MOF-Derived Subnanometer Cobalt Catalyst for Selective C-H Oxidative Sulfonylation of Tetrahydroquinoxalines with Sodium Sulfinates

Article abstract of DOI:10.1021/acscatal.9b00037

The development and utilization of reusable base-metal catalysts is a central topic in catalysis. Herein, via a catalyst design strategy, we present the preparation of a highly dispersed and acid-resistant subnanometer cobalt catalyst (<1 nm) by a MOF-templated method, which has been utilized for selective C-H oxidative sulfonylation of tetrahydroquinoxalines with odorless sodium sulfinates. The transformation enables generation of a variety of sulfonylquinoxalines with the merits of good substrate and functional group compatibility, high regio- and chemoselectivity, and the use of a naturally abundant and reusable metal catalyst. The work presented offers the potential for further design of heterogeneous nanocatalysts and fabrication of functional products that are difficult to prepare or inaccessible by homogeneous catalysis.

Full text of DOI:10.1021/acscatal.9b00037

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Article
MOF-Derived Subnanometer Cobalt Catalyst for Selective C-H Oxidative
Sulfonylation of Tetrahydroquinoxalines with Sodium Sulfinates
Feng Xie, Guangpeng Lu, Rong Xie, Qinghua Chen, Huanfeng Jiang, and Min Zhang
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b00037 • Publication Date (Web): 13 Feb 2019
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ACS Catalysis
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MOF-Derived Subnanometer Cobalt Catalyst for Selective C−H
Oxidative Sulfonylation of Tetrahydroquinoxalines with
Sodium Sulfinates
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Feng Xie, Guang-Peng Lu, Rong Xie, Qing-Hua Chen, Huan-Feng Jiang, and Min Zhang*
Key Lab of Functional Molecular Engineering of Guangdong Province, School of Chemistry and Chemical Engineering,
South China University of Technology, Guangzhou 510641, People’s Republic of China
ABSTRACT: The development and utilization of reusable base-metal catalysts is a central topic in catalysis. Herein, via a catalyst
design strategy, we present the preparation of a highly dispersed and acid-resistant subnanometer cobalt catalyst (< 1nm) by a
MOF-templated method, which has been utilized for selective C−H oxidative sulfonylation of tetrahydroquinoxalines with odorless
sodium sulfinates. The transformation enables to generate a variety of sulfonylquinoxalines with the merits of good substrate and
functional group compatibility, high regio and chemoselectivity, and the use of naturally abundant and reusable metal catalyst. The
work presented offers the potential for further design of heterogeneous nanocatalysts, and fabrication of functional products that are
difficult to prepare or inaccessible by homogeneous catalysis.
KEYWORDS: MOF-templated method, ultrafine nanoparticles, cobalt, selective C–H sulfonylation, sulfonylquinoxalines
Selective introduction of a sulfonyl group into an organic
molecule is of important significance in synthetic chemistry,
as it enables to alter the charge distribution of the entire
molecule, and result in enhanced hydrophilicity and biological
affinity. These switched properties contribute to the
development of new medicines and functional materials.
Among various organosulfones, sulfonyl (hetero)arenes are of
particular importance due to the extensive applications in
reagent) is expected to generate the N-radical 1-1 via SEO of
the N-atom of THQX 1 and deprotonation (from 1 to 1-1),
which then isomerizes to the aryl radical 1-2 due to the SOMO
stabilized by the aryl ring. Similarly, the SEO of sulfinate 2 by
iodide radical generates the electrophilic sulfonyl radical 2-1,
which combines with iodide radical to form the reversible
sulfonyl iodide (2-2). Then, the radical-radical coupling
between 1-2 and 2-1 would yield the adduct 3’. Finally, the
dehydroaromatization of 3’ would give rise to the C−H
sulfonylation product 3. However, it is noteworthy that full
1
2
a-b
biological and pharmaceutical chemistry,
synthesis,
organic
and material science. Conventionally, the
synthesis of such compounds relies on the Friedel-Crafts
2
c-2d
2e
dehydrogenation of THQX
1
to quinoxaline is
3
a-b
sulfonylation of arenes with sulfonic acids
or sulfonyl
In addition, the strategies, via the oxidation of
sulfides, the cross-coupling of sulfinates or the SO surrogates
thermodynamically favorable. Moreover, the radical coupling
3
c-d
halides.
