[Bis-(trifluoroacetoxy)iodo]benzene-Mediated Oxidative Direct Amination C–N Bond Formation: Synthesis of 1H-Indazoles

Article abstract of DOI:10.1002/jhet.2839

An efficient [bis-(trifluoroacetoxy)iodo]benzene (PIFA)-mediated oxidative C-N bond formation is developed for the synthesis of 1H-indazoles from readily available arylhydrazones. The reaction tolerates a wide range of functional groups and has broad scope of substrates. Moreover, this method is a relative green and reliable method for rapid preparation of substituted 1H-indazoles under mild conditions.

Full text of DOI:10.1002/jhet.2839

Month 2017 [Bis-(trifluoroacetoxy)iodo]benzene-Mediated Oxidative Direct Amination
C–N Bond Formation: Synthesis of 1H-Indazoles
a
a
b
a
a
*
*
Zhiguo Zhang, Yuanyuan Huang, Guoqing Huang, Guisheng Zhang, and Qingfeng Liu
aCollaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of
Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan
Normal University, Xinxiang, Henan 453007, Peopleˈs Republic of China
bHandan Purification Equipment Research Institute, Handan, Hebei 056027, Peopleˈs Republic of China
*
E-mail: zhangzg@htu.edu.cn; zgs6668@yahoo.com
Additional Supporting Information may be found in the online version of this article.
Received April 20, 2016
DOI 10.1002/jhet.2839
Published online 00 Month 2017 in Wiley Online Library (wileyonlinelibrary.com).
An efficient [bis-(trifluoroacetoxy)iodo]benzene (PIFA)-mediated oxidative C-N bond formation is
developed for the synthesis of 1H-indazoles from readily available arylhydrazones. The reaction tolerates
a wide range of functional groups and has broad scope of substrates. Moreover, this method is a relative
green and reliable method for rapid preparation of substituted 1H-indazoles under mild conditions.
J. Heterocyclic Chem., 00, 00 (2017).
1H-Indazoles-based molecules are important synthetic
application of ring transformation at a high temperature
(Fig. 1, type e) [8], coupling of arylamino oximes, or their
analogs via an intermolecular or intramolecular N–N bond
formation reaction, are also included (Fig. 1, type f ) [7,9].
Herein, we report an alternative approach for the
preparation of 1H-indazoles by joining the N-moiety on
the side-chain to the aryl ring via an intramolecular
oxidative amination C–N bond formation mediated by
[bis-(trifluoroacetoxy)iodo]benzene (PIFA).
Organoiodine (III) reagents [10] have been widely used
for the synthesis of various five-membered, six-
membered, and seven-membered N-containing spiro and
fused heterocycles, including indoles [11], 1,4-diazepines
[12], 1,2,4-triazolo[1,5-a]pyridines [13], pyrazole [9],
oxazoles [14], indazoles [9], and pyrrolidinones [15], via
an intramolecular nitrenium ion azaspirocyclization
reaction [16]. Combining with our recent research on the
synthesis of N-containing heterocycles from readily
available acyclic amine precursors [17], we made efforts
to realize an intramolecular cyclization of 1 to 2 by
means of hypervalent iodine-mediated oxidative direct
C–N bond formation (Table 1). As a model substrate
[5], compound 1-(diphenylmethylene)-2-phenylhydrazine
(1a) was first prepared and evaluated the feasibility to
targets in biologically active molecules, synthetic drugs,
and drug candidates [1]. In addition, they are used as
ligands for generating metallic complexes [2]. To date,
many methods have been established for the construction
of the indazole skeleton (Fig. 1) [3]. Among them,
BuchwaldꢀHartwig coupling, Ullmann-type aminations,
and Goldberg-type N-arylations are the most reliable and
widely used strategies, although prefunctionalized
reactants are required in the conversion. (Fig. 1, type a)
[4]. In addition, intramolecular direct CꢀH bond
activation/oxidative C–N bond coupling method is also
applied frequently for 1H-indazoles synthesis starting
from arylhydrazones via an intramolecular cyclization,
which realizes the direct C–N bond formation reaction
(Fig. 1, type b) [5]. Besides, a highly active aryne
intermediate is often introduced effectively in some cases
via the strategy of [3 + 2] cycloaddition (Fig. 1, type c)
[6]. In recent years, azides have emerged as powerful
amino sources in the transition-metal-catalyzed direct
amination/amidation of aromatic CꢀH bonds due to their
readily availability, structural diversity, and environmental
benignity of the reaction byproduct, gaseous N2 (Fig. 1,
type d) [7]. Other useful approaches, such as the
© 2017 Wiley Periodicals, Inc.

Z. Zhang, Y. Huang, G. Huang, G. Zhang, and Q. Liu
Vol 000
Figure 1. General synthetic routes to the indazole motif.
the desired 1,3-diphenyl-1H-indazole (2a) in the presence
of a hypervalent iodine. After many attempts, compound
2a was obtained in the yield of 84% as a white solid,
along with a byproduct benzophenone (3a: 7% yield)
when we treated 1a with 120 mol% of PIFA in
hexafluoroisopropanol (HFIP) [7] after 5 min at ambient
temperature (Table 1, entry 1). It was found that decreasing
or increasing the amount of PIFA was not useful to
improve the yield of 2a (Table 1, entries 2 and 3). Several
other hypervalent iodine oxidants were also screened to
the reaction, including 1,1,1-triacetoxy-1,1-dihydro-1,2-
benziodoxol-3(1H)-one (DMP), 2-iodoxybenzoic acid,
phenyliodonium diacetate, and PhIO (Table 1, entries).
