Palladium-Catalyzed Regio- and Stereoselective Coupling-Addition of Propiolates with Arylsulfonyl Hydrazides: A Pattern for Difunctionalization of Alkynes

Article abstract of DOI:10.1021/acs.orglett.8b01585

A new pattern for difunctionalization of alkynes via a palladium-catalyzed regio- and stereoselective coupling-addition of propiolates with arylsulfonyl hydrazides is disclosed. The approach enables the synthesis of various highly functionalized (E)-vinylsulfones in satisfactory yields. Arylsulfonyl hydrazides act as both aryl and sulfonyl sources via selective cleavage of Ar(C)-S and S-N bonds, which are simultaneously incorporated onto the terminal carbon atom of an alkyne molecule.

Full text of DOI:10.1021/acs.orglett.8b01585

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
Palladium-Catalyzed Regio- and Stereoselective Coupling−Addition
of Propiolates with Arylsulfonyl Hydrazides: A Pattern for
Difunctionalization of Alkynes
Lixin Liu,† Kang Sun,† Lebin Su,† Jianyu Dong,*,† Lei Cheng,† Xiaodong Zhu,† Chak-Tong Au,‡
Yongbo Zhou,*,† and Shuang-Feng Yin*,†
†College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
‡College of Chemistry and Chemical Engineering, Hunan Institute of Engineering, Xiangtan 411104, China
S
* Supporting Information
ABSTRACT: A new pattern for difunctionalization of alkynes
via a palladium-catalyzed regio- and stereoselective coupling−
addition of propiolates with arylsulfonyl hydrazides is disclosed.
The approach enables the synthesis of various highly function-
alized (E)-vinylsulfones in satisfactory yields. Arylsulfonyl
hydrazides act as both aryl and sulfonyl sources via selective
cleavage of Ar(C)−S and S−N bonds, which are simultaneously
incorporated onto the terminal carbon atom of an alkyne
molecule.
ransition-metal-catalyzed transformation of alkynes into
polyfunctionalized compounds is at the forefront of
Interestingly, arylsulfonyl hydrazides can simultaneously act as
coupling partners and addition reagents via selective cleavage of
the C−S and N−S bond, respectively. Arylsulfonyl hydrazides
are usually employed as aryl or sulfonyl sources via desulfitation
or denitrification,7 but there is no report on the dual roles of
arylsulfonyl hydrazides being simultaneously utilized. The
reaction that incorporates two different functional groups
onto the terminal carbon atom of an alkyne for the synthesis of
1,1-disubstituted alkene derivatives via a coupling-addition
represents a new pattern for alkyne difunctionalization.
Vinylsulfone derivatives are useful synthetic intermediates8
and unique motifs in biologically active molecules.9 A plethora
of methods,10−14 including sulfonamination,11 sulfonyloxida-
tion,12 halosulfonylation,13 and sulfonylcarbonation of al-
kynes,14 have been developed for efficient construction of
these compounds. However, the sulfonative functionalization of
alkynes was limited to 1,2-difunctionalization, and the
introduction of aryl and sulfonyl groups at a terminal carbon
atom of alkynes has not been realized.
T
research activities in modern organic and organometallic
chemistry.1−4 In this context, one-pot difunctionalization of
alkynes is an appealing strategy that provides straightforward
and flexible access to polyfunctionalized alkene derivatives.2−4
In recent decades, efficient protocols for 1,2-difunctionalization
of alkynes have been developed and extensively applied in
organic synthesis, material chemistry, and biochemistry,3d,5 in
which two functional groups are incorporated onto the two
carbon atoms of an alkyne, respectively (Scheme 1).2,3 In
Scheme 1. Difunctionalization of Alkynes to Alkenes
We commenced our study with the treatment of
benzenesulfonyl hydrazide (1a, 0.2 mmol) and ethyl propiolate
(2a, 0.2 mmol) in the presence of Pd(OAc)2 (5 mol %), 1,3-
bis(diphenylphosphino)propane (dppp) (5 mol %), and
Cu(OAc)2·H2O (2.0 equiv) in N,N-dimethylformamide
(DMF) at 80 °C for 30 min. A difunctionalized product (E)-
ethyl 3-phenyl-3-(phenylsulfonyl)acrylate 3a was obtained in
44% yield (Table 1, entry 1, yield based on 0.1 mmol), in which
the corresponding Sonogashira coupling product was not
observed,6b probably due to the strong electron-withdrawing
contrast, 1,1-difunctionalization of alkynes that requires
dehydrogenation and addition of two functional groups onto
the terminal carbon atom of a alkyne, especially in a regio- and
stereoselective manner, is challenging, and thus, successful
achievements of this kind are rarely reported.4
Herein, as a result of our continuous interest in selective
transformation of alkynes,6 we report the regio- and stereo-
selective 1,1-difunctionalization of alkynes with arylsulfonyl
hydrazides for the formation of (E)-β-aryl sulfonyl acrylates.
