Palladium-Catalyzed Decarboxylative Coupling Reactions of Propiolic Acid Derivatives and Arylsulfonyl Hydrazide

Article abstract of DOI:10.1055/s-0036-1591596

Arylsulfonyl hydrazides were employed as coupling partners for the decarboxylative coupling reaction of propiolic acid derivatives. When the reaction was conducted using Pd(TFA) ₂ (1.0 mol%), dppp (1.0 mol%), and Cu(OAc) ₂ (2.4 equiv

Full text of DOI:10.1055/s-0036-1591596

SYNTHESIS
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©
Georg Thieme Verlag Stuttgart · New York
2018, 50, A–H
special topic
A
en
Synthesis
J. Park et al.
Special Topic
Palladium-Catalyzed Decarboxylative Coupling Reactions of
Propiolic Acid Derivatives and Arylsulfonyl Hydrazide
Jaerim Parka
Kwang Ho Song*b
Sunwoo Lee*a
1 mol% Pd(TFA)2
mol% dppp
O
1
R
H NHNO S
2
2
Ar
R
Ar
+
OH
Cu(OAc)2 (2.4 equiv)
DMF
100 °C, 0.5 h
2
5 examples
a
R = aryl, alkyl
Department of Chemistry, Chonnam National University,
Gwangju 61186, Republic of Korea
sunwoo@chonnam.ac.kr
up to 95% yield
b
Department of Chemical & Biological Engineering, Korea
University, Seoul 02841, Republic of Korea
khsong@korea.ac.kr
Published as part of the Special Topic Modern Coupling
Approaches and their Strategic Applications in Synthesis
5
Received: 07.05.2018
Accepted after revision: 29.05.2018
Published online: 16.07.2018
agricultural, pharmaceutical, and materials sciences. In ad-
dition, a variety of coupling partners have been developed.
Recently, Dong and Zhou’s group employed arylsulfonyl
hydrazides in palladium-catalyzed coupling reactions with
DOI: 10.1055/s-0036-1591596; Art ID: ss-2018-c0313-st
Abstract Arylsulfonyl hydrazides were employed as coupling partners
for the decarboxylative coupling reaction of propiolic acid derivatives.
When the reaction was conducted using Pd(TFA) (1.0 mol%), dppp (1.0
terminal alkynes for the synthesis of arylalkyne derivatives
Scheme 1, a). They demonstrated that the Sonogashira-
6
(
2
type coupling reaction with arylsulfonyl hydrazide is acid-
and base-free and shows good tolerance toward the bro-
mide group. However, this reaction requires a high palladi-
um catalyst loading.
mol%), and Cu(OAc)2 (2.4 equiv) in DMF at 100 °C for 0.5 hour, the de-
sired coupled products were formed in moderate to good yields. The
reaction showed good tolerance toward functional groups such as es-
ter, ketone, cyano, nitro, chloro, and bromo groups.
Keywords decarboxylative coupling, propiolic acid, arylsulfonyl hy-
drazide, palladium, arylalkyne
a)
5
mol% Pd
R
R
H
H NHNO S Ar
R
Ar
+
2
2
O
Palladium-catalyzed cross-coupling reactions are
among the most straightforward tools for the construction
of carbon–carbon or carbon–heteroatom bonds. Palladium
b)
cat. metal
+
X
Ar
R
Ar
OH
1
X = I, Br, Cl,
OTf, OTs
metal = Pd, Ni,
Cu, Ag
is known to activate a nucleophile or/and an electrophile to
be coupled with both of them. Among the wide variety of
coupling partners that can serve as an electrophile, organic
halides such as iodides, bromides, and chlorides are the
most frequently employed. These electrophiles are activat-
ed by palladium to produce the corresponding organopalla-
dium complex, which can further react with a nucleophile.
This is an oxidative step and is generally known to be a
O
c)
cat. Pd or Ni
R
+
Y
Ar
R
R
Ar
Ar
OH
Y = B, Si
This work
O
1
mol% Pd
R
+
H NHNO S Ar
2
2
OH
2
rate-determining step. As an alternative method, oxidative
Scheme 1 Synthesis of arylalkynes using coupling reactions
coupling has been developed, in which the coupling partner
is substituted with a palladium ligand to provide the or-
ganopalladium complex. A number of coupling partners
Decarboxylative coupling of alkynoic acids has received
much attention as an alternative tool for the synthesis of
3
have been developed in this type of reactions.
7
Sonogashira coupling, an important cross-coupling re-
action carried out using a palladium catalyst, is a very use-
arylalkynes. The use of an arylalkynoic acid has several ad-
8
vantages such as simple preparation and easy handling.
2
4
ful tool for constructing sp-carbon and sp -carbon bonds.
Since our first report in this regard, a variety of coupling
partners, including aryl halides, have been developed for
the decarboxylative coupling of alkynoic acids (Scheme 1,
Terminal alkynes have been coupled with aryl halides to
provide arylalkynes, which are important building blocks in
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

B
Synthesis
J. Park et al.
Special Topic
9
b). Recently, we developed oxidative decarboxylative cou-
pling reactions using arylboronic acid and arylsiloxane
(
came interested in using arylsulfonyl hydrazides as cou-
pling partners. Herein we report the decarboxylative cou-
pling reaction of propiolic acid derivatives with arylsulfonyl
hydrazides in the presence of a palladium catalyst.
