A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-nitrobenzylidene)(thio)barbiturates

Article abstract of DOI:10.1016/j.crci.2017.10.002

2,1-Benzisoxazoles, also called anthranils, are one of the two types of aromatic bicyclic heterocycles having a benzene ring fused with an isoxazole, which are particularly recognized as valuable intermediates in organic synthesis. Nevertheless several methods can be found in the literature to prepare 2,1-benzisoxazoles, we herein report a new, efficient, simple, mild, and alternative procedure to prepare 3-substituted-2,1-benzisoxazoles from 5-(2-nitrobenzylidene)barbiturates in moderate to good yields (51–82%). All the novel benzisoxazoles showed spectral data fully consistent with the assigned structures, which were unequivocally confirmed by single crystal X-ray analysis. A possible mechanism of the reaction is proposed. In addition, a screening of the bioactivity of these benzisoxazoles as xanthine oxidase inhibitors, antioxidants, and cytotoxic compounds was performed. The benzisoxazole formed from barbituric acid revealed moderate xanthine oxidase inhibitory effects (IC₅₀ = 22.10 μM).

Full text of DOI:10.1016/j.crci.2017.10.002

C. R. Chimie xxx (2017) 1e6
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Preliminary communication/Communication
A synthetic route to novel 3-substituted-2,1-benzisoxazoles
from 5-(2-nitrobenzylidene)(thio)barbiturates
a
a
b
b
~
ꢀ
~
Joao L. Serrano , Eunice Cavalheiro , Sonia Barroso , Maria J. Romao ,
Samuel Silvestre a c, Paulo Almeida a
CICS-UBI e Health Sciences Research Centre, University of Beira Interior, Av. Infante D. Henrique, 6200-506 Covilha, Portugal
,
, *
a
~
b
^
Departamento de Química, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
c CNC e Center for Neuroscience and Cell Biology, University of Coimbra, Rua Larga, 3004-517 Coimbra, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
2,1-Benzisoxazoles, also called anthranils, are one of the two types of aromatic bicyclic
heterocycles having a benzene ring fused with an isoxazole, which are particularly
recognized as valuable intermediates in organic synthesis. Nevertheless several methods
can be found in the literature to prepare 2,1-benzisoxazoles, we herein report a new,
efficient, simple, mild, and alternative procedure to prepare 3-substituted-2,1-
benzisoxazoles from 5-(2-nitrobenzylidene)barbiturates in moderate to good yields (51
e82%). All the novel benzisoxazoles showed spectral data fully consistent with the
assigned structures, which were unequivocally confirmed by single crystal X-ray analysis.
A possible mechanism of the reaction is proposed. In addition, a screening of the bioac-
tivity of these benzisoxazoles as xanthine oxidase inhibitors, antioxidants, and cytotoxic
compounds was performed. The benzisoxazole formed from barbituric acid revealed
Received 8 September 2017
Accepted 2 October 2017
Available online xxxx
Keywords:
2,1-Benzisoxazoles
Anthranils
Barbiturates
Single crystal X-ray
Xanthine oxidase inhibition
moderate xanthine oxidase inhibitory effects (IC50 ¼ 22.10
mM).
© 2017 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
1. Introduction
Since the first described synthesis of 2,1-benzisoxazoles
by reductive cyclization of ortho-nitrobenzaldehydes by
Benzisoxazoles are aromatic ring heterocycles con-
taining one oxygen atom adjacent to one nitrogen atom in
Friedlander, in 1882, which wrongly assigned the resulting
product as an anthranil lactam [3], several other methods
have been described (see Supplementary information) and
recently reviewed [2,4].
a
five-membered ring fused with a benzo moiety.
There are two types of benzisoxazoles, namely 1,2-ben-
zisoxazoles (indoxazene) and 2,1-benzisoxazoles (2,1-
benzoisoxazoles or anthranil). The first one is more
widely used due to its high therapeutic interest [1]. The
second is more useful in the preparation of biologically
active compounds. Indeed, several important heterocy-
cles such as quinolones, acridines, or quinazolines can be
prepared directly from 2,1-benzisoxazoles or via amino-
arylketones easily obtained by treatment with iron in
acetic acid [2].
