Copper-catalyzed decarboxylative sulfonylation of α,β-unsaturated carboxylic acids

Article abstract of DOI:10.1021/jo501314y

Copper-catalyzed, ligand-promoted decarboxylative coupling of readily available α,β-unsaturated acids with sodium aryl sulfinates is presented. This method provides a new avenue for the synthesis of vinyl sulfones via a decarboxylative radical coupling st

Full text of DOI:10.1021/jo501314y

Article
pubs.acs.org/joc
Copper-Catalyzed Decarboxylative Sulfonylation of α,β-Unsaturated
Carboxylic Acids
Balaji V. Rokade and Kandikere Ramaiah Prabhu*
Department of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India
S
* Supporting Information
ABSTRACT: Copper-catalyzed, ligand-promoted decarboxylative
coupling of readily available α,β-unsaturated acids with sodium aryl
sulfinates is presented. This method provides a new avenue for the
synthesis of vinyl sulfones via a decarboxylative radical coupling
strategy by employing a catalytic amount of Cu(ClO4)2·6H2O,
TBHP in decane as an oxidant, and 1,10-phenanthroline as a ligand. The salient feature of this method is that it furnishes
exclusively the (E)-isomer.
Scheme 1. Reported Methods for the Synthesis of Vinyl
Sulfone derivatives
INTRODUCTION
■
Transition-metal-catalyzed decarboxylative coupling reactions
have shown great promise in synthetic organic chemistry and
are fast emerging as powerful tools for the formation of
carbon−carbon1 and carbon−heteroatom bonds.2 Because
carboxylic acids and their derivatives are inexpensive and
commercially available or readily synthesized by Knoevenagel
condensation3 or Horner−Wittig reaction4 followed by
hydrolysis (for α,β-unsaturated acids), a number of reports
on decarboxylative couplings of carboxylic acids or their salts
with aromatic halides5 or triflates,6 amines,2e alcohols,7 ethers,7
hydrocarbons,8 sodium trifluoromethanesulfinate,9 t-BuONO,10
etc., for synthesizing a variety of organic compounds have been
reported.
Vinyl sulfones are versatile building blocks11 that find their
utility as Michael acceptors and are used in cycloaddition
reactions. Vinyl sulfones are prominent in medicinal chem-
istry11 owing to their wide presence in pharmaceutical
molecules, such as enzyme inhibitors and biologically active
antagonists; e.g., aspartic vinyl sulfones are inhibitors of a
caspase-3-dependent pathway,12 aza vinyl sulfones are well-
known antiplasmodial agents,13 eletriptan is a drug intended for
treatment of migraine headaches, etc. Considering the
significance of vinyl sulfones, various synthetic approaches
have been reported in the literature.14 For example,
sulfonylation of alkynes,14a,b olefins,14c−i epoxides,14j vinyl
halides,14k,l or boronic acids14m and Heck coupling14n,o are a
few prominent methods of synthesizing sulfones14p−r (Scheme
1). Recently, Liu and co-workers reported a copper-catalyzed
C−S cross-coupling reaction between arylpropionic acids and
thiols to synthesize vinyl sulfides.2b In light of the literature
precedence1,2,5−10 and continuation of our work on the utility
of copper catalyst for C-hetero bond-forming reactions,10a,15 we
thought it would be of interest to develop a method by a
decarboxylative radical sulfonylation of α,β-unsaturated carbox-
ylic acids using sodium aryl sulfinates. Herein, we disclose the
synthesis of vinyl sulfone via decarboxylative coupling of α,β-
unsaturated acids employing sodium aryl sulfinates through a
ligand-promoted, copper-catalyzed radical pathway.
RESULTS AND DISCUSSION
■
Optimization Studies. The investigation for screening the
reaction conditions began with (E)-4-methoxycinnamic acid
(1a) and sodium p-toluenesulfinate (2a) as a model substrate
using copper catalysts, and results are summarized in Table 1.
Preliminary investigations were carried out by using 1a (1
equiv), 2a (1.2 equiv), and CuCl (10 mol %) as a catalyst with
various oxidizing agents (2 equiv) such as TBHP in decane
(tert-butyl hydroperoxide), TBHP in water, DTBP (di-tert-butyl
peroxide), TBPB (tert-butyl perbenzoate), and K2S2O8 at 80 °C
using CH3CN as a solvent (entries 1−5, Table 1). During the
preliminary screening studies, it was found that TBHP in
decane was a suitable oxidizing agent, which furnished the
expected sulfone 3a in 37% yield (entry 1, Table 1), while other
oxidants were found to be less effective (entries 2−5, Table 1).
