A novel synthesis of 1-aryl-1H-benzotriazoles via oxidative C-H amination

Article abstract of DOI:10.3987/COM-11-12264

A facile, novel and regiospecific protocol for the synthesis of 1-aryl-1H-benzotriazoles via oxidative C-H amination of corresponding 1,3-diaryltriazenes in DMF in the presence of K2CO3 at moderate temperature was developed.

Full text of DOI:10.3987/COM-11-12264

HETEROCYCLES, Vol. 83, No. 9, 2011
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HETEROCYCLES, Vol. 83, No. 9, 2011, pp. 2057 - 2065. © The Japan Institute of Heterocyclic Chemistry
Received, 21st May, 2011, Accepted, 30th June, 2011, Published online, 6th July, 2011
DOI: 10.3987/COM-11-12264
A NOVEL SYNTHESIS OF 1-ARYL-1H-BENZOTRIAZOLES VIA
OXIDATIVE C-H AMINATION
Zhou Zhou, Qi-Lun Liu, Wen Li, and Yong-Ming Zhu*
School of Pharmacy, Soochow University, Suzhou, 215123, P. R. China, Phone:
+86-512-62880109; Fax: +86-512-67166591; E-mail: zhuyongming@suda.edu.cn
Abstract – A facile, novel and regiospecific protocol for the synthesis of
1-aryl-1H-benzotriazoles via oxidative C-H amination of corresponding
1,3-diaryltriazenes in DMF in the presence of K2CO3 at moderate temperature was
developed.
INTRODUCTION
Benzotriazoles are an important class of compounds used in synthetic organic chemistry.1 They are found
to exhibit a broad spectrum of pharmacological activities including antibacterial, antitubercular,
anticancer, antidepressant and antifungal activities.2 Besides, benzotriazoles are widely used as corrosion
inhibitor, anti-freeze reagents, UV absorber, anti-fog agents and synthetic auxiliaries.3
Inter- and intramolecular C-N bond formation is important in both academic and industrial chemistry, due
to the high prevalence of nitrogen-containing biologically active compounds and pharmaceuticals.
Particularly, Pd- or Cu-catalyzed amination reactions of aryl halides or pseudohalides have been widely
used to construct such compounds, and highly active catalyst systems have been reported.4,5 In these cases,
aryl electrophiles must possess a halide or pseudohalide moiety which limited the application of such
reactions. On the other hand, notable advances in C-H functionalization catalyzed by Ru,6 Rh7 and Pd8-10
have been described. Buchwald reported Pd(II)-catalyzed C-H activation/intramolecular amidation for
carbazole synthesis in 2005.8 Moreover, Che disclosed that it was possible to activate sp3 as well as sp2
C-H bonds in the presence of Pd(OAc)2, followed by intermolecular amination.9 Recently, Cu11 and Pd12
catalyzed processes for the synthesis of benzotriazoles have been reported, which showed high
regiospecificity and wild functional group tolerance. Herein we describe a novel approach to the synthesis
of 1-aryl-1H-benzotriazoles via nitro group participated oxidative C-H amination reactions with easily
obtained 1,3-diaryltriazenes compounds as substrates (Scheme 1).

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HETEROCYCLES, Vol. 83, No. 9, 2011
O2N
N
N
H
N
N
X
N
N
R1
R1
X
R2
NO2
1
2
R2
Scheme 1
RESULTS AND DISCUSSION
Our investigation began by examining the conversion of 1-(3-nitrophenyl)-3-phenyltriaz-1-ene (1a) into
the corresponding benzotriazole (2a). Firstly, 1a, which was easily obtained according to the reported
protocol,13 Pd(OAc)2 and oxidant in DMF was reacted under N2. Unfortunately, no desired cyclized
product was obtained probably due to the instability of 1a under our utilized reaction conditions (entries 1
and 2). In the light of kinetic and mechanistic studies of the decomposition of triazenes14 base was applied
in the following study of the cyclization process. Replacement of chemical oxidant with oxygen gave an
isolated 77% yield of desired product though the catalyst Pd(OAc)2 was removed (entry 4). This result
promoted us to further optimize this annulation chemistry, and the results were summarized in Table1.
Table 1. Optimization of reaction conditiona
O2N
N
H
base (3 equiv.)
additives
N
N
A
N
N
N
A
B
solvent
o
110-115 C
B
NO2
1a
2a
Entry
1
Solvent
DMF
Base
Additives
Yield(%) b
10% Pd(OAc)2
c
---
---
-
1equiv Cu(OAc)2
10% Pd(OAc)2
c
2
DMF
-
1equiv PhI(OAc)2
3
4
5
6
DMF
DMF
K2CO3
K2CO3
K2CO3
K2CO3
10% Pd(OAc)2
75
77
78c
-
-
-
DMF
DMSO
76

