A simple and efficient preparation of pyrazolo[3,4-b]-pyridine derivatives through an unexpected reaction of cyanothioacetamide under microwave irradiation

Article abstract of DOI:10.1002/hc.20497

An unexpected multicomponent reaction of cyanothioacetamide with aromatic aldehydes and aminopyrazole under MWI was found and reported. It turned out to be an efficient and simple procedure for the preparation of pyrazolo[3,4-b] pyridine derivatives. The structure of the product was characterized by IR,MS, ¹Hand ¹³CNMR, COSY and NOESY spectroscopy, X-ray crystallographic analysis, and by comparison with the authentic sample prepared with the known procedure.

Full text of DOI:10.1002/hc.20497

Heteroatom Chemistry
Volume 19, Number 7, 2008
A Simple and Efficient Preparation
of Pyrazolo[3,4-b]-pyridine Derivatives
Through an Unexpected Reaction
of Cyanothioacetamide
Under Microwave Irradiation
Xuesen Fan, Xia Wang, Xinying Zhang, Xiaoyan Li, and Guirong Qu
School of Chemical and Environmental Sciences, Henan Key Laboratory for Environmental
Pollution Control, Henan Normal University, Xinxiang 453007, People’s Republic of China
Received 13 November 2007; revised 9 June 2008
INTRODUCTION
ABSTRACT: An unexpected multicomponent reac-
tion of cyanothioacetamide with aromatic aldehydes
and aminopyrazole under MWI was found and re-
ported. It turned out to be an efficient and simple pro-
cedure for the preparation of pyrazolo[3,4-b]pyridine
derivatives. The structure of the product was charac-
terized by IR, MS, 1H and 13C NMR, COSY and NOESY
spectroscopy, X-ray crystallographic analysis, and by
comparison with the authentic sample prepared with
Development of novel synthetic methodology for the
preparation of drug-like heterocyclic compounds is
an intense research area. One approach to address
this challenge involves the development of multi-
component reactions, in which three or more reac-
tants are combined together to generate a product
incorporating most of the atoms contained in the
starting materials. In addition to the intrinsic atom
economy and selectivity underlying such reactions,
simpler procedures, time, and energy savings as well
as environmental friendliness have led to rapidly
increasing efforts to design and implement multi-
component reactions (MCRs) in both academia and
industry [1]. In the meantime, the utility of mi-
crowave energy in synthetic organic chemistry has
been increasingly recognized as compared with con-
ventional heating, reactions promoted by microwave
irradiation (MWI) have shown an environmental
friendly nature, greater selectivity, and enhanced re-
action rate. Therefore, the MWI-mediated multicom-
ponent reaction has constituted an especially attrac-
tive synthetic strategy for the rapid and efficient li-
brary generation [2].
ꢀ
C
the known procedure.
2008 Wiley Periodicals, Inc.
Heteroatom Chem 19:694–699, 2008; Published online
in Wiley InterScience (www.interscience.wiley.com). DOI
10.1002/hc.20497
Correspondence to: Xuesen Fan; e-mail: fanxs88@263.net,
Xinying Zhang; e-mail: xyzh518@sohu.com
Contract grant sponsor: The National Natural Science Founda-
tion of China.
Contract grant number: 20772025.
Contract grant sponsor: Program for Science & Technology In-
novation Talents in Universities of Henan Province.
Contract grant number: 2008HASTIT006.
Contract grant sponsor: Department of Education of Henan
Province.
On the other hand, there is a rapidly increas-
ing recognition of the thioamide group as a use-
ful moiety in organic synthesis. As an example,
Contract grant number: 2008A150013.
2008 Wiley Periodicals, Inc.
c
ꢀ
694

Simple and Efficient Preparation of Pyrazolo[3,4-b]-pyridine Derivatives 695
Ar1
comprehensive reviews of the use of thioamides in
H3C
CN
S
organic synthesis have been published to date and
some of them are specifically concerned with the
use of thioamides as universal and versatile build-
ing blocks in the synthesis of heterocyclic com-
pounds [3]. In this regard, thioamides with active
α hydrogen atoms, such as 2-cyanothioacetamide,
can be condensed with aldehydes to give 2-cyano-2-
enethioamide, which can act as a good Michael ad-
dition receptor to undergo addition-cyclization reac-
tions to afford the corresponding heterocyclic frame-
works [4]. In this field, we have demonstrated that
the one-pot reaction of aromatic aldehydes, cyanoth-
ioacetamide, and malononitrile under MWI is an ef-
ficient way for the synthesis of thiopyran derivatives
[5]. Recently, Ghattas et al. reported a novel prepa-
ration of pyrazolo[3,4-b]-pyridine-thiones from
the reaction of arylidene–cyanothioacetamide with
1-phenylpyrazolidine-3,5-dione [6]. Although the
preparative procedure reported there is relatively
simple, improvements are still needed in terms of
the reaction time and operational simplicity because
arylidene–cyanothioacetamide needs to be prepared
separately from aldehyde and cyanothioacetamide
and the reaction needs several hours to complete.