They showed a lower oxidative activity than PIFA
(Table 1, entries 4–7). The screening of other fluorine-
containing solvents including 2,2,2-trifluoroethanol,
2,2,3,3,4,4,5,5-octafluoro-1-pentanol, 2,2,3,3-tetrafluoro-
1-propanol, and ethyl trifluoroacetate showed that they
Table 1
Survey of the reaction conditions.a
Entry
Oxidant (equiv)
Solvent
HFIP
Time
5 min
3 h
5 min
4 h
Yield of 2a/%
Recovered 1a/% or yield of 3a/%
1
2
3
4
5
6
7
8
9
PIFA (1.2)
PIFA (1.0)
PIFA (1.5)
DMP (1.2)
IBX (1.2)
PIDA (1.2)
PhIO (1.2)
PIFA (1.2)
PIFA (1.2)
PIFA (1.2)
PIFA (1.2)
73
66b
72
8
3a: 7
1a: 11
0
3a: 70
3a: 73
HFIP
HFIP
HFIP
HFIP
HFIP
HFIP
TFE
OFP
TFP
ETFA
3 h
5 h
5
50
35
20
60b
24b
13b
3a: 25
24 h
10 min
1 h
30 min
4 h
1a: 20, 3a: 13
0
1a: 21
1a: 18, 3a: 37
1a: 36, 3a: 22
10
11
aUnless otherwise indicated, all reactions were carried out with 1a (0.5 mmol), and oxidant (1.2 equiv) in solvent (2.5 mL) at ambient temperature.
bThe yield of 2a could not be increased by prolonging the reaction time.
IBX, 2-iodoxybenzoic acid; PIDA, phenyliodonium diacetate; TFE, 2,2,2-trifluoroethanol; OFP, 2,2,3,3,4,4,5,5-octafluoro-1-pentanol; TFP, 2,2,3,3-
tetrafluoro-1-propanol; ETFA, 2,2,3,3-tetrafluoro-1-propanol
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of 1H-Indazoles
were less effective than HFIP for this intramolecular
coupling (Table 1, entries 8–11, and for more details, see
the Supporting Information).
improved, and some of them were isolated even in a
slightly lower yield when the reactions were performed
under strict moistureless conditions in nitrogen
atmosphere.
After screening various conditions, we have chosen 1.2
equiv. of PIFA in HFIP at ambient temperature to
examine the further scope of this intramolecular oxidative
C–N bond-forming reaction using various starting
materials 1. The results are summarized in Table 2. The
starting materials with same of Ar and R1 groups were
extended first. It was found that the phenyl group (1a)
and a variety of four-substituted phenyl groups with
electron-withdrawing groups (e.g., ꢀCl and ꢀF) (1b–c)
and electron-donating groups (EDGs) (e.g., ꢀMe and
ꢀOMe) (1d–e) could be easily tolerated to afford the
corresponding products (2a–e) in 66–90% yields. In
addition, the reaction led to some expected results as
previous reports [5,18] when we used the starting
materials which substituent R1 was different from Ar.
The reaction gave products 2f and 2g in the yields
of 75% and 70%, respectively, when R1 group was 4-Cl-
phenyl or 4-F-phenyl, and no isomers were detected in
the two reactions. However, the starting material 1h with
4-Me-phenyl (R1) substituent afforded a mixture of two
products 2h and 2h0 with same polar in the ratio of 5:1
Based on the results of the information from the
previous works, a plausible mechanism is proposed in
Scheme 1. Initially, intermediate A is formed by the
oxidation reaction of 1a with PIFA by losing one
molecule of CF3COOH [12]. Then, followed by the
liberation of iodobenzene, an N-nitrenium ion B is
generated [9,11,16,22]. Next, the nitrenium ion leads to
the target product 2a [5] via a tandem procedure of
nucleophilic arene attacks (C) and release of CF3COOH.
On the other hand, 2,2,6,6-tetramethylpiperidine-1-oxyl
was added into the reaction of 1a with the amount of 1
equiv (78 mg) and 10 equiv (780 mg), respectively,
under the optimal conditions. Thus result, compound 2a
was isolated in the yield of 72% and 73%, respectively.
This observation indicated that a radical pathway may not
be involved in this transformation [5]. In addition,
another possible mechanism involving the formation of
π-complex could not be excluded at present [23].
In summary, a metal-free, oxidative direct C–N coupling
method has been developed for the synthesis of
1H-indazoles heterocycles from easily accessible starting
materials. PIFA is employed as the oxidant in this
transformation, and the method has been found to be
generally useful for the preparation of a variety of
multisubstituted 1H-indazoles derivatives. Compared with
present metal-catalyzed and metal-free reactions, this
reaction demonstrates better reactivity, functional group
tolerance, and broader scope in the presence of sole
catalyst PIFA. We believe this facile and efficient method
will serve as a useful alternative to the existing methods
for the synthesis of substituted 1H-indazoles.
1
judging from the H NMR [5,18,19]. As expected, only
sole product 2i was obtained in 72% yield in the case of
1i (R1 = 4-MeO-phenyl), which indicated that a slightly
strong EDG, like methoxy group, was favor for the
electrophilic reaction. In addition, the effect of
heterocyclic substituent (R1) was also investigated.
Starting materials 1j and 1l gave the phenyl ring bonded
products 2j [20] and 2k in 91% and 94% yields,
respectively. While compound 1k afforded a thiophene
ring bonded product 2l in the yield of 95%. To our
delight, the reaction still worked well when R1 was
methyl (1m), n-butyl (1n) and benzoyl (1o), and
compounds 2m, 2n, and 2o were obtained in the yields
of 93%, 71%, and 65%, respectively.
The scope of R2 group was also investigated carefully.
The results showed that all of the tested starting materials
bearing an electron-withdrawing group (e.g.,ꢀCN,
ꢀCO2Et, and ꢀCl) (1p–t) and EDG (e.g., ꢀMe) (1u–w)
at the ortho-, meta-, or para-position could be well
tolerated and afforded the desired products 2p–w in
65–88% yields. N-Benzyl substituted starting material 1x
afforded the desired 2x in 53% yield. However, fewer
experiments were conducted toward varying the aliphatic
R2 group because of the limited number of available
substrates bearing tert-butyl and cyclohexyl groups at this
position. In addition, the cyclization of starting materials
1y bearing a tosyl group at the nitrogen atom [5,21]
and 1z did not react under the current optimal conditions.
