Sequential C-S and S-N Coupling Approach to Sulfonamides

Article abstract of DOI:10.1021/acs.orglett.0c00183

A one-pot three-component reaction involving nitroarenes, (hetero)arylboronic acids, and potassium pyrosulfite leading to sulfonamides was described. A broad range of sulfonamides bearing different reactive functional groups were obtained in good to excellent yields through sequential C-S and S-N coupling that does not require metal catalysts.

Full text of DOI:10.1021/acs.orglett.0c00183

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Sequential C−S and S−N Coupling Approach to Sulfonamides
Kai Chen, Wei Chen, Bing Han, Wanzhi Chen,* Miaochang Liu, and Huayue Wu*
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ABSTRACT: A one-pot three-component reaction involving
nitroarenes, (hetero)arylboronic acids, and potassium pyrosulfite
leading to sulfonamides was described. A broad range of
sulfonamides bearing different reactive functional groups were
obtained in good to excellent yields through sequential C−S and
S−N coupling that does not require metal catalysts.
Scheme 1. Synthesis of Sulfonamides from Boronic Acids
ulfonamides constitute a medicinally privileged structural
1
Sscaffold. Numerous structurally novel sulfonamide deriv-
atives have been found to show diverse pharmacological
properties including anticancer, antibacterial, anti-inflamma-
tory, antituberculosis, anticarbonic anhydrase, as well as
protease inhibitory activity in vitro and in vivo.1 The
conventional approach to sulfonamides is the nucleophilic
substitution of sulfonyl chlorides with amines2a or nitro-
arenes.2b−d Although it is highly effective, the protocol is
restricted because sulfonyl chlorides are not readily available and
they are toxic and unstable. Development of a synthetic
methodology that avoids the use of sulfonyl chlorides is of
great importance in the pharmaceutical industry. Metal-
catalyzed S−N coupling of sulfinates with amines3 or nitro-
arenes4 was developed. However, commercially available
arylsulfinates are scarce, and they are generally prepared from
the reduction of sulfonyl chlorides5 or the reaction of
organometallic reagents with SO2 or DABSO (1,4-
diazabicyclo[2.2.2]octane bis(sulfur dioxide)).6 An electro-
chemically oxidative coupling between thiols and amines was
most recently reported involving S−N coupling.7
derivatives is still required to have broader substrate scope and
to prevent heavy metal residues.
Nitroarenes are feedstocks of dyes, pesticides, and the
pharmaceutical industry and are cheap and readily available.
Exploration of the synthetic transformation of nitroarenes as
either amine sources15 or electrophilic arylating reagents16 is of
significance. Sulfonamides are usually prepared from aniline
derivatives, which basically originate from nitroarenes. Although
a few precedents exist for the synthesis of sulfonamides from
organometallic reagents,10b,d,12,14 we were interested in the
heavy-metal-free sequential C−S and S−N coupling because the
procedure is operator- and environment-friendly and the
resulting products are valuable intermediates for many
pharmaceuticals and agricultural chemicals. The employment
of nitroarenes as the amine source is attractive as the reaction
would be step-economical and could avoid the use of external
oxidants. Herein, we disclose a novel three-component reaction
between nitroarenes, boronic acids, and potassium pyrosulfite in
which new C−S and S−N bonds are simultaneously formed
Multicomponent cross-coupling approaches are attractive and
strategically efficient using commercially available chemicals,
which could increase diversity. In this context, Willis et al.
described the Pd-catalyzed coupling reaction of aryl iodides,
DABSO, and hydrazines to generate N-aminosulfonamides.8
The metal-catalyzed procedure could be extended to chloroar-
enes9 and organometallic reagents.10 Later, Wu et al. reported
the aminosulfonylation of aryldiazonium salts, DABSO, and
hydrazines under metal-free conditions.11 These protocols were
restricted to the synthesis of N-aminosulfonamides. In 2016,
Willis et al. developed a palladium-catalyzed one-pot two-step
coupling of arylboronic acids, DABSO, and electrophilic amines
(Scheme 1a).12 Sulfonamides were also obtained through
gold(I)-catalyzed sulfination of arylboronic acids and oxidative
S−N coupling (Scheme 1b).13 More recently, a copper-
catalyzed approach was disclosed in which various sulfonamides
were furnished using DABSO as the SO2 precursor (Scheme
1c).14 Despite these developments, new access to sulfonamide
Received: January 13, 2020
https://dx.doi.org/10.1021/acs.orglett.0c00183
© XXXX American Chemical Society
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A

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a
under heavy-metal-free conditions, delivering a number of
sulfonamides in good to excellent yields.
Scheme 2. Scope of Nitroarenes
Initially, we explored the Pd/NHC-catalyzed coupling
reaction of nitrobenzene, phenylboronic acid, and K2S2O5, and
only a trace amount of sulfonamide was obtained. Further
studies showed that palladium was not responsible for the C−S
and S−N bond formation. Thus we tested the coupling of 4-
nitroanisole, phenylboronic acid, and K2S2O5 under heavy-
metal-free conditions (Table 1). After screening various reaction
Table 1. Optimization of Reaction Conditions
a
entry
variation from the standard
standard
in N2 instead of air
1.67 equiv of K2S2O5
no base
Et3N or KOtBu instead of K2CO3
CsF instead of K2CO3
dioxane instead of CH3CN
DMSO instead of CH3CN
DMF or tBuOH instead of CH3CN
nBu4NI instead of nBu4NCl
18-crown-6 instead of nBu4NCl
H2O instead of nBu4NCl
yield (%)
b
c
1
2
3
4
5
6
7
8
9
84 (73) (67)
85
c
14
c
38
c
trace
c
67
c
23
c
30
c
nd
10
11
12
30
74
49
a
Reaction conditions: 4-nitroanisole (0.3 mmol, 1.0 equiv), phenyl-
boronic acid (0.6 mmol, 2.0 equiv), K2S2O5 (3.3 equiv), base (0.6
mmol, 2.0 equiv), additive (1.1 equiv), solvent (1.5 mL), 24 h.
Determined by 1H NMR analysis using CH2Br2 as the internal
a
Reaction conditions: nitroarene (0.6 mmol, 1.0 equiv), phenyl-
boronic acid (1.2 mmol, 2.0 equiv), K2S2O5 (2.0 mmol, 3.3 equiv),
K2CO3 (1.2 mmol, 2.0 equiv), nBu4NCl (0.66 mmol, 1.1 equiv),
b
c
n
standard. Isolated yield. No Bu4NCl.
b
CH3CN (3.0 mL), 130 °C, air, 24 h. 36 h.
parameters (Tables S1−S6 in the Supporting Information), we
obtained 3aa in 84% yield together with a trace amount of p-
methoxyaniline (Table 1, entry 1). Butyl benzenesulfonate, 1,2-
diphenyldisulfane, and 2,4,6-triphenylboroxin were also ob-
served as the side products, and thus an excess of arylboronic
acid is required. This process is not sensitive to air (Table 1,
entry 2). The key to the success was the employment of 3.3 equiv
of K2S2O5, and the yield was dramatically decreased to 14%
when the amount of K2S2O5 was reduced to 1.67 equiv (Table 1,
entry 3). Most likely, the reduction of nitrobenzene requires an
additional 2 molar equiv of K2S2O5. Bases promote the three-
component coupling reaction (Table 1, entries 4−6). However,
the stronger base KOtBu and organic base Et3N are ineffective
(Table 1, entry 5). When the reaction was performed in solvents
such as dioxane, DMSO, DMF, and tBuOH, diminished yields
and amines successfully afforded sulfonamides, the copper-
catalyzed reaction did not proceed when DABSO was replaced
with K2S2O5.14 K2S2O5 is superior to other SO2 surrogates
because it is cheaper and nontoxic. Nitroarenes bearing electron-
donating groups such as methoxy, alkyl, phenyl, alkynyl, and
amino substituents at o-, m-, and p-positions underwent the
sequential C−S and S−N coupling, furnishing 3aa−3an in good
yields. Importantly, the heavy-metal-free protocol without use of
strong bases allows the synthesis of sulfonamides bearing
reactive functional groups such as ester, amide, thioether, cyano,
and alkynyl substituents. In particular, unprotected amino and
carboxylic acid groups are very compatible, which is very
important as these groups often exist in many pharmaceutically
active sulfonamides. Protection and deprotection sequences
could be avoided. In the cases of 3- and 4-nitroanilines, 3al and
3ak were obtained in 57 and 68% yields, respectively, and no
(phenylene)dibenzenesulfonamide was observed. The results
imply that aniline is not the intermediate of the sulfonamidation
process. The thioether moiety is also tolerated, and 3ao and 3ap
were afforded in 75 and 67% yields, respectively. Unfortunately,
nitroarenes containing hydroxyl and formyl groups are not
compatible. Nitroarenes bearing electron-withdrawing groups
such as cyano, trifluoromethyl, acetyl, carboxylic acid,
alkoxycarbonyl, and carbamoyl were successfully transformed
to 3aq−3ay in 60−80% yields. The reactivities of halo-
n
were obtained (Table 1, entries 7−9). Bu4NCl was found to
favor the reaction, serving as a phase transfer catalyst. Other
additives such as 18-crown-6 and nBu4NI resulted in decreased
yields (Table 1, entries 10−12). When the reaction was
performed in mixed CH3CN/H2O solvent, diphenyl disulfide
was isolated in 70% yield as the sole product.
The substrate scope of the transformation was explored, and
the scope of nitroarenes is presented in Scheme 2. A variety of
substituted nitroarenes were transformed to sulfonamides in
good yields (39−93%). It is notable that although copper-
catalyzed three-component coupling of boronic acids, DABSO,
B
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containing nitroarenes were tested. Ar−X (X = F, Cl, Br, and I)
bonds are maintained in products 3az and 3ba−3bf, thus
offering opportunities for the synthesis of complex sulfonamide
molecules through further coupling reactions. Heteroaryl
sulfonamides exhibit important biological activity and are
important scaffolds in the development of drugs. We thus
investigated the compatibility of nitro-containing heteroarenes.
Sulfonamides 3bh−3bo containing pyridine, quinoline, iso-
quinoline, indole, and benzofuran rings were successfully
obtained in 54−93% yields. However, imidazolyl, thiophenyl,
and furyl were not compatible.
Aliphatic methylboronic acid afforded methanesulfonamide 4bh
in less than 10% yield. The results listed in Schemes 2 and 3
showed that the coupling is not electronically sensitive for both
nitroarene and boronic acid partners.
To illustrate the practicality of the heavy-metal-free approach,
a gram-scale reaction using 1.17 g of ethyl 4-nitrobenzoate, 1.46
g of phenylboronic acid, and 4.6 g K2S2O5 was performed. The
expected sulfonamide 3aw was isolated in 66% yield. The utility
was also demonstrated using more complex molecules (Scheme
4). Nitrendipine is a common antihypertensive drug,17 and
Scheme 3 shows that the protocol is tolerant to various
electron-rich and -deficient boronic acids. Under standard
Scheme 4. Gram-Scale Derivation of Drugs and Drug-like
Product Synthesis
a
Scheme 3. Scope of Boronic Acids
Flutamide is used to treat prostate cancer,18 and their derivatives
M1 and M3 could be delivered in 61 and 69% yields,
respectively. Moreover, drug-like product M2, an analogue of
Celecoxib as COX2 inhibitor, could be obtained by the one-step
approach in 73% yield.
A few control experiments were designed to gain some
insights into the mechanism (Scheme S1). It has been reported
that Au-,13,19 Cu-,20 and Pd-catalyzed12,21 reactions of
arylboronic acids and SO2 surrogate lead to sulfinate salts.
Recently, similar activation of organosilanes to generate
sulfinates under metal-free conditions has been reported.22 We
found that the three-component reaction between phenyl-
boronic acids, K2S2O5, and CH3I gave PhSO2Me in 25% yield
under heavy-metal-free conditions. The reaction of p-
tolylsulfinate and nitrobenzene in the absence of K2S2O5 did
not afford the desired sulfonamide, whereas sulfonamide was
obtained in 73% yield in the presence of K2S2O5. This
demonstrates that arylsulfinate salts would be the key
intermediate, and K2S2O5 plays a crucial role in the C−S and
S−N bond formation. Reaction of aniline with either the
combination of boronic acid and K2S2O5 or preformed
phenylsulfinate failed to give the sulfonamide. In contrast,
sulfonamide was formed in less than 20% yields from reactions
of nitrosobenzene or N-phenylhydroxylamine with phenyl-
sulfinate regardless of whether K2S2O5 was present. These
reactions illustrate that PhNH2, PhNO, and PhNHOH might
not be the key intermediates. Furthermore, treatment of N-
phenyl-N-tosylhydroxylamine with K2S2O5 under the standard
conditions gave sulfonamide in 72% yield. Based on these
observations and literature reports,4b,23 a plausible mechanism
in Scheme 5 was proposed. Decomposition of K2S2O5 results in
the formation of SO2 upon heating. Nucleophilic addition of
arylboronic acid to SO2 in the presence of a base would form
benzenesulfinate I. Further nucleophilic addition to nitroarene
would give II. Under the reduction of SO2, intermediate II went
through double deoxygenation to form sulfonamide finally.
a
Reaction conditions: nitrobenzene (0.6 mmol, 1.0 equiv), boronic
acid (1.2 mmol, 2.0 equiv), K2S2O5 (2.0 mmol, 3.3 equiv), K2CO3
(1.2 mmol, 2.0 equiv), nBu4NCl (0.66 mmol, 1.1 equiv), CH3CN (3.0
b
c
mL), 130 °C, air, 24 h. 36 h. 4-Aminophenylboronic acid
hydrochloride was used.
conditions, the reaction of nitrobenzene furnished the
corresponding 4aa−4bh in good to excellent yields. Unpro-
tected hydroxy is compatible, and 4ag was obtained in a
moderate yield. Halo-containing sulfonamides 4al−4ao were
also produced in 65−73% yields. Furthermore, heteroarylbor-
onic acids with pyridine, indole, benzofuran, thiophenyl,
benzothiophenyl, and isoxazole rings also worked well to furnish
the corresponding sulfonamides in good to excellent yields.
Styrylboronic acid was tolerated to give 4bg in 35% yield.
C
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Scheme 5. Plausible Mechanism
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AUTHOR INFORMATION
Corresponding Authors
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Wanzhi Chen − Department of Chemistry, Zhejiang University,
Hangzhou 310027, China; orcid.org/0000-0002-7076-
1521; Email: chenwzz@zju.edu.cn
Huayue Wu − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou 325027, China; orcid.org/
0000-0003-3431-561X; Email: huayuewu@wzu.edu.cn
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Authors
Kai Chen − Department of Chemistry, Zhejiang University,
Hangzhou 310027, China
Wei Chen − Department of Chemistry, Zhejiang University,
Hangzhou 310027, China
Bing Han − Department of Chemistry, Zhejiang University,
Hangzhou 310027, China
Miaochang Liu − College of Chemistry and Materials Engineering,
Wenzhou University, Wenzhou 325027, China; orcid.org/
0000-0002-4603-3022
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Complete contact information is available at:
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation (NSF) of China (21572203 and 21472140) and the
NSF of Zhejiang Province (LZ16B020001).
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