To the best of our knowledge, 2,1-benzisoxazoles con-
taining an exo double bond at 3-position have been scarcely
described [5]. In this context, in the reinvestigation of the
synthesis of indoles from BayliseHillman adducts [5a],
three new 2,1-benzisoxazoles possessing an exo double
bond were obtained as secondary products. In fact, the
reduction of ortho-nitro adducts of nitrobenzaldeyde using
tin(II) chloride in refluxing 1,4-dioxane originated these
2,1-benzisoxazoles in 26% yield [5b]. Later, the intra-
molecular FeBr2-catalyzed NeO bond formation from an
aryl azide possessing an ortho-isopropylcarbonyl group
* Corresponding author.
E-mail address: paulo.almeida@ubi.pt (P. Almeida).
https://doi.org/10.1016/j.crci.2017.10.002
1631-0748/© 2017 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002

2
J.L. Serrano et al. / C. R. Chimie xxx (2017) 1e6
affording the corresponding 1H-benzisoxazole in 72% yield
after SiO2 purification was also described [5c].
at 11.31 or 10.69 ppm can be found, corresponding to the
proton bond to the nitrogen of the pyrimidine scaffold
suggesting the symmetry of this ring. In addition, four
signals observed for all 8aed in the range of 7.90e6.71 ppm
indicated an ortho-substituted benzene ring. In the 8aed
13C NMR spectrum, the signals at 178.6e174.5,162.7e150.8,
and 85.4e82.5 ppm were attributed to carbons directly
attached to a sulfur atom, to an oxygen atom, and to a
methylenic carbon, respectively. Within these, the signal at
162.7e159.6 ppm was associated with two carbonyls,
confirming the symmetry of this pyrimidine scaffold. The
13C NMR spectrum of the benzisoxazoles 8aed presented
two signals at 167.4e163.6 and 156.4e155.9 ppm related to
30 and 7a0 isoxazole ring carbon atoms. The remaining ar-
omatic carbon atoms can be found between 141.8 and
112.9 ppm. In addition, attenuated total reflectance infrared
(ATR-IR) spectroscopy and high-resolution mass spec-
trometry (HRMS) were also performed. In conclusion, all
the novel compounds showed spectral and analytical data
fully consistent with the assigned structures. In addition,
single crystal X-ray data clearly confirmed the structure of
8d (Fig. 1 and Supplementary information).
2. Results and discussion
2.1. Synthesis and structural characterization
As a part of our ongoing research on the development
of new barbiturate[4,5-b]quinolones
7 as potential
xanthine oxidase (XO) inhibitors and antitumor agents,
we herein report a new route to prepare 3-substituted-
2,1-benzisoxazoles 8 from 5-(2-nitrobenzylidene)barbi-
turates 3 (Scheme 1).
The starting materials thiobarbituric acid (1a), barbitu-
ric acid (1c), N,N-dimethylbarbituric acid (1d), and ortho-
nitrobenzaldehyde were purchased from sigma aldrich,
whereas N,N-diphenylthiobarbituric acid (1b) was pre-
pared as described [6]. (2-Nitrobenzylidene)barbiturates 3a
ed were prepared in a simple and mild way based on the
method described by Deb and Bhuyan [7], using water as
the solvent, in 90e97% yield. Surprisingly after refluxing for
2
h
the methanolic acid suspension containing the
On the basis of the results mentioned previously and
described in Scheme 1, a possible reaction mechanism for
the formation of 8 is proposed considering an intra-
molecular attack of a nucleophilic intermediate in the
reduction of the nitro group, specifically a nitroso [8]
compound (Scheme 2). At first, the nitrosoarene 4 formed
by the partial reduction of the nitro group behaves as a
nucleophile capable to attack the C-5 of the (thio)barbitu-
rate in a typical Michael addition reaction. Moreover, this
cyclization path is activated by carbonyl acid catalysis.
Several mechanisms proposed for the 2,1-benzisoxazole
cyclization also involved radical anion nitroso or nitroso
as nucleophilic (methods D, E G, Scheme S1) [2] or elec-
trophilic (method F, Scheme S1) [2b] species. Besides,
respective 5-(2-nitrobenzylidene)barbiturate and tin
3
chloride dihydrate, the 5-benzo[c]isoxazolbarbiturates 8
were easily obtained by a direct filtration of the solid
formed, in moderate to good yields (51e82%), instead of the
expected barbiturate[4,5-b]quinolones 7 (Scheme 1).