HETEROCYCLES, Vol. 83, No. 9, 2011
2059
7
8
toluene
1,4-dioxane
DMF
K2CO3
K2CO3
Cs2CO3
K3PO4
Na2CO3
TEA
-
-
-
-
-
-
-
N.R.d
N.R.
46
9
10
11
12
13
DMF
43
DMF
75
DMF
N.R.
DMF
-
N.R.
a Reaction condition: A solution of 1a (0.5 mmol) and base (1.5 mmol) in 5
mL anhydrous solvent was heated under air at 110-115 °C and monitored by
TLC. b Isolated yield by FC on silica gel. c Under N2. d N. R.= no reaction.
As shown in Table 1, while a nitro group was attached meta to triazene in A ring, almost equal yield was
obtained in the absence of Pd(OAc)2 (entries 3 and 4). While the reaction was carried out under nitrogen,
we also obtained almost the same isolated yield of 2a (entry 5). DMF was the best solvent compared with
other solvents used in our experiment (entries 4-8). Base was indispensable in the present protocol and the
best yield was obtained with K2CO3 (entries 4, 9-13). Thus the optimal cyclization reaction was carried
out in DMF at 110-115 °C under air in the presence of K2CO3.
On the basis of the above results, the scope of the reaction was explored with different substrates. As
shown in Table 2, the reaction condition was of quite general character and tolerant of a wide range of
functionalities. Best yield was obtained while R1 was H, R2 was 4-F, followed by R2 was 3-CO2Et, and
3-CF3 (entries 4, 13 and 10). As can be seen from entries 5 and 8, steric hindrance led to slightly lower
yields and prolonged reaction time. The substituents on the two aromatic rings had different effects on the
yields (entries 2, 3, 14 and 15). Both electron-donating and electron-withdrawing substituents on A ring
decreased the yields drastically due to steric hindrance, which possibly obstruct the conversion of the
conjugation system by affecting the coplanarity of nitro group and A ring (entries 14-16). The plausible
mechanism was shown in Scheme 2, the reaction possibly proceeded via a vicarious nucleophilic
substitution.15 The oxidation process possibly proceeds via abstraction the leaving H by O2 in a radical
manner, recombination of the radical with hydroperoxide radical, and elimination of hydroperoxide anion
by electron donation from the anionic nitro group. Electron-donating and electron-withdrawing groups on
the other aromatic ring had no significant effects on the yields (entries 1-4, 6, 7, 10-13).

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HETEROCYCLES, Vol. 83, No. 9, 2011
Table 2. Cyclization of Triazenesa
O2N
N
N
H
N
N
X
N
K2CO3 (3 equiv.)
N
R1
R1
DMF
110-115 oC
air
R2
X
NO2
1
2
R2
Entry
1
Substrates
1a
R1
R2
H
Products
2a
t(h)
9
Yield[%]b
77
H
H
2
1b
4-Me
4-OMe
4-F
2b
2c
9
74
3
1c
H
9
72
4
1d
H
2d
2e
8
87
5
1e
H
2-Me
4-Cl
40
24
11
40
11
36
40
24
24
24
13
24
55
6
1f
H
2f
73
7
1g
H
3-CF3
2-Me, 5-Cl
H, (X=Nc)
3-NO2
3-SO2Ph
3-CN
3-CO2Me
H
2g
80
8
1h
H
2h
2i
59
9
1i
H
67
10
11
12
13
14
15
16
1j
H
2j
79
1k
H
2k
2l
77
1l
H
65
1m
1n
H
2m
2n
2o
81
4-Me
4-OMe
4-Cl
23
1o
H
33
1p
H
2p
Trace
a Reaction condition: 1 (0.5 mmol), K2CO3 (1.5 mmol), DMF (5 mL). b Isolated
yield by FC. c For entry 9, X=N, for others, X=C.
In conclusion, a novel pathway for the synthesis of 1-aryl-1H-benzotriazoles via nitro group participated
oxidative C-H amination under relatively mild condition has been developed. The synthetic strategy, with
readily available substituted 1,3-diaryltriazenes as starting materials, provides regiospecifically and
atom-economically corresponding 1-aryl-1H-benzotriazoles in good yields.

