Synthesis of 2-Arylbenzothiazole and 2-Arylthiazole Derivatives via a Ru-Catalyzed meta-Selective C-H Nitration Reaction

Article abstract of DOI:10.1021/acs.joc.9b01194

A Ru-catalyzed meta-selective C-H nitration of 2-arylbenzothiazoles and 2-arylthiazoles has been developed. A wide range of functional groups are tolerated, providing the meta-nitrated products in good to excellent yields using Cu(NO₃)₂

Full text of DOI:10.1021/acs.joc.9b01194

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Article
Synthesis of 2-Arylbenzothiazole and 2-Arylthiazole Derivatives
via a Ru-Catalyzed meta-Selective C-H Nitration Reaction
Deming Liu, Puying Luo, Junying Ge, Zilin Jiang, Yiyuan Peng, and Qiuping Ding
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.9b01194 • Publication Date (Web): 19 Jul 2019
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Synthesis of 2-Arylbenzothiazole and 2-Arylthiazole Derivatives via
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a Ru-Catalyzed meta-Selective C−H Nitration Reaction
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Deming Liu,a Puying Luo,*b Junying Ge,a Zilin Jiang,a and Yiyuan Peng,a
Qiuping Ding,*,a
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aKey Laboratory of Small Functional Organic Molecule, Ministry of Education and
Jiangxi's Key Laboratory of Green Chemistry, Jiangxi Normal University, Nanchang,
Jiangxi 330022, P.R. of China. E-mail: dqpjxnu@gmail.com;
bDepartment of Obstetrics and Gynecology, Jiangxi Provincial people’s Hospital,
Nanchang, Jiangxi 330006, P. R. China. E-mail: luopuying1979@126.com
Cu(NO3)2 3H2O (2.0 equiv)
NO2
Ru3(CO)12 (5 mol%)
N
S
N
R1
R1
R2
R2
AgTFA (1.5 equiv)
K2S2O8 (1.5 equiv)
S
20 examples
up to 95% yield
o
DCE, 80 C
Abstract: A Ru-catalyzed meta-selective C−H nitration of 2-arylbenzothiazoles and
2-arylthiazoles has been developed. A wide range of functional groups are tolerated,
providing the meta-nitrated products in good to excellent yields by using
Cu(NO3)2·3H2O as the nitro source. The nitration could be carried out on gram-scale
and used to the synthesis of promising therapeutic leads for Human African
Trypanosomiasis.
INTRODUCTION
Benzothiazole derivatives are versatile motifs in synthetic chemistry, material
chemistry, and the areas related to therapeutic agents, pharmaceuticals, due to their
good biological activities and fluorescent properties.1 In addition, nitroarenes are
invaluable building blocks or precursors in organic synthesis, medicinal chemistry
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and material science.2 For example, a series of meta-nitro substituted
2-arylbenzothiazole derivatives have been detected as COMT inhibitors, P388
inhibitor, and potential drugs with in vitro antimicrobial activity (Figure 1).3 Recently,
transition-metal catalyzed inert C–H bond activation and directly functionalization
offers an attractive strategy for the synthesis of various C–C bond or C–X bonds (X =
O, N, S, halogen atoms).4 Remarkable progress has been made in directing
group-assisted ortho-selective C–H bond functionalization.5 Recently, considerable
efforts have been devoted to developing various ortho-functionalized
2-arylbenzothiazole derivatives by us1a,6-8 and other groups,9,10 including amidation,1a
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arylation,6a acetoxylation,6b halogenations,6c
sulfonamidation,7a acylation,7b,9a,b
cyanation,8a alkylation,8b,9ghydroxylation,10a,b nitration,10c and so on.
OMe
OH
NO2
N
R
N
MeO
N
O
S
N
S
S
N
H
N
HN
NO2
N
N
MeO2C
NO2
O
R = benzyl, naphth-2-yl
COMT inhibitors
In vitro antimicrobial activity
Inhibitor for P388 (IC50 = 1.49 uM)
Figure 1. Chemical structures meta-nitro substituted 2-arylbenzothiazoles with bioactivities
Although some excellent work11-15 concerning transition-metal-catalyzed meta-C–H
bond functionalizations has been reported, study in this area is still in its infancy.
Among these, the pioneering work in meta-C–H functionalizations mainly reflected in
Pd-catalyzed U-shaped nitrile-containing ligand-assisted meta-C–H activation or
ortho-directing group-assisted norbornene-mediated meta-C–H functionalizations,
which were mainly developed by the Yu,11,12 Dong13 and Maiti14 groups. Additionally,
the meta-selective functionalizations have been reported by standard Friedel-Crafts
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reactions via combination of ligand and electronic effect.15 Recently, several
ruthenium-catalyzed chelation-assisted meta-C−H activation in the formation of
various C–C, C–S, and C–Br bonds have been well studied.16 Li described the
Ru-catalyzed meta-C–H bond alkylation of 2-phenpxypyridines16a and azoarenes16b.
Shi also reported the Ru-catalyzed meta-C–H benzylation of pyridyl, pyrimidyl, and
pyrazolyl directed arenes with toluene derivatives.16c Recently, the methods for
regioselective nitration of arenes using various nitro sources also have been
developed.17,18 For instance, Zhang reported the Ru-catalyzed meta-C–H nitration of
2-arylpyridines17a and oximes17b using Cu(NO3)2·3H2O as the nitro source. Stimulated
by the recent Ru-catalyzed meta-selective C–H functionalizations, we wish to find an
efficient method for the synthesis of meta-nitrated 2-arylbenzothiazole derivatives to
examine their bioactivities.