This prompted us to investigate the multicompo-
nent reaction of cyanothioacetamide with aldehyde
and 5-amino-3-methyl-1-phenylpyrazole under MWI
with the aim to develop more efficient and sim-
pler method for the preparation of pyrazolo[3,4-
b]pyridine-thione derivatives.
N
N
H
N
H3C
Ph
5a
S
MWI
C
NH2
N
+
Ar1
N
Ar1CHO
+
NH2
N
Ph
3
CN
H3C
CN
1a
2
N
NH2
N
Ar1=4-NO2C6H4
Ph
4a
SCHEME 1
1
The H NMR spectrum showed a broad singlet at
7.34 ppm (2 protons) due to the NH2 protons. MS
showed the molecular weight of this product and is
370 rather than 387 for 5a.
To explain the formation of the unexpected prod-
uct 4a, a mechanism is proposed as outlined in
Scheme 2. The reaction was initiated with the in situ
formation of intermediate A through a condensation
between 1a and 2. Subsequent Michael addition re-
action of 3 and intermediate A gave intermediate
B. An intramolecular cyclization process then took
place via the attack of the free amino group onto
the thioamide moiety to afford intermediate C, from
which two different intermediates, namely D or Dꢁ,
were possibly to be formed. As shown in Scheme 2,
if a H2S molecule was eliminated from C, D would
be formed and subsequent aromatization by loss of a
hydrogen molecule would eventually gives 4a as the
final product. On the other hand, if a NH3 molecule
was removed from C, Dꢁ would be formed and 5a
would be the final product. As mentioned earlier,
only 4a was obtained, indicating that H2S acted as a
better leaving group than NH3 in this case.
RESULTS AND DISCUSSION
Thus, the mixture of 4-nitrobenzaldehyde (1a, 1
mmol), cyanothioacetamide (2, 1 mmol), and 5-
amino-3-methyl-1-phenylpyrazole (3, 1 mmol) in
5 mL ethanol was put into a commercially available
microwave synthesizer without any added catalyst.
The reaction process was monitored by TLC anal-
ysis. After being irradiated for 10 min, the reaction
gave a complex mixture of several new substances to-
gether with the remaining starting materials. After-
ward, the reaction was run again but with addition
of piperidine (50 μL). In this case, the reaction was
completed in several minutes and afforded a solid
product, which was easily collected by suction. Sub-
sequent characterization of the product indicated
that it was a pyrazolo[3,4-b]pyridine derivative 4a
(Scheme 1), rather than the expected pyrazolo[3,4-
b]pyridine-thione 5a. The structure of 4a was estab-
lished on the basis of its spectroscopic data. The IR
spectrum showed two strong absorptions between
3300 and 3500 cm−1 due to the NH2 group and one
absorption around 2200 cm−1 due to the CN group.
At the same time, it seems reasonable to propose
that the amino group instead of the CH moiety on
the pyrazole ring could also initiate the Michael ad-
dition on the intermediate A and subsequently gave
1
6a as the final product (Scheme 3), whose H and
13C NMR and IR should be similar to that of 4a.
To exclude this possibility, the nuclear Over-
hauser enhancement spectroscopy (NOESY) of the
product was then carried out (Scheme 4). It showed
clear coupling between the protons of the methyl
group on the pyrazole ring and the protons meta
to the nitro group on the nitro-substituted phenyl
ring. Since NOESY depends on the distance be-
tween two kinds of protons, it is safe to say that
the nitro-substituted phenyl ring is on the same side
with the methyl group, which means that the nitro-
substituted phenyl ring must be on the fourth posi-
tion of the pyridine ring (as in 4a), allowing the pro-
tons on the nitro-substituted phenyl ring to be close
Heteroatom Chemistry DOI 10.1002/hc