HETEROCYCLES, Vol. 83, No. 9, 2011
2061
O
N
O
N
O
N
O
K2CO3
O
O
N
N
H
N N N
N N N
N
H
O2
O
N
O
O
N
O
N
N
N
N
O
O
N
N
O2H
N
N
N
N
H
HO2
O O
Scheme 2. Plausible mechanism
EXPERIMENTAL
General
DMF and DMSO were dried over CaH2, toluene and 1,4-dioxane were dried over Na and distilled. Flash
chromatography (FC): silica gel (SiO2; 300-400 mesh) from Qingdao Ocean Chemicals, P. R. China. TLC:
Silica-gel GF254 plates. Melting points were determined without correction on an XT5 digital
1
melting-point apparatus purchased from Beijing Keyi Elec-opti Instrument Factory. H NMR and 13C
NMR spectra were obtained from a solution in CDCl3 or DMSO-d6 with tetramethylsilane (TMS) as
internal standard using Varian Inova 400/101 MHz (1H/13C) or 300/75 MHz (1H/13C) spectrometer, δ in
parts per million (ppm), and J in hertz (Hz). IR data were recorded on Varian 1000 FT-IR using KBr
tablets, wavenumbers in cm-1. HRMS analyses were carried out using a time-of-flight mass spectrometry
(TOFMS) or Saturan2200 (ESI) instrument.
General procedure for the synthesis of benzotriazoles (2):
A mixture of 1 (0.5 mmol), K2CO3 (1.5 mmol) and DMF (5 mL) in a flask filled with a magnetic stirring
bar under air was stirred at 110-115 °C. The process of the reaction was monitored by TLC using
n-hexane/EtOAc or CHCl3/n-hexane. After the reaction mixture was cooled to room temperature and 30
mL EtOAc was added. The organic layer was washed with water and brine, dried over anhydrous Na2SO4.
After removing the solvent, the residue was purified by FC on silica gal eluting with n-henane/EtOAc or
CHCl3/n-hexane to give 2.
5-Nitro-1-phenyl-1H-benzo[d][1,2,3]triazole (2a): Pale yellow crystals (EtOAc/n-hexane), mp 171-
172 °C. 1H NMR (400 MHz, CDCl3):  7.61 (t, J = 7.39 Hz, 1H), 7.69 (t, J = 7.78 Hz, 1H), 7.78 (d, J =

