Copper-Catalyzed Disulfonation of Terminal Alkynes with Sodium Arylsulfinates

Article abstract of DOI:10.1021/acs.orglett.0c00575

A novel and direct disulfonylation reaction of commercially available terminal alkynes under copper(I)/bromodifluoroacetate cocatalyst has been realized. This protocol provides a facile and practical pathway to selectively access (E)-1,2-disulfonylethenes, in which features good functional group compatibility, easily available starting materials, and excellent stereoselectivity with good yields.

Full text of DOI:10.1021/acs.orglett.0c00575

pubs.acs.org/OrgLett
Letter
Copper-Catalyzed Disulfonation of Terminal Alkynes with Sodium
Arylsulfinates
Zhenhua Liu, Lin Yang, Kaining Zhang, Wanjiao Chen, Tian Yu, Lianxiao Wang, Wen Gao,*
and Bo Tang*
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ABSTRACT: A novel and direct disulfonylation reaction of commercially available
terminal alkynes under copper(I)/bromodifluoroacetate cocatalyst has been
realized. This protocol provides a facile and practical pathway to selectively access
(E)-1,2-disulfonylethenes, in which features good functional group compatibility,
easily available starting materials, and excellent stereoselectivity with good yields.
Scheme 1. Generation of 1,2-Disulfonylethenes by Alkynes
inyl sulfide moiety has attracted extensive attention in the
territories of biochemistry, medicinal chemistry, materials
V
science, and organic chemistry.1 Among them, 1,2-disulfony-
lethenes are considerable organosulfone molecules2,3 and
emerge as versatile synthons in synthetic applications such as
cycloaddition,4 radical elimination,5 and 1,2-rearrangement
reaction.6 To date, several classic methods including
oxidation,7 condensation,8 and addition reactions9 were well
established for the production of the 1,2-disulfonylethenes.
However, these approaches are always restricted to predeco-
rated feedstocks, narrow substrate scopes, and/or multiple
synthetic steps.
Alkynes with flexible reactivity are easily available building
blocks and widely used in modern organic synthesis.10 Direct
1,2-difunctionalization of alkynes, an ideal strategy for
generating the functionalized olefins, has been substantially
streamlined in last few decades.11 Among these, radical-
involved vicinal difunctionalization of alkynes by both
carbon-12 and heteroatom-centered radicals13 appears as the
efficient and modular means to deliver polysubstituted alkenes
via excellent step- and atom-economy. During this process, the
reactive vinyl radical intermediates are suggested to further
couple with another partner to produce the target alkenes.14
However, such vinyl radical species easily undergo hydro-
genation by H atom abstraction,15 which is a significant
challenge in utilization of alkyne via radical 1,2-difunctionaliza-
tion reaction. Therefore, achieving the alternative and direct
efficient strategy to constitute 1,2-disulfonylethene skeleton is
of significant interesting and appealing in the synthetic
chemistry. Considerable attention has been fixed on the
construction of adjacent C−S bonds by the addition of
preactivated alkynes with sulfinyl precursors. For example,
Kataoka et al. provided a reaction between alkynylselenonium
salts and sodium benzenesulfinates for assembling 1,2-bis-
(phenylsulfonyl)ethylenes (Scheme 1a).16 Tang and co-
workers developed the HCl-dependent disulfonylation of
alkynyl bromides with sodium arylsulfinates (Scheme 1b).17
Recently, a Cu-catalyzed disulfonylation reaction after
decarboxylation of alkynyl carboxylic acids was also discovered
by Li’s group by using excess amounts of oxidants (Scheme
1c).18 Despite these advances, the composition of 1,2-
disulfonylethenes still suffered from some drawbacks such as
preactivated aryl-substituted alkynes, excessive strong oxidants,
or acidic conditions. Given our substantial interest in copper
catalyzed organic reactions,19 we herein report an initial
copper-catalyzed 1,2-disulfonation of unactivated terminal
Received: February 13, 2020
https://dx.doi.org/10.1021/acs.orglett.0c00575
© XXXX American Chemical Society
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A