10
Scheme 1, c).
As part of our continuous efforts to develop decarboxyl-
ative coupling reactions with arylalkynoic acids, we be-
Table 1 Optimization of Decarboxylative Coupling Reaction with 1a and 2aa
1
mol% Pd
O
H2NHNO2S
1 mol% ligand
Ph
Me
Ph
+
oxidant (2.4 equiv)
solvent
OH
Me
100 °C, 0.5 h
1a
2a
3a
Entry
Pd (mol %)
Ligand (mol%)
Oxidant
Solvent
3a
Yield (%)b
1c
2
3
4
5
6
7
8
9
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
dppp
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
·H
·H
·H
·H
·H
·H
·H
·H
·H
·H
·H
·H
O
O
O
O
O
O
O
O
O
O
O
O
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMSO
diglyme
toluene
DMF
DMF
68
65
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
dppp
dppbz
dppf
61
58
Xantphos
1,10-Phen
dppp
59
42
Pd(dba)
PdCl
2
74
2
dppp
72
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
Pd(TFA)
2
dppp
90
10
11
12
13
14
15
16
17
18
19
20
21
2
2d
2
3e
2
2
2
2
2
2
2
2
2
2
2
2
2
2
dppbz
dppf
83
72
Xantphos
dppp
87
Cu(acac)
2
trace
5
dppp
Cu(OTf)
CuO
2
dppp
19
dppp
CuS
11
dppp
CuBr
CuCl
2
trace
trace
38
dppp
2
dppp
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
Cu(OAc)
2
2
2
2
2
·H
·H
·H
·H
·H
2
2
2
2
2
O
O
O
O
O
dppp
12
dppp
14
dppp
70
dppp
40
Structures of the ligands:
Me
Me
PPh2
PPh2 PPh2
dppp
Fe
O
Ph2P
dppbz
PPh2
PPh2
N
N
PPh2
PPh2
dppf
Xantphos
1,10-Phen
a
Reaction conditions: 1a (0.33 mmol), 2a (0.3 mmol), Pd (0.003 mmol), ligand (0.003 mmol), and oxidant (0.72 mmol) were allowed to react in a solvent (1.0
mL) at 100 °C for 0.5 h.
b
Yield was determined by gas chromatography with an internal standard.
Pd(OAc) (0.015 mmol) and dppp (0.015 mmol) were used.
2
Reaction temperature: 80 °C; time: 2 h.
Reaction temperature: 50 °C; time: 6 h.
c
d
e
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

C
Synthesis
J. Park et al.
Special Topic
First, phenylpropiolic acid (1a) and p-tolylsulfonyl hy-
drazide (2a) were chosen as standard substrates for the
coupling reaction and allowed to react under various condi-
tions. Under the optimized conditions reported for the cou-
pling of terminal alkynes, the desired product 3a was
formed in 68% yield. Surprisingly, the product yield was
of oxidants were tested instead of Cu(OAc) , but they did
2
not give satisfactory results (entries 13–18). The reaction
gave much lower yields when carried out in solvents such
as DMSO, diglyme, and toluene as compared to that in DMF
(entries 19–21). Decreasing the reaction temperature to 80
°C and 50 °C lowered the product yield to 70% and 40%, re-
spectively (entries 22 and 23).
6
(
5% when 1.0 mol% of palladium and the ligand was used
Table 1, entry 2). Among the tested ligands, 1,3-bis(di-
phenylphosphino)propane (dppp) gave the highest yield
entries 2–6). Then, using dppp as the ligand, we tested dif-
ferent palladium sources such as PdCl , Pd(TFA) , and
The optimized conditions were as follows: arylpropiolic
acid (1.1 equiv), arylsulfonyl hydrazide (1.0 equiv), Pd(TFA)2
(1.0 mol%), dppp (1.0 mol%), and Cu(OAc) ·H O (2.4 equiv)
(
2
2
were allowed to react in DMF at 100 °C for 0.5 hour. To eval-
uate the reaction efficiency under these optimized condi-
tions, a variety of substituted arylpropiolic acids were al-
lowed to react with phenylsulfonyl hydrazide. As shown in
Scheme 2, phenylpropiolic acid reacted with phenylsulfonyl
hydrazide to give the desired product 3b in 81% yield. Al-
kyl-substituted arylpropiolic acids afforded the coupled
2
2
Pd(dba) (entries 7–9), and found that the combination of
2
Pd(TFA) and dppp provided the highest yield of 90% (entry
2
9
). The combination of Pd(TFA) and other ligands such as
2
dppbz, dppf, and Xantphos afforded the desired product in
good yields, although the yields were lower than those ob-
tained with Pd(TFA) and dppp (entries 10–12). A number
2
1
mol% Pd(TFA)2
mol% dppp
1
O
R
Ar
+
H2NHNO2S
Ar
R
Cu(OAc)2 (2.4 equiv)
DMF
OH
2
3
1
100 °C, 0.5 h
Me
Me
Me
Me
3
e (86%)
3
b (81%)
3c (66%)
OMe
3d (85%)
O
O
Br
O
MeO
3
f (61%)
3g (62%)
3i (82%)
3h (71%)
Cl
F
F3C
MeO
3
j (72%)
3l (57%)
3p (99%)
3m (66%)
3
k (63%)
O
Ph
NC
Me
3n (84%)
3o (84%)
3q (84%)
Me
Me
n-Pent
Me
Me
n-Pr
3r (66%)
3s (85%)
3t (76%)
3u (95%)
Br
OMe
MeO
Me
F
Me
Br
Cl
3v (71%)
3x (90%)
3y (77%)
3w (73%)
Scheme 2 Synthesis of arylalkynes. Reagents and conditions: 1 (3.3 mmol), 2 (3.0 mmol), Pd(TFA) (0.03 mmol), dppb (0.03 mmol), and Cu(OAc) (7.2
2
2
mmol) were allowed to react in DMF (10 mL) at 100 °C for 0.5 h.
