Nitrosoarenes as Nitrogen Source for Generation of Sulfonamides with the Insertion of Sulfur Dioxide under Metal-Free Conditions?

Article abstract of DOI:10.1002/cjoc.202000053

A metal-free reaction of nitrosoarenes, aryldiazonium tetrafluoroborates, and sulfur dioxide under mild conditions is developed, giving rise to sulfonamides in moderate to good yields. This transformation proceeds efficiently at room temperature in the presence of cyclohexa-1,4-diene with a broad reaction scope. Good functional group compatibility is observed, including cyano, halo, and ester. A plausible mechanism involving a radical process with the insertion of sulfur dioxide is proposed, and cyclohexa-1,4-diene serves as the reductant during the transformation.

Full text of DOI:10.1002/cjoc.202000053

Chinese Journal
of Chemistry
CJC
中 国 化 学 - An International Journal
Accepted Article
Title: Nitrosoarenes as the Nitrogen Source for the Generation of Sulfonamides
with the Insertion of Sulfur Dioxide under Metal-free Conditions
Authors: Xuefeng Wang, Yanmei Lin, Jin-Biao Liu, Fu-Sheng He,* Yunyan Kuang,*
and Jie Wu*
This manuscript has been accepted and appears as an Accepted Article online.
This work may now be cited as: Chin. J. Chem. 2020, 38, 10.1002/cjoc.202000053.
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Chinese Journal
of Chemistry
Sulfonamide, Sulfur dioxide, Sulfonylation, Nitrosoarene
Report
CJC
中
国 化 学 - An International Journal
Nitrosoarenes as the Nitrogen Source for the Generation of
Sulfonamides with the Insertion of Sulfur Dioxide under Metal-free
Conditions
Xuefeng Wang,a,b Yanmei Lin,a Jin-Biao Liu,c Fu-Sheng He,*b Yunyan Kuang,*a and Jie Wu*,b,d
a Department of Chemistry, Fudan University, 2005 Songhu Road, Shanghai 200438 (China)
b School of Pharmaceutical and Materials Engineering & Institute for Advanced Studies, Taizhou University, 1139 Shifu Avenue, Taizhou 318000 (China)
c School of Metallurgical and Chemical Engineering, Jiangxi University of Science and Technology, Ganzhou 341000 (China)
d State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai
200032 (China)
Dedicated to the 70th anniversary of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences
Abstract A metal-free reaction of nitrosoarenes, aryldiazonium tetrafluoroborates, and sulfur dioxide under mild conditions is developed, giving rise to
sulfonamides in moderate to good yields. This transformation proceeds efficiently at room temperature in the presence of cyclohexa-1,4-diene with a broad
reaction scope. Good functional group compatibility is observed, including cyano, halo, and ester. A plausible mechanism involving a radical process with
the insertion of sulfur dioxide is proposed, and cyclohexa-1,4-diene serves as the reductant during the transformation.
Scheme 1 Methods for the generation of sulfonyl compounds
and co-workers, ref
Willis
14a
(a)
Background and Originality Content
mol
%)
Cu(OTf)2 (10
mol
O2
S
R1
%)
ligand (10
Cs2CO3
DMSO, 130 ο 16 h
+
It is known that nitrosoarenes are versatile building blocks in
organic synthesis, and a wide range of nitrogen-containing
compounds can be accessed starting from nitrosoarenes.1-3 The
reactivity of nitrosoarenes has been well explored, which can be
applied as nucleophiles, electrophiles, and radical precursors.4 For
instance, Zhu and co-workers reported the synthesis of
functionalized indanone-fused tetrahydroisoxazole through a
catalyst-free domino reaction of nitrosoarenes and 1,6-ynenones
with good chemo- and regioselectivity.3c
Recently, much attention has been drawn to the synthesis of
sulfonyl compounds through the insertion of sulfur dioxide into
small molecules via radical processes,5 due to the importance of
sulfonyl compounds in pharmaceuticals and materials.6 We and
others have demonstrated several radical approaches for the
generation of sulfonyl compounds with the insertion of sulfur
dioxide.7-9 These routes provide the direct access to sulfonyl
radicals, avoiding the use of sulfonyl precursors. For example, the
combination of aryldiazonium tetrafluoroborates and the sulfur
dioxide surrogates of DABCO·(SO2)2 or potassium/sodium
metabisulfite is powerful to provide arylsulfonyl radicals under
extremely mild conditions.7 Further exploration discovered that
+
Ar
DABCO
R1
HN
R2
OMe
B(OH)2
(SO2)2
Ar
N
R2
C,
MeO
ligand
N
N
and co-workers, ref
Jiang
14b
(b)
PPh3 TBAB
,
+
+
Na2S2O5
Ar N2BF4
Ar SO2NH2
NaN3
MeCN/H2O
and co-workers, ref
14c
Ramon
(c)
Cl-
N
O
O
:
O
NH2
1:2
M)
(0.4
+
+
Na2S2O5
Ph3Bi