between 1-1 and 2-1, or the nucleophilic substitution between
4
11
2
THQX 1 and 2-2 can generate sulfonamide 4. So, to achieve
5
6
with aryl halides, Suzuki-type reaction, and direct C−H
sulfonylation, have also provided interesting alternatives to
a chemoselective synthesis of sulfonylquinoxaline 3, two
challenging issues have to be resolved: (1) The rate of
para-aryl C−H sulfonylation should be much faster than the
formation of sulfonamide 4. (2) The formation of
non-coupling quinoxaline should be as slow as possible, thus
favoring the cross-coupling of 1-2 and 2-1 to form
intermediate 3’.
7
realize various synthetic purposes. Despite the significant
utility, these transformations are mainly focused on the
sulfonylation of aryl systems. Moreover, they suffer from the
shortcomings such as difficult catalyst reusability, the use of
corrosive acids and less eco-friendly oxidants, the need for
preinstallation of directing groups and specific coupling
agents, and harsh conditions. In this context, selective
sulfonylation of heteroarenes with reusable catalysts,
preferably earth-abundant metals, constitutes a new topic to be
studied.
[Cat.] / [O]
O
S
O
O
S
I
R
S
2
O-
I
I-
I
R
O
R
O
2-2
2-1
R
S
N
H
N
O
S
O
O
R
O
N
R'
Our efforts toward the functionalization of N-heterocycles8
+
+
RSO Na
2
R'
9
N
H
and the interesting applications of sulfonylquinoxalines
1
2
R'
N
3
N
H
motivated us to introduce sulfonyl functionality into the
quinoxalyl skeleton. Here, an envisioned synthetic protocol,
via in situ capture of single electron oxidation (SEO)1 induced
tetrahydroquinoxalyl radical by sulfonyl radical, is illustrated
in Scheme 1. By employing the coupling of
4
I
2-1
-H+
[Cat.] / [O]
[
Cat.]
I-
0
+
[
O]
O
S
H
H
N
H
N
R
N
O
2-1
tetrahydroquinoxaline (THQX)
sulfinate 2 as a prototypical example, the presence of a
compatible catalyst (Cat.) and radical initiator (e.g., iodide
1
and odorless sodium
N
R'
N
H
N
R'
R' 1-1
1-2
3'
Scheme 1. Envisioned new synthetic protocol
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Based on the above information, we believed that, via a
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which prevents the agglomeration of the dispersed cobalt
particles.
1
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1
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1
2
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2
2
3
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catalyst design strategy, the development of a low-loading
cobalt nanocatalyst would provide a solution to achieve a
chemoselective synthesis. On one hand, the cobalt metal has
weak interacting ability with hard bases such as the N-atoms
of THQXs. On the other hand, such type of heterogeneous
catalyst has low density of active sites exposed on the solid
surface. These two key factors would result in low oxidation
efficiency toward THQXs, and favor the capture of transient
intermediates by sodium sulfinates 2. In recent years,
metal-organic frameworks (MOFs) as the precursors have
been elegantly employed to develop various nanomaterials
a
b
10 nm
2
nm
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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0
1
2
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0
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0
1
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3
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9
0
BF
1
0 nm
1
2
2 nm
supported on N-doped carbon. Interestingly, such a method
enables to afford the desired materials with high specific
surface areas, abundant micropores, and controllable
c
d
1
3
coordination environment of metal with heteroatoms.
Attracted by the natural abundance and the capability toward
1
4
10 nm
dehydrogenation of cobalt, and the distinct reactivity of tiny
1
5
metal clusters, we wish herein to report the development of a
new subnanometer cobalt catalyst via a MOF-templated
method, and describe its utility toward the first para-aryl C−H
sulfonylation of THQXs with sodium sulfinates.
10 nm
The catalyst was prepared through pyrolysis of the MOF
precursors immobilized on the commercially available carbon
1
6
Figure 1. (a) HR-TEM image and Bright field (BF) TEM image
b) of Co–N–C. (c) HAADF-STEM image of Co–N–C. (d) The
corresponding EDS elemental maps of Co, N, O, C.
powder. First, the assembly of ZIF-8 framework was
performed in methanol by introducing Zn(NO and organic
(
3 2
)
linker 2-methylimidazole (MeIm). After that, Co precursor
was introduced into the pores of ZIF-8 via double-solvent
impregnating method. Then, the in situ generated MOF-Co–
ZIF–8 was deposited on the carbon support (Vulcan XC-72R).
Further pyrolysis of the resulting material at 1000 °C for 2 h
under argon flow produced the N-doped carbon-supported
subnanometer cobalt catalyst (denoted as Co–N–C, see
supporting information (SI) for details).
27000
26500
26000
25500
N 1s
Raw
Sum
Co-N-C
Pyrrolic N
Graphitic N
oxidizedN
The XRD analysis of the catalyst (Figure S1 in the SI) only
discloses the characteristic peaks of graphitic carbon, and the
peaks assigned to cobalt are not observed, suggesting that the
25000
24500
24000
23500
23000
Co species are either amorphous or highly dispersed. The N
2
adsorption–desorption measurements (BET) of the catalyst
clearly present a typical IV isotherm with hysteresis loop
(Figure S2), indicating a hierarchically micro-mesoporous
structure. Moreover, the specific surface area is detected as
2
-1
2
86 m g , and the relevant distribution curve of the pore
diameter displays that the dominant micropores are centered at
.58 nm and 1.08-1.77 nm, and the regions at 2.62-3.42 nm
392 394 396 398 400 402 404 406 408 410
Binding energy/ eV
0
Figure 2. N1s XPS spectra of Co–N–C.
and 8.30-9.90 nm are ascribed to typical mesopores. Such a
micro-mesoporous structure is beneficial to mass transfer, and
exposes sufficiently active catalytic sites.
X-ray photoelectron spectroscopy (XPS) was then employed
to investigate the surface chemistry of the prepared material.
The element contents are as follows: Co (1.14 wt %), N (1.41
wt %), O (22.45 wt %), and C (75 wt %), and no residue Zn is
detected as it has been evaporated (> 907 °C) during the
pyrolysis process. Furthermore, an ultralow Co loading was
confirmed by ICP-OES (0.88 wt%). The N 1s spectrum
(Figure 2) can be deconvoluted into four peaks with Co–N–C
(399.0 eV), pyrrolic N (400.01 eV), gra phitic-N (401.31 eV),
The morphology and size distribution of the prepared
material were further studied by TEM, HRTEM, and EDS.
The images in Figure 1a and Figure S3a of SI show the
existence of graphite carbon layers, but fail to observe any
larger cobalt nanoparticulates, which is in consistent with the
XRD results. In Figure 1, the bright field (BF) TEM image
(
(
Figure1b), and high-angle annular dark-field scanning TEM
HAADF-STEM) image (Figure1c, and Figure S3d, SI)
1
7a-b
and N-oxide species (403.56 eV).
The graphitic-N and
further demonstrate that the cobalt species are uniformly
dispersed. The average diameter of Co particles is 0.40 ± 0.08
nm (Figure S4a). Meanwhile, as shown in the elemental
mapping images (Figure 1c, and Figure S5a-5f), the signals of
Co, N and C overlap completely, implying that the cobalt is
embedded in the N-doped carbon by bonding with the N-atom,
N-oxide derives from the graphitization of uncoordinated
nitrogen-containing organic linker, while the Co–N–C
structure originates from the graphitization of the coordinative
Co–ZIF–8. Similarly, the Co 2p spectrum (Figure S6) shows
2+
the characteristic peak of Co species with a binding energy
of 780.7 ev, which is further confirmed by the corresponding
1
7c
satellite peaks at 786.9 ev and 802.8 ev, the peak with
2
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typical binding energy of 796.5 eV of the Co 2p1/2 electrons
H
N
N
N
1
7d
1
2
3
4
5
6
7
8
9
is ascribed to Co
O
.
1
Co-N-C (2.5 mol%), DMF, O2
NH4I (1.2 eq), 60 oC,16 h
3
4
+
R SO2Na
O
N
H
With the availability of the ultrafine nanomaterial, we
subsequently evaluated its catalytic performance toward the
benchmark reaction of 1,2,3,4-tetrahydroquinoxaline 1a and
sodium benzenesulfinate 2a. Various reaction parameters,
involving the effect of catalysts, iodide-containing additives,
temperatures, and reaction mediums were screened (Table S1).
