Microwave assisted aqueous phase synthesis of benzothiazoles and benzimidazoles in the presence of Ag2O

Article abstract of DOI:10.1134/S1070363216120343

A simple and high yielding method for synthesized benzothiazoles and benzimidazole in water under micro wave irradiation by the reaction of 2-amino thiophenol and o-phenylenediamine with various aromatic aldehydes in the presence of Ag₂O. Ag

Full text of DOI:10.1134/S1070363216120343

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 87, No. 12, pp. 2737–2743. © Pleiades Publishing, Ltd., 2016.
Microwave Assisted Aqueous Phase Synthesis
of Benzothiazoles and Benzimidazoles
in the Presence of Ag2O1
B. Sakram*, S. Rambabu, K. Ashok, B. Sonyanaik, and D. Ravi
Department of Chemistry, Osmania University, Hyderabad, 500007 India
*e-mail: bschemou@gmail.com
Received January 8, 2016
Abstract—A simple and high yielding method for synthesized benzothiazoles and benzimidazole in water
under micro wave irradiation by the reaction of 2-amino thiophenol and o-phenylenediamine with various
aromatic aldehydes in the presence of Ag2O. Ag2O can be recovered and reused without significant loss of
activity.
Keywords: benzothiazoles, benzimidazole, 2-amino thiophenol, o-phenylenediamine, aromatic aldehydes, Ag2O,
microwave irradiation
DOI: 10.1134/S1070363216120343
Benzothiazoles and benzimidazoles belong to one
of the most important classes of heterocycles for the
synthesis of natural products, pharmaceuticals, dyes
and various other biologically active molecules, such
as Riluzole a drug used to treat amyotrophic lateral
sclerosis [1] and Mebendazole a drug used to treat
parasitic worm infestations [2].
wet DMF at room temperature. Saha et al. [11]
described the synthesis of 2-substituted benzimida-
zoles by using o-phenylenediamine with aromatic
aldehydes in the presence of an ionic liquid, 1-methyl-
3-methylimidazolium tetrauoroborate, [pmim]BF4 at
room temperature. Mirkhani et al. [12] has reported the
synthesis of 2-imidazolines and bis-imidazolines by
the reaction of ethylenediamine, and nitriles in the
presence of sulfur under ultrasonic irradiation. Katla
et al. [13] has reported the aqueous phase synthesis of
benzothiazoles and benzimidazoles by using 2-amino
thiophenol and o-phenylenediamine with aromatic
aldehyde in the presence of β-cd. Banerjee et al. [14]
developed synthesis of biologically active 2-aryl-1,3-
benzothiazole and 1,3-benzoxazole derivatives in
presence of a green efficient catalyst (ZnO nano-
particles) at room temperature.
Benzothiazole derivatives have been used for
diabetes [3], antitumor drugs [4], and amyloid
inhibitors for treatment of Alzheimer’s disease [5].
Especially benzimidazoles are useful in controlling the
diseases such as hypertension [6], ischemiareperfu-
sion injury [7], as well as obesity [8].
A number of methodologies have been developed
for the synthesis of benzothiazoles and benzimidazoles.
Hornberger et al. [9] have developed one-pot synthesis
of disubstituted benzimidazoles from 2-nitro anilines
with palladium charcoal as a catalyst in the presence of
trimethyl orthoformate and catalytic pyridinium p-
toluenesulfonate (PPTS) at room temperature.
Beaulieu et al. [10] demonstrated the oxone mediated
benzimidazoles, benzoxazoles and benzothiazoles by
using phenylene diamines, 2-amino thiophenol, 2-
aminothiol, and acid one-pot synthesis of benzimida-
zoles using 1,2-phenylenediamines and aldehydes in
However, the above mentioned methods have
different draw backs, including the use of toxic and ex-
pensive reagents or catalysts, strongly acidic condi-
tions, long reaction time, harsh reaction conditions,
side reactions and low yields. In continuation of our
attempts to develop environmentally benign metho-
dologies, herein we report an Microwave assisted
aqueous phase Ag2O catalyzed method for the syn-
thesis of benzothiazoles and benzimidazoles by a two
component reaction, involving 2-amino thiophenol and
1,2-diamino benzene with various benzaldehydes
(Scheme 1).