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RESULTS AND DISCUSSION
According to Zhang’s research,17 we initially screened the Ru-catalysts using
2-arylbenzothiazole 1a as the model substrate and Cu(NO3)2·3H2O as the nitro source
in the presence of oxone and AgTFA (Table 1, entries 1-4). The initial results
indicated that Ru3(CO)12 performed better than [RuCl2(p-cymene)2]2 , affording the
desired meta-nitrated product 2a in 64% yield (Table 1, entries 1 vs 2). Using other
ruthenium complexes, such as RuCl2(PPh3)4 and RuCl3, only trace amounts of desired
product was observed (Table 1, entries 3 and 4). Control experiments confirmed that
no reaction was observed in the absence of [Ru]-catalyst (Table 1, entry 5), while
moderate yield (52%) of product 2a was obtained in the absence of oxidant (Table 1,
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entry 6). Among the oxidants examined, the inexpensive K2S2O8 afforded the best
results (Table 1, entry 10), whereas Cu(OAc)2·H2O, chloranil and Cu(OAc)2 gave the
desired product 2a in moderate yields (Table 1, entries 7-9, 56-68%). We then
screened several silver salts as radical initiators, AgTFA exhibited superior results
compared to AgBF4, AgOAc and AgNO3 (Table 1, entries 10-13). Only trace amounts
of desired product was observed in the absence of silver salts (Table 1, entry 14).
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o
Increasing the reaction temperature (T = 100 C) decreased the yield of desired
product 2a (70%) (Table 1, entry 15). The same result was obtained at 80 oC, and the
yield remained satisfactory (86%) at 70 oC (Table 1, entries 16 and 17). However, the
yield (51%) of product 2a declined dramatically when the reaction proceeded at 60 oC
(Table 1, entry 18). Among the solvents examined, DCE gave the best results, and
toluene afforded inferior yield (64%) (Table 1, entry 19), other solvents such as
CH3CN, EtOH, and DMSO only afforded trace amount of desired product 2a.
Table 1. Optimization of reaction conditionsa
[Ru] catalyst (5 mol%)
Oxidant (1.5 equiv)
[Ag] salt (1.5 equiv)
Me
Me
NO2
N
S
N
S
Cu(NO ) 3H O
·
3 2
2
Solvent, T oC, 20 h
Me
Me
1a
2a
Entry
[Ru] catalyst
[RuCl2(p-cymene)2]2
Ru3(CO)12
RuCl2(PPh3)4
RuCl3
Oxidant
Oxone
[Ag]
Solvent
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
T/℃
90
90
90
90
90
90
90
90
90
Yieldb
1
2
3
4
5
6
7
8
9
AgTFA
AgTFA
AgTFA
AgTFA
AgTFA
AgTFA
50
64
Oxone
Oxone
trace
trace
0
Oxone
-
Oxone
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
-
52
AgTFA
AgTFA
AgTFA
64
Cu(OAc)2·H2O
Chloranil
Cu(OAc)2
56
68
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Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
Ru3(CO)12
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
K2S2O8
AgTFA
AgBF4
AgOAc
AgNO3
-
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
DCE
toluene
90
90
90
90
90
100
80
70
60
80
88
50
39
trace
trace
70
AgTFA
AgTFA
AgTFA
AgTFA
AgTFA
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aReaction conditions: 1a (0.2 mmol), Cu(NO3)2·3H2O (0.4 mmol), [Ru] catalyst (5
mol%), oxidant (1.5 equiv), [Ag] salt (1.5 equiv), solvent (2 mL), 20 h. bIsolated yield
by flash column chromatography.
With the optimized conditions in hand, we investigated the substrate scope of
2-arylbenzothiazoles 1. As shown in Scheme 1, a broad range of 2-arylbenzothiazole
derivatives 1 could be smoothly transformed into the corresponding meta-selective
nitration products
2
in moderate to excellent yields. For instance,
ortho-Me) substituted substrates
ortho-electron-donating group (R2
=
2-(o-tolyl)benzo[d]thiazoles 1a–c delivered the desired meta-nitrated products (2a–c)
in good yields (85-88%). While ortho-electron-withdrawing group (R2 = ortho-Cl and
F) substituted substrates 2-arylbenzo[d]thiazoles 1d–f provided the corresponding
desired products 2d-f in moderate yields (51-58%) under the standard conditions.
Subsequently, meta-electron-donating or -withdrawing groups (R2 = meta-Me and Cl)
substituted 2-arylbenzo[d]thiazoles 1g–j showed good reactivity and provided the
desired meta-selective nitration products 2g-j in good to excellent yields (81-92%).
The para-substituted 2-arylbenzo[d]thiazoles 1k–l also performed well and gave the
corresponding mono-nitrated products 2k–l in good yields. The meta-nitration
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structure of 2k was confirmed by single-crystal X-ray analysis. In addition,
2-phenylbenzo[d]thiazoles 1m–o (R2 = H) underwent the meta-nitration smoothly
under standard reaction conditions, leading to the corresponding mono-nitrated
products 2m–o in high yields (71-87%).
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Scheme 1. Scope of 2-arylbenzo[d]thiazolesa,b
Cu(NO3)2 3H2O (2.0 equiv)
NO2
Ru3(CO)12 (5 mol%)
N
S
N
R1
R1
R2
R2
S
AgTFA (1.5 equiv)
K2S2O8 (1.5 equiv)
2
1
o
DCE, 80 C
Me
NO2
Me
NO2
Me
NO2
N
S
N
N
S
S
Me
F
2a
2b
2c
, 88%
Cl
, 88%
, 85%
F
Cl
N
NO2
NO2
NO2
Me
N
N
S
S
S
Me
2d
2e
2f
, 58%
, 51%
, 54%
Me
Me
N
S
N
S
N
S
Me
F
NO2
NO2
NO2
2g
2h
2i
, 92%
, 83%
, 85%
Cl
N
N
S
N
S
Me
NO2
Me
NO2
S
Cl
NO2
2j
2k
2l
, 81%
, 72%
, 78%
N
N
S
N
S
S
Me
Cl
NO2
NO2
NO2
2m
2n
2o
, 81%
, 71%
, 87%
aReaction conditions: 2-arylbenzothiazoles 1 (0.2 mmol), Cu(NO3)2·3H2O (0.4 mmol),
Ru3(CO)12 (5 mol %), K2S2O8 (0.3 mmol), AgTFA (0.3 mmol), DCE (2 mL), 80 oC,
20 h. bIsolated yield by flash column chromatography.
