monoxide
with sulfur. Synth. Commun. 2000, 30 (9), 1675–1688.
. Vidalu, J. L.; Calmel, F.; Bigg, D. Novel [2-(4-piperidinyl)ethyl](thio)ureas:
Synthesis and antiacetylcholinesterase activity. J. Med. Chem. 1994, 37 (5),
689–695.
. Gil, M. J.; Ma n˜ u´ , M. A.; Arteaga, C.; Migliaccio, M.; Enc ´ı o, I.; Gonz a´ lez, A.;
Mart ´ı nez, M. V. Synthesis and cytotoxic activity of N-(2-pyridylsulfenyl)urea
derivatives. A new class of potential antineoplastic agents. Bioorg. Med. Chem.
Lett. 1999, 9 (16), 2321–2324.
5
. Chalina, E. G.; Chakarova, L.; Staneva, D. T. Synthesis, antiarrhythmic and hypo-
tensive activity of some novel 1,3-disubstituted ureas and phenyl N-substituted
carbamates. Eur. J. Med. Chem. 1998, 33 (12), 985–990.
0
6. Arrieta, A.; Palomo, C. A new method of preparing N,N -disubstituted aryl ureas
0
using phenyl N -phenylphosphoramidoazidate reagent. Tetrahedron Lett. 1981,
22 (18), 1729–1732.
7
. Wang, X. C.; Li, Z.; Da, Y. X. Synthesis of 1-aryloxyacetyl-4-(4-chlorophenyl-
oxyacetyl)semicarbazides. Synth. Commun. 2000, 30 (24), 4543–4553.
. Wang, X. C.; Li, Z.; Da, Y. X.; Chen, J. C. A facile method to 1,4-diacyl semicar-
bazides: Syntheses of 1-aryloxyacetyl-4-(4-chlorobenzoyl)thiosemicarbazides and
semicarbazides. Synth. Commun. 2000, 30 (18), 3405–3411.
8

6
52
X.-C. Wang et al.
9
. Wang, X. C.; Quan, Z. J.; Li, Z. Microwave-assisted synthesis of 1,4-disubstituted
thiosemicarbazides and semicarbazides under solvent-free conditions in absence of
catalyst. J. Chem. Res., Synop. 2005, 71–72.
1
0. Batey, R. A.; Santhakumar, V.; Yoshina-Ishii, C.; Taylor, S. D. An efficient new
protocol for the formation of unsymmetrical tri- and tetra-substituted ureas.
Tetrahedron Lett. 1998, 39 (35), 6267–6270.
1
1
1
1. Tanaka, S. Coumarones from o-hydroxyaldehydes and bromomalonic ester. J. Am.
Chem. Soc. 1951, 73 (6), 872–874.
2. Fan, N. T. Dictionary of Organic Synthesis; Beijing University of Technology
Publishing: Beijing, 1992, p. 214 (in Chinese).
3. Husain, M. I.; Amir, M. Synthesis of some new substituted thiosemicarbazides and
triazoles as possible anticonvulsants. J. Indian Chem. Soc. 1986, 63 (3), 317–319.