696 Fan et al.
H3C
Ar1
N
CN
S
NH2
N
Ph
3
S
H3C
CN
C
NH2
C
2O
Ar1
C
C
S
NH2
Ar CHO
+
N
1
NH2
H
NH2
N
CN
Ph
B
1a
2
A
Ar1
Ar1
Ar1
H3C
CN
H3C
2S
CN
H3C
CN
2
N
N
N
N
N
NH2
NH2
N
NH2
SH
N
N
N
Ph
Ph
Ph
H
4a
C
D
Ar1
Ar1
N
Ar1
Ar1
H3C
CN
S
H3C
CN
SH
H3C
CN
SH
H3C
CN
SH
3
2
N
N
N
N
N
N
N
N
N
N
N
H
NH2
Ph
Ph
Ph
Ph
H
5a
5a
C
D′
SCHEME 2
enough in space to the protons of the methyl group
to show nuclear Overhauser enhancement (NOE) ef-
fect (see Scheme 4). On the other hand, if the product
was 6a, no such NOE effect should be observed be-
cause these two kinds of protons are too remote in
space to show any NOE effects.
The structure of 4a was further established by
X-ray crystallographic analysis (Fig. 1). It is observed
that in the crystal structure a pyridine ring has been
formed, and the pyridine ring and the pyrazole ring
are almost coplanar with a dihedral angle of 1.9◦,
which is very important for the two rings to give a
conjugated and stable structure.
Finally, the identification is proved beyond
doubt by comparing it with the authentic sample
prepared with the known method [7].
From the synthetic point of view, the high effi-
ciency and good selectivity of this three-component
reaction make it attractive as an alternative for the
preparation of pyrazolo[3,4-b]pyridine derivatives.
Therefore, further efforts were then made to inves-
tigate the scope and generality of this process by
screening a series of aldehyde substrates (Scheme 5).
The results are presented in Table 1.
As shown in Table 1, under our reaction con-
ditions, both aldehydes with an electron-donating
group and aldehydes with an electron-withdrawing
substituent underwent the above process smoothly
and gave the corresponding product with high yields
in a very short reaction period. It is worth noting
that this result is significant since to the best of our
knowledge; there is no literature precedent for the
synthesis of pyrazolo[3,4-b]pyridine derivatives di-
rectly from a thioamide moiety under MWI. In ad-
dition, in our process arylidenecyanothioacetamide
is generated in situ instead of being prepared sepa-
rately, which makes the whole process simpler and
more practical.
To draw a direct comparison between mi-
crowave irradiation and conventional heating, a few
selected reactions were also carried out at 78◦C un-
der conventional heating mode by ethanol refluxing.
The results are presented in Table 2.
By comparing the results presented in Table 1
with that of Table 2, we found that the reactions
were efficiently promoted by MWI in that the reac-
tion time was strikingly shortened to 8–15 min from
7–10 h as required in a traditional heating condition,
and the yields were remarkably increased from 58%–
72% to 82%–91%, reflecting the specific nonthermal
effects under MWI conditions.
S
H3C
S
H3C
Ar1
Ar1
NH2
CN
NH2
N
N
N
H
NH2
H3C
N
N
Ph
3
CN
A
E
Ph
NH2
NH2
CN
HS
CN
Ar1
H3C
2S
N
N
N
N
Ar1
N
2
N
H
Ph
Ph
F
6a
SCHEME 3
Heteroatom Chemistry DOI 10.1002/hc

Simple and Efficient Preparation of Pyrazolo[3,4-b]-pyridine Derivatives 697
NO2
No NOE
NH2
4
H
3
H
H
NOE
C
2
CN
H
H
H
H
3
H
No NOE
NO2
4
C
2
N
1
3
CN
3
H
N
1
2
N
N
1
Ph
H
NH
N
1
2
N
2
Ph
Structrue of proposed product 6a
Structure of 4a
ppm
7.0
ppm
2
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
ppm
3
4
5
6
7
8
8.8
8.6
8.4
8.2
8 .0
7.8
7 .6
7.4
7.2
7 .0
8
7
6
5
4
3
2
ppm
COSY of 4a
NOESY of 4a
SCHEME 4
Ar
In conclusion, an unexpected reaction of cyan-
othioacetamide with aldehyde and aminopyrazole
was found, and this reaction proved to be an effi-
cient and simple procedure for the preparation of
pyrazolo[3,4-b]pyridine derivatives. Further efforts
to find more uses of thioamides and more applica-
tions of MWI in the preparation of novel heterocyclic
compounds are currently underway in our labora-
tory.