It is worth mentioning that byproduct 3 could not be
inhibited, but the yield of 2 could not be further
EXPERIMENTAL
General remarks. All reactions were carried out at ambient
temperature, unless otherwise indicated. Other all reagents were
purchased from commercial sources and used without further
treatment, unless otherwise indicated. All of the hydrazones
1
were obtained under literature conditions [5]. H NMR and 13C
NMR spectra were recorded on a 400 MHz spectrometer (1H:
400 MHz, 13C: 100 MHz at 25°C) and TMS as internal
standard. Data are represented as follows: chemical shift,
integration, multiplicity (br = broad, s = singlet, d = doublet,
dd = double doublet, t = triplet, q = quartet, m = multiplet),
coupling constants in Hertz (Hz). All high-resolution mass
spectra (HRMS) were measured on a mass spectrometer (ESI-
oa-TOF). Melting points were measured on an apparatus. All
reactions were monitored by TLC with GF254 silica gel coated
plates. Flash column chromatography was carried out using
200–300 mesh silica gel at increased pressure.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Z. Zhang, Y. Huang, G. Huang, G. Zhang, and Q. Liu
Vol 000
Table 2
Extension of the Reaction Scope.a
2a: 73%
2d: 66%
2b: 70%
2c: 72%
2e: 90%
2i: 72%
2j: 91%
2g: 70%
2f: 75%
2h+2h’: 71% (5:1)
2m: 93%
2l: 95%
2n: 71%
2o: 65%
2k: 94%
2t: 88%e
2s: 87%
2q: 82%d
2r: 83%
2p: 88%
2y: 0%i
2x: 53%h
2v: 65% f
2w: 66%g
2u: 71%
(Continued)
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of 1H-Indazoles
Table 2
(Continued)
2z: 0%j
aUnless otherwise indicated, all reactions were carried out with 1a (0.5 mmol), and PIFA (1.2 equiv) in HFIP (2.5 mL) under room temperature in 5 min.
bIsolated yield.
c10% of 3a was obtained.
d13% of 3a was obtained.
e8% of 3a was obtained.
f14% of 3a was obtained.
g11% of 3a was obtained.
hAlong with some unidentified complex mixture.
i70% of 3a was obtained.
j52% of 3a was obtained, along with some unidentified complex mixture.
General procedure for the synthesis of 2. To a solution of
hydrazone (0.5 mmol, 1.0 equiv) in HFIP 2.5 mL was added
PIFA (0.6 mmol, 1.2 equiv). The reaction mixture was then stirred
at ambient temperature for 5–30 min, which was monitored by
TLC. After the completion, the reaction was quenched by water
(10 mL), and the mixture was extracted with dichloromethane
(3 × 5 mL). The combined organic layers were dried over
Na2SO4. After filtration and concentration, the crude product was
purified by a short flash silica gel column chromatography
(eluent: petroleum ether and EtOAc) to give product.
6-Chloro-3-(4-chlorophenyl)-1-phenyl-1H-indazole
[5]. The product was isolated by flash chromatography
(2b)
(eluent: ethyl acetate/petroleum ether = 1/80) as a white solid
1
(119 mg, 70%): mp 148–150°C; H NMR (400 MHz, CDCl3) δ
7.96–7.92 (m, 3H), 7.76–7.23 (m, 3H), 7.60–7.56 (m, 2H),
7.52–7.48 (m, 2H), 7.42 (t, J = 7.6 Hz, 1H), 7.28–7.25 (m, 1H).
13C NMR (100 MHz, CDCl3) δ 145.0, 140.8, 139.4, 134.5,
133.8, 131.1, 129.6, 129.1, 128.8, 127.3, 123.12, 123.09, 122.2,
121.4, 110.6. HRMS (ESI), m/z Calcd for C19H13Cl2N2
([M + H]+) 339.0450, found: 339.0450.
1,3-Diphenyl-1H-indazole (2a) [5]. The product was isolated
by flash chromatography (eluent: ethylacetate/petroleum ether = 1/100)
as a white solid (99 mg, 73%): mp 95–97°C; 1H NMR (400 MHz,
CDCl3) δ 8.11 (d, J = 8.4 Hz, 1H), 8.07 (d, J = 7.6 Hz, 2H), 7.81 (t,
J = 7.8 Hz, 3H), 7.56 (dd, J = 15.2, 7.6 Hz, 4H), 7.50–7.44 (m,
2H), 7.39 (t, J = 7.4 Hz, 1H), 7.31 (t, J = 7.6 Hz, 1H). 13C NMR
(100 MHz, CDCl3) δ 146.1, 140.3, 140.1, 133.2, 129.5, 128.9,
128.3, 127.8, 127.2, 126.7, 123.1, 123.0, 122.0, 121.6, 110.7.
HRMS (ESI), m/z Calcd for C19H15N2 ([M + H]+) 271.1230,
found: 271.1232.
6-Fluoro-3-(4-fluorophenyl)-1-phenyl-1H-indazole
[5]. The product was isolated by flash chromatography
(2c)
(eluent: ethyl acetate/petroleum ether = 1/80) as a white solid
1
(110 mg, 72%): mp 132–134°C; H NMR (400 MHz, CDCl3) δ
7.99–7.93 (m, 3H), 7.76–7.73 (m, 2H), 7.57 (t, J = 7.8 Hz, 2H),
7.43–7.38 (m, 2H), 7.26–7.20 (m, 2H), 7.09–7.04 (m, 1H). 13C
NMR (100 MHz, CDCl3) δ 164.0 (d, J = 246.5 Hz, C), 161.6 (d,
J = 244.6 Hz, C), 145.4, 140.7 (d, J = 12.4 Hz, C), 139.6, 129.6,
129.4 (d, J = 8.2 Hz, CH), 128.9 (d, J = 3.1 Hz, C), 127.1,
122.8, 122.7, 119.8, 115.9 (d, J = 21.5 Hz, CH), 111.7 (d,
J = 25.7 Hz, CH), 96.6 (d, J = 27.0 Hz, CH). HRMS (ESI), m/z
Calcd for C19H13F2N2 ([M + H]+) 307.1041, found: 307.1046.
Scheme 1. Proposed mechanism.
6-Methyl-1-phenyl-3-(p-tolyl)-1H-indazole (2d) [5].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/100) as a white solid (98 mg, 66%):
1
mp 87–88°C; H NMR (400 MHz, CDCl3) δ 7.96 (dd, J = 8.0,
1.6 Hz, 3H), 7.81 (dd, J = 8.8, 1.2 Hz, 2H), 7.59–7.55 (m, 3H),
7.37 (dd, J = 13.6, 7.2 Hz, 3H), 7.13 (d, J = 8.0 Hz, 1H), 2.54
(s, 3H), 2.46 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 145.9,
140.8, 140.2, 138.0, 137.4, 130.4, 129.5, 129.4, 127.5, 126.4,
123.9, 123.0, 121.24, 121.16, 22.0, 21.4. HRMS (ESI), m/z
Calcd for C21H19N2 ([M + H]+) 299.1543, found: 299.1543.