Apart from precursors, all 5-benzo[c]isoxazolbarbit
urates 8aed prepared have not hitherto been described.
Consequently, their full spectroscopic characterization was
performed, including 1H and 13C NMR shift assignments,
which were established with the aid of distortionless
enhancement by polarization transfer 135, heteronuclear
simple quantum coherence, and heteronuclear multiple
bond correlation experiments. In the 1H NMR spectrum of
5-benzo[c]isoxazolbarbiturates 8a,c a characteristic signal
Scheme 1. Attempt to prepare (thio)barbiturate[4,5-b]quinolines 7 with the formation of 2,1-benzisoxazoles 8.
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002

J.L. Serrano et al. / C. R. Chimie xxx (2017) 1e6
3
Fig. 1. Molecular structure of 5-benzo[c]isoxazolbarbiturate 8d. (Left) ORTEP-3 plot (30% thermal ellipsoids). (Right) Packing showing N1eH1/O2 hydrogen
bonds (dashed light blue lines).
Scheme 2. Proposed mechanism for the formation of 2,1-benzisoxazoles.
considering the local reactivity descriptors applied on the
nitroso group of the nitrosobenzene, it has been shown that
both N and O nitroso atomic centers can be suitable
nucleophilic reactive sites in aqueous solutions [9]. Because
tin chloride is a rather effective reducing agent [10], the
unlikely partial reduction of the nitroarene to nitrosoarene
can be explained by the intramolecular trapping of this
unstable species by the reaction with the
b-keto
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002

4
J.L. Serrano et al. / C. R. Chimie xxx (2017) 1e6
unsaturated system. Finally, elimination of a proton and the
conversion of the enol form to the corresponding ketone
leads to the formation of 2,1-benzisoxazole 8. Therefore, a
novel system and associated reactivity different from all of
those previously described for the preparation of 2,1-
benzisoxazoles are reported in the present work. In addi-
tion, the simplicity and mildness of the reaction, the easy
access to the starting materials, and the straightforward
workup and good yields of the products obtained clearly
are interesting advantages of this new method.
4. Materials and methods
Reagents and solvents were purchased from standard
sources and were of analytical grade. Melting points were
measured in open capillary tubes in a Büchi B-540 appa-
ratus and were uncorrected. ATR-IR spectra were collected
using a Thermo-scientific Nicolet iS10: smart iTR, equip-
ped with a diamond ATR crystal using OMNIC 8.2 soft-
ware. For ATR data acquisition the sample was placed onto
the crystal and the spectrum was recorded, using an air
spectrum as a reference in absorbance calculations. The
sample spectra were collected at room temperature in the
4000e600 cmꢀ1 range by averaging 32 scans with a
spectral resolution of 4 cmꢀ1. NMR spectra were acquired
at room temperature using a Brüker Avance III 400 MHz
spectrometer (1H NMR at 400.13 MHz and 13C NMR at
100.62 MHz) and were processed with the software
MestReNova 11.0.3 (trial). Deuterated dimethyl sulfoxide
(DMSO-d6) and chloroform (CDCl3) were used as solvents
and as an internal standard. The 13C NMR chemical shifts
were attributed based on distortionless enhancement by
polarization transfer 135, heteronuclear multiple bond
correlation, and heteronuclear simple quantum coherence
experiments. Electrospray ionization (ESI) HRMS was
performed by the microanalysis service using a QSTAR XL
instrument (Salamanca, Spain).
2.2. Biological evaluation
Following our initial aim of study and considering the
growing interest on (thio)barbiturates by medicinal
chemists because of their increasingly wide range of bio-
logical activities [11], in addition to their most important
and classical use as sedative hypnotics [12], these new
benzisoxazoleebarbiturate systems were also screened as
XO inhibitors, radical 2,2-diphenyl-1-picrylhydrazyl
(DPPH) scavengers, and cytotoxic compounds (Table 1).
From the results of Table 1, it is important to stress the
moderate XO inhibition of the isoxazolbarbiturate 8c
(IC50 ¼ 22.10
mM). In addition, the thiobarbiturates 8a and
8b have some DPPH radical scavenger effects, especially for
compound 8b. Moreover, a marked reduction in MCF-7 cell
proliferation was observed with the benzisoxazole 8c.