H3C
N
S
H3C
CN
C
NH2
ArCHO
+
+
MWI
NH2
N
Ph
3
N
CN
NH2
N
N
Ph
1
2
4
SCHEME 5
EXPERIMENTAL
Melting points were measured by a Kofler mi-
cromelting point apparatus and were uncorrected.
Infrared spectra were recorded on a Bruker Vector
22 spectrometer in KBr with absorption in cm−1. 1H
NMR spectra were determined on a Bruker AC 400
spectrometer as DMSO-d6 solution. Chemical shifts
(δ) were expressed in ppm downfield from the inter-
nal standard tetramethylsilane, and coupling con-
stants J are given in Hz. Mass spectra were obtained
by a Bruke Esquire 3000 mass spectrometer.
A Typical Procedure for the Preparation of 4a
To a mixture of 4-nitrobenzaldehyde (1a, 1 mmol),
2-cyanothioacetamide (2, 1 mmol), and 5-amino-
3-methyl-1-phenylpyrazole (3, 1 mmol) was added
5 mL of ethanol and 50 μL of piperidine. The mixture
FIGURE 1 The molecular structure of 4a.
Heteroatom Chemistry DOI 10.1002/hc

698 Fan et al.
4c: mp. 200–202◦C; IR (KBr): 3474, 3348 (NH2),
2216 (CN) cm−1; 1H NMR (DMSO-d6) : 1.84 (s,
3H, CH3), 7.26–7.31 (m, 3H, Ar-H, NH2) 7.49 (t,
J = 8.0 Hz, 2H, Ar-H), 7.88 (t, J = 8.0 Hz, 1H, Ar-H),
8.03 (d, J = 7.2 Hz, 1H, Ar-H), 8.15 (d, J = 8.0 Hz,
2H, Ar-H), 8.42 (d, J = 8.0 Hz, 2H, Ar-H); 13C NMR
(DMSO-d6): 14.4, 88.1, 108.0, 116.2, 120.6, 123.7,
124.6, 125.7, 129.1, 130.4, 135.4, 135.7, 138.8, 143.5,
147.7, 149.9, 151.2, 159.2; MS (ESI): m/z 393 (M+ +
Na).
TABLE 1 Preparation of Pyrazolo[3,4-b]pyridines under
MWI
Reaction
Time (min)
Ar
Product
Yield (%)a
p-NO2C6H4
C H5
4a
4b
4c
4d
4e
4f
4g
4h
4i
8
91
85
85
83
81
86
82
88
81
78
82
12
10
10
13
10
13
10
15
15
12
m6-NO2C6H4
p-ClC6H4
o-ClC6H4
p-BrC6H4
o-BrC6H4
p-FC6H4
4d: mp 197–198◦C (Lit. [7] 195◦C); IR (KBr):
3456, 3329 (NH2), 2218 (CN) cm−1; 1H NMR (DMSO-
d6): 1.86 (s, 3H, CH3), 7.25–7.28 (m, 3H, Ar-H, NH2),
7.47 (t, J = 8.0 Hz, 2H, Ar-H), 7.56 (d, J = 8.4 Hz,
2H, Ar-H), 7.63 (d, J = 8.4 Hz, 2H, Ar-H), 8.14 (d,
J = 7.6 Hz, 2H, Ar-H); 13C NMR (DMSO-d6): 14.4,
88.2, 108.0, 116.4, 120.5, 125.7, 128.7, 129.1, 130.7,
133.0, 134.6, 138.9, 143.7, 151.2, 151.3, 159.3; MS
(ESI): m/z 382 (M+ + Na).
o-FC6H4
p-CH3OC6H4
p-CH3C6H4
4j
4k
aIsolated yields.
was then put into a commercially available single-
mode microwave synthesis apparatus equipped with
a high sensitivity infrared sensor for temperature
control and measurement (MAS-I, Sineo Microwave
Chemical Technology Co. Ltd., Shanghai, People’s
Republic of China) and irradiated at 250 W (inter-
nal temperature 80◦C) for 8 min. Upon completion,
the reaction mixture was allowed to cool to room
temperature, and the solid product was collected by
filtration and washed with ethanol to give the desired
product. Other products were obtained in a similar
manner.