Received: June 12, 2014
© XXXX American Chemical Society
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a
Table 1. Optimization Studies
entry
2a (equiv)
catalyst (mol %)
CuCl (10)
oxidant (equiv)
temp (°C)
yield (%)
1
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
1.2
2
TBHP in decane (2)
TBHP in H2O (2)
DTBP (2)
80
80
37
29
20
18
20
32
31
2
CuCl (10)
3
CuCl (10)
80
4
CuCl (10)
TBPB (2)
80
5
CuCl (10)
K2S2O8 (2)
80
6
CuBr (10)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (2)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
K2S2O8 (3)
80
7
Cu(OTf)2 (10)
80
8
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (20)
Cu(ClO4)2·6H2O (10)
Cu(ClO4)2·6H2O (20)
Cu(ClO4)2·6H2O (20)
Cu(ClO4)2·6H2O (20)
Cu(ClO4)2·6H2O (20)
Cu(ClO4)2·6H2O (20)
FeCl3 (20)
80
44
b
9
80
25
c
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
80
nr
d
80
nr
e
80
trace
58
f
80
2
80
63
67
70
74
76
81
2
110
110
110
110
110
120
110
110
110
110
110
110
110
110
110
110
110
3
2
2
2
2
70
g
2
83
h
2
72
i
2
66
2
nr
nr
nr
2
NiCl2·6H2O (20)
Co(OAc)2·4H2O (20)
V2O5 (20)
K2S2O8 (3)
2
K2S2O8 (3)
2
K2S2O8 (3)
nr
g
2
FeCl3 (20)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
TBHP in decane (3)
nr
g
g
g
2
NiCl2·6H2O (20)
Co(OAc)2·4H2O (20)
V2O5 (20)
nr
nr
nr
2
2
a
b
Reaction conditions: 1a (0.25 mmol, 1 equiv), 2a (equiv), catalyst (mol %), oxidant (equiv) in CH3CN (2.0 mL), open air. ClCH2CH2Cl as a
c
d
e
f
g
solvent instead of CH3CN. CH3COOH as an additive. TFA as an additive. TfOH as an additive. 2-Naphthol as an additive (20 mol %). 1,10-
Phen·H2O as a ligand (20 mol %).
hL-Proline as a ligand (20 mol %), TMEDA (tetramethylethylenediamine) as a ligand (20 mol %).
i
Further, other copper salts such as CuBr and Cu(OTf)2 yielded
sulfone 3a in 32% and 31% yields, respectively (entries 6 and 7,
Table 1). Among the various copper catalysts that were
screened, Cu(ClO4)2·6H2O was found to be the appropriate
catalyst (44% yield, entry 8, Table 1). Changing the solvent to
dichloroethane was not helpful (25% yield, entry 9, Table 1).
Additives such as CH3COOH, TFA (trifloroacetic acid), TfOH
(triflic acid), and 2-naphthol were found to be ineffective
(entries 10−13, Table 1). Interestingly, increasing the amount
of sodium p-toluenesulfinate (2a) from 1.2 to 2 equiv increased
the yield of the expected product 3a to 63% (entry 14, Table
1). Increasing the temperature of the reaction to 110 °C has
shown the formation of 3a in 67% yield. Finally, by increasing
the amount of catalyst (Cu(ClO4)2·6H2O) and oxidant (TBHP
in decane) the product 3a was obtained in 81% yield (entries
15−19, Table 1). Unexpectedly, heating the reaction at 120 °C
decreased the yield of 3a to 70% (entry 20, Table 1). In
addition, use of 1,10-phenanthroline as a ligand has brought a
marginal increase in the yield of 3a (81% to 83%, entry 21,
Table 1). Later it was noticed that the addition of 1,10-
phenanthroline as a ligand brought a considerable improvement
in the yields.16 On the other hand, the utility of ligands such as
L-proline and TMEDA decreased the yield of product 3a to
72% and 66%, respectively (entries 22 and 23, Table 1). Our
attempts to enhance the yield by using a variety of metal
catalysts such as FeCl3, NiCl2·6H2O, Co(OAc)2·4H2O, and
V2O5 in the presence of either K2S2O8 or TBHP were not
successful (entries 24−31, Table 1). Finally, it was pleasing to
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a
Table 2. Substrate Scope
a
Reaction conditions: 1a (0.25 mmol, 1 equiv), 2a (0.50 mmol, 2 equiv), Cu(ClO4)2·6H2O (0.05 mmol, 20 mol %), TBHP in decane (0.75 mmol, 3
b
equiv), 1,10-Phen.H2O (0.05 mmol, 20 mol %). Yields in parentheses indicate the yields after 48 h.
find that 1a (0.25 mmol), 2a (0.50 mmol), Cu(ClO4)2·6H2O
(0.050 mmol), TBHP in decane (0.750 mmol), and 1,10-
phenanthroline (0.050 mmol) at 110 °C in CH3CN as a
solvent is required for the efficient synthesis of sulfone via a
decarboxylative coupling reaction (entry 21, Table 1).
presented in Table 2. (E)-4-Methoxycinnamic acid underwent a
smooth decarboxylative coupling reaction with a variety of
sulfinates such as sodium p-toluenesulfinate (2a), sodium
benzenesulfinate (2b), sodium 4-bromobenzenesulfinate (2c),
and sodium 4-chlorobenzenesulfinate (2d) to furnish the
corresponding sulfones 3a, 3b, 3c, and 3d in good to moderate
yields (entries 1−4, Table 2). (E)-3-(2,4-Dimethoxyphenyl)-
The scope of the decarboxylative coupling reaction has been
explored with a variety of substituted carboxylic acids as
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a
Scheme 2. Selectivity Study
a
Reaction conditions: cis-isomer of 1a (0.25 mmol, 1 equiv), 2a (0.50 mmol, 2 equiv), Cu(ClO4)2·6H2O (0.05 mmol, 20 mol %), TBHP in decane
(0.75 mmol, 3 equiv), 1,10-Phen·H2O (0.05 mmol, 20 mol %, 20 h.
a
Scheme 3. Scaling up Experiment
a
Reaction conditions: 1b (4.80 mmol), 2a (2 equiv), Cu(ClO4)2·6H2O (20 mol %), TBHP in decane (3 equiv), 1,10-Phen·H2O (20 mol %), 20 h.
