Synthesis of Terminal Allenes via a Copper-Catalyzed Decarboxylative Coupling Reaction of Alkynyl Carboxylic Acids

Article abstract of DOI:10.1021/acs.joc.5b02361

Synthesis of terminal allenes via a copper-catalyzed decarboxylative coupling reaction was developed. Aryl alkynyl carboxylic acid, paraformaldehyde, and dicyclohexylamine were reacted with CuI (20 mol %) in diglyme at 100°C for 2 h to produce the terminal allene in moderate to good yields. The method showed good functional group tolerance.

Full text of DOI:10.1021/acs.joc.5b02361

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Note
Synthesis of Terminal Allenes via a Copper-Catalyzed
Decarboxylative Coupling Reaction of Alkynyl Carboxylic Acids
Jeongah Lim, Jinseop Choi, Han-Sung Kim, In Seon Kim, Kye Chun Nam, Jimin Kim, and Sunwoo Lee
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b02361 • Publication Date (Web): 30 Nov 2015
Downloaded from http://pubs.acs.org on December 1, 2015
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Synthesis of Terminal Allenes via a Copperꢀ
Catalyzed Decarboxylative Coupling Reaction of
Alkynyl Carboxylic Acids
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Jeongah Lim,† Jinseop Choi,† Han-Sung Kim,† In Seon Kim,‡ Kye Chun Nam,†
Jimin Kim,†* Sunwoo Lee†*
†Department of Chemistry, Chonnam National University, Gwangju, 61186, Republic of
Korea
‡Department of Agricultural Chemistry, College of Agriculture and Life Sciences, Chonnam
National University, Gwangju, 61186, Republic of Korea
Corresponding Author: J. Kim (jiminkim@chonnam.ac.kr), S. Lee (sunwoo@chonnam.ac.kr)
Keywords: allene, copper, propargyl amine, decarboxylative coupling, propiolic acids
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Abstract
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Synthesis of terminal allenes via a copperꢀcatalyzed decarboxylative coupling reaction was
developed. Aryl alkynyl carboxylic acid, paraformaldehyde, and dicyclohexylamine were
reacted with CuI (20 mol%) in diglyme at 100 °C for 2 h to produce the terminal allene in
moderate to good yields. The method showed good functional group tolerance.
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Allene is one of the most versatile compounds and intermediates in organic synthesis because
it has high reactivity and a unique structural feature in which one carbon atom has two double
bonds.1 Allene structures are also found in nature, as shown in Figure 1.2
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Figure 1. Natural compounds bearing an allene group.
In addition, an allene can be converted to many useful building blocks for the synthesis of
pharmaceutical compounds.3 A number of synthetic methods have been developed.4 Both
classic and recently developed methods are shown in Scheme 1. Tang and Zhou reported that
the ironꢀcatalyzed reaction of an αꢀdiazoester and a ketene afforded the allene in the presence
of PPh3 under neutral conditions (Scheme 1a).5 Also, the reaction of an aldehyde with an
activated vinyl halide in the presence of BuLi to afford the corresponding allene has been
reported (Scheme 1b).6 Copperꢀmediated SN2′ꢀsubstitution of propargyl electrophile has been
developed (Scheme 1c).7 Buchwald reported the palladiumꢀcatalyzed coupling of a terminal
alkyne and benzyl chloride to afford the allene in good yield (Scheme 1d).8 In the presence of
a copper or zinc catalyst, the terminal alkyne was reacted with a diazoester or an Nꢀ
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tosylhydrazone to form 1,3ꢀdisubstituted allene (Scheme 1e).9 In 1979, Crabbé reported that
the coupling of a terminal alkyne and paraformaldehyde in the presence of a copper catalyst
and a secondary amine afforded the terminal allene(Scheme 1f).10. This process was named
the Crabbé homologation reaction, has been regarded as a useful synthetic tool along a Cu(I)
catalyzed SN2’ substitution of propargylic electrophiles with Grignard reagents in the
construction of allenyl functionalities. Also, this reaction method has been employed for the
synthesis of chiral allenes.11
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A variety of transition metalꢀcatalyzed decarboxylative coupling reaction of propiolic
acids have been developed since our first report in 2008.12 Recently, we reported that
propargyl amine can be obtained from the coupling of propiolic acid derivatives,
paraformaldehyde, and amines under metalꢀfree conditions.13 Moreover, the employment of a
copper catalyst enabled the application of this methodology to the synthesis of propargyl
amines via coupling with aryl or alkyl aldehydes.14 During this study, we found that the
allene was formed as a sideꢀproduct in some cases. This result inspired us to develop a
synthetic method for the allene via decarboxylative coupling of propiolic acids, because aryl
propiolic acid derivatives are readily prepared from the coupling reaction of aryl halides and
propiolic acid.15 Herein, we report a copperꢀcatalyzed decarboxylative coupling reaction for
the synthesis of terminal allenes (Scheme 1g).