6-Methoxy-3-(4-methoxyphenyl)-1-phenyl-1H-indazole
(2e) [5].
The product was isolated by flash chromatography
(eluent: ethyl acetate/petroleum ether = 1/100) as a white solid
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Z. Zhang, Y. Huang, G. Huang, G. Zhang, and Q. Liu
Vol 000
1
(149 mg, 90%): mp 130–132°C; H NMR (400 MHz, CDCl3) δ
(100 MHz, CDCl3) δ 148.1, 143.0, 141.0, 139.8, 139.0,
129.7, 128.2, 128.0, 124.2, 123.4, 122.8, 120.3, 111.7. HRMS
(ESI), m/z Calcd for C18H14N3 ([M + H]+) 272.1182, found:
272.1195.
7.96–7.89 (m, 3H), 7.77 (dd, J = 8.4, 0.8 Hz, 2H), 7.58–7.54
(m, 2H), 7.37 (t, J = 7.4 Hz, 1H), 7.11 (d, J = 2.0 Hz, 1H),
7.07–7.04 (m, 2H), 6.92 (dd, J = 8.8, 2.4 Hz, 1H), 3.89 (s, 6H).
13C NMR (100 MHz, CDCl3) δ 159.8, 159.7, 145.9, 141.5,
140.2, 129.4, 128.8, 126.5, 125.8, 122.9, 122.3, 117.6, 114.2,
113.3, 91.8, 55.5, 55.3. HRMS (ESI), m/z Calcd for
C21H19N2O2 ([M + H]+) 331.1441, found: 331.1440.
1-Phenyl-3-(pyridin-3-yl)-1H-indazole (2k) [24].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/20) as a white solid (127 mg, 94%):
1
mp 80–82°C; H NMR (400 MHz, CDCl3) δ 9.51 (s, 1H), 8.84
(d, J = 8.0 Hz, 1H), 8.78 (d, J = 5.2 Hz, 1H), 8.10 (d,
J = 8.0 Hz, 1H), 7.87–7.80 (m, 2H), 7.78 (d, J = 7.6 Hz, 2H),
7.60 (t, J = 8.0 Hz, 2H), 7.56–7.52 (m, 1H), 7.48–7.40 (m,
2H).13C NMR (101 MHz, CDCl3) δ 149.3, 148.7, 143.0, 140.3,
139.8, 134.8, 129.5, 129.4, 127.4, 127.0, 123.7, 123.1, 122.9,
122.4, 121.1, 110.9. HRMS (ESI), m/z Calcd for C18H14N3
([M + H]+) 272.1182, found: 272.1173.
3-(4-Chlorophenyl)-1-phenyl-1H-indazole (2f ) [5].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/100) as a white solid (114 mg,
75%): mp 122–125°C; 1H NMR (400 MHz, CDCl3) δ 8.04
(d, J = 8.4 Hz, 1H), 8.01–7.98 (m, 2H), 7.79 (d, J = 8.0 Hz,
3H), 7.59–7.55 (m, 2H), 7.52–7.45 (m, 3H), 7.40 (t, J = 7.4 Hz,
1H), 7.33–7.29 (m, 1H). 13C NMR (100 MHz, CDCl3) δ 144.9,
140.4, 139.9, 134.1, 131.7, 129.5, 129.0, 128.9, 127.2, 126.9,
123.0, 122.9, 122.1, 121.3, 110.8. HRMS (ESI), m/z Calcd for
C19H14ClN2 ([M + H]+) 305.0840, found: 305.0840.
1,3-Diphenyl-1H-thieno[3,2-c]pyrazole (2l) [18].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/50) as a white solid (131 mg, 95%):
1
mp 135–138°C; H NMR (400 MHz, CDCl3) δ 8.08–8.05 (m,
3-(4-Fluorophenyl)-1-phenyl-1H-indazole (2g) [5].
The
2H), 7.87 (dd, J = 8.4, 0.8 Hz, 2H), 7.56–7.51 (m, 5H), 7.44–7.40
(m, 1H), 7.34–7.30 (m, 1H), 7.28 (d, J = 5.2 Hz, 1H). 13C NMR
(100 MHz, CDCl3) δ 147.7, 143.2, 140.4, 132.8, 132.0, 129.4,
128.8, 128.2, 125.94, 125.87, 121.4, 119.6, 110.8. HRMS (ESI),
m/z Calcd for C17H12N2SNa ([M + Na]+) 299.0613, found:
299.0614.
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/100) as a white solid (101 mg,
1
70%): mp 96–99°C; H NMR (400 MHz, CDCl3) δ 7.84–7.79
(m, 3H), 7.60–7.53 (m, 3H), 7.36–7.31 (m, 2H), 7.25–7.21 (m,
1H), 7.18–7.14 (m, 1H), 7.08–6.99 (m, 3H). 13C NMR
(100 MHz, CDCl3) δ 162.8 (d, J = 246.1 Hz, C), 145.1, 140.2,
140.0, 129.44, 129.41, 129.3, 127.2, 126.7, 122.9, 122.0, 121.3,
115.9, 115.7, 110.7. HRMS (ESI), m/z Calcd for C19H14FN2
([M + H]+) 289.1136, found: 289.1122.
3-Methyl-1,5-diphenyl-1H-pyrazole (2m) [19].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/100) as a light yellow oil (109 mg,
1
Mixture of compounds 6-methyl-1,3-diphenyl-1H-
93%); H NMR (400 MHz, CDCl3) δ 7.34–7.26 (m, 8H), 7.24–
indazole (2h) and 1-phenyl-3-(p-tolyl)-1H-indazole (2h0)
7.21 (m, 2H), 6.32 (s, 1H), 2.39 (s, 3H). 13C NMR (100 MHz,
CDCl3) δ 149.4, 143.6, 140.1, 130.7, 128.8, 128.6, 128.4,
128.0, 127.0, 125.1, 107.7, 13.6. HRMS (ESI), m/z Calcd for
C16H15N2 ([M + H]+) 235.1230, found: 235.1240.