Scheme 4. Control Experiments
acrylic acid in reaction with 2b, 2c, 2a, and 2d yielded the
products 3e, 3f, 3g, and 3h in moderate yields (65%, 61%, 54%,
and 56%, respectively (entries 5−8, Table 2). Similarly, (E)-3-
(4-methoxyphenyl)but-2-enoic acid reacted well with 2c and 2a
to furnish the corresponding sulfones 3i and 3j in 62% (E:Z;
83:17) and 49% (E:Z; 86:14) yields, respectively (entries 9 and
10, Table 2). Further, it was noticed that acid such as (E)-3-(4-
(allyloxy)phenyl)acrylic acid in a similar coupling reaction with
2c and 2d furnished the coupled products 3k and 3l in 42% and
33%, yields, respectively (entries 11 and 12, Table 2). The
decarboxylative coupling of (E)-3-(4-(benzyloxy)phenyl)acrylic
acid with 2a, 2d, 2c, and 2b resulted in the formation of 3m,
3n, 3o, and 3p in 45%, 49%, 48%, and 36% yields, respectively
(entries 13−16, Table 2). The coupling reaction of (E)-3-(3,4-
dimethoxyphenyl)acrylic acid with 2d, 2c, and 2a proceeded
well to afford the products 3q, 3r, and 3s in 54%, 52%, and 34%
yields, respectively (entries 17−19, Table 2). Further, (E)-3-
(benzo[d][1,3]dioxol-5-yl)acrylic acid reacted with 2d to afford
the coupled products 3t in 52% yield (entry 20, Table 2). The
coupling reaction of heterocyclic derivatives such as (E)-3-
(thiophene-2-yl)acrylic acid with 2d and 2a furnished the
corresponding products 3u and 3v in 33% and 31% yield,
respectively (entries 21 and 22, Table 2). To improve the yields
of the reaction, a few of the substrates (3c, 3k, 3l, and 3s) that
were furnishing the products in low yields were allowed to
undergo the reaction for extended reaction time (48 h).
However, these reactions resulted in a marginal increase in the
formation of products (2−5%).
As seen from these examples, various sodium aryl sulfinates
furnished the vinyl sulfones in moderate to good yields.17a
Although, in few examples, the yields are low, it is important to
recognize that the present strategy provides a potentially useful
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Scheme 5. Tentative Mechanism
method for the synthesis of vinyl sulfones.17a Under the
reaction conditions, Br and Cl substituents were well tolerated,
leading to the corresponding substituted sulfones in moderate
yields, which can be further functionalized. Further, it was
found that the reaction was stereoselective toward the
formation of the E-isomer exclusively, which can be attributed
to the thermodynamic stability of the product. This was further
elaborated by the reaction of the cis-isomer of 4-methoxycin-
namic acid with sodium p-toluenesulfinate (2a) under the
optimal reaction conditions, which furnished the E-isomer of
the product 3a exclusively in 77% yield (Scheme 2). However,
our attempts to explore the scope of this strategy using a variety
of acid derivatives such as cinnamic acid, (E)-3-(4-nitrophenyl)-
acrylic acid, (E)-3-(1H-indol-3-yl)acrylic acid, (E)-3-(4-
aminophenyl)acrylic acid, (E)-3-(4-hydroxyphenyl)acrylic
acid, 2-(4-methoxyphenyl)acrylic acid, (E)-3-(4-
methoxyphenoxy)acrylic acid, (E)-4-(4-methoxyphenyl)-4-ox-
obut-2-enoic acid, 2-(4-methoxyphenyl)acetic acid, 4-methox-
ybenzoic acid, and 1-benzylpyrrolidine-2-carboxylic acid was
not fruitful (see SI-Table 1, Supporting Information).17b
Further to this, our attempts on the reaction of sodium 2-
nitrobenzenesulfinate and sodium 4-methoxy-3-nitrobenzene-
sulfinate were not successful. However, a similar reaction with
sodium methyl sulfinate furnished trace amounts of corre-
sponding sulfones.
and 2a (eq d, Scheme 4). This reaction did not furnish the
expected product 3a and instead produced trace amounts of 5,
indicating that the reaction does not involve a corresponding
styrene as an intermediate. During preparation of this
manuscript, Liu and co-workers reported a cascade reaction
to obtain styrene 2-sulfonylbenzo[b]furans via styrene as an
intermediate18 using well-known reaction sequences.14c−i,19
On the basis of this information, a tentative reaction
mechanism has been proposed as presented in Scheme 5.
Cinnamic acid derivatives in the presence of Cu(II) form the
corresponding intermediate I, which reacts with the sulfone
radical II, which is generated by the reaction of sodium aryl
sulfinate with Cu(II) and TBHP to furnish the radical species
III.7−9,20 Further, the species III undergoes a decarboxylation
to provide the expected product.
CONCLUSION
■
In summary, formation of a C−S bond via ligand-promoted
decarboxylative radical sulfonylation of a α,β-unsaturated
carboxylic acids strategy has been developed to synthesize
vinyl sulfones using Cu catalyst. This reaction is selective and
exclusively furnishes the corresponding E-isomer. This method
provides a new route for the synthesis of vinyl sulfones using a
decarboxylation strategy to obtain vinyl sulfones via a radical
pathway.
A scaling up experiment between 1b and 2a under the
optimized conditions furnished 3g in 73% yield, indicating the
reaction is more efficient on large scale (Scheme 3).
EXPERIMENTAL SECTION
■
General Experimental Procedures. All reactions were carried
out using distilled solvents. Reactions were monitored by using
precoated silica TLC plates. Mass spectra were recorded on EI, and
ESI (TOF) modes. NMR spectra were recorded in at 400 MHz.