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We subsequently explored the generality of the meta-selective nitration using
2-arylthiazoles 3 as substrates under the standard conditions. As illustrated in Scheme
2, various substituted 2-arylthiazoles 3 were proceeded meta-selective nitration in
good to excellent yields. The reactivity is similar to that of 2-arylbenzo[d]thiazoles.
Among these, the nitration of meta-methyl substituted substrate 3b gave the desired
product 4b in excellent yield (95%). Furthermore, the reaction of
2-(naphthalen-2-yl)thiazole 3d occurred smoothly, providing the desired product 4d
in 66% yield. Unfortunately, no desired product 4f was observed when
2-(2-methoxyphenyl)thiazole 3f was used as substrate, which was possibly caused by
the strong electron donation of the methoxy group.19
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Scheme 2. Scope of 2-Arylthiazolesa,b
Cu(NO3)2 3H2O (2.0 equiv)
NO2
N
S
N
Ru3(CO)12 (5 mol%)
R3
R3
S
AgTFA (1.5 equiv)
K2S2O8 (1.5 equiv)
4
3
o
DCE, 80 C
Me
F
N
N
N
S
S
S
NO2
NO2
NO2
4a
4d
4b
4c
, 71%
, 71%
NO2
, 95%
N
S
N
S
N
S
Me
NO2
MeO
NO2
4e
4f
, 66%
, 74%
, ND
aReaction conditions: 2-arylthiazoles 3 (0.2 mmol), Cu(NO3)2·3H2O (0.4 mmol),
Ru3(CO)12 (5 mol %), K2S2O8 (0.3 mmol), AgTFA (0.3 mmol), DCE (2 mL), 80 oC,
20 h. bIsolated yield by flash column chromatography.
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To demonstrate the efficiency of the present method, we tried the nitration of 1l at the
gram-scale. Predictably, nitrated product 2l was obtained in 75% yield (Scheme 3).
According to previous work, nitroarenes are versatile aromatic building blocks, which
could be easily undergone various functionalization by transition metal-catalyzed
denitration-cross coupling reactions,20 such as arylation, amination, etherification, and
thioetherification. In addition, the selective reduction nitro group of 2l to amine 5 was
achieved in 92% yield in the presence of SnCl2·2H2O (5.0 equiv) (Scheme 4).21
Amine 5 was previously converted into compound 6 by amidation reaction, which
was reported as promising therapeutic leads for Human African Trypanosomiasis,
which also displayed suitable physiochemical characteristics and microsomal
stability.21 Furthermore, 2-(3-aminophenyl)-benzothiazole derivatives could be
effectively synthesized from the corresponding reduction products. Recently, Zhang
and co-workers described that 2-(3-aminophenyl)-benzothiazoles displayed good in
vitro antiproliferative activity against various human cancer cell lines, such as A549,
HeLa, HepG2, MCF-7, and so on.22
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Scheme 3. Gram-Scale Nitration of 1l
N
S
N
S
Ru3(CO)12 (5 mol%)
Me
Me
Cu(NO3)2 3H2O
(2.0 equiv)
AgTFA (1.5 equiv)
K2S2O8 (1.5 equiv)
NO2
1l
1.125 g (5 mmol)
2l
o
DCE, 80 C
1.014 g (75% yield)
Scheme 4. Reduction and the Application of 2l
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N
S
N
S
SnCl2 2H2O (5.0 equiv)
Me
Me
NH2
EtOH, 80 oC, 5 h
NO2
92% yield
2l
5
7
8
9
Me
Cl
O
N
S
Ref 20
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S
Me
NH2
N
H
N
N
HN
NO2
5
6
Therapeutic Leads for Human
African Trypanosomiasis
To explore the reaction mechanism, two control experiments were performed.
2-(2,6-Dimethylphenyl)-6-methylbenzo[d]thiazole 1p bearing two methyl groups to
block the two ortho positions of the phenyl ring was used as the substrate, resulting in
no conversion. This result confirms that the initial ruthenium-mediated ortho-C–H
bond activation to form a cyclometalated complex is a key step (Scheme 5-1).
Subsequently, we found that no desired product 2a was obtained when the reaction
was
carried
out
in
the
presence
of
radical
scavenger
2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO, 4.0 equiv), suggesting that this
meta-nitration reaction may involve a radical process (Scheme 5-2). Based on our
control experiments and the recent Ru-catalyzed meta-C−H functionalization, the
possible catalytic pathway may similar to that of Ru-catalyzed chelation-assisted
meta-selective C−H nitration of arenes bearing derecting group, such as vrious
N-heterocycles or oximido.17
Scheme 5. Preliminary mechanistic studies
(1) 2-(2,6-Dimethylphenyl)-6-methylbenzo[d]thiazole (1p) as substrate:
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Me
Me
NO2
Me
Me
N
S
standard conditions
Cu(NO3)2 3H2O
N
S
No reaction
Me
Me
1p
2p
9
(2) Radical Mechanism Experiment:
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Me
Me
NO2
standard conditions
TEMPO (4.0 equiv)
N
N
S
Cu(NO3)2 3H2O
S
Me
Me
1a
2a
(trace)
Conclusion
In summary, we have successfully obtained a series of meta-nitrated
2-arylbenzothiazole and 2-arylthiazole derivatives via ruthenium-catalyzed
meta-selective C-H nitration using Cu(NO3)2·3H2O as the nitro source. The reaction
shows a wide range of functional groups tolerance giving the desired meta-nitrated
products in good to excellent yields. In addition, the nitration could be carried out on
gram-scale and used to the synthesis of promising therapeutic leads for Human
African Trypanosomiasis. The reaction may involve the Ru−C(sp2) σ-bond assisted
electrophilic aromatic substitution and a silver-mediated radical process. The
biological and therapeutic activities of the meta-nitrated products are underway in our
laboratory.
EXPERIMENTAL SECTION:
Nuclear magnetic resonance (NMR) spectra are recorded in parts per million
from internal tetramethylsilane on the δ scale. H and C{1H} NMR spectra were
recorded on a Bruker AV-400 spectrometer operating at 400 MHz and 100 MHz,
respectively. All chemical shift values are quoted in ppm and coupling constants
quoted in Hz. High resolution mass spectrometry (HRMS) spectra were obtained on a
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Synthesis of starting substrates 1 and 3.