1 The text was submitted by the authors in English.
2737

2738
SAKRAM et al.
Scheme 1.
CHO
R1
NH2
XH
N
X
microwave, Ag2O
H2O
+
R1
X = S, NH; R1 = F, Br, Cl, NO2, Me, OMe, OEt, OH, H.
RESULTS AND DISCUSSION
dissolved completely, then was added to a mixture of
2-aminobenzenethiols and o-phenylenediamine
Optimization of the reaction conditions. In order
to optimize the reaction conditions, primary efforts
were focused on the use of Ag2O, water as solvent and
2-aminobenzenethiols/o-phenylenediamine (1) and
benzaldehyde (2) were chosen as the model reactants
to detect the microwave reaction conditions. The
screening of different solvents was summarized in
Table 1. It turned out that in the absence of theAg2O,
the product was obtained in only 20% yield (Table 1,
entry 5). Among the four selected solvents. Water has
the most effective (Table 1, entry 1).
(1.1 mmol) and various benzaldehyde 2 (1.0 mmol)
and mixed thoroughly. The reaction mixture was
irradiated in a microwave oven at 700 W for specific
period of time. The progress of the reaction was
monitored by TLC upon completion of the reaction.
The reaction mixture was cooled to room temperature,
and then evaporated in vacuum. The product purified
by column chromatography (PE–EtOAc = 20 : 1) to
give solid 3a–3i, 4a–4h.
Above two methods, microwave method is
convenient method for synthesis of 2-aryl-1,3-
benzothiazoles (or) 2-aryl-1,3-benzimidazoles due to
less reaction time and high percentage of yield.
a. Conventional method. A mixture of 2-amino-
benzenethiols and o-phenylenediamine (1.1 mmol)
various benzaldehyde (1 mmol), and water (5 mL) was
refluxed for 1 h in the presence of Ag2O (5 mmol). The
progress of the reaction was monitored by TLC upon
completion of the reaction. The reaction mixture was
cooled down to room temperature and poured over
crushed ice. The residue was filtered off, washed with
water and purified by column chromatography (PE–
EtOAc = 20 : 1) to yield title compounds 3a–3i, 4a–4h.
Encouraged by the above experiments, we further
explored the synthetic protocol and the scope by
employing different kinds of aldehydes functionalized
with electron-rich groups (F, -Cl, -Br, -OH, -OMe).
The results were summarized in Table 2. Clearly, all
reactions worked well irrespective of the substituents
on the aldehydes substrates (Table 2, compounds 3a–
3i). It is noteworthy that the reaction with 1H-indole-3-
carbaldehyde (Table 2, compound 3i) also afforded the
desired product in satisfactory yield.
b. Microwave method. Ag2O (5 mmol) were
dissolved in 10 mL water and stirred until the solid
Table 1. Optimization of the reaction conditionsa
Viability of the methodology was examined for a
series of aryl/hetero aryl aldehydes bearing electron
donating as well as electron withdrawing groups under
the optimized reaction conditions and corresponding
products were obtained in good to excellent yields.
Presence of electron withdrawing group (eg-NO2) in
aldehyde system fixed firmly the reaction while
opposite effect was observed for electron donating
substituent’s like Cl, Me, OMe, OEt (4b to 4h). Using
these reaction conditions exclusively formation of 2-
substituted benzimidazoles was observed. The
products were characterized by their physical and
spectral data. Thus, Table 3 illustrates generality and
efficiency of this method for the synthesis of
benzimidazoles.
Conventional
method
time, h yield,b % time, h yield,b %
Microwave
irradiation method
Enry
no.
Solvent
1
2
3
4
5
H2O
EtOH
CH2Cl2
THF
–
1
3
2
5
8
62
45
58
54
15
5
98
95
92
80
20
10
8
12
14
a
Reaction conditions: Ag2O (5 mmol) phenylenediamine 1
(1.1 mmol), and benzaldehyde 2 (1.0 mmol) 10 mL water.