Therefore, these structures can be considered in further
studies concerning the development of antioxidants and/or
XO inhibitors.
4.1. Synthesis
4.1.1. 1,3-Diphenylthiourea [13]
To a stirred solution of phenyl isothiocyanate (1 mmol;
135 mg) in dichloromethane (0.5 mL) at room temperature
was added dropwise a solution of aniline (1 mmol; 93 mg)
in dichloromethane (0.5 mL). The reaction was followed by
thin-layer chromatography (dichloromethane) and
completed in 3 h. The product so formed in suspension was
filtered and washed with ethyl ether; 217 mg (95%); white
crystals; mp 142e144 ꢁC (lit. [14], 140e142 ꢁC). 1H NMR
3. Conclusions
A new, efficient, simple, and mild method to prepare
bioactive 5-benzo[c]isoxazolbarbiturates from 5-(2-
nitrobenzylidene)barbiturates has been developed and for
the first time described. Single crystal X-ray data un-
equivocally confirmed the presence of this ring system,
whose formation can involve a nitroso intermediate in the
reduction of the nitroaromatic group. In addition, the iso-
xazolbarbiturate 8c has potential to be a starting point in
the development of new and improved XO inhibitors.
(400 MHz, DMSO-d6)
d (ppm) 9.79 (s, 2H), 7.48 (d,
J ¼ 7.4 Hz, 4H), 7.33 (t, J ¼ 8.2 and 7.6 Hz, 4H), 7.12 (t,
J ¼ 7.4 Hz, 2H); 13C NMR (101 MHz, DMSO-d6)
d (ppm)
179.6, 139.5, 128.5, 124.4, 123.7.
4.1.2. 1,3-Diphenylthiobarbituric acid (1b) [6]
Table 1
A stirred solution of 1,3-diphenylthiourea (1 mmol;
228 mg), malonic acid (1.3 mmol; 135 mg), and acetyl
XO inhibitory, antioxidant, and antiproliferative effects on MCF-7 cells of
5-benzo[c]isoxazolbarbiturates 8aed.a
chloride (3 mmol; 235 mg; 214 m
L) was heated at 60 ꢁC for
Compound
XO inhibition DPPH scavenging Relative MCF-7
30 min. The solid product so obtained was divided into
finer pieces, filtered, washed with water, and recrystallized
from acetic acid; 282 mg (95%); needle yellow crystals; mp
252e253 ꢁC (lit. [6], 258e259 ꢁC). 1H NMR (400 MHz,
(IC50
,
m
M)
(IC50
,
mM)
cell proliferation
8a
8b
8c
8d
12.65
15.50
52.26 (22.10)
29.89
24.62 (70.91)
57.28 (46.99)
5.39
72.79
58.06
43.48
64.82
n.d.b
CDCl3)
d
(ppm) 7.55 (m, 6H), 7.21 (d, J ¼ 7.3 Hz, 4H), 4.10 (s,
ꢀ0.64
2H); 13C NMR (101 MHz, CDCl3)
129.7, 129.2, 128.6, 41.2.
d (ppm) 181.6, 163.3, 138.8,
Allopurinol 80.41 (3.17)
Trolox
5-FU
n.d.b
n.d.b
n.d.b
70.35 (35.93)
n.d.b
n.d.b
11.88
a
4.1.3. 5-Benzylidenepyrimidines 3aed [7]
The screening was effected at a concentration of 30 mM, and the re-
sults are presented as % of XO inhibition, % of DPPH reduction, and % of the
negative control in cell proliferation, respectively. For the most relevant
compounds, doseeresponse curves to determine the half-medium
inhibitory concentrations (IC50) were then performed and presented
within parentheses.
A stirred mixture of (thio)barbituric acid 1aed (1 mmol)
and 2-nitrobenzaldehyde (2) (1 mmol) in water (5 mL) was
refluxed for 2 h. The product so formed after cooling was
filtered, washed with water, ethanol, and ethyl ether to
afford the following 5-benzylidenepyrimidines.
b
n.d., Not determined.
