Copper-catalyzed cross-coupling of chloramine salts and arylboronic acids in water: A green and practical route to N-arylsulfonamides

Article abstract of DOI:10.1016/j.tetlet.2018.09.001

A green and practical method for the synthesis of N-arylsulfonamides from chloramine salts and arylboronic acids is herein developed. The reaction proceeds readily in the presence of 5 mol% of CuI and 2.5 equiv. K₂CO₃ in water at room temperature, generating a variety of N-arylsulfonamides in moderate to good yields with good functional group tolerance.

Full text of DOI:10.1016/j.tetlet.2018.09.001

Accepted Manuscript
Copper-catalyzed cross-coupling of chloramine salts and arylboronic acids in
water: a green and practical route to N-arylsulfonamides
Banlai Ouyang, Yanxia Zheng, Yi Liu, Fei Liu, Juying Yao, Yiyuan Peng
PII:
S0040-4039(18)31073-6
https://doi.org/10.1016/j.tetlet.2018.09.001
TETL 50240
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
7 July 2018
28 August 2018
1 September 2018
Please cite this article as: Ouyang, B., Zheng, Y., Liu, Y., Liu, F., Yao, J., Peng, Y., Copper-catalyzed cross-coupling
of chloramine salts and arylboronic acids in water: a green and practical route to N-arylsulfonamides, Tetrahedron
Letters (2018), doi: https://doi.org/10.1016/j.tetlet.2018.09.001
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1
Tetrahedron Letters
Copper-catalyzed cross-coupling of chloramine salts and arylboronic acids in water: a
green and practical route to N-arylsulfonamides
Banlai Ouyang a, b, , Yanxia Zheng b, Yi Liu b, Fei Liu b, Juying Yao b, Yiyuan Peng a, 
a Key Laboratory of Functional Small Organic Molecule, Ministry of Education, Key Laboratory of Green Chemistry, Jiangxi Province, College of Chemistry &
Chemical Engineering, Jiangxi Normal University, Nanchang, Jiangxi 330022, P. R. China. E-mail: nsouyang@outlook.com or yiyuanpeng@jxnu.edu.cn;
b Department of Chemistry, Nanchang Normal University, Nanchang 330032, P. R. China.
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A green and practical method for the synthesis of N-arylsulfonamides from chloramine salts and
arylboronic acids is herein developed. The reaction proceeds readily in the presence of 5 mol%
of CuI and 2.5 equiv. K2CO3 in water at room temperature, generating a variety of N-
arylsulfonamides in moderate to good yields with good functional group tolerance.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
chloramine salt
cross-coupling reaction
copper-catalyzed
green chemistry
N-arylsulfonamide
Introduction
Chloramine salts have been recognized as an important source for N-building blocks due to its ready commercial availability.
Significantly, we found chloramine salts have highly attractive practical characteristics: easy and amenable preparation on large
scales, nontoxic byproducts, high stability to air and heat, and excellent reactivity as a sulfonamidation reagent.1 By using
chloramine salts, chlorosulfonamidation, aminohydroxylation, or aziridination of olefins, sulfonamidation of relatively highly
reactive alkanes, and decarboxylative sulfonamidation of carboxylic acids can be performed to give chlorosulfonamidated
products,2 β-sulfonamido alcohols,3 aziridines4 and sulfonamidated compounds,5 respectively. In these procedures, nitrene species
derived from chloramine salts by metal- or nonmetal-assisted removal of sodium chloride are generally regarded as intermediates.
In 2011, Chandrasekaran and co-workers found that chloramine salts can behave as a dual nucleophile when its chlorine atom is
removed in the form of BrCl.6 Recently, it was further found that chloramine salts can react with arylboronic acids in the present of
a copper catalyst to generate N-arylsulfonamides. These results indicated that chloramine salts can also serve as an electrophile to
undergo oxidative addition at the N-Cl bond .7
N-Arylsulfonamide is a kind of common structural motif in pharmaceutical agents and agrochemicals.8 Traditionally, N-
arylsulfonamides were prepared by nucleophilic substitution of sulfonyl chlorides with aromatic amines. However, this classical
approach requires the use of mutagenic sulfonyl chlorides and genotoxic aryl amines. As an alternative, the metal-catalyzed N-
arylation of sulfonamides with aromatic halides allows the synthesis of N-arylsulfonamides free of the use of sulfonyl chloride, but
these reactions generally require harsh reaction conditions due to the low nucleophilicity of sulfonamides (Scheme 1-a).9 To avoid
harsh reaction conditions, Chan and Lam etc. developed the copper-catalyzed cross-coupling of sulfonamides with arylboronic
acids, which generally go through under relatively mild reaction conditions with short reaction time,10 but the Chan–Lam coupling
reaction typically requires a stoichiometric amount of copper salt and suffers from the limited substrate scope (Scheme 1-b).
Although significant progress has been achieved in the transition metal-catalyzed direct sulfonamidation of C-H bonds using
sulfonyl azides as the amine source recently, these reactions involve precious Rh, Ir or Ru catalysts and toxic organic solvents
(Scheme 1-c).11 In 2014, Kim and co-workers developed a copper-catalyzed cross-coupling between arylboronic acids and sulfonyl
azides to give N-arylsulfonamides in the absence of ligands and bases.12 This reaction proceeds efficiently under mild conditions
———
 Corresponding author.
e-mail: nsouyang@outlook.com or yiyuanpeng@jxnu.edu.cn