2-Arylbenzothiazoles 123 and 2-arylthiazoles 324 were synthesized according to
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the reported procedures. 23,24 All the starting substrates 1 and 3 are known compounds,
and their NMR data were identical with those in literature.23,24 The reactions were
carried out on a1.0 mmol scale.
6-methyl-2-(o-tolyl)benzo[d]thiazole (1a), 196.0 mg (82% yield), 1H NMR (400 MHz,
CDCl3) δ 7.97 (d, J = 8.4 Hz, 1H), 7.75-7.71 (m, 2H), 7.36-7.30 (m, 4H), 2.65 (s, 3H),
2.51 (s, 3H). 1H NMR data were identical with those in literature.23a HRMS (ESI):
m/z [M + H]+ calcd for C15H14NS+: 240.0841; found: 240.0845.
2-(o-tolyl)benzo[d]thiazole (1b), 180.0 mg (80 % yield), 1H NMR (400 MHz, CDCl3)
δ 8.16 (d, J = 8.0 Hz, 1H), 7.93 (d, J = 8.0 Hz, 1H), 7.80 (s, 1H), 7.80-7.76 (m, 1H),
7.55-7.50 (m, 1H), 7.44-7.30 (m, 4H), 2.68 (s, 3H). 1H NMR data were identical with
those in literature.23b HRMS (ESI): m/z [M + H]+ calcd for C14H12NS+: 226.0685;
found: 226.0682.
6-fluoro-2-(o-tolyl)benzo[d]thiazole (1c), 196.8 mg (81% yield), 1H NMR (400 MHz,
CDCl3) δ 8.04-8.01 (m, 1H), 7.72 (d, J = 7.6 Hz, 1H), 7.59-7.56 (m, 1H), 7.39-7.28
(m, 3H), 7.25-7.20 (m, 1H), 2.65 (s, 3H). 1H NMR data were identical with those in
literature.23c HRMS (ESI): m/z [M + H]+ calcd for C14H11FNS+: 244.0591; found:
244.0587.
2-(2-chlorophenyl)benzo[d]thiazole (1d), 225.4 mg (92% yield), 1H NMR (400 MHz,
CDCl3) δ 8.21-8.19 (m, 1H), 8.13 (d, J = 8.0 Hz, 1H), 7.93 (d, J = 8.0 Hz, 1H),
1
7.53-7.50 (m, 2H), 7.43-7.39 (m, 3H). H NMR data were identical with those in
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literature.23d HRMS (ESI): m/z [M + H]+ calcd for C13H9ClNS+: 246.0139; found:
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246.0142.
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2-(2-chlorophenyl)-6-methylbenzo[d]thiazole (1e), 230.5 mg (89% yield), H NMR
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(400 MHz, CDCl3) δ 8.21-8.18 (m, 1H), 8.01 (d, J = 8.4 Hz, 1H), 7.73 (s, 1H),
7.54-7.51 (m, 1H), 7.42-7.37 (m, 2H), 7.35-7.32 (m, 1H), 2.52 (s, 3H). 1H NMR data
were identical with those in literature.23a HRMS (ESI): m/z [M + H]+ calcd for
C14H11ClNS+: 260.0295; found: 260.0295.
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2-(2-fluorophenyl)benzo[d]thiazole (1f), 199.2 mg (87% yield), H NMR (400 MHz,
CDCl3) δ 8.43-8.38 (m, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.91 (d, J = 8.0 Hz, 1H),
1
7.52-7.37 (m, 3H), 7.30-7.18 (m, 2H). H NMR data were identical with those in
literature.23d HRMS (ESI): m/z [M + H]+ calcd for C13H9FNS+: 230.0434; found:
230.0436.
1
6-methyl-2-(m-tolyl)benzo[d]thiazole (1g), 217.5 mg (91% yield), H NMR (400
MHz, CDCl3) δ 7.95-7.91 (m, 1H), 7.83 (d, J = 8.0 Hz, 1H), 7.66 (s, 1H), 7.35 (t, J =
1
7.6 Hz, 1H), 7.28-7.27 (m, 1H), 2.47 (s, 3H), 2.43 (s, 3H). H NMR data were
identical with those in literature.23b HRMS (ESI): m/z [M + H]+ calcd for C15H14NS+:
240.0841; found: 240.0838.
2-(m-tolyl)benzo[d]thiazole (1h), 191.3 mg (85% yield), 1H NMR (400 MHz, CDCl3)
δ 8.08 (d, J = 8.0 Hz, 1H), 7.93 (s, 1H), 7.87-7.84 (m, 2H), 7.47 (t, J = 7.6 Hz, 1H),
1
7.35 (t, J = 7.6 Hz, 2H), 7.27 (d, J = 6.8 Hz, 1H), 2.42 (s, 3H). H NMR data were
identical with those in literature.23b HRMS (ESI): m/z [M + H]+ calcd for C14H12NS+:
226.0685; found: 226.0682.
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6-fluoro-2-(m-tolyl)benzo[d]thiazole (1i), 213.8 mg (88% yield), 1H NMR (400 MHz,
CDCl3) δ 8.00 (dd, J = 9.2, 4.8 Hz, 1H), 7.89 (s, 1H), 7.82 (d, J = 7.6 Hz, 1H),
7.58-7.56 (m, 1H), 7.37 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 7.6 Hz, 1H), 7.24-7.18 (m,
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1H), 2.45 (s, 3H). H NMR data were identical with those in literature.23b HRMS
(ESI): m/z [M + H]+ calcd for C14H11FNS+: 244.0591; found: 244.0593.
2-(3-chlorophenyl)benzo[d]thiazole (1j), 222.9 mg (91% yield), 1H NMR (400 MHz,
CDCl3) δ 8.09-8.05 (m, 2H), 7.92-7.86 (m, 2H), 7.51-7.47 (m, 1H), 7.44-7.36 (m,
3H).23d HRMS (ESI): m/z [M + H]+ calcd for C13H9ClNS+: 246.0139; found:
246.0142.