[19].
Compounds 2h and 2h0 were isolated by flash
chromatography (eluent: ethyl acetate/petroleum ether = 1/100)
as a light yellow oil (101 mg, 71%), the regioisomer ratio was
obtained from 1H NMR spectrum about (5:1); 1H NMR
(400 MHz, CDCl3) δ 8.12–8.08 (m, 1.8H), 7.99 (d, J = 8.4 Hz,
1.2H), 7.84–7.80 (m, 2.23H), 7.61–7.55 (m, 4.52H), 7.50–7.44
(m, 1.05H), 7.42–7.37 (m, 1.39H), 7.33–7.29 (m, 0.17H, 2h0-
isomer), 7.15 (dd, J = 8.4 Hz, 0.8 Hz, 0.87H, 2h-isomer), 2.55
(s, 2.50H, 2h-isomer), 2.48 (s, 0.50H, 2h0-isomer). 13C NMR
(100 MHz, CDCl3) δ 145.8, 140.8, 140.1, 137.4, 133.3, 129.4,
128.7, 128.1, 127.6, 127.6, 126.5, 124.0, 123.0, 121.1, 110.1,
22.0 (2h-isomer). HRMS (ESI), m/z Calcd for C20H17N2
([M + H]+) 285.1386, found: 285.1384.
3-Butyl-1-phenyl-1H-indazole (2n).
The product was
isolated by flash chromatography (eluent: ethyl acetate/petroleum
1
ether = 1/100) as yellow oil (89 mg, 71%); H NMR (400 MHz,
CDCl3) δ 7.76 (d, J = 8.0 Hz, 1H), 7.73–7.71 (m, 3H), 7.54–7.50
(m, 2H), 7.43–7.39 (m, 1H), 7.32 (t, J = 7.4 Hz, 1H), 7.22–7.18
(m, 1H), 3.07–3.03 (m, 2H), 1.89–1.82 (m, 2H), 1.48 (dd,
J = 15.2, 7.5 Hz, 2H), 0.98 (t, J = 7.4 Hz, 3H). 13C NMR
(100 MHz, CDCl3) δ 148.3, 140.3, 139.5, 129.4, 127.0, 126.1,
124.4, 122.5, 120.72, 120.67, 110.4, 31.5, 26.8, 22.8, 13.9.
HRMS (ESI), m/z Calcd for C17H19N2 ([M + H]+) 251.1543,
found: 251.1555.
6-Methoxy-1,3-diphenyl-1H-indazole (2i) [19].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/100) as a white solid (108 mg,
72%): mp 132–134°C; 1H NMR (400 MHz, CDCl3) δ 8.05–
8.03 (m, 2H), 7.94 (d, J = 8.8 Hz, 1H), 7.81–7.79 (m, 2H),
7.60–7.52 (m, 4H), 7.46–7.38 (m, 2H), 7.13 (d, J = 2.0 Hz,
1H), 6.95 (dd, J = 8.8, 2.0 Hz, 1H), 3.89 (s, 3H). 13C NMR
(100 MHz, CDCl3) δ 159.9, 146.0, 141.6, 140.1, 133.1, 129.5,
128.8, 128.2, 127.6, 126.6, 123.0, 122.3, 117.7, 113.5, 91.8,
55.5. HRMS (ESI), m/z Calcd for C20H17N2O ([M + H]+)
301.1335, found: 301.1327.
Phenyl(1-phenyl-1H-indazole-3-yl)methanone
[18]. The product was isolated by flash chromatography
(2o)
(eluent: ethyl acetate/petroleum ether = 1/100) as a white
solid (97 mg, 65%): mp 146–147°C; 1H NMR (400 MHz,
CDCl3) δ 8.57 (d, J = 8.4 Hz, 1H), 8.43–8.41 (m, 2H), 7.80
(d, J = 7.6 Hz, 3H), 7.63–7.56 (m, 3H), 7.55–7.51 (m, 3H),
7.48–7.43 (m, 2H). 13C NMR (100 MHz, CDCl3) δ 188.6,
143.5, 139.9, 139.5, 137.8, 132.6, 130.7, 129.6, 128.2,
127.9, 127.8, 125.5, 124.2, 123.6, 123.5, 110.7. HRMS
(ESI), m/z Calcd for C20H14N2ONa ([M + Na]+) 321.0998,
found: 321.0998.
1-Phenyl-3-(pyridin-4-yl)-1H-indazole (2j) [5].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/20) as a white solid (123 mg,
91%): mp 100–102°C; 1H NMR (400 MHz, CDCl3) δ 8.89
(d, J = 5.6 Hz, 2H), 8.49 (d, J = 5.2 Hz, 2H), 8.16 (d,
J = 8.0 Hz, 1H), 7.85 (d, J = 8.4 Hz, 1H), 7.79–7.77 (m,
2H), 7.64–7.55 (m, 3H), 7.52–7.46 (m, 2H). 13C NMR
4-(3-Phenyl-1H-indazole-1-yl)benzonitrile (2p) [5].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/60) as a white solid (130 mg, 88%):
mp 160–161°C; 1H NMR (400 MHz, CDCl3) δ 8.11 (d,
J = 8.4 Hz, 1H), 8.04–7.99 (m, 4H), 7.87–7.82 (m, 3H), 7.58–7.52
(m, 3H), 7.50–7.47 (m, 1H), 7.38–7.35 (m, 1H). 13C NMR
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2017
Synthesis of 1H-Indazoles
(100 MHz, CDCl3) δ 147.9, 143.7, 139.9, 133.5, 132.4, 128.94,
128.86, 128.0, 127.8, 124.1, 122.9, 122.1, 122.0, 118.6, 110.7,
109.1. HRMS (ESI), m/z Calcd for C20H14N3 ([M + H]+)
296.1182, found: 296.1183.