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EtO2C
R
R'
R'
cat. Fe
PPh3
EtO2C
R
(a)
(b)
+
O
N2
R"
R"
7
8
9
X
Y
R
R
R"
H
R"
n-BuLi
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+
O
R'
R'
H
X = I, Y = POPh2
X = SiMe2, Y = Br
R
cat. Cu
cat. Pd
(c)
(d)
R'MgBr
+
R
R
R'
MsO
R
H
+
+
Cl
Ar
Ar
R'
cat. Cu or Zn
Z
(e)
R
H
R'
R
R"
Z = N2, NNTs
R"
H
cat. Cu
R'2NH
(f)
O
H
R
R
H
+
This work
H
cat. Cu
R'2NH
R
CO2H
+
O
H
(g)
R
Scheme 1. Synthesis of allenes.
We chose phenyl propiolic acid as a standard substrate to optimize the reaction, and allowed
it to react with paraformaldehyde and cyclohexylamine under a variety of conditions. The
results are summarized in Table 1. First, we investigated the ratio of substrates. Increasing the
amount of paraformaldehyde and cyclohexylamine increases the yield of the allene. However,
the yield of the undesired homocoupled product remains unchanged. We found that a 1 to
paraformaldehyde to dicyclohexylamine ratio of 1:3:3 is optimal (entry 3). Employing this
ratio, the source of copper catalyst was investigated. CuBr decreases the yield of sideꢀproduct;
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however, the yield of 2a is lower than that obtained with CuI (entry 4). Unfortunately, other
copper catalysts such as Cu2O, Cu(OAc)2, and Cu(OTf)2 afford the homocoupled species as
the major product (entries 5ꢀ7). Instead of toluene, different solvents were investigated.
Xylene affords 3a in 30% yield (entry 8). However, DMSO and DMF give poor yields
(entries 9 and 10). Reaction under monoglyme and diglyme affords 2a in 57% and 77%
yields, respectively (entries 11 and 12). The formation of the sideꢀproduct is especially low in
diglyme. Temperatures higher or lower than 100 °C do not give satisfactory results (entries 13
and 14). The employment of diisopropyl amine, which is most commonly used amine in the
Crabbé reaction, affords 3a in 45% yield (entry 15). Decreasing the amount of CuI to 5 mol%
decreased the yield of 3a to 32% (entry 16). When 20 mol% CuI is employed, 2a is formed in
82% yield (entry 17). Consequently, the following are the optimized conditions: aryl alkynyl
carboxylic acid (1.0 equiv), paraformaldehyde (3.0 equiv), and dicyclohexylamine (3.0 equiv)
reacted with CuI (20 mol%) in diglyme at 100 °C for 2 h.
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Table 1. Optimization of the synthesis of a terminal allene via a copperꢀcatalyzed
decarboxylative threeꢀcomponent reaction.a
Cy
Cy
cat. Cu
Ph
O
Ph
CO2H
+
+
HN
+
Ph
Ph
H
H
solvent
Temp, 2 h
2a
3a
1a
Entry
Ratiob
Cu/(mol%)
Solvent
Temperature Yield (%)c
(°C)
2a (3a)
1
2
3
4
5
6
7
8
1/1.2/1.2
1/1.5/1.5
1/3/3
1/3/3
1/3/3
1/3/3
1/3/3
1/3/3
1/3/3
CuI (10)
CuI (10)
CuI (10)
CuBr (10)
Cu2O (10)
Cu(OAc)2 (10)
Cu(OTf)2 (10)
CuI (10)
toluene
toluene
toluene
toluene
toluene
toluene
toluene
xylene
DMSO
DMF
100
100
100
100
100
100
100
80
27 (42)
33 (39)
40 (41)
32 (12)
5 (90)
9 (63)
15 (65)
30 (51)
9 (3)
9
10
11
CuI (10)
CuI (10)
CuI (10)
100
100
100
1/3/3
1/3/3
9 (5)
57 (12)
monoglyme
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15d
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1/3/3
1/3/3
1/3/3
1/3/3
1/3/3
1/3/3
CuI (10)
CuI (10)
CuI (10)
CuI (10)
CuI (5)
diglyme
diglyme
diglyme
diglyme
diglyme
diglyme
100
130
80
100
100
100
77 (6)
25 (2)
45 (36)
45 (25)
32 (14)
82 (5)
CuI (20)
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aReaction conditions: 1a (0.3 mmol), paraformaldehyde (0.36, 0.45, 0.9 mmol),
dicyclohexylamine (0.36, 0.45, 0.9 mmol), and Cu (0.015, 0.03, 0.06 mmol) were reacted for
b
c
2 h. Ratio of 1a/paraformaldehyde/dicyclohexylamine. Yield obtained from GC analysis
with standard substrate. dInstead of dicyclohexylamine, diisopropylamine was used.