The highest GC yield of product 3aa (85%) and the best
chemoselectivity were obtained when the reaction in DMF
1 S
R
3
1a
2
O
N
N
N
O
O
O
S
O
N
S
O
N
S
N
Ph
O
3aa,80%
3
ab,63%
3ac,75%
MeO
N
N
N
N
N
N
O
S
O
S
O
S
charged with a O
2
balloon was performed at 60 °C for 16 h by
O
O
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
O
using 2.5 mol% of Co–N–C, and 1.2 equiv of ammonium
iodide (standard conditions, entry 16 of Table S1). Further, we
compared the catalytic performance of this newly developed
catalyst with other relevant materials with the model reaction,
including various homogeneous catalysts (Table 1, entries 1-5)
and MOF-derived nanocatalysts (Table 1, entries 6-9). The
results show that Co–N–C exhibits the best activity (entry 10).
F
3af, 65%
3
ae, 54%
3
ad, 68%
N
N
N
N
O
S
O
S
O
S
N
N
O
O
O
3ah, 68%
3ai, 70%
3
ag, 47%
Cl
Br
F
N
N
N
N
N
N
O
S
O
O
S
Table 1. Comparison on the Catalytic Performance of the
New Catalyst and Other Relevant Systems
S
O
O
O
S
H
F3C
3aj, 73%
N
3ak,78%
3al, 71%
N
N
Catalyst (2.5 mol%)
N
N
N
+
PhSO2Na
N
O
NH4I (1.2 eq), 60 oC,16
S
N
O
h
N
O
O
N
Ph
1
a H
2a
S
O
S
N
O
3aa
S
N
N
O
3ao, 67%
O
3aa Yield %a
O
Entry
Catalyst
3am,38%
3an, 61%
N
1
2
3
4
5
6
7
8
9
[Cp*IrCl
[Ru(p-cymene)Cl
Pd(OAc)
Co (CO)
Cp*Co(CO)I
2
]
2
2
3
3
7
N
O
O
S
O
2 2
]
S
N
N
O
2
3ap, 65%
3aq, 84%
Scheme 2. Variation of Sodium Sulfinates.
2
8
12
32b
2
Subsequently, we focused on the variation of both coupling
partners. As listed in Scheme 3, various combinations of
THQXs 1 bearing different functional groups (−Me, and −Cl,
Co-DABCO-TPA@C-800
Co-ZIF8
58
68c
15d
Co-ZrO
Ru SA
Co-N-C
2
/N-C
−
Br, ester) with a series of sodium sulfinates 2 were tested.
S
/N-C
Similar to the outcomes illustrated in Scheme 2, all the
substrates underwent smooth dehydrogenative cross-coupling,
affording the sulfonylquinoxalines in a regioselective manner.
Notably, the substituents on the aryl ring of THQXs 1
significantly influenced the product yields. In particular,
electron-donating groups can give the products (3ba-3ca) in
higher yields than those of electron-withdrawing ones
1
0
85 (this work)
a
Unless otherwise stated, all reactions were performed at 60 °C
for 16 h under 1 atm of O atmosphere (using O balloon) by
2
2
using 1a (1.2 eq, 0.3 mmol), 2a (0.25 mmol), catalyst (2.5 mol %),
DMF (1.5 mL), ammonium iodide (1.2 eq, 0.3 mmol),
temperature (60 °C), GC yield using hexadecane as an internal
b,c,d
standard.
The catalysts were prepared according to the
(3ea-3ga). Such a phenomenon is attributed to the
references 12e，8a, and 12b, respectively.
electron-rich groups enhancing the electron-density of the
N-atoms in THQXs, thus favoring the oxidation process to
form more stable aryl radicals (Scheme 1, see intermediate
-2). In addition, the reactions of unsymmetrical THQX 1d
with sulfinates 2a and 2q produced two groups of
With the optimal conditions established, we next tested the
substrate scope of the sulfonylation reaction. Initially, the
coupling of THQX 1a with various sodium arylsulfinates 2
(2a-2j, see Scheme S1 for substrate information) were
explored. As shown in Scheme 2, all the reactions underwent
efficient sulfonylation at the site para to the N-atom of THQX
1
regioisomers in the ratios of 43 : 57 and 45 : 55, respectively
3da and 3da’, 3dq and 3dq’). Similarly, THQX 1e containing
(
an electron-withdrawing ester group also was able to couple
with sulfinate 2a, generating two isomers (3ea : 3ea’) in a
ratio of 41 : 59. These three examples demonstrate that the
reaction utilizing unsymmetrical THQXs has no specific
regioselectivity.
1
a, delivering the desired products in moderate to good
isolated yields (see 3aa-3aj). The structure of product 3aa was
identified by single-crystal X-ray diffraction (See Table S4 in
SI). It was found that a range of functionalities (i.e., −Me,
−
3
OMe, −CF , −F, −Cl and −Br) on the aryl ring of sodium
sulfinates 2 were well tolerated, and these substituents had
little influence on the product formation. In addition, sodium
heteroarylsulfinates (2k-2n) and alkylsulfinates (2o-2q) were
also proven to be compatible agents to react with THQX 1a,
generating the 6-heteroarylsulfonyl and 6-alkylsulfonyl
quinoxalines (3ak-3aq) in moderate to high yields upon
isolation.
3
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Page 4 of 8
R2
slight deactivation of the catalyst. Further, we conducted acid
H
N
N
N
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Co-N-C (2.5 mol%), DMF, O2
leaching experiments to discriminate CoOx and Co−Nx as
catalytic centers. The fresh catalyst treated with sulfuric acid
still exhibited excellent catalytic efficiency (Figure S7),
implying that the developed catalyst material is acid-resistant.
Moreover, the present control experiment and the
characterization of N1s XPS spectrum suggest that the Co−Nx
species embedded in the carbon sheets serve as the
catalytically active sites.
R2
1
O
+
R SO2Na
NH4I (1.2 eq), 60 oC, 16 h
S
N
H
2
R1
3
1
O
N
N
N
O
O
S
O
S
N
N
S
O
N
Ph
O
O
3
ba, 86%
MeO
N
3bc, 75%
F3C
3bj, 78%
N
N
O
S
O
S
To gain insights into the reaction mechanism, we performed
several control experiments (Scheme 4). First, the reaction of
1a and 2a under the standard conditions was terminated after 2
h. Except for product 3aa detected in 18% yield, 6-sulfonyl
tetrahydroquinoxaline 3aa’ and quinoxaline 1a’ were detected
in 45% and 15% yields, respectively (eq.1). Meanwhile, the
time-yield profile of the same reaction was depicted in Figure
S8, compound 3aa’ accumulated to a maximum content within
the first 2 hours, and then gradually consumed in the left 14
hours. Further, the reaction of 1a’ and 2a was unable to yield
product 3aa (eq.2). Treating substrate 1a under the standard
condtions produced 1a’ in almost quantitative yield, and no
O
S
N
N
N
N
O
O
O
O
3bq, 82%
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
bn, 72%
3
bk,74%
N
N
N
N
O
O
S
O
S
O
N
N
S
O
N
N
O
Ph
O
3cq, 50%
3
cn, 41%
3ca, 58%
N
N
N
N
N
N
O
S
O
O
O
O
S
+
Ph
N
+
S
S
O
N
Ph
O
O
(3da + 3da'), 56%
(3dq + 3dq'), 51%
(45 : 55)
(
43 : 57)
6
-iodoquinoxaline was detected. The results show that 3aa’ is
N
N
CO2Et
+
N
a crucial intermediate. Further, the reaction of freshly prepared
O
O
18
benzenesulfonyl iodide 2-2a with 1a only resulted in trace of
S
O
S
O
N
CO2Et
Ph
Ph
(
3ea + 3ea'), 37%
41 : 59)
product 3aa (eq.3), implying that an electrophilic
sulfonylation is less likely. The addition of excess TEMPO,
(
Cl
N
Br
N
N
2
(
,6-di-tert-butyl-4-methylphenol (BHT), or benzoquinone
BQ) into the reaction of 1a and 2a significantly suppressed
the product formation (eq.4). The product of
1,1-diphenylethylene trapping sulfonyl group was
O
O
S
S
O
N
Ph
Ph
O 3ga, 41%
3fa, 43%
Scheme 3. Variation of Both Coupling Partners
a
determined by HR-MS (eq.5), which suggests that, at least, the
reaction involves sulfonyl radical. Moreover, in consideration
7d
that the sulfonyl unit can be reduced to sulfur group, the
100
80
para-aryl C−H sulfuration of 1a with 2a to
3aa
6
-(phenylthio)quinoxaline 3aa’’ followed by the oxidation of
sulfur atom might offer another way to give product 3aa.
However, subjection of 3aa’’to the standard conditions failed
to yield 3aa (eq.6). Thus, such a pathway can be ruled out.
These control experiments are well consistent with the
60
proposed pathway in Scheme 1.
4
2
0
0
0
H
standard PhO S
N
PhO S
N
N
2
2
conditions
(1)
1a
+
2a
+
+
2 h
N
N
H
N
3aa, 18%
3aa', 45%
1a', 15%
standard conditions
standard conditions
1a'
+
+
2a
3aa, 0%
(2)
(3)
0
1
2
3
4
5
Recycle number
SO2I
1a
3aa, trace + 1a', 86%
Figure 3. Reuse of the Co–N–C catalysts.
2-2a
To check the reusability of the developed Co–N–C catalyst,
it was recycled to run the model reaction for additional 5
consecutive times. As shown in Figure 3, the catalytic activity
and reaction selectivity remained very well, albeit with a slight
decrease of yield, which demonstrates the high durability of
this catalyst. After five recyclings, the Co content slightly
decreased from 0.88 wt% to 0.71 wt% (ICP-OES analysis).
Meanwhile, the HRTEM images and HAADF-STEM images
TEMPO (1 equiv), 3aa, 36%
TEMPO (5 equiv), 3aa, 3%
BHT (3 equiv), 3aa, 12%
standard conditions
1a
+
+
2a
2a
(4)
(5)
BQ
(3 equiv), 3aa, 0%
3aa, 26%
standard conditions
Ph2C CH2 (3 equiv)
+
1a
Ph2C CHSO2Ph
HR-MS: [M+1]=321.0946
S
N
N
standard conditions
(6)
3aa, 0%
(Figure S3e-3h, SI) of the reused catalyst show that there are
3aa''
no obvious Co cluster aggregation during the reaction. The
mean particle size of the used catalyst is 0.72 ± 0.19 nm
(Figure S4b), which is close to the fresh one and still
maintains the subnanometer scale. The nanoparticle leaching
during the process of mechanical abrasion accounts for the
Scheme 4. Control Experiments
Finally, we were interested in demonstrating the utility of
the developed chemistry. The sulfonylation reaction was
successfully
applied
for
rapid
synthesis
of
4
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-(phenylsulfonyl)-1,4-dihydroquinoxaline-2,3-dione 4aa, an
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6
1
9
1
2
3
4
5
6
7
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9
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gram-scale synthesis of compound 3aa with high isolated
yield (75%). Then, the treatment of compound 3aa with
hypervalent iodinane agent (BTI) afforded product 4aa in 68%
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2
0
yield.
Moreover, the bromination of 3aa with
N-bromosuccinimide gave compound 5aa-1 in 74% yield in
2
1a
H
2
SO
4
.
Then, the C-N coupling between 5aa-1 and
4
5
-methoxyaniline under palladium catalysis afforded product
1
1
1
1
1
1
1
1
1
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2
2
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9
0
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8
9
0
21b
aa-2 in 81% yield. This example shows the potential of the
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HN
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Scheme 5. Synthetic Utility.
In summary, via a catalyst design strategy, we have
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features of high dispersion and acid-resistance, it exhibits
good catalytic performace toward the first selective C−H
oxidative sulfonylation of tetrahydroquinoxalines with
odorless sodium sulfinates. The catalytic transformation
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merits of good functional tolerence, broad substrate scope,
excellent regio and chemoselectivity, and the use of naturally
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ASSOCIATED CONTENT
Supporting Information
Palladium-Catalyzed
Heteroaryl
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The Supporting Information is available free of charge on the
ACS Publications website at DOI:
The detail of catalyst preparation, more characterization results,
complete experimental procedures and spectral data (PDF)
AUTHOR INFORMATION
Corresponding Author
*
minzhang@scut.edu.cn
Notes
The authors declare no competing financial interests.
3
121-3125.
ACKNOWLEDGMENT
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We thank the National Key Research and Development Program of
China (2016YFA0602900), National Natural Science Foundation of
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(201607010306), Science Foundation for Distinguished Young
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