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HETEROCYCLES, Vol. 83, No. 9, 2011
8.30 Hz, 1H), 7.86 (d, J = 9.10 Hz, 1H), 8.45-8.49 (m, 1H), 9.10 (s, 1H). 13C NMR (75 MHz, CDCl3):
111.13, 117.62, 123.22, 123.36, 129.79, 130.30, 135.05, 136.06, 145.00, 145.67. IR (KBr): 3100, 1614,
1523, 1458, 1069, 801, 740, 690. HRMS (EI) calcd for C13H10N4O2 [M+]: 240.0647, found: 240.0647.
5-Nitro-1-p-tolyl-1H-benzo[d][1,2,3]triazole (2b): Pale yellow crystals (EtOAc/n-hexane), mp 173.5-
1
174.5 °C. H NMR (400 MHz, CDCl3):  2.51 (s, 1H), 7.47 (d, J = 7.52 Hz, 1H), 7.64 (d, J = 7.97 Hz,
13
1H), 7.81 (d, J = 9.10 Hz, 1H), 8.45 (d, J = 8.98 Hz, 1H), 9.09 (s, 1H). C NMR (75 MHz, CDCl3): 
21.38, 111.13, 117.53, 123.10, 123.18, 130.78, 133.55, 135.12, 144.90, 140.12. IR (KBr): 3019, 2926,
1616, 1524, 1352, 1075, 1055, 814, 799, 736. HRMS (EI) calcd for C13H10N4O2 [M+]: 254.0804, found:
254.0804.
1-(4-Methoxyphenyl)-5-nitro-1H-benzo[d][1,2,3]triazole (2c): Pale yellow crystals (CHCl3/n-hexane),
mp 251-252 °C. 1H NMR (400 MHz, CDCl3): 3.93 (s, 3H), 7.16 (d, J = 8.95 Hz, 2H), 7.66 (d, J = 8.92
13
Hz, 1H), 7.77 (d, J = 9.22 Hz, 2H), 8.44 (dd, J = 9.13, 1.87 Hz, 1H), 9.09 (s, 1H). C NMR (75 MHz,
DMSO -d6): 55.64, 112.05, 115.20, 116.70, 123.06, 125.14, 128.36, 134.97, 144.52, 144.56, 160.01. IR
(KBr): 3107, 3182, 2982, 1614, 1521, 1351, 822, 802, 739. HRMS (EI) calcd for C13H10N4O3 [M+]:
270.0750, found: 270.0753.
1-(4-Fluorophenyl)-5-nitro-1H-benzo[d][1,2,3]triazole (2d): Pale yellow crystals (EtOAc/n-hexane),
mp 190.5-191.5 °C. 1H NMR (400 MHz, CDCl3): 7.39 (t, J = 8.40 Hz, 1H), 7.74-7.80 (m, 2H), 7.82 (d,
J = 9.13 Hz, 1H), 8.07 (d, J = 9.09 Hz, 1H), 8.47 (dd, J = 9.08, 1.65 Hz, 1H), 9.07 (d, J = 1.52 Hz, 1H).
13C NMR (75 MHz, DMSO-d6): δ 163.90, 160.62, 144.71, 144.64, 134.91, 131.96, 126.04, 125.92,
123.35, 117.29, 116.98, 116.88, 112.21. IR (KBr): 3107, 3070, 1603, 1526, 1525, 1352, 1231, 841, 742.
HRMS (EI) calcd for C12H7FN4O2 [M+]: 258.0553, found: 258.0556.
5-Nitro-1-o-tolyl-1H-benzo[d][1,2,3]triazole (2e): Pale brown crystals (EtOAc/n-hexane), mp 113.5-
114.5 °C. 1H NMR (400 MHz, CDCl3): 2.14 (s, 3H), 7.41 (d, J = 7.63 Hz, 1H), 7.44-7.59 (m, 4H), 8.42
(d, J = 8.96 Hz, 1H), 9.10 (s, 1H). 13C NMR (75 MHz, CDCl3): 17.84, 110.88, 117.55, 123.27, 126.85,
127.45, 130.93, 132.08, 134.29, 135.26, 136.54, 144.78, 144.97. IR (KBr):3107, 3090, 2926, 1616, 1605,
1518, 1466, 1348, 1071, 1032, 804, 762. HRMS (EI) calcd for C13H10N4O2 [M+]: 254.0804, found:
254.0802.
1-(4-Chlorophenyl)-5-nitro-1H-benzo[d][1,2,3]triazole (2f): Pale yellow crystals (EtOAc/n-hexane),
mp 218.5-219.5 °C. 1H NMR (400 MHz, CDCl3):  7.66 (d, J = 8.83 Hz, 2H), 7.74 (d, J = 8.82 Hz, 2H),
13
7.82 (d, J = 9.13 Hz, 1H), 8.49 (dd, J = 9.13, 1.93 Hz, 1H), 9.11 (d, J = 1.39 Hz, 1H). C NMR (101
MHz, CDCl3): 110.87, 1117.83, 123.69, 124.40, 130.60, 134.59, 134.92, 135.81, 145.16, 145.80. IR
(KBr): 3109, 1616, 1522, 1499, 1347, 1098, 1040, 827, 802, 741. HRMS (EI) calcd for C12H7ClN4O2
[M+]: 274.0258, found: 274.0260.