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002

J.L. Serrano et al. / C. R. Chimie xxx (2017) 1e6
5
5-(2-Nitrobenzylidene)-2-thioxodihydropyrimidine-
4,6(1H,5H)-dione (3a), from thiobarbituric ꢁacid (1a);
250 mg (90%); pale yellow solid; mp 239e241 C (lit. [15],
5-(Benzo[c]isoxazol-3(1H)-ylidene)-1,3-diphenyl-2-
thioxodihydropyrimidine-4,6(1H,5H)-dione (8b), from 5-
(2-nitrobenzylidene)-1,3-diphenyl-2-
246e250 ꢁC). 1H NMR (400 MHz, DMSO-d6)
d
(ppm) 12.56
thioxodihydropyrimidine-4,6(1H,5H)-dione (3b); 278 mg
(s, 1H),12.33 (s,1H), 8.63 (s,1H), 8.24 (dd, J ¼ 8.3 and 1.0 Hz,
1H), 7.80 (td, J ¼ 7.6 and 1.1 Hz, 1H), 7.72e7.66 (m, 1H), 7.62
(dt, J ¼ 7.7 and 1.2 Hz, 1H); 13C NMR (101 MHz, DMSO-d6)
(67%); yellow solid; mp 255e256 ꢁC. 1H NMR (400 MHz,
DMSO-d6)
d
(ppm) 7.80 (d, J ¼ 8.8 Hz, 1H, 40-ArCH), 7.40 (t,
J ¼ 7.7 Hz, 4H, 300- and 500-ArCH), 7.35 (d, J ¼ 8.9 Hz, 1H, 70-
ArCH), 7.29 (t, J ¼ 7.4 Hz, 2H, 400-ArCH), 7.24e7.19 (m, 5H, 200-
, 600- and 60-ArCH), 6.71 (dd, J ¼ 8.9 and 6.2 Hz,1H, 50-ArCH);
d
(ppm) 179.1, 160.6, 159.2, 153.3, 146.3, 133.8, 131.6, 130.5,
130.4, 124.1, 120.6.
5-(2-Nitrobenzylidene)-1,3-diphenyl-2-
13C NMR (101 MHz, DMSO-d6)
d (ppm) 178.6 (2-CS), 166.3
thioxodihydropyrimidine-4,6(1H,5H)-dione (3b), from 1,3-
diphenylthiobarbituric acid (1b); 387 mg (90%); pale or-
ange solid; mp 235 ꢁC decomposes (lit. [16], 232 ꢁC). 1H
(30-C), 159.6 (4 and 6-CO), 156.1 (7a0-ArC), 141.8 (100-ArC),
130.2 (60-ArCH), 129.6 (200- and 600-ArCH), 128.4 (300- and 500-
ArCH), 126.9 (400-ArCH), 125.3 (40-ArCH), 119.3 (50-ArCH),
NMR (400 MHz, DMSO-d6)
d
(ppm) 8.80 (s, 1H), 8.19 (d,
114.3 (3a0-ArC), 113.1 (70-ArCH), 85.4 (5-C); IR nmax (cmꢀ1
)
J ¼ 8.2 Hz, 1H), 7.71 (t, J ¼ 7.5 Hz, 1H), 7.59 (t, J ¼ 7.9 Hz, 2H),
3200e2200 (br), 3041, 2791, 2718, 1684, 1614, 1592, 1467,
1412, 1347, 1297, 1246, 1183, 955, 902, 764, 741, 684, 603;
HMRS (ESI-TOF) m/z: (MþþH) calcd for C23H16N3O3S
414.0907, found 414.0908.
7.45 (t, J ¼ 7.6 Hz, 2H), 7.40e7.28 (m, 6H), 7.20 (d, J ¼ 7.7 Hz,
2H); 13C NMR (101 MHz, DMSO-d6)
d (ppm) 181.4, 160.3,
158.8, 155.0, 146.2, 140.0, 139.7, 134.0, 131.8, 130.4, 130.2,
129.1, 128.9, 128.8, 128.7, 128.3, 128.1, 124.1, 121.3.