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

D
Synthesis
J. Park et al.
Special Topic
O
H
OH
(
1.0 equiv)
2 mol% Pd(TFA)2
mol% dppp
2
Me
Me
+
Cu(OAc)2 (4.0 equiv)
DMF
H2NHNO2S
100 °C, 2.0 h
4a
Me
20%
2a
(
2.2 equiv)
Scheme 3 Synthesis of symmetrical diarylalkyne
products 3c, 3d, and 3e in 66%, 85%, and 86% yield, respec-
tively. Alkoxide-substituted arylpropiolic acids provided
the desired products 3f, 3g, and 3h in 61%, 62%, and 71%
yield, respectively. Bromo-, chloro-, fluoro-, and trifluoro-
methyl-substituted arylpropiolic acids furnished 3i, 3j, 3k,
and 3l in good yields. Arylpropiolic acids bearing ester, ke-
tone, and cyano groups on the phenyl ring coupled with
phenylsulfonyl hydrazide to give the corresponding prod-
ucts 3m, 3n, and 3o in good yields. 3-(Naphthalen-1-yl)-
and 3-[(1,1′-biphenyl)-4-yl]propiolic acids showed good
yields in the formation of 3p and 3q. Alkyl-substituted
propiolic acids such as hexynoic and octynoic acids provid-
ed 3r and 3s in 66% and 85% yield, respectively.
Table 2 Role of Palladium and Coppera
O
Ph
OH
1a
conditions
+
Ph
Me
DMF
H NHNO S
2
2
100 °C, 0.5 h
3
a
Me
2a
Entry
Pd(TFA)
2
dppp
Cu(OAc)
2
·H
2
O
3a
Yield (%)b
1
2
3
4
5
–
–
–
–
0
0
Next, we investigated the use of substituted arylsulfonyl
hydrazides in the decarboxylative coupling reactions. p-
Tolylsulfonyl hydrazide coupled with substituted arylpropi-
olic acids to give the desired products in good yields. When
1.0 mol%
–
1.0 mol%
–
2.4 equiv
2.4 equiv
0.6 equiv
1.2 equiv
0
–
1.0 mol%
1.0 mol%
1.0 mol%
0
3-(4-bromophenyl)propiolic acid was allowed to react with
1.0 mol%
1.0 mol%
5
substituted arylsulfonyl hydrazide, the desired products 3x,
and 3y were formed in good yields. These bromo-substitut-
ed products could be employed as starting materials for
further coupling reactions.
6
10
a
Reaction conditions: 1a (0.3 mmol) and 2a (0.3 mmol) were reacted at
00 °C for 0.5 h under the described conditions.
Yield was determined by gas chromatography with an internal standard.
1
b
We then attempted to apply this reaction system for the
synthesis of symmetrical diarylalkyne. When p-tolysulfonyl
hydrazide (2.2 equiv) and propiolic acid (1.0 equiv) were al-
lowed to react under the modified optimal conditions, sym-
metrical diarylalkyne 4a was formed in 20% yield, as shown
in Scheme 3.
Based on a previous report and the experimental results
in the present study, we propose a plausible mechanism for
this coupling reaction, as shown in Scheme 4. Arylpalladi-
um(II) complex A may be formed via the reaction pathway
proposed by Dong and Zhou’s group. The arylpropiolic acid
reacts with Cu(OAc)2 to give alkynylcopper complex B
through decarboxylation. Complex B reacts with the aryl-
palladium complex to provide arylalkynylpalladium com-
plex C via transmetalation, which undergoes reductive
elimination to afford the desired coupling product. Finally,
To study the role of palladium, ligand, and Cu(OAc) in
2
this coupling reaction, the reaction was conducted in the
absence of one of these entities. As shown in Table 2, the
desired product was not formed in any of the reactions (Ta-
ble 2, entries 1–4). These results supported that both palla-
dium and copper are important in this coupling reaction
and that copper acts as both the oxidant and the coupling
reagent. When using 0.6 equivalent and 1.2 equivalents of
Pd(0) is oxidized by Cu(OAc) to give the Pd(II) active cata-
2
lytic species.
In summary, we have developed decarboxylative cou-
pling reactions of propiolic acid derivatives with arylsulfo-
nyl hydrazide using a palladium catalyst. We found that
Cu(OAc) , the desired product was formed in 5% and 10%
2
yield, respectively (entries 5 and 6). It was found that 2.4
equivalents of Cu(OAc) was required to obtain the desired
Cu(OAc) played the role of a an oxidant and a coupling re-
2
2
product in good yields.
agent. As opposed to previous methods in which a terminal
alkyne was used as a coupling partner, the present method
using propiolic acid derivatives required only 1 mol%
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

E
Synthesis
J. Park et al.
Special Topic
1
,2-Diphenylethyne (3b)10c
Ar SO2NHNH2
3-Phenylpropiolic acid (1a; 482.3 mg, 3.3 mmol) and benzenesulfonyl
hydrazide (2b; 516.6 mg, 3.0 mmol) afforded 3b (433.1 mg, 2.43
mmol, 81%); white solid; mp 59–61 °C.