Received: May 19, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b01585
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
a
Table 1. Optimization of the Reaction Conditions
Scheme 2. Substrate Scope
yield
b
entry
catalyst
ligand
additive
solvent
(%)
1
2
3
4
5
6
7
8
9
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
PdCl2
dppp
dppm
dppe
PPh3
Phen
dppp
dppp
dppp
dppp
dppp
dppp
−
−
−
−
−
−
−
−
−
−
−
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
44
25
39
27
32
39
Pd(TFA)2
Pd(PPh3)2Cl2
Pd(PPh3)4
Pd(OAc)2
Pd(OAc)2
45
41
42
c
10
none
52
11
DMF/DMAc
(3:1)
12
13
Pd(OAc)2
Pd(OAc)2
dppp
dppp
Na2CO3
DMF/DMAc
DMF/DMAc
trace
58
salicylic
acid
d
14
Pd(OAc)2
Pd(OAc)2
Pd(OAc)2
dppp
dppp
dppp
β-alanine
β-alanine
β-alanine
DMF/DMAc
DMF/DMAc
70(64)
65
e
15
f
16
DMF/DMAc
(3:1)
71
a
Reaction conditions: 1a (0.2 mmol), 2a (0.2 mmol), catalyst (5.0 mol
%), ligand (5.0 mol %), Cu(OAc)2·H2O (2.0 equiv), additive (15 mol
b
%), solvent (2.0 mL), N2, 80 °C, 30 min. GC yield using dodecane as
c
an internal standard. Other oxidants, such as O2, BQ, K2S2O8,
d
e
f
PhI(OAc)2, and TBHP. Isolated yields. 70 °C. 100 °C.
ability of the ester group, making the internal alkyne very
electrophilic, and resulting in the consequent addition (vide
infra). On the basis of this finding, we tuned the reaction
parameters for the optimum reaction conditions. Initially,
ligands such as bis(diphenylphosphino)methane (dppm), 1,2-
bis(diphenylphosphino)ethane (dppe), PPh3, and Phen were
examined (Table 1, entries 2−5; for details, see Supporting
Information (SI)), and dppp gave the best yield (44%, Table 1,
entry 1). For palladium catalysts, PdCl2, Pd(TFA)2, Pd-
(PPh3)2Cl2, and Pd(PPh3)4 showed good efficiency (Table 1,
entries 6−9). An assessment of oxidants revealed that
Cu(OAc)2·H2O was optimal for the reaction (Table 1, entry
1), whereas molecular oxygen, benzoquinone (BQ), K2S2O8,
PhI(OAc)2, and tert-butyl hydroperoxide (TBHP) were
ineffective (Table 1, entry 10). Other solvents such as N,N-
dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), 1-
methyl-2-pyrrolidinone (NMP), acetonitrile, and toluene were
inferior to DMF (for details, see SI). The mixed solvents were
more effective than DMF (for details, see SI), and a DMF to
DMAc ratio of 3:1 gave the best yield (52%, entry 11).
Excitedly, a catalytic amount of additives could further improve
the reaction performance (Table 1, entries 13 and 14; for
details, see SI). When 15 mol % β-alanine was added,15 a 70%
yield of 3a was achieved (Table 1, entry 14), whereas the
loading of Na2CO3 completely blocked the reaction (Table 1,
entry 12). A slightly lower 3a yield was observed at 70 °C
(Table 1, entry 15), and the rise of temperature to 100 °C did
not result in significant enhancement of 3a yield (Table 1, entry
16).
a
Reaction conditions: 1 (0.2 mmol), 2 (0.2 mmol), Pd(OAc)2 (5.0
mol %), dppp (5.0 mol %), β-alanine (15 mol %), Cu(OAc)2·H2O
(2.0 equiv), DMF/DMAc (2.0 mL, v/v = 3:1), N2, 80 °C, 30 min,
b
c
isolated yields. 1.0 mmol gram scale. 1 (0.4 mmol), 2 (0.4 mmol).
d
1:1 ratio of two different arylsulfonyl hydrazides.
this one-pot coupling−addition approach displayed a wide
scope of substrates and outstanding tolerance toward functional
groups, producing various (E)-β-aryl sulfonyl acrylates in
satisfactory yields with excellent regio- and stereoselectivity.
