Pd-catalyzed decarboxylative coupling of propiolic acids: One-pot synthesis of 1,4-disubstituted 1,3-diynes via Sonogashira-homocoupling sequence

Article abstract of DOI:10.1021/jo200096x

One-pot synthesis of symmetric 1,4-disubstituted 1,3-diynes from iodoarenes and propiolic acid via Sonogashira reaction followed by Pd-catalyzed decarboxylative homocoupling is developed in high yields. Also, this system allows the one-pot synthesis of unsymmetric 1,4-disubstituted 1,3-diynes by cross-coupling of two different 3-substituted propiolic acids.

Full text of DOI:10.1021/jo200096x

ARTICLE
pubs.acs.org/joc
Pd-Catalyzed Decarboxylative Coupling of Propiolic Acids: One-Pot
Synthesis of 1,4-Disubstituted 1,3-Diynes via Sonogashira-
Homocoupling Sequence
Jihye Park,† Eonjeong Park,† Aejin Kim,† Seul-A Park,† Youngil Lee,† Ki-Whan Chi,† Young Hoon Jung,‡ and
In Su Kim*,†
†Department of Chemistry, University of Ulsan, Ulsan, 680-749, Republic of Korea
‡School of Pharmacy, Sungkyunkwan University, Suwon 440-746, Republic of Korea
S Supporting Information
b
ABSTRACT: One-pot synthesis of symmetric 1,4-disubstitut-
ed 1,3-diynes from iodoarenes and propiolic acid via Sonoga-
shira reaction followed by Pd-catalyzed decarboxylative
homocoupling is developed in high yields. Also, this system
allows the one-pot synthesis of unsymmetric 1,4-disubstituted 1,3-diynes by cross-coupling of two different 3-substituted
propiolic acids.
’ INTRODUCTION
required the prefunctionalization to prepare haloalkynes or
propiolic acids as well as terminal alkynes. The multistep
syntheses required for the preparation of such substrates can
pose additional barriers to their use. Therefore, it is highly
desirable to develop more efficient methodologies saving
synthetic steps and avoiding waste formation for synthesizing
conjugate 1,3-diynes.
Conjugated 1,3-diynes are very crucial materials in the fields of
chemistry, biology, and material science because they have been
used in the preparation of natural products,1 organic and
inorganic composites,2 pharmaceuticals,3 and π-conjugated
polymers,4 as well as the molecular recognition process.5 The
traditional method for the construction of symmetric 1,3-diynes
is oxidative homocoupling reactions of terminal alkynes, re-
ported by Glaser, via the treatment of Cu(I) salt in the presence
of aqueous ammonia followed by air oxidation (Scheme 1, eq 1).6
Later related modified methods to improve the disadvantage of
the original reaction condition were developed by Eglinton7 and
Hay.8 The method for constructing unsymmetrical 1,3-diynes
was described by Chodkiewicz-Cadiot via Cu-catalyzed cou-
pling between haloalkynes and terminal alkynes (Scheme 1,
eq 2).9 Yu and Jiao also reported Cu-catalyzed decarboxylative
cross-coupling of propiolic acids and terminal alkynes for the
synthesis of unsymmetrical conjugate diynes (Scheme 1, eq 3).10
Pioneering work for the preparation of symmetrical 1,3-diynes
using palladium catalysis was reported by Rossi et al. in 1985
(Scheme 1, eq 4).11 Recently, Lei et al. demonstrated a new
process for the construction of unsymmetrical 1,3-diynes, which
includes Ni-catalyzed oxidative coupling of two different terminal
alkynes with a high loading of one alkyne partner (Scheme 1,
eq 5).12 However, these methodologies present intrinsic draw-
backs, namely the need for prefunctionalization of both coupling
partners. For example, in the case of homocoupling of terminal
alkynes, the preparation of terminal alkynes was often required, i.e. via
Corey-Fuchs reaction with aldehydes,13 Fritsch-Buttenberg-
Wiechell rearrangement of vinyl bromides,14 Seyferyth-Gilbert
homologation with aldehydes,15 and Sonogashira reaction16
between haloarenes and metal (Si or Sn)-substituted acety-
lenes followed by reductive hydrogenation. Moreover, the
methods for the synthesis of unsymmetrical 1,3-diynes have
Transition metal-catalyzed decarboxylative sp2-sp2 cross-
coupling of aryl carboxylic acids or aryl carboxylates with aryl
halides is an established method for the synthesis of biaryl
compounds.17 Lee and co-workers first described palladium-
catalyzed sp-sp2 cross-coupling reaction of propiolic acid and