Ethyl 4-(3-phenyl-1H-indazole-1-yl)benzoate (2q) [5]. The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 1/60) as colorless oil (140 mg, 82%);
1H NMR (400 MHz, CDCl3) δ 8.25–8.23 (m, 2H), 8.09
(d, J = 8.4 Hz, 1H), 8.06–8.04 (m, 2H), 7.95–7.92 (m, 2H),
J = 8.8 Hz, 1H), 7.64–7.60 (m, 2H), 7.55 (t, J = 7.6 Hz, 2H),
7.49–7.43 (m, 3H), 7.32–7.28 (m, 1H), 7.21 (d, J = 7.6 Hz,
1H), 2.49 (s, 3H). 13C NMR (100 MHz, CDCl3) δ 146.0, 140.4,
140.0, 139.7, 133.3, 129.2, 128.9, 128.3, 127.8, 127.6, 127.1,
123.9, 123.1, 121.9, 121.6, 120.0, 110.8, 21.6. HRMS (ESI), m/z
Calcd for C20H17N2 ([M + H]+) 285.1386, found: 285.1387.
3-Phenyl-1-(o-tolyl)-1H-indazole (2w) [6].
The product
was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as a colorless oil (94 mg,
1
7.86 (d,
J
=
8.4 Hz, 1H), 7.57–7.45 (m, 4H), 7.32
66%); H NMR (400 MHz, CDCl3) δ 8.18–8.12 (m, 3H), 7.58
(t, J = 7.6 Hz, 1H), 4.46–4.41 (m, 2H), 1.45 (t, J = 7.0 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ 165.9, 147.1, 143.7, 140.0,
132.7, 130.9, 128.8, 128.6, 127.82, 127.78, 127.6, 123.7, 122.4,
121.8, 121.5, 110.8, 61.1, 14.3. HRMS (ESI), m/z Calcd for
C22H19N2O2 ([M + H]+) 343.1441, found: 343.1438.
(t, J = 7.6 Hz, 2H), 7.52–7.48 (m, 1H), 7.49–7.38 (m, 5H),
7.34–7.29 (m, 2H), 2.25 (s, 3H). 13C NMR (100 MHz, CDCl3)
δ 145.4, 142.0, 138.2, 135.9, 133.6, 131.6, 128.9, 128.2,
127.72, 127.65, 126.9, 126.8, 121.8, 121.6, 121.4, 110.5, 18.1.
HRMS (ESI), m/z Calcd for C20H16N2Na ([M
+
Na]+)
307.1206, found: 307.1208.
1-(4-Chlorophenyl)-3-phenyl-1H-indazole (2r) [5].
The
1-Benzyl-3-phenyl-1H-indazole (2x) [24]. The product was
isolated by flash chromatography (eluent: ethyl acetate/petroleum
ether = 1/50) as a white solid (75 mg, 53%): mp 79–82°C; H
NMR (400 MHz, CDCl3) δ 8.04 (d, J = 8.0 Hz, 1H), 8.00 (d,
J = 7.2 Hz, 2H), 7.52 (t, J = 7.6 Hz, 2H), 7.41 (t, J = 7.4 Hz,
1H), 7.36 (d, J = 4.0 Hz, 2H), 7.33–7.27 (m, 3H), 7.26–7.19
(m, 3H), 5.68 (s, 2H). 13C NMR (100 MHz, CDCl3) δ 142.2,
139.1, 134.9, 131.6, 126.8, 126.7, 125.9, 125.7, 125.5, 125.1,
124.4, 120.1, 119.4, 119.1, 107.6, 51.1. HRMS (ESI), m/z
Calcd for C20H17N2 ([M + H]+) 285.1386, found: 285.1389.
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as white solid (126 mg, 83%):
mp 120–121°C; 1H NMR (400 MHz, CDCl3) δ 8.10 (d,
J = 8.4 Hz, 1H), 8.07–8.05 (m, 2H), 7.78–7.73 (m, 3H), 7.58–
7.52 (m, 4H), 7.50–7.45 (m, 2H), 7.31 (t, J = 7.6 Hz, 1H). 13C
NMR (100 MHz, CDCl3) δ 146.4, 140.1, 138.6, 132.9, 131.9,
129.5, 128.8, 128.4, 127.7, 127.3, 123.8, 123.2, 122.1, 121.7,
110.4. HRMS (ESI), m/z Calcd for C19H14ClN2 ([M + H]+)
305.0840, found: 305.0844.
1
1-(3-Chlorophenyl)-3-phenyl-1H-indazole (2s) [5].
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as colorless oil (132 mg, 87%);
1H NMR (400 MHz, CDCl3) δ 8.10 (d, J = 8.0 Hz, 1H), 8.07–
8.05 (m, 2H), 7.87 (t, J = 2.0 Hz, 1H), 7.80 (d, J = 8.8 Hz, 1H),
7.74–7.72 (m, 1H), 7.56 (t, J = 7.6 Hz, 2H), 7.52–7.46 (m, 3H),
7.36–7.30 (m, 2H). 13C NMR (100 MHz, CDCl3) δ 146.7,
141.1, 140.1, 135.1, 132.8, 130.4, 128.9, 128.5, 127.8, 127.5,
126.5, 123.3, 122.8, 122.2, 121.7, 120.5, 110.5. HRMS (ESI),
m/z Calcd for C19H14ClN2 ([M + H]+) 305.0840, found:
305.0839.
Acknowledgments. We thank the NSFC (21272057 and
21372065), Young Backbone Teachers Fund of Henan
(2014GGJS-049), Key Project of Henan Educational Committee
(15B610005, 14A150019, 14B150042, and 15A150015),
Science and Technology Innovation Talents in Universities of
Henan Province (17HASTIT002), the Program of Foundation
and Frontier Technology Research of Henan Province
(122300410296), Outstanding Young Talent Cultivation Project
Funding of Henan Normal University (14YR002), and Open
Project of Jilin Province Key Laboratory of Organic Functional
Molecular Design and Synthesis (130028651).
1-(2-Chlorophenyl)-3-phenyl-1H-indazole
(2t).
The
product was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as a colorless oil (134 mg,
1
88%); H NMR (400 MHz, CDCl3) δ 8.12 (d, J = 8.0 Hz, 1H),
8.08–8.06 (m, 2H), 7.65–7.60 (m, 2H), 7.57–7.53 (m, 2H),
7.47–7.43 (m, 4H), 7.33–7.28 (m, 2H). 13C NMR (100 MHz,
CDCl3) δ 146.4, 141.8, 137.0, 133.1, 131.6, 130.7, 129.8,
129.7, 128.8, 128.3, 127.74, 127.71, 126.9, 122.1, 121.8, 121.4,
110.8. HRMS (ESI), m/z Calcd for C19H14ClN2 ([M + H]+)
305.0840, found: 305.0840.