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5-Nitro-1-(3-(trifluoromethyl)phenyl)-1H-benzo[d][1,2,3]triazole (2g): Pale yellow crystals (EtOAc/n-
1
hexane), mp 109.5-110.5 °C. H NMR (400 MHz, CDCl3): 7.86 (m, 3H), 8.03 (d, J = 6.94 Hz, 1H),
13
8.09 (s, 1H), 8.52 (d, J = 9.05 Hz, 1H), 9.12 (s, 1H). C NMR (101 MHz, CDCl3): δ 110.77, 117.91,
120.07, 120.11, 120.15, 120.18, 121.95, 123.98, 124.66, 126.19, 126.40, 126.44, 126.47, 126.50, 131.19,
132.57, 132.90, 133.23, 133.58, 134.82, 136.64, 145.27, 145.92. IR (KBr): 3096, 1616, 1541, 1462, 1354,
1327, 1116, 903, 807, 739, 696. HRMS (EI) calcd for C13H7F3N4O2 [M+]: 308.0521, found: 308.0515.
1-(5-Chloro-2-methylphenyl)-5-nitro-1H-benzo[d][1,2,3]triazole (2h): Pale brown crystals (CHCl3/n-
hexane), mp 176.8-177.8 °C. 1H NMR (300 MHz, CDCl3):  2.12 (s, 3H), 7.41-7.57 (m, 4H), 8.46 (dd, J
= 9.06, 1.91 Hz, 1H), 9.12 (d, J = 1.76 Hz, 1H). 13C NMR (101 MHz, CDCl3): δ 17.53, 110.68, 117.72,
123.65, 126.95, 131.06, 132.78, 133.16, 133.85, 135.09, 136.31, 144.86, 145.15. IR (KBr): 3086, 1616,
1531, 1497, 1354, 1045, 901, 824, 800, 739. HRMS (EI) calcd for C13H9ClN4O2 [M+]: 288.0414, found:
288.0415.
5-Nitro-1-(pyridin-2-yl)-1H-benzo[d][1,2,3]triazole (2i): White crystals (CHCl3/n-hexane), mp 212.5-
1
213.5 °C. H NMR (400 MHz, CDCl3) 7.43 (dd, J = 7.40, 4.92 Hz, 1H), 8.02 (dt, J = 8.27, 7.94, 1.80
Hz, 1H), 8.35 (d, J = 8.30 Hz, 1H), 8.50 (dd, J = 9.17, 2.08 Hz, 1H), 8.66 (d, J = 4.84 Hz, 1H), 8.86 (d, J
= 9.17 Hz, 1H),9.07 (d, J = 1.90 Hz, 1H). 13C NMR (101 MHz, CDCl3): 114.68, 115.89, 116.97, 123.42,
123.71, 134.28, 139.46, 145.34, 146.06, 148.70, 151.08. IR (KBr): 3069, 1611, 1589, 1522, 1483, 1445,
1356, 1042, 926, 804, 781, 737. HRMS (EI) calcd for C11H7N5O2 [M+]: 241.0600, found: 241.0600.
5-Nitro-1-(3-nitrophenyl)-1H-benzo[d][1,2,3]triazole (2j): Pale yellow crystals (EtOAc/n-hexane), mp
182-183 °C. 1H NMR (300 MHz, DMSO-d6): 8.03 (t, J = 8.18 Hz, 1H), 8.23 (d, J = 9.16 Hz, 1H), 8.41
(dd, J = 8.05, 1.12 Hz, 1H), 8.45-8.55 (m, 2H), 8.71 (t, J = 1.91 Hz, 1H), 9.20 (d, J = 1.58 Hz, 1H). 13C
NMR (75 MHz, DMSO-d6): 112.42, 117.06, 118.47, 123.80, 124.18, 129.65, 131.85, 134.93, 136.33,
144.90, 145.02, 148.64. IR (KBr): 3104, 1616, 1531, 1354, 1043, 804, 737, 677. LCMS (ESI) calcd for
C12H8N5O4 [M++H]: 286.0571, found: 286.0572.
5-Nitro-1-(3-(phenylsulfonyl)phenyl)-1H-benzo[d][1,2,3]triazole (2k): Pale yellow crystals (EtOAc/
n-hexane), mp 224-224.5 °C. 1H NMR (300 MHz, CDCl3):  7.62-7.79 (m, 3H), 7.98 (t, J = 8.00 Hz, 1H),
8.11 (t, J = 8.56 Hz, 3H), 8.25 (dd, J = 15.74, 8.02 Hz, 2H), 8.46-8.55 (m, 2H), 9.21 (d, J = 1.12 Hz, 1H).
13C NMR (101 MHz, DMSO-d6): δ112.30, 116.92, 122.00, 123.64, 127.70, 128.16, 129.91, 131.99,
134.18, 134.79, 136.43, 140.29, 143.04, 144.82, 144.97. IR (KBr): 3084, 3071, 1618, 1595, 1530, 1491,
1447, 1348, 1321, 1306, 1155, 911, 816, 739, 687. HRMS (ESI) calcd for C18H13N4O4S [M++H]:
381.0652, found: 381.0667.
3-(5-Nitro-1H-benzo[d][1,2,3]triazol-1-yl)benzonitrile (2l): Pale yellow crystals (EtOAc/n-hexane), mp
1
219-220 °C. H NMR (300 MHz, DMSO-d6): 7.94 (t, J = 8.00 Hz, 1H), 8.16-8.10 (m, 1H), 8.28 (t, J =