4e: mp 192–194◦C (Lit. [8] 198–199◦C); IR (KBr):
3472, 3341 (NH2), 2216 (CN) cm−1. 1H NMR (DMSO-
d6): 1.78 (s, 3H, CH3), 7.27 (t, J = 7.2 Hz, 1H, Ar-
H), 7.33 (br s, 2H, NH2), 7.48 (t, J = 8.0 Hz, 2H,
Ar-H), 7.52–7.62 (m, 5H, Ar-H), 7.70 (d, J = 7.6 Hz,
1H, Ar-H) 8.15 (d, J = 8.0 Hz, 2H, Ar-H); 13C NMR
(DMSO-d6): 13.0, 88.4, 108.0, 115.8, 120.5, 125.7,
127.7, 129.1, 129.7, 130.5, 131.4, 131.6, 133.1, 138.8,
143.5, 149.4, 151.1, 159.3; MS (ESI): m/z 382 (M+ +
Na).
4a: mp 213–214◦C (Lit. [7] 215◦C); IR (KBr):
3464, 3336 (NH2), 2214 (CN) cm−1; 1H NMR (DMSO-
d6): 1.82 (s, 3H, CH3), 7.27 (t, J = 7.6 Hz, 1H, Ar-H),
7.34 (br s, 2H, NH2), 7.48 (t, J = 8.0 Hz, 2H, Ar-H),
7.85 (d, J = 8.0 Hz, 2H, Ar-H), 8.14 (d, J = 7.6 Hz,
2H, Ar-H), 8.40 (d, J = 8.0 Hz, 2H, Ar-H); 13C NMR
(DMSO-d6): 14.3, 87.7, 107.7, 116.1, 120.5, 123.7,
125.7, 129.1, 130.5, 138.8, 140.7, 143.5, 148.3, 150.2,
151.1, 159.2; MS (ESI): m/z 393 (M+ + Na).
4f: mp 211–213◦C (Lit. [8] 222–223◦C); IR (KBr):
3465, 3332 (NH2), 2213 (CN) cm−1; 1H NMR (DMSO-
d6): 1.87 (s, 3H, CH3), 7.26–7.28 (m, 3H, Ar-H, NH2),
7.46–7.50 (m, 4H, Ar-H), 7.77 (d, J = 8.0 Hz, 2H, Ar-
H), 8.14 (d, J = 7.6 Hz, 2H, Ar-H); 13C NMR (DMSO-
d6): 14.4, 88.0, 107.9, 116.4, 120.6, 123.3, 125.7,
129.1, 130.9, 131.6, 133.4, 138.9, 143.7, 151.2, 151.3,
159.3; MS (ESI): m/z 426 (M+ + Na).
4g: mp 200–202◦C; IR (KBr): 3470, 3338 (NH2),
4b: mp 205–206◦C (Lit. [7] 208◦C); IR (KBr):
3468, 3336 (NH2), 2211 (CN) cm−1; 1H NMR (DMSO-
d6): 1.83 (s, 3H, CH3), 7.21 (br s, 2H, NH2), 7.26 (t,
J = 7.2 Hz, 1H, Ar-H), 7.45–7.56 (m, 7H, Ar-H), 8.15
(d, J = 8.0 Hz, 2H, Ar-H); 13C NMR (DMSO-d6) : 14.3,
88.0, 108.1, 116.5, 120.5, 125.6, 128.5, 128.6, 129.0,
129.7, 134.2, 138.9, 143.8, 151.1, 152.6, 159.3; MS
(ESI): m/z 348 (M+ + Na).
1
2215 (CN) cm−1. H NMR (DMSO-d6): 1.77 (s, 3H,
CH3), 7.27 (t, J = 7.2 Hz, 1H, Ar-H), 7.33 (br s, 2H,
NH2), 7.46–7.60 (m, 5H, Ar-H), 7.85 (d, J = 8.0 Hz,
1H, Ar-H), 8.15 (d, J = 8.0 Hz, 2H, Ar-H); 13C NMR
(DMSO-d6): 13.0, 88.3, 107.9, 115.8, 120.5, 121.3,
125.7, 128.2, 129.1, 130.3, 131.6, 132.7, 135.2, 138.9,
143.5, 151.0, 151.1, 159.3; MS (ESI): m/z 426 (M+ +
Na).
