The homocoupling of arylsulfonylhydrazides by palladium-catalysed desulfonation in air

Article abstract of DOI:10.3184/174751913X13813357379921

A simple and efficient preparation of biaryl derivatives from arylsulfonyl hydrazides has been developed using Pd(OAc)2 as the catalyst in a mixed solvent of DMA and THF and without the use of any ligand and base.

Full text of DOI:10.3184/174751913X13813357379921

674 RESEARCH PAPER
NOVEMBER, 674–676
JOURNAL OF CHEMICAL RESEARCH 2013
The homocoupling of arylsulfonylhydrazides by palladium-catalysed
desulfonation in air
Wei Zhanga, Baoli Zhaob* and Ke Lic
aDepartment of Chemistry and Chemical Engineering; Xinxiang University; Xinxiang 453003, P.R. China
bInstitute of Applied Chemistry and Department of Chemistry, Shaoxing University, Shaoxing, Zhejiang Province 312000, P.R. China
cJiaozuo City Environmental Protection Bureau, Jiaozuo, Henan Province, 453003, P.R. China
A simple and efficient preparation of biaryl derivatives from arylsulfonyl hydrazides has been developed using Pd(OAc)2 as the
catalyst in a mixed solvent of DMA and THF and without the use of any ligand and base.
Keywords: homocoupling,arylsulfonylhydrazide, desulfonation
Table 1 Solvent selection of Pd-catalysed homocoupling
Biaryl skeletons are found in many natural products,
pharmaceuticals and ligands for catalysis.1–4 Symmetrical
biaryls are synthesised by homocoupling reactions, which
include reductive coupling of aryl halides (known as the
Ullmann reaction) and oxidative coupling of arylmetal
compounds. The Ullmann reaction5–10 was the first efficient
process for the synthesis of symmetrical biaryls, but harsh
conditions were required. Recently, extensive studies on the
homocoupling reactions of arylboronic acids11–19, potassium
aryltrifluoroborates20–22 aryl Grignard reagents23,24 and
arenediazonium salts25–28 have been used because of their ready
availability and stability.
The development of new electrophilic partners for these
reactions has led to cross-coupling chemistry. Decarboxylative
homocoupling using benzoic acids as substrates have been
developed to afford corresponding symmetrical bi-aryl
structures.29,30 However, a strong electron-withdrawing group
such as the nitro-substituent is essential for the reaction and
harsh conditions are required.
More recent developments involve the use of arenesulfonates,
which are readily available, inexpensive, and highly versatile.
Last year, You and coworkers31 reported the first example of the
homocoupling of sodium benzenesulfinate. The transformation
required the addition of 2.0 equiv. oxidant and a phase transfer
catalyst (tetra-n-butylammonium bromide) to give a yield of
81% at 110°C under nitrogen. Luo et al.32 reported a green
heterogeneous catalysed homocoupling under oxygen in water.
Tian33 reported that arylsulfonyl hydrazides were new coupling
partners in Heck-type reaction. Subsequently, You34 and Li35
independently reported similar results concerning the direct
arylation of heteroarenes with arylsulfonyl hydrazides. Here,
we describe another application of arylsulfonyl hydrazides in
homocoupling reaction to afford biaryls using a more convenient
palladium catalysed homocoupling by desulfonation without
oxidants and additives.
cat Pd(OAc)2
Cu(OAc)2
O
H
N
S
Solvent
80 oC
NH2
O
Entry
1
2
3
4
5
6
7
8
Solvent
DMSO
DMF
DMA
NMP
toluene
CH3CN
1,4-dioxane
THF
Yield/%b Entry
Solvent
Yield/%b
65
77
83
89
80
77
79
73
46
49
55
34
26
38
36
40
71
70
11
12
13
14
15
16
17
18
19
20
DMA/toluene(1:1)
DMA/THF(1:1)
DMA/THF(9:1)
DMA/THF(4:1)
DMA/THF(3:1)
DMA/THF(2:1)
DMA/THF(1:2)
DMA/THF(1:3)
DMA/THF(1:4)
DMA/THF(1:9)
9
10
DMA/dioxane (1:1)
DMA/CH3CN(1:1)
66
57
aReaction conditions: phenylsulfonyl hydrazides (0.5 mmol), Pd(OAc)2
(3 mol%), Cu(OAc)2 (0.5 mmol), solvent (1.0 mL) at 80 °C for 3 hours
unless otherwise indicated.
bIsolated cross-coupling yield, the v/v ratio of solvents was shown in
parentheses.