aryl halides to afford unsymmetrical diaryl acetylenes.18 Lee and
Kim reported palladium-catalyzed decarboxylative sp-sp2 cross-
coupling reactions between alkynyl carboxylic acids and aryl
halides or aryl triflates in the presence of Ag2O and LiX (X = I,
Cl).19 Also, Loh and Feng reported Pd-catalyzed decarboxylative
sp-sp2 cross-coupling reactions of alkynyl carboxylic acids with
aryl boronic acids.20 Recently, Li et al. demonstrated palladium-
catalyzed sp-sp3 cross-coupling reaction to synthesize internal
alkynes using alkynyl carboxylic acids and benzyl halides in the
presence of Cs2CO3.21 While there has been considerable
research into the preparation of diaryl alkynes through metal-
catalyzed decarboxylative cross-coupling reactions, an efficient
metal-catalyzed decarboxylative homocoupling and cross-coupling
reaction for the construction of 1,4-diaryl 1,3-diynes remains
relatively unexplored.22
Herein, we demonstrate direct synthesis of symmetrical 1,4-
disubstituted 1,3-diynes 4 from iodoarenes 1 and propiolic acid
(2) via Sonogashira reaction followed by Pd-catalyzed decarbox-
ylative homocoupling. Furthermore, one-pot synthesis of
Received: January 14, 2011
Published: March 04, 2011
r
2011 American Chemical Society
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|

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ARTICLE
Scheme 1. Strategies for the Construction of 1,3-Diynes
Scheme 2. One-Pot Synthesis of 1,3-Diynes 4 or 5 from
Iodoarenes 1 and Propiolic Acid (2)
Table 2. Selected Optimization of One-Pot Synthesis of 1,4-
Diphenylbuta-1,3-diyne (4a)a
entry
catalyst
2 (mol %) CuI (mol %) yield (%) ratio (4a:6a)b
1
2
3
4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)2Cl2
200
200
300
200
10
20
10
10
82
76
65
90
86:14
83:17
27:73
95:5
Table 1. Selected Optimization of Decarboxylative Homo-
coupling of 3-Phenylpropiolic Acid (3a)a
a All reactions were performed in 13 mm ꢀ 100 mm pressure tubes. The
cited yields are of an inseparable mixture of 4a and 6a isolated by column
chromatography. b Ratio was determined by GC-MS analysis.
entry
catalyst
additive
solvent
yield (%)
an oxidant, and the use of Pd(PPh3)4 afforded our desirable
adduct 4a in 82% yield (Table 1, entry 5). In the absence of either
palladium catalyst or Ag2CO3, no homocoupling product 4a was
observed even when using 100 mol % of Pd(PPh3)4, indicating
both metals are required in the reaction (Table 1, entries 6 and 7).
Next, our study focused on the use of additives such as AgI,
AgNO3, CuCO3, and Ag2O, but the chemical yield was not
improved, as shown in entries 8-11. Solvent screening showed
that optimum results could be obtained with DMF solvent, provid-
ing the desired product 4a in 96% yield (Table 1, entry 12),
whereas the use of other solvents such as THF, dioxane, DMSO,
and AcOH was relatively ineffective.
On the basis of the established reaction conditions for
decarboxylative homocoupling, we attempted to expand this
transformation to the one-pot synthesis of symmetrical 1,4-diaryl
1,3-diynes from iodoarenes and propiolic acid. Our investigation
started to find optimal reaction conditions for the formation of
1,4-diphenylbuta-1,3-diyne (4a). As shown in Table 2, the
coupling of iodobenzene (1a) and propiolic acid (2) under
standard Sonogashira conditions, such as 5 mol % of Pd(PPh3)4,
10 mol % of CuI, 350 mol % of Et3N, and DMF, followed by the
treatment of 200 mol % of Ag2CO3 afforded an inseparable
mixture of the desired product 4a and diaryl alkyne byproduct 6a
in 82% yield with a moderate chemoselectivity of 86:14 (Table 2,
entry 1). Increasing the amount of CuI to 20 mol % provided
a slightly reduced yield (76%) and chemoselectivity (83:17)
1
2
Pd(OAc)2
Pd(PPh3)2Cl2
Pd(TFA)2
Pd2(dba)3
Pd(PPh3)4
Pd(PPh3)4
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
Ag2CO3
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
56
78
80
76
82
0
3
4
5
6
7
Ag2CO3
AgI
0
8
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
Pd(PPh3)4
trace
trace
38
60
96
9
AgNO3
CuCO3
Ag2O
10
11
12
Ag2CO3
a All reactions were performed in 13 mm ꢀ 100 mm pressure tubes. The
cited yields are of material isolated by column chromatography.