3
with a broad functional groups tolerance, but sulfonyl azides are
not shelf stable and require precautions in handling (Scheme 1-
d). Very recently, we described a copper catalyzed cross-
coupling between arylboronic acids and chloramine salts with
low catalyst loading at room temperature, but this procedure
suffers from some disadvantages such as the use of an organic
solvent and a strong base.7a Compared to sulfonyl azides,
chloramine salts are stable and readily accessible. Therefore, we
reason that it will be advantageous that chloramine salts serving
as an alternative to sulfonyl azides react with arylboronic acids
to give N-arylsulfonamides. In this work, we describe an
improved approach to furnish N-arylsulfonamides from
arylboronic acids and chloramine salts with weak base in water
at room temperature (Scheme 1-e).
Results and discussions
Initially, the reaction of p-tolylboronic acid (1j) and
chloramine T (2a) was employed as the model reaction for
condition optimization. To our delight, the desired N-
arylsulfonamide 3j was obtained when the model reaction was
treated with 5 mol% Cu(OAc)2 and 1.3 equiv. K2CO3 with H2O
as solvent at room temperature (Table 1, entry 1). Encouraged
by this positive result, further optimization of the reaction
conditions was carried out. The results were presented in Table
1. For copper catalysts, the results demonstrated that CuI is the
Scheme 1 Selected examples for synthesis of N-
arylsulfonamides
optimal catalyst for this transformation (Table 1, entries 1-9). When precious Pd(OAc)2 was used as the catalyst, a homocoupling
product of p-tolylboronic acid was obtained in 65% yield (Table 1, entry 10), whereas no desired product were observed. In the
absence of a metal catalyst, a complex mixture was obtained with very low conversion (Table 1, entry 11). Subsequently, various
bases were explored. The results revealed that K2CO3 was the best base, producing the desired N-arylsulfonamide 3j in 63% isolated
yield (Table 1, entry 7), while other bases including AcONa·3H2O, NaOH, KOH and Na2CO3 did not give better yields (Table 1
entries 12-15). Interestingly, increasing the catalyst loading from 5 mol% to 10 mol% did not show any improvement in the reaction
efficiency (Table 1, entry 16). Gratifyingly, when the amount of K2CO3 was increased to 2.5 equiv., the yield reached 85% (Table 1,
entry 20). However, further increase of the amount of base did not improve the isolated yield (Table 1, entry 21). Finally, when 4-
methylphenylboronic acid pinacol ester was used instead of 4-methylphenylboronic acid (1j) to react with chloramine T, N-
arylsulfonamide 3j was isolated only in 55% yield.
Table 1 Optimization of reaction conditionsa
Entry
Catalyst
Base
Yield%b
1
2
Cu(OAc)2
Cu(OTf)2
CuCl2
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
60
44
45
47
60
58
63
56
59
0
3
4
CuCl
5
CuBr2
6
CuBr
7
CuI
8
CuSO4·5H2O
CuTC
9
10
11
Pd(OAc)2
/
0

4
12
13
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
CuI
AcONa·3H2O
NaOH
32
49
51
54
63
53
69
77
85
85
55
14
KOH
15
Na2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
16c
17d
18e
19f
20g
21h
22i
a Reaction condition: 0.3 mmol TsNNaCl, 1.2 equiv 4-Me-PhB(OH)2, 1.3 equiv base, 0.05 equiv catalyst, 1.5 mL H2O, 25 oC; 18 hrs; b Isolated yield; c 0.1
equiv CuI was used; d 1.0 equiv K2CO3 was used; e 1.5 equiv K2CO3 was used; f 2.0 equiv K2CO3 was used; g 2.5 equiv K2CO3 was used; h 3.0 equiv K2CO3
was used, i 4-methylphenylboronic acid pinacol ester was used instead of 4-Me-PhB(OH)2.
With the optimized conditions in hand (5 mol% CuI and 2.5 equiv. K2CO3 in H2O at room temperature), we then examined the
scope and generality of the reaction with respect to the arylboronic acid. As shown in Table 2, a broad range of arylboronic acids 1
with electron-donating or -withdrawing substituents in the para or meta position of the aryl ring are compatible with this
transformation, delivering the corresponding N-arylsulfonamides in moderate to good yields. However, this reaction does not seem
to work with ortho-substituted arylboronic acids presumably due to the steric hindrance. For example, the reaction of (4-
fluorophenyl)boronic acid (1b) and (3-fluorophenyl)boronic acid (1c) with chloramine T (2a) offered corresponding N-
arylsulfonamides 3b and 3c in 76% and 67%
Table 2 Substrate scope.a
Entry
R1
R2
Product
yield (%)b
1
2
H
4-F
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
69
76
67
15
30
65
51
49
54
61
52
38
41
85
3a
3b
3c
3d
3e
3f
3
4c
3-F
2-F
5
4-CF3
4-Cl
6
7
3-Cl
3g
3h
3i
8
3,5-Cl
4-Br
9
10
11
12d
13e, f
14
3-CH2OH
3-CHO
4-COOMe
4-COOH
4-Me
3j
3k
3l
3m
3n

5
15
16
17
13
14
15
16
17
18
19
3-Me
4-OMe
4-OH
H
Me
Me
Me
Cl
74
53
0
3o
3p
3q
4a
4b
4c
4d
4e
4f
75
71
66
65
64
57
59
4-Me
3-Me
4-F
Cl
Cl
Cl
3-F
Cl
4-Cl
4-Br
Cl
Cl
4g
a
b
c
Reaction condition: 0.3 mmol TsNNaCl, 1.2 equiv. arylboronic acids, 2.5 equiv. K2CO3, 0.05 equiv. CuI, 1.5 mL H2O, 18 hrs;
Isolated yield; p-
Toluenesulfonamide was isolated in 55% yield; d Methyl 4-hydroxybenzoate was obtained in 43% yield; e 4-Hydroxybenzoic acid was isolated in 36% yield;
f 3.5 equiv K2CO3 was used.
yields, respectively, whereas the use of a ortho-substituted
arylboronic acid such as (2-fluorophenyl)boronic acid (1d) afforded
p-toluenesulfonamide instead of the expected N-arylsulfonamide as
the major product, presumably by a Cu-catalyzed reducing reaction
of chloramine T. When a trifluoromethyl-substituted arylboronic
acid was employed, it showed less reactivity and provided a
relatively lower yield. Moreover, chloro-substituted arylboronic
acids were tolerated, providing the corresponding products 3f-3h in
moderate yields. Particularly, a bromo substituent survived the
reaction, which is valuable for further transformations. The reaction
of (4-bromophenyl)boronic acid with chloramine T (2a) produced
N-arylsulfonamide 3i in 54% yield. Furthermore, alcohol and
formyl
group
were
also
acid
tolerated.
(1j) and
(3-
(3-
T
(Hydroxymethyl)phenyl)boronic
formylphenyl)boronic acid (1k) reacted with chloramine
Scheme 3 Proposed reaction pathway
smoothly affording the corresponding N-arylsulfonamides in 61%
and 52% yield respectively. Unexpectedly, carbomethoxy- and carboxyl-substituted arylboronic acids 1l and 1m showed low
efficiency in this reaction due to the oxidative hydroxylation.
Electron-donating group-attached arylboronic acids were also efficient for the reactions with chloramine T (2a) to produce the
corresponding N-arylsulfonamides 3n-3p. For example, the reactions of methyl-substituted arylboronic acid 1n and 1o gave the N-
arysulfonamide 3n in 85% yield and 3o in 74% yield, respectively. In addition, (4-methoxyphenyl)boronic acid (1p) was also
suitable for this reaction, affording the corresponding N-arylsulfonamides 3p in 53% yield. Unfortunately, free phenol moiety was
not tolerated due to its high reducibility. The reaction of (4-hydroxyphenyl)boronic acid (1q) with chloramine T gave a complex
mixture, and no desired product was observed.
To further explore the potential of our methodology, chloramine salt 2b was also tested for the synthesis of N-arylsulfonamide
4a-4g. The results indicated chloramine salt 2b was also normally efficient in the reaction of arylboronic acids, giving the desired
N-arylsulfonamides in moderate to good yields. However, alkyl chloramine salts were not compatible with this transformation.
We then tried to gain some insights into the mechanism of this sulfonamidation reaction. Provided that the key step of the
reaction involves a copper-nitrene complex, the reaction would be promoted by silver ion, which facilitates the expulsion of the
chloridion in the form of AgCl. To test this assumption, AgSbF6 and AgOTf was added to the standard reaction respectively. The
result showed that a complex reaction mixture was obtained instead of the desired product. (Scheme 2) This result indicated that the
transformation should not proceed via a copper-nitrene intermediate.
Based on above data and previous studies,7c, 13 a plausible mechanism is illustrated in Scheme 3. Initially, transmetalation of the
aryl group of the arylboronic acid with copper(I) under basic condition gives rise to complex A, followed by oxidative addition of
N-Cl bond of chloramine T (2a) at the Cu(I) center to afford complex B. Finally, the C-N reductive elimination of complex B
delivers the desired N-arylsulfonamides and regenerates the copper(I) catalyst.
To demonstrate the potential synthetic application of the
present method, the sulfonamidation of 1j on a gram scale was
Scheme 2 Preliminary mechanistic studies
Scheme 4 Gram-scale sulfonamidation of arylboronic acids

6
also examined. The desired product 3j was obtained with a yield of 80% (Scheme 4).
Conclusions
In conclusion, we have developed a green and practical method for the synthesis of N-arylsulfonamides from easily available
chloramine salts and arylboronic acids. In this process, the chloramine salt is assumed to serve as an electrophile to oxidize the
copper catalyst through oxidative addition. Importantly, this reaction can be performed on a gram scale under mild conditions,
which is important to industry applications. Further exploration based on this new method for the synthesis of well-known bioactive
N-arylsulfonamides in a convenient and economical manner is ongoing in our lab.
Acknowledgments
Financial support from the Natural Science Foundation of China (No. 31560152), the Open Project Program of Key Laboratory
of Functional Small Organic Molecule, Ministry of Education, Jiangxi Normal University (No. KLFS-KF-201721) and the Key
Discipline Project of Nanchang Normal University (No: NSXK20141003) are gratefully acknowledged.
A. Supplementary data
1
Experimental procedure, characterization data, H and 13C NMR spectra of compounds 3 and 4 can be found, in the online
version.
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Graphical Abstract
Copper-catalyzed cross-coupling of
chloramine salts and arylboronic acids in
water: a green and practical route to N-
arylsulfonamides
Leave this area blank for abstract info.
Banlai Ouyang a, b, , Yanxia Zhengb, Yi Liu b, Fei Liu b, Juying Yao b, Yiyuan Peng a, 

9
Highlights
1) A green and practical method for the synthesis
of N-arylsulfonamides
2) Copper-catalyzed sulfonamidation reaction of
arylboronic acids with chloramine salts
3) The reaction goes through in water at room
temperature
4) A broad range of arylboronic acids are
compatible with this transformation
5) This transformation can be conducted on a
gram scale