Isolated yields.
b
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MICROWAVE ASSISTED AQUEOUS PHASE SYNTHESIS
2739
Table 2. Synthesis of 2-aryl-1,3-benzothiazoles in the presence of Ag2O under micro wave irradiation
mp, °C
Comp.
no.
Aldehyde
CHO
Product
Time, min
5
Yeild, %
found
96–97
calculated
3a
98–99 [15]
98
N
S
F
F
6
4
CHO
3b
3c
231–232
131–132
230–234 [16]
130–131 [17]
96
N
S
OH
OH
CHO
97
98
N
S
Br
Br
5
CHO
3d
111–113
112–114 [18]
N
S
7
5
4
CHO
MeO
3e
3f
OMe
122–123
68–69
122–123 [18]
66–68 [19]
93
95
96
N
S
CHO
Br
N
S
Br
CHO
OH
3g
152–154
154–156 [20]
N
S
OH
OH
OH
Me
Me
8
6
CHO
3h
3i
120–122
180–182
122–124 [21]
92
95
N
S
Me
Me
CHO
–
S
N
HN
N
H
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2740
SAKRAM et al.
Table 3. Synthesis of 2-aryl-1,3-benzimidazoles in the presence of Ag2O under micro wave irradiation
mp, °C
Comp.
no.
Aldehyde
CHO
Product
Time, min
5
Yeild, %
98
found
calculated
296–298
299–301 [22]
4a
N
NO2
N
H
NO2
6
4
287–289
274–275
287–289 [23]
276–278 [24]
CHO
4b
4c
96
97
N
Cl
N
H
Cl
CHO
N
Me
N
H
Me
CHO
5
220–222
221–223 [24]
N
4d
98
OMe
N
H
OMe
CHO
7
5
293–294
192–195
293–295 [24]
N
4e
4f
93
95
N
H
CHO
–
N
OEt
N
H
OEt
MeO
CHO
4
8
180–182
232–234
181–182 [24]
231–233 [25]
N
4g
4h
OMe
96
92
N
H
CHO
Cl
N
Cl
N
H
EXPERIMENTAL
silica-gel precoated thin-layer chromatography (TLC)
plates using hexane:ethyl acetate (8 : 3) as eluent, and
the developed chromatogram was visualized under
ultraviolet (UV) light and iodine vapors. Infrared (IR)
spectra were recorded on a Bruker Tensor 27 series
Fourier-transform (FT)-IR spectrophotometer using
KBr pellets. Proton nuclear magnetic resonance (1H
All reagents and solvents were procured from
Aldrich/Merck and used without further purification.
Melting points were recorded using a Cintex melting
point apparatus and are uncorrected. Reaction progress
as well as compound purity were monitored with F254
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

MICROWAVE ASSISTED AQUEOUS PHASE SYNTHESIS
2741
NMR) spectra were recorded on a Bruker 400-MHz
spectrometer using deuterated dimethyl sulfoxide
(DMSO-d6) as solvent and tetramethylsilane (TMS) as
internal standard. Mass spectra were recorded on a Jeol
JMSD-400 spectrometer. Elemental analyses were
performed on a Carlo-Erba model EA1108 analytical
unit, and the values are within ±0.4% of theoretical
values. The reactions were carried out in a BPL 800 G
domestic microwave oven.
132.17, 128.85, 126.45, 125.39, 123.27, 121.64,
132.16, 128.84, 126.44, 125.39, 123.26, 121.64. MS
(ESI): m/z 290 [M + 2]+.
2-Phenylbenzo[d]thiazole (3d). 1H NMR spectrum
(300 MHz, CDCl3), δ, ppm: 8.12–8.05 m (3H, ArH),
7.89 d (1H, ArH, J = 7.8 Hz), 7.53–7.45 m (3H, ArH),
7.41–7.35 m (2H, ArH). 13C NMR spectrum
(100 MHz, CDCl3), δ, ppm: 130.94, 128.99, 127.51,
126.27, 125.13, 123.19, 121.58. MS (ESI): m/z 212
[M + H]+.
