Iron-catalyzed tetrasubstituted alkene formation from alkynes and sodium sulfinates

Article abstract of DOI:10.1039/c4ob00816b

An iron-catalyzed sulfenylation and arylation of alkynes with aryl sulfinic acid sodium salts is described. Various aromatic sodium sulfinates acted both as aryl and sulfenylation reagents, affording tetrasubstituted alkenes in one pot with good yields. T

Full text of DOI:10.1039/c4ob00816b

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Biomolecular Chemistry
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Iron-catalyzed tetrasubstituted alkene formation
from alkynes and sodium sulfinates†
Saiwen Liu,a Lichang Tang,a Hui Chen,a Feng Zhaoa and Guo-Jun Deng*a,b
Cite this: Org. Biomol. Chem., 2014,
12, 6076
Received 21st April 2014,
Accepted 26th June 2014
DOI: 10.1039/c4ob00816b
www.rsc.org/obc
An iron-catalyzed sulfenylation and arylation of alkynes with aryl functionalized alkenyl triflates were synthesized via electro-
sulfinic acid sodium salts is described. Various aromatic sodium philic carbofunctionalization.14
sulfinates acted both as aryl and sulfenylation reagents, affording
As an important class of substituted alkenes, vinyl sulfides
are ubiquitous in biologically active compounds and natural
products.15 They can also be used as starting materials to
prepare other substituted alkenes via C–S bond cleavage.16
Among the various methods developed, the addition of thiols
to alkynes is the most convenient approach to synthesize vinyl
sulfides.17 Transition metals such as rhodium, palladium, acti-
nides and lanthanides and nickel were proved to be efficient
catalysts for this kind of reaction. This transformation has
also been achieved under transition-metal-free conditions.18
However, to the best of our knowledge, there were only a few
methods developed to synthesize multi-substituted arylvinyl
sulfides, especially to triarylvinyl sulfides.19 Recently, we and
others developed various methods for C–C bond formation
using stable aromatic sodium sulfinates as aryl sources via
extrusion of SO2.20 This strategy was successfully employed for
trisubstituted alkene preparation using palladium as the cata-
lyst.21 We also developed the iodine-catalyzed regioselective
sulfenylation or sulfonylation of indoles using sodium sulfi-
nates as the sulfenylation or sulfonylation reagents.22 In these
reactions, aromatic sodium sulfinates can act as aryl sources
and sulfonylation or sulfenylation reagents depending on the
reaction conditions. Based on these observations, we envision
that it might be possible to synthesize triarylvinyl sulfides in
one pot using aromatic sodium sulfinates both as aryl sources
and sulfenylation reagents. Herein, we describe an iron-
catalyzed tetrasubstituted alkene formation from internal
alkynes and two aromatic sodium sulfinates, affording various
highly functionalized tetrasubstituted alkenyl sulfides in one
pot (Scheme 1).
tetrasubstituted alkenes in one pot with good yields.
Alkenes are ubiquitous in natural products and biologically
active compounds. Many alkenes are also versatile starting
materials in the synthesis of functional materials.1 Various
methods have been developed to prepare alkenes, such as the
Aldol-type condensation, the Wittig–Horner reaction, olefin
metathesis and cross-coupling reactions.2 Tetrasubstituted
alkenes are frequently found in drugs, such as Tamoxifen and
Vioxx,3 and natural products such as Stemona alkaloids and
Nileprost analogues.4 Importantly, tetrasubstituted alkenes
also contribute extensively to materials sciences and building
blocks for synthetic chemistry.5 However, the congested nature
of the double bond makes it difficult to access these important
chemicals efficiently and stereoselectively.6 Although the
McMurry reaction,7 Wittig olefination or Julia–Kocienski olefi-
nation8 and metathesis9 can provide different routes for tetra-
substituted alkenes, the efficiency, regio- and stereoselectivity
are major problems. The transition-metal-catalyzed cross-coup-
ling reaction of internal alkynes with two different coupling
reagents such as aryl halides and aryl boronic acids can
provide an alternative synthetic route to tetrasubstituted
alkenes.10 In recent years, the most reliable method to form
these compounds is alkyne carbometalation,11 although there
are few other catalytic methods available.12 Using copper as
the catalyst, Gaunt and co-workers successfully employed
diaryliodonium triflates as coupling agents to selectively
afford all-carbon tetrasubstituted alkenes.13 Similarly, highly
aKey Laboratory of Environmentally Friendly Chemistry and Application of Ministry
of Education, College of Chemistry, Xiangtan University, Xiangtan 411105, China.