4h: mp 211–212◦C (Lit. [8] 216–218◦C); IR (KBr):
3474, 3338 (NH2), 2212 (CN) cm−1; 1H NMR (DMSO-
d6): 1.85 (s, 3H, CH3), 7.23–7.28 (m, 3H, Ar-H, NH2),
7.40 (t, J = 8.8 Hz, 2H, Ar-H), 7.47 (t, J = 8.0 Hz, 2H,
Ar-H), 7.57–7.61 (m, 2H, Ar-H), 8.14 (d, J = 8.0 Hz,
2H, Ar-H); 13C NMR (DMSO-d6): 14.3, 88.2, 108.2,
115.5, 115.7, 116.4, 120.5, 125.6, 129.0, 130.5, 131.1,
131.2, 138.9, 143.7, 151.1, 151.6, 159.3, 161.7, 164.1;
MS (ESI): m/z 366 (M+ + Na).
TABLE 2 Preparation of 4 Using Conventional Heating
Reaction
Time (h)
Entry
Product
Yield (%)a
1
2
3
4
4a
4b
4d
4k
7
9
9
72
66
62
58
10
aIsolated yields.
Heteroatom Chemistry DOI 10.1002/hc

Simple and Efficient Preparation of Pyrazolo[3,4-b]-pyridine Derivatives 699
4i: mp 188–190◦C; IR (KBr): 3472, 3346 (NH2),
REFERENCES
2215 (CN) cm−1; 1H NMR (DMSO-d6): 1.87 (s,
3H, CH3), 7.26–7.31 (m, 3H, Ar-H, NH2), 7.39–7.50
(m, 4H, Ar-H), 7.56–7.65 (m, 2H, Ar-H), 8.14 (d,
J = 8.0 Hz, 2H, Ar-H); 13C NMR (DMSO-d6): 13.3,
88.8, 108.2, 115.9, 116.0, 116.1, 120.6, 121.6, 121.7,
124.9, 125.8, 129.1, 131.1, 132.4, 132.5, 138.8, 143.5,
146.1, 151.1, 157.3, 159.2, 159.7; MS (ESI): m/z 366
(M+ + Na).
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4j: mp 199–200◦C (Lit. [7] 197◦C); IR (KBr):
3476, 3368 (NH2), 2213 (CN) cm−1; 1H NMR (DMSO-
d6): 1.90 (s, 3H, CH3), 3.83 (s, 3H, OCH3), 7.10 (d,
J = 8.4 Hz, 2H, Ar-H), 7.15 (br s, 2H, NH2), 7.26 (t,
J = 7.2 Hz, 1H, Ar-H), 7.44–7.49 (m, 4H, Ar-H), 8.15
(d, J = 8.0 Hz, 2H, Ar-H); 13C NMR (DMSO-d6): 14.6,
55.4, 88.1, 108.3, 113.9, 116.7, 120.5, 125.6, 126.1,
129.0, 130.3, 139.0, 143.9, 151.2, 152.6, 159.4, 160.3;
MS (ESI): m/z 378 (M+ + Na).
4k: mp 188–190◦C; IR (KBr): 3480, 3352 (NH2),
[5] Fan, X. S.; Wang, X.; Zhang, X. Y.; Li, X. Y.; Qu, G.
R. J Chem Res (s) 2007, 693.
1
2216 (CN) cm−1; H NMR (DMSO-d6): 1.86 (s, 3H,
[6] Ghattas, A.-B. A. G.; Khodairy, A.; Abd-Rahman,
M. A.; Younes, S. Phosphorus, Sulfur Silicon Relat
Elem. 2003, 178, 1781.
[7] Quiroga, J.; Alvarado, M.; Insuasty, B.; Moreno, R.;
Ravina, E.; Estevez, I.; Almeida, R. H. J Heterocyclic
Chem 1999, 36, 1311.
CH3), 2.40 (s, 3H, CH3), 7.16 (br s, 2H, NH2), 7.26
(t, J = 7.2 Hz, 1H, Ar-H), 7.34–7.40 (m, 4H, Ar-H),
7.47 (t, J = 8.0 Hz, 2H, Ar-H), 8.15 (d, J = 8.0 Hz, 2H,
Ar-H); 13C NMR (DMSO-d6): 14.4, 21.0, 88.1, 108.1,
116.6, 120.5, 125.6, 128.6, 129.0, 131.3, 139.0, 139.3,
143.9, 151.2, 152.8, 159.3; MS (ESI): m/z 362 (M+ +
Na).
[8] Zhu, S. L.; Tu, S. J.; Li, D. J.; Zhang, X.J.; Ji,
S. J.; Zhang, Y. Chin
987.
J Org Chem 2005, 25,
Heteroatom Chemistry DOI 10.1002/hc