2-(2-Methoxyphenyl)benzo[d]thiazole (3e). 1H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.52 d (1H, ArH,
J = 1.8 Hz), 8.51 d(1H, ArH, J = 1.6 Hz), 8.08 d (1H,
ArH, J = 8.2 Hz), 7.49 d (1H, ArH, J = 1.2 Hz), 7.48–
7.43 m (2H, ArH), 7.36–7.33 m (2H, ArH), 4.04 s (3H,
OCH3). 13C NMR spectrum (100 MHz, CDCl3), δ,
ppm: 157.13, 152.06, 131.73, 129.43, 125.84, 124.53,
122.73, 121.14, 111.58. MS (ESI): m/z 242 [M + H]+.
General procedure for the synthesis of 2-sub-
stituted benzothiazoles (3a–3i). Ag2O (5mmol) were
dissolved in 10 mL water and stirred until the solid
dissolved completely, then was added to a mixture of
2-amino thiophenol 1 (1.1 mmol) and benzaldehyde 2
(1.0 mmol) and mixed thoroughly. The reaction
mixture was irradiated in a microwave oven at 700 W
for specific period of time as indicated in Table 2, the
reaction was complete monitored by TLC analysis The
reaction mixture was cooled to room temperature, and
then evaporated in vacuum. The product purified by
column chroma-tography (PE–EtOAc = 20 : 1) to give
white solid 3 (0.2092 g, 99%). Other products were
1
2-(2-Bromophenyl)benzo[d]thiazole (3f). H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.14 d (1H, ArH,
J = 7.9 Hz), 8.02–7.93 m (2H, ArH), 7.72 d (1H, ArH,
J = 7.9 Hz), 7.54–7.29 m (4H, ArH). 13C NMR
spectrum (100 MHz, CDCl3), δ, ppm: 165.62, 152.49,
133.95, 132.04, 131.18, 127.46, 126.25, 125.39,
123.41, 121.35. MS (ESI): m/z 290 [M + 2]+.
1
synthesized through the same procedure. All H NMR
13
and C NMR results were summarized in Supporting
information. The configuration of compounds was
1
assigned by comparing H and 13C NMR data with
known compounds.
1
4-(Benzo[d]thiazol-2-yl)benzene-1,2-diol (3g). H
2-(4-Fluorophenyl)benzo[d]thiazole (3a). 1H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.08–8.04 m
(1H, ArH), 7.88 d (1H, ArH), J = 7.5 Hz), 7.48 t (1H,
ArH, J = 7.1 Hz), 7.17 t (2H, ArH, J = 7.0 Hz). 13C
NMR spectrum (100 MHz, CDCl3), δ, ppm: 166.62,
153.93, 134.92, 129.43, 129.38, 126.32, 125.14,
123.07, 121.49, 116.13, 115.95. MS (ESI): m/z 230
[M + H]+.
NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.21–7.16
m (2H, ArH), 7.12–7.06 m (2H, ArH), 7.01–6.96 m
(2H, ArH), 6.83–6.76 m (1H, ArH), 5.27 s (2H, OH).
13C NMR spectrum (100 MHz, CDCl3), δ, ppm:
143.63, 128.21, 128.09, 127.82, 127.68, 127.61,
127.23, 126.92, 125.63, 36.91, 36.68, 31.93, 31.80,
30.16, 30.04, 29.71, 29.34, 29.24, 27.72, 27.64, 22.82,
22.68, 22.58, 14.11.MS (ESI): m/z 244 [M + H]+.
4-(Benzo[d]thiazol-2-yl)phenol (3b). 1H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.35 s (1H,
ArH), 8.04–7.96 m (2H, ArH), 7.88–7.76 m (2H,
ArH), 7.46 t (1H, ArH, J = 7.1 Hz), 7.34 t (1H, ArH,
J = 6.9 Hz), 6.93–6.91 m ( 2H, ArH). 13C NMR
spectrum (100 MHz, CDCl3), δ, ppm: 167.14, 159.73,
153.26, 133.78, 128.33, 125.32, 123.98, 123.85,
121.64, 120.74, 115.31. MS (ESI): m/z 228 [M + H]+.
2-(3,4,5-Trimethoxyphenyl)benzo[d]thiazole (3h).