6-chloro-2-(p-tolyl)benzo[d]thiazole (1k), 220.1 mg (85% yield). 1H NMR (400 MHz,
CDCl3) δ 7.93 (d, J = 8.4 Hz, 1H), 7.82 (d, J = 2.0 Hz, 1H), 7.43-7.40 (m, 1H), 7.27
1
(d, J = 8.0 Hz, 2H), 2.41 (s, 3H). H NMR data were identical with those in
literature.23d HRMS (ESI): m/z [M + H]+ calcd for C14H11ClNS+: 260.0295; found:
260.0296.
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2-(p-tolyl)benzo[d]thiazole (1l), 180.0 mg (80% yield), H NMR (400 MHz, CDCl3)
δ 8.06 (d, J = 8.0 Hz, 1H), 7.99 (d, J = 8.0 Hz, 1H), 7.90 (d, J = 8.0 Hz, 1H), 7.49 (t, J
= 7.6 Hz, 1H), 7.37 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 7.6 Hz, 1H), 2.43 (s, 4H). 1H
NMR data were identical with those in literature.23d HRMS (ESI): m/z [M + H]+ calcd
for C14H12NS+: 226.0685; found: 226.0682.
2-phenylbenzo[d]thiazole (1m), 183.5 mg (87% yield), 1H NMR (400 MHz, CDCl3) δ
8.09-8.06 (m, 3H), 7.87 (d, J = 8.0 Hz, 1H), 7.49-7.46 (m, 4H), 7.35 (t, J = 7.6 Hz,
1H). 1H NMR data were identical with those in literature.23b HRMS (ESI): m/z [M +
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H]+ calcd for C14H12NS+: 212.0528; found: 212.0526
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6-methyl-2-phenylbenzo[d]thiazole (1n), 200.2 mg (89% yield), 1H NMR (400 MHz,
CDCl3) δ 8.06 (d, J = 3.6 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H), 7.68 (s, 1H), 7.47 (s, 2H),
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7.29 (d, J = 8.0 Hz, 1H), 2.49 (s, 3H). H NMR data were identical with those in
literature.23b HRMS (ESI): m/z [M + H]+ calcd for C14H12NS+: 226.0685; found:
226.0684.
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6-chloro-2-phenylbenzo[d]thiazole (1o), 210.7 mg (86% yield), H NMR (400 MHz,
CDCl3) δ 7.96-9.94 (m, 3H), 7.71 (d, J = 8.0 Hz, 1H), 7.35-7.31 (m, 4H), 7.21 (t, J =
7.6 Hz, 1H). 1H NMR data were identical with those in literature.23b HRMS (ESI):
m/z [M + H]+ calcd for C13H9ClNS+: 246.0139; found: 246.0142.
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2-phenylthiazole (3a), 122.3 mg (76% yield), H NMR (400 MHz, CDCl3) δ
8.06-8.04 (m, 2H), 7.96 (d, J = 8.4 Hz, 1H), 7.85 (s, 1H), 7.50-7.42 (m, 3H). 1H NMR
data were identical with those in literature.24a HRMS (ESI): m/z [M + H]+ calcd for
C9H8NS+: 162.0372; found: 162.0370.
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2-(m-tolyl)thiazole (3b), 141.7 mg (81% yield), H NMR (400 MHz, CDCl3) δ 7.84
(d, J = 3.2 Hz, 1H), 7.80 (s, 1H), 7.74 (d, J = 8.0 Hz, 1H), 7.33-7.27 (m, 2H), 7.21 (d,
J = 7.6 Hz, 1H), 2.40 (s, 3H). 1H NMR data were identical with those in literature. 24b
HRMS (ESI): m/z [M + H]+ calcd for C10H10NS+: 176.0528; found: 176.0530.
2-(3-fluorophenyl)thiazole (3c), 153.9 mg (86% yield), 1H NMR (400 MHz, CDCl3) δ
7.88 (d, J = 7.2 Hz, 2H), 7.78 (s, 1H), 7.35 (d, J = 6.8 Hz, 3H), 7.23 (s, 1H). 1H NMR
data were identical with those in literature. 24b HRMS (ESI): m/z [M + H]+ calcd for
C9H7FNS+: 180.0278; found: 180.0276.
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2-(naphthalen-2-yl)thiazole (3d), 166.7 mg (79% yield), 1H NMR (400 MHz, CDCl3)
δ 8.42 (s, 1H), 8.07-8.04 (m, 1H), 7.89-7.78 (m, 4H), 7.50-7.46 (m, 2H), 7.30 (d, J =
3.6 Hz, 1H). 1H NMR data were identical with those in literature. 24b HRMS (ESI):
m/z [M + H]+ calcd for C13H10NS+: 212.0528; found: 212.0530.
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2-(o-tolyl)thiazole (3e), 143.5 mg (82% yield), 1H NMR (400 MHz, CDCl3) δ 7.83 (d,
J = 3.6 Hz, 1H), 7.63 (d, J = 7.6 Hz, 1H), 7.29 (d, J = 3.6 Hz, 1H), 7.24-7.17 (m, 3H),
2.50 (s, 3H). 1H NMR data were identical with those in literature. 24b HRMS (ESI):
m/z [M + H]+ calcd for C10H10NS+: 176.0528; found: 176.0531.
General procedure for Ru-catalyzed meta-selective C–H nitration of
2-arylbenzothiazoles 1 and 2-arylthiazoles 3:
1 or 3 (0.2 mmol), Cu(NO3)2·3H2O (96.6 mg, 0.4 mmol), Ru3(CO)12 (12.8 mg, 5
mol%), K2S2O8 (81.1 mg, 1.5 equiv), CF3COOAg (66.6 mg, 1.5 equiv), DCE (2 mL)
under air was stirred at 80 oC for 20 h in a sealed pipe using heating mantle. After the
completion of the reaction (monitored by TLC), the solvent was concentrated in
vacuum, and the residue was purified by flash column chromatography on silica gel
with petroleum ether/EtOAc (20:1–10:1) as the eluent to give the desired products 2
or 4.
