Palladium-Catalyzed Mono-Selective ortho C H Arylation of Aryl Sulfonamides in Water: A Concise Access to Biaryl Sulfoamide Derivatives

Article abstract of DOI:10.1002/adsc.201501104

A green atom-economical method for the synthesis of biaryl sulfonamide derivatives via palladium(II)-catalyzed C H bond activation by employing an amino acid moiety as the bidentate directing group has been developed. The protocol proceeded efficiently in water; high yields and broad substrate scope were achieved. The reaction shows good functional group compatibility and proceeds in a highly selective manner at the ortho position of arenes connected to sulfonamide sulfur atoms. This auxiliary can be easily removed either by acidic hydrolysis, or converted into primary biaryl sulfomamides with a 30 mol % amount of CuO as catalyst. Mechanistic studies show that the present bidentate directing group is essential for promoting ortho C H bond activation of arenes connected to sulfonamide sulfur atoms. (Figure presented.) .

Full text of DOI:10.1002/adsc.201501104

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DOI: 10.1002/adsc.201501104
À
Palladium-Catalyzed Mono-Selective ortho C H Arylation of
Aryl Sulfonamides in Water: A Concise Access to Biaryl
Sulfoamide Derivatives
a
a
a
a
a,
Wei Liu, Dongyin Wang, Yongli Zhao, Fei Yi, and Junmin Chen *
a
Department of Chemistry, Jiangxi Normal University, Nanchang 330022, Peopleꢀs Republic of China
Fax:+86 0791 8812 0380; Phone:+86 0791 8812 0380; e-mail: jxnuchenjm@163.com
Received: December 3, 2015; Revised: March 28, 2016; Published online: May 12, 2016
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201501104.
Abstract: A green atom-economical method for the can be easily removed either by acidic hydrolysis, or
synthesis of biaryl sulfonamide derivatives via palla- converted into primary biaryl sulfomamides with
dium(II)-catalyzed CÀH bond activation by employ- a 30 mol% amount of CuO as catalyst. Mechanistic
ing an amino acid moiety as the bidentate directing studies show that the present bidentate directing
group has been developed. The protocol proceeded group is essential for promoting ortho CÀH bond ac-
efficiently in water; high yields and broad substrate tivation of arenes connected to sulfonamide sulfur
scope were achieved. The reaction shows good func- atoms.
tional group compatibility and proceeds in a highly
selective manner at the ortho position of arenes con- Keywords: amino acids; aryl sulfonamides; bidentate
nected to sulfonamide sulfur atoms. This auxiliary directing group; CÀH arylation; palladium
Introduction
cally installed metal-active groups and such starting
materials require additional steps to prepare them
The sulfonamides have been extensively used as phar- from feedstock chemical sources. Moreover, harsh re-
maceutical and agricultural agents because of their di- action conditions are generally needed, thus reducing
[
1]
[10a–d]
verse biological properties. Among them, biaryl- their versatility and simplicity.
based sulfonamide motifs have emerged as privileged
structures in drug discovery due to their promising
bioactivities and diverse medicinal uses (Figure 1).
For instance, compound MK-996 and its analogues
such as L-159,894 are a series of new potent angioten-
[2]
sin II antagonists for treating hypertension. PF-
455242 is a selective, short-acting antagonist of the
k-opioid receptor, it was pursued in a phase I clinical
4
[
3]
trial for the treatment of bipolar disorder. BPBTS
represents a structurally novel and potent sodium
channel blocker that may be used as a template for
[
4]
the development of analgesic agents. Meanwhile,
cyclic sulfonamides (e.g., benzosultams) have also
shown broad inhibitory activities against a diverse
[
5]
[6]
array of enzymes, such as COX-2, HIV integrase,
[
7]
[8]
[9]
lipoxygenase, Calpain 1, and MMP-2.
As a consequence, many efficient methods have
been developed to access different biaryl scaffolds.
However, palladium-catalyzed cross-coupling reac-
tions such as the Suzuki and Stille were still important
tools in the synthesis of 1,1’-biaryl 2-sulfonamide com- Figure 1. Selected bioactive biaryl-based sulfonamide skele-
[
10]
pounds (Scheme 1a). These tactics rely on strategi- tons.
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attempt to extend this analogous strategy to the cor-
responding aryl sulfonamide substrates. Initially, a va-
riety of amino acid auxiliaries were examined as a bi-
dentate directing group for the palladium-catalyzed
direct arylation of p-tolyl sulfonamides 1 with iodo-
benzene 2a (Table 1). Gratifyingly, substrate 1a,
which contains an glycine auxiliary, can be coupled
with 2a to afford the desired monoarylation product
3
a in 38% yield along with unreacted starting materi-
al in the presence of Pd(OAc) (10 mol%), AgOAc
2
(
2 equiv) in DMSO at 1108C for 24 h (Table 1,
entry 1). We next examined the effect of various
amino acids under the same reaction conditions. It
was found that the alfa-alanine auxiliary (substrate
Scheme 1. Strategies for building the biaryl-based sulfona-
mide scaffolds.
1
b) can improve the activity and gave the desired
product in 51% yield (Table 1, entry 2). We envision
In the recent decade, transition-metal-catalyzed CÀ
H bond activation has received tremendous attention, Table 1. Optimization of various directing groups and reac-
[11]
[a]
and great advances in this area have been made.
A
tion conditions
directing group (oxygen, nitrogen and sulfur contain-
ing) assisted CÀH bond activation is frequently used
to realize regio- and chemoselective transformations
[
12]
of selected CÀH bonds. Recent studies reveal that
the sulfonamide group can act as a directing group in
[
13]
promoting CÀH activation;
however, the CÀH
[b]
Entry
Substrate
Additive
Solvent
Yield (%)
bonds activation of arenes connected to sulfonamide
sulfur atoms is less developed. With the assistance
of SO NHC F as a directing group, Yu and co-work-
[
14]
1
2
3
4
5
6
7
8
9
1a
1b
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1c
1d
1e
1 f
AgOAc
AgOAc
AgOAc
Ag CO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
xylene
DMF
38
51
66
37
55
64
55
59
48
46
78
71
56
62
69
72
2
6
5
ers have successfully developed a series of palladium-
[
15]
catalyzed CÀH functionalization reactions;
excel-
2
3
lent yields of the carbonylation and methylation were
obtained. However, only moderate yields were ob-
tained in CÀH arylation reactions. Furthermore, the
AgOTf
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
NaOAc
AgOAc
Ag CO
selectivity for monoarylation versus diarylation was
DMA
AcOH
low (mono/di=3:1). Therefore, the direct CÀH aryla-
10
11
12
13
14
tion of arenes connected to sulfonamide sulfur atoms
H O
[
16]
2
still remains a significant challenge. Inspired by the
recently elegant work, which showed that bidentate
directing groups can drastically accelerate both
H O
2
H O
2
3
2
AgOTf
H O
2
[17]
C(sp2)ÀH and C(sp3)ÀH activation reactions,
15
K PO
3
H O
4
2
herein, we describe our efforts to employ a bidentate 16
directing group (DG) strategy to construct diverse 17
K
Cs
CO
CO
H
H
O
O
2
3
2
61
51
47
trace
trace
trace
2
3
2
1
1
2
2
2
8
9
0
1
2
t-BuOLi
NaOAc
NaOAc
NaOAc
NaOAc
H O
biaryl sulfonamide motifs by palladium-catalyzed
2
c
H O
direct ortho CÀH arylation of aryl sulfonamides in
2
H O
2
a single step (Scheme 1b).
H O
2
H O
2
[
a]
Results and Discussion
All reactions were carried out with 1 (0.5 mmol), 2a
(1.0 mmol), Pd(OAc)2 (0.05 mmol), and additive
(
1.0 mmol) solvents (0.5 mL) at 1108C for 24 h.
Recently, Yu and Chatani independently reported
that the complexes of Pd /amino acids (N,O-biden-
[
[
b]
II
Isolated yield.
5
c]
mol% of Pd(OAc) was used.
2
tate) can promote site-selective functionalization of
[
18]
C(sp2)ÀH and (sp3)ÀH bonds. Previously, we also
demonstrated that a glycine based N,O-bidentate di-
recting group can dramatically accelerate ortho CÀH
[
19]
arylation of benzoic acid derivatives. Therefore, we
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[
a]
that the bulkier amino acid could enhance the activity. Table 2. Scope of aryl iodides
As expected, its gem-dimethyl analogue (substrate
1
c) led to the corresponding product 3ca in 66%
yield (Table 1, entry 3). Then, substrate 1c and iodo-
benzene 2a were chosen as model substrates for sur-
veying the optimal reaction conditions. First, several
additives were tested; we found that Ag CO and
2
3
AgOTf could also promote the reaction, albeit with
lower yield (Table 1, entries 4, 5). Notably, NaOAc
could give similar promising results (Table 1, entries 3
vs 6). Then, various solvents were investigated with
NaOAc as additive. Screening of other solvents such
as xylene, DMF, DMA, and AcOH did not improve
the yield of the reaction (Table 1, entries 7–10). Grati-
fyingly, a 78% yield of 3ca was achieved when H O
2
was used as the solvent (Table 1, entry 11). Then, vari-
ous additives including silver and non-silver salts were
screened once again in H O. Additive screening led
2
us to discover NaOAc as the best choice (Table 1, en-
tries 12–18). When the loading of Pd(OAc) was re-
2
duced to 5 mol%, only a 47% yield was obtained
(
Table 1, entry 19). Finally, other mono- and bidentate
directing groups were also evaluated under the opti-
mized conditions. Curiously, beta-alanine (substrate
1
d), acetamide (substrate 1e), and 8-aminoquinoline
auxiliary (substrate 1 f) were ineffective and only
trace amounts of products were obtained (Table 1, en-
tries 20–22).
With the optimized conditions in hand, the scope of
aryl iodides was examined and the results are shown
in Table 2. In general, substrate 1c was arylated with
a wide range of aryl iodides to afford the mono-aryla-
tion products 3cb–3cq in good to excellent yields.
Both electron-donating and electron-withdrawing
groups at either the meta or para positions of the aryl
iodides were tolerated. Specifically, electron-deficient
aryl iodides afforded the arylation products in higher
yields (2g–i) than electron-rich ones (2b–f) (Table 2,
entries 1–8). The structure of compound 3ch was con-
[20]
firmed by X-ray crystallography analysis (Figure 2).
The reaction also proceeded well with heterocyclic
coupling partners; for example, 3-iodopyridine 1p
and 3-iodothiophene 1q gave the desired products in
good yields (Table 2, entries 15 and 16). Aryl iodides
with ortho substituents failed to afford the corre-
sponding products, presumably due to the steric hin-
drance. It should be pointed out that the reaction
mixtures were clear and the diarylation product was
not detected.
Next, the scope of aryl sulfonamides containing dif-
ferent substituents on arenes was investigated as
shown in Table 3. A broad range of aryl sulfonamides
were also applicable to this arylation process. When
phenyl sulfonamide 1g was used as the substrate,
a range of para-substituted aryl iodides underwent
this transformation to afford the corresponding prod-
ucts, 3gb, 3gc, and 3gg, in 75%, 77% and 82% yield,
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Table 2. (Continued)
fonamides containing an ortho substituents worked
well, affording the desired products, 3na, 3oa, and
ob, in 84%, 78%, and 70% yield, respectively. How-
3
ever, an attempt to employ a 3,5-disubstituted arylsul-
fonamide (1p) as the substrate failed to yield the ex-
pected product, showing that the present reaction was
also sensitive to the steric hindrance of aryl sulfona-
mide substrates.
[a,b]
Table 3. Scope of aryl sulfonamides with aryl iodides
[
[
a]
b]
All reactions were carried out with 1c (0.5 mmol), 2
(1.0 mmol), Pd(OAc)2 (0.05 mmol), and NaOAc
(1.0 mmol) in water (0.5 mL) at 1108C for 24 h.
Isolated yield.
Figure 2. X-ray crystal structure of 3ch (ORTEP diagram).
respectively. Substrate 1h with an electron-donating
p-MeO reacted smoothly with various aryl iodides
and gave the corresponding products 3hb, 3hc, and
3
1
hg in 68–81% yield. Notably, heterocyclic substrate
i was arylated with various aryl iodides and afforded
the products 3ia, 3ib and 3ig in good yield. Interest-
ingly, substrates 1j–k containing electron-withdrawing
groups were less reactive with the present catalysis
system. It was found that the yield dramatic increased
when AgOAc was used in place of NaOAc, and
[
a]
All reactions were carried out with 1 (0.5 mmol), 2
1.0 mmol), Pd(OAc)2 (0.05 mmol), and NaOAc
(
Bu NBr (10 mol%) was also added (1j, 1k). Aryl sul-
4
(1.0 mmol) in water (0.5 mL) at 1108C for 24 h.
Isolated yield.
[
[
b]
c]
fonamides containing a meta substituent such as 1l
and 1m also proceeded well, and offered satisfactory
yields (3lc, 3le, 3lg, and 3ma). Furthermore, aryl sul-
AgOAc was used in place of NaOAc and Bu NBr
4
(10 mol%) was added.
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Some preliminary mechanistic studies were carried
out to probe the details of this CÀH arylation reac-
tion. As a control experiment, the substrate 1q with
an ester group was not reactive, and only a trace
amount of product were obtained when substrate 1r
was used, indicating that both the free NH and car-
boxylic acid moieties play a key role in the CÀH acti-
vation reaction (Scheme 2, eqs. a and b). To gain fur-
ther insight into the mechanism of the arylation reac-
tion, the H/D exchange was also examined by heating
the substrate 1g with a catalytic amount of Pd(OAc)2
in D O (1M). After 24 h at 1108C, 89% deuterium
2
incorporation was observed at the ortho position of
1
g, whereas no deuterated product was observed in
the absence of NaOAc (Scheme 2, eq. c).
Scheme 3. Plausible reaction mechanism.
An intermolecular competitive reaction in which an
equimolar amount of 1g and 1g-D was used was
stopped at 26% conversion to give an intermolecular
kinetic isotope effect. The observed low KIE value
(
KIE value of 1.2) (Scheme 2, eq. d) suggests that the
CÀH bond cleavage step is not involved in the turn-
over-limiting step. These experiments indicated the
palladation process is reversible and CÀH activation
could take place under the reaction conditions with-
out the involvement of the ArI substrate. However,
an attempt to obtain the putative palladacycle inter-
mediate was unsuccessful.
Scheme 4. Transformation and removal of directing group.
[18b]
Based on the previous studies
and our experi-
mental results, a plausible reaction mechanism is pro-
posed in Scheme 3. The coordination of substrate 1 to
Pd(OAc) followed by a ligand exchange process gen-
2
erates palladium complex A, which give rise to the
II
Pd intermediate B by cyclopalladation via CÀH
cleavage. The oxidative addition of intermediate B
with an aryl iodide followed by reductive elimination
affords the arylation product 3 and regenerates the
palladium catalyst.
To further demonstrate the synthetic versatility of
this new directing group, the amino acid auxiliary
could be efficiently removed and converted. As
shown in Scheme 4, 3ca was readily converted into
the corresponding biaryl sulfonamide 4 in excellent
yield (96%) via CuO-catalyzed decarboxylation/elimi-
[21]
nation reaction.
The corresponding biaryl sulfonic
acid 5 was obtained by simple acidic hydrolysis with
[22]
hydrochloric acid.
Conclusions
In conclusion, we have demonstrated an efficient and
atom-economical methodology for the palladium-cat-
alyzed regioselective monoarylation of aryl sulfona-
Scheme 2. Preliminary mechanistic studies.
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mides by employing an amino acid moiety as the bi-
dentate directing group. This protocol enables the ef-
ficient preparation of 1,1’-biaryl 2-sulfonamides from
simple aryl sulfonamides and aryl iodides bearing
a wide variety of functional groups. Meanwhile, the
amino acid auxiliary could be efficiently removed and
converted. Further investigation on the mechanism of
this reaction and applications of this new directing
group in other types of CÀH functionalization are cur-
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General Procedure for Palladium-Catalyzed Direct
Arylation
A mixture of aryl sulfonamide 1 (0.5 mmol), aryl iodide 2
(
1.0 mmol), Pd(OAc) (0.05 mmol), NaOAc (1.0 mmol), and
2
H O (0.5 mL) was placed in a 25 mL Schlenk tube with
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9424.
2
a rubber plug. The tube was stirred at 1108C for 24 h. The
reaction mixture was cooled, and acidified (pH 2); the prod-
uct was extracted with EtOAc (3”5 mL). Combined organic
layer was dried over Na SO and concentrated in vacuo. The
2
4
residue was purified by silica gel column chromatography to
afford the desired products 3.
[
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Acknowledgements
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We are grateful for the financial support of Educational
Commission of Jiangxi Province, China (No GJJ13246), and
Science and Technology Planning Project of Jiangxi Prov-
ince, China (20142BAB203007). We also thank Prof. Jian
Liao from Chinese Academy of Sciences for constructive dis-
cussion of reaction mechanism.
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