Synthesis of N-Aryl Oxindole Nitrones through a Metal-Free Selective N-Arylation Process

Article abstract of DOI:10.1021/acs.joc.6b02774

An efficient selective N-arylation of 3-(hydroxyimino)indolin-2-ones with diaryliodonium salts to prepare (Z)-N-aryl oxindole nitrones has been achieved under simple base-mediated conditions. The reaction tolerated a variety of diaryliodonium salts with diverse and sensitive functional groups. Studies on the oxime structures revealed that the pyrroline ring and carbonyl group in 3-(hydroxyimino)indolin-2-ones played important roles in the selective N-arylation process. The N-aryl oxindole nitrones could be prepared rapidly and easily at the gram scale.

Full text of DOI:10.1021/acs.joc.6b02774

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Note
Synthesis of N-Aryl Oxindole Nitrones through
Metal-Free Selective N-Arylation Process
Si-Yi Wu, Xiao-Pan Ma, Cui Liang, and Dong-Liang Mo
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02774 • Publication Date (Web): 22 Feb 2017
Downloaded from http://pubs.acs.org on February 23, 2017
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Synthesis of N-Aryl Oxindole Nitrones through Metal-Free
Selective N-Arylation Process
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SiꢀYi Wu†, XiaoꢀPan Ma†, Cui Liang, and DongꢀLiang Mo*
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State Key Laboratory for Chemistry and Molecular Engineering of Medicinal
Resources, Ministry of Science and Technology of China; School of Chemistry &
Pharmaceutical Sciences, Guangxi Normal University, 15 Yu Cai Road, Guilin
541004, China
Ar1
OH
N
O
N
KOH
O
+
Ar1
I
OTf
R
O
R
N
MeOH, r.t
25 examples
60-99% yields
Ar2
N
H
H
§ Selective N-arylation
§ Broad substrate scope
§ High selective (Z)-nitrones
§ Gram-scale preparation
ABSTRACT: An efficient selective Nꢀarylation of 3ꢀ(hydroxyimino)indolinꢀ2ꢀones
with diaryliodonium salts to prepare (Z)ꢀNꢀaryl oxindole nitrones has been achieved
under simple baseꢀmediated conditions. The reaction tolerated a variety of
diaryliodonium salts with diverse and sensitive functional groups. Studies on the
oxime structures revealed that the pyrroline ring and carbonyl group in
3ꢀ(hydroxyimino)indolinꢀ2ꢀones played important roles in the selective Nꢀarylation
process. The Nꢀaryl oxindole nitrones could be prepared rapidly and easily at the
gramꢀscale.
NꢀAryl nitrones are one of the most important and useful types of 1,3ꢀdipoles used
in cycloaddition chemistry since the discovery of this reaction in the last century.1
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Their valuable applications are illustrated in the development of methodologies
towards heterocycle and total syntheses.2 Traditional strategies to prepare Nꢀaryl
nitrones involve oxidation of aryl imines and aryl amines,3 or condensation of ketones
with Nꢀarylhydroxylamines.4 Recently, copperꢀpromoted Nꢀarylation of oximes with
arylboronic acids was developed as an efficient strategy to prepare Nꢀaryl nitrones.5
However, the aforementioned strategies suffered from several drawbacks such as
harsh conditions, limited substrate scope, poor functional group tolerance, the need of
excess amount of copper salts, and lack of gramꢀscale preparation. An alternative
strategy is direct Nꢀarylation of oximes with diaryliodonium salts under metalꢀfree
conditions. Diaryliodonium salts serve as efficient arylation reagents because of their
easy preparation, high reactivity and nonꢀtoxicity.6 These iodonium salts have been
extensively used for Oꢀ or Nꢀarylation.7, 8
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Recently, we presented a metalꢀfree Nꢀarylation of α, βꢀunsaturated ketoximes with
diaryliodonium salts to synthesize α, βꢀunsaturated Nꢀaryl ketonitrones (Scheme
1ꢀA).9 The DFT calculations demonstrated that Nꢀaryl nitrones were formed by an
initial Oꢀattack on the diaryliodonium salts and followed by a [1,3]ꢀaryl migration via
a fourꢀcentered transition state. Although this Nꢀarylation with diaryliodonium salts
has been achieved successfully, the substrates bear one NꢀO bond as the nucleophilic
group. A selective Nꢀarylation of a substrate bearing multiple nucleophilic sites
without protection or deprotection is still challenging.10 Exploring a more efficient
selective Nꢀarylation process would be desirable and valuable for rapid entry to target
complex molecules with minimum synthetic operations. We hypothesized that direct
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selective Nꢀarylation of 3ꢀ(hydroxyimino)indolinꢀ2ꢀones possessing three nucleophilic
sites without protection would afford Nꢀaryl oxindole nitrones. Nꢀaryl oxindole
nitrones were valuable synthetic intermediates to access spirooxindole derivatives
through [3+2] or [3+3] cycloadditions.11 Synthesis of Nꢀaryl oxindole nitrones has
been developed by Shi’s group11a via trifluoroacetic acidꢀcatalyzed condensation of
isatin with Nꢀarylhydroxylamines. Huang and coworkers also achieved this
transformation through silica gelꢀpromoted reaction of diazooxindoles and
nitrosoarenes.12 However, both these strategies gave Eꢀisomer nitrones (Scheme 1ꢀB).
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Herein, we reported
a
practical and generally selective Nꢀarylation of
3ꢀ(hydroxyimino)indolinꢀ2ꢀones to prepare (Z)ꢀNꢀaryl oxindole nitrones under
metalꢀfree conditions (Scheme 1ꢀC).