Column chromatography was carried out on silica gel 230−400 mesh
or 100−200 mesh. Chemicals obtained from commercial suppliers
were used without further purification. Sodium sulphinates 2a, 2b, 2c
and 2d were purchased from commercial suppliers. All cinnamic acid
1a, 1b, 1c, 1d, 1e, 1f, 1g and 1h were prepared according to literature
procedure.21−24 Unless otherwise noted, materials obtained from
commercial suppliers were used without further purification.
Typical General Experimental Procedure: Synthesis of Vinyl
Sulfone from α,β-Unsaturated Acid and Sodium Aryl Sulfinate.
TBHP in decane (0.15 mL, 0.75 mmol, 3 equiv, 5. 0 M soluion) was
added dropwise at room temperature to a well-stirred mixture of α,β-
unsaturated acid (1a, 44.5 mg, 0.25 mmol, 1 equiv), sodium aryl
sulfinate (2a, 90 mg, 0.50 mmol, 2 equiv), Cu(ClO4)2·6H2O (18.5 mg,
0.05 mmol, 20 mol %), and 1,10-phenathroline·H2O (9.9 mg, 0.05
mmol, 20 mol %) in CH3CN (2 mL) and then heated at 110 °C until
the reaction was complete (20 h, monitored by TLC). After
completion of the reaction, the reaction mixture was cooled to room
Mechanistic Considerations. A tentative mechanism has
been proposed on the basis of literature precedence7−10 and the
following control experiments. The reaction of 4-methoxycin-
namic acid (1a) with 2a was conducted under the optimal
reaction conditions in the presence of radical inhibitors such as
TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and BHT (2,4-
di-tert-butyl-4-methylphenol). As can be seen from Scheme 4,
these two radical scavengers retarded the reaction, and the
reaction did not proceed. These two experiments indicate that
the reaction is probably proceeding via a radical intermediate
(eqs a and b, Scheme 4). However, using sulfinic acid under the
optimized reaction conditions did not furnish the expected
product (eq c, Scheme 4), which shows the importance of
sodium salt. We speculated that the decarboxylation reactions
of cinnamic acid may proceed via a protodecarboxylation step
to furnish styrene, which further reacts to yield the
corresponding products. Therefore, a reaction was performed
using a styrene derivative such as 1-methoxy-4-vinylbenzene 4
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temperature, solvent was removed under reduced pressure, and the
product was directly loaded on silica column for the purification.
(E)-1-Methoxy-4-(2-tosylvinyl)benzene (3a): white solid; yield 83%
(59.8 mg); mp 176−178 °C (lit.25 mp 177−180 °C); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
Hz, 1H), 6.49 (dd, J1 = 8.8 Hz, J2 = 2.4 Hz, 1H), 6.43 (d, J = 2 Hz,
1H), 3.84 (s, 3H), 3.82 (s, 3H), 2.42 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3) δ 163.3, 160.3, 143.7, 138.6, 138.0, 132.4, 129.7, 127.4,
125.2, 114.4, 105.3, 98.4, 55.5, 55.4, 21.5; HRESI-MS (m/z) calcd for
C17H18SO4 (M + Na) 341.0824, found (M + Na) 341.0827.
1
procedure; IR (KBr, cm−1) 2923, 1603, 1514, 1260, 1142; H NMR
(E)-1-(2-((4-Bromophenyl)sulfonyl)vinyl)-2,4-dimethoxybenzene
(3h): yellow gummy liquid; yield 56% (53.6 mg); Rf (25% EtOAc/
hexane) 0.45; prepared as shown in the general experimental
procedure; IR (neat, cm−1) 2918, 1601, 1576, 1457, 1299, 1288,
(400 MHz, CDCl3) δ 7.81 (d, J = 8 Hz, 2H), 7.60 (d, J = 16 Hz, 1H),
7.43−7.32 (m, 4H), 6.89 (d, J = 8 Hz, 2H), 6.70 (d, J = 16 Hz, 1H),
3.82 (s, 3H), 2.42 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 161.9,
144.1, 141.7, 138.1, 130.2, 129.8, 127.5, 125.0, 124.7, 114.4, 55.4, 21.5;
HRESI-MS (m/z) calcd for C16H16O3S (M + Na) 311.0718, found (M
+ Na) 311.0717.
1
1211, 1141, 1084, 1025; H NMR (400 MHz, CDCl3) δ 7.80−7.72
(m, 3H), 7.65 (d, J = 8.4 Hz, 2H), 7.34 (d, J = 8.8 Hz, 1H), 6.93 (d, J
= 15.2 Hz, 1H), 6.50 (dd, J1 = 8.4 Hz, J2 =2 Hz, 1H), 6.44 (d, J = 2 Hz,
1H), 3.85 (s, 3H), 3.83 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
163.6, 160.5, 140.7, 139.2, 132.8, 132.4, 129.0, 127.9, 124.3, 114.2,
105.4, 98.5, 55.5, 55.4; HRESI-MS (m/z) calcd for C16H15SBrO4 (M +
Na) 404.9772, found (M + Na) 404.9775.
(E)-1-Methoxy-4-(2-(phenylsulfonyl)vinyl)benzene (3b): yellow
gummy liquid; yield 51% (34.9 mg); Rf (25% EtOAc/hexane) 0.60;
prepared as shown in the general experimental procedure; IR (KBr,
cm−1) 3056, 2932, 1601, 1513, 1306, 1259, 1144; 1H NMR (400
MHz, CDCl3) δ 7.94 (d, J = 8 Hz, 2H), 7.65−7.52 (m, 4H), 7.44 (d, J
= 8 Hz, 2H), 6.90 (d, J = 8 Hz, 2H), 6.71 (d, J = 16 Hz, 1H), 3.83 (s,
3H); 13C{1H} NMR (100 MHz, CDCl3) δ 162.0, 142.3, 141.1, 133.1,
130.4, 129.2, 127.5, 124.9, 124.4, 114.5, 55.4; HRESI-MS (m/z) calcd
for C15H14O3S (M + Na) 297.0561, found (M + Na) 297.0562.