To demonstrate the general applicability of this method for the synthesis of terminal allenes,
various substituted aryl alkynyl carboxylic acids were investigated (Table 2). As expected,
phenyl propiolic acid is smoothly converted into propaꢀ1,2ꢀdienylbenzene (1a) in 82% yield
(entry 1).16 Methyl or ethylꢀsubstituted phenyl propiolic acids 1b, 1c, and 1d afford
corresponding terminal allenes in 77%, 65%, and 75% yields, respectively (entries 2ꢀ4). 2ꢀ
Methoxyꢀ and 3,4,5ꢀtrimethoxyꢀsubstituted phenyl propiolic acids are transformed to the
corresponding allenes 2e and 2f in 62% and 87% yields, respectively (entries 5 and 6). Aryl
alkynyl carboxylic acids bearing a ketone, an ester, or a cyano group show moderate yields
(entries 7ꢀ9). 2ꢀNaphthyl and 4ꢀbiphenyl propiolic acids afford corresponding allenes 2j and
2k in 62% and 84% yields, respectively (entries 10 and 11). 4ꢀFluoro and 4ꢀchloro phenyl
propiolic acids also give desired products 2l and 2m, respectively (entries 12 and 13). 4ꢀ
(Trimethylsilyl)phenyl propiolic acid (1n) shows 51% yield of product (entry 14). Vinyl
substituted phenyl and thiophenyl propiolic acid give the corresponding product 2o and 2p,
with 32% and 31% yields, respectively (entries 15 and 16). However, the alkyl substituted
propiolic acid such as 2ꢀoctynoic acid does not give the desired allene (entry 17).
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Table 2. Synthesis of terminal allenes from aryl alkynyl carboxylic acids.
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9
Cy
Cy
Ar
20 mol% CuI
O
Ar
CO2H
+
+
HN
H
H
diglyme
100 oC, 2 h
2
1
10
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12
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Entry
1
1 (Ar = )
Product
Yield (%)
82
1a
1b
2a
2b
2
3
4
5
77
65
75
62
1c
1d
1e
2c
2d
2e
MeO
MeO
6
87
1f
2f
MeO
O
7
8
53
59
1g
1h
2g
2h
Me
9
62
84
1i
1j
2i
2j
10
11
12
13
65
72
79
52
1k
1l
2k
2l
1m
1n
2m
2n
14
15
32
31
1o
1p
2o
2p
16
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0
1q
2q
aReaction conditions: 1 (3.0 mmol), (H2CO)n (9.0 mmol), Cy2NH (9.0 mmol), and CuI (0.06
mmol) were reacted in diglyme at 100 °C for 2 h.
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To investigate the reaction pathway, we monitored a reaction mixture of phenyl propiolic acid,
paraformaldehyde, and dicyclohexylamine in the presence of CuI by gas chromatography
using an internal standard. As shown in Figure 2, the terminal allene and threeꢀcomponent
coupled propargyl amine are found in the reaction mixture. As the reaction proceeded, the
yield of the allene increases. Propargyl amine 4a (NꢀcyclohexylꢀNꢀ(3ꢀphenylpropꢀ2ꢀ
ynyl)cyclohexanamine) is found in 24% yield at 30 min. The amount of propargyl amine
slowly decreases proportionally as the amount of allene increases. We found that 3a is formed
in 81% yield in 30 min at 130 °C and slowly decomposes with time.
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100o-2a
100
130o-2a
90
100o-4a
130o-4a
80
70
60
50
40
30
20
10
0
0
50
100
150
200
250
time (minute)
Figure 2. Reaction profile for the formation of terminal allene 2a and intermediate 4a.
It has been reported that the threeꢀcomponent reaction of aryl alkynyl carboxyl acid,
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paraformaldehyde, and a secondary amine produced the corresponding propargyl amine via a
copperꢀfree decarboxylative coupling reaction. However, when the standard reaction is
carried out in the absence of copper catalyst, neither propargyl amine nor allene is formed. In
addition, it was found that propargyl amine is not converted to the allene in the absence of a
copper catalyst. From these results, we infer that propargyl amine is an intermediate and is
formed by the copper catalyst, and that the allene is also formed by the copper catalyst and is
unstable over 130 °C. We propose the reaction pathway shown in Scheme 2. Aryl alkynyl
carboxylic acid reacts with CuI to afford copper alkynide A. This copper complex reacts with
imine intermediate B, which was formed by the reaction between paraformaldehyde and
dicyclohexylamine, to form propargyl amine 4. Propargyl amine is activated by the copper
catalyst to give allene 2.
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Cy
O
HN
+
H
H
Ar
Cu
Cy
A
CO2
H
H
Cy
Cy
Cy
N
Ar
CO2H
B
1
CuI
N Cy
Ar
Ar
4
2
I
H
Cu
N Cy
I
N Cy
Ar
Ar
H
Cu
Scheme 2. Proposed reaction pathway.
In summary, we have developed a synthesis of terminal allenes via decarboxylative coupling
with aryl alkynyl carboxylic acid, paraformaldehyde, and dicyclohexylamine in the presence
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of a copper catalyst. The optimized conditions converted the alkynyl carboxylic acid to the
terminal allene in moderate to good yields. These reactions were completed in 2 h, and
exhibited good functional group tolerance. We found that copper was vital for the formation
of both propargylamine and terminal allene.