The structure of the products was unambiguously confirmed by
single-crystal X-ray crystallography (3q and 3af, for details, see
SI).
For arylsulfonyl hydrazides derivatives, functional groups
such as alkyl, methoxyl, halogen, nitro, cyano, trifluoromethyl,
and trifluoromethoxyl are all tolerated in this method of alkyne
arylsulfonylation, and the corresponding products (3a−o) were
gained in 30−72% yields. Notably, the halogenated (Cl, Br, and
With the optimized conditions in hand, we investigated the
scope and generality of the reaction. As shown in Scheme 2,
B
DOI: 10.1021/acs.orglett.8b01585
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
I) substrates that are reactive in palladium-catalyzed coupling
reactions were found to be suitable for the 1,1-difunctionaliza-
tion reaction, producing the corresponding products 3g−k in
35−62% yields. This chemoselectivity could be utilized for
further functionalization to realize the synthesis of more
complex targets by stepwise coupling. The reaction of sterically
hindered naphthalene substrates 2p and 2aa could also
proceed, giving the corresponding products 3p and 3aa in
30% and 32% yields, respectively.
Scheme 3. Reaction Scope of Late-Stage Modification
Different electronic effects of substituent groups existed in
the steps of desulfitative cross-coupling and sulfonative
addition; i.e., the electron-withdrawing (donating) groups
facilitate (disfavor) the cross-coupling reaction via cleavage of
the Ar(C)−S bond, but disfavor (facilitate) the subsequent
addition reaction via cleavage of the S−N bond (vide infra).
However, the attachment of strong electron-withdrawing
groups, such as NO2 (3l), CN (3m), and CF3 (3n and 3z),
resulted in reaction efficiency (yields: 30−40%) much inferior
to that of electron-donating groups (3b−d, and 3y, yields 62−
74%). Indeed, the direct addition of benzenesulfonyl hydrazide
bearing an electron-withdrawing group (CF3, Scheme 4, eq 3)
to internal alkyne 4A gave a much lower yield (32%) of
sulfonative addition product (3am) in comparison with the
direct addition of the other benzenesulfonyl hydrazides (3a,
70% yield; 3al, 68% yield; Scheme 4, eq 3). These results
demonstrate that sulfonative addition is more difficult and may
be the rate-determining step of the reaction. Other propargylic
carboxylates, bearing benzyl (3q), alkyl (3r−t), hydroxyl (3u),
morpholine (3v), sulfide (3w), and bromine (3x), also reacted
smoothly with benzenesulfonyl hydrazide 1a to produce a range
of (E)-β-aryl sulfonyl acrylates in 38−66% yields. It is
considered that the yields are satisfactory, albeit moderate to
good. It is because the strategy is more efficient than the two-
step Sonogashira-type cross-coupling and addition reactions
(for details, see SI). Gratifyingly, when two different
arylsulfonyl hydrazides were subjected to the reaction system,
the reaction took place selectively, furnishing the desired
products in 30−43% yields (3ab−ag). The arylsulfonyl
hydrazides substituted with an electron-donating group afford
the sulfonyl sources via S−N bond cleavage, and those
substituted with an electron-withdrawing group afford the aryl
groups via C−S bond cleavage.
Scheme 4. Control Experiments
take place (Scheme 4, eq 4). The results demonstrate that the
reaction proceeds via the pattern of Sonogashira-type
desulfitative coupling and subsequent sulfonative addition (for
more details, see SI).
Based on the results of the above studies, and those reported
in literature,6b,7c a plausible mechanism is illustrated in Scheme
5. The reaction of Pd(OAc)2 with arylsulfonyl hydrazide gives
Scheme 5. Possible Reaction Mechanism
In addition to propiolates, terminal alkynes substituted with
carbonyl (1-phenylprop-2-yn-1-one, 2ah) and acylamino (N-
ethynyl-N-methylbenzamide, 2ai) were also suitable for the
reaction, producing the desired product in 37% (3ah) and 33%
(3ai) yields, respectively, with concomitant generation of
internal alkynes (4aa, 30% yield; 4ab, 37% yield; for details, see
SI).