(E)-1-Chloro-4-((4-methoxystyryl)sulfonyl)benzene (3c): white
solid; yield 44% (33.9 mg); mp 140−142 °C (lit.26 mp 144−145
°C); Rf (25% EtOAc/hexane) 0.60; prepared as shown in the general
experimental procedure; IR (KBr, cm−1) 2926, 1626, 1311, 1256,
1142; 1H NMR (400 MHz, CDCl3) δ 7.87 (d, J = 8 Hz, 2H), 7.63 (d, J
= 16 Hz, 1H), 7.51 (d, J = 8 Hz, 2H), 7.44 (d, J = 8 Hz, 2H), 6.91 (d, J
= 8 Hz, 2H), 6.68 (d, J = 16 Hz, 1H), 3.84 (s, 3H); 13C{1H} NMR
(100 MHz, CDCl3) δ 162.2, 142.9, 139.8, 139.6, 130.5, 129.5, 129.0,
124.7, 123.8, 114.5, 55.4; HRESI-MS (m/z) calcd for C15H13ClO3S
(M + Na) 331.0172, found (M + Na) 331.0173.
(E)-1-Bromo-4-((2-(4-methoxyphenyl)prop-1-en-1-yl)sulfonyl)-
benzene (3i): E/Z = 83:17; yellowish gummy liquid; yield 62% (56.9
mg); Rf (25% EtOAc/hexane) 0.60; prepared as shown in the general
experimental procedure; IR (neatr, cm−1) 3422, 2933, 1637, 1307,
1257, 1141; major isomer E: 1H NMR (400 MHz, CDCl3) δ 7.83 (d, J
= 8 Hz, 2H), 7.69 (d, J = 8 Hz, 2H), 7.37 (d, J = 8 Hz, 2H), 6.88 (d, J
= 8 Hz, 2H), 6.56 (s, 1H), 3.82 (s, 3H), 2.49 (s, 3H); 13C{1H} NMR
(100 MHz, CDCl3) δ 161.2, 153.6, 141.4, 132.4, 131.7, 128.7, 128.2,
127.8, 124.8, 114.1, 55.4, 16.9; HRESI-MS (m/z) calcd for
C16H15BrO3S (M + Na) 388.9823, found (M + Na) 388.9824.
(E)-1-Methoxy-4-(1-tosylprop-1-en-2-yl)benzene (3j): E/Z =
86:14; yellow solid; yield 49% (37.0 mg); mp 66−69 °C; Rf (25%
EtOAc/hexane) 0.50; prepared as shown in the general experimental
procedure; IR (KBr, cm−1) 3439, 2925, 1649, 1383, 1020; major
1
isomer E: H NMR (400 MHz, CDCl3) δ 7.85 (d, J = 8 Hz, 2H),
(E)-1-Bromo-4-((4-methoxystyryl)sulfonyl)benzene (3d): yellowish
solid; yield 44% (38.8 mg); mp 144−147 °C (lit.27 mp 149 °C); Rf
(25% EtOAc/hexane) 0.60; prepared as shown in the general
experimental procedure; IR (KBr, cm−1) 2935, 1602, 1514, 1310,
7.37−7.33 (m, 4H), 6.87 (d, J = 8 Hz, 2H), 6.57 (s, 1H), 3.81 (s, 3H),
2.48 (s, 3H), 2.43 (s, 3H) ; 13C{1H} NMR (100 MHz, CDCl3) δ
161.0, 152.3, 143.9, 139.5, 132.1, 129.8, 127.7, 127.2, 125.8, 114.0,
55.3, 21.6, 16.8; HRESI-MS (m/z) calcd for C17H18O3S (M + Na)
325.0874, found (M + Na) 325.0871.
1
1255, 1139; H NMR (400 MHz, CDCl3) δ 7.80 (d, J = 8 Hz, 2H),
7.67 (d, J = 8 Hz, 2H), 7.63 (d, J = 16 Hz, 1H), 7.43 (d, J = 8 Hz, 2H),
6.90 (d, J = 8 Hz, 2H), 6.68 (d, J = 16 Hz, 1H), 3.84 (s, 3H); 13C{1H}
NMR (100 MHz, CDCl3) δ 162.2, 142.9, 140.2, 132.5, 130.5, 129.1,
128.3, 124.7, 123.8, 114.5, 55.4; HRESI-MS (m/z) calcd for
C15H13BrO3S (M + Na) 374.9666, found (M + Na) 374.9666.
(E)-2,4-Dimethoxy-1-(2-(phenylsulfonyl)vinyl)benzene (3e): yel-
low gummy liquid; yield 65% (49.4 mg); Rf (25% EtOAc/hexane)
0.40; prepared as shown in the general experimental procedure; IR
(neat, cm−1) 2939, 1600, 1567, 1505, 1446, 1302, 1211, 1142, 1084,
(E)-1-(Allyloxy)-4-(2-((4-bromophenyl)sulfonyl)vinyl)benzene
(3k): white solid; yield 42% (39.8 mg); Rf (25% EtOAc/hexane) 0.40;
prepared as shown in the general experimental procedure; IR (KBr,
cm−1) 3093, 2920, 1603, 1574, 1510, 1388, 1310, 1255, 1138, 1081,
1
1010, 810; H NMR (400 MHz, CDCl3) δ 7.79 (d, J = 8.4 Hz, 2H),
7.68 (d, J = 8.8 Hz, 2H), 7.62 (d, J = 15.2 Hz, 1H), 7.42 (d, J = 8.8 Hz,
2H), 6.92 (d, J = 8.8 Hz, 2H), 6.67 (d, J = 15.2 Hz, 1H), 6.03 (m, 1H),
5.36 (dd, 2H), 4.57 (d, J = 5.2 Hz, 2H); 13C{1H} NMR (100 MHz,
CDCl3) δ 161.2, 142.8, 140.2, 132.5, 132.4, 130.4, 129.1, 128.3, 124.9,
123.9, 118.2, 115.3, 68.9; HRESI-MS (m/z) calcd for C17H15BrO3S
(M + Na) 400.9823, found (M + Na) 400.9823.