Common organic solvents were examined but without
improvement in yield (Table 1, entries 5–8). We then considered
the use of mixed solvents. We chose DMA which was best in
the first solvent screen, to mix with other solvents. The mixture
displayed a sharp increase in the yield of the reaction (65–71%)
(Table 1, entries 9–11). It proceeded smoothly in a solvent
comprising DMA and THF (volume ratio is 1:1) with a yield
of 77% (Table 1, entry 12). Finally, we varied the composition
of DMA and THF in the range of 9:1 to 1:9 (Table 1, entries
13–20). In general, an increase of DMA favoured the formation
of biphenyl and the volume ratio of 4:1 was the best (Table 1,
entry 14).
The optimisation of the catalysts and oxidants in the reaction
then followed. The screening of palladium catalysts, such as
PdCl2, PdI2, PdCl2(CH3CN)2, provided biphenyl in 79%, 80%,
77% yield, respectively (Table 2, entries 1–3). Decreased yields
were obtained with the introduction of phosphine ligands (Table
2, entries 4 and 5). Pd(0) catalysts gave moderate yields (Table
2, entries 6 and 7). No product was formed in the absence of
Pd (Table 2, entry 8). The formation of biphenyl was up to 89%
using Pd(OAc)2 as catalyst (Table 2, entry 9). Oxidants were
crucial for this transformation. Among the oxidants examined
[Cu(OAc)2, AgOAc, BPO, DDQ, Oxone and TBHP], Cu(OAc)2
was the best (Table 2, entries 9–14). Under O2, the yield of
biphenyl decreased to 61%, while under N2, no product was
formed (Table 2, entries 15 and 16).
Results and discussion
We initiated our investigation on the model reaction of
phenylsulfonyl hydrazide to optimise the critical reaction
parameters. Homocoupling took place in the presence of
Pd(OAc)2 (3 mol%) and Cu(OAc)2 (1 equiv.) in DMSO under air
(Table 1, entry 1). Then we investigated the effect of solvents
which had an obvious influence on the reaction obviously. The
carefully optimised results are shown in Table 1. The yield
obtained in other polar aprotic solvents such as DMF, DMA
and NMP were also in the range 34–55% (Table 1, entries 2–4).
With the optimised reaction conditions in hand, we
investigated the effect of electronic and structural variations
* Correspondent. E-mail: babygarfield@126.com
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JOURNAL OF CHEMICAL RESEARCH 2013 675
Table 2 Optimisation with catalyst and oxidant of Pd-catalysed
with these reaction conditions, which further expanded its good
chemical selectivity (Table 3, entries 6–8). Steric hindrance on
the phenyl ring of the arylsulfonyl hydrazides had a slight effect
on the efficiency (Table 3, entries 9–11). It was interesting that
polycyclic aromatic hydrocarbons (PAHs) substrates worked
under the procedure (Table 3, entries 12 and 13). Importantly,
the product with a heterocyclic ring was formed in moderate
yield when 2-benzofuran was subjected to the procedure (Table
3, entry 14).
homocoupling
cat catalyst
Oxidant
O
H
N
S
DMA THF
/
80 oC
NH2
O
Entry
1
2
3
4
5
6
7
8
Catalyst
PdCl2
PdI2
Oxidant
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
AgOAc
BPO
Yield/%b
79
80
77
46
53
72
76
–
89
82
78
69
83
68
61
–
PdCl2(CH3CN)2
PdCl2(dppf)
PdCl2 (PPh3)3
Pd(PPh3)4
Pd2(dba)3
–
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Mechanism
A plausible mechanism to rationalise this transformation is
illustrated in Scheme 1. The release of SO2 and N2 may be the
crucial driving force to the catalytic process. First, the Pd(II)
acetate reacts with the 4-tolylsulfonyl hydrazide to form a
TsNHNH2-Pd(II)-OAc intermediate A, which is subsequently
oxidised to intermediate B. Tolyl-Pd(II)-OAc was generated
accompanied by the release of nitrogen and sulfur dioxide. This
was then displaced by another 4-tolylsulfonyl hydrazide to form
intermediate C. The oxidised intermediate species D undergoes
a similar sequence to generate the di-tolyl-palladium complex
E. A reductive elimination of E affords the desired product
and the Pd(0) catalyst is reoxidised to Pd(II) by Cu(OAc)2, thus
completing the catalytic cycle.
9
10
11
12
13
14
15
16
DDQ
Oxone
TBHP
O2
N2
aReaction conditions: phenylsulfonyl hydrazides (0.5 mmol), catalyst
(3 mol%), oxidant (0.5 mmol), solvent (1.0 mL, the v/v ratio of solvents
was 1:1) at 80 °C for 3 hours unless otherwise indicated.
bIsolated cross-coupling yield.