A) Our previous work, N-arylation of α, β-unsaturated ketoximes
Ar1
O
OH
KOH
N
Ar1
I
OTf
N
+
CCl4, rt
R1
R2
Ar2
R1
R2
E / Z = 1:1 to 10:1
B) Shi and Huang's procedures for synthesis of (E)-N-aryl nitrone
O
R1
+ ArNHOH
O
N
CF3COOH
silica gel
O
Ar
O
N
R2
R1
N
N2
R2
E-isomer
O
R1
OH
N
+
Ar
N
R2
C) This work, selective N-arylation of oximes to prepare (Z)-N-aryl nitrone
3
OH
Ar1
2
O
N
N
KOH
+
Ar1
I
OTf
O
R
O
R
MeOH, rt
Ar2
N
N
1
H
H
Z-isomer
Scheme 1. Strategies to Construct NꢀArylnitrones
Initially, 3ꢀ(hydroxyimino)indolinꢀ2ꢀone (1a) and diphenyliodonium triflate (2a)
were treated with KOH in CCl4 under an ambient atmosphere for 2 h. Only the
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desired N2ꢀphenylation product 3aa was obtained in high yield, which was assigned
the (Z)ꢀconfiguration for the C=N bond. The NOESY spectrum of 3aa showed an
obvious correlation between Ha and a proton in the phenyl group on the Nꢀatom,
which indicated the Zꢀisomer (See Table 1).13 No Oꢀ or N1ꢀphenylation products were
observed (Table 1, entry 1). The high selectivity of the Nꢀphenylation inspired us to
further study the generality of this reaction to synthesize Nꢀaryl nitrones. Solvent
screening revealed that most of solvents gave product (Z)ꢀ3aa in high yields except
for DMF (Table 1, entries 2ꢀ9). In fact, the (E)ꢀisomer of nitrone 3aa was also
observed as a minor isomer in DCE, toluene, THF, DMF and DMSO solvents but the
yield of (E)ꢀ3aa was in less than 8%. The Zꢀ and Eꢀisomers of 3aa can be separated
easily by flash chromatography. The best result was afforded in MeOH giving (Z)ꢀ3aa
in 98% yield (Table 1, entry 9). The yield of (Z)ꢀ3aa slightly decreased when
inceassing the temperature to 40 °C (Table 1, entry 10). The influence of different
bases was also examined (Table 1, entries 11ꢀ14). It was shown that high yields were
obtained using inorganic bases while a lower yield was achieved with pyridine. No
desired product 3aa was observed when no base was added, and only the oxime 1a
and triflate 2a were recovered (Table 1, entry 15). Product Zꢀ3aa could also be
obtained in 96% yield when the amount of diaryliodonium triflate 2a was decreased
to 1.0 equivalent (Table 1, entry 16).
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Table 1. Optimization of Reaction Conditions a
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NOE
4
5
6
7
2
N
Ph
OH
O
Ha
O
N
conditions
Ph2IOTf
+
O
N
1
N
H
8
H
9
2a
1a
(Z)-3aa
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entry
solvent
CCl4
base
T (°C) 3aa %b
1
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
tꢀBuOK
NaOH
Cs2CO3
pyridine
ꢀ
25
25
25
25
25
25
25
25
25
40
25
25
25
25
25
25
91
80
92
77
93
51
73
95
98
96
80
96
98
7
2
DCE
3
MeCN
THF
4
5
dioxane
DMF
6
7
DMSO
toluene
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
8
9
10
11
12
13
14
15
16
0
KOH
96c
a
Reaction conditions: 1a (0.5 mmol), 2a (0.75 mmol, 1.5 equiv), base (0.75 mmol,
1.5 equiv), solvent (5 mL), 25 °C, 0.5−18 h; b Isolated yield; 2a (0.5 mmol, 1.0
c
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equiv).
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The scope of the selective Nꢀarylation was studied firstly by reacting 1a with
various diaryliodonium salts (2a-n). The diaryliodonium salts were easily synthesized
by Olofsson’s methods.14 Most of symmetrical diaryliodonium salts with either
electronꢀrich or electronꢀdeficient substituents in para, meta, or orthoꢀpositions could
be successfully converted to Nꢀaryl nitrones 3 in high yields (Table 2). When
unsymmetrical diaryliodonium salts were examined, the selective Nꢀarylation took
place with high chemoselectivity. As expected, the more electronꢀdeficient aryl
moieties were favorably transferred to the nitrones (Table 2, entries 10ꢀ14).
Functional groups such as bromo, chloro, and ester groups were compatible with this
selective Nꢀarylation process.
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Table 2. The Scope of Diaryliodonium Salts 2.a
R1
OH
O
N
R1
O
N
I
OTf
R2
KOH
+
O
MeOH, rt
N
N
H
H
1a
2
3
entry
2
R1
R2
3
yield %b
98
1
2
3
4
5
6
2a
2b
2c
2d
2e
2f
H
H
3aa
3ab
3ac
3ad
3ae
3af
4ꢀMeO
4ꢀMe
4ꢀtꢀBu
4ꢀCl
4ꢀF
4ꢀMeO
4ꢀMe
4ꢀtꢀBu
4ꢀCl
4ꢀF
60
92
94
90
97
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2g
2h
2i
4ꢀCF3
3,5ꢀMe2
2ꢀMe
H
4ꢀCF3
3ag
97
93
99
79
85
97
83
99
8
3,5ꢀMe2 3ah
9
2ꢀMe
3ai
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10
11
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13
14
2j
4ꢀMeO
4ꢀMeO
4ꢀMeO
4ꢀMeO
3aa
3ak
3al
2k
2l
4ꢀBr
3ꢀBr
2m 2ꢀBr
2n
4ꢀCO2Me Ph
3am
3an
a Reaction conditions: 1a (0.5 mmol), 2 (0.75 mmol, 1.5 equiv), KOH (0.75 mmol, 1.5
equiv), MeOH (5 mL), 25 °C, 0.5−18 h; b Isolated yield.
In addition to diaryliodonium salts, a variety of 3ꢀ(hydroxyimino)indolinꢀ2ꢀones
(1a-l) were subjected to the optimal conditions to test the efficiency of the Nꢀarylation
process. The reaction of 3ꢀ(Hydroxyimino)indolinꢀ2ꢀones 1 with electronꢀdonating or
electronꢀwithdrawing groups in the 4, 5, 6, or 7ꢀpositions and diaryliodonium salts
proceeded smoothly to give the desired nitrones 3 in excellent yields.
Electronꢀdonating groups gave better yields of nitrones than electronꢀwithdrawing
groups (Table 3, entries 2ꢀ4 vs 5). Interestingly, even oxime 1j with a 4ꢀBr group,
afforded the desired product 3ja in 95% yield (Table 3, entry 10). This might suggest
that steric hindrance of the oxime had little effect on the formation of nitrones. When
the N1ꢀatom in oxime was protected with methyl or phenyl groups, the nitrone 3ka
and 3la were obtained in 96% and 83% yields, respectively (Table 3, entries 11ꢀ12).
Table 3. The Scope of Oximes 1a
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3
2
Ph
OH
N
O
N
4
7
5
6
KOH
O
+
R
Ph2IOTf
O
R
1
MeOH, rt
N
N
R1
R1
1
2a
3
9
entry
1
1
R
R1
3
yield %b
98
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1a
1b
1c
1d
1e
1f
H
H
H
H
H
H
H
H
H
H
H
3aa
3ba
3ca
3da
3ea
3fa
3ga
3ha
3ia
3ja
2
5ꢀOMe
5ꢀOCF3
5ꢀMe
5ꢀF
94
3
99
4
86
5
80
6
6ꢀBr
6ꢀCl
7ꢀF
92
7
1g
1h
1i
98
8
97
9
7ꢀCF3
4ꢀBr
H
78
10
11
12
1j
95
1k
1l
Me 3ka
Ph
3la
96
H
83
a Reaction conditions: 1 (0.5 mmol), 2a (0.75 mmol, 1.5 equiv), KOH (0.75 mmol, 1.5
equiv), MeOH (5 mL), 25 °C, 0.5−18 h; b Isolated yield.