6-methyl-2-(2-methyl-3-nitrophenyl)benzo[d]thiazole (2a), white solid, 50.0 mg
1
(88%), Rf = 0.5 (petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ
7.90 (d, J = 8.4 Hz, 1H), 7.79-7.74 (m, 2H), 7.64 (s, 1H), 7.33 (t, J = 8.0 Hz, 1H),
7.26 (d, J = 8.4 Hz, 1H), 2.56 (s, 3H), 2.43 (s, 3H).; 13C{1H} NMR (100 MHz, CDCl3)
δ 164.2, 151.7, 145.0, 136.3, 136.1, 136.0, 134.3, 131.7, 128.2, 126.6, 125.2, 123.3,
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121.2, 21.6, 16.7; HRMS (ESI): m/z [M + H]+ calcd for C15H13N2O2S+: 285.0692;
found: 285.0690.
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2-(2-methyl-3-nitrophenyl)benzo[d]thiazole (2b), white solid, 47.6 mg (88%), Rf = 0.6
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(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.13 (d, J = 8.0 Hz,
1H), 7.96 (d, J = 7.6 Hz, 1H), 7.90-7.86 (m, 2H), 7.56 (dt, J = 1.2, 7.2 Hz, 1H),
13
7.50-7.44 (m, 2H), 2.67 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 165.3, 153.5,
151.9, 137.5, 136.2, 135.8, 134.3, 131.7, 126.6, 125.8, 125.3, 123.8, 121.5, 16.7;
HRMS (ESI): m/z [M + H]+ calcd for C14H11N2O2S+: 271.0536; found: 271.0530.
6-fluoro-2-(2-methyl-3-nitrophenyl)benzo[d]thiazole (2c), white solid, 49.1 mg (85%),
Rf = 0.5 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.07 (dd, J =
9.2, 4.8 Hz, 1H), 7.90-7.84 (m, 2H), 7.63 (dd, J = 8.0, 2.8 Hz, 1H), 7.46 (t, J = 8.0 Hz,
1H), 7.32-7.26 (m, 1H), 2.66 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 165.0,
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161.3 (d, JCF = 245.7 Hz), 151.9, 150.2, 141.2, 136.8 (d, JCF = 11.2 Hz), 134.2,
126.7, 125.4, 124.8 (d, 3JCF = 9.4 Hz), 120.0, 115.4 (d, 2JCF = 24.7 Hz), 107.7 (d, 2JCF
= 26.7 Hz), 16.6; HRMS (ESI): m/z [M + H]+ calcd for C14H10FN2O2S+: 289.0442;
found: 289.0466.
2-(2-chloro-3-nitrophenyl)benzo[d]thiazole (2d), pale yellow solid, 33.7 mg (58%),
Rf =0.5 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.40 (dd, J =
8.0, 1.6 Hz, 1H), 8.16 (d, J = 8.4 Hz, 1H), 7.99 (d, J = 7.6 Hz, 1H), 7.85 (dd, J = 8.0,
1.6 Hz, 1H), 7.61-7.53 (m, 2H), 7.49 (dt, J = 1.2, 8.0 Hz, 1H); C{1H} NMR (100
13
MHz, CDCl3) δ 161.9, 152.4, 150.2, 136.2, 135.1, 134.7, 127.5, 126.7, 126.2, 126.0,
125.0, 123.9, 121.5; HRMS (ESI): m/z [M + H]+ calcd for C13H8ClN2O2S+: 290.9990;
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2-(2-chloro-3-nitrophenyl)-6-methylbenzo[d]thiazole (2e), white solid, 31.1 mg
(51%), Rf = 0.4 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.39
(dd, J = 8.0, 1.6 Hz, 1H), 8.02 (d, J = 8.4 Hz, 1H), 7.83 (dd, J = 8.0, 1.6 Hz, 1H), 7.76
(s, 1H), 7.54 (t, J = 8.0 Hz, 1H), 7.38 (d, J = 8.4 Hz, 1H), 2.54 (s, 3H); 13C{1H} NMR
(100 MHz, CDCl3) δ 160.8, 150.5, 150.2, 136.5, 136.4, 135.2, 134.6, 128.4, 127.4,
125.8, 124.8, 123.3, 121.1, 21.6; HRMS (ESI): m/z [M + H]+ calcd for
C14H10ClN2O2S+: 305.0146; found: 305.0152.
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2-(2-fluoro-3-nitrophenyl)benzo[d]thiazole (2f), yellow solid, 29.6 mg (54%), Rf = 0.4
(petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 9.38 (dd, J = 6.0, 2.8
Hz, 1H), 8.37-8.33 (m, 1H), 8.18 (d, J = 8.4 Hz, 1H), 7.98 (d, J = 8.0 Hz, 1H),
13
7.60–7.56 (m, 1H), 7.50–7.46 (m, 1H), 7.41 (t, J = 9.6 Hz, 1H); C{1H} NMR (100
1
MHz, CDCl3) δ 163.3 (d, JCF = 261.7 Hz), 158.1, 152.4, 144.8, 135.9, 135.8, 126.8
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3
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(d, JCF = 8.9 Hz), 126.1, 125. 9 (d, JCF = 4.8 Hz), 123.9, 122.9 (d, JCF = 13.4 Hz),
2
121.6, 117.7 (d, JCF = 24.6 Hz); HRMS (ESI): m/z [M + H]+ calcd for
C13H8FN2O2S+: 275.0285; found: 275.0281.
6-methyl-2-(3-methyl-5-nitrophenyl)benzo[d]thiazole (2g), white solid, 52.3 mg
(92%), Rf = 0.5 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.67
(s, 1H), 8.23 (s, 1H), 8.13 (s, 1H), 7.98 (d, J = 8.4 Hz, 1H), 7.73 (s, 1H), 7.35 (d, J =
13
8.4 Hz, 1H), 2.57 (s, 3H), 2.52 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 164.2,
152.1, 148.7, 140.8, 136.3, 135.3, 135.1, 133.4, 128.4, 125.5, 123.1, 121.5, 119.6,
21.6, 21.3; HRMS (ESI): m/z [M + H]+ calcd for C15H13N2O2S+: 285.0692; found:
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2-(3-methyl-5-nitrophenyl)benzo[d]thiazole (2h), white solid, 52.8 mg (83%), Rf = 0.6
(petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.66 (s, 1H), 8.21 (s,
1H), 8.12-8.07(m, 2H), 7.92 (d, J = 8.0 Hz, 1H), 7.54-7.50 (m, 1H), 7.42 (t, J = 7.6
Hz, 1H), 2.55 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 165.2, 153.9, 148.8, 140.8,
135.1, 135.0, 133.5, 126.8, 125.9, 125.7, 123.6, 121.8, 119.7, 21.3; HRMS (ESI): m/z
[M + H]+ calcd for C14H11N2O2S+: 271.0536; found: 271.0537.
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6-fluoro-2-(3-methyl-5-nitrophenyl)benzo[d]thiazole (2i), white solid, 46.0 mg (85%),
Rf = 0.6 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.65 (s, 1H),
8.19 (s, 1H), 8.14 (s, 1H), 8.04 (dd, J = 8.8, 4.8 Hz, 1H), 7.61 (dd, J = 8.0, 2.4 Hz,
1H), 7.27 (dd, J = 8.8, 2.4 Hz, 1H), 2.57 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
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3
164.9, 160.9 (d, JCF = 245.9 Hz), 150.6, 148.8, 141.0, 136.2 (d, JCF = 11.2 Hz),
3
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134.7, 133.4, 125.8, 124.7 (d, JCF = 9.4 Hz), 119.6, 115.6 (d, JCF = 24.6 Hz), 108.0
2
(d, JCF = 26.8 Hz), 21.3; HRMS (ESI): m/z [M + H]+ calcd for C14H10FN2O2S+:
289.0442; found: 289.0443.
2-(3-chloro-5-nitrophenyl)benzo[d]thiazole (2j), pale yellow solid, 47.1 mg (81%), Rf
1
= 0.6 (petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.88 (s, 1H),
8.35 (m, 2H), 8.00 (d, J = 8.4 Hz, 1H), 7.90 (s, 1H), 7.68 (t, J = 7.6 Hz, 1H), 7.49 (d,
13
J = 8.4 Hz, 1H); C{1H} NMR (100 MHz, CDCl3) δ 165.3, 152.5, 148.8, 136.3,
134.9, 132.9, 132.1, 130.2, 127.7, 125.4, 124.5, 122.3, 121.4; HRMS (ESI): m/z [M +
H]+ calcd for C13H8ClN2O2S+: 290.9990; found: 290.9988.
6-chloro-2-(4-methyl-3-nitrophenyl)benzo[d]thiazole (2k),25 pale yellow solid, 43.9
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mg (72%), Rf = 0.5 (petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ
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8.64 (s, 1H), 8.17 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 8.8 Hz, 1H), 7.89 (s, 1H), 7.48 (d, J
= 7.2 Hz, 2H), 2.68 (s, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 165.4, 152.5, 149.7,
136.3, 136.2, 133.6, 132.5, 131.8, 131.1, 127.6, 124.3, 123.4, 121.4, 20.5.
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2-(4-methyl-3-nitrophenyl)benzo[d]thiazole (2l),26 white solid, 42.1 mg (78%), Rf =
0.6 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.65 (s, 1H), 8.19
(d, J = 8.0 Hz, 1H), 8.08 (d, J = 8.0 Hz, 1H), 7.91 (d, J = 7.6 Hz, 1H), 7.52 (t, J = 7.6
13
Hz, 1H), 7.47-7.40 (m, 2H), 2.66 (s, 3H); C{1H} NMR (100MHz, CDCl3) δ 165.0,
154.0, 149.7, 136.0, 135.1, 133.5, 132.9, 131.2, 126.7, 125.8, 123.6, 123.4, 121.8,
20.4.
2-(3-nitrophenyl)benzo[d]thiazole (2m),27 white solid, 36.4 mg (71%), Rf = 0.5
1
(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.93 (t, J = 1.2 Hz,
1H), 8.42 (d, J = 8.0 Hz, 1H), 8.3 (dd, J = 8.0, 1.2 Hz, 1H), 8.12 (d, J = 8.0 Hz, 1H),
7.95 (d, J = 8.0 Hz, 1H), 7.69 (t, J = 8.0 Hz, 1H), 7.57-7.53 (m, 1H), 7.47-7.43 (m,
13
1H); C{1H} NMR (100 MHz, CDCl3) δ 164.9, 154.0, 148.8, 135.3, 135.2, 133.0,
130.1, 126.8, 126.0, 125.2, 123.8, 122.4, 121.8.
6-methyl-2-(3-nitrophenyl)benzo[d]thiazole (2n),28 yellow solid, 47.2 mg (87%), Rf =
0.6 (petroleum ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.87 (s, 1H), 8.37
(d, J = 7.6 Hz, 1H), 8.29 (dd, J = 8.4, 1.0 Hz, 1H), 7.97 (d, J = 8.0 Hz, 1H), 7.71 (s,
13
1H), 7.65 (t, J = 8.0 Hz, 1H), 7.33 (d, J = 8.4 Hz, 1H), 2.51 (s, 3H); C{1H} NMR
(100 MHz, CDCl3) δ 163.8, 152.1, 148.8, 136.4, 135.4, 135.4, 132.8, 130.0, 128.5,
124.9, 123.2, 122.2, 121.5, 21.6.
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2-(3-chloro-5-nitrophenyl)benzo[d]thiazole (2o), white solid, 47.1 mg (81%), Rf = 0.7
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7
1
(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.76 (t, J = 2.0 Hz,
8
9
1H), 8.41 (t, J = 2.0 Hz, 1H), 8.29 (t, J = 2.0 Hz, 1H), 8.11 (d, J = 8.0 Hz, 1H), 7.95
(d, J = 8.0 Hz, 1H), 7.58-7.54 (m, 1H), 7.49-7.45 (m, 1H); 13C{1H} NMR (100 MHz,
CDCl3) δ 163.4, 153.8, 149.2, 136.5, 136.3, 135.2, 132.7, 127.1, 126.4, 125.2, 124.0,
121.9, 120.4; HRMS (ESI): m/z [M + H]+ calcd for C13H8ClN2O2S+: 290.9990; found:
290.9990.
