Primary sulfonamide as a coupling partner: Copper(I)-catalyzed regioselective cross-coupling of 2-nitro benzenesulfonamides with thiol through the cleavage of Ar–SO2NH2 bonds

Article abstract of DOI:10.1080/00397911.2018.1441420

In this article, we have presented a novel and efficient method for the direct synthesis of unsymmetrical sulfides through the copper(I)-catalyzed cross-coupling of 2-nitro benzenesulfonamides with thiols in the presence of catalytic amount of CuI in DMF as solvent at 100 °C. In addition, the products were obtained in high to excellent yields. More importantly, the novel system showed the primary 2-nitro benzenesulfonamides as a new coupling partner and regioselectively promoted C–S bond-forming transformations through the cleavage of Ar–SO₂NH₂ bonds.

Full text of DOI:10.1080/00397911.2018.1441420

Synthetic Communications
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Primary sulfonamide as a coupling partner:
Copper(I)-catalyzed regioselective cross-coupling
of 2-nitro benzenesulfonamides with thiol through
the cleavage of Ar–SO2NH2 bonds
Junmin Chen, Kuo Zhang, Yongli Zhao & Shouzhi Pu
To cite this article: Junmin Chen, Kuo Zhang, Yongli Zhao & Shouzhi Pu (2018): Primary
sulfonamide as a coupling partner: Copper(I)-catalyzed regioselective cross-coupling of 2-
nitro benzenesulfonamides with thiol through the cleavage of Ar–SO2NH2 bonds, Synthetic
Communications, DOI: 10.1080/00397911.2018.1441420
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SYNTHETIC COMMUNICATIONS®
https://doi.org/10.1080/00397911.2018.1441420
Primary sulfonamide as a coupling partner: Copper(I)-
catalyzed regioselective cross-coupling of 2-nitro
benzenesulfonamides with thiol through the
cleavage of Ar–SO2NH2 bonds
Junmin Chena,b, Kuo Zhangb, Yongli Zhaob, and Shouzhi Pua
aJiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang,
b
Jiangxi, P. R. China; Key Laboratory of Functional Small Organic Molecules, Ministry of Education and College
of Chemistry & Chemical Engineering, Jiangxi Normal University, Nanchang, Jiangxi, P. R. China
ABSTRACT
ARTICLE HISTORY
Received 1 December 2017
In this article, we have presented a novel and efficient method for the
direct synthesis of unsymmetrical sulfides through the copper(I)-
catalyzed cross-coupling of 2-nitro benzenesulfonamides with thiols in
the presence of catalytic amount of CuI in DMF as solvent at 100 °C. In
addition, the products were obtained in high to excellent yields. More
importantly, the novel system showed the primary 2-nitro benzene-
sulfonamides as a new coupling partner and regioselectively
promoted C–S bond-forming transformations through the cleavage
of Ar–SO2NH2 bonds.
KEYWORDS
Copper(I)-catalyzed;
cross-coupling;
regioselective;
sulfonamide; thiol
GRAPHICAL ABSTRACT
Introduction
Sulfides and their derivatives were important and were widely used in pharmaceutical,
biological molecules, and chemical materials.[1–3] Since Migita et al.[4] first reported the
palladium-catalyzed C(aryl)–S bond formation from the corresponding aryl halides and
thiols, transition metal-catalyzed cross-coupling reaction is the most common and
powerful method for the formation of C–S bonds.[5] Up to now, different transition
metal-catalyzed systems including Pd,[6] Cu,[7] Ni,[8] Co,[9] Fe,[10] and other metals[11] have
been reported. In general, the cross-coupling reactions are conducted between aryl donors
and thiols or disulfides, the aryl halides were the most common electrophilic counterparts.
CONTACT Shouzhi Pu
pushouzhi@tsinghua.org.cn
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi
Science & Technology Normal University, Nanchang, Jiangxi 330013, P. R. China.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data (Characterization data, and copies of 1H spectra for all of the products 4) can be accessed on the
publisher’s website.
© 2018 Taylor & Francis

2
J. CHEN ET AL.
The copper-catalyzed cross-coupling reactions with the use of diaryl disulfides and aryl
boric acids or silicones as substrates have been disclosed.[12] Recently, the direct thiolation
of arene C–H bonds has been developed as an attractive method to form C–S bonds from
unfunctionalized arenes. However, the activity and selectivity observed in these systems
rely on either the use of directing groups[13] or activated or acidic arene C–H bonds.[14]
Very recently, Wu et al.[15] reported for first time that the cross-coupling of activated
nitroarenes and arylboronic acids in the presence of rhodium(I) complex produces
unsymmetrical diaryl ethers in excellent yields. Nitroarenes have also been used as a
new coupling partner for the unsymmetrical diaryl sulfides using thiophenols,[16]
sulfinates[17], and also the synthesis of alkyl aryl sulfides using alkyl halides (Br, Cl),
triphenyltin chloride, and arylboronic acids as the coupling partners in the presence of
Na2S2O3 · 5H2O or S8 as sulfur source under ligand-free conditions.[18] More recently,
nitroarenes have also been reported to be active as an electrophilic coupling partner in
the synthesis of biaryls through the palladium-catalyzed Suzuki−Miyaura coupling reaction
through the cleavage of Ar–NO2 bonds.[19] Similarly, sulfonamides are valuable intermedi-
ates in synthetic organic chemistry and were extensively used as pharmaceutical agents
because of their diverse biological properties. Therefore, the search for new methodologies
for the conversion of sulfonamide functional group is very important in organic chemistry.
Significantly, desulfonative couplings have become attractive alternatives to the use of
prefunctionalized organometallic reagents. However, the reactions mainly focused on the
development of C–C bond-forming transformations through the cross-coupling of vinyl
sulfones or aryl sulfonates with Grignard reagents.[20] Nevertheless, aryl sulfonamides have
not yet been reported to undergo the transition metal-catalyzed cross-coupling reactions
with the SO2NH2 group serving as a leaving group. Herein we report a novel copper(I)-
catalyzed regioselective cross-coupling of 2-nitro benzenesulfonamides with thiol under
mild conditions through the cleavage of Ar–SO2NH2 bonds.
Results and discussion
Recently, Shinde et al.[16] reported a novel copper(I)-catalyzed cross-coupling of
nitroarenes with thiol through the cleavage of Ar–NO2 bonds. Based on the aforemen-
tioned availability, we attempt to extend this analogous strategy to get the corresponding
2-phenylsulfanyl-benzenesulfonamide substrates 3. Initially, the reaction of 1a with
thiophenol 2a was investigated in the presence of Cu(OAc)2 as a catalyst and Cs2CO3 as
a base in DMF at 100 °C for 12 h (Scheme 1). Curiously, the product 3aa through the
cleavage of Ar–NO2 bonds was not detected, the Ar–SO2NH2 bond was cleaved and the
corresponding cross-coupling product 4aa was obtained in 86% yield.
Scheme 1. Synthesis of unsymmetrical sulfides through the cleavage of Ar–SO2NH2 bonds.

SYNTHETIC COMMUNICATIONS®
3
Inspired by the above positive results, we then considered screening the reaction
conditions. The primary 2-nitro benzylsulfonamide (1a) and thiophenol (2a) were first
chosen as the substrates for the model reaction to optimize the reaction conditions. The
reaction was screened with several copper salts, solvents, and reaction temperature to
enhance the competence of the coupling reactions, and the results are summarized in
Table 1. Initially, the base was investigated under similar conditions (Table 1, entry 1),
the trace amount of product was obtained using Ag2CO3 as a base (Table 1, entry 2);
furthermore, K3PO4 only gave the desired product in 11% yield (Table 1, entry 3). KOAc
or K2CO3 produces the desired product in 72 and 80% yields, respectively (Table 1, entries
4 and 5), and the yields are less compared to Cs2CO3. To our delight, the 92% yield was
obtained when Na2CO3 was a base under similar conditions (Table 1, entry 6). To further
optimize the reaction conditions, the copper courses were screened in the presence of
Na2CO3 (2 equiv.) with DMF as solvent under air for 12 h. Cu2O, CuO, and CuCl2
produced the desired product in moderate yield (Table 1, entries 7–9). Significantly, the
yield was dramatically improved to 96% in presence of CuI (Table 1, entry 10). Finally,
the solvents were screened, it was found that reaction works in various solvents such as
DMA, DMSO, CH3CN, or 1,4-dioxane but yields are less compared to DMF under the
identical conditions (Table 1, entries 11–14). DMF was turnout as the best solvent among
those examined. In addition, the amounts of copper salts were investigated, and the 82%
Table 1. Optimization of conditions.
Entrya
Cu salt
Base
Solvent
Yield/%b
1
2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu2O
CuO
Cs2CO3
Ag2CO3
K3PO4
DMF
DMF
86
Trace
11
3
DMF
4
KOAc
DMF
72
5
K2CO3
DMF
80
6
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
DMF
92
7
DMF
41
8
DMF
43
9
CuCl2
CuI
DMF
60
10
11
12
13
14
15c
16d
17e
18f
19
DMF
96
CuI
DMA
DMSO
CH3CN
1,4-dioxane
DMF
46
CuI
74
CuI
69
CuI
78
CuI
82
CuI
DMF
75
CuI
DMF
50
CuI
DMF
21
/
DMF
Trace
aReaction conditions: 2-nitro benzylsulfonamide (1a) (0.25 mmol), thiophenol (2a) (0.5 mmol), copper salt (10 mol%), base
(0.5 mmol), and solvent (0.5 mL), at 100 °C for 12 h.
bIsolated yield.
cIn presence of 5 mol% CuI.
dReaction at 75 °C.
eReaction at 50 °C.
fReaction at 25 °C.

4
J. CHEN ET AL.
Table 2. Copper(I)-catalyzed regioselective cross coupling of 2-nitro benzenesulfonamide 1 with
various thiols 2.
Entrya
1
Substrate 1
Substrate 2
Product 4
Yield (%)b
96
2
3
4
5
91
86
89
93
6
7
86
95
8
9
97
98
94
96
10
11
(Continued)

SYNTHETIC COMMUNICATIONS®
5
Table 2. Continued.
Entrya
Substrate 1
Substrate 2
Product 4
Yield (%)b
93
12
aReaction conditions: 2-nitro benzenesulfonamides (1) (0.25 mmol), thiol (2) (0.5 mmol), CuI (10 mol%), NaCO3 (0.5 mmol),
and DMF (0.5 mL), at 100 °C for 12 h under air.
bIsolated yield.
yield was obtained in presence of 5 mol% CuI (Table 1, entry 15). The reaction temperature
was also screened; the desired product was obtained in 75 and 51% yield in 75 and 50 °C,
respectively (Table 1, entries 16 and 17). In further decrease to 25 °C, only 21% yield was
obtained (Table 1, entry 18). It should be mentioned that in the absence of Cu salt, a trace
amount of desired product was formed (Table 1, entry 19), which also further proved that
the present reaction was not aromatic nucleophilic substitution (SNAr) reactions. Finally,
these experiments suggest that CuI is the choice of transition metal catalyst and that
Na2CO3 serves as the base in DMF at 100 °C for 12 h under air.
After having the set of optimized conditions, we focused our attention on extending
the scope of this process using 2-nitro benzenesulfonamide 1 and various thiols (2) (-
Table 2). Primarily, we set on to evaluate 2-nitro benzenesulfonamide 1a and different
aryl thiols 2. The 2-nitro benzenesulfonamide 1a reacted with 4-methyl-benzenethiol
2b to give the desired product in 91% yield (Table 2, entry 2), it should be mentioned
that halo-substituted aryl thiols have tolerated well to give the corresponding products,
for example, 4-chlorobenzethiol 2c and 4-bromobenzetyhiol 2d can offer the correspond-
ing product in 86 and 89% yields, respectively (Table 2, entries 3 and 4). Interestingly, it
turned out that ortho-substituted benzylthiol, such as 2-methylbenzethiol 2e and 2-
methoxyl benzetyhiol 2f, can afford 93 and 86% yields of the desired products, respect-
ively (Table 2, entries 5 and 6). To our delight, alkyl thiols were also active substrates
under the present reaction conditions and gave excellent yields of the desired products.
For example, the reaction of 2-nitro benzenesulfonamide 1a with benzyl thiol 2g gave the
desired product in 95% yield (Table 2, entry 7). Furthermore, n-ethyl thiol 2h, n-propyl
thiol 2i, and n-butyl thiol 2j can also afford the expected products in excellent
yields (Table 2, entries 8–10). It is also interesting to note that the secondary and tertiary
2-nitro benzenesulfonamide derivatives 1c–d served as good substrates provided the
corresponding products in excellent yields (Table 2, entries 11 and 12). However, we
attempted to use various benzenesulfonamide 1 bearing nitro group at meta- or para-
position as the substrate with thiophenol (2a), and only trace amount of product was
obtained.
Conclusion
In summary, we have successfully developed the first copper(I)-catalyzed cross-coupling
of 2-nitro benzenesulfonamides with thiol to form unsymmetrical sulfides under mild
conditions with excellent yields. Notably, this method furnished the direct synthesis of
unsymmetrical sulfides through the regiochemical cleavage of C–SO2NH2 without the
cleavage of C–NO2. This study illustrates the potential of sulfonamides to act as versatile
electrophiles in new types of catalytic C–S forming reactions. Further studies toward

6
J. CHEN ET AL.
investigating the detail reaction mechanism and expanding the scope of this reaction are
under way in our laboratory.
Experimental
All reactions were performed under air. Chemicals were purchased from Aldrich, Acros, or
Alfa Asar, and, unless otherwise noted, were used without further purification. Flash
1
chromatography was performed on silica gel (silica gel, 200–300 mesh). H NMR spectra
were recorded on Bruker 400 MHz spectrometers with CDCl3 as the solvent. Compounds
1b and 1c were prepared according to the literature.[20]
General procedure for the synthesis of unsymmetrical sulfides 4
A mixture of 2-nitro benzylsulfonamide 1 (0.25 mmol), thiol 2 (0.5 mmol), CuI
(0.025 mmol), NaCO3 (0.5 mmol), and DMSO (0.5 mL) was placed in a 25-mL round-
bottom flask. The mixture was stirred for 12 h at 100 °C under air. Then, the reaction
mixture was cooled, diluted with ethyl acetate, filtered through celite, and concentrated
in vacuo. The residue was purified by silica gel column chromatography with ethyl
acetate/petroleum ether to afford the desired product 4.
Funding
We are grateful for the financial support from the National Natural Science Foundation of China
(Grant No. 21762022) and Foundation of Jiangxi Educational Committee (Grant No. GJJ160287).
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