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a
alkynes with arylsulfinates with the help of bromodifluor-
oacetate to rapidly furnish diverse (E)-1,2-disulfonylethenes
without any oxidant or acid (Scheme 1d).
Scheme 2. Scope of Alkynes
We carried out our investigation with 1a and 2a as model
reactants to optimize the best conditions for disulfonylation
conversion. The desired product 3a was not observed under
metal-free conditions (Table1, entry 1). Excitingly, the yield of
a
Table 1. Optimization of the Reaction Conditions.
entry
[M]
CuI
CuI
CuI
sol
yield (%)
1
2
3
4
5
6
7
8
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
0
85
0
70
61
b
c
d
CuI
Ag2CO3
NiCl2
Cu(OAc)2
CuCl2
CuBr
CuI
CuI
CuI
CuI
CuI
0
0
75
80
69
70
0
9
10
11
12
13
14
15
16
17
EG
toluene
CH3CN
DCE
DMSO
DMSO
0
0
a
0
trace
56
Conditions: 1 (0.5 mmol), 2a (2.0 mmol), CuI (0.1 mmol),
BrCF2CO2Et (1.0 mmol), in DMSO (1 mL) at 100 °C under air for 3
h. Yields of isolated products.
e
CuI
CuI
f
a
Conditions: 1a (0.5 mmol), 2a (2.0 mmol, 4.0 equiv), CuI (0.1
functional groups intact for further coupling modification.
Additionally, the absolute configuration was precisely con-
firmed by the crystal structure of product 3k (CCDC
1954576). The electron-deficient substrate 1l with an acetyl
group also gave 1,2-disulfonylethene 3l under standard
conditions. Subsequently, terminal alkynes containing meta-
substitutions on the aryl ring (1m−1p) also underwent
disulfonylation reactions in all cases (3m−3p) without a
hitch, thus furnishing the satisfactory yield of products with
different deactivating substituents. When the substrates
anchored ortho-substituted groups (1q−1s), the yield of 3q−
3s exhibited that the groups in the ortho position were well
compatible in the reaction. Replacing the phenyl group with a
condensed ring (1t−1u) or thienyl derivatives (1v−1x) proved
good adaptability for the corresponding adducts 3t−3x in good
yields. As the clearly more challenging substrates of nonaryl
alkynes in radical difunctionalization,14 eneynes 1y−1z proved
to be the good coupling partner with appreciable yield of the
product. To the best of our knowledge, this protocol gives the
first access to synthesis of the 1,2-diarylsulfonyl 1,3-diene.
However, Alkyl substituted alkynea 1za−1zb were shut down
in the reaction, presumably caused by the instability of the
involved sulfone radical species.14
mmol, 0.1 equiv), BrCF2CO2Et (1.0 mmol, 2.0 equiv), in solvent (1
mL) at 100 °C in oil bath under air for 3 h; yields of isolated
b
c
d
products. Without BrCF2CO2Et (2.0 equiv). 80 °C. At 120 °C.
e
f
With 2.0 equiv of NaI. With 2.0 equiv of Et3N. EG = ethanediol.
product 3a was remarkable increased to 85% when CuI (0.2
equiv) was employed into the reaction (Table1, entry 2). The
next control experiments (Table1, entry 3) identified that
BrCF2CO2Et was found to be the vital parameter for the
reaction. The adverse impact on the yield of product 3a was
showed whether the reaction was took place at higher or lower
temperature (Table 1, entries 4 and 5). The poor efficiency to
construct disulfonylated product 3a were obtained by using
other metal catalysts (Table1, entries 6−10). Varying other
solvents (Table1, entries 11−15) for the reaction led to the
low conversion of 3a, confirming DMSO as best the choice.
Similarly, other additives and the decreased amount of
BrCF2CO2Et were also studied, revealing that the standard
reaction was hampered (Table1, entries 16−17, and
Supporting Information).
Based on above optimal reaction conditions, we focused on
the efficacy of this disulfonylation by reacting various alkynes
with 2a to produce desired products 3 (Scheme 2). Initially,
alkynes with para-substituted functional groups were injected
into the standard reaction and proceeded well for products
3b−3l with good yields, regardless of their electronic
properties and steric effect. For instance, the substrates with
alkyl chains (1b−1f) and alkoxy substituents (1g−1h) were
good substrates, delivering the expected product 3b−3h in
80−86% yields. The substrates 1i−1k bearing halogen atoms
worked smoothly for the products 3i−3k, while leaving labile
Moreover, sulfonates 2 with a variety of aryl groups were
next performed to study the efficiency of the copper-catalyzed
disulfonylation process, generating the target products under
the standard reaction conditions (Scheme 3). For instance, the
use of phenylsulfinates 2a−2c with electron-rich groups,
sulfinate 2d with condensed rings, as well as sulfinate 2e
with sulfur heterocycle were favorably competent for the
construction of privileged vinyl sulfones 4a−4e in 70−82%
B
https://dx.doi.org/10.1021/acs.orglett.0c00575
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a
Scheme 3. Reaction Scope of Sodium Sulfonates
Scheme 5. Mechanistic Investigations
a
Conditions: 1a (0.5 mmol), 2 (2.0 mmol), CuI (0.1 mmol),
BrCF2CO2Et (1.0 mmol), in DMSO (1 mL) at 100 °C under air for 3
h. Yields of isolated products.
yield. Unfortunately, ethyl-substituted sulfonate 2f did not
share this disulfonylation conversion.
Furthermore, to extend the scalability and practicality of this