1
1026; H NMR (400 MHz, CDCl3) δ 7.94 (d, J = 7.2 Hz, 2H), 7.79
(d, J = 15.6 Hz, 1H), 7.58−7.50 (m, 3H), 7.34 (d, J = 8.4 Hz, 1H),
6.96 (d, J = 15.2 Hz, 1H), 6.49 (dd, J1 = 8.8 Hz, J2 = 2.4 Hz, 1H), 6.40
(d, J = 2 Hz, 1H), 3.85 (s, 3H), 3.83 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3) δ 163.4, 160.4, 141.6, 138.6, 132.8, 132.5, 129.1, 127.4,
124.8, 114.4, 105.3, 98.5, 55.5, 55.4; HRESI-MS (m/z) calcd for
C16H16SO4 (M + Na) 327.0667, found (M + Na) 327.0665.
(E)-1-(2-((4-Chlorophenyl)sulfonyl)vinyl)-2,4-dimethoxybenzene
(3f): yellow gummy liquid; yield 61% (51.6 mg); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure; IR (neat, cm−1) 2939, 1601, 1505, 1468, 1439, 1303,
1277, 1212, 1144, 1086, 1028; 1H NMR (400 MHz, CDCl3) δ 7.87 (d,
J = 8.4 Hz, 2H), 7.78 (d, J = 15.6 Hz, 1H), 7.48 (d, J = 8.4 Hz, 2H),
7.34 (d, J = 8.4 Hz, 1H), 6.93 (d, J = 15.2 Hz, 1H), 6.50 (dd, J1 = 8.4
Hz, J2 = 2 Hz, 1H), 6.44 (d, J = 2 Hz, 1H), 3.85 (s, 3H), 3.83 (s, 3H);
13C{1H} NMR (100 MHz, CDCl3) δ 163.6, 160.5, 140.2, 139.4, 139.2,
(E)-1-(Ellyloxy)-4-(2-((4-chlorophenyl)sulfonyl)vinyl)benzene (3l):
white solid; yield 33% (27.6 mg); mp 132−136 °C; Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure; IR (KBr, cm−1) 3094, 2923, 1603, 1583, 1509, 1395,
1
1311, 1255, 1142, 1087, 1014, 811; H NMR (400 MHz, CDCl3) δ
7.87 (d, J = 8.8 Hz, 2H), 7.62 (d, J = 15.2 Hz, 1H), 7.50 (d, J = 8.8 Hz,
2H), 7.43 (d, J = 8.8 Hz, 2H), 6.91 (d, J = 8.8 Hz, 2H), 6.68 (d, J =
15.2 Hz, 1H), 6.07−5.98 (m, 1H), 5.36 (dd, 2H), 4.57 (d, J = 5.2 Hz,
2H); 13C{1H} NMR (100 MHz, CDCl3) δ 161.2, 142.8, 139.8, 139.7,
132.5, 130.4, 129.6, 129.0, 124.9, 124.0, 118.2, 115.3, 68.9; HRESI-MS
(m/z) calcd for C17H15BrO3S (M + Na) 400.9823, found (M + Na)
400.9823.
(E)-1-(Benzyloxy)-4-(2-tosylvinyl)benzene (3m): yellow solid; yield
45% (41.0 mg); mp 156−161 °C; Rf (25% EtOAc/hexane) 0.60;
prepared as shown in the general experimental procedure; IR (KBr,
132.8, 129.4, 128.9, 124.4, 114.3, 105.4, 98.5, 55.5, 55.4; HRESI-MS
(m/z) calcd for C16H15SClO4 (M + Na): 361.0277, found (M + Na)
361.0277.
1
cm−1) 3445, 1606, 1256, 1175, 1141, 1084; H NMR (400 MHz,
CDCl3) δ 7.81 (d, J = 7.2 Hz, 2H), 7.60 (d, J = 15.2 Hz, 1H), 7.40−
7.31 (m, 9H), 6.96 (d, J = 7.6 Hz, 2H), 6.79 (d, J = 15.2 Hz, 1H), 5.09
(s, 2H), 2.42 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 161.1,
144.1, 141.6, 138.1, 136.2, 130.3, 129.9, 128.6, 128.2, 127.5, 127.4,
125.2, 124.9, 115.3, 70.1, 21.6; HRESI-MS (m/z) calcd for C22H20O3S
(M + Na) 387.1031, found (M + Na) 387.1032.