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HETEROCYCLES, Vol. 83, No. 9, 2011
13
7.70 Hz, 2H), 8.45-8.51 (m, 2H), 9.19 (s, 1H). C NMR (75 MHz, DMSO-d6): 112.61, 113.17, 116.95,
117.75, 123.61, 126.76, 128.29, 131.59, 133.34, 134.72, 136.22, 144.88, 144.96. IR (KBr): 3093, 2235,
1616, 1582, 1497, 1450, 1352, 1043, 802, 741, 685. HRMS (ESI) calcd for C13H8N5O2 [M++H]:
266.0673, found: 266.0657.
Ethyl 3-(5-nitro-1H-benzo[d][1,2,3]triazol-1-yl)benzoate (2m): Pale yellow crystals (EtOAc/n-hexane),
mp 142.5-143.5 °C. 1H NMR (300 MHz, CDCl3):  1.45 (t, J = 7.12 Hz, 3H), 4.47 (q, J = 7.12, 7.09 Hz,
2H), 7.78 (t, J = 7.91 Hz, 1H), 7.88 (d, J = 9.12 Hz, 1H), 7.98-8.05 (m, 1H), 8.27 (d, J = 7.81 Hz, 1H),
8.50 (dd, J = 9.11, 1.93 Hz, 1H), 8.45 (s, 1H), 9.11 (d, J = 1.84 Hz, 1H).13C NMR (75 MHz,
CDCl3):14.43, 61.95, 110.98, 117.76, 123.72, 123.84, 127.29, 130.56, 130.51, 132.87, 134.95, 136.33,
145.15, 145.82, 165.16IR (KBr): 3105, 2988, 1724, 1607, 1587, 1532, 1458, 1354, 1292, 1049, 802, 750,
739. HRMS (ESI) calcd for C15H13N4O4 [M++H]: 313.0931, found: 313.0929.
6-Methyl-5-nitro-1-phenyl-1H-benzo[d][1,2,3]triazole (2n): Pale yellow crystals (EtOAc/n-hexane),
mp 183-184 °C. 1H NMR (400 MHz, CDCl3): 2.76 (s, 3H), 7.58 (t, J = 7.37 Hz, 1H), 7.70-7.64 (m, 3H),
13
7.76 (d, J = 8.02 Hz, 2H), 8.82 (s, 1H). C NMR (75 MHz, CDCl3): 21.66, 112.92, 118.12, 123.21,
129.61, 130.27, 130.42, 133.95, 136.25, 144.25, 147.05. IR (KBr): 3065, 2926, 2855, 1624, 1595, 1524,
1501, 1462, 1435, 1351, 1285, 1055, 889, 856, 789, 764, 696. HRMS (ESI) calcd for C13H11N4O2
[M++H]: 255.0877, found: 256.0877.
6-Methoxy-5-nitro-1-phenyl-1H-benzo[d][1,2,3]triazole (2o): Pale yellow crystals (CHCl3/n-hexane),
mp 183-184 °C. 1H NMR (400 MHz, CDCl3):  4.02 (s, 3H), 7.15 (s, 1H), 7.59 (t, J = 7.29 Hz, 1H), 7.68
13
(t, J = 7.68 Hz, 2H), 7.73 (d, J = 7.74 Hz, 2H), 8.58 (s, 1H). C NMR (75 MHz, DMSO-d6):  57.49,
93.86, 116.70, 123.31, 129.39, 130.26, 133.69, 152.11. IR (KBr): 3100, 2968, 2930, 1626, 1595, 1532,
1483, 1433, 1350, 1269, 899, 793, 762, 691. HRMS (ESI) calcd for C13H11N4O2 [M++H]: 271.0826,
found: 271.0828.
ACKNOWLEDGE
This work was partially supported by the National Natural Science Foundation of China (Grants
20472062 and 20672079) and the Natural Science Foundation of Jiangsu Province (No. BK2006048).
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