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Experimental
All commercially available reagents were used without further purification unless otherwise
stated. Thin layer chromatography was conducted on silica gel. Column chromatography was
1
performed with silica gel (60ꢀ120 mesh). NMR spectra were recorded on a H NMR (300,
500 MHz) and 13C NMR (75, 126 MHz) spectra were recorded in DMSOꢀd6 or CDCl3.
Chemical shifts are reported in ppm. Coupling constants (J values) are reported in Hertz.
General procedure for the preparation of aryl alkynyl carboxylic acids
Propiolic acid (3.6 mmol, 252 mg) was diluted with DMSO (3.0 mL). The solution was
added to a mixture of Pd(PPh3)4 (0.25 mmol, 288.9 mg), aryl bromide (5.0 mmol), DBU
(11.0 mmol, 1.67 g), and DMSO (7.0 mL) in a small roundꢀbottom flask. The resulting
mixture was stirred at 35 or 25 °C for 24 h, poured into ethyl acetate (25.0 mL), and extracted
with saturated aqueous NaHCO3 solution. The aqueous layer was separated, acidified to pH
2.0 by adding cold HCl (1 M), and extracted with CH2Cl2. The combined organic layers were
dried with MgSO4, filtered, and the solvent was removed under reduced pressure.
3-(4-Vinylphenyl)propiolic acid (1o)
1ꢀBromoꢀ4ꢀvinylbenzene (915 mg, 5.0 mmol) provided 1o (251 mg, 1.15 mmol, 32% yield,
colorless oil ); 1H NMR (500 MHz, DMSO) δ 7.64–7.53 (m, 4H), 6.79 (dd, J = 17.7, 11.0 Hz,
1H), 5.97 (dd, J = 17.7, 0.8 Hz, 1H), 5.41 (dd, J = 10.9, 0.7 Hz, 1H); 13C NMR (126 MHz,
DMSO) δ 154.7, 139.9, 136.1, 133.4, 127.1, 118.5, 117.5, 84.9, 82.7; HRMS (ESI, TOF)
calcd. for C11H9O2 [M+H]+ 173.0603 found, 173.0601.
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General methods for the synthesis of allenes from aryl propiolic acids and aryl
aldehydes with amines
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Aryl alkynyl carboxylic acids (3.0 mmol), paraformaldehydes (9.0 mmol), dicyclohexylamines
(9.0 mmol), CuI (0.06 mmol, 114 mg) and diglyme (10 mL) was charged in a 20 mL reaction vial.
The mixture was stirred at 100 °C for 2 h. The reaction mixture was poured into water and
extracted with Et2O (3 × 20 mL). The combined extracts were dried over MgSO4, and passed
through a filter paper. The solvent was removed under vacuum, and the resulting crude
product was purified by flash chromatography on silica gel. The product was eluted with
pentane or Et2O
.
Propa-1,2-dienylbenzene (2a)17
Phenyl propiolic acid (438 mg, 3.0 mmol) was reacted with dicyclohexylamine (1.63 g, 9.0
mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2a) (290 mg, 2.5 mmol, 82% yield,
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colorless oil); H NMR (300 MHz, CDCl3) δ 7.29–7.28 (d, J = 4.5 Hz, 4H), 7.19 (m, 1H),
6.15 (t, J = 6.8 Hz, 1H), 5.12 (d, J = 6.9 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3) δ 209.7,
133.9, 128.6, 126.8, 126.6, 93.9, 78.7; EIMS (70 eV) m/z M+ 116.
1-Methyl-4-(propa-1,2-dienyl)benzene(2b)17
3ꢀpꢀTolylpropiolic acid (481 mg, 3.0 mmol) was reacted with dicyclohexylamine (1.63 g, 9.0
mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2b) (301 mg, 2.31 mmol) 77%
yield, colorless oil); 1H NMR (600 MHz, CDCl3) δ 7.19 (d, J = 7.8 Hz, 2H), 7.11 (d, J = 7.8
Hz, 2H), 6.13 (t, J = 6.6 Hz, 1H), 5.12 (d, J = 7.2 Hz, 2H), 2.32 (s, 3H); 13C{1H} NMR (75
MHz, CDCl3) δ 209.5, 136.6, 130.8, 129.3, 126.5, 93.7, 78.7, 21.2; EIMS (70 eV) m/z M+
130.