(E)-2,4-Dimethoxy-1-(2-tosylvinyl)benzene (3g): yellow gummy
liquid; yield 73% (58.1 mg) and 54% (42.9 mg); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure. IR (neat, cm−1) 2918, 1601, 1575, 1457, 1303, 1275,
1211, 1159, 1141; H NMR (400 MHz, CDCl3) δ 7.81 (d, J = 8 Hz,
2H), 7.77 (d, J = 15.2 Hz, 1H), 7.34−7.30 (m, 3H), 6.94 (d, J = 15.6
1
F
dx.doi.org/10.1021/jo501314y | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(E)-1-(Benzyloxy)-4-(2-((4-chlorophenyl)sulfonyl)vinyl)benzene
(3n): white solid; yield 49% (47.1 mg); mp 132−135 °C; Rf (15%
EtOAc/hexane) 0.35; prepared as shown in the general experimental
15.2 Hz, 1H), 6.01 (s, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ
150.5, 148.5, 142.8, 139.9, 139.5, 129.6, 129.0, 126.4, 125.5, 124.4,
108.7, 106.8, 101.8; HRESI-MS (m/z) calcd for C15H11ClO4S(M +
Na) 344.9964, found (M + Na) 344.9964.
1
procedure; IR (KBr, cm−1) 3438, 2920, 1625, 1261, 1140; H NMR
(400 MHz, CDCl3) δ 7.86 (d, J = 8 Hz, 2H), 7.62 (d, J = 16 Hz, 1H),
7.56−7.33 (m, 9H), 6.97 (d, J = 8 Hz, 2H), 6.67 (d, J = 16 Hz, 1H),
5.10 (s, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ 161.3, 142.8, 139.8,
139.7, 136.1, 130.5, 129.6, 129.0, 128.7, 128.2, 127.4, 125.0, 124.1,
115.4, 70.1; HRESI-MS (m/z) calcd for C21H17ClO3S(M + Na)
407.0485, found (M + Na) 407.0488.
(E)-1-(Benzyloxy)-4-(2-((4-bromophenyl)sulfonyl)vinyl)benzene
(3o): yellow solid; yield 48% (51.5 mg); mp 129−133 °C; Rf (15%
EtOAc/hexane) 0.40; Prepared as shown in the general experimental
procedure. IR (KBr, cm−1) 3448, 2921, 1602, 1314, 1261, 1143, 1086,
1013; 1H NMR (400 MHz, CDCl3) δ 7.82−7.38 (m, 12H), 6.97 (d, J
= 8.8 Hz, 2H), 6.67 (d, J = 15.6 Hz, 1H), 5.10 (s, 2H); 13C{1H} NMR
(100 MHz, CDCl3) δ 161.3, 142.8, 140.2, 136.1, 132.7, 132.6, 130.5,
129.1, 128.7, 128.2, 127.4, 125.0, 124.0, 115.4, 70.1; HRESI-MS (m/z)
calcd for C21H17BrO3S (M + Na) 450.9979, found (M + Na)
450.9977.
(E)-2-(2-((4-Chlorophenyl)sulfonyl)vinyl)thiophene (3u): yellow
gummy solid; yield 33% (23.4 mg); Rf (25% EtOAc/hexane) 0.70;
prepared as shown in the general experimental procedure. IR (KBr,
1
cm−1) 3421, 2918, 1601, 1317, 1143, 1010, 960, 816; H NMR (400
MHz, CDCl3) δ 7.81−7.77 (m, 3H), 7.69 (d, J = 8.8 Hz, 2H), 7.46 (d,
J = 4.8 Hz, 1H), 7.32 (d, J = 4.8 Hz, 1H), 7.08 (t, J = 4 Hz, 1H), 6.61
(d, J = 15.2 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 139.9,
136.8, 135.7, 132.7, 132.6, 130.3, 129.1, 128.6, 128.4, 124.9; HRESI-
MS (m/z) calcd for C12H9ClO2S2 (M + Na) 306.9630, found (M +
Na) 306.9626.
(E)-2-(2-Tosylvinyl)thiophene (3v): yellow solid; yield 31% (20.4
mg); mp 121−124 °C; Rf (15% EtOAc/hexane) 0.45; prepared as
shown in the general experimental procedure. IR (KBr, cm−1) 3454,
2922, 1605, 1303, 1142, 1085, 960, 814; 1H NMR (400 MHz, CDCl3)
δ 7.81 (d, J = 8 Hz, 2H), 7.77 (d, J = 16 Hz, 1H), 7.43 (d, J = 4 Hz,
1H), 7.34 (d, J = 8 Hz, 2H), 7.30 (d, J = 4 Hz, 1H), 7.06 (t, J = 4 Hz,
1H), 6.63 (d, J = 16 Hz, 1H), 2.44 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3) δ 144.3, 137.8, 137.0, 134.6, 132.3, 130.0, 129.8, 128.3, 127.6,
125.8, 21.6; HRESI-MS (m/z) calcd for C13H12O2S2 (M + Na)
287.0176, found (M + Na) 287.0174.
(E)-1-(Benzyloxy)-4-(2-(phenylsulfonyl)vinyl)benzene (3p): white
solid; yield 36% (31.5 mg); Rf (15% EtOAc/hexane) 0.40; prepared as
shown in the general experimental procedure; IR (KBr, cm−1) 3449,
1
2925, 2854, 1601, 1306, 1254, 1145, 1083, 1010, 974; H NMR (400
MHz, CDCl3) δ 7.94 (d, J = 7.2 Hz, 2H), 7.61−7.35 (m, 11H), 6.97
(d, J = 8 Hz, 2H), 6.71 (d, J = 15.6 Hz, 1H), 5.09 (s, 2H); 13C{1H}
NMR (100 MHz, CDCl3) δ 161.2, 142.2, 141.8, 136.1, 133.2, 130.4,
129.2, 128.7, 128.2, 127.5, 127.4, 125.2, 124.5, 115.4, 70.1; HRESI-MS
(m/z) calcd for C21H18O3S (M + Na) 373.0874, found (M + Na)
373.0874.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C spectra and spectral data . This material is available
free of charge via the Internet. http://pubs.acs.org
(E)-4-(2-((4-Chlorophenyl)sulfonyl)vinyl)-1,2-dimethoxybenzene
(3q): yellowish gummy liquid; yield 54% (45.7 mg); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure; IR (neat, cm−1) 3853, 3743, 3617, 1699, 1684, 1524,
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: prabhu@orgchem.iisc.ernet.in. Tel: +91-80-22932887.