A variety of oximes were investigated under the optimal conditions to study the
structural effect of oxime substrates on the Nꢀ or Oꢀarylation process (Scheme 2).
When oximes 1m, 1n, and 1o were treated with 2a in the presence of KOH in MeOH,
only the Oꢀarylation products 3ma, 3na, and 3oa were afforded in 81%, 82% and 85%
yields, respectively (Scheme 2ꢀ1, 2, 3). Interestingly, reaction of hydroxybenzimidoyl
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cyanide (1p) with 2a gave the Oꢀarylation product 3pa in 72% yield accompanied
with Nꢀarylation of the cyanide group to give product 3pa’ in 27% yield (Scheme 2ꢀ4).
When chalcone oxime 1q was used as substrate, Oꢀarylation product 3qo and
Nꢀarylation product 3qa’ were given in 34% and 58% yields, respectively (Scheme
2ꢀ5). No reaction occurred when methyl protected oxime 1r was subjected to the
optimal conditions (Scheme 2ꢀ6). Removing the carbonyl group in oxime 1s provided
Oꢀarylation product 3sa in 67% yield (Scheme 2ꢀ7). These results show that the
pyrroline ring and carbonyl group in oxime 1a played important roles in the
Nꢀarylation process.
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O
O
N
KOH
N
Ph
O Ph
Ph2IOTf
+
OH
Ph
1)
2)
MeOH
Me
Me
2a
3ma
, 81%
1m
OH
O
N
Ph
N
KOH
O
O
+
CO2Me
1n
Ph2IOTf
CO2Me
MeOH
Ph
Ph
3na, 82%
2a
OH
O
Ph
N
N
KOH
Ph2IOTf
+
CO2Me
MeO2C
3)
4)
MeOH
MeO2C
CO2Me
, 85%
2a
1o
3oa
OH
OH
N
O
Ph
N
N
KOH
N
Ph
+
+
Ph2IOTf
Ph
Ph
CN
MeOH
Ph
3pa
CN
2a
OMe
1p
3pa',
, 72%
27%
OH
Ph
O
Ph
O
N
KOH
N
N
+
5)
+
Ph2IOTf
MeOH
Ph
Ph
Ph
3qa', 58%
Ph
2a
Ph
Ph
3qa, 34%
1q
OMe
O
N
KOH
6)
7)
+
Ph2IOTf
No Reaction
MeOH
N
H
2a
1r
OH
Me
O
Ph
N
N
KOH
Ph2IOTf
+
Me
MeOH
N
N
2a
H
H
1s
3sa
, 67%
Scheme 2. NꢀArylation vs OꢀArylation of Oximes
A gramꢀscale reaction was performed to demonstrate the utility of this metalꢀfree
strategy for the preparation of Nꢀaryl oxindole nitrones (Scheme 3). Reaction of 1.6 g
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of oxime 1a with 2a under the optimal conditions for 30 min gave 2.16 g desired
nitrone 3aa in 91% yield. This facile method to synthesize Nꢀarylnitrone will enable
more applications to further access the spirooxindoleꢀscaffolds through cycloaddition
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chemistry.
Ph
OH
O
N
N
KOH
+
Ph2IOTf
O
O
MeOH, rt, 30 min
N
N
H
H
2a
1a
1.6 g, 10 mmol
3aa
2.16 g, 91%
Scheme 3. Gramꢀscale Preparation of 3aa
In summary, we have developed a highly efficient method to prepare (Z)ꢀNꢀaryl
oxindole
nitrones
by
selective
Nꢀarylation
of
readily
available
3ꢀ(hydroxyimino)indolinꢀ2ꢀones with diaryliodonium salts promoted by an inorganic
base under metalꢀfree conditions. With this efficient approach towards Nꢀarylnitrone’s
synthesis, varioius of 3ꢀ(hydroxyimino)indolinꢀ2ꢀones and diaryliodonium salts
bearing different functional groups were well tolerated to give the arylated products as
Zꢀisomers in good yields. Another feature of this method is selective Nꢀarylation of
oximes bearing multiple nucleophilic sites. Therefore, this metalꢀfree Nꢀarylation
strategy to prepare Nꢀaryl nitrones will provide more potential applications in
synthetic chemistry.
EXPERIMENTAL SECTION
General Methods. All reactions were performed under an air atmosphere.
Commercially available reagents were used without further purification. The NMR
spectra were recorded in CDCl3 or DMSOꢀd6 on 400, or 500 MHz instrument with
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TMS as the internal standard. NMR data are represented as follows: chemical shift
(ppm), multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet),
coupling constants in hertz (Hz), and integration. IR spectra were recorded on FTꢀIR
spectrometer, and only major peaks are reported in cm‒1. HRMS were measured in
ESI mode and the mass analyzer of the HRMS was TOF. Flash column
chromatography was performed on silica gel (300ꢀ400 mesh).
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General procedure for preparing nitrone 3: A round bottle flask was charged with
oxime 1 (0.5 mmol), MeOH (5 mL) and KOH (0.75 mmol, 1.5 equiv) under an air
atmosphere. The mixture was stirred vigorously at room temperature for 5 min. Then
diaryliodonium salt 2 (0.75 mmol, 1.5 equiv) was added in one portion. The reaction
was monitored by TLC until the oxime was consumed completely. At this time,
MeOH was removed under reduced pressure and the crude product was purified by
flash chromatography (the crude residue was dryꢀloaded on silica gel; 1:10ꢀ1:4 ethyl
acetate:petroleum ether) to provide nitrones 3 as solid.
(Z)-N-(2-Oxoindolin-3-ylidene)aniline oxide (3aa), 0.118 g, 98% yield, yellow
solid. mp: 170−171 °C; 1H NMR (500 MHz, CDCl3): δ 8.63 (brs, 1H), 8.20 (d, J = 7.5
Hz, 1H), 7.45−7.38 (m, 5H), 7.17−7.12 (m, 2H), 6.96 (d, J = 7.5 Hz, 1H); 13C NMR
(125 MHz, CDCl3): δ 165.7, 158.9, 146.0, 142.4, 133.5, 129.4, 128.7, 124.1, 123.3,
116.0, 115.2, 111.1; IR (thin film) 3454, 3097, 1739, 1615, 1204, 971, 748 cm−1;
HRMS (ESI) m/z calcd for C14H9N2O2 (M−H)− 237.0664, found 237.0653.