5-(Benzo[c]isoxazol-3(1H)-ylidene)pyrimidine-
5-(2-Nitrobenzylidene)pyrimidine-2,4,6(1H,3H,5H)-tri-
one (3c), from barbituric acid (1c); 254 mg (97%); white
solid; mp 274e275 ꢁC (lit. [17], 274e276 ꢁC). 1H NMR
2,4,6(1H,3H,5H)-trione (8c), from 5-(2-nitrobenzylidene)
pyrimidine-2,4,6(1H,3H,5H)-trione (3c); 195 mg (79%);
yellow solid; mp 266e268 ꢁC decomposes. 1H NMR
(400 MHz, DMSO-d6)
d
(ppm) 11.49 (s, 1H), 11.24 (s, 1H),
(400 MHz, DMSO-d6)
d
10.69 (s, 1H), 7.77 (dt, J ¼ 8.8 and
8.60 (s, 1H), 8.23 (d, J ¼ 7.9 Hz, 1H), 7.79 (t, J ¼ 7.4 Hz, 1H),
1.7 Hz, 1H, 40-ArCH), 7.46 (dt, J ¼ 9.1 and 1.7 Hz, 1H, 70-
ArCH), 7.32 (ddd, J ¼ 9.1, 6.4, and 0.8 Hz, 1H, 60-ArCH), 6.89
(ddd, J ¼ 8.8, 6.4, and 0.8 Hz, 1H, 50-ArCH); 13C NMR
7.68 (t, J ¼ 7.7 Hz, 1H), 7.57 (d, J ¼ 7.7 Hz, 1H); 13C NMR
(101 MHz, DMSO-d6)
d (ppm) 162.4, 161.2, 152.5, 150.3,
146.3, 133.8, 131.7, 130.4, 130.2, 124.1, 120.5.
(101 MHz, DMSO-d6) d
(ppm) 163.6 (30-C), 162.7 (4 and 6-
1,3-Dimethyl-5-(2-nitrobenzylidene)pyrimidine-
2,4,6(1H,3H,5H)-trione (3d), from 1,3-dimethylbarbituric
acid (1d); 281 mg (97%); white solid; mp 158e159 ꢁC (lit.
CO), 156.4 (7a0-ArC), 150.8 (2-CO), 131.8 (60-ArCH), 124.1 (40-
ArCH), 122.0 (50-ArCH), 116.2 (3a0-C), 113.7 (70-ArCH), 82.7
(5-C); IR nmax (cmꢀ1) 3200e2200 (br), 3174, 2960, 2813,
1722, 1666, 1648, 1601, 1440, 1403, 1360, 1320, 1286, 1238,
1142, 906, 841, 766, 752; HMRS (ESI-TOF) m/z: (MþþH)
calcd for C11H8N3O4 246.0509, found 246.0511.
[16], 159e161 ꢁC). 1H NMR (400 MHz, DMSO-d6)
d (ppm)
8.71 (s, 1H), 8.26 (dd, J ¼ 8.3 and 1.2 Hz, 1H), 7.80 (td, J ¼ 7.6
and 1.3 Hz, 1H), 7.69 (t, J ¼ 7.7 Hz, 1H), 7.53 (d, J ¼ 7.8 Hz,
1H), 3.25 (s, 3H), 3.06 (s, 3H); 13C NMR (101 MHz, DMSO-d6)
5-(Benzo[c]isoxazol-3(1H)-ylidene)-1,3-
d
(ppm) 161.2, 160.0, 153.7, 151.1, 146.2, 133.9, 132.0, 130.1,
dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (8d), from 1,3-
dimethyl-5-(2-nitrobenzylidene)pyrimidine-
130.0, 124.1, 120.1, 28.4, 27.8.
2,4,6(1H,3H,5H)-trione (3d); 140 mg (51%); yellow solid;
yellow crystals by crystallization in dichloromethane/
ethanol; mp 211e213 ꢁC. 1H NMR (400 MHz, DMSO-d6)
4.1.4. 3-Substituted-2,1-benzisoxazoles 8aed
A
stirred
suspension
of
related
5-
benzylidenepyrimidine 3aed (1 mmol), tin chloride dihy-
drate (2 mmol), and concentrated hydrochloric acid
(1.1 mL) was refluxed in methanol (35 mL) for 2 h. The
obtained hot mixture was filtered. The solid was washed
with ethanol and ethyl ether to afford the following 3-
substituted-2,1-benzisoxazoles.