Fax: +91-80-23600529.
1
1270, 1144, 1019; H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 8 Hz,
2H), 7.62 (d, J = 16 Hz, 1H), 7.51 (d, J = 8 Hz, 2H), 7.09 (d, J = 8 Hz,
1H), 6.97 (s, 1H), 6.87 (d, J = 8 Hz, 1H), 6.70 (d, J = 16 Hz, 1H),
3.91 (s, 3H), 3.88 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 152.0,
149.3, 143.1, 139.8, 139.6, 129.6, 129.0, 125.0, 124.1, 123.6, 111.0,
109.9, 56.0, 55.9; HRESI-MS (m/z) calcd for C16H15ClO4S (M + Na)
361.0277, found (M + Na) 361.0277.
(E)-4-(2-((4-Bromophenyl)sulfonyl)vinyl)-1,2-dimethoxybenzene
(3r): yellowish gummy liquid; yield 52% (49.8 mg); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure. IR (neat, cm−1) 3853, 3744, 3617, 2934, 1699, 1521,
1270, 1141, 1022, 1010; 1H NMR (400 MHz, CDCl3) δ 7.80 (d, J = 8
Hz, 2H), 7.68 (d, J = 8 Hz, 2H), 7.62 (d, J = 16 Hz, 1H), 7.10 (d, J = 8
Hz, 1H), 6.97 (s, 1H), 6.87 (d, J = 8 Hz, 1H), 6.70 (d, J = 16 Hz, 1H),
3.91 (s, 3H), 3.89 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 152.0,
149.3, 143.1, 140.1, 132.5, 129.1, 128.4, 125.0, 124.0, 123.6, 111.0,
109.9, 56.0, 55.9; HRESI-MS (m/z) calcd for C16H15BrO4S (M + Na)
404.9772, found (M + Na) 404.9772.
(E)-1,2-Dimethoxy-4-(2-tosylvinyl)benzene (3s): yellow solid; yield
34% (27.0 mg); mp 125−127 °C (lit.28 mp 126−127 °C); Rf (25%
EtOAc/hexane) 0.30; prepared as shown in the general experimental
procedure; IR (KBr, cm−1) 3853, 3742, 3392, 2925, 1590, 1540, 1516,
1508, 1269, 1142, 1085, 1021; 1H NMR (400 MHz, CDCl3) δ 7.83 (d,
J = 8 Hz, 2H), 7.60 (d, J = 16 Hz, 1H), 7.34 (d, J = 8 Hz, 2H), 7.09 (d,
J = 8 Hz, 1H), 6.97 (s, 1H), 6.87 (d, J = 8 Hz, 1H), 6.72 (d, J = 16 Hz,
1H), 3.91 (s, 3H), 3.88 (s, 3H), 2.43 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3) δ 151.7, 149.2, 144.1, 142.0, 138.1, 129.1, 127.5, 125.2,
125.0, 123.3, 111.0, 109.9, 56.0, 55.9, 21.5; HRESI-MS (m/z) calcd for
C17H18O4S(M + Na) 341.0824, found (M + Na) 341.0824.
(E)-5-(2-((4-Chlorophenyl)sulfonyl)vinyl)benzo[d][1,3]dioxole
(3t): yellow gummy solid; yield 52% (41.9 mg); Rf (25% EtOAc/
hexane) 0.40; prepared as shown in the general experimental
procedure. IR (KBr, cm−1) 3393, 1684, 1522, 1257, 1146, 1086,
1037; 1H NMR (400 MHz, CDCl3) δ 7.86 (d, J = 8 Hz, 2H), 7.58 (d, J
= 15.2 Hz, 1H), 7.51 (d, J = 8 Hz, 2H), 7.00 (dd, J1 = 1.2 Hz, J2 = 8
Hz, 1H), 6.94 (d, J = 1.2 Hz, 1H), 6.82 (d, J = 8 Hz, 1H), 6.64 (d, J =
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank IISc, CSIR (01(2415)/10/EMR-II), and RL Fine
Chem for financial support and Dr. Ramesha A. R. (RL Fine
Chem) for useful discussions. B.R. thanks CSIR for a
fellowship.
DEDICATION
■
This paper is dedicated to Professor H. Ila, JNCASR,
Bangalore, on the occasion of her 70th birthday.
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dx.doi.org/10.1021/jo501314y | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
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(16) The decarboxylative sulfonylation was successful with 1a and 2a
in the absence of ligands (entry 19, Table 1). However, this
observation could not be generalized, as many of the reactions in
Table 2 gave low yields in the absence of ligand (1,10-Phen).
Therefore, 1,10-Phen was used in all subsequent experiments.
(17) (a) In most of the examples (Table 2), the reaction did not go
to completion. As a result, we observed that the acid precursors were
present even after an extended reaction time. Interestingly, scale-up
experiments resulted in the formation of product (3g) in better yield
(Scheme 3). (b) Free hydroxy group is known to quench the radical
H
dx.doi.org/10.1021/jo501314y | J. Org. Chem. XXXX, XXX, XXX−XXX