Pd(TFA)2
Cu(OAc)2
Pd(0)
1
H NMR (500 MHz, CDCl ): δ = 7.55–7.53 (m, 4 H), 7.37–7.33 (m, 6 H).
3
13
C NMR (126 MHz, CDCl ): δ = 131.6, 128.3, 128.2, 123.2, 89.3.
3
Pd
Ar
TFA
MS (EI): m/z = 178 (M+).
A
O
R
1
-Methyl-2-(phenylethynyl)benzene (3c)9d
HO
Cu(OAc)2
3-(o-Tolyl)propiolic acid (1b; 528.6 mg, 3.3 mmol) and 2b (516.6 mg,
Ar
R
R
3
.0 mmol) afforded 3c (380.7 mg, 1.98 mmol, 66%); colorless oil.
Pd
Ar
1
H NMR (500 MHz, CDCl ): δ = 7.55–7.52 (m, 2 H), 7.50 (d, J = 7.2 Hz, 1
C
Cu
R
3
H), 7.36–7.31 (m, 3 H), 7.23–7.22 (m, 2 H), 7.18–7.15 (m, 1 H), 2.52 (s,
B
3
H).
Scheme 4 Proposed mechanism
13
C NMR (126 MHz, CDCl ): δ = 140.2, 131.9, 131.5, 129.5, 128.4,
3
128.2, 125.6, 123.6, 123.0, 93.4, 88.4, 20.8.
MS (EI): m/z = 192 (M+).
Pd(TFA) and gave good yields in most cases. This method-
2
1-Methyl-3-(phenylethynyl)benzene (3d)10c
ology showed good tolerance toward functional groups
such as ester, ketone, cyano, nitro, bromo, and chloro
groups. In addition, the reaction with propiolic acid afford-
ed a symmetrical diarylalkyne.
3-(m-Tolyl)propiolic acid (1c; 528.6 mg, 3.3 mmol) and 2b (516.6 mg,
3
.0 mmol) afforded 3d (490.3 mg, 2.55 mmol, 85%); colorless oil.
1H NMR (500 MHz, CDCl
): δ = 7.53–7.51 (m, 2 H), 7.34–7.32 (m, 5 H),
.23 (t, J = 7.6 Hz, 1 H), 7.14 (d, J = 7.6 Hz, 1 H), 2.35 (s, 3 H).
13C NMR (126 MHz, CDCl
): δ = 138.0, 132.2, 131.6, 129.2, 128.7,
28.4, 128.3, 128.2, 123.4, 123.1, 89.6, 89.1, 21.3
MS (EI): m/z = 192 (M+).
3
7
General Information
3
1
All reagents and solvents were purchased and used without further
purification. Analytical thin layer chromatography (TLC) was per-
formed on Merck pre-coated silica gel 60 F254 plates. The TLC plates
were visualized by shortwave (254 nm) or long-wave (360 nm) UV
light. Flash chromatography on silica gel (230–400 mesh) was per-
,4-Dimethyl-1-(phenylethynyl)benzene (3e)10c
2
3-(2,4-Dimethylphenyl)propiolic acid (1d; 574.9 mg, 3.3 mmol) and
1
13
formed. H NMR (500 MHz) and C NMR (126 MHz) was recorded in
2b (516.6 mg, 3.0 mmol) afforded 3e (532.2 mg, 2.58 mmol, 86%);
CDCl on VARIAN VnmrJ.
3
pale yellow oil.
1
H NMR (500 MHz, CDCl ): δ = 7.53–7.51 (m, 2 H), 7.39 (d, J = 7.8 Hz, 1
3
Decarboxylative Coupling Reaction of Propiolic Acid Derivatives
and Arylsulfonyl Hydrazide; General Procedure
H), 7.35–7.30 (m, 3 H), 7.04 (s, 1 H), 6.97 (d, J = 7.8 Hz, 1 H), 2.48 (s, 3
H), 2.32 (s, 3 H).
A 5 mL vial equipped with a magnetic stir bar was charged with aryl-
sulfonyl hydrazide 2 (3.0 mmol, 1.0 equiv), arylpropiolic acid 1 (3.3
mmol, 1.1 equiv), Pd(TFA)2 (10.5 mg, 0.03 mmol, 1 mol%), dppp (12
mg, 0.03 mmol, 1 mol%), Cu(OAC) ·H O (1437.5 mg, 7.2 mmol, 2.4
13
C NMR (126 MHz, CDCl ): δ = 140.0, 138.4, 131.8, 131.5, 130.4,
3
128.4, 128.0, 126.4, 123.8, 120.0, 92.7, 88.6, 21.5, 20.7.
MS (EI): m/z = 206 (M+).
2
2
equiv), and DMF (10 mL). The reaction mixture was heated at 100 °C
for 0.5 h, then cooled to r.t., and quenched with H O. The crude prod-
1-Methoxy-4-(phenylethynyl)benzene (3f)10c
2
uct was extracted with EtOAc, and the combined organic layers were
3-(4-Methoxyphenyl)propiolic acid (1e; 581.4 mg, 3.3 mmol) and 2b
dried (anhyd MgSO ), and concentrated under vacuum. The desired
4
(516.6 mg, 3.0 mmol) afforded 3f (381.1 mg, 1.83 mmol, 61%); light
product was isolated by silica gel column chromatography using hex-
ane/EtOAc as the eluent.
yellow solid; mp 151–153 °C.
1
H NMR (500 MHz, CDCl ): δ = 7.51 (dt, J = 8.3, 2.2 Hz, 2 H), 7.49–7.46
3
(
1
m, 2 H), 7.35–7.30 (m, 3 H), 6.89–6.86 (m, 2 H), 3.82 (s, 3 H).
1
-Methyl-4-(phenylethynyl)benzene (3a)9d
3
C NMR (126 MHz, CDCl ): δ = 159.6, 133.1, 131.5, 128.3, 127.9,
3
3-Phenylpropiolic acid (1a; 482.3 mg, 3.3 mmol) and 4-methylben-
1
23.6, 115.4, 114.0, 89.4, 88.1, 55.3.
zenesulfonyl hydrazide (2a; 558.7 mg, 3.0 mmol) afforded 3a (519.1
mg, 2.7 mmol, 90%); white solid; mp 54–56 °C.
MS (EI): m/z = 208 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.53–7.51 (m, 2 H), 7.44–7.42 (m, 2 H),
3
1
-Methoxy-2-(phenylethynyl)benzene (3g)10c
3-(2-Methoxyphenyl)propiolic acid (1f; 581.4 mg, 3.3 mmol) and 2b
516.6 mg, 3.0 mmol) afforded 3g (387.4 mg, 1.86 mmol, 62%); pale
7
.36–7.31 (m, 3 H), 7.17–7.15 (m, 3 H), 2.37 (s, 3 H).
13
C NMR (126 MHz, CDCl ): δ = 138.4, 131.5, 131.5, 129.1, 128.3,
3
(
128.1, 123.5, 120.2, 89.5, 88.7, 21.5.
yellow oil.
MS (EI): m/z = 192 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.57–7.55 (m, 2 H), 7.50 (dd, J = 7.6, 1.7
3
Hz, 1 H), 7.35–7.28 (m, 4 H), 6.93 (t, J = 7.5 Hz, 1 H), 6.89 (d, J = 8.4 Hz,
1
H), 3.90 (s, 3 H).
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

F
Synthesis
J. Park et al.
Special Topic
13
Methyl 4-(Phenylethynyl)benzoate (3m)10c
C NMR (126 MHz, CDCl ): δ = 159.9, 133.6, 131.7, 129.8, 128.3,
3
1
28.1, 123.6, 120.5, 112.4, 110.7, 93.5, 85.8, 55.9.
3
-[4-(Methoxycarbonyl)phenyl]propiolic acid (1l; 673.8 mg, 3.3
MS (EI): m/z = 208 (M+).
mmol) and 2b (516.6 mg, 3.0 mmol) afforded 3m (467.8 mg, 1.98
mmol, 66%); light yellow solid; mp 121–122 °C.
-(Phenylethynyl)benzo[d][1,3]dioxole (3h)10c
1
H NMR (500 MHz, CDCl ): δ = 8.02 (d, J = 8.2 Hz, 2 H), 7.59 (d, J = 8.7
5
3
Hz, 2 H), 7.56–7.54 (m, 2 H), 7.38–7.36 (m, 3 H), 3.93 (s, 3 H).
3
-(Benzo[d][1,3]dioxol-5-yl)propiolic acid (1g; 627.5 mg, 3.3 mmol)
13
and 2b (516.6 mg, 3.0 mmol) afforded 3h (473.4 mg, 2.13 mmol,
C NMR (126 MHz, CDCl ): δ = 166.6, 131.7, 131.5, 129.5, 129.4,
3
71%); white solid; mp 105–108 °C.
128.8, 128.4, 128.0, 122.7, 92.3, 88.7, 52.3.
1
MS (EI): m/z = 236 (M+).
H NMR (500 MHz, CDCl ): δ = 7.52–7.50 (m, 2 H), 7.34–7.33 (m, 3 H),
3
7.07 (dd, J = 8.0, 1.6 Hz, 1 H), 6.99–6.98 (m, 1 H), 6.80–6.79 (m, 1 H),
6
.00 (s, 2 H).
-[4-(Phenylethynyl)phenyl]ethanone (3n)10b
1
13
C NMR (126 MHz, CDCl ): δ = 147.9, 147.4, 131.5, 128.3, 128.1,
3
3-(4-Acetylphenyl)propiolic acid (1m; 620.1 mg, 3.3 mmol) and 2b
516.6 mg, 3.0 mmol) afforded 3n (555.1 mg, 2.52 mmol, 84%); light
yellow solid; mp 124–125 °C.
126.3, 123.3, 116.5, 111.5, 108.5, 101.3, 89.3, 87.8.
(
MS (EI): m/z = 222 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.94 (d, J = 8.7 Hz, 2 H), 7.61 (d, J = 8.7
3
1
-Bromo-4-(phenylethynyl)benzene (3i)11
Hz, 2 H), 7.56–7.54 (m, 2 H), 7.38–7.36 (m, 3 H), 2.62 (s, 3 H).
13
3-(4-Bromophenyl)propiolic acid (1h; 742.6 mg, 3.3 mmol) and 2b
C NMR (126 MHz, CDCl ): δ = 197.4, 136.2, 131.7, 131.7, 128.8,
3
(516.6 mg, 3.0 mmol) afforded 3i (632.5 mg, 2.46 mmol, 82%); white
128.5, 128.3, 128.2, 122.6, 92.7, 88.6, 26.7.
solid; mp 82–83 °C.
MS (EI): m/z = 220 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.53–7.51 (m, 2 H), 7.49–7.47 (m, 2 H),
3
7
.40–7.38 (m, 2 H), 7.37–7.34 (m, 2 H).
-(Phenylethynyl)benzonitrile (3o)10c
4
13
C NMR (126 MHz, CDCl ): δ = 133.8, 133.0, 131.8, 131.6, 131.6,
3
3-(4-Cyanophenyl)propiolic acid (1n; 564.8 mg, 3.3 mmol) and 2b
516.6 mg, 3.0 mmol) afforded 3o (512.2 mg, 2.52 mmol, 84%); light
yellow solid; mp 109–111 °C.
128.5, 128.4, 122.9, 122.4, 122.2, 90.5, 88.3.
(
MS (EI): m/z = 256 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.65–7.60 (m, 4 H), 7.56–7.54 (m, 2 H),
3
1
-Chloro-2-(phenylethynyl)benzene (3j)12
7.39–7.38 (m, 3 H).
13
3-(4-Bromophenyl)propiolic acid (1i; 596.0 mg, 3.3 mmol) and 2b
C NMR (126 MHz, CDCl ): δ = 132.0, 132.0, 131.8, 129.1, 129.0,
3
(516.6 mg, 3.0 mmol) afforded 3j (459.4 mg, 2.16 mmol, 72%); color-
128.2, 122.2, 118.6, 111.5, 93.8, 87.7, 30.0.
less oil.
MS (EI): m/z = 203 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.55–7.53 (m, 3 H), 7.42 (dt, J = 7.2, 1.5
3
Hz, 1 H), 7.38–7.36 (m, 3 H), 7.32–7.29 (m, 2 H).
-(Phenylethynyl)naphthalene (3p)10c
1
13
C NMR (126 MHz, CDCl ): δ = 134.2, 132.5, 131.7, 131.4, 129.7,
3
3-(Naphthalen-1-yl)propiolic acid (1o; 647.5 mg, 3.3 mmol) and 2b
516.6 mg, 3.0 mmol) afforded 3p (678.0 mg, 2.97 mmol, 99%); pale
yellow oil.
129.6, 128.6, 128.5, 128.4, 128.4, 128.4, 125.0, 122.7, 90.5, 87.9.
(
MS (EI): m/z = 212 (M+).
1
H NMR (500 MHz, CDCl ): δ = 8.46–8.44 (m, 1 H), 7.84–7.79 (m, 2 H),
3
1
-Fluoro-4-(phenylethynyl)benzene (3k)10c
7.76–7.74 (m, 1 H), 7.65–7.63 (m, 2 H), 7.60–7.56 (m, 1 H), 7.52–7.49
(
1
m, 1 H), 7.44–7.41 (m, 1 H), 7.38–7.32 (m, 3 H).
3
-(4-Fluorophenyl)propiolic acid (1j; 541.6 mg, 3.3 mmol) and 2b
3
(516.6 mg, 3.0 mmol) afforded 3k (370.9 mg, 1.89 mmol, 63%); off-
C NMR (126 MHz, CDCl ): δ = 133.3, 133.2, 131.8, 130.5, 128.9,
3
white solid; mp 91–94 °C.
128.5, 128.5, 128.4, 126.9, 126.5, 125.4, 123.5, 121.0, 94.4, 87.6.
1
MS (EI): m/z = 228 (M+).
H NMR (500 MHz, CDCl ): δ = 7.53–7.50 (m, 4 H), 7.36–7.33 (m, 3 H),
3
7.07–7.02 (m, 2 H).
13
4-(Phenylethynyl)-1,1′-biphenyl (3q)13
C NMR (126 MHz, CDCl ): δ = 162.5 (d, J = 250 Hz), 133.5 (d, JC,F
=
3
C,F
8
.5 Hz), 131.5, 128.4, 128.3, 123.1, 119.4 (d, JC,F = 3.5 Hz), 115.6 (d,
3-([1,1′-Biphenyl]-4-yl)propiolic acid (1p; 733.4 mg, 3.3 mmol) and
2b (516.6 mg, 3.0 mmol) afforded 3q (641.0 mg, 2.52 mmol, 84%);
white solid; mp 156–158 °C.
JC,F = 22.1 Hz), 89.0, 88.3.
MS (EI): m/z = 196 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.64–7.56 (m, 8 H), 7.47 (t, J = 7.6 Hz, 2
3
1
-(Phenylethynyl)-4-(trifluoromethyl)benzene (3l)10c
H), 7.40–7.35 (m, 4 H).
13
3-[4-(Trifluoromethyl)phenyl]propiolic acid (1k; 707.7 mg, 3.3
C NMR (126 MHz, CDCl ): δ = 141.0, 140.3, 132.0, 131.6, 128.9,
3
mmol) and 2b (516.6 mg, 3.0 mmol) afforded 3l (421.1 mg, 1.71
128.4, 128.3, 127.6, 127.0 (2C), 123.3, 122.2, 90.1, 89.3.
mmol, 57%); white solid; mp 87–88 °C.
MS (EI): m/z = 254 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.62 (q, J = 8.5 Hz, 4 H), 7.56–7.54 (m, 2
3
H), 7.39–7.36 (m, 3 H).
Pent-1-yn-1-ylbenzene (3r)14
13
C NMR (126 MHz, CDCl ): δ = 132.5, 131.8, 131.7, 129.9 (q, J = 33.4
3
C,F
Hex-2-ynoic acid (1q; 370.0 mg, 3.3 mmol) and 2b (516.6 mg, 3.0
mmol) afforded 3r (285.5 mg, 1.98 mmol, 66%); pale yellow oil.
Hz), 128.8, 128.2, 126.0 (q, JC,F = 266.9 Hz), 125.3 (q, JC,F = 3.8 Hz),
122.5, 91.7, 88.0.
1
H NMR (500 MHz, CDCl ): δ = 7.40–7.38 (m, 2 H), 7.27–7.21 (m, 3 H),
3
MS (EI): m/z = 246 (M+).
2.37 (t, J = 7.1 Hz, 2 H), 1.65–1.58 (m, 2 H), 1.04 (t, J = 7.4 Hz, 3 H).
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

G
Synthesis
J. Park et al.
Special Topic
13
MS (EI): m/z = 210 (M+).
C NMR (126 MHz, CDCl ): δ = 131.5, 128.1, 127.4, 124.0, 90.2, 80.7,
3
22.2, 21.3, 13.5.
MS (EI): m/z = 144 (M+).
1-Bromo-4-[(4-methoxyphenyl)ethynyl]benzene (3x)13
-(4-Bromophenyl)propiolic acid (1h; 742.6 mg, 3.3 mmol) and 4-
3
Hept-1-yn-1-ylbenzene (3s)15
methoxybenzenesulfonyl hydrazide (2d; 606.7 mg, 3.0 mmol) afford-
ed 3x (775.3 mg, 2.70 mmol, 90%); white solid; mp 153–155 °C.
Oct-2-ynoic acid (1r; 462.6 mg, 3.3 mmol) and 2b (516.6 mg, 3.0
mmol) afforded 3s (439.3 mg, 2.55 mmol, 85%); colorless oil.
1
H NMR (500 MHz, CDCl ): δ = 7.47–7.45 (m, 4 H), 7.36 (d, J = 8.7 Hz, 2
3
1
H), 6.87 (d, J = 8.9 Hz, 2 H), 3.82 (s, 3 H).
H NMR (500 MHz, CDCl ): δ = 7.40–7.38 (m, 2 H), 7.29–7.25 (m, 3 H),
.40 (t, J = 7.2 Hz, 2 H), 1.66–1.56 (m, 2 H), 1.47–1.40 (m, 1 H), 1.39–
.33 (m, 2 H), 0.92 (t, J = 7.2 Hz, 3 H).
3
13
2
1
C NMR (126 MHz, CDCl ): δ = 159.7, 133.0, 132.8, 131.5, 122.5,
3
122.0, 115.0, 114.0, 90.5, 87.0, 55.3.
13
MS (EI): m/z = 286 (M+).
C NMR (126 MHz, CDCl ): δ = 131.5, 128.2, 127.5, 124.1, 90.5, 80.5,
3
31.2, 28.5, 22.2, 19.4, 14.0.
MS (EI): m/z = 172 (M+).
1-Bromo-4-[(4-chlorophenyl)ethynyl]benzene (3y)6
3
-(4-Bromophenyl)propiolic acid (1h; 742.6 mg, 3.3 mmol) and 4-
1
-Methyl-2-(p-tolylethynyl)benzene (3t)6
chlorobenzenesulfonyl hydrazide (2e; 620.0 mg, 3.0 mmol) afforded
3
y (673.5 mg, 2.31 mmol, 77%); white solid; mp 176–179 °C.
3-(o-Tolyl)propiolic acid (1b; 528.6 mg, 3.3 mmol) and 4-methylben-
1
zenesulfonyl hydrazide (2c; 558.7 mg, 3.0 mmol) afforded 3t (470.3
H NMR (500 MHz, CDCl ): δ = 7.49 (d, J = 8.6 Hz, 2 H), 7.45 (d, J = 8.7
3
mg, 2.28 mmol, 76%); white solid; mp 47–49 °C.
Hz, 2 H), 7.38 (d, J = 8.6 Hz, 2 H), 7.33 (d, J = 8.7 Hz, 2 H).
1
13
H NMR (500 MHz, CDCl ): δ = 7.54 (d, J = 7.4 Hz, 1 H), 7.49–7.48 (m, 2
C NMR (126 MHz, CDCl ): δ = 134.5. 133.0. 132.8. 131.7. 128.8.
3
3
H), 7.27–7.26 (m, 2 H), 7.21–7.19 (m, 3 H), 2.56 (s, 3 H), 2.41 (s, 3 H).
122.7. 121.9. 121.4. 89.3. 89.2.
13
MS (EI): m/z = 290 (M+).
C NMR (126 MHz, CDCl ): δ = 140.1, 138.1, 131.8, 131.4, 129.5,
3
129.2, 128.2, 125.6, 123.2, 120.5, 93.6, 87.7, 21.6, 20.1.
MS (EI): m/z = 206 (M+).
1,2-Di-(p-tolyl)ethyne (4a)9c
A 5 mL vial equipped with a magnetic stir bar was charged with 4-
methylbenzenesulfonyl hydrazide (2a; 1.352 g, 7.26 mmol), propiolic
1
-Methyl-3-(p-tolylethynyl)benzene (3u)6
acid (231.6 mg, 3.3 mmol), Pd(TFA) (21.9 mg, 0.066 mmol, 2 mol%),
3
3
7
1
-(m-Tolyl)propiolic acid (1c; 528.6 mg, 3.3 mmol) and 2c (558.7 mg,
.0 mmol) afforded 3u (587.9 mg, 2.85 mmol, 95%); white solid; mp
1–72 °C.
2
dppp (27.2 mg, 0.066 mmol, 2 mol%), Cu(OAc) ·H O (2635.4 mg, 13.2
2
2
mmol, 4.0 equiv), and DMF (10 mL). The reaction mixture was heated
at 100 °C for 2 h, then cooled to r.t., and quenched with H O. The
2
H NMR (500 MHz, CDCl ): δ = 7.44 (d, J = 7.9 Hz, 2 H), 7.38–7.34 (m, 2
3
crude product was extracted with EtOAc, and the combined organic
H), 7.25 (t, J = 7.6 Hz, 1 H), 7.18–7.14 (m, 3 H), 2.39 (s, 3 H), 2.37 (s, 3
H).
layers were dried (anhyd MgSO ) and concentrated under vacuum.
4
The desired product 4a (136.1 mg, 0.66 mmol, 20%) was isolated by
silica gel column chromatography using hexane/EtOAc as the eluent;
13
C NMR (126 MHz, CDCl ): δ = 138.3, 138.0, 132.1, 131.5, 129.1,
3
129.0, 128.6, 128.2, 123.2, 120.3, 89.2, 88.9, 21.5, 21.3.
white solid; mp 139–140 °C.
MS (EI): m/z = 206 (M+).
1
H NMR (500 MHz, CDCl ): δ = 7.42–7.40 (m, 4 H), 7.13 (dd, J = 8.14,
3
0
13
.6 Hz, 4 H), 2.34 (s, 6 H).
1
-Methoxy-4-(p-tolylethynyl)benzene (3v)10c
C NMR (126 MHz, CDCl ): δ = 138.1, 131.4, 129.0, 120.3, 88.8, 21.5.
3
3
-(4-Methoxyphenyl)propiolic acid (1e; 581.4 mg, 3.3 mmol) and 2c
MS (EI): m/z = 206 (M+).
(558.7 mg, 3.0 mmol) afforded 3v (473.5 mg, 2.13 mmol, 71%); light
yellow solid; mp 126–128 °C.
1
H NMR (500 MHz, CDCl ): δ = 7.46 (d, J = 8.9 Hz, 2 H), 7.40 (d, J = 8.0
3
Funding Information
Hz, 2 H), 7.14 (dd, J = 7.9, 0.6 Hz, 2 H), 6.87 (d, J = 8.9 Hz, 2 H), 3.82 (s,
3
H), 2.36 (s, 3 H).
This research was supported by the National Research Foundation of
Korea (NRF) grant funded by the Korean government (MSIP) (NRF-
13
C NMR (126 MHz, CDCl ): δ = 159.4, 138.0, 133.0, 131.3, 129.0,
3
2015R1A4A1041036, NRF-2017R1A2B2002929).
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9)
120.4 116.0, 114.0, 86.6, 88.2, 55.3, 21.5.
MS (EI): m/z = 222 (M+).
Acknowledgment
1
-Fluoro-4-(p-tolylethynyl)benzene (3w)6
The spectral data were obtained from Korea Basic Science Institute,
Gwangju Branch.
3
-(4-Fluorophenyl)propiolic acid (1j; 541.6 mg, 3.3 mmol) and 2c
(558.7 mg, 3.0 mmol) afforded 3w (460.4 mg, 2.19 mmol, 73%); white
solid; mp 90–91 °C.
1
H NMR (500 MHz, CDCl ): δ = 7.49–7.46 (m, 2 H), 7.40 (d, J = 8.1 Hz, 2
3
Supporting Information
H), 7.12 (dd, J = 8.4, 0.6 Hz, 2 H), 7.00 (t, J = 8.8 Hz, 2 H), 2.33 (s, 3 H).
13
C NMR (126 MHz, CDCl ): δ = 162.4 (d, J = 249.8 Hz), 138.5, 133.4
Supporting information for this article is available online at
3
C,F
(
d, JC,F = 8.8 Hz), 131.5, 129.2, 120.0, 119.6 (d, JC,F = 3.8 Hz), 115.6 (d,
https://doi.org/10.1055/s-0036-1591596.
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JC,F = 21.4 Hz), 89.3, 87.7.
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H

H
Synthesis
J. Park et al.
Special Topic
References
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2018, 50, A–H