(E)-N-(2-Oxoindolin-3-ylidene)aniline oxide (3aa),12 0.006 g, 8% yield in DCE,
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yellow solid. mp: 165−166 °C; H NMR (500 MHz, DMSOꢀd6): δ 10.77 (brs, 1H),
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8.31 (d, J = 7.5 Hz, 1H), 7.60−7.54 (m, 5H), 7.45 (t, J = 7.5 Hz, 1H), 7.11 (t, J = 7.5
Hz, 1H), 6.94 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 160.4, 146.8,
141.4, 134.9, 132.7, 130.6, 129.2, 124.6, 124.4, 122.2, 118.9, 110.2.
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(Z)-4-Methoxy-N-(2-oxoindolin-3-ylidene)aniline oxide (3ab), 0.082 g, 60%
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yield, yellow solid. mp: 165−166 °C; H NMR (400 MHz, CDCl3): δ 8.92 (brs, 1H),
8.09 (d, J = 7.6 Hz, 1H), 7.33−7.26 (m, 3H), 7.06−7.02 (m, 1H), 7.89−7.82 (m, 3H),
3.74 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 165.3, 156.4, 153.1, 145.5, 142.2, 133.3,
128.6, 123.2, 116.7, 116.1, 114.4, 110.8, 55.6; IR (thin film) 3430, 3070, 2945, 1736,
1620, 1225, 730 cm−1; HRMS (ESI) m/z calcd for C15H11N2O3 (M−H)− 267.0770,
found 267.0789.
(Z)-4-Methyl-N-(2-oxoindolin-3-ylidene)aniline oxide (3ac), 0.116 g, 92% yield,
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yellow solid. mp: 170−171 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.96 (brs, 1H),
8.16 (d, J = 7.2 Hz, 1H), 7.51 (t, J = 7.6 Hz, 1H), 7.35 (d, J = 8.0 Hz, 2H), 7.28 (d, J =
8.0 Hz, 2H), 7.15 (d, J = 7.6 Hz, 1H), 6.98 (d, J = 7.6 Hz, 1H), 2.34 (s, 3H); 13C NMR
(100 MHz, DMSOꢀd6): δ 163.9, 157.1, 146.7, 144.5, 134.5, 134.4, 130.4, 128.9, 122.9,
115.7, 115.1, 111.3, 20.7; IR (thin film) 3330, 3056, 2922, 1734, 1611, 1205, 967, 809,
746 cm−1; HRMS (ESI) m/z calcd for C15H11N2O2 (M−H)− 251.0821, found 251.0810.
(Z)-4-(tert-Butyl)-N-(2-oxoindolin-3-ylidene)aniline oxide (3ad), 0.138 g, 94%
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yield, yellow solid. mp: 172−173 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.97 (brs,
1H), 8.16 (d, J = 7.6 Hz, 1H), 7.51 (m, 3H), 7.37 (d, J = 7.6 Hz, 2H), 7.16 (d, J = 7.6
Hz, 1H), 6.98 (d, J = 8.0 Hz, 1H), 1.32 (s, 9H); 13C NMR (100 MHz, DMSOꢀd6): δ
163.9, 156.9, 146.8, 144.5, 134.4, 128.9, 126.8, 123.0, 115.7, 114.7, 114.8, 111.3, 34.5,
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31.7; IR (thin film) 3417, 3092, 2961, 1724, 1608, 1452, 1213, 952, 746 cm−1; HRMS
(ESI) m/z calcd for C18H17N2O2 (M−H)− 293.1290, found 293.1278.
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(Z)-4-Chloro-N-(2-oxoindolin-3-ylidene)aniline oxide (3ae), 0.123 g, 90% yield,
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yellow solid. mp: 174−175 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.99 (brs, 1H),
8.18 (d, J = 7.6 Hz, 1H), 7.54−7.47 (m, 5H), 7.15 (t, J = 7.6 Hz, 1H), 6.98 (d, J = 8.0
Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.8, 157.8, 147.4, 144.7, 134.8, 130.0
129.2, 128.1, 123.0, 117.0, 115.6, 111.4; IR (thin film) 3454, 3179, 3053, 1729, 1617,
1482, 1210, 978, 776 cm−1; HRMS (ESI) m/z calcd for C14H8ClN2O2 (M−H)−
271.0274, found 271.0269.
(Z)-4-Fluoro-N-(2-oxoindolin-3-ylidene)aniline oxide (3af), 0.125 g, 97% yield,
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yellow solid. mp: 165−166 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.95 (brs, 1H),
8.15 (d, J = 7.6 Hz, 1H), 7.49−7.44 (m, 3H), 7.31 (t, J = 8.8 Hz, 2H), 7.13−7.09 (m,
1H), 6.95 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.9, 160.1 (d, J =
237.7 Hz), 155.4, 147.1, 144.6, 134.6, 129.1, 123.0, 117.1 (d, J = 8.8 Hz), 116.8 (d, J
= 23.3 Hz), 115.6, 111.3; IR (thin film) 3428, 3119, 3058, 1738, 1619, 1499, 1180,
975, 748 cm−1; HRMS (ESI) m/z calcd for C14H8FN2O2 (M−H)− 255.0570, found
255.0559.
(Z)-N-(2-Oxoindolin-3-ylidene)-4-(trifluoromethyl)aniline oxide (3ag), 0.148 g,
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97% yield, yellow solid. mp: 183−184 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.99
(brs, 1H), 8.20 (d, J = 7.2 Hz, 1H), 7.85 (d, J = 7.6 Hz, 2H), 7.67 (d, J = 8.4 Hz, 2H),
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7.51 (t, J = 7.6 Hz, 1H), 7.14 (t, J = 7.6 Hz, 1H), 6.96 (d, J = 8.0 Hz, 1H); C NMR
(100 MHz, DMSOꢀd6): δ 163.2, 161.0, 147.4, 144.4, 134.5, 133.8 (d, J = 160.4 Hz),
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128.9, 128.2 (q, J = 269.7 Hz), 127.2 (d, J = 2.9 Hz), 124.6 (q, J = 32.0 Hz), 122.5,
115.0, 110.9; IR (thin film) 3311, 3070, 1744, 1614, 1331, 958, 836, 748 cm−1; HRMS
(ESI) m/z calcd for C15H8F3N2O2 (M−H)− 305.0538, found 305.0529.
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(Z)-3,5-Dimethyl-N-(2-oxoindolin-3-ylidene)aniline oxide (3ah), 0.125 g, 93%
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yield, yellow solid. mp: 183−184 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.93 (brs,
1H), 8.13 (d, J = 7.6 Hz, 1H), 7.49 (m, 1H), 7.12 (t, J = 7.6 Hz, 1H), 7.04 (s, 2H),
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6.95 (d, J = 7.6 Hz, 1H), 6.81 (s, 1H), 2.31 (s, 6H); C NMR (100 MHz, DMSOꢀd6):
δ 164.0, 159.1, 146.8, 144.5, 139.6, 134.5, 128.9, 125.8, 123.0, 115.7, 112.7, 111.3,
21.4; IR (thin film) 3300, 3058, 2919, 1737, 1612, 1464, 1292, 983, 747 cm−1; HRMS
(ESI) m/z calcd for C16H13N2O2 (M−H)− 265.0977, found 265.0970.
(Z)-2-Methyl-N-(2-oxoindolin-3-ylidene)aniline oxide (3ai), 0.125 g, 99% yield,
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yellow solid. mp: 158−159 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.95 (brs, 1H),
8.08 (d, J = 7.2 Hz, 1H), 7.50−7.47 (m, 2H), 7.31 (t, J = 7.2 Hz, 2H), 7.16−7.08 (m,
2H), 6.07 (d, J = 12.0 Hz, 1H), 2.38 (s, 3H); 13C NMR (100 MHz, DMSOꢀd6): δ 164.0,
157.3, 147.0, 144.6, 134.5, 131.5, 128.6, 127.8, 125.1, 124.3, 123.1, 115.7, 115.1,
111.4, 16.4; IR (thin film) 3423, 3095, 2952, 1727, 1609, 1220, 975, 747, 650 cm−1;
HRMS (ESI) m/z calcd for C15H11N2O2 (M−H)− 251.0821, found 251.0816.
(Z)-4-Bromo-N-(2-oxoindolin-3-ylidene)aniline oxide (3ak), 0.136 g, 85% yield,
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yellow solid. mp: 176−177 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.95 (brs, 1H),
8.20−8.15 (m, 1H), 7.64−7.60 (m, 2H), 7.50−7.40 (m, 3H), 7.15−7.10 (m, 1H),
7.00−6.90 (m, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.8, 158.3, 147.4, 144.7,
134.8, 132.9, 129.2, 123.0, 117.4, 115.9, 115.6, 111.4; IR (thin film) 3454, 3172, 3095,
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1733, 1613, 1481, 979, 815, 744 cm−1; HRMS (ESI) m/z calcd for C14H8BrN2O2
(M−H)− 314.9769, found 314.9753.
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(Z)-3-Bromo-N-(2-oxoindolin-3-ylidene)aniline oxide (3al), 0.154 g, 97% yield,
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yellow solid. mp: 190−191 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.98 (brs, 1H),
8.18 (d, J = 7.6 Hz, 1H), 7.68 (s, 1H), 7.50−7.36 (m, 4H), 7.13 (t, J = 7.6 Hz, 1H),
6.96 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.8, 159.7, 147.6,
144.8, 134.9, 132.0, 129.4, 127.1, 123.1, 122.5, 118.0, 115.5, 114.3, 111.4; IR (thin
film) 3454, 3161, 3092, 1738, 1615, 1465, 1204, 976, 769 cm−1; HRMS (ESI) m/z
calcd for C14H8BrN2O2 (M−H)− 314.9769, found 314.9764.
(Z)-2-Bromo-N-(2-oxoindolin-3-ylidene)aniline oxide (3am), 0.132 g, 83% yield.
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mp: 195−196 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.99 (brs, 1H), 8.36 (d, J = 7.6
Hz, 1H), 7.74 (d, J = 7.2 Hz, 1H), 7.67 (d, J = 8.0 Hz, 1H), 7.51−7.47 (m, 2H), 7.16 (t,
J = 7.6 Hz, 2H), 6.96 (d, J = 7.6 Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.7,
155.4, 148.1, 145.0, 135.1, 133.7, 129.9, 129.2, 125.9, 123.1, 116.5, 115.4, 111.5,
108.9; IR (thin film) 3431, 3157, 3016, 1736, 1618, 1465, 1216, 965, 753 cm−1;
HRMS (ESI) m/z calcd for C14H8BrN2O2 (M−H)− 314.9769, found 314.9756.
(Z)-4-(Methoxycarbonyl)-N-(2-oxoindolin-3-ylidene)aniline oxide (3an), 0.088
g, 99% yield, yellow solid. mp: 196−197 °C; 1H NMR (400 MHz, DMSOꢀd6): δ 10.99
(brs, 1H), 8.18 (d, J = 7.6 Hz, 1H), 8.07 (d, J = 8.8 Hz, 2H), 7.57 (d, J = 8.8 Hz, 2H),
7.51 (t, J = 7.6 Hz, 1H), 7.14 (t, J = 7.6 Hz, 1H), 6.96 (d, J = 8.0 Hz, 1H), 3.86 (s, 3H);
13C NMR (100 MHz, DMSOꢀd6): δ 166.1, 163.7, 162.4, 147.9, 144.9, 135.0, 131.8,
129.4, 125.3, 123.1, 115.5, 114.9, 111.4, 52.5; IR (thin film) 3431, 3075, 2924, 1752,
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1619, 1499, 1299, 951, 768 cm−1; HRMS (ESI) m/z calcd for C16H11N2O4 (M−H)−
295.0719, found 295.0705.
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(Z)-N-(5-Methoxy-2-oxoindolin-3-ylidene)aniline oxide (3ba), 0.127 g, 94%
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yield, yellow solid. mp: 150−152 °C; H NMR (500 MHz, CDCl3): δ 9.55 (brs, 1H),
7.72 (s, 1H), 7.42−7.36 (m, 4H), 7.16−7.13 (m, 1H), 6.91−6.86 (m, 2H), 3.79 (m, 3H);
13C NMR (125 MHz, CDCl3): δ 165.7, 158.9, 155.8, 146.4, 136.2, 129.4, 124.1, 118.5,
116.5, 115.2, 114.9, 111.6, 55.8; IR (thin film) 3466, 3162, 2954, 1735, 1592, 1480,
1203, 977, 758 cm−1; HRMS (ESI) m/z calcd for C15H11N2O3 (M−H)− 267.0770,
found 267.0766.
(Z)-N-(2-Oxo-5-(trifluoromethoxy)indolin-3-ylidene)aniline oxide (3ca), 0.160 g,
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99% yield, yellow solid. mp: 174−175 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.14
(brs, 1H), 8.04 (s, 1H), 7.51−7.43 (m, 5H), 7.23 (t, J = 6.4 Hz, 1H), 7.04 (d, J = 8.8
Hz, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.3, 158.3, 145.8, 143.1, 142.9, 129.7,
127.0, 124.2, 123.9 (q, J = 254.5 Hz), 121.3, 115.7, 114.8, 111.9; IR (thin film) 3452,
3283, 3075, 1740, 1623, 1286, 978, 751 cm−1; HRMS (ESI) m/z calcd for
C15H8F3N2O3 (M−H)− 321.0487, found 321.0511.
(Z)-N-(5-Methyl-2-oxoindolin-3-ylidene)aniline oxide (3da), 0.109 g, 86% yield,
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yellow solid. mp: 176−177 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.82 (brs, 1H),
7.93 (s, 1H), 7.47−7.43 (m, 4H), 7.26 (d, J = 7.6 Hz, 1H), 7.19 (t, J = 6.0 Hz, 1H),
6.82 (d, J = 8.0 Hz, 1H), 2.31 (s, 3H); 13C NMR (100 MHz, DMSOꢀd6): δ 164.0,
159.1, 147.1, 142.2, 134.9, 132.0, 130.1, 129.3, 124.4, 115.7, 115.3, 111.1, 21.0; IR
(thin film) 3467, 3171, 3069, 2921, 1735, 1620, 1203, 974, 754 cm−1; HRMS (ESI)
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m/z calcd for C15H11N2O2 (M−H)− 251.0821, found 251.0815.
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(Z)-N-(5-Fluoro-2-oxoindolin-3-ylidene)aniline oxide (3ea), 0.103 g, 80% yield,
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yellow solid. mp: 189−190 °C; H NMR (400 MHz, DMSOꢀd6): δ 10.98 (brs, 1H),
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7.91−7.89 (m, 1H), 7.47−7.44 (m, 4H), 7.36−7.32 (m, 1H), 7.21−7.18 (m, 1H),
6.96−6.93 (m, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.4, 158.8 (d, J = 236.2 Hz),
158.5, 146.2, 140.4, 129.7, 124.1, 120.6 (d, J = 24.1 Hz), 115.6 (d, J = 9.5 Hz), 115.3
(d, J = 25.5 Hz), 114.8, 111.9 (d, J = 7.3 Hz); IR (thin film) 3430, 3163, 3019, 1738,
1624, 1472, 1188, 980, 757 cm−1; HRMS (ESI) m/z calcd for C14H8FN2O2 (M−H)−
255.0570, found 255.0558.
(Z)-N-(6-Bromo-2-oxoindolin-3-ylidene)aniline oxide (3fa), 0.153 g, 92% yield,
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yellow solid. mp: 190−191 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.08 (brs, 1H),
8.07 (d, J = 8.4 Hz, 1H), 7.47−7.40 (m, 4H), 7.30 (d, J = 8.0 Hz, 1H), 7.20−7.17 (m,
1H), 7.10 (s, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.8, 158.9, 146.2, 145.8,
130.3, 130.2, 127.6, 125.8, 124.6, 115.2, 114.8, 114.2; IR (thin film) 3454, 3180, 3088,
1737, 1697, 1591, 1205, 976, 760 cm−1; HRMS (ESI) m/z calcd for C14H8BrN2O2
(M−H)− 314.9769, found 314.9760.
(Z)-N-(6-Chloro-2-oxoindolin-3-ylidene)aniline oxide (3ga), 0.134 g, 98% yield,
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yellow solid. mp: 180−181 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.09 (brs, 1H),
8.14 (d, J = 8.0 Hz, 1H), 7.47−7.40 (m, 4H), 7.20−7.13 (m, 2H), 6.96 (s, 1H); 13C
NMR (100 MHz, DMSOꢀd6): δ 163.0, 158.0, 145.1, 144.9, 137.7, 129.3, 123.6, 123.5,
121.9, 114.3, 113.6, 110.5; IR (thin film) 3454, 3077, 1739, 1610, 1331, 971, 749
cm−1; HRMS (ESI) m/z calcd for C14H8ClN2O2 (M−H)− 271.0274, found 271.0265.
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(Z)-N-(7-Fluoro-2-oxoindolin-3-ylidene)aniline oxide (3ha), 0.125 g, 97% yield,
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yellow solid. mp: 159−160 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.49 (brs, 1H),
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8.02 (d, J = 7.6 Hz, 1H), 7.48−7.40 (m, 5H), 7.21 (t, J = 6.8 Hz, 1H), 7.15−7.10 (m,
1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.3, 158.5, 147.7 (d, J = 242.8 Hz), 145.9,
131.2 (d, J = 12.2 Hz), 129.8, 124.6, 124.2, 123.5 (d, J = 5.1 Hz), 120.9 (d, J = 17.5
Hz), 117.8 (d, J = 4.4 Hz), 114.8; IR (thin film) 3430, 3176, 3099, 1731, 1591, 1196,
951, 762 cm−1; HRMS (ESI) m/z calcd for C14H8FN2O2 (M−H)− 255.0570, found
255.0559.
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(Z)-N-(2-Oxo-7-(trifluoromethyl)indolin-3-ylidene)aniline oxide (3ia), 0.120 g,
1
78% yield, yellow solid. mp: 155−156 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.41
(brs, 1H), 8.43 (d, J = 7.6 Hz, 1H), 7.73 (d, J = 7.6 Hz, 1H), 7.48−7.44 (m, 4H),
7.29−7.25 (m, 1H), 7.21−7.18 (m, 1H); 13C NMR (100 MHz, DMSOꢀd6): δ 163.8,
158.5, 144.7, 141.1, 132.1, 129.8, 129.7 (d, J = 4.4 Hz), 124.6 (d, J = 270.6 Hz),
124.2, 122.6, 116.8, 114.8, 112.1 (q, J = 32.8 Hz); IR (thin film) 3455, 3125, 1742,
1592, 1484, 1121, 976, 764 cm−1; HRMS (ESI) m/z calcd for C15H8F3N2O2 (M−H)−
305.0538, found 305.0527.
(Z)-N-(4-Bromo-2-oxoindolin-3-ylidene)aniline oxide (3ja), 0.158 g, 95% yield,
1
yellow solid. mp: 168−169 °C; H NMR (400 MHz, DMSOꢀd6): δ 11.14 (brs, 1H),
7.46−7.39 (m, 4H), 7.31−7.28 (m, 2H), 7.18−7.14 (m, 1H), 6.90 (d, J = 6.8 Hz, 1H);
13C NMR (100 MHz, DMSOꢀd6): δ 158.9, 157.0, 145.0, 144.9, 133.4 129.7, 126.4,
123.6, 117.3, 116.5, 114.1, 109.7; IR (thin film) 3410, 3178, 3054, 1731, 1603, 1439,
1195, 954, 780 cm−1; HRMS (ESI) m/z calcd for C14H8BrN2O2 (M−H)− 314.9769,
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found 314.9767.
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(Z)-N-(1-Methyl-2-oxoindolin-3-ylidene)aniline oxide (3ka), 0.121 g, 96% yield,
yellow solid. mp: 127−128 °C; 1H NMR (400 MHz, DMSOꢀd6): δ 8.17 (d, J = 7.2 Hz,
1H), 7.56−7.52 (m, 1H), 7.47−7.41 (m, 4H), 7.20−7.11 (m, 3H)，3.18 (s, 3H); 13C
NMR (100 MHz, DMSOꢀd6): δ 162.1, 158.5, 146.0, 145.2, 134.0, 129.7, 128.2, 124.0,
123.0, 114.7, 114.5, 109.5, 26.0; IR (thin film) 3437, 3055, 2929, 1721, 1597, 1485,
1186, 948, 747 cm−1; HRMS (ESI) m/z calcd for C15H11N2O2 (M−H)− 251.0821,
found 251.0809.
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(Z)-N-(2-Oxo-1-phenylindolin-3-ylidene)aniline oxide (3la), 0.131 g, 83% yield,
yellow solid. mp: 144−145 °C; 1H NMR (400 MHz, DMSOꢀd6): δ 8.31 (d, J = 7.6 Hz,
1H), 7.63−7.59 (m, 2H), 7.53−7.48 (m, 8H), 7.26−7.20 (m, 2H), 6.82 (d, J = 8.0 Hz,
1H); 13C NMR (100 MHz, DMSOꢀd6): δ 161.6, 158.6, 145.8, 145.1, 134.0, 133.3,
129.8, 129.7, 129.6, 128.6, 128.5, 126.9, 124.1, 123.6, 114.8, 109.8; IR (thin film)
3060, 1728, 1608, 1591, 1188, 968, 752 cm−1; HRMS (ESI) m/z calcd for C20H13N2O2
(M−H)− 313.0977, found 313.0965.
2-(Phenoxyimino)-1-phenylpropan-1-one (3ma), 0.048 g, 81% yield, brown
1
liquid. H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 7.6 Hz, 2H), 7.52−7.48 (m, 1H),
7.40−7.36 (m, 2H), 7.25−7.21 (m, 2H), 7.12 (d, J = 8.0 Hz, 2H), 7.00−6.96 (m, 1H),
2.28 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 190.8, 158.9, 157.4, 136.1, 132.9, 130.6,
129.4, 128.1, 123.1, 114.8, 11.5; IR (thin film) 3064, 2927, 2854, 1665, 1488, 1211,
709 cm−1; HRMS (ESI) m/z calcd for C15H14NO2 (M+H)+ 240.1025, found 240.1018.
Methyl 3-oxo-2-(phenoxyimino)-3-phenylpropanoate (3na), 0.122 g, 82% yield,
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light yellow solid. mp: 63−64 °C; 1H NMR (400 MHz, CDCl3): δ 7.93 (d, J = 7.6 Hz,
2H), 7.67−7.63 (m, 1H), 7.54−7.50 (m, 2H), 7.31−7.27 (m, 2H), 7.15 (d, J = 8.0 Hz,
2H), 7.11 (t, J = 7.2 Hz, 1H), 3.90 (s, 3H); 13C NMR (100 MHz, CDCl3): δ 188.8,
160.6, 158.2, 150.8, 134.8, 133.9, 129.3, 129.2, 129.1, 124.2, 115.3, 53.3; IR (thin
film) 3059, 2956, 2852, 1721, 1678, 1487, 1203, 750, 686 cm−1; HRMS (ESI) m/z
calcd for C16H14NO4 (M+H)+ 284.0916, found 284.0923.
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Dimethyl 2-(phenoxyimino)malonate (3oa), 0.100 g, 85% yield, brown solid. mp:
1
45−46 °C; H NMR (400 MHz, CDCl3): δ 7.28−7.25 (m, 2H), 7.17 (d, J = 8.0 Hz,
2H), 7.07 (t, J = 7.2 Hz, 1H), 3.89 (s, 3H), 3.85 (s, 3H); 13C NMR (100 MHz, CDCl3):
δ 160.3, 159.8, 158.1, 145.2, 129.4, 124.4, 115.4, 53.3, 53.0; IR (thin film) 3016, 2958,
2851, 1754, 1592, 1486, 1096, 756, 690 cm−1; HRMS (ESI) m/z calcd for C11H12NO5
(M+H)+ 238.0710, found 238.0715.
N-Phenoxybenzimidoyl cyanide (3pa), 0.080 g, 72% yield, yellow solid. mp:
1
74−75 °C; H NMR (400 MHz, CDCl3): δ 7.97 (d, J = 7.2 Hz, 2H), 7.59−7.51 (m,
3H), 7.45−7.41 (m, 2H), 7.38 (d, J = 8.0 Hz, 2H), 7.22 (m, 1H); 13C NMR (100 MHz,
CDCl3): δ 158.4, 134.3, 131.9, 129.5, 129.1, 128.7, 126.7, 124.2, 115.0, 109.2; IR
(thin film) 3060, 2236, 1589, 1486, 1198, 755, 685 cm−1; HRMS (ESI) m/z calcd for
C14H11N2O (M+H)+ 223.0864, found 223.0871.
Methyl 2-(hydroxyimino)-N,2-diphenylacetimidate (3pa’), 0.034 g, 27% yield,
brown liquid. 1H NMR (400 MHz, CDCl3): δ 7.63 (d, J = 6.8 Hz, 2H), 7.56 (brs, 1H),
7.39−7.32 (m, 3H), 7.27−7.23 (m, 2H), 7.19 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 7.2 Hz,
13
1H), 3.89 (s, 3H); C NMR (100 MHz, CDCl3): δ 162.7, 158.9, 153.8, 130.8, 130.7,
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129.2, 128.7, 127.0, 122.9, 114.8, 53.2; IR (thin film) 3429, 3062, 2946, 2852, 1654,
1489, 1208, 754, 690 cm−1; HRMS (ESI) m/z calcd for C15H15N2O2 (M+H)+ 255.1127,
found 255.1134.
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Chalcone O-phenyl oxime (3qa), 0.051 g, 34% yield, light yellow liquid. 1H NMR
(500 MHz, CDCl3): δ 7.79 (d, J = 16.5 Hz, 1H), 7.62 (d, J = 6.5 Hz, 2H), 7.53 (d, J =
7.5 Hz, 2H), 7.47−7.46 (m, 3H), 7.38−7.32 (m, 7H), 7.05−7.02 (m, 1H), 6.88 (d, J =
16.0 Hz, 1H); 13C NMR (125 MHz, CDCl3): δ 159.6, 159.4, 140.8, 135.9, 134.3,
129.6, 129.5, 129.4, 129.2, 128.8, 128.4, 127.6, 122.3, 117.7, 114.9; IR (thin film)
3060, 1608, 1591, 1482, 1058, 968, 752, 692 cm−1; HRMS (ESI) m/z calcd for
C21H18NO (M+H)+ 300.1368, found 300.1388.