E-mail: gjdeng@xtu.edu.cn; Fax: (+86)0731-5829-2251; Tel: (+86)0731-5829-8601
bKey Laboratory of Molecular Recognition and Function, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, China
†Electronic supplementary information (ESI) available. CCDC 988537 and
988538. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c4ob00816b
Scheme 1 Iron-catalyzed arylation and sulfenylation of alkynes.
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Table 1 Optimization of the reaction conditionsa
Entry
Catalyst
Ligand
Additive
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
TFA–MsOH
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
1,4-Dioxane–H2O
CH3CN–H2O
52
77
63
69
73
65
80
90
59
54
68
73
55
51
74
61
Trace
FeCl3·3H2O
Fe2O3
Fe(NO3)3
Fe2(SO4)3
FeCl2
1,8-naph
1,8-naph
1,8-naph
1,8-naph
1,8-naph
1,8-naph
1,8-naph
DMAP
Fe(acac)3
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
FeSO4·7H2O
9
10
11
12
13
14
15
16
17
Bipyridine
DABCO
1,8-naph
1,8-naph
1,8-naph
1,8-naph
1,8-naph
1,8-naph
Anisole–H2O
Diglyme–H2O
DCE–H2O
H2O
1,4-Dioxane–H2O
a Conditions: 1a (0.8 mmol), 2a (0.2 mmol), catalyst (1 mol%), ligand (2 mol%), TFA (0.2 mmol), MsOH (0.2 mmol), solvent (0.3 mL), H2O
(0.1 mL), 120 °C, 24 h under argon unless otherwise noted, 1,8-naph = 1,8-naphthalenediamine. b GC yield based on 2a.
In the first experiment we examined the reaction between
sodium benzenesulfinate (1a) and diphenylethyne (2a) in 1,4-
dioxane–water (3 : 1) using trifluoroacetic acid and methane-
sulfonic acid as additives (Table 1). We were pleased to observe
the desired product 3a in 52% yield without any metal-catalyst
under argon at 120 °C (entry 1). Using FeCl3·3H2O/1,8-
naphthalenediamine (1,8-naph) as the catalyst, the yield of 3a
could increase to 77% (entry 2). Furthermore, other iron salts
were also investigated for this reaction under similar reaction
conditions (entries 3–7). The best result was obtained using
FeSO4·7H2O as the catalyst (entry 8). Replacing 1,8-naphthalene-
diamine with other nitrogen-containing ligands led to lower
yields (entries 9–11). Solvents screening revealed that dioxane–
water (3 : 1) was the most efficient reaction medium (entries
12–15). Notably, the desired product 3a could be obtained in
61% yield using water as the sole solvent (entry 16). The use of
acidic additives is necessary for this kind of transformation,
and only trace 3a was detected in their absence (entry 17). To
get satisfactory reaction yield, four equivalents (0.8 mmol) of
1a were necessary.
Table 2 Vinyl thioether formation from sodium sulfinates and alkynes
with the same substituentsa
Entry Ar
Sodium sulfinate Alkyne Product Yieldb (%)
1c
2c
3
4
5
Ph
4-Me–Ph
4-Et–Ph
4-MeO–Ph 1d
4-F–Ph
1a
1b
1c
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
78
72
50
48
70
60
1e
1f
6
4-Cl–Ph
a Conditions: 1 (0.8 mmol), 2 (0.2 mmol), FeSO4·7H2O (5 mol%), 1,8-
naph (10 mol%), TFA (0.2 mmol), MsOH (0.2 mmol), 1,4-dioxane
(0.3 mL), H2O (0.1 mL), 120 °C, 24 h under argon unless otherwise
noted. b Isolated yield based on 2. c FeSO4·7H2O (1 mol%), 1,8-naph
(2 mol%).
optimal reaction conditions, and the desired products 3e and
3f were obtained in 70% and 60% yield, respectively (entries 5
and 6).
With the optimized reaction conditions established, we
explored the scope and generality of this transformation in the
presence of various substituents in aromatic ring. Firstly, we
investigated the reaction between aromatic alkynes and aryl-
sulfinic acid sodium salts with the same substituents (Table 2).
A slightly lower yield was obtained when a methyl group was
presented at the para position, and the corresponding product
3b was obtained in 72% yield (entry 2). Stronger electron-
donating groups such as the methoxy group affected the reac-
tion yield significantly (entry 4). Halogen functional groups
such as fluoro and chloro were well tolerated under the
Next, the formation of triarylvinyl sulfides with various sub-
stituents in sodium sulfinates and internal alkynes was
explored in this reaction and the results are summarized in
Table 3. The reactions with sulfinic acid sodium salts bearing
electron-donating (entries 1–3) and electron-withdrawing sub-
stituents (entries 4 and 6) at the aromatic ring proceeded
smoothly to give the desired products in moderate to
good yields. Common functional groups, including fluoro
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Table 3 Vinyl thioether formation from sodium sulfinates and alkynesa
Scheme 2 Synthetic application.