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 8.05 d
(1H, ArH, J = 8.2 Hz), 7.88 d (1H, ArH, J = 7.6 Hz),
7.50–7.47m (2H, ArH), 7.31 s (1H, ArH), 7.11 s (1H,
ArH), 3.98 s (9H, CH3). 13C NMR spectrum
(100 MHz, CDCl3), δ, ppm: 153.88, 153.46, 134.82,
126.33, 125.08, 122.98, 121.46, 104.62, 60.92, 56.28.
MS (ESI): m/z 302 [M + H]+.
1
2-(4-Bromophenyl)benzo[d]thiazole (3c). 1H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.07 d (1H, ArH,
J = 8.1 Hz), 7.98–7.95 m (2H, ArH), 7.92 d (1H, ArH,
J = 7.9 Hz), 7.66–7.62 m (2H, ArH), 7.52–7.47 m (1H,
ArH), 7.42–7.37 m (1H, ArH). 13C NMR spectrum
(100 MHz, CDCl3), δ, ppm: 166.63, 154.03, 135.01,
2-(1H-Indol-3-yl)benzo[d]thiazole (3i). H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.92 s (1H,
ArH), 8.43 d (1H, ArH, J = 7.1 Hz), 8.03 d (1H, ArH,
J = 8.1 Hz), 7.92 d (1H, ArH, J = 2.8 Hz), 7.86 d (1H,
13
ArH, J = 7.9 Hz), 7.46–7.26 m (5H, ArH). C NMR
spectrum (100 MHz, CDCl3), δ, ppm: 163.23, 153.63,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2742
SAKRAM et al.
136.43, 133.79, 126.41, 126.04, 124.83, 124.17, 123.33,
121.96, 121.73, 121.28, 120.92, 112.22, 111.73. MS
(ESI): m/z 251 [M + H]+.
2-Phenyl-1H-benzo[d]imidazole (4e). 1H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.06 d (1H, ArH,
J = 6.2 Hz), 7.67–7.63 m (3H, ArH), 7.48–7.43 m (2H,
ArH), 7.28–7.26 m (2H, ArH), 7.12 d (1H, ArH, J =
6.8 Hz), 5.46 s (1H).13C NMR spectrum (100MHz,
CDCl3), δ, ppm: 151.53, 129.92, 129.23, 128.28,
126.36, 121.76. MS (ESI): m/z 195 [M + H]+.
General procedure for the synthesis of 2-sub-
stituted benzimidazoles (4a–4h). Ag2O (5 mmol)
were dissolved in 10 mL water and stirred until the
solid dissolved completely, then was added to a
mixture of o-phenylenediamine 1 (1.1 mmol) and
benzaldehyde 2 (1.0 mmol) and mixed thoroughly. The
reaction mixture was irradiated in a microwave oven at
700 W for specific period of time as indicated in Table
3, the reaction was complete monitored by TLC
analysis The reaction mixture was cooled to room
temperature, and then evaporated in vacuum. The
product purified by column chromatography (PE–
EtOAc = 20 : 1) to give white solid 3a (0.2092 g,
99%). Other products were synthesized through the
2-(4-Ethoxyphenyl)-1H-benzo[d]imidazole (4f).
1H NMR spectrum (300 MHz, DMSO-d6), δ, ppm:
7.58–7.54 m (2H, ArH), 7.24–7.12 m (3H, ArH), 6.78
d (1H, ArH, J = 8.3 Hz), 6.91–6.87 m (2H, ArH),
4.09–3.95 q (2H, OCH2), 1.42 t (3H, CH3, J = 7.5 Hz).
13C NMR spectrum (100 MHz, DMSO-d6), δ, ppm:
160.27, 158.49, 153.98, 143.08, 136.02, 130.65,
128.13, 127.12 122.64, 119.69, 114.61, 110.31, 63.32,
14.82. MS (ESI): m/z 239 [M + H]+.
2-(2-Methoxyphenyl)-1H-benzo[d]imidazole (4g).