Cu(I)
TsNHNH2
Cu(OAc)2
AcO
HOAc
AcO
Pd(II)
AcO
in the phenylsulfonyl hydrazides. The scope of the reaction
is presented in Table 3. As expected, a series of functional
groups on the phenyl ring of phenylsulfonyl hydrazides, such
as bromo, chloro, fluoro, iodo and cyano were compatible
with this procedure, and the products were isolated in
moderate to good yields (Table 3, entries 1–5). Halogens
were tolerant of the palladium catalysed homocoupling of the
arylsulfonyl hydrazides (Table 3, entries 1–4), suggesting that
arylsulfonyl hydrazides may have higher coupling reactivities
than the related aromatic halides. This revealed the excellent
chemoselectivity of this method. Notably, many heteroatom
functional groups, such as OCH3, SCH3 and N(CH3)2 all coped
( )
Pd 0
-
T l T l
o
o
Pd(II)
TsNHNH
A
T l
o
( )
Pd II
Cu(II)
E
T l
o
AcO
Cu(0)
N +
SO2
Pd II
( )
2
T l
o
TsN
N
B
( )
Pd II
T N
s
N
C
A
cO
o
T l
D
( )
Pd II
( )
Pd II
( )
Cu 0
T l
o
N +
SO2
2
T NHNH
s
u( )
II
C
H A
O c
T NHNH
s
2
Table 3 Pd-catalysed homocoupling of various substrates
cat Pd(OAc)2
Cu(OAc)2
O
H
N
Scheme 1 Possible mechanism.
S
R
DMA THF
/
80 oC
NH2
O
R
R
Conclusion
In conclusion, we have described a new homocoupling reaction
using arylsulfonyl hydrazides as the coupling partners under
palladium catalysis. Importantly, this transformation is practical
as it does not require the use of strong bases, expensive ligands
nor rigorous exclusion of air. The transformation was promoted
by mixed solvent and proceeds with the release of N2 and SO2.
The detailed mechanism is being studied in our lab.
Entry
R
Yield/%b
M.p./oC
M.p./oC lit.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
4-F
4-Cl
4-Br
4-I
4-CN
4-N(CH3)2
4-OCH3
4-SCH3
4-CH3
3-CH3
2-CH3
85
90
88
84
78
83
91
89
92
86
79
85
78
69
87–88
146–147
164–165
201–203
230–232
192–193
175–176
186–187
119–120
–
88–90 36
149–154 36
168–170 36
205–206 36
233–234 37
194–196 36
173–174 36
188–189 36
122–124 36
–
Experimental
All solvents were purified and dried according to standard methods
prior to use. Proton NMR spectra were recorded in CDCl3 on a Bruker
Avance III spectrometer. 1H NMR spectra were recorded at 400 MHz
and 13C NMR spectra were recorded at 100 MHz using TMS as internal
standard. The multiplicities are reported as follows: singlet (s), doublet
(d), doublet of doublets (dd), multiplet (m), and broad resonances (br).
HRMS (EI) data were collected on a high resolution mass spectrometer
AT95XP, Thermo Finnigan, USA. All materials were purchased from
common commercial sources and used without additional purification.
–
–
2-Naphthyl
1-Naphthyl
2-benzofuran
184–185
143–145
196–197
180–182 36
142–144 38
198–200 36
aReaction conditions: phenylsulfonyl hydrazides (0.5 mmol), Pd(OAc)2
(3 mol%), Cu(OAc)2 (0.5 mmol), solvent (1.0 mL, DMA/THF=1:1) at
80 °C for 3 hours unless otherwise indicated.
bIsolated cross-coupling yield.
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676 JOURNAL OF CHEMICAL RESEARCH 2013
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Typical procedure
A mixture of the arylsulfonyl hydrazides (0.5 mmol), Pd(OAc)2
(3 mol%) and Cu(OAc)2 (0.5 mmol) was stirred in DMA/THF=1:1
(1 mL) at 80 °C for 3 h. Afterwards, 1 mL water was added to the
reaction solution which was then filtered through a filter paper. The
solution was extracted by Et2O (1 mL) three times. The organic phase
was combined and evaporated under reduced pressure. The residue was
purified on a SiO2 column, and eluted with mixtures of petrol and ethyl
acetate to afford the desired product.
This study was financially supported by the Education
Department of Zhejiang Province (Grant # Y201328443) and
Shaoxing University (Grant # 2012LG1008).
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Electronic Supplementary Information
All products are known compounds, and the spectroscopic data
for the products is given in the ESI available through:
stl.publisher.ingentaconnect.com/content/stl/jcr/supp-data.
Received 18 July 2013; accepted 23 August 2013
Paper 1302070 doi: 10.3184/174751913X13813357379921
Published online: 11 November 2013
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