2,4-Dimethyl-1-(propa-1,2-dienyl)benzene(2c)
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dicyclohexylamine (1.63 g, 9.0 mmol) and paraformaldehyde 270 mg, 9.0 mmol) to give (2c)
( 281 mg, 1.95 mmol, 65% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.27 (d, J =
8.4 Hz, 1H), 6.98–6.96 (m, 2H), 6.31 (t, J = 6.9 Hz, 1H), 5.09 (d, J = 6.9 Hz, 2H), 2.31 (s,
3H), 2.29 (s, 3H); 13C{1H} NMR (75 MHz, CDCl3) δ 210.2, 136.5, 134.7, 131.2, 129.0, 127.1,
126.9, 91.0, 77.9, 21.0, 19.7; HRMS (ESI, TOF) calcd. for C11H13 [M+H]+ 145.1017, found
145.1017 HRMS (ESI, TOF) calcd. for C11H13 [M+H]+ 145.1017, found 145.1015.
1-Ethyl-4-(propa-1,2-dienyl)benzene(2d)
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3ꢀ(4ꢀEthylphenyl)propiolic acid (523 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2d) (324.5 mg, 2.25
mmol 75% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.22 (m, 2H), 7.13 (m, 2H),
6.14 (t, J = 6.9 Hz, 1H), 5.12 (d, J = 6.9 Hz, 2H), 2.62 (q, J = 7.5 Hz, 2H), 1.22 (t, J = 7.5 Hz,
3H); 13C{1H} NMR (75 MHz, CDCl3) δ 209.6, 143.1, 131.1, 128.1, 126.6, 93.7, 78.6, 28.6,
15.6; HRMS (ESI, TOF) calcd. for C11H13 [M+H]+ 145.1017, found 145.1016.
1-Methoxy-2-(propa-1,2-dienyl)benzene(2e)17
3ꢀ(2ꢀMethoxyphenyl)propiolic acid (529 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2e) (272 mg, 1.86
mmol, 62% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.41 (dd, J = 7.8, 1.5 Hz, 1H),
7.19 (td, J = 7.8, 1.5 Hz, 1H), 6.93 (td, J = 7.5, 0.8 Hz, 1H), 6.87 (d, J = 8.4 Hz, 1H), 6.59 (t,
J = 6.9 Hz, 1H), 5.12 (d, J = 6.9 Hz, 2H), 3.85 (s, 3H); 13C{1H} NMR (75 MHz, CDCl3) δ
210.1, 155.8, 127.9, 127.7, 122.3, 120.7, 110.9, 87.8, 78.0, 55.5; EIMS (70 eV) m/z M+ 146.
1,2,3-Trimethoxy-5-(propa-1,2-dienyl)benzene(2f)18
3ꢀ(3,4,5ꢀTrimethoxyphenyl)propiolic acid (709.7 mg, 3.0 mmol) was reacted with
dicyclohexylamine (1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2f)
(538.3 mg, 2.61 mmol, 87% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 6.52 (s, 2H),
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6.09 (t, J = 6.8 Hz, 1H), 5.16 (d, J = 6.6 Hz, 2H), 3.86 (s, 6H), 3.83 (s, 3H); 13C{1H} NMR
(75 MHz, CDCl3) δ 209.5, 153.4, 137.0, 129.4, 103.6, 94.1, 79.2, 60.9, 56.0; EIMS (70 eV)
m/z M+ 206.
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1-(4-(Propa-1,2-dienyl)phenyl)ethanone(2g)19
3ꢀ(4ꢀAcetylphenyl)propiolic acid (564.5 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2g) (252 mg, 1.6
mmol, 53% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.90 (d, J = 8.5 Hz, 2H), 7.37
(d, J = 8.3 Hz, 2H), 6.21 (t, J = 6.8 Hz, 1H), 5.22 (d, J = 6.8 Hz, 2H), 2.59 (s, 3H); 13C{1H}
NMR (75 MHz, CDCl3) δ 210.7, 197.5, 139.2, 135.5, 128.7, 126.7, 93.6, 79.3, 26.6; EIMS
(70 eV) m/z M+ 158.
Methyl 4-(propa-1,2-dienyl)benzoate(2h)9a
3ꢀ(4ꢀ(Methoxycarbonyl)phenyl)propiolic acid (613 mg, 3.0 mmol) was reacted with
dicyclohexylamine (1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2h)
(308.3 mg, 1.77 mmol, 59% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.90 (d, J =
8.5 Hz, 2H), 7.37 (d, J = 8.3 Hz, 2H), 6.21 (t, J = 6.8 Hz, 1H), 5.22 (d, J = 6.8 Hz, 2H), 2.59
(s, 3H); 13C{1H} NMR (75 MHz, CDCl3) δ 210.6, 166.9, 138.9, 129.9, 128.4, 126.5, 93.6,
79.3, 52.1; EIMS (70 eV) m/z M+ 174.
4-(Propa-1,2-dienyl)benzonitrile(2i)
3ꢀ(4ꢀCyanophenyl)propiolic acid (513.5 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2i) (262.6 mg, 1.86
mmol, 62% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.58 (d, J = 8.4 Hz, 2H), 7.37
(d, J = 8.4 Hz, 2H), 6.18 (t, J = 6.8 Hz, 1H), 5.25 (d, J = 6.7 Hz, 2H); 13C{1H} NMR (75
MHz, CDCl3) δ 210.8, 139.2, 132.4, 127.1, 119.0, 110.1, 93.3, 79.8; HRMS (ESI, TOF) calcd.
for C10H8N [M+H]+ 142.0657, found 142.0652.
2-(Propa-1,2-dienyl)naphthalene(2j)9a
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3ꢀ(Naphthalenꢀ2ꢀyl)propiolic acid (588.6 mg, 3.0 mmol) was reacted with dicyclohexylamine
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(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2j) (419 mg, 2.52
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mmol, 84% yield, colorless oil); H NMR (300 MHz, CDCl3) δ 8.21 (m, 1H), 7.85 (m, 1H),
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7.74 (d, J = 8.1 Hz, 1H), 7.59 (d, J = 7.2 Hz, 1H), 7.55–7.39 (m, 3H), 6.86 (t, J = 6.9 Hz, 1H),
5.20 (d, J = 6.9 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3) δ 211.0, 133.9, 130.8, 130.1, 128.6,
127.4, 126.0, 125.7, 125.6, 125.3, 123.5, 90.4, 77.8; EIMS (70 eV) m/z M+ 166.
4-(Propa-1,2-dienyl)biphenyl(2k)9a
3ꢀ(Biphenylꢀ4ꢀyl)propiolic acid (666.7 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2k) (375 mg, 1.95
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mmol, 65% yield, white solid); H NMR (300 MHz, CDCl3) δ 7.64–7.53 (m, 4H), 7.49–7.31
(m, 5H), 6.23 (t, J = 6.8 Hz, 1H), 5.20 (d, J = 6.8 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3) δ
210.0, 140.8, 139.7, 132.9, 128.7, 127.3, 127.2, 127.1, 126.9, 93.6, 78.9; EIMS (70 eV) m/z
M+ 192.
1-Fluoro-4-(propa-1,2-dienyl)benzene(2l)20
3ꢀ(4ꢀFluorophenyl)propiolic acid (492.4 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270.0 mg, 9.0 mmol) to give (2l) (185mg, 1.38
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mmol, 46% yield, colorless oil); H NMR (300 MHz, CDCl3) δ 7.24 (m, 2H), 6.98 (m, 2H),
6.13 (t, J = 6.9 Hz, 1H), 5.14 (d, J = 6.9 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3) δ 209.5 (d,
JCꢀF = 2.3 Hz), 161.8 (d, JCꢀF = 245.9 Hz), 129.8 (d, JCꢀF = 3.3 Hz), 128.0 (d, JCꢀF = 8.0 Hz),
115.5 (d, J CꢀF = 21.7 Hz), 93.0 , 79.0; EIMS (70 eV) m/z M+ 134.
1-Chloro-4-(propa-1,2-dienyl)benzene(2m)20
3ꢀ(4ꢀChlorophenyl)propiolic acid (541.8 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2m) (357 mg, 2.37
mmol, 79% yield, colorless oil); 1H NMR (300 MHz, CDCl3) δ 7.31–7.12 (m, 4H), 6.11 (t, J
= 6.8 Hz, 1H), 5.15 (d, J = 6.8 Hz, 2H); 13C{1H} NMR (75 MHz, CDCl3) δ 209.8, 132.4,
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132.40, 128.7, 127.8, 93.1, 79.2; EIMS (70 eV) m/z M+ 150.
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Trimethyl(4-(propa-1,2-dienyl)phenyl)silane (2n)
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3ꢀ(4ꢀ(Trimethylsilyl)phenyl)propiolic acid (655 mg, 3.0 mmol) was reacted with
dicyclohexylamine (1.63 g, 9.0 mmol) and paraformaldehyde (270mg, 9.0 mmol) to give (2n)
(287 mg, 1.53 mmol, 51% yield, colorless oil); 1H NMR (500 MHz, CDCl3) δ 7.50 (d, J = 7.8
Hz, 2H), 7.32 (d, J = 7.8 Hz, 2H), 6.19 (t, J = 6.8 Hz, 1H), 5.17 (d, J = 6.8 Hz, 2H), 0.29 (s,
9H);13C{1H} NMR (126 MHz, CDCl3) δ 210.0, 139.0, 134.4, 133.6, 126.0, 94.0, 78.8, ꢀ1.1;
HRMS (ESI, TOF) calcd. for C12H17Si [M+H]+ 189.1100, found 189.1130.
1-(Propa-1,2-dienyl)-4-vinylbenzene (2o)
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3ꢀ(4ꢀVinylphenyl)propiolic acid (516 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270 mg, 9.0 mmol) to give (2o) (171 mg, 1.2
mmol, 32% yield, colorless oil); 1H NMR (500 MHz, CDCl3) δ 7.35 (d, J = 8.2 Hz, 2H), 7.24
(d, J = 8.2 Hz, 2H), 6.69 (dd, J = 17.6, 10.9 Hz, 1H), 6.15 (t, J = 6.8 Hz, 1H), 5.73 (d, J =
17.6 Hz, 1H), 5.21 (d, J = 10.9 Hz, 1H), 5.15 (d, J = 6.8 Hz, 2H);13C{1H} NMR (126 MHz,
CDCl3) δ 210.1, 136.6, 136.4, 133.6, 127.0, 126.6, 113.6, 93.9, 79.0; HRMS (ESI, TOF)
calcd. for C11H11 [M+H]+ 143.0861, found 143.0858.
2-(Propa-1,2-dienyl)thiophene (2p)
3ꢀ(Thiophenꢀ2ꢀyl)propiolic acid (456 mg, 3.0 mmol) was reacted with dicyclohexylamine
(1.63 g, 9.0 mmol) and paraformaldehyde (270mg, 9.0 mmol) to give (2p) (113 mg, 0.93
mmol, 31% yield, colorless oil); 1H NMR (500 MHz, CDCl3) δ 7.17 (d, J = 5.1 Hz, 1H), 6.94
(dd, J = 5.1, 3.5 Hz, 1H), 6.90 (m, 1H), 6.39 (t, J = 6.8 Hz, 1H), 5.16 (d, J = 6.8 Hz, 2H);
13C{1H} NMR (126 MHz, CDCl3) δ 209.4, 137.9, 127.4, 124.7, 124.5, 88.5, 79.2; HRMS
(ESI, TOF) calcd. for C7H7 [M+H]+ 123.0268, found 123.0264.
N-cyclohexyl-N-(3-phenylprop-2-ynyl)cyclohexanamine (4a)21
Phenyl propiolic acid (438 mg, 3.0 mmol) was reacted with dicyclohexylamine (1.63 g, 9.0
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mmol) and paraformaldehyde (270 mg, 9.0 mmol) at 100 °C for 30 min to give (4a) (212 mg,
0.7 mmol 24% yield, colorless oil, 90% purity);1H NMR (300 MHz, CDCl3) δ 7.39 (m, 2H),
7.33–7.23 (m, 3H), 3.70 (s, 2H), 2.82 (tt, J = 10.9, 3.2 Hz, 2H), 1.90 (d, J = 10.9 Hz, 4H),
1.79 (d, J = 12.3 Hz, 4H), 1.62 (m, 2H), 1.46–1.03 (m, 10H); 13C{1H} NMR (75 MHz, CDCl3)
δ 131.4, 128.2, 127.8, 123.7, 88.3, 84.0, 57.7, 35.6, 30.8, 26.9; EIMS (70 eV) m/z M+ 295.
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Author Information
Corresponding Author
Eꢀmail : jiminkim@chonnam.ac.kr(J. Kim); sunwoo@chonnam.ac.kr (S. Lee).
Notes
The authors declare no competing financial interest.
Acknowledgements
This research was supported by a National Research Foundation of Korea (NRF) grant
provided by the Korean government (MSIP) (NRFꢀ2014R1A2A1A11050018, NRFꢀ
2015R1A4A1041036). Spectral data were obtained from the Korea Basic Science Institute,
Gwangju branch.
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at
DOI:
Copies of 1H and 13C{1H} NMR spectra of products (1n, 1o, 2aꢀ2p and 4a)
References
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(1) (a) Tius, M. Acc. Chem. Res. 2003, 36, 284–290. (b) Wei, L. L.; Xiong, H.; Hsung, R. P.,
Acc. Chem. Res. 2003, 36, 773–782. (c) Brasholz, M.; Reissig, H.ꢀU.; Zimmer, R. Acc. Chem.
Res. 2009, 42, 45–56. (d) Ma, S. Acc. Chem. Res. 2009, 42, 1679–1688.
10
11
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17
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60
(2) For selected recent examples: (a) HoffmannꢀRödar, A.; Krause, N. Angew. Chem. Int. Ed.
2004, 43, 1196–1216. (b) Yu, S.; Ma, S. Angew. Chem. Int. Ed. 2012, 51, 3074–3112. (c)
Werness, J. B.; Tang, W. Org. Lett. 2011, 13, 3664–3666.
(3) (a) Alcaide, B.; Almendros, P.; Aragoncillo, C.; Fernández, I.; GómezꢀCampillos, G. J.
Org. Chem. 2014, 79, 7075–7083. (b) Gobé, V.; Retailleau, P.; Guinchard, X. Org. Lett. 2014,
16, 5438–5441. (c) Kim, H.; Kim, G. Bull. Korean Chem. Soc. 2015, 36, 1743–1744. (d)
Ondet, P.; Joffrin, A.; Diaf, I.; Lemière, G.; Dunach, E. Org. Lett. 2015, 17, 1002–1005.
(4) (a) Ma, S. Chem. Rev. 2005, 105, 2829–2871. (b) Brummond, K. M.; Deforrest, J. E.
Synthesis 2007, 6, 795–818. (c) Yu, S.; Ma, S. Chem. Commun. 2011, 47, 5384–5418. (d)
Neff, R. Frantz, D. ACS. Catal. 2014, 4, 519–528.
(5) Li, C.ꢀY.; Wang, X.ꢀB.; Sun, X.ꢀL.; Tang, Y.; Zheng, J.ꢀC.; Xu, Z.ꢀH.; Zhou, Y.ꢀG.; Dai,
L.ꢀX. J. Am. Chem. Soc. 2007, 129, 1494–1495.
(6) (a) Tsubouchi, A.; Kira, T.; Takeda, T. Synthesis 2006, 16, 2577–2580. (b) Xi, Z.; Zhang,
W.ꢀX.; Song, Z.; Zheng, W.; Kong, F.; Takahashi, T. J. Org. Chem. 2005, 70, 8785–8789.
(7) (a) Thorand, S.; Vögtle, F.; Krause, N. Angew. Chem. Int. Ed. 1999, 38, 3721–3723. (b)
Brummond, K. M.; Kerekes, A. D.; Wan, H. J. Org. Chem. 2002, 67, 5156–5163.
(8) Larsen, C. H.; Anderson, K. W.; Tundel, R. E.; Buchwald, S. L. Synlett 2006, 2941–2946.
(9) (a) Ye, F.; Wang, C.; Ma, X.; Hossain, M. L.; Xia, Y.; Zhang, Y.; Wang, J. J. Org. Chem.
2015, 80, 647–652. (b) Kuang, J.; Ma, S. J. Am. Chem. Soc. 2010, 132, 1786–1787. (c)
Hassink, M.; Liu, X. Fox, J. M. Org. Lett. 2011, 13, 2388–2391. (d) Hossan, M. L.; Ye, F.;
Zhang, Y.; Wang, J. J. Org. Chem. 2013, 78, 1236–1241.
(10) (a) Baret, P.; Barreiro, E.; Greene, A. E.; Luche, J.ꢀL.; Teixeira, M.ꢀA.; Crabbe, P.
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7
8
9
Tetrahedron 1979, 35, 2931–2938. (b) Crabbe, P.; Andre, D.; Fillion, H. Tetrahedron Lett.
1979, 20, 893–896. (c) Crabbe, P.; fillion, H.; Andre, D.; Luche, J.ꢀL. J. Chem. Soc. Chem.
Commun. 1979, 19, 859–860. (d) Fillion, H.; Andre, D.; Luche, J.ꢀL. Tetrahedron Lett. 1980,
21, 929–930. (e) Kumar, V.; Chipeleme, A.; Chibale, K. Eur. J. Org. Chem. 2008, 43–46. (f)
Jiang, G.ꢀJ.; Zheng, Q.ꢀH.; Dou, M.; Zhuo, L.ꢀG.; Meng, W.; Yu, Z.ꢀX. J. Org. Chem. 2013,
78, 11783–11793.
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(11) (a) Gurubrahamam, R.; Periasamy, M. J. Org. Chem. 2013, 78, 1463–1470. (b) Tang, X.;
Huang, X.; Cao, T.; Han, Y.; Jiang, X.; Ling, W.; Tang, Y.; Zhang, J.; Yu, Q.; Fu, C.; Ma, S.
Org. Chem. Front. 2015, 2, 688–691.
(12) (a) Moon, J.; Jeong, M.; Nam, H.; Ju, J. H.; Moon, J. H.; Jung, H. M.; Lee, S. Org. Lett.
2008, 10, 945–948. (b) Moon, J.; Jang, M.; Lee, S. J. Org. Chem. 2009, 74, 1403–1406; (c)
Park, K.; Lee, S. RSC Adv. 2013, 3, 14165ꢀ14182. (d) Xiang, L.; Yan, F.; Wu, Y.; Wu, Y. Org.
Lett. 2014, 16, 992–995. (e) Sun, F.; Gu, Z. Org. Lett. 2015, 17, 2222–2225.
(13) Park, K.; Heo, Y.; Lee, S. Org. Lett. 2013, 15, 3322–3325.
(14) Lim, J.; Park, K.; Byeun, A.; Lee, S. Tetrahedron Lett. 2014, 55, 4875–4878.
(15) (a) Park, K.; Palani, T.; Pyo, A.; Lee, S. Tetrahedron Lett. 2012, 53, 733–737. (b) Park,
K.; You, J.ꢀM.; Jeon, S.; Lee, S. Eur. J. Org. Chem. 2013, 1973–1978.
(16) When phenyl propiolic acid was employed with 1.2 g (8.2 mmol), the desired product 2a
was obtained with 76% yield. In addition, when phenyl acetylene was allow to react under
the optimized condition, the terminal allene 2a was formed with 65% yield.
(17) Li, Q.ꢀH.; Liao, J.ꢀW.; Huang, Y.ꢀL.; Chiang, R.ꢀT.; Gau, H.ꢀM. Org. Biomol. Chem.,
2014, 12, 7634–7642.
(18) Petasis, N. A.; Hu, Y.ꢀH. J. Org. Chem. 1997, 62, 782–783.
(19) Huang, C.ꢀW.; Shanmugasundaram, M.; Chang, H.ꢀM.; Cheng, C.ꢀH. Tetrahedron
2003, 59, 3635–3641.
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(20) Hu, J.; Xie Y.; Huang, H. Angew. Chem. Int. Ed. 2014, 53, 7272–7276.
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(21) Sugiishi, T.; Kimura, A.; Nakamura, H. J. Am. Chem. Soc. 2010, 132, 5332–5333
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