d
7.90 (dt, J ¼ 8.8 and 1.1 Hz, 1H, 40-ArCH), 7.37 (dt, J ¼ 8.9
and 1.0 Hz, 1H, 70-ArCH), 7.29 (ddd, J ¼ 8.9, 6.2, and 1.1 Hz,
1H, 60-ArCH), 6.80 (ddd, J ¼ 8.8, 6.3, and 0.9 Hz, 1H, 50-
ArCH), 3.17 (s, 6H, 1- and 3-NCH3); 13C NMR (101 MHz,
DMSO-d6)
d
(ppm) 167.4 (30-C), 160.9 (4- and 6-CO), 155.9
(7a0-ArC), 152.3 (2-CO), 131.1 (60-ArCH), 125.5 (40-ArCH),
120.0 (50-ArCH), 114.9 (3a0-C), 112.9 (70-ArCH), 82.5 (5-C),
27.7 (1 and 3-NCH3); IR nmax (cmꢀ1) 3200e2200 (br), 2922,
2852, 2715, 1707, 1644, 1604, 1445, 1353, 1230, 1175, 1142,
1068, 899, 760, 749, 683; HMRS (ESI-TOF) m/z: (MþþH)
calcd for C13H12N3O4 274.0822, found 274.0827.
5-(Benzo[c]isoxazol-3(1H)-ylidene)-2-
thioxodihydropyrimidine-4,6(1H,5H)-dione (8a), from 5-
(2-nitrobenzylidene)-2-thioxodihydropyrimidine-
4,6(1H,5H)-dione (3a); 215 mg (82%); yellow solid; mp
207e208 ꢁC decomposes. 1H NMR (400 MHz, DMSO-d6)
d
11.05 (s, 2H, 1- and 3-NH), 7.88 (d, J ¼ 8.8 Hz, 1H, 40-
ArCH), 7.34 (d, J ¼ 9.0 Hz, 1H, 70-ArCH), 7.22 (dd, J ¼ 9.0
4.2. X-ray analysis
and 6.3 Hz, 1H, 60-ArCH), 6.73 (dd, J ¼ 8.8 and 6.3 Hz, 1H,
50-ArCH); 13C NMR (101 MHz, DMSO-d6)
d
(ppm) 174.5 (2-
Crystals suitable for single-crystal X-ray analysis were
grown from a mixture of ethanol and dichloromethane.
Selected crystals were covered with polyfluoroether oil
(Fombling, Sigma Aldrich) and mounted on a nylon loop.
The data were collected at 110(2) K using a Bruker D8
Venture diffractometer equipped with a Photon 100 de-
tector and an Oxford Cryostem Cooler, using graphite
CS), 166.1 (30-C), 161.0 (4 and 6-CO), 156.3 (7a0-ArC), 130.3
(60-ArCH), 125.4 (40-ArCH), 119.3 (50-ArCH), 114.2 (3a0-C),
113.1 (70-ArCH), 85.0 (5-C); IR nmax (cmꢀ1) 3200e2200
(br), 3381, 2879, 2709, 1664, 1607, 1506, 1466, 1357, 1282,
1251, 1164, 1005, 939, 907, 785, 754, 714; HMRS (ESI-TOF)
m/z: (MþþH) calcd for C11H8N3O3S 262.0281, found
262.0281.
monochromated Mo K
a
radiation (
l
¼ 0.71073 Å). Table S1
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002

6
J.L. Serrano et al. / C. R. Chimie xxx (2017) 1e6
(b) Y. Uto, Expert Opin. Ther. Pat. 25 (2015) 643e662;
(c) R.A. Shastri, Chem. Sci. Trans. 5 (2016) 8e20;
(d) S.Y. Kwan, Y.C. Chuang, C.W. Huang, T.C. Chen, S.B. Jou, A. Dash,
CNS Neurosci. Ther. 21 (2015) 683e691;
(Supplementary information) contains crystallographic
experimental data and structure refinement parameters.
CCDC 1557900 contains the supplementary crystallo-
graphic data for this article. The data can be obtained free of
charge from the Cambridge Crystallographic Data Centre
via http://www.ccdc.cam.ac.uk/structures.
(e) J.H. Cox, S. Seri, A.E. Cavanna, Adv. Ther. 31 (2014) 276e288.
[2] (a) M. Wieclaw, M. Bobin, A. Kwast, R. Bujok, Z. Wrobel,
K. Wojciechowski, Mol. Divers. 19 (2015) 807e816 and references
cited therein;
(b) A.V. Budruev, D.Y. Dzhons, Chem. Heterocycl. Compd. 52 (2016)
441e443 and references therein.
[3] P. Friedlander, R. Henriques, Ber. Dtsch. Chem. Ges. 15 (1882)
4.3. Biological evaluation
€
2105e2110.