REFERENCES AND NOTES
[1] For biological activity of 1H-indazole derivatives, see:
(a) Chen, H.-S.; Kuo, S.-C.; Teng, C.-M.; Lee, F.-Y.; Wang, J.-P.; Lee,
Y.-C.; Kuo, C.-W.; Huang, C.-C.; Wu, C.-C.; Huang, L.-J. Bioorg Med
Chem 2008, 16, 1262; (b) Lee, F.-Y.; Lien, J.-C.; Huang, L.-J.; Huang,
T.-M.; Tsai, S.-C.; Teng, C.-M.; Wu, C.-C.; Cheng, F.-C.; Kuo, S.-C. J
Med Chem 2001, 44, 3746; (c) Thangadurai, A.; Minu, M.; Wakode, S.;
Agrawal, S.; Narasimhan, B. Med Chem Res 2012, 21, 1509; and further
references cited therein; (d) Haddadin, M. J.; Conrad, W. E.; Kurth, M. J.
Mini-Rev Med Chem 2012, 12, 1293; (e) Ali, N. A. S.; Dar, B. A.;
Pradhan, V.; Farooqui, M. Mini-Rev Med Chem 2013, 13, 1792.
[2] (a) Dolzhenko, A. V.; Dolzhenko, A. V.; Chui, W. K.
Heterocycles 2008, 75, 1575; (b) Wrobleski, S. T.; Chen, P.; Hynes,
J. Jr.; Lin, S.; Norris, D. J.; Pandit, C. R.; Spergel, S.; Wu, H.;
Tokarski, J. S.; Chen, X.; Gillooly, K. M.; Kiener, P. A.; McIntyre,
K. W.; Patil-Koota, V.; Shuster, D. J.; Turk, L. A.; Yang, G.;
Leftheris, K. J Med Chem 2003, 46, 2110; (c) Magano, J.; Waldo,
M.; Greene, D.; Nord, E. Org Process Res Dev 2008, 12, 877.
[3] For synthesis of 1H-indazoles from arynes, see: (a) Jin, T.;
Yamamoto, Y. Angew Chem Int Ed 2007, 46, 3323; (b) Liu, Z.; Shi, F.;
Martinez, P. D. G.; Raminelli, C.; Larock, R. C. J Org Chem 2008,
3-Phenyl-1-(p-tolyl)-1H-indazole (2u) [19].
The product
was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as a white solid (101 mg,
71%): mp 89–91°C; 1H NMR (400 MHz, CDCl3) δ 8.11 (dd,
J = 15.2, 8.4 Hz, 3H), 7.78 (d, J = 8.8 Hz, 1H), 7.72 (d,
J = 8.0 Hz, 2H), 7.58 (t, J = 7.6 Hz, 2H), 7.49–7.45 (m, 2H),
7.38 (d, J = 8.0 Hz, 2H), 7.33–7.29 (m, 1H), 2.48 (s, 3H). 13C
NMR (100 MHz, CDCl3) δ 145.7, 140.3, 137.5, 136.5, 133.3,
129.9, 128.8, 128.1, 127.7, 126.9, 122.91, 122.85, 121.7, 121.4,
110.6, 21.1. HRMS (ESI), m/z Calcd C20H17N2 for ([M + H]+)
285.1386, found: 285.1382.
3-Phenyl-1-(m-tolyl)-1H–indazole (2v) [5].
The product
was isolated by flash chromatography (eluent: ethyl
acetate/petroleum ether = 3/100) as colorless oil (92 mg, 65%);
1H NMR (400 MHz, CDCl3) δ 8.11–8.05 (m, 3H), 7.79 (d,
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Z. Zhang, Y. Huang, G. Huang, G. Zhang, and Q. Liu
Vol 000
[12] (a) Malamidou-Xenikaki, E.; Spyroudis, S.; Tsanakopoulou,
M.; Hadjipavlou-Litina, D. J Org Chem 2009, 74, 7315; (b) Li, X.; Yang,
L.; Zhang, X.; Zhang-Negrerie, D.; Du, Y.; Zhao, K. J Org Chem 2014,
79, 955; (c) Correa, A.; Tellitu, I.; Domínguez, E.; Moreno, I.; SanMartin,
R. J Org Chem 2005, 70, 2256.
[13] Zheng, Z.; Ma, S.; Tang, L.; Zhang-Negrerie, D.; Du, Y.;
Zhao, K. J Org Chem 2014, 79, 4687.
[14] Zheng, Y.; Li, X.; Ren, C.; Zhang-Negrerie, D.; Du, Y.; Zhao,
K. J Org Chem 2012, 77, 10353.
[15] (a) Wardrop, D. J.; Burge, M. S. J Org Chem 2005, 70,
10271; (b) Miyazawa, E.; Sakamoto, T.; Kikugawa, Y. J Org Chem
2003, 68, 5429; (c) Dohi, T.; Maruyama, A.; Minamitsuji, Y.; Takenaga,
N.; Kita, Y. Chem Commun 2007, 12, 1224; (d) Wardrop, D. J.; Bowen, E. G.;
Forslund, R. E.; Sussman, A. D.; Weerasekera, S. L. J Am Chem Soc
2010, 132, 1188; (e) Tellitu, I.; Serna, S.; Herrero, M. T.; Moreno, I.;
Domínguez, E.; SanMartin, R. J Org Chem 2007, 72, 1526.
[16] (a) Couto, I.; Tellitu, I.; Domínguez, E. J Org Chem 2010, 75,
7954; (b) Huang, P.; Fu, X.; Liang, Y.; Zhang, R.; Dong, D. Aust J Chem
2012, 65, 121; (c) Huang, J.; Lu, Y.; Qiu, B.; Liang, Y.; Li, N.; Dong, D.
Synthesis 2007, 2007, 2791; (d) Correa, A.; Tellitu, I.; Domínguez, E.;
SanMartin, R. Org Lett 2006, 8, 4811.