It is worth noting that this one-pot coupling−addition
reaction can be applied to modify highly functionalized
molecules, further demonstrating its applicational potential in
drug discovery and synthesis of natural products. For example,
propiolates bearing natural groups such as L-menthol and
cholesterol could well react with benzenesulfonyl hydrazide 1a
to produce the corresponding products 3aj and 3ak in 49% and
46% yields under the optimized conditions, respectively
(Scheme 3).
ArPdIIOAc intermediate III, which is formed via successive
dehydrogenation of arylsulfonyl hydrazide, together with the
liberation of N2 and SO2. Transmetalation of III with copper
acetylides IV gives palladium arylacetylides V, which undergoes
reductive elimination to generate the cross-coupling product
VI, simultaneously releasing Pd0. Intermediate II undergoes
migratory insertion into the internal of alkynes VI, followed by
protonolysis of the alkenyl16 C−Pd bond of VII to afford
product 3 and the PdII catalyst.
In summary, we have developed a novel strategy for one-pot
1,1-difunctionalization of terminal alkynes via a palladium-
catalyzed coupling−addition reaction of propiolates with
readily available arylsulfonyl hydrazides, providing a broad
range of highly functionalized (E)-vinylsulfones in satisfactory
yield. Arylsulfonyl hydrazides act as both arylation and
sulfonylation reagents via selective Ar(C)−S and S−N bond
Finally, a number of control experiments were performed to
gain mechanistic insight into this reaction. Only ethyl 3-
phenylpropiolate 4A reacted with 1a to give the desulfitative
coupling product (Scheme 4, eq 3), whereas the reaction of 1a
with the other probable intermediates (4B, 4C, or 4D) did not
C
DOI: 10.1021/acs.orglett.8b01585
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Letter
Chem. Soc. 2017, 139, 15724. (e) Iwamoto, T.; Nishikori, T.;
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but also substantially expands the scope of sulfonylation
reactions. Displaying stereoselectivity, functional group diver-
sity, and step economy, the method has high applicational
potential in organic and biochemistry.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b01585.
■
S
Experimental procedures, full spectroscopic data, and
1
copies of H, 13C and 19F spectroscopies (PDF)
Accession Codes
CCDC 1821769 and 1821777 contain 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
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: djyustc@hotmail.com.
*E-mail: zhouyb@hnu.edu.cn.
*E-mail: sf_yin@hnu.edu.cn.
(8) Selected examples: (a) Yang, X.; Cheng, F.; Kou, Y.-D.; Pang, S.;
Shen, Y.-C.; Huang, Y.-Y.; Shibata, N. Angew. Chem., Int. Ed. 2017, 56,
1510. (b) Noshi, M. N.; El-awa, A.; Torres, E.; Fuchs, P. L. J. Am.
ORCID
́ ́
Chem. Soc. 2007, 129, 11242. (c) Lopez-Perez, A.; Robles-Machín, R.;
Yongbo Zhou: 0000-0002-3540-8618
Notes
Adrio, J.; Carretero, J. C. Angew. Chem., Int. Ed. 2007, 46, 9261.
(d) Guo, H.-M.; Zhou, Q.-Q.; Jiang, X.; Shi, D.-Q.; Xiao, W.-J. Adv.
Synth. Catal. 2017, 359, 4141. (e) Forristal, I. J. Sulfur Chem. 2005, 26,
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1001.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
́
(9) Selected examples: (a) Chauhan, P.; Hadad, C.; Lopez, A. H.;
■
Silvestrini, S.; La Parola, V.; Frison, E.; Maggini, M.; Prato, M.;
Carofiglio, T. Chem. Commun. 2014, 50, 9493. (b) Dunny, E.;
Doherty, W.; Evans, P.; Malthouse, J. P. G.; Nolan, D.; Knox, A. J. S. J.
Med. Chem. 2013, 56, 6638. (c) van der Westhuyzen, R.; Strauss, E. J.
Am. Chem. Soc. 2010, 132, 12853. (d) Uttamchandani, M.; Liu, K.;
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2004, 126, 3404.
Financial support by the National NSF of China (Grant Nos.
21573065, 21706058, 21725602, and 21573064) and the NSF
of Hunan Province (Grant No. 2016JJ1007) is appreciated.
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