Preparation of sample solutions and experimental pro-
cedures are presented in Supplementary information.
[4] A.D. Kotov, M.A. Prokaznikov, E.A. Antonova, A.I. Rusakov, Chem.
Heterocycl. Compd. 50 (2014) 647e657 and references cited therein.
[5] (a) K.Y. Lee, J.M. Kim, J.N. Kim, Bull. Korean Chem. Soc. 23 (2002)
1493e1495;
Acknowledgments
(b) K.Y. Lee, H.S. Lee, J.N. Kim, Bull. Korean Chem. Soc. 28 (2007)
333e335;
(c) B.J. Stokes, C.V. Vogel, L.K. Urnezis, M. Pan, T.G. Driver, Org. Lett.
12 (2010) 2884e2887.
This work is supported by FEDER funds through the
POCIdCOMPETE 2020dOperational Programme Compet-
itiveness and Internationalisation in Axis IdStrengthening
research, technological development and innovation
(Project POCI-01-0145-FEDER-007491) and National Funds
by FCTdFoundation for Science and Technology (Project
UID/Multi/00709/2013). The SCXR determinations were
performed at UCIBIO/FCT-NOVA, financed by national
funds from FCT/MEC (UID/Multi/04378/2013), and cofi-
nanced by the ERDF under the PT2020 Partnership Agree-
ment (POCI-01-0145-FEDER-007728).
[6] H. Schulte, Chem. Ber. 87 (1954) 820e824.
[7] M.L. Deb, P.J. Bhuyan, Tetrahedron Lett. 46 (2005) 6453e6456.
[8] H. Faustino, R.M. El-Shishtawy, L.V. Reis, P.F. Santos, P. Almeida,
Tetrahedron Lett. 49 (2008) 6907e6909.
ꢀ
ꢁ ꢀ
[9] V. Pilepic, S. Ursic, J. Mol. Struct. (Theochem.) 538 (2001) 41e49.
[10] L.F. Fieser, M. Fieser, Reagents for Organic Synthesis, Wiley, New
York, 1967, pp. 1113e1116.
[11] (a) R.M. Shaker, E.A. Ishak, Z. Naturforsch. 66b (2011) 1189e1201;
(b) G.M. Ziarani, F. Aleali, N. Lashgari, RSC Adv. 6 (2016) 50895
e50922;
(c) K.M. Khan, M. Khan, A. Karim, M. Taha, N. Ambreen, A. Gojayev,
S. Perveen, M.I. Choudhary, J. Chem. Soc. Pak. 35 (2013) 495e498.
ꢀ
~
[12] (a) F. Lopez-Munoz, R. Ucha-Udabe, C. Alamo, Neuropsychiatric Dis.
Treat. 1 (2005) 329;
(b) T.L. Lemke, D.A. Williams, Wolters Kluwer Health (2012) 485
e507.
Appendix A. Supplementary data
[13] A. Lu, Z. Wang, Z. Zhou, J. Chen, Q. Wang, J. Agric. Food Chem. 63
(2015) 1378e1384.
Supplementary data related to this article can be found
at https://doi.org/10.1016/j.crci.2017.10.002.
[14] F. Wang, P. Zhao, C. Xi, Tetrahedron Lett. 52 (2011) 231e235.
[15] M. Kuanar, B.K. Mishra, Indian J. Chem., Sect. A: Inorg., Bio-inorg.,
Phys., Theor. Anal. Chem. 34 (1995) 721e723.
[16] N. Seyyedi, F. Shirini, M.S. Nikoo Langarudi, RSC Adv. 6 (2016)
44630e44640.
References
[17] M.K. Haldar, M.D. Scott, N. Sule, D.K. Srivastava, S. Mallik, Bioorg.
Med. Chem. Lett. 18 (2008) 2373e2376.
[1] (a) M.A. Barmade, P.R. Murumkar, M.K. Sharma, M.R. Yadav, Curr.
Top. Med. Chem. 16 (2016) 2863e2883;
Please cite this article in press as: J.L. Serrano, et al., A synthetic route to novel 3-substituted-2,1-benzisoxazoles from 5-(2-
nitrobenzylidene)(thio)barbiturates, Comptes Rendus Chimie (2017), https://doi.org/10.1016/j.crci.2017.10.002