[17] (a) Zhang, Z.; Zhang, F.; Wang, H.; Wu, H.; Duan, X.; Liu,
Q.; Liu, T.; Zhang, G. Adv Synth Catal 2015, 357, 2681; (b) Zhang,
Z.; Zhang, L.; Duan, X.; Yan, X.; Yan, Y.; Liu, Q.; Liu, T.; Zhang,
G. Tetrahedron 2015, 71, 7745; (c) Zhang, Z.; Li, J.; Zhang, G.; Ma,
N.; Liu, Q.; Liu, T. J Org Chem 2015, 80, 6875;l (d) Zhang, Z.; Zhang, W.;
Li, J.; Liu, Q.; Liu, T.; Zhang, G. J Org Chem 2014, 79, 11226; (e) Zhang,
L.; Zhang, Z.; Liu, Q.; Liu, T.; Zhang, G. J Org Chem 2014, 79, 2281.
[18] Yu, J.; Lim, J. W.; Kim, S. Y.; Kim, J.; Kim, J. N. Tetrahedron
Lett 2015, 56, 1432.
73, 219; (c) Spiteri, C.; Keeling, S.; Moses, J. E. Org Lett 2010, 12,
3368; (d) Li, P.; Wu, C.; Zhao, J. J.; Rogness, D. C.; Shi, F. J Org
Chem 2012, 77, 3149.
[4] (a) Pabba, C.; Wang, H.-J.; Mulligan, S. R.; Chen, Z.-J.; Stark,
T. M.; Gregg, B. T. Tetrahedron Lett 2005, 46, 7553; (b) Inamoto, K.;
Katsuno, M.; Yoshino, T.; Suzuki, I.; Hiroya, K.; Sakamoto, T. Chem Lett
2004, 33, 1026; (c) Inamoto, K.; Katsuno, M.; Yoshino, T.; Arai, Y.;
Hiroya, K.; Sakamoto, T. Tetrahedron 2007, 63, 2695; (d) Xiong, X.;
Jiang, Y.; Ma, D. Org Lett 2012, 14, 2552; (e) Evano, G.; Blanchard,
N.; Toumi, M. Chem Rev 2008, 108, 3054; (f ) Hartwig, J. F. Acc Chem
Res 2008, 41, 1534; (g) Surry, D. S.; Buchwald, S. L. Angew Chem Int
Ed 2008, 47, 6338; (h) Wang, C.; Liu, L.; Wang, W.; Ma, D.-S.; Zhang,
H. Molecules 2010, 15, 1154.
[5] (a) Hu, J.; Xu, H.; Nie, P.; Xie, X.; Nie, Z.; Rao, Y. Che Eur J
2014, 20, 3932; (b) Inamoto, K.; Saito, T.; Katsuno, M.; Sakamoto, T.;
Hiroya, K. Org Lett 2007, 9, 2931; (c) Li, X.; He, L.; Chen, H.; Wu,
W.; Jiang, H. J Org Chem 2013, 78, 3636; (d) Thomé, I.; Besson, C.;
Kleine, T.; Bolm, C. Angew Che Int Ed 2013, 52, 7509; (e) Kashiwa,
M.; Sonoda, M.; Tanimori, S. Eur J Org Chem 2014, 2014, 4720; (f )
Liang, D.; Zhu, Q. Asian J Org Chem 2015, 4, 42.
[6] (a) Liu, Z.; Shi, F.; Martinez, P. D. G.; Raminelli, C.; Larock,
R. C. J Org Chem 2008, 7, 219; (b) Jin, T.; Yamamoto, Y. Angew Chem
Int Ed 2007, 46, 3323; (c) Spiteri, C.; Keeling, S.; Moses, J. E. Org Lett
2010, 12, 3368; (d) Li, P.; Zhao, J.; Wu, C.; Larock, R. C.; Shi, F. Org
Lett 2011, 13, 3340; (e) Li, P.; Wu, C.; Zhao, J.; Rogness, D. C.; Shi,
F. J Org Chem 2012, 77, 3149.
[7] (a) Yu, D.-G.; Suri, M.; Glorius, F. J Am Chem Soc 2013,
135, 8802; (b) Peng, J.; Xie, Z.; Chen, M.; Wang, J.; Zhu, Q. Org Lett
2014, 16, 4702.
[8] Korbonits, D.; Kanzel-Szvoboda, I.; Horvath, K. J Chem Soc
Perkin Trans 1982, 1, 759.
[19] Zhang, T.; Bao, W. J Org Chem 2013, 78, 1317.
[20] The structure of 2j was also confirmed by X-ray diffraction.
For more information, please see Supporting Information.
[21] Selected matal-catalyzed C-N coupling method of this type
starting materials see references: 5b, 5c, and Cyr, P.; Régnier, S.; Bechara,
W. S.; Charette, A. B. Org Lett 2015, 17, 3386.
[22] Alla, S. K.; Kumar, R. K.; Sadhu, P.; Punniyamurthy, T. Org
Lett 2013, 15, 1334.
[23] Chu, J.-H.; Hsu, W.-T.; Wu, Y.-H.; Chiang, M.-F.; Hsu, N.-H.;
Huang, H.-P.; Wu, M.-J. J Org Chem 2014, 79, 11395.
[9] (a) Correa, A.; Tellitu, I.; Domínguez, E.; SanMartin, R. J Org
Chem 2006, 71, 3501; (b) Kotali, A.; Harris, P. A. J Heterocyclic Chem
1996, 33, 605; (c) Paul, S.; Panda, S.; Manna, D. Tetrahedron Lett
2014, 55, 2480; (d) Counceller, C. M.; Eichman, C. C.; Wray, B. C.;
Stambuli, J. P. Org Lett 2008, 10, 1021.
[10] (a) Zhdankin, V. V. ARKIVOC 2009, i, 1; (b) Varvoglis, A.
Chem Soc Rev 1981, 10, 377.
[11] (a) Du, Y.; Liu, R.; Linn, G.; Zhao, K. Org Lett 2006, 8, 5919;
(b) Ban, X.; Pan, Y.; Lin, Y.; Wang, S.; Du, Y.; Zhao, K. Org Biomol
Chem 2012, 10, 3606.
[24] Hattori, K.; Yamaguchi, K.; Yamaguchi, J.; Itami, K.
Tetrahedron 2012, 68, 7605.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet