A Catalyst-Free Minisci-Type Reaction: the C–H Alkylation of Quinoxalinones with Sodium Alkylsulfinates and Phenyliodine(III) Dicarboxylates

Article abstract of DOI:10.1002/ejoc.201901266

A direct C–H alkylation of quinoxalinones at the C-3 position with sodium alkylsulfinates and phenyliodine(III) dicarboxylates has been developed under catalyst-free conditions. A series of 3-alkylquinoxalinones were afforded in moderate to excellent yields in this protocol, which offers a practical and efficient access to biologically interesting 3-alkylquinoxalin-2(1H)-one derivatives.

Full text of DOI:10.1002/ejoc.201901266

DOI: 10.1002/ejoc.201901266
Full Paper
C–H Alkylation
A Catalyst-Free Minisci-Type Reaction: the C–H Alkylation of
Quinoxalinones with Sodium Alkylsulfinates and
Phenyliodine(III) Dicarboxylates
Liping Wang,[a] Jiquan Zhao,[a] Yuting Sun,[a] Hong-Yu Zhang,*[a] and Yuecheng Zhang*[a]
Abstract: A direct C–H alkylation of quinoxalinones at the ate to excellent yields in this protocol, which offers a practical
C-3 position with sodium alkylsulfinates and phenyliodine(III)
dicarboxylates has been developed under catalyst-free condi-
tions. A series of 3-alkylquinoxalinones were afforded in moder-
and efficient access to biologically interesting 3-alkylquinoxalin-
2(1H)-one derivatives.
Introduction
Recently, difunctionalization of alkenes with phenyliodine(III) di-
carboxylates also attracted considerable attention. For instan-
ces, Liu and Zhu respectively demonstrated the efficiently intra-
molecular alkylarylation of 1,1-disubstituted N-arylacrylamides
to synthesize oxindoles.[10a–10b] Meanwhile, Wang, Du and Kuni-
nobu respectively reported the intermolecular acyloxyalkylation
of olefin derivatives.[10c,10f] Jamison, Li and Xu respectively de-
veloped cyclization of isocyano derivatives to various alkylated
N-heterocycles.[10d,10g] In the above transformations, phenyl-
iodine(III) dicarboxylates can act as both the oxidants and alkyl
sources, but expensive photocatalyst or transition metal catalyst
is generally required (Scheme 1b). Although notable progresses
have been achieved in the alkylation with phenyliodine(III) di-
carboxylates, the scope of alkylation is still limited. Clearly, the
Construction of C–C bonds is an eternal theme in organic
chemistry. Over the past decades, catalyzed C–H functionaliza-
tion reactions have made remarkable progress in the construc-
tion of C–C bonds to introduce long chain alkyl or aryl groups
into organic molecules.[1] However, it is still challenging to de-
velop efficient and convenient approaches for the introduction
of short chain alkyl groups, especially for methyl, which may
improve the bioactivity of pharmaceutical molecules.[2] Re-
cently, some methylations with HOAc,[3] peroxides,[4] DMSO,[5]
and other reagents[6] as the methyl sources, instead of toxic
iodomethane or dimethyl sulfate, have been achieved.
Minisci-type reactions, pioneered by F. Minisci since 1970s,
have witnessed significant advances in the construction of C–C
bonds via radical process.[7,8] And alkylsulfinates, generating
alkyl radicals in situ, have been recognized as the ideal radical
sources for the alkylation of heterocycles,[8a–8g,8j,8l–8p,8s] aryl hal-
ides[8i,8q] and unsaturated alkanes[8h,8r] (Scheme 1a). Moreover,
hypervalent iodine(III) reagents (HIRs) have been extensively
utilized in organic synthetic chemistry owing to their facile
availability, ease of operation and environmentally benign
nature.[9] However, only a handful of radical alkylations with
phenyliodine(III) dicarboxylates as the alkyl radical precursors
have been accomplished.[10] As early as 1989, Minisci disclosed
the alkylation of heterocycles using HIRs with carboxylic
acids.[7b] After a period of silence, Qing, Genovino, Frenette,
Chen, and Xia independently realized the introduction of alkyl
or trifluoromethyl into (hetero)arenes in the last year.[10h–10k]
[a] School of Chemical Engineering and Technology, Hebei Provincial Key Lab
of Green Chemical Technology & High Efficient Energy Saving, Tianjin Key
Laboratory of Chemical Process Safety, Hebei University of Technology,
Guangrong Road No. 8, Tianjin 300130, P. R. China
E-mail: zhanghy@hebut.edu.cn
yczhang@hebut.edu.cn
https://www.scholarmate.com/psnweb/homepage/show?des3PsnId=
9gUY7RqEQ3s%253D
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejoc.201901266.
Scheme 1. Construction of C–C bonds with sulfinates or phenyliodine(III) di-
carboxylates.
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exploration of low-cost and efficient alkylation with phenyl- cal alkylation particular the methylation of quinoxalinones util-
iodine(III) dicarboxylates is of great interest.
izing sodium alkylsulfinates and phenyliodine(III) dicarboxylates
under catalyst-free conditions (Scheme 2e).
Quinoxalin-2(1H)-ones, representing important fundamental
units, are widely distributed in natural products as well as phar-
maceutical molecules.[11] Especially, 3-alkylquinoxalinones have
drawn extensive attention due to their outstanding biological
activities (Scheme 2a).[12] So, it is urgent in demand to install
various functional groups into the C-3 position of quinoxalin-
ones. In fact, several important achievements have been re-
ported in this field,[13] including alkylation,[14] alkoxylation,[15]
Results and Discussion
Initially, refering to our previous study on the C3–H trifluoro-
methylation of quinoxalin-2(1H)-ones with sodium trifluoro-
methanesulfinate and PhI(O2CCF3)2, we wondered whether 3-
methylquinoxalin-2(1H)-one would be received in the presence
of sodium methanesulfinate and PhI(O2CMe)2. To verify our in-
ference, we carried the reaction of 1-methylquinoxalin-2(1H)-
one (1a) with sodium methanesulfinate (2a) and PhI(O2CMe)2
(3a) under different catalyst-free conditions. The results re-
vealed that solvents have an obvious influence on this transfor-
mation. CH3CN, which was selected as suitable solvent in our
previous trifluoromethylation, could also promote the methyl-
ation to afford the target product 4a in 33 % yield (Table 1,
entry 1). However, dichloroethane (DCE) was not as efficient as
CH3CN, and the methylated product 4a was isolated in 26 %
yield (Table 1, entry 2). To our delight, cyclohexane and toluene
were performed better than CH3CN, and the yields of 4a in-
creased to 61 % and 65 %, respectively (Table 1, entries 3, 4).
Moreover, benzotrifluoride was found to be the optimal solvent
and the target product 4a was obtained in 75 % yield (Table 1,
entry 5). Further investigation on reagents loading shown that
the suitable molar ratio of MeSO2Na to PhI(O2CMe)2 was 1.5:2.5,
affording the target product 4a in an exciting 88 % yield
(Table 1, entries 6–16). It is noticeable that no desired alkylated
product was detected in the absence of 2a or 3a, which indi-
cated that MeSO2Na and PhI(O2CMe)2 were essential to this
(hetero)arylation,[16]
trifluoromethylation,[17]
difluoroalkyl-
ation,[18] acylation,[19] phosphonation[20] and amination[21]
(Scheme 2b). In spite of these significant progresses on the
C3–H functionalization of quinoxalin-2(1H)-ones have been de-
veloped, there are only few examples for the introduction of
short chain alkyl groups from Baran's group.[8g,8l–8n] Recent
days, Hu and He respectively developed a visible-light pro-
moted decarboxylative alkylation of quinoxalin-2(1H)-ones with
phenyliodine(III) dicarboxylates (Scheme 2c).[14j–14k] Although
the achievements have been realized to introduce short chain
alkyl groups including methyl, expensive photocatalyst is still
required in the reactions. Meanwhile, we recently have dis-
closed a direct C3–H trifluoromethylation of quinoxalin-2(1H)-
ones using sodium trifluoromethanesulfinate and PhI(O2CCF3)2
under transition-metal-free conditions, which provides a conve-
nient and efficient access to pharmacologically active 3-tri-
fluoromethyl-quinoxalinone derivatives (Scheme 2d).[17a] In-
spired by our previous work, we herein describe the direct radi-
Table 1. Screening of solvent and reagent loadings.[a]
Entry
1a/2a/3a
Solvent
t [°C]
Yield [%][b]
1
2
3
4
5
6
7
8
1:2:2
1:2:2
1:2:2
1:2:2
1:2:2
1:1.5:2
1:1:2
1:0.5:2
1/–/2
1:1.5/–
1:1.5:0.5
1:1.5:1
1:1.5:1.5
1:1.5:2.5
1:1.5:3
1:2:2.5
1:1.5:2.5
1:1.5:2.5
CH3CN
DCE
cyclohexane
toluene
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
50
70
33
26
61
65
75
83
77
37
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
benzotrifluoride
9
N. D.[c]
N. D.
12
34
49
88
83
85
86
83
10
11
12
13
14
15
16
17
18
[a] Unless specifically noted otherwise, reaction conditions: 1a (0.3 mmol),
MeSO2Na (2a), PhI(O2CMe)2 (3a), and solvent (3 mL) under an argon atmos-
phere. [b] Yield of isolated product. [c] N. D. = No detected.
Scheme 2. Quinoxalinone pharmaceutical molecules and C3–H functionaliza-
tion of quinoxalin-2(1H)-ones.
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transformation (Table 1, entries 9–10). Moreover, when the mal reaction conditions. The ethylated product 4s was obtained
amount of 2a or 3a was decreased to 0.5 equivalent, the yield only in 34 % yield. Unexpectedly, the methylated product 4a
of the target product 4a was reduced drastically, and 4a was was isolated in 47 % yield (Table 3, entry 1). These results im-
obtained respectively in 37 % or 12 % yield (Table 1, entry 8, plied that both sodium alkylsulfinates (2) and phenyliodine(III)
11). Finally, it was shown that 60 °C was the optimal reaction dicarboxylates (3) might act as the alkyl sources in this transfor-
temperature in this transformation (Table 1, entries 14, 17–18). mation. Next, PhI(O2CEt)2 (3b) instead of PhI(O2CMe)2 (3a) was
In summary, the screened conditions of the methylation were employed under the optimal conditions. The ethylated product
found to be 1a (0.3 mmol), MeSO2Na (0.45 mmol), PhI(O2CMe)2 4s was obtained in 71 % yield, with the yield of the methylated
(0.75 mmol), and running the reaction in benzotrifluoride at product 4a decreased to 11 % (Table 3, entry 2). For the aim to
60 °C (Table 1, entry 14).
improve the yield of product 4s, the amount of MeSO2Na was
decreased to 1.0 equivalent. The yield of the ethylated product
4s increased to 75 %, while the yield of the methylated product
4a decreased to 6 % (Table 3, entry 3). However, when the
amount of MeSO2Na was further decreased to 0.5 equivalent,
the yield of 4s was dropped obviously to 60 %, though the
formation of methylated product 4a was suppressed (Table 3,
entry 4). Subsequently, in the presence of 1.0 equivalent of
MeSO2Na, we investigated several phenyliodine(III) dicarboxyl-
ates (3c–3f). The alkylation reaction proceeded well in the pres-
ence of phenyliodine(III) dicarboxylates 3c and 3d as the alkyl-
ation reagents, affording the corresponding products 4t and
4u in good yields, respectively (Table 3, entries 5–6). However,
phenyliodine(III) dicarboxylates 2e and 2f gave inferior results,
and the expected products 4v and 4w were obtained in low
yields (Table 3, entries 7–8). This could be attributed to steric
hindrance or slower decarboxylation process.[10b] Additionally,
no methylated product 4a or trifluoromethylated product 4x
was detected, but the substrate 1a was decomposed in the
presence of MeSO2Na and PhI(O2CCF3)2 (Table 3, entry 9). Be-
To generalize the substrate scope of our method, various
quinoxalin-2(1H)-one derivatives were screened, and the results
are listed in Table 2. Initially, a series of N-protected quinoxalin-
2(1H)-ones were carried out under the optimal reaction condi-
tions. To our delight, these transformations proceeded effec-
tively and provided the anticipated products in excellent yields
(4a–4e). Unfortunately, N-free protected quinoxalin-2(1H)-one
exhibited a poor result, affording the expected product in low
yield (4f). Subsequently, a variety of quinoxalin-2(1H)-ones
bearing either electron-rich or electron-deficient substituents
matched the reaction well to provide the corresponding prod-
ucts (4g–4k) in moderate to excellent yields (56–90 %). Gener-
ally, the substrate bearing an electron-donating group (-CH3)
afforded a high yield (4g). But the one bearing electron-with-
drawing group (-CN) showed a bit poor result, giving the ex-
pected product in a moderate yield (4i). Notably, when disubsti-
tuted quinoxalin-2(1H)-ones were chosen as substrates, the
target products were obtained in moderate to good yields
(4l–4p). Moreover, 2H-benzo[b][1,4]oxazin-2-one (1q) was also
tolerated in this reaction system, providing the expected prod-
uct in an acceptable yield (4q). It should be point out that our
protocol could be applied to the quinoxalinone derivative 1r
under the optimal reaction conditions, and the corresponding
product was achieved in 63 % yield (4r).
Table 3. Products from various combinations of R3SO2Na and PhI(O2CR4)2.[a]
Table 2. Substrate scope.[a,b]
Entry
R3SO2Na
(1.5 equiv.)
PhI(O2CR4)2
(2.5 equiv.)
4 Yield
4′ Yield
[%][b]
[%][b]
1
2
2b: R3=Et
3a: R4 = Me
3b: R4 = Et
3b: R4 = Et
3b: R4 = Et
3c: R4 = nPr
3d: R4 = iPr
3e: R4 = tBu
3f: R4 = Ph
3g: R4 = CF3
3a: R4 = Me
3b: R4 = Et
3f: R4 = Ph
47 (4a)
71 (4s)
75 (4s)
60 (4s)
81 (4t)
75 (4u)
28 (4v)
46 (4w)
N. D.
34 (4s)
11 (4a)
6 (4a)
trace
trace
trace
trace
trace
N. D.
7 (4x)
–
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2a: R3 = Me
2g: R3 = CF3
2b: R3 = Et
2f: R3 = Ph
3[c]
4[d]
5[c]
6[c]
7[c]
8[c]
9
10
11
12
N. D.
82 (4s)
53 (4w)
[a] Unless specifically noted otherwise, reaction conditions: substrates 1a–1r
(0.3 mmol), 2a (0.45 mmol), 3a (0.75 mmol) and solvent (3 mL) at 60 °C under
an argon atmosphere. [b] Yield of isolated product.
–
[a] Unless specifically noted otherwise, reaction conditions: 1a (0.3 mmol), 2
(0.45 mmol), 3 (0.75 mmol) and solvent (3 mL), stirred at 60 °C under an
argon atmosphere. [b] Yield of isolated product. [c] 2a (0.3 mmol, 1.0 equiv.).
[d] 2a (0.15 mmol, 0.5 equiv.).
To enlarge the scope of chain alkyl groups, we firstly re-
placed MeSO2Na (2a) with EtSO2Na (2b) under the above opti-
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sides, only 7 % yield of 4x was received when CF3SO2Na and by LC-MS (Scheme 3, Equation 2). These results indicated that
PhI(O2CMe)2 were introduced into the reaction system (Table 3, alkyl radical was involved in this transformation.
entry 10). Notably, the sole product could be obtained in higher
yield when R3 is same as R4 in the combination of R3SO2Na and
PhI(O2CR4)2 (Table 3, entries 11–12).
To probe a primary mechanism of the C–H alkylation reac-
tion, a radical trapping experiment was carried out. When
MeSO2Na (2a, 2.5 equiv.) and PhI(O2CEt)2 (3b, 2.5 equiv.) were
employed, the ethylated product 4s and methylated product
In order to further verify the hypothetical intermediate, an
additional experiment was carried out. A mixture of MeSO2Na
(1.0 equiv.) and PhI(O2CMe)2 (1.0 equiv.) in CDCl3 was stirred at
room temperature for 1 h. After that, the intermediate
PhI(O2CMe)O2SMe was formed via anion exchange between
MeSO2Na and PhI(O2CMe)2 (Figure 1).[22]
Based on the above radical trapping and additional experi-
4a were obtained in 73 % yield and 11 % yield, respectively mental results, and previous reports,[7h,14j–14k] a possible mecha-
(Scheme 3, Equation 1). In contrast, when 1.0 equivalent of nism of this alkylation reaction is depicted in Scheme 4. Initially,
TEMPO as the radical-trapping reagent was introduced into the anion exchange between MeSO2Na and PhI(O2CR)2 provides
reaction system, the desired reaction was partly suppressed. the high reactive intermediate PhI(O2CR)O2SMe (A).[22] Then,
The yield of ethylated product 4s was dropped to 47 %, and I-radical B and Me radical (C) are generated via decomposition
the yield of methylated product 4a decreased to trace amount. of the intermediate A, releasing SO2 simultaneously.[17a,23] Next,
Meanwhile, the starting material 1a was recovered in 41 % I-radical B integrates quinoxalin-2(1H)-one (1a) to afford the
yield, and the TEMPO-alkyl adducts 5a and 6a were detected carbonyl group-coordinated iodine radical species D, which un-
Scheme 3. Radical trapping experiment.
Figure 1. 1H NMR spectrum of the intermediate PhI(O2CMe)O2SMe.
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Scheme 4. Proposed reaction mechanism.
lets. The starting materials were purchased from Energy Chemical
or Shanghai Shaoyuan Co. Ltd. and used without further purifica-
tion. Some reactions were tried on microreactor (Chemtrix BV, Kilo
Flow, Labtrix Start or Protrix) in order to obtain the product in a
better yield during the preparation of the substrates. Solvents were
dried and purified according to the procedure from “Purification of
Laboratory Chemicals book”. The residual crude was purified by
flash column chromatography on silica gel to obtain the corre-
sponding product in actual isolated yield.
dergoes a decarboxylation process to form the aminyl radical
intermediate E and extrude CO2 as well as PhI.[7b,10b,24] In addi-
tion, an alternative route to the intermediate E is also feasible,
namely, alkyl radical B′ which is generated form the decomposi-
tion of I-radical B attacks the substrate 1a to furnish intermedi-
ate E. Then, intermediate E leads to the target product G
through oxidation and deprotonation. Additionally, Me radical
(C) is trapped by 1a to afford the aminyl radical intermediate F.
Subsequently, the methylated product 4a is obtained from the
intermediate F via sequential oxidation and deprotonation pro-
cedures. In this transformation, both sodium alkylsulfinates and
phenyliodine(III) dicarboxylates act as the alkyl sources.
Preparation of the Substrates: The substrates (1a–1p) in Table 2
were synthesized according to the procedures described in the pre-
vious literatures.[16a,16c,16e,19a,25] The substrate 2H-benzo[b][1,4]-
oxazin-2-one (1q) in Table 2 was prepared according to the re-
ported procedures.[26] The substrate 1-methyl-5,6-diphenylpyrazin-
2(1H)-one (1r) in Table 2 was prepared from 5,6-diphenylpyrazin-
2(1H)-one and iodomethane.
Conclusions
In summary, we have described a practical and convenient ap-
proach for the direct C–H alkylation in particular the methyl-
ation of quinoxalinones utilizing readily available sodium alkyl-
sulfinates and phenyliodine(III) dicarboxylates as the alkyl sour-
ces without catalyst. The phenyliodine(III) dicarboxylates are
adopted as both the oxidants and alkyl sources in this modified
Minisci reaction. Additionally, this protocol exhibits good func-
tional group tolerance, providing a variety of 3-alkylquinoxalin-
ones in moderate to excellent yields. Predictably, this method
would provide a facile way for the synthesis of pharmaceuti-
cal molecules containing 3-alkylquinoxalinone skeletons.
Preparation of the Phenyliodine(III) Dicarboxylates: The phen-
yliodine(III) dicarboxylates (3b–3f) in Table 3 were prepared
according to the procedures described in the previous litera-
tures.[10b–10c,27] In a round-bottom flask was equipped with a mag-
netic stir bar, aliphatic(aromatic) carboxylic acid (2.5 equiv.),
PhI(O2CMe)2 (1.0 equiv.) and CHCl3 (0.2
M), then the flask was
heated in 50 °C under reduced pressure (about 35 Torr) until com-
plete dryness. The residual solid was stirred with petroleum ether
(PE) for 30 minutes, filtered and washed with PE to afford the
phenyliodine(III) dicarboxylates (3), which could be used directly in
the following reaction without purification.
General Procedures for the Direct C–H Alkylation of Quinoxalin-
ones
Experimental Section
General Methods and Materials: All reactions involving air- and
General Procedures for Product 4a–4r: To a Schlenk tube charged
with a magnetic stirring bar, substrates (1a–1r, 0.3 mmol), MeSO2Na
(0.45 mmol) and PhI(O2CMe)2 (0.75 mmol) were added successively
moisture-sensitive reagents were carried out under an argon atmos-
1
phere. H and 13C NMR spectra were recorded on Bruker AC-P 400 and the Schlenk tube was purged with argon for three times. Subse-
spectrometer (400 MHz for 1H and 100 MHz for 13C) in CDCl3 or
[D6]DMSO. Chemical shifts (δ) were measured in ppm. Coupling
constants, J, are reported in Hertz. High-resolution mass spectra
(HRMS) were recorded on Bruker micro TOF-Q mass spectrometer
using ESI-Q-TOF reflection experiments. Melting points (uncor-
rected) were afforded on Shanghai Inesa WRS-3 melting point appa-
ratus. IR spectra were recorded on Bruker ALPHA Fourier transform
quently, anhydrous benzotrifluoride (3 mL) was added via syringe
and the mixture was stirred at 60 °C under an argon atmosphere in
an oil bath until the substrates were consumed (8 h–12 h, moni-
tored by TLC). After that, the reaction mixture was cooled to room
temperature, and the solvent was removed under reduced pressure.
Then, the residue crude was purified by flash column chromatogra-
phy on silica gel to afford the corresponding alkylated product (4a–
infrared spectrophotometer using a thin film supported on KBr pel- 4r).
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General Procedures for Product 4s–4w: To a Schlenk tube
charged with a magnetic stirring bar, substrate 1a (0.3 mmol), so-
Iodobenzene Diisobutyrate (3d): Reaction of isobutyric acid with
PhI(O2CMe)2 was carried out according to the general procedure to
dium alkylsulfinates 2 (0.3 mmol) and phenyliodine(III) dicarboxyl- afford the phenyliodine(III) dicarboxylates 3d in 83 % yield, white
ates 3 (0.75 mmol) were added successively and the Schlenk tube
was purged with argon for three times. Subsequently, anhydrous
benzotrifluoride (3 mL) was added via syringe and the mixture was
stirred at 60 °C under an argon atmosphere in an oil bath until the
substrate was consumed (8 h–12 h, monitored by TLC). After that,
the reaction mixture was cooled to room temperature, and the sol-
vent was removed under reduced pressure. Then, the residue crude
was purified by flash column chromatography on silica gel to afford
the corresponding alkylated product (4s–4w).
solid, m.p. 102–103 °C. 1H NMR (400 MHz, CDCl3) δ: 8.05 (d, J =
7.2 Hz, 2H), 7.58 (t, J = 7.6 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H), 2.54–2.47
(m, 2H), 1.08 (d, J = 6.8 Hz, 12H). NMR data matched previously
reported values.[10c]
Iodobenzene Dipivalate (3e): Reaction of pivalic acid with
PhI(O2CMe)2 was carried out according to the general procedure to
afford the phenyliodine(III) dicarboxylates 3e in 66 % yield, white
solid, m.p. 111–113 °C. 1H NMR (400 MHz, CDCl3) δ: 8.01 (d, J =
7.6 Hz, 2H), 7.56 (t, J = 7.2 Hz, 1H), 7.48 (t, J = 7.2 Hz, 2H), 1.12 (s,
18H). NMR data matched previously reported values.[10c]
Radical Trapping Experiments: To a Schlenk tube charged with a
magnetic stirring bar, 1-methylquinoxalin-2(1H)-one (1a, 0.3 mmol),
MeSO2Na (2a, 0.75 mmol) and PhI(O2CEt)2 (3b, 0.75 mmol) were
added successively and the Schlenk tube was purged with argon
for three times. Subsequently, anhydrous benzotrifluoride (3 mL)
was added via syringe and the mixture was stirred at 60 °C in an
oil bath under an argon atmosphere for 10 h. The target products
4s and 4a were respectively obtained in 73 % yield and 11 % yield
after purification through flash column chromatography on silica
gel (Scheme 3, Equation 1).
Iodobenzene Dibenzoate (3f): Reaction of benzoic acid with
PhI(O2CMe)2 was carried out according to the general procedure to
afford the phenyliodine(III) dicarboxylates 3f in 93 % yield, white
solid, m.p. 153–155 °C. 1H NMR (400 MHz, CDCl3) δ: 8.24 (d, J =
7.6 Hz, 2H), 7.93 (d, J = 7.6 Hz, 4H), 7.63–7.48 (m, 5H), 7.37 (t, J =
7.6 Hz, 4H). NMR data matched previously reported values.[10c]
Characterization of the Products
1,3-Dimethylquinoxalin-2(1H)-one (4a): The crude product was
purified by flash column chromatography on silica gel (petroleum
ether/ethyl acetate = 2:1 as an eluent) to afford the product 4a
(88 % yield, 46.2 mg) as pale yellow solid, m.p. 78–80 °C. IR (KBr)
In the control experiment, 1-methylquinoxalin-2(1H)-one (1a,
0.3 mmol), MeSO2Na (2a, 0.75 mmol), PhI(O2CEt)2 (3b, 0.75 mmol)
and TEMPO (0.3 mmol) were added successively and the Schlenk
tube was purged with argon for three times. Subsequently, anhy-
drous benzotrifluoride (3 mL) was added via syringe and the mix-
ture was stirred at 60 °C in an oil bath under an argon atmosphere
for 10 h. The ethylated product 4s was obtained in 47 % yield,
the methylated product 4a was received in trace amount, and the
substrate 1a was recovered in 41 % yield after purification through
flash column chromatography on silica gel. Meanwhile, the TEMPO-
Et adduct 5a was detected by LC-MS (HRMS (ESI): m/z calcd. for
νm(cm–1): 3030, 1649, 1595, 1469, 1413, 1329, 1213, 1095, 757, 453;
˜
1H NMR (400 MHz, CDCl3) δ: 7.81 (d, J = 7.2 Hz, 1H), 7.53 (t, J =
7.2 Hz, 1H), 7.36–7.29 (m, 2H), 3.71 (s, 3H), 2.60 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ: 158.40, 155.21, 133.26, 132.67, 129.58, 129.46,
123.61, 113.61, 29.05, 21.63; HRMS (ESI): m/z calcd. for C10H11N2O+
[M + H]+ 175.0866, found 175.0865. NMR data matched previously
reported values.[28]
1-Ethyl-3-methylquinoxalin-2(1H)-one (4b): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4b (80 % yield, 45.3 mg) as white solid, m.p. 87–88 °C. IR (KBr)
C
11H24NO+ [M + H]+ 186.1852, found 186.1853), and the TEMPO-Me
adduct 6a was also detected by LC-MS (HRMS (ESI): m/z calcd. for
C10H22NO+ [M + H]+ 172.1696, found 172.1701) (Scheme 3, Equa-
tion 2).
νm(cm–1): 2968, 1652, 1597, 1463, 1365, 1200, 1102, 759, 457; 1H
˜
NMR (400 MHz, CDCl3) δ: 7.81 (d, J = 8 Hz, 1H), 7.53 (t, J = 7.6 Hz,
1H), 7.35–7.31 (m, 2H), 4.32 (q, J = 7.2 Hz, 2H), 3.60 (s, 3H), 1.38 (t,
J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ: 158.42, 154.66, 132.96,
132.14, 129.70, 129.54, 123.39, 113.45, 37.25, 21.51, 12.40; HRMS
(ESI): m/z calcd. for C11H13N2O+ [M + H]+ 189.1022, found 189.1023.
Anion Exchange Experiment: To a Schlenk tube charged with a
magnetic stirring bar, MeSO2Na (2a, 0.15 mmol) and PhI(O2CMe)2
(3b, 0.15 mmol) were added successively and the Schlenk tube was
purged with argon for three times. Subsequently, anhydrous CDCl3
(1 mL) was added via syringe and the mixture was stirred at room
temperature under an argon atmosphere for 1 h. After that, the
intermediate PhI(O2CMe)O2SMe (A) was detected by 1H NMR (Fig-
ure 1).
1-Benzyl-3-methylquinoxalin-2(1H)-one (4c): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4c (84 % yield, 63.4 mg) as yellow solid, m.p. 93–95 °C. IR (KBr)
νm(cm–1): 3037, 2926, 1650, 1599, 1449, 1307, 1185, 978, 757, 694,
˜
Characterization of the Phenyliodine(III) Dicarboxylates
1
459; H NMR (400 MHz, CDCl3) δ: 7.83 (d, J = 8 Hz, 1H), 7.41 (t, J =
7.6 Hz, 1H), 7.34–7.24 (m, 7H), 5.51 (s, 2H), 2.68 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ: 158.52, 155.29, 135.26, 132.92, 132.59, 129.62,
129.57, 128.95, 127.71, 126.88, 123.70, 114.47, 45.91, 21.76; HRMS
(ESI): m/z calcd. for C16H15N2O+ [M + H]+ 251.1179, found 251.1183.
NMR data matched previously reported values.[28b]
Iodobenzene Dipropionate (3b): Reaction of propionic acid with
PhI(O2CMe)2 was carried out according to the general procedure to
afford the phenyliodine(III) dicarboxylates 3b in 71 % yield, white
solid, m.p. 68–69 °C. 1H NMR (400 MHz, CDCl3) δ: 8.08 (d, J = 7.6 Hz,
2H), 7.59 (t, J = 7.2 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H), 2.27 (q, J =
7.6 Hz, 4H), 1.07 (t, J = 7.6 Hz, 6H). NMR data matched previously
reported values.[10c]
Methyl 2-(3-Methyl-2-oxoquinoxalin-1(2H)-yl)acetate (4d): The
crude product was purified by flash column chromatography on
silica gel (petroleum ether/ethyl acetate = 2:1 as an eluent) to afford
the product 4d (80 % yield, 55.7 mg) as pale yellow solid, m.p. 128–
Iodobenzene Dibutyrate (3c): Reaction of butyric acid with
PhI(O2CMe)2 was carried out according to the general procedure to
afford the derived phenyliodine(III) dicarboxylates 3c in 84 % yield,
129 °C. IR (KBr) νm(cm–1): 3010, 2959, 1737, 1653, 1600, 1465, 1424,
˜
1
1
white solid, m.p. 79–80 °C. H NMR (400 MHz, CDCl3) δ: 8.08 (d, J = 1365, 1237, 1189, 974, 761, 461; H NMR (400 MHz, CDCl3) δ: 7.83
7.6 Hz, 2H), 7.59 (t, J = 7.6 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H), 2.24 (t,
J = 7.6 Hz, 4H), 1.57 (q, J = 7.6 Hz, 4H), 0.88 (t, J = 7.6 Hz, 6H). NMR
data matched previously reported values.[10c]
(d, J = 8 Hz, 1H), 7.50 (t, J = 7.2 Hz, 1H), 7.35 (t, J = 7.2 Hz, 1H), 7.06
(d, J = 8 Hz, 1H), 5.05 (s, 2H), 3.78 (s, 3H), 2.62 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ: 165.34, 155.88, 152.43, 130.42, 130.02, 127.51,
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121.67, 110.71, 50.57, 41.07, 19.20; HRMS (ESI): m/z calcd. for J = 2 Hz, 1H), 7.46 (dd, J = 1.6 Hz, J = 8.8 Hz, 1H), 7.21 (d, J = 8.4 Hz,
C12H13N2O3 [M + H]+ 233.0921, found 233.0925.
1H), 3.68 (s, 3H), 2.59 (s, 3H); 13C NMR (100 MHz, CDCl3) δ: 159.89,
154.82, 133.18, 131.95, 129.53, 128.84, 114.73, 29.21, 21.70; HRMS
(ESI): m/z calcd. for C10H10ClN2O+ [M + H]+ 209.0476, found
209.0480.
+
1-Allyl-3-methylquinoxalin-2(1H)-one (4e): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4e (85 % yield, 51.3 mg) as yellow solid, m.p. 54–55 °C. IR (KBr)
1,3-Dimethyl-6-(trifluoromethyl)quinoxalin-2(1H)-one (4k): The
νm(cm–1): 3079, 3004, 2924, 1657, 1598, 1437, 1351, 1187, 994, 934, crude product was purified by flash column chromatography on
˜
1
755, 462; H NMR (400 MHz, CDCl3) δ: 7.81 (d, J = 7.6 Hz, 1H), 7.49
(t, J = 8 Hz, 1H), 7.34–7.26 (m, 2H), 5.99–5.89 (m, 1H), 5.27 (d, J =
10.4 Hz, 1H), 5.16 (d, J = 17.2 Hz, 1H), 4.91 (d, J = 8 Hz, 2H), 2.61 (s,
silica gel (petroleum ether/ethyl acetate = 2:1 as an eluent) to afford
the product 4k (65 % yield, 47.4 mg) as yellow solid, m.p. 148–
150 °C. IR (KBr) νm(cm–1): 3043, 2961, 1655, 1612, 1510, 1459, 1333,
˜
3H); 13C NMR (100 MHz, CDCl3) δ: 158.44, 154.75, 132.80, 132.45, 1295, 1221, 1164, 1120, 1080, 848, 727, 618, 466; 1H NMR (400 MHz,
130.61, 129.52, 129.50, 123.59, 118.05, 114.18, 44.47, 21.57; HRMS CDCl3) δ: 7.91 (d, J = 8.4 Hz, 1H), 7.57 (d, J = 8 Hz, 1H), 7.54 (s, 1H),
(ESI): m/z calcd. for C12H13N2O+ [M + H]+ 201.1022, found 201.1020.
3.74 (s, 3H), 2.63 (s, 3H); 13C NMR (100 MHz, CDCl3) δ: 161.18, 154.86,
134.32, 133.31, 131.14 (q, J = 32.6 Hz), 130.18, 123.67 (q, J = 271 Hz),
120.13 (d, J = 3.5 Hz), 110.06 (d, J = 4.1 Hz), 29.24, 21.83; HRMS (ESI):
m/z calcd. for C11H10F3N2O+ [M + H]+ 243.0740, found 243.0747.
3-Methylquinoxalin-2(1H)-one (4f): The crude product was puri-
fied by flash column chromatography on silica gel (petroleum
ether/ethyl acetate = 1:1 as an eluent) to afford the product 4f
(47 % yield, 22.4 mg) as white solid, m.p. 238–240 °C. IR (KBr)
1,3,6,7-Tetramethylquinoxalin-2(1H)-one (4l): The crude product
νm(cm–1): 3099, 3009, 2964, 2895, 2842, 1666, 1566, 1493, 1431, was purified by flash column chromatography on silica gel (petro-
˜
1349, 1193, 891, 755, 590, 469; 1H NMR (400 MHz, [D6]DMSO) δ:
12.31 (s, 1H), 7.68 (d, J = 7.6 Hz, 1H), 7.46 (t, J = 7.6 Hz, 1H), 7.25 (t,
leum ether/ethyl acetate = 1:1 as an eluent) to afford the product
4l (90 % yield, 54.6 mg) as white solid, m.p. 163–165 °C. IR (KBr)
˜
J = 8.4 Hz, 2H), 2.39 (s, 3H); 13C NMR (100 MHz, [D6]DMSO) δ: 159.66, νm(cm–1): 3346, 2962, 2921, 1646, 1463, 1353, 1265, 1092, 1024, 805,
155.38, 132.39, 132.12, 129.73, 128.32, 123.45, 115.67, 20.97; HRMS 538; 1H NMR (400 MHz, CDCl3) δ: 7.44 (s, 1H), 6.95 (s, 1H), 3.57 (s,
(ESI): m/z calcd. for C9H9N2O+ [M + H]+ 161.0709, found 161.0710.
3H), 2.48 (s, 3H), 2.31 (s, 3H), 2.25 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ: 156.96, 155.23, 139.21, 132.40, 131.19, 131.03, 129.50, 114.16,
28.92, 21.53, 20.26, 19.19; HRMS (ESI): m/z calcd. for C12H15N2O+
[M + H]+ 203.1179, found 203.1180.
1,3,7-Trimethylquinoxalin-2(1H)-one (4g): The crude product was
purified by flash column chromatography on silica gel (petroleum
ether/ethyl acetate = 2:1 as an eluent) to afford the product 4g
(90 % yield, 51.2 mg) as white solid, m.p. 129–130 °C. IR (KBr)
6,7-Difluoro-1,3-dimethylquinoxalin-2(1H)-one (4m): The crude
νm(cm–1): 3063, 2920, 1649, 1605, 1456, 1300, 1216, 1105, 1025, 826, product was purified by flash column chromatography on silica gel
˜
767, 521; 1H NMR (400 MHz, CDCl3) δ: 7.66 (d, J = 8 Hz, 1H), 7.14
(d, J = 8 Hz, 1H), 7.07 (s, 1H), 3.67 (s, 3H), 2.57 (s, 3H), 2.50 (s, 3H);
13C NMR (100 MHz, CDCl3) δ: 156.98, 155.29, 140.22, 133.07, 130.78,
(petroleum ether/ethyl acetate = 2:1 as an eluent) to afford the
product 4m (66 % yield, 41.6 mg) as light yellow solid, m.p. 205–
207 °C. IR (KBr) νm(cm–1): 3048, 1655, 1604, 1514, 1463, 1370, 1268,
˜
1
129.05, 124.85, 113.75, 28.95, 22.02, 21.51; HRMS (ESI): m/z calcd. 1098, 900, 771, 500; H NMR (400 MHz, CDCl3) δ: 7.61 (t, J = 10 Hz,
for C11H12N2NaO+ [M + Na]+ 211.0842, found 211.0843.
J = 8.4 Hz, 1H), 7.10 (dd, J = 4 Hz, J = 7.2 Hz, 1H), 3.66 (s, 3H), 2.57
(s, 3H); 13C NMR (100 MHz, CDCl3) δ: 159.01, 154.76, 150.96 (dd, J =
14.2 Hz, J = 251 Hz), 146.60 (dd, J = 13.9 Hz, J = 245.4 Hz), 130.37
(d, J = 8.8 Hz), 128.89 (dd, J = 2.8 Hz, J = 9.3 Hz), 117.15 (dd, J =
1.8 Hz, J = 18 Hz), 102.11 (d, J = 23 Hz), 29.57, 21.58; HRMS (ESI):
m/z calcd. for C10H9F2N2O+ [M + H]+ 211.0677, found 211.0680.
7-Fluoro-1,3-dimethylquinoxalin-2(1H)-one (4h): The crude
product was purified by flash column chromatography on silica gel
(petroleum ether/ethyl acetate = 2:1 as an eluent) to afford the
product 4h (77 % yield, 44.7 mg) as white solid, m.p. 177–179 °C.
IR (KBr) νm(cm–1): 3072, 2960, 1662, 1615, 1458, 1356, 1313, 1225,
˜
1098, 995, 874, 836, 627, 481; 1H NMR (400 MHz, CDCl3) δ: 7.77 (dd, 6,7-Dichloro-1,3-dimethylquinoxalin-2(1H)-one (4n): The crude
J = 6 Hz, J = 8.8 Hz, 1H), 7.07–6.96 (m, 2H), 3.66 (s, 3H), 2.57 (s, 3H);
product was purified by flash column chromatography on silica gel
(petroleum ether/ethyl acetate = 1:1 as an eluent) to afford the
13C NMR (100 MHz, CDCl3) δ: 164.10, 161.62, 156.10 (d, J = 213.5 Hz),
134.62 (d, J = 11.4 Hz), 131.26 (d, J = 10.4 Hz), 129.37 (d, J = 2 Hz), product 4n (50 % yield, 36.5 mg) as yellow solid, m.p. 217–219 °C.
111.31 (d, J = 23.2 Hz), 100.56 (d, J = 27.7 Hz), 29.29, 21.45; HRMS
IR (KBr) νm(cm–1): 3092, 2927, 1660, 1595, 1552, 1466, 1407, 1297,
˜
(ESI): m/z calcd. for C10H10FN2O+ [M + H]+ 193.0772, found 193.0776.
1207, 1113, 890, 768, 634, 505; 1H NMR (400 MHz, CDCl3) δ: 7.87 (s,
1H), 7.38 (s, 1H), 3.66 (s, 3H), 2.58 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ: 160.00, 154.58, 133.58, 132.65, 131.72, 130.32, 127.32, 115.11,
29.31, 21.70; HRMS (ESI): m/z calcd. for C10H9Cl2N2O+ [M + H]+
243.0086, found 243.0087.
2,4-Dimethyl-3-oxo-3,4-dihydroquinoxaline-6-carbonitrile (4i):
The crude product was purified by flash column chromatography
on silica gel (petroleum ether/ethyl acetate = 1:1 as an eluent) to
afford the product 4i (56 % yield, 34.1 mg) as yellow solid, m.p.
202–204 °C. IR (KBr) νm(cm–1): 3056, 2921, 2224, 1657, 1605, 1557, 6-Bromo-1,3,7-trimethylquinoxalin-2(1H)-one (4o): The crude
˜
1499, 1461, 1429, 1347, 1099, 820, 507; 1H NMR (400 MHz, CDCl3) product was purified by flash column chromatography on silica gel
δ: 8.09 (d, J = 1.2 Hz, 1H), 7.76 (dd, J = 1.2 Hz, J = 8.8 Hz, 1H), 7.39
(d, J = 8.8 Hz, 1H), 3.73 (s, 3H), 2.61 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ: 160.44, 154.74, 137.14, 133.23, 132.71, 131.96, 118.81,
116.62, 105.90, 29.70, 21.75; HRMS (ESI): m/z calcd. for C11H10N3O+
[M + H]+ 200.0818, found 200.0818.
(petroleum ether/ethyl acetate = 2:1 as an eluent) to afford the
product 4o (75 % yield, 60.4 mg) as white solid, m.p. 166–167 °C.
IR (KBr) νm(cm–1): 3451, 2917, 1648, 1602, 1552, 1483, 1454, 1349,
˜
1
1214, 1010, 899, 621, 449; H NMR (400 MHz, CDCl3) δ: 7.61 (s, 1H),
7.46 (s, 1H), 3.64 (s, 3H), 2.56 (s, 3H), 2.46 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ: 158.80, 154.81, 133.29, 132.14, 131.76, 130.53, 126.25,
117.14, 29.13, 22.32, 21.68; HRMS (ESI): m/z calcd. for C11H12BrN2O+
[M + H]+ 267.0128, found 267.0129.
6-Chloro-1,3-dimethylquinoxalin-2(1H)-one (4j): The crude prod-
uct was purified by flash column chromatography on silica gel (pe-
troleum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4j (69 % yield, 43.4 mg) as light yellow solid, m.p. 137–138 °C. IR
7-Bromo-1,3,6-trimethylquinoxalin-2(1H)-one (4p): The crude
(KBr) νm(cm–1): 3082, 2926, 1664, 1599, 1455, 1419, 1374, 1323, product was purified by flash column chromatography on silica gel
˜
1206, 1100, 889, 804, 729, 500; 1H NMR (400 MHz, CDCl3) δ: 7.76 (d, (petroleum ether/ethyl acetate = 2:1 as an eluent) to afford the
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product 4p (73 % yield, 58.2 mg) as white solid, m.p. 189–191 °C.
123.37, 113.44, 31.18, 29.01, 20.18; HRMS (ESI): m/z calcd. for
IR (KBr) νm(cm–1): 3044, 2948, 1652, 1599, 1554, 1456, 1420, 1353, C12H15N2O+ [M + H]+ 203.1179, found 203.1180.
˜
1296, 1111, 879, 767, 651, 498; 1H NMR (400 MHz, CDCl3) δ: 7.92 (s,
3-(tert-Butyl)-1-methylquinoxalin-2(1H)-one (4v): The crude
1H), 7.12 (s, 1H), 3.65 (s, 3H), 2.56 (s, 3H), 2.52 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ: 158.60, 154.99, 139.59, 132.42, 132.33, 131.83,
118.96, 115.06, 29.09, 23.61, 21.60; HRMS (ESI): m/z calcd. for
C11H12BrN2O+ [M + H]+ 267.0128, found 267.0124.
product was purified by flash column chromatography on silica gel
(petroleum ether/ethyl acetate = 2:1 as an eluent) to afford the
product 4v (28 % yield, 18.2 mg) as yellow solid, m.p. 64–65 °C. IR
(KBr) νm(cm–1): 3438, 2957, 1649, 1592, 1468, 1357, 1315, 1157,
˜
1078, 970, 756, 533; 1H NMR (400 MHz, CDCl3) δ: 7.83 (dd, J = 8 Hz,
J = 8 Hz, 1H), 7.52–7.48 (m, 1H), 7.33–7.26 (m, 2H), 3.67 (s, 3H), 1.49
(s, 9H); 13C NMR (100 MHz, CDCl3) δ: 165.29, 153.73, 133.31, 132.17,
130.11, 129.51, 123.17, 113.25, 39.46, 28.75, 27.87; HRMS (ESI): m/z
calcd. for C13H17N2O+ [M + H]+ 217.1335, found 217.1339.
3-Methyl-2H-benzo[b][1,4]oxazin-2-one (4q): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 10:1 as an eluent) to afford the product
4q (45 % yield, 21.8 mg) as white solid, m.p. 92–93 °C. IR (KBr)
νm(cm–1): 3027, 2926, 1728, 1607, 1575, 1459, 1370, 1281, 1218,
˜
1089, 958, 757, 594, 464; 1H NMR (400 MHz, CDCl3) δ: 7.61 (d, J =
8 Hz, 1H), 7.48 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 7.6 Hz, 1H), 7.28 (d, J =
8.4 Hz, 1H), 2.58 (s, 3H); 13C NMR (100 MHz, CDCl3) δ: 155.15, 153.22,
146.57, 131.12, 130.50, 128.61, 125.44, 116.38, 21.32; HRMS (ESI):
1-Methyl-3-phenylquinoxalin-2(1H)-one (4w): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4w (53 % yield, 37.6 mg) as light yellow solid, m.p. 129–131 °C. IR
+
m/z calcd. for C9H8NO2 [M + H]+ 162.0550, found 162.0551.
(KBr) νm(cm–1): 3056, 2928, 1644, 1594, 1462, 1295, 1233, 1177, 952,
˜
1
753, 691, 539, 460; H NMR (400 MHz, CDCl3) δ: 8.31–8.29 (m, 2H),
1,3-Dimethyl-5,6-diphenylpyrazin-2(1H)-one (4r): The crude
product was purified by flash column chromatography on silica gel
(petroleum ether/ethyl acetate = 1:1 as an eluent) to afford the
product 4r (63 % yield, 52.4 mg) as white solid, m.p. 145–147 °C. IR
7.92 (d, J = 8 Hz, 1H), 7.54 (t, J = 8 Hz, 1H), 7.47 (t, J = 3.2 Hz, 3H),
7.36–7.29 (m, 2H), 3.74 (s, 3H); 13C NMR (100 MHz, CDCl3) δ: 154.66,
154.10, 136.06, 133.33, 133.06, 130.41, 130.28, 129.53, 128.05,
123.68, 113.55, 29.26; HRMS (ESI): m/z calcd. for C15H12N2NaO+ [M
+ Na]+ 259.0842, found 259.0847. NMR data matched previously
reported values.[16]
(KBr) νm(cm–1): 3447, 3057, 2994, 2947, 1643, 1581, 1488, 1415,
˜
1
1375, 1275, 1158, 967, 770, 705, 509; H NMR (400 MHz, CDCl3) δ:
7.38–7.35 (m, 3H), 7.21–7.19 (m, 2H), 7.13 (s, 5H), 3.32 (s, 3H), 2.60
(s, 3H); 13C NMR (100 MHz, CDCl3) δ: 156.04, 155.28, 137.90, 136.55,
132.56, 132.44, 130.14, 129.33, 129.29, 128.97, 127.77, 126.89, 33.97,
21.10; HRMS (ESI): m/z calcd. for C18H17N2O+ [M + H]+ 277.1335,
found 277.1332.
Conflicts of interest
The authors declare no conflict of interest.
3-Ethyl-1-methylquinoxalin-2(1H)-one (4s): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4s (82 % yield, 46.3 mg) as yellow solid, m.p. 96–97 °C. IR (KBr)
Acknowledgments
We acknowledge the financial support from the National
Natural Science Foundation of China (Grant No. 21776056), the
Natural Science Foundation of Hebei Province (CN) (Grant
No. B2018202253) and the Program for the Top Young Innova-
tive Talents of Hebei Province (CN) (Grant No. BJ2017010).
νm(cm–1): 3036, 2974, 2929, 1645, 1597, 1464, 1373, 1315, 1186,
˜
1098, 961, 756, 632, 460; 1H NMR (400 MHz, CDCl3) δ: 7.84 (d, J =
8 Hz, 1H), 7.54–7.50 (m, 1H), 7.36–7.29 (m, 2H), 3.71 (s, 3H), 2.98 (q,
J = 7.2 Hz, 2H), 1.34 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ:
161.99, 154.87, 133.10, 132.77, 129.65, 129.48, 123.50, 113.53, 28.99,
27.54, 10.83; HRMS (ESI): m/z calcd. for C11H13N2O+ [M + H]+
189.1022, found 189.1029. NMR data matched previously reported
values.[28b]
Keywords: Minisci-type reactions · Quinoxalinones ·
Sodium alkylsulfinates · Phenyliodine(III) dicarboxylates ·
Catalyst-free reaction
1-Methyl-3-propylquinoxalin-2(1H)-one (4t): The crude product
was purified by flash column chromatography on silica gel (petro-
leum ether/ethyl acetate = 2:1 as an eluent) to afford the product
4t (81 % yield, 49.2 mg) as light yellow solid, m.p. 79–81 °C. IR (KBr)
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νm(cm–1): 3041, 2961, 2874, 1642, 1596, 1463, 1413, 1373, 1309,
˜
1180, 1086, 996, 757, 705, 456; 1H NMR (400 MHz, CDCl3) δ: 7.83
(dd, J = 0.8 Hz, J = 8 Hz, 1H), 7.54–7.50 (m, 1H), 7.35–7.30 (m, 2H),
3.70 (s, 3H), 2.92 (t, J = 7.6 Hz, 2H), 1.83 (q, J = 7.6 Hz, 2H), 1.05 (t,
J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ: 161.16, 154.92, 133.10,
132.72, 129.61, 129.50, 123.51, 113.54, 36.26, 29.02, 20.24, 14.10;
HRMS (ESI): m/z calcd. for C12H15N2O+ [M + H]+ 203.1179, found
203.1181.
3-Isopropyl-1-methylquinoxalin-2(1H)-one (4u): The crude prod-
uct was purified by flash column chromatography on silica gel (pe-
troleum ether/ethyl acetate = 2:1 as an eluent) to afford the product
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˜
1
1316, 1198, 1075, 986, 760, 636, 464; H NMR (400 MHz, CDCl3) δ:
7.84 (d, J = 8 Hz, 1H), 7.51 (t, J = 7.2 Hz, 1H), 7.34–7.30 (m, 2H), 3.71
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Received: August 25, 2019
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Full Paper
C–H Alkylation
L. Wang, J. Zhao, Y. Sun,
H.-Y. Zhang,* Y. Zhang* ................. 1–11
A Catalyst-Free Minisci-Type Reac-
tion: the C–H Alkylation of Quinox-
alinones with Sodium Alkylsulfin-
ates and Phenyliodine(III) Dicarbox-
ylates
A direct C–H alkylation of quinoxalin- moderate to excellent yields in this
ones at the C-3 position with sodium protocol, which offers a practical and
alkylsulfinates and phenyliodine(III) di- efficient access to biologically interest-
carboxylates has been developed un- ing 3-alkylquinoxalin-2(1H)-one deriva-
der catalyst-free conditions. A series of tives.
3-alkylquinoxalinones were afforded in
DOI: 10.1002/ejoc.201901266
Eur. J. Org. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim