Desulfinative and denitrogenative palladium-catalyzed cross-coupling of arylsulfonyl hydrazides with aryl diazonium salts

Article abstract of DOI:10.1002/aoc.4484

Palladium-catalyzed cross-coupling of arylsulfonyl hydrazides with aryl diazonium salts to provide biaryl products under relatively mild conditions is established. This reaction proceeded smoothly with tetrabutylammonium iodide and gave the corresponding

Full text of DOI:10.1002/aoc.4484

Received: 29 January 2018
DOI: 10.1002/aoc.4484
Revised: 13 April 2018
Accepted: 6 May 2018
C O M M U N I C A T I O N
Desulfinative and denitrogenative palladium‐catalyzed
cross‐coupling of arylsulfonyl hydrazides with aryl
diazonium salts
Yonghui Shang
School of Chemistry and Chemical
Palladium‐catalyzed cross‐coupling of arylsulfonyl hydrazides with aryl diazo-
Engineering, Xianyang Normal
University, Xianyang, Shaanxi 712000,
nium salts to provide biaryl products under relatively mild conditions is
People's Republic of China
established. This reaction proceeded smoothly with tetrabutylammonium
iodide and gave the corresponding products with C―C bonds formed using
Correspondence
Yonghui Shang, School of Chemistry and
PdCl2/bis (dicyclohexylphosphino) methane catalyst under air. This method
Chemical Engineering, Xianyang Normal
also allowed easy access to significant functional biaryls for potential applica-
University, Xianyang, Shaanxi 712000,
People's Republic of China.
tions in medicinal and organic chemistry.
Email: yonghui_shang@126.com
KEYWORDS
Funding information
aryl diazonium salts, arylsulfonyl hydrazides, Pd‐catalyzed cross‐coupling
National Natural Science Foundation of
China, Grant/Award Number: 21475113;
Natural Science Foundation of Shaanxi
Province of China, Grant/Award Number:
2012JQ2013; Blue talent funding project of
Xianyang Normal University, Grant/
Award Number: XSYQL201507
1 | INTRODUCTION
Recently, C―C bond formation via C―N bond cleav-
age has attracted considerable attention, and versatile
activated C―N bond‐containing partners, such as diazo-
nium salts, have been explored in cross‐coupling reac-
tions under transition metal catalysis. Aryl diazonium
salts are certainly one of the most reactive aryl halide sur-
rogates and have found many applications in palladium‐
catalyzed cross‐coupling reactions during the last thirty
years.[12–14] Aryl diazonium salts are easily accessed and
isolated as crystalline compounds by diazotization of the
corresponding aniline. To some extent, the use of diazo-
nium salts follows many principles of green chemistry
as it features cost, energy and waste benefits.[15–20]
Aryl–aryl scaffolds are highly important structural motifs
frequently found in natural products, pharmaceuticals
and functional materials.[1–3] Transition metal‐catalyzed
C―C bond forming reactions represent powerful syn-
thetic methods in organic synthesis,[4–8] which have been
broadly applied in medicinal chemistry, organometallic
chemistry and materials science.[9–11] Catalysis using pal-
ladium as the transition metal is certainly one of the most
modern and powerful strategies for C―C bond forma-
tion, and the development of new palladium‐catalyzed
systems has aroused vigorous interest. Despite huge inter-
est, palladium‐catalyzed couplings involving very hin-
dered structures and/or aryl chlorides as electrophiles
are frequently beyond reach. Aryl iodides and, to a lesser
extent, aryl bromides are not ideal electrophiles for devel-
oping sustainable chemistry, and thus the search for
highly reactive electrophiles as substitutes has been a
major concern.
Commercial
arylsulfonyl
halides,[5,21–24]
sulfinates[25–28] and hydrazines[29–33] are recognized as
new aryl sources that recently have been universally uti-
lized in desulfinative arylation reactions.[34–36] Notably,
owing to the features of good stability, versatile transfor-
mation models, compatibility with water and being free
of unpleasant odor, arylsulfonyl hydrazines are regarded
Appl Organometal Chem. 2018;e4484.
wileyonlinelibrary.com/journal/aoc
© 2018 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4484

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SHANG
hydrazides as aryl sources in Hiyama and Suzuki coupling
reactions by desulfination. Dong and co‐workers reported
palladium‐catalyzed desulfinative Sonogashira coupling of
arylsulfonyl hydrazides with terminal alkynes.[42] How-
ever, the new‐type palladium‐catalyzed denitrogenative
and desulfinative cross‐coupling of arylsulfonyl hydra-
zides with aryl diazonium salts is still rarely reported.
Herein we report the first example of desulfinative cou-
pling of aryl diazonium salts with arylsulfonyl hydrazides
with good to excellent efficiency.
SCHEME
1
Palladium‐catalyzed
denitrogenative
and
2 | RESULTS AND DISCUSSION
desulfinative cross‐coupling of arylsulfonyl hydrazides
Initial experiments were carried out using phenylsulfonyl
hydrazide and phenyl diazonium salt as model substrates,
and we screened various catalysts and ligands (Table 1). Pd
(II)–phosphine ligand systems were first examined on the
basis of several recent reports.[43,44] However, the PdCl2/P
(OPh)3‐catalyzed reaction using tetrabutylammonium
iodide (TBAI) as the additive and KOAc as the base in
dimethylsulfoxide (DMSO) at 100°C gave only a trace
amount of cross‐coupling product (Table 1, entry 1).
The screening of monodentate phosphine‐based
ligands, such as PCy3, TFP (trifurylphosphine) and Xphos
(2‐dicyclohexylphosphino‐2′,4′,6′‐triisopropylbiphenyl), gave
as particularly favorable aryl precursors in desulfination
reactions by C―S bond cleavage. Palladium‐catalyzed
denitrogenative and desulfinative cross‐couplings of
arylsulfonyl hydrazides have been studied (Scheme 1).
Tian and co‐workers first employed arylsulfonyl hydra-
zides as aryl sources in Heck‐type coupling reactions via
desulfination processes.[37] Zhao and co‐workers[38]
reported homocoupling of arylsulfonyl hydrazides and
Deng and co‐workers[39] reported desulfinative iodination
with iodine. It is noted that the groups of Zhou[40] and
Dou[41] have independently employed arylsulfonyl
TABLE 1 Desulfinative coupling of phenylsulfonyl hydrazides with phenyl diazonium salt with various catalysts and ligandsa
Entry
Ligand
Yield (%)b
Entry
Catalyst
Yield (%)c
1
P (OPh)3
PCy3
<5
28
33
47
70
81
77
83
89
93
90
91b
13
14
15
16
17
18
19
20
21
22
23
24
Pd (PPh3)4
Pd (dba)2
8
2
12
15
76
69
62
79
73
86
82
87
3
TFP
Pd3 (dba)2
4
Xphos
Dppe
Pd (OAc)2
5
Pd (TFA)2
6
Dppp
Pd (OTf)2
7
Xantphos
DPEphos
Dcype
Dcypm
Dcypp
Dcypm
Pd (CH3CN)2Cl2
Pd (PhCN)2Cl2
Pd (dppf)Cl2
Pd (dppe)Cl2
Pd (dppp)Cl2
PdCl2
8
9
10
11
12
e
88
aReaction conditions: phenylsulfonyl hydrazide (1.0 mmol), phenyl diazonium salt (1.1 mmol), TBAI (1.5 mmol), KOAc (2.0 mmol), DMSO (2 ml), 100 °C, 12 h.
Isolated yields.
bPdCl2 (5 mol%), ligand (10 mol%).
cCatalyst (5 mol%), Dcypm (10 mol%).
dPdCl2 (5 mol%), Dcypm (20 mol%).
ePdCl2 (10 mol%), Dcypm (10 mol%).

SHANG
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modest yields (Table 1, entries 2–4). We then screened a
combination of PdCl2 and some common and bidentate
phosphine ligands including Dppe, Dppp, Xantphos
16–18). We also tried to use the palladium source with
nitrogen ligands using Dcypm as diphosphine ligand.
However, these combinations behaved with lower catalytic
activity than the PdCl2–Dcypm system (Table 1, entries 19
and 20). The introduction of various palladium complexes
with phosphine ligands (Pd (dppf)Cl2, Pd (dppe)Cl2 and Pd
(dppp)Cl2) did not increase the yields (Table 1, entries
21–23). Among the Pd (II) catalysts tested, PdCl2 was the
most effective affording the addition product in 93% yield.
Marked improvement was observed when the PdCl2 load-
ing was increased to 10 mol%, achieving an 88% yield
(Table 1, entry 24). Not surprisingly, the reaction did not
produce biphenyl in the absence of the Pd (II) catalyst or
ligand.
(4,5‐bis
(diphenylphosphino)‐9,9‐dimethylxanthene),
DPEphos (bis[2‐(diphenylphosphino)phenyl] ether),
Dcype (1,2‐bis (dicyclohexylphosphino)ethane), Dcypm
(bis (dicyclohexylphosphino)methane) and Dcypp
(1,3‐bis (dicyclohexylphosphino)propane) (Table 1, entries
5–11). Among them a 1:2 PdCl2‐to‐Dcypm combination
gave the best result. A higher Dcypm loading resulted in
a decrease of the yield (Table 1, entry 12). Application of
Pd (PPh3)4, Pd (dba)2 and Pd3 (dba)2 as catalysts yielded
traces of desired product (Table 1, entries 13–15). It was
observed that most of the Pd (II) catalysts could success-
fully promote the reaction (Table 1, entries 16–24). There-
fore, Pd (OAc)2, Pd (TFA)2 and Pd (OTf)2 in combination
with Dcypm were applied with less effect affording biphe-
nyl in yields varying between 62 and 76% (Table 1, entries
Next we examined the effect of additive, base and
solvent on the reaction with PdCl2 catalyst at 100°C using
Dcypm as ligand. The additives NaI, KI and NH4I instead
of TBAI were not suitable (Table 2, entries 1–4).
TABLE 2 Desulfinative coupling of phenylsulfonyl hydrazides with phenyl diazonium salt with various additives, bases and solventsa
Entry
Additive
Base
Solvent
Yield (%)b
1
NH4I
NaI
KOAc
KOAc
KOAc
KOAc
K2CO3
Na2CO3
NaOAc
KOH
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
42
55
71
93
81
76
86
17
13
7
2
3
KI
4
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
TBAI
5
6
7
8
9
Cs2CO3
CsF
10
11
12
13
14
15
16
17
18
19
20
DABCO
DBU
<5
<5
90
85
62
56
73
60
—
—
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
KOAc
DMA
Toluene
Xylene
DME
1,4‐Dioxane
t‐BuOH
DCE
aReaction conditions: phenylsulfonyl hydrazide (1.0 mmol), phenyl diazonium salt (1.1 mmol), PdCl2 (5 mol%), Dcypm (10 mol%), additive (1.5 mmol), base
(2.0 mmol), solvent (2 ml), 100 °C, 12 h.
bIsolated yields.

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SHANG
Subsequently, the influence of base was studied (Table 2,
entries 5–12). Potassium acetate proved superior, though
potassium carbonate, sodium carbonate and sodium
acetate afforded low yields of the coupled adducts
(Table 2, entries 5–7). Reactions with potassium hydrox-
ide, cesium carbonate and cesium fluoride afforded only
trace amounts of products (Table 2, entries 8–10). Two
alternative bases, DABCO and DBU, were demonstrated
to be not effective for this transformation (Table 2, entries
11 and 12). Various solvents were screened by further
optimization, and the results revealed that aprotic solvent
is a better choice for the reaction (Table 2, entries 13–19).
Both DMF and DMA were as effective as DMSO as
solvent (Table 2, entries 13 and 14). The use of other
solvents such as toluene, xylene, DME and/or 1,4‐dioxane
resulted in yields of biphenyl of 56–73% (Table 2, entries
15–18). Unfortunately, the desired products were not
obtained in t‐BuOH and DCE (Table 2, entries 19 and
TABLE 3 Cross‐coupling of phenylsulfonyl hydrazides with various aryl diazonium saltsa
aReaction conditions: phenylsulfonyl hydrazide (1.0 mmol), aryl diazonium salt (1.1 mmol), PdCl2 (5 mol%), Dcypm (10 mol%), TBAI (1.5 mmol), KOAc
(2.0 mmol), DMSO (2 ml), 100 °C, 12 h. Products are shown with isolated yields.
TABLE 4 Cross‐coupling of various arylsulfonyl hydrazides with phenyl diazonium saltsa
aReaction conditions: arylsulfonyl hydrazide (1.0 mmol), phenyl diazonium salt (1.1 mmol), PdCl2 (5 mol%), Dcypm (10 mol%), TBAI (1.5 mmol), KOAc
(2.0 mmol), DMSO (2 ml), 100 °C, 12 h. Products are shown with isolated yields.

SHANG
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20). The reaction could not be further improved by
lengthening the reaction time to 24 h. Moreover, the yield
was slightly decreased when the reaction was performed
at a lower or higher temperature. Controlled experiments
were conducted without the addition of base or iodide;
however, no desired products were observed.
Encouraged by these results, we applied the
desulfinative protocol described above to a range of aryl
diazonium salts and arylsulfonyl hydrazides (Table 3).
The scope of aryl diazonium salts was initially explored
in the presence of phenylsulfonyl hydrazide. Gratifyingly,
introduction of methoxy, fluoro, chloro, cyano and
trifluoromethyl groups into the phenyl ring of diazonium
salts was well tolerated, and the coupling products were
isolated in good to excellent yields (Table 3, 3a–3e).
Notably, 4‐(diazenyl) benzoic acid successfully
underwent coupling to give 3f, albeit in a low yield. Steric
hindrance, often problematic in metal‐catalyzed coupling
reactions, does not pose a problem. The majority of the
phenyl diazonium salts with para‐substitutions gave good
yields, while the ortho‐ and meta‐substituted phenyl
diazonium salts afforded a slightly lower yield (Table 3,
3g–3l). Naphthyl‐substituted diazonium salts could also
be employed in this reaction to afford the products 3 m
and 3n in good yields. It is worth noting that this protocol
is also applicable to heterocyclic aromatics such as
pyridine and pyrazine (Table 3, 3o–3q).
Then, the scope of arylsulfonyl hydrazides was
explored in the reaction with phenyl diazonium salts. It
is noteworthy that either an electron‐donating or an elec-
tron‐withdrawing group such as methoxy, fluoro, chloro,
cyano and acetyl was introduced into the diaryls without
any problem by employing phenylsulfonyl hydrazides
bearing such a group on the aromatic ring at para posi-
tion (Table 4, 4a–4e). In general, the expected product
yields were higher with arylsulfonyl hydrazides bearing
electron‐donating substituents, whereas the use of
arylsulfonyl hydrazides containing electron‐withdrawing
SCHEME 2 Polyarylation of
phenylsulfonyl hydrazides using the
method presented
SCHEME 3 Possible mechanism for
cross‐coupling

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SHANG
substituents led to the products in modest isolated yields.
It is important to note that unprotected hydroxyl groups
or amino groups in the arylsulfonyl hydrazides did not
hinder the reaction and no O‐ or N‐arylating product
was detected in these cases (Table 4, 4f and 4g). Steric
hindrance in the arylsulfonyl hydrazides was not a prob-
excellent yields. Advantages of this reaction include good
functional group tolerance, high reactivity, relatively mild
conditions and easy access to the coupling partners.
Terphenyls were effectively transformed in the reaction
with phenyl diazonium salt, and the reaction could be
scalable with good efficiency.
lem.
Reaction
of
meta‐
or
ortho‐substituted
phenylsulfonyl hydrazides delivered the biaryls in high
yields (Table 4, 4h–4m). Naphthylsulfonyl hydrazides
selectively transferred the aryl moiety, furnishing
products 4n and 4o. This method can be extended to
ACKNOWLEDGMENTS
The authors gratefully acknowledge the financial support
of this study by the National Natural Science Foundation
of China (21475113), the Natural Science Foundation of
Shaanxi Province of China (2012JQ2013), and Blue
talent funding project of Xianyang Normal University
(XSYQL201507).
heteroarylsulfonyl
hydrazides
to
synthesize
arylheteroaryls 4p–4 t, which are of particular interest
for the development of new drugs.
We next examined the reactivity of di‐ or tri‐arylation
of phenylsulfonyl hydrazides to afford terphenyls
(Scheme 2). The reaction of arylsulfonyl hydrazides with
various amounts of phenyl diazonium salt furnished the
p‐terphenyl, m‐terphenyl and 3‐phenyl‐m‐terphenyl in
good to excellent yields (Scheme 2, equations (1)–(3)).
ORCID
Yonghui Shang http://orcid.org/0000-0002-6627-2426
Under the same conditions,
a 5 mmol scale of
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How to cite this article: Shang Y. Desulfinative
and denitrogenative palladium‐catalyzed cross‐
coupling of arylsulfonyl hydrazides with aryl
diazonium salts. Appl Organometal Chem. 2018;
e4484. https://doi.org/10.1002/aoc.4484
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