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2-(3-nitrophenyl)thiazole (4a),29 white solid, 29.6 mg (71%), Rf = 0.6 (petroleum
ether/EtOAc = 10:1). 1H NMR (400 MHz, CDCl3) δ 8.80 (s, 1H), 8.30-8.25 (m, 2H),
13
7.94 (d, J = 3.2 Hz, 1H), 7.64 (t, J = 8.0 Hz, 1H), 7.45 (d, J = 3.2 Hz, 1H); C{1H}
NMR (100 MHz, CDCl3) δ 165.4, 148.8, 144.3, 135.2, 132.1, 130.0, 124.3, 121.4,
120.2.
2-(3-methyl-5-nitrophenyl)thiazole (4b), white solid, 42.3 mg (95%), Rf = 0.6
1
(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.54 (d, J = 1.6 Hz,
1H), 8.08 (dd, J = 8.0, 1.6 Hz, 1H), 7.90 (d, J = 3.2 Hz, 1H), 7.43-7.40 (m, 2H), 2.64
(s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 165.5, 149.6, 144.1, 134.9, 133.5, 132.8,
130.3, 122.5, 119.8, 20.3; HRMS (ESI): m/z [M + H]+ calcd for C10H9N2O2S+:
221.0379; found: 221.0373.
2-(3-fluoro-5-nitrophenyl)thiazole (4c), white solid, 32.1 mg (71%), Rf = 0.5
(petroleum ether/EtOAc = 10:1). 1H NMR 1H NMR (400 MHz, CDCl3) δ 8.60 (s, 1H),
8.07-8.04 (m, 1H), 7.98-7.95 (m, 2H), 7.49 (d, J = 3.2 Hz, 1H); 13C{1H} NMR (100
1
2
MHz, CDCl3) δ 163.9, 162.7 (d, JCF = 272.1 Hz), 149.6, 144.5, 136.8 (d, JCF = 8.4
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Hz), 120.9, 119.2 (d, JCF = 23.7 Hz), 117.3 (d, JCF = 3.3 Hz), 112.0 (d, JCF = 26.6
Hz); HRMS (ESI): m/z [M + H]+ calcd for C9H6FN2O2S+: 225.0129; found:
225.0127;
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2-(4-nitronaphthalen-2-yl)thiazole (4d), white solid, 34.1 mg (66%), Rf = 0.6
1
(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 8.83 (d, J = 1.6 Hz,
1H), 8.66 (s, 1H), 8.54 (d, J = 8.8 Hz, 1H), 8.03 (d, J = 8.4 Hz, 1H), 7.96 (d, J = 3.2
Hz, 1H), 7.75 (dt, J = 1.2, 6.8 Hz, 1H), 7.66 (t, J = 7.2 Hz, 1H), 7.46 (d, J = 3.2 Hz,
13
1H); C{1H} NMR (100 MHz, CDCl3) δ 165.6, 147.3, 144.3, 134.5, 131.3, 130.2,
130.0, 129.2, 128.2, 125.4, 123.4, 122.0, 120.1; HRMS (ESI): m/z [M + H]+ calcd for
C13H9N2O2S+: 257.0379; found: 257.0371.
2-(2-methyl-3-nitrophenyl)thiazole (4e), yellow solid, 32.6 mg (74%), Rf = 0.6
1
(petroleum ether/EtOAc = 10:1). H NMR (400 MHz, CDCl3) δ 7.97 (d, J = 3.2 Hz,
1H), 7.84 (d, J = 8.0 Hz, 1H), 7.81 (d, J = 8.0 Hz, 1H), 7.50 (d, J = 3.2 Hz, 1H), 7.41
13
(t, J = 8.0 Hz, 1H), 2.60 (s, 3H); C{1H} NMR (100 MHz, CDCl3) δ 165.4, 151.9,
143.5, 136.0, 134.1, 131.3, 126.5, 124.8, 120.7, 16.6; HRMS (ESI): m/z [M + H]+
calcd for C10H9N2O2S+: 221.0379; found: 221.0378.
Gram-scale experiment for the synthesis of nitrated product 2l.
Substrate 1l (1.125 g, 5.0 mmol), Cu(NO3)2·3H2O (2.415 g, 10 mmol), Ru3(CO)12
(120 mg, 5 mol%), K2S2O8 (2.027 g, 37.5 mmol), CF3COOAg (1.665 g, 37.5 mmol),
DCE (50 mL) under air was stirred at 80 oC for 20 h in a sealed flask using heating
mantle. After the completion of the reaction (monitored by TLC), the mixture was
filtrated, and the solvent was concentrated in vacuum. Then the residue was purified
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by flash column chromatography on silica gel with petroleum ether/EtOAc (20:1–10:1)
as the eluent to give the desired product 2l in 75% yield (1.014 g).
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5-(benzo[d]thiazol-2-yl)-2-methylaniline 5.21 1H NMR (400 MHz, DMSO-d6) δ 8.12
(d, J = 7.6 Hz, 1H), 8.03 (d, J = 8.0 Hz, 1H), 7.56-7.52 (m, 1H), 7.47-7.43 (m, 2H),
7.22 (dd, J = 7.6, 1.2 Hz, 1H), 7.12 (d, J = 7.7 Hz, 1H), 5.28 (s, 2H), 2.17 (s, 3H);
13C{1H} NMR (100 MHz, DMSO) δ 168.8, 154.1, 147.8, 134.7, 131.7, 131.2, 126.9,
125.6, 125.5, 123.0, 122.6, 115.5, 112.4, 18.0.
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Notes
The authors declare no competing financial interest.
Acknowledgement
Financial Supported from National Natural Science Foundation of China (21662017),
Natural Science Foundation of Jiangxi Province of China (20171BAB205015), and
Graduate Innovation Fund in Jiangxi Normal University (YJS2017021) is gratefully
acknowledged.
Supporting Information
1
1
13
Copies of H NMR spectra for compounds 1 and 3, and H, C NMR spectra for
compounds 2, 4, and 5, X-ray for compound 2k (CCDC 1818469). This material is
available free of charge via the Internet at http://pubs.acs.org.
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