2-Methylindolin-3-one O-phenyl oxime (3sa), 0.080 g, 67% yield, colorless liquid.
1H NMR (400 MHz, CDCl3): δ 7.94 (d, J = 8.4 Hz, 1H), 7.73−7.70 (m, 3H),
7.55−7.51 (m, 2H), 7.45−7.41 (m, 1H), 7.37−7.33 (m, 1H), 7.23 (d, J = 7.2 Hz, 1H),
5.43 (q, J = 6.8 Hz, 1H), 2.58 (brs, 1H), 1.79 (d, J = 6.8 Hz, 3H); 13C NMR (100 MHz,
CDCl3): δ 150.1, 140.1, 140.0, 129.4, 127.3, 126.5, 122.7, 122.6, 122.2, 121.3, 110.5,
65.5, 23.4; IR (thin film) 3415, 3029, 2954, 2846, 1593, 1209, 752, 697 cm−1; HRMS
(ESI) m/z calcd for C15H15N2O (M+H)+ 239.1179, found 239.1184.
The spectra data of nitrone 3qa’ matched literature values. 9
Preparation of oximes 1: A mixture of indolineꢀ2,3ꢀdione (10 mmol) and
hydroxylamine hydrochloride (10.6 mol) in water (25 ml) was heated to reflux for 30
min. Then sodium acetate (10 mmol) was added in one portion and the solution was
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continued to stir for 30 min. The mixture was cooled down to room temperature. The
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solid was filtered out and dried to afford a yellow solid 1.
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(Z)-3-(Hydroxyimino)-5-(trifluoromethoxy)indolin-2-one (1c), 0.197 g, 80%
yield, yellow solid. mp: 233−234 °C; 1H NMR (400 MHz, CDCl3): δ 10.92 (brs, 1H),
7.87 (s, 1H), 7.45−7.35 (m, 1H), 7.00−6.98 (m, 1H), 3.39 (brs, 1H); 13C NMR (100
MHz, CDCl3): δ 164.8, 144.0, 143.3, 142.1, 125.6, 124.5 (q, J = 254.5 Hz), 120.3,
116.8, 111.7; IR (thin film) 3435, 3167, 1716, 1625, 1463, 1292, 733, 751 cm‒1;
HRMS (ESI) m/z calcd for C9H6F3N2O3 (M+H)+ 247.0331, found 247.0325.
The oxime 1a,15 1b,16 1d, 15 1e,15 1f,17 1g,15 1h,18 1i,19 1j,20 1k,21 1l,22 1m,23 1n,24
1o,25 1p,26 1q,27 1r,28 and 1s29 were prepared according to literature methods and their
spectra data matched literature values.
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General procedure for synthesis of diaryliodonium salts 2: Aryl boronic acid (10
mmol, 1.0 equiv) and CH2Cl2 (40 mL) were combined in a dried roundꢀbottom flask.
The mixture was cooled to 0 °C for 5 min, BF3•OEt2 (1.12 mL, 1.10 equiv) was added,
and the mixture was stirred for 10 min. A solution of 2ꢀ(diacetoxyiodo)arene (1.05
equiv) in CH2Cl2 (20 mL) was added slowly for 10−15 min and stirred for additional
10 min. The mixture was warmed to room temperature and stirred for 1 h. The
reaction was cooled to 0 °C again and TfOH (1.67 mL, 1.1 equiv) was dropped into
the mixture. Then, the mixture was stirred for 10 min at 0 °C and warmed to room
temperature for additional 10 min. At this time, the solvent was removed under
reduced pressure and the residual ran through a short silica gel column (about 5 cm)
with 5% of MeOH in CH2Cl2 quickly. The mixture was concentrated under vacuum
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and Et2O (100 mL) was added to the residual to form a white solid. Filtrated and
obtained the diaryliodonium salts 2 as white solid.
The diaryliodnium salts 2a,30 2b,312c,30 2d,31 2e,31 2f,31 2g,32 2h,33 2i,31 2j,30 2k,34 2l,35
2m,9 and 2n9 were prepared according to literature methods and their spectral data
matched literature values.
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ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge via the Internet at
http://pubs.acs.org.
Spectra of compounds 3aa-3an, 3ba-3sa, and 1c (PDF)
AUTHOR INFORMATION
Corresponding Authors
Email: moeastlight@mailbox.gxnu.edu.cn
†These authors contributed equally.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the “Oversea 100 Talents Program” of Guangxi
Education, State Key Laboratory for Chemistry and Molecular Engineering of
Medicinal Resources, Ministry of Science and Technology of China
(CMEMR2015ꢀA05), IRT−16R15 and National Natural Science Foundation of China
(21562005,
21602037),
Natural
Science
Foundation
of
Guangxi
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(2015GXNSFCA139001, 2016GXNSFFA380005).
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Chem. Int. Ed. 2009, 48, 9052; (b) Merritt, E. A.; Olofsson, B. Synthesis 2011, 4, 517;
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Lett. 2014, 16, 1830; (b) Castro, L. C. M.; Chatani, N. Synthesis 2014, 46, 2312; (c)
Yang, Y.; Wu, X.; Han, J.; Mao, S.; Qian, X.; Wang, L. Eur. J. Org. Chem. 2014, 6854;
(d) Ghosh, R.; Stridfeldt, E.; Olofsson, B. Chem. Eur. J. 2014, 20, 8888; (e) Gao, H.;
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Lundberg, H.; Adolfosson, H.; Olofsson, B. Org. Lett. 2015, 17, 2688; (b) Bihari, T.;
Baninszki, B.; Gonda, Z.; Kovacs, S.; Novák, Z.; Stirling, A. J. Org. Chem. 2016, 81,
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(12) Zhang, Y. H.; Wu, M. Y.; Huang, W. C. RSC Adv. 2015, 5, 105825.
(13) The nitrone 3aa was assigned Zꢀisomer by NOESY spectra. In fact, we still
isolated the minor Eꢀisomer of nitrone 3aa in less than 10% yield. And the NMR data
of Eꢀ3aa we isolated by our method matched the reported reference 12. Please see the
spectra of Zꢀ and Eꢀisomers of 3aa in the supporting information.
(14) For some examples to prepare the diaryliodionium salts, see: (a) Bielawski, M.;
Zhu, M.; Olofsson, B. Adv. Synth. Catal. 2007, 349, 2610; (b) Bielawski, M.; Aili, D.;
Olofsson, B. J. Org. Chem. 2008, 73, 4602.
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(15) Wang, Z.; Wang, C. L.; Sun, Y. N.; Zhang, N.; Liu, Z. L.; Liu, J. L.
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