ArNO2
Ph SO2NHAr
mol
CuCl
%)
(1
80 ο 24 h
C,
and co-workers, ref
Wu
14d
(d)
mol
PF
%)
mol
Cu(MeCN)4 6 (20
K2S2O5
O
O
Ar NO2
%)
Ar
1,10-phenanthroline (10
S
+
N
(Het)Ar
iPrOH
NMP
H
(2.0 equiv),
70 ο 48 h
C,
(Het)Ar B(OH)2
and co-workers, ref
Chen
14e
various
radical
precursors
including
potassium
K2CO3 nBu4NCl
O
Ar1
O
,
alkyltrifluoroborates,10 aryl/alkyl halides,11 diaryliodonium salts,12
and others13 were workable with sulfur dioxide giving rise to
aryl/alkyl sulfonyl radical intermediates. Prompted by the
advances of nitrosoarenes as radical precursors, we envisioned that
nitrosoarene might be combined with sulfonyl radical for further
transformation. After the addition of sulfonyl radical to the N=O
bond of nitrosoarene, we reasoned that sulfonamide would be
S
Ar2
Ar1
K2S2O5
Ar2 NO2
+
+
B(OH)2
MeCN, 130 o
C
N
H
work
this
(e)
1
Ar N2BF4
NO
O
O
reductant
R
+
S
R
N
Ar
DABCO SO
(
)
2 2
2
H
3
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
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Running title
Chin. J. Chem.
formed in the presence of suitable reductant.
7
2.0 equiv
2.0 equiv
60
60
MeCN
MeCN
84 (81)
Although there are numerous approaches for the synthesis of
sulfonamides, only several methods employed the sulfur dioxide
surrogates of DABCO·(SO2)2 or sodium metabisulfite. For example,
Willis and co-workers reported the synthesis of sulfonamides
8b
69
a 1H NMR yield using 1,3,5-trimethoxybenzene as internal standard. Isolated
yield of entry 7 is shown in parentheses. 2.0 equiv of DABCO·(SO2)2 was
b
through
a
copper-catalyzed three-component reaction of
added.
arylboronic acids, amines, and DABCO·(SO2)2 at high temperature
(130 °C) (Scheme 1, eq. a).14a Jiang and co-workers described the
formation of primary sulfonamides via a reaction of aryldiazonium
tetrafluoroborates, sodium metabisulfite, and sodium azide in the
presence of triphenylphosphine (Scheme 1, eq. b).14b Preparation
Since we have demonstrated that aryldiazonium
tetrafluoroborates would react with DABCO·(SO2)2 efficiently under
extremely mild conditions leading to arylsulfonyl radical via a single
electron transfer (SET), initial studies were performed for the
reaction of p-methylphenyldiazonium tetrafluoroborate 1a,
DABCO·(SO2)2 and nitrosobenzene 2a. At the outset, cyclohexa-1,4-
diene was used as the reductant as well as the proton source. The
reaction was carried out at room temperture in 1,2-dichloroethane
(DCE) under argon atmosphere (Table 1, entry 1). To our delight,
the corresponding sulfonamide was obtained in 22% yield. The
result could be improved when the reaction took place in
acetonitrile (57% yield, Table 1, entry 2). A lower yield was
produced when the reaction occurred at 0 °C while changing the
reaction temperature to 60 °C gives slightly higher yield (Table 1,
entries 3 - 5). The yield of product 3a was improved to 69% when
the amount of p-methylphenyldiazonium tetrafluoroborate 1a was
increased to 1.5 equiv (Table 1, entry 6). A better result was formed
when 2.0 equiv of p-methylphenyldiazonium tetrafluoroborate 1a
was employed (Table 1, entry 7). No advantage was observed when
2.0 equiv of DABCO·(SO2)2 was utilized (Table 1, entry 8). The yield
was lower (42%) without the addition of cyclohexa-1,4-diene (data
not shown in Table 1).
of sulfonamides through
a copper-catalyzed reaction of
triarylbismuthines, sodium metabisulfite, and nitro compounds
was developed by using deep eutectic solvent as a reaction
medium (Scheme 1, eq. c).14c In these transformations, harsh
reaction conditions with high temperature, transition metal
catalyst, large excess amount of phosphine, or triarylbismuthines
had to be used. Therefore, it is highly desirable to develop a general
and efficient route to sulfonamides from sulfur dioxide. As
mentioned above, nitrosoarene might act as the nitrogen source
with the combination of sulfur dioxide for the preparation of
sulfonamides. Herein, we report a metal-free reaction of
nitrosoarenes, aryldiazonium tetrafluoroborates, and sulfur
dioxide under mild conditions, giving rise to sulfonamides in
moderate to good yields (Scheme 1, eq. d). This transformation
proceeds efficiently at room temperature in the presence of
cyclohexa-1,4-diene with a broad reaction scope. Good functional
group compatibility is observed, including cyano, halo, and ester. A
plausible mechanism involving a radical process with the insertion
of sulfur dioxide is proposed, and cyclohexa-1,4-diene serves as the
reductant during the transformation.
Table 2 Scope exploration for the metal-free reaction of aryldiazonium
Results and Discussion
Results (sample title, optional)
Table 1 Initial studies for the reaction of p-methylphenyldiazonium
tetrafluoroborate 1a, sulfur dioxide and nitrosobenzene 2a
cyclohexa-1,4-diene
1a
p-Tol N2BF4
equiv)
(2.0
O
O
+
PhN
O
Ph
S
N
p-Tol
solvent, Ar, 16 h
DABCO
SO
(
)
2 2
2a
H
mmol
0.2
1.5
3a
equiv
Entry
Substrate 1a
T (°C)
Solvent
DCE
Yield (%)a
1
2
3
4
5
6
1.2 equiv
25
22
1.2 equiv
1.2 equiv
1.2 equiv
1.2 equiv
1.5 equiv
25
0
MeCN
MeCN
MeCN
MeCN
MeCN
57
47
54
58
69
40
60
60
Chin. J. Chem. 2019, 37, XXX－XXX
© 2019 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Running title
Chin. J. Chem.
tetrafluoroborates 1, sulfur dioxide and nitrosoarenes 2 a
was obtained 70% yield. The acetyl-containing sulfonamide 3j was
generated in 60% yield. Subsequently, reactions of aryldiazonium
1
Ar N2BF4
cyclohexa-1,4-diene
NO
O
O
equiv)
R
tetrafluoroborates
nitrosobenzene were investigated. Different substituted
aryldiazonium tetrafluoroborates were suitable in the
1,
DABCO·(SO2)2,
and
1-methyl-4-
(2.0
+
S
R
MeCN, 60ο
Ar, 16 h
N
Ar
DABCO
SO
(
)
2 2
C,
H
2
3
1
transformation, and converted into the corresponding
sulfonamides as expected. Heteroaryldiazonium tetrafluoroborate
was workable as well. For example, methyl 3-(N-(p-
tolyl)sulfamoyl)thiophene-2-carboxylate 3t was produced in 46%
yield under the standard conditions.
Cl
Me
CO2
O
O
O
O
O
O
S
S
S
N
H
N
H
N
H
3a
,
81%
3b
,
72%
3c
63%
,
In our previous reports, we identified that arylsulfonyl radical
would be formed in situ from the combination of aryldiazonium
tetrafluoroborates 1 and DABCO·(SO2)2 under catalyst- and
Br
F
O
O
O
O
O
O
O
S
S
S
N
H
N
H
N
H
additive-free conditions. Thus,
a control experiment was
3e
,
3f 77%
,
3d
70%
70%
,
performed for the model reaction of p-methylphenyldiazonium
tetrafluoroborate 1a, DABCO·(SO2)2 and nitrosobenzene 2a in the
presence of cyclohexa-1,4-diene with the addition of 3.0 equiv of
2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) under the standard
conditions. As expected, the formation of the corresponding
sulfonamide 3a was not observed. On the basis of previous reports
and this result, we proposed a plausible mechanism as shown in
Scheme 2. We hypothesized that the arylsulfonyl radical generated
in situ from aryldiazonium tetrafluoroborate 1 and DABCO·(SO2)2
would attack the N=O bond of nitrosoarene 2, leading to radical
intermediate A. With the assistance of cyclohexa-1,4-diene,
compound B would be formed, which would be further reduced to
sulfonamide 3. However, another reaction pathway could not be
excluded: Radical intermediate A would combine with arylsulfonyl
radical, and the resulting compound would further undergo N-O
bond cleavage to provide the final product.
OMe
Me
O
CN
tBu
O
O
O
O
O
S
S
S
N
N
H
N
H
H
3i 71%
3g
,
82%
3h
,
,
70%
O
O
O
O
O
O
S
S
S
N
H
Cl
N
N
H
H
3j
60%
3l
,
3k
,
64%
58%
,
O
O
O
O
O
O
S
S
S
N
N
H
N
H
H
Br
F
F
3C
3n 57%
3o 71%
,
3m
,
80%
,
O
O
O
O
O
O
Scheme 2 Plausible mechanism
S
S
N
S
N
N
H
H
H
1
Ar N2BF4
+
EtOOC
O
SO2
O
3q
3p
73%
,
Ar
58%
,
3r
63%
,
S
OMe
Cl
Ar
DABCO
SO
(
)
2 2
DABCO
N2
O
O
O
O
NO
S
S
SO
,
2
N
N
O
O
R
R
H
H
S
S
N
2
Ar
COOMe
H
3
3s
3t 46%
,
38%
,
reductant
reductant
H+
O
O
O
O
R
R
S
S
a
Reaction conditions: Aryldiazonium tetrafluoroborate 1 (0.4 mmol),
Ar
N
Ar
N
DABCO·(SO2)2 (0.3 mmol), nitrosoarene 2 (0.2 mmol), cyclohexa-1,4-diene
(0.4 mmol) and MeCN (2.0 mL), stirred under argon at 60 C for 16 h.
OH
A
O
B
o
Isolated yield based on nitrosoarene 2.
With the preliminary optimized reaction conditions in hand, we
next explored the scope generality for the synthesis of
Conclusions
sulfonamides through
a
three-component reaction of
In conclusion, we have developed a metal-free reaction of
nitrosoarenes, aryldiazonium tetrafluoroborates, and sulfur
dioxide under mild conditions, giving rise to sulfonamides in
moderate to good yields. This transformation proceeds efficiently
at room temperature in the presence of cyclohexa-1,4-diene with
a broad reaction scope. Good functional group compatibility is
observed, including cyano, halo, and ester. A plausible mechanism
involving a radical process with the insertion of sulfur dioxide is
proposed, and cyclohexa-1,4-diene serves as the reductant during
aryldiazonium tetrafluoroborates 1, DABCO·(SO2)2, and
nitrosoarenes 2. The result is presented in Table 2. It was found
that all reactions worked efficiently in the presence of cyclohexa-
1,4-diene. A range of nitrosoarenes 2 was firstly examined in the
reaction of p-methylphenyldiazonium tetrafluoroborate 1a with
DABCO·(SO2)2. A broad reaction scope was achieved, and good
functional group compatibility was observed including cyano, halo,
acetyl, and ester. For instance, the cyano-substituted product 3h
Chin. J. Chem. 2019, 37, XXX－XXX
© 2019 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Running title
Chin. J. Chem.
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General procedure for the reaction of aryldiazonium
tetrafluoroborates 1, DABCO·(SO2)2 and nitrosoarenes 2: MeCN
(2.0 mL) and 1,4-cyclohexadiene (0.4 mmol, 2.0 equiv) were added
to
a
rubber-septa-sealed tube containing aryldiazonium
tetrafluoroborate 1 (0.4 mmol, 2.0 equiv), DABCO·(SO2)2 (0.3 mmol,
1.5 equiv) and nitrosoarene 2 (0.2 mmol, 1.0 equiv) under Ar
o
atmosphere via syringe. The mixture was then stirred at 60 C for
16 h. After the scheduled time, the solvent was evaporated under
reduced pressure and the residue was purified directly by flash
column chromatography (Eluent: 20-40 % EtOAc/n-hexane) to
afford the corresponding product 3.
Supporting Information
The supporting information for this article is available on the
WWW under https://doi.org/10.1002/cjoc.2018xxxxx.
Acknowledgement
Financial support from National Natural Science Foundation of
China (Nos. 21871053, 21532001 and 21762018) and Natural
Science Foundation of Jiangxi Province (20192BCBL23009) is
gratefully acknowledged.
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www.cjc.wiley-vch.de
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Running title
Chin. J. Chem.
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Running title
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(The following will be filled in by the editorial staff)
Manuscript received: XXXX, 2019
Manuscript revised: XXXX, 2019
Manuscript accepted: XXXX, 2019
Accepted manuscript online: XXXX, 2019
Version of record online: XXXX, 2019
Chin. J. Chem. 2019, 37, XXX－XXX
© 2019 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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This article is protected by copyright. All rights reserved.

Running title
Chin. J. Chem.
Entry for the Table of Contents
Page No.
Nitrosoarenes as the Nitrogen Source for the
Generation of Sulfonamides with the Insertion
of Sulfur Dioxide under Metal-free Conditions
Ar N2BF4
DABCO
cyclohexa-1,4-diene
NO
O
O
R
equiv)
(2.0
MeCN, 60 ο
+
S
R
N
Ar
SO
Ar, 16 h
C,
(
)
2 2
H
insertion of sulfur dioxide under metal-free conditions
as source
nitrosoarenes
the nitrogen
for the
of sulfonamides
generation
Xuefeng Wang, Yanmei Lin, Jin-Biao Liu, Fu-
Sheng He,* Yunyan Kuang,* and Jie Wu*
Chin. J. Chem. 2019, 37, XXX－XXX
© 2019 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
This article is protected by copyright. All rights reserved.