method, we conducted the large-scale reaction with this
bromodifluoroacetate-induced disulfonation of alkyne
(Scheme 4). The corresponding product 3a was delivered in
Scheme 4. Large-Scale Reaction
In light of the above preliminary results and previous
literature,17−20 a plausible mechanism via radical pathway for
this transformation was proposed and described in Scheme 6.
Scheme 6. Possible Mechanism for the Reaction
good yield, which demonstrated the preferably potential value
of the convenient fabrication pathway to access 1,2-
disulfonylethenes in the industry.
To probe the insights on the mechanism of disulfonylation
reaction, the contrast experiments were designed and
implemented as shown in Scheme 5. When 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO) as radical scavenger
was subjected into the reaction, the desired conversion was
shut down (Scheme 5a). This meant that the reaction was
probably involved in the radical species.20 Replacing 2a with
TsH caused the sharp suppression of the standard disulfony-
lated reaction (Scheme 5b). This indicated that TsH was not
the supposed intermediate in the reaction (Scheme 5b). The
assumed acetylene copper intermediate 1a-Cu yielded the
vinylsulfone 5 instead of 3a (Scheme 5c), implying the absence
of simple 1a-Cu compound in the reaction. When 5 as partner
was further treated with 2a in standard reaction, no desired
product 3a was observed (Scheme 5d), confirming the missing
formation of intermediate 5 in the reaction. The subjection of
1a-D in place of 1a produced the mixture of 3a/3a-D. When
2.0 equiv of H2O was added in the reaction, only product 3a
was obtained (Scheme 5e). Those results suggested the
cleavage of C(sp)−H bond during the standard reaction.
Copper catalyst could accelerate the target transformation
from intermediate 6 to product 3a, which probably signified
the presence of 6 in the formation of 3a (Scheme 5f).
These results (Scheme 5c,e) implied that the activation of 1a
might occurred in the help of some copper complex via
cleavage of the C(sp)−H bond. In addition, some literature21
reported the complex between copper and BrCF2CO2Et during
the reaction. Therefore, we proposed that a Cu(III) species
A21 was first afforded by an oxidative addition of copper
catalyst into the C−halogen bond of BrCF2CO2Et. Inter-
mediate A subsequently reacted with A and led to the Cu(III)
complex B, which could coordinate with 2a for the formation
of C. The in situ generation of Ts radical from complex C and
a consecutive radical addition quickly occurred to give vinyl
radical D.22 An elimination23 of D produced 6 and regenerated
Cu(I) for the next catalytic cycle. Finally, product 3a was
C
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Letter
obtained through nucleophilic addition between 6 and 2a with
the assistance of copper species.
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China
In summary, we have successfully achieved a novel and
efficient copper-catalyzed disulfonylation protocol to straight-
forwardly synthesize a wide range of (E)-1,2-disulfonylethenes
from readily available terminal alkynes in good yields.
Compared to the existing preactivated synthetic strategy, this
is an attractive alternative for preparing 1,2-disulfonylethene
motifs in synthetic chemistry. A possible radical mechanism
was also proposed on the base of preliminary control studies.
Further exploitations of the difluorobromoacetate-triggered
catalytic system in organic synthesis are currently underway in
our laboratory.
Kaining Zhang − College of Chemistry, Chemical Engineering
and Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China
Wanjiao Chen − College of Chemistry, Chemical Engineering
and Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China
Tian Yu − College of Chemistry, Chemical Engineering and
Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c00575.
Typical experimental procedure and characterization for
all products (PDF)
Accession Codes
Lianxiao Wang − College of Chemistry, Chemical Engineering
and Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China
CCDC 1954576 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c00575
AUTHOR INFORMATION
■
Corresponding Authors
Wen Gao − College of Chemistry, Chemical Engineering and
Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China; Email: gaowen@
sdnu.edu.cn
Bo Tang − College of Chemistry, Chemical Engineering and
Materials Science, Collaborative Innovation Center of
Functionalized Probes for Chemical Imaging in Universities of
Shandong, Key Laboratory of Molecular and Nano Probes,
Ministry of Education, Shandong Provincial Key Laboratory of
Clean Production of Fine Chemicals, Shandong Normal
University, Jinan 250014, P. R. China; orcid.org/0000-
0002-8712-7025; Email: tangb@sdnu.edu.cn
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21535004, 91753111, 21605097,
21775092, 21390411), the Key Research and Development
Program of Shandong Province (2018YFJH0502), and the
Natural Science Foundation of Shandong Province of China
(ZR2018JL008).
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