Entry
Sodium sulfinate 1
Alkyne 2
Product
Yieldb (%)
presence of [NiCl2(PPh3)2] catalyst (3 mol%).24 When phenyl-
(1,2,2-triphenylvinyl)sulfane 3a was treated with phenylmagne-
sium bromide, the desired product was obtained in 65% iso-
lated yield (Scheme 2).
Ar =
R =
Ph 2a
Ph 2a
Ph 2a
1c
2
4-Me–Ph 1b
4-Isopropyl-Ph 1g
4-MeO–Ph 1d
4-CF3–Ph 1h
4-OCF3–Ph 1i
4-F–Ph 1e
4-Cl–Ph 1f
4-Br–Ph 1j
4-CN–Ph 1k
Ph 1a
Ph 1a
Ph 1a
4-Me–Ph 1b
4-Me–Ph 1b
4-Me–Ph 1b
Ph 1a
3g + 4g
3h + 4h
3i + 4i
3j + 4j
3k + 4k
3l + 4l
3m + 4m
3n + 4n
3o + 4o
3p + 4p
3q + 4q
3r + 4r
3s + 4s
3t + 4t
74 (1.2 : 1)
50 (1.2 : 1)
67 (1 : 1)
62 (1 : 1)
70 (1 : 1)
68 (1 : 1)
70 (1 : 1)
72 (1 : 1)
65 (1 : 1)
71 (1 : 1)
73 (1 : 1.1)
68 (1 : 1)
72 (1 : 1)
78 (1 : 1)
51 (1 : 1.5)
20 (1 : 1)
3
4c
5
4-Me–Ph 2b
4-Me–Ph 2b
4-Me–Ph 2b
4-Me–Ph 2b
4-Me–Ph 2b
Ph 2a
4-Me–Ph 2b
4-Ethyl-Ph 2c
4-MeO–Ph 2d
4-F–Ph 2e
4-Cl–Ph 2f
2-Thienyl 2g
n-Propyl 2h
In summary, we have developed an iron-catalyzed addition
of aromatic sodium sulfinates to internal alkynes. Aromatic
sodium sulfinates acted both as aryl sources and sulfenylation
reagents. The C–C and C–S bond forming reactions were rea-
lized in one pot using iron as an environmentally benign
catalyst. Acid was found to be crucial for the formation of
tetrasubstituted alkenes. Although the stereoselectivity is not
satisfactory at this stage, this novel process can provide an
efficient approach to triarylvinyl sulfides. The mechanism,
selectivity and synthetic application of this transformation are
under investigation.
6
7c
8c
9
10
11
12
13
14
15
16
3u + 4u
3v + 4v
a Conditions: 1 (0.8 mmol), 2 (0.2 mmol), FeSO4·7H2O (5 mol%), 1,8-
naph (10 mol%), TFA (0.2 mmol), MsOH (0.2 mmol), 1,4-dioxane
(0.3 mL), H2O (0.1 mL), 120 °C, 24 h under argon unless otherwise
noted. b Isolated yield based on 2, ratios were determined by NMR.
c FeSO4·7H2O (1 mol%), 1,8-naph (2 mol%).
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (21172185, 21372187), the Hunan Provin-
cial Natural Science Foundation of China (11JJ1003, 12JJ7002),
the New Century Excellent Talents in University from Ministry
of Education of China (NCET-11-0974), and the Hunan Provin-
cial Innovative Foundation for Postgraduate (CX2013B269).
(entries 4–6, 13), chloro (entries 7 and 14) and bromo (entry 8)
were all compatible with this catalytic reaction. Sodium sulfi-
nates with strong electron-withdrawing groups such as cyano
also smoothly coupled with 2a, and gave 3o and 4o in 65%
yield (entry 9). It is noteworthy that hetero 1,2-di(thiophen-
2-yl)ethyne (2g) also participated in the reaction to afford the
corresponding products 3u and 4u in 51% total yield (entry
15). In addition, the reaction of 1a with aliphatic alkyne oct-4-
yne 2h afforded the desired product in 20% yield (entry 16). In
most cases, a mixture of two isomers (near 1 : 1 ratio) was
obtained which is difficult to separate. Isomer 3r was success-
fully separated from 4r, and the structure of 3r is confirmed by
X-ray crystallography (Fig. 1). The exact reaction mechanism is
not clear at this stage since it is hard to trap some key inter-
mediates during the reaction process.23
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Fig. 1 X-ray structure of 3r.
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