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 8.03–
7.97 m (5H, ArH), 6.92–6.88 m (4H, ArH), 3.84 s (3H,
OCH3). 13C NMR spectrum (100 MHz, CDCl3), δ,
ppm: 157.45, 156.36, 152.31, 143.02, 135.36, 132.24,
131.36, 128.31, 127.62, 122.42, 121.92, 120.68,
120.28, 119.58, 110.71, 109.82, 55.13, 55.04, 43.46.
MS (ESI): m/z 225 [M + H]+.
1
same procedure. All H and 13C NMR results were
summarized in Supporting information. The configura-
1
tion of compounds was assigned by comparing H and
13C NMR data with known compounds.
1
2-(4-Nitrophenyl)-1H-benzo[d]imidazole (4a). H
NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.64–7.62
m (2H, ArH), 7.43–7.41 m (3H, ArH), 7.31–7.26 m
13
(3H, ArH). C NMR spectrum (100 MHz, CDCl3), δ,
2-(2-Chlorophenyl)-1H-benzo[d]imidazole (4h).
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 8.61 s
(1H, ArH), 7.94 d (3H, ArH, J = 5.8 Hz), 7.46 s (2H,
ArH), 7.24 s (1H, ArH), 6.71 d (1H, ArH, J = 8.3 Hz),
4.91 s (1H, NH).13C NMR spectrum (100 MHz,
CDCl3), δ, ppm: 158.21, 130.94, 128.98, 127.54,
126.24, 125.12, 123.18, 121.55. MS (ESI): m/z 229
[M + H]+.
ppm: 160.25, 158.53, 153.97, 143.09, 136.02, 130.62,
128.13, 127.11, 122.63, 119.71, 114.62, 110.35.MS
(ESI): m/z 240 [M + H]+.
2-(4-Chlorophenyl)-1H-benzo[d]imidazole (4b).
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 7.58 d
(1H, ArH, J = 7.6 Hz), 7.40 d (2H, ArH, J = 7.6 Hz),
7.30–7.22 m (3H, ArH), 7.14 d (1H, ArH, J = 7.6 Hz),
7.03 d (1H, ArH, J = 7.6 Hz).13C NMR spectrum (100
MHz, CDCl3), δ, ppm: 130.91, 128.96, 127.51, 126.26,
125.13, 123.16, 121.58. MS (ESI): m/z 229 [M + H]+.
In summary, we have developed an efficient syn-
thetic protocol for the synthesis of benzothiazoles and
benzimidazoles derivatives in the presence of Ag2O
under micro wave irradiation. Using of Ag2O as a
highly efficient, easy handling, and nontoxic reducing
reagent makes the present procedure ecofriendly and
economically acceptable. The yields obtained are
excellent and the products were recovered in pure form
from the reaction mixture.
1
2-(p-Tolyl)-1H-benzo[d]imidazole (4c). H NMR
spectrum (300 MHz, CDCl3), δ, ppm: 8.14 d (4H, ArH,
J = 8.3 Hz), 7.34 d (4H, ArH, J = 8.1 Hz), 3.12 s (1H,
NH), 2.42 s (3H, CH3).13C NMR spectrum (50 MHz,
CDCl3), δ, ppm: 140.33, 137.78, 132.72, 129.75,
129.43, 128.83, 125.71, 123.22, 120.54, 110.44, 21.0.
MS (ESI): m/z 209 [M + H]+.
ACKNOWLEDGMENTS
2-(4-Methoxyphenyl)-1H-benzo[d]imidazole (4d).
1H NMR spectrum (300 MHz, CDCl3), δ, ppm: 8.12 d
(1H, ArH, J = 8.6 Hz), 7.64–7.44 m (3H, ArH), 6.96–
6.91 m (3H, ArH), 6.78 d (1H, ArH, J = 8.6 Hz), 3.71
We thanks to the Head, Department of Chemistry,
Osmania University, Hyderabad for providing
laboratory facilities. One of the author (S. Rambabu)
thanks to UGC-BSR, India for financial assistance
[F.4-1/2006(BSR)11-38/2008(BSR)/2013-2014/04].
13
s (3H, OCH3) C NMR spectrum (100 MHz, CDCl3),
δ, ppm: 166.61, 164.12, 154.84, 132.96, 58.41. MS
(ESI):m/z 225 [M + H]+.
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13C NMR spectra).
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