unsymmetrical 1,4-disubstituted 1,3-diynes 5 by cross-coupl-
ing of two different 3-substituted propiolic acids 3 and 3a is
described, as depicted in Scheme 2.
’ RESULTS AND DISCUSSION
Our investigation started with Pd-catalyzed decarboxylative
homocoupling of 3-phenylpropiolic acid (3a), and the selected
results are summarized in Table 1. As shown in entries 1-5, a
range of Pd catalysts was screened in the presence of Ag2CO3 as
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Table 3. Substrate Scope of One-Pot Synthesis of 1,4-Disubstituted-1,3-diynes (4)a
a All reactions were performed in 13 mm ꢀ 100 mm pressure tubes. The cited yields are of material isolated by column chromatography. b Ratio was
determined by GC-MS analysis.
(Table 2, entry 2). Interestingly, the increased use of propiolic
acid (2) gave the byproduct 6a as a major compound (Table 2,
entry 3). After further optimization, the best results were
obtained when 5 mol % of Pd(PPh3)2Cl2 was employed as a
palladium catalyst, affording selectively the homocoupling pro-
duct 4a in 90% yield with a 95:5 ratio (Table 2, entry 4).
With the standard reaction conditions established, the sub-
strate scope and limitations were explored, and the results are
summarized in Table 3. As shown in entries 2-5, a variety of
substrates with para-substituted electron-donating groups (Me,
OMe, and OH) and an electron-withdrawing group (CO2Et)
provided the corresponding products 4b-e in high yield (72-
89%) with excellent chemoselectivities (91:9-99:1).
p-Halogen-substituted iodobenzene 1f was compatible under
the optimal reaction condition, and the desired 1,3-diyne product
4f was produced in 73% yield with a 90:10 ratio (Table 3,
entry 6). Electron-rich meta- and ortho-substituted iodobenzenes
1g and 1h also can be converted to the corresponding products
4g and 4h, respectively, in high yields (Table 3, entries 7 and 8).
1-Iodonaphthalene (1i) participated in this reaction to provide
the corresponding product 4i in 63% yield with a ratio of 94:6
(Table 3, entry 9). Finally, the heterocyclic iodides 1j and 1k also
reacted smoothly in the decarboxylative coupling to furnish 4j
and 4k in 54% and 71% yields with excellent selectivities,
respectively (Table 3, entries 10 and 11).
To further explore the utility of our decarboxylative coupling
reaction, the one-pot cross-coupling reaction between two
different 3-substituted propiolic acids was examined, as shown
in Table 4. Interestingly, the results reveal that the amount of
coupling partner 3a and base controls the reaction outcome. For
example, an increase of unsymmetrical 1,3-diyne 5c was observed
with the use of triethylamine (Table 4, entries 1 and 2). However,
the use of an excess amount of 3a provided the reduced chemical
yield of both unsymmetrical 1,3-diyne 5c and symmetrical 1,3-
diynes 4c and 4a (Table 4, entries 4 and 5). Eventually, the
treatment of 200 mol % of phenylpropiolic acid (3a) and 200 mol %
of Et3N, under otherwise standard conditions, afforded the
desired unsymmetrical 1,3-diyne 5c in a good yield (55%)
(Table 4, entry 3).
To evaluate the electronic effect in the cross-coupling reaction,
iodobezene 1e with the CO2Et electron-withdrawing group was
chosen as a substrate. As was expected, 1e can accelerate the cross-
coupling reaction to give unsymmetrical 1,3-diyne 5e, compared
to the case of electron-donating substrate 1c (Table 4, entries 2
and 6). In particular, the reaction of 1e with 200 mol % of
phenylpropiolicacid (3a) and 200 mol % ofEt3N, underotherwise
standard conditions, furnished the desired product 5e in a
remarkably increased yield (73%) (Table 4, entry 7).
A proposed reaction pathway for the formation of 1,4-disub-
stituted 1,3-diynes is shown in Scheme 3. At the initial stage of
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ARTICLE
Table 4. One-Pot Cross-Coupling of 3-Substituted Propiolic Acidsa
yield (%)
entry
3a (mol %)
Et3N (mol %)
5c
4c
4a
1
2
3
4
5
150
150
200
300
500
44
50
55
46
35
25
26
30
28
22
34
48
59
59
47
150
200
300
500
yield (%)
entry
3a (mol %)
Et3N (mol %)
5e
4e
4a
6
7
150
200
150
200
68
73
17
17
22
35
a All reactions were performed in 13 mm ꢀ 100 mm pressure tubes. The cited yields are confirmed by GC-MS analysis of combined materials isolated by
column chromatography. 1,3-Diphenylacethylene was used as an internal standard.
Scheme 3. Proposed Reaction Mechanism
currently underway to extend this protocol to vinyl iodides,
and the results will be reported in due course.
’ EXPERIMENTAL SECTION
Typical Experimental Procedure for the Decarboxylative
Homocoupling of 3-Phenylpropiolic Acid (3a) (Table 1). To
an oven-dried sealed tube under 1 atm of nitrogen gas charged with
3-phenylpropiolic acid (3a) (43.9 mg, 0.3 mmol, 100 mol %) and
palladium catalyst (0.015 mmol, 5.0 mol %) in anhydrous DMF (1.0 mL,
0.3 M) was added silver or copper salts (0.6 mmol, 200 mol %). The
reaction mixture was allowed to stir at 130 °C for 20 h, at which point the
reaction mixture was evaporated onto silica gel. Purification of the
product by column chromatography (SiO2: n-hexanes:ethyl acetate)
provided 1,4-diphenylbuta-1,3-diyne (4a).
Typical Experimental Procedure for One-Pot Synthesis of
1,3-Diynes from Iodoarenes and Propiolic Acid (Table 3). To
an oven-dried sealed tube under 1 atm of nitrogen gas charged with
iodoarenes 1a-k (0.3 mmol, 100 mol %), Pd(PPh3)2Cl2 (10.5 mg,
0.015 mmol, 5.0 mol %), and CuI (5.7 mg, 0.03 mmol, 10 mol %) in
anhydrous DMF (1.0 mL, 0.3 M) was added propiolic acid (2) (37.1 μL,
0.6 mmol, 200 mol %) and triethylamine (0.146 mL, 1.05 mmol,
350 mol %). The reaction mixture was allowed to stir at room tem-
perature for 6 h, and then Ag2CO3 (165.5 mg, 0.6 mmol, 200 mol %) was
added to the reaction mixture. The reaction mixture was allowed to stir
at 130 °C for 20 h, at which point the reaction mixture was evaporated
onto silica gel. Purification of the product by column chromatography
(SiO2: n-hexanes:ethyl acetate) provided the desired 1,3-diynes 4a-k
and diarylalkyne byproducts 6a-k. The ratio between 1,3-diynes and
diarylalkynes was confirmed by GC-MS analysis.
the reaction, Pd(0) catalyst is oxidized by silver carbonate to
Pd(II) catalyst. Also, 3-substituted propiolic acid, generated
from the corresponding iodoarene, can be converted into
Ag(I)-acetylide intermediate II through the decarboxylation of
Ag(I)-carboxylate intermediate I. Transmetalation of two Ag(I)-
acetylides to Pd(II) would directly give dialkynylpalladium
intermediate III, which can afford the desired 1,3-diyne product
IV via reductive elimination and regenerate Pd(0) catalyst.
’ CONCLUSION
In conclusion, an efficient Pd-catalyzed decarboxylative homo-
coupling reaction of iodoarenes with propiolic acid using silver
carbonate has been developed. Furthermore, unsymmetrical 1,3-
diynes can be readily prepared by Pd-catalyzed cross-coupling
reaction between 3-substituted propiolic acids generated in situ
and commercial available 3-phenylpropiolic acid. Efforts are
TypicalExperimentalProcedure for One-Pot Cross-Coupling
of 3-Substituted Propiolic Acids (Table 4). To an oven-dried
sealed tube under 1 atm of nitrogen gas charged with 4-methoxyiodo-
benzene (1c) or ethyl 4-iodobenzoate (1e) (0.3 mmol, 100 mol %),
Pd(PPh3)2Cl2 (10.5 mg, 0.015 mmol, 5.0 mol %), and CuI (5.7 mg,
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ARTICLE
0.03 mmol, 10 mol %) in anhydrous DMF (1.0 mL, 0.3 M) were added
propiolic acid (2) (37.1 μL, 0.6 mmol, 200 mol %) and triethylamine
(0.146 mL, 1.05 mmol, 350 mol %). The reaction mixture was allowed to
stir at room temperature for 6 h, and then 3-phenylpropiolic acid (3a),
triethylamine, and Ag2CO3 (165.5 mg, 0.6 mmol, 200 mol %) were
added to the reaction mixture. The reaction mixture was allowed to stir
at 130 °C for 20 h, at which point the reaction mixture was evaporated
onto silica gel. Purification of the product by column chromatography
(SiO2: n-hexanes:ethyl acetate) provided the desired unsymmetrical 1,3-
diynes (5c or 5e) and unsymmetrical 1,3-diynes, respectively.
1,4-Diphenylbuta-1,3-diyne (4a):23 1H NMR (300 MHz,
CDCl3) δ 7.29-7.39 (m, 6H), 7.50-7.54 (m, 4H); 13C NMR (75
MHz, CDCl3) δ 74.1, 81.8, 122.0, 128.6, 129.4, 132.7; GC (HP-5MS
capillary column, 0.32 mm ꢀ 60 m, Agilent Technologies) carrier gas
flow rate = He gas, 1 mL/min, initial column temp = 273 K, final column
temp = 573 K, progress rate = 20 deg/min, retention time = 10.3 min;
MS (EI) m/z (%) 202.6 (100%) [Mþ].
1,4-Bis(2-methoxyphenyl)buta-1,3-diyne (4h):24 1H NMR
(300 MHz, CDCl3) δ 3.88 (s, 6H), 6.84-6.92 (m, 4H), 7.30 (dt, J = 7.5,
1.8 Hz, 2H), 7.46 (dd, J = 7.5, 1.8 Hz, 2H); 13C NMR (75 MHz, CDCl3)
δ 56.0, 78.1, 78.8, 110.8, 111.5, 120.7, 130.7, 134.6, 161.5; GC (HP-5MS
capillary column, 0.32 mm ꢀ 60 m, Agilent Technologies) carrier gas
flow rate = He gas, 1 mL/min, initial column temp = 273 K, final column
temp = 573 K, progress rate = 20 deg/min, retention time = 13.1 min;
MS (EI) m/z (%) 262.4 (100%) [Mþ].
1,4-Di(naphthalen-1-yl)buta-1,3-diyne (4i):24 1H NMR (300
MHz, CDCl3) δ 7.42-7.48 (m, 2H), 7.51-7.57 (m, 2H), 7.59-7.65
(m, 2H), 7.81-7.89 (m, 6H), 8.40-8.46 (m, 2H); 13C NMR (75 MHz,
CDCl3) δ 78.9, 81.2, 119.7, 125.5, 126.4, 126.9, 127.5, 128.7, 130.0,
132.3, 133.3, 134.1; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m,
Agilent Technologies) carrier gas flow rate = He gas, 1 mL/min, initial
column temp = 273 K, final column temp = 573 K, progress rate = 20
deg/min, retention time = 23.6 min; MS (EI) m/z (%) 302.6 (100%)
[Mþ].
1,4-Di(thiophen-3-yl)buta-1,3-diyne (4j):25 1H NMR (300
MHz, (CD3)2CO) δ 7.25 (dd, J = 5.1, 1.2 Hz, 2H), 7.57 (dd, J = 5.1,
3.0 Hz, 2H), 7.89 (dd, J = 3.0, 1.2 Hz, 2H); 13C NMR (75 MHz,
(CD3)2CO) δ 73.9, 77.5, 121.3, 127.5, 130.9, 133.0; GC (HP-5MS
capillary column, 0.32 mm ꢀ 60 m, Agilent Technologies) carrier gas
flow rate = He gas, 1 mL/min, initial column temp = 273 K, final column
temp = 573 K, progress rate = 20 deg/min, retention time = 10.7 min;
MS (EI) m/z (%) 214.7 (100%) [Mþ].
1,4-Di(p-tolyl)buta-1,3-diyne (4b):23 1H NMR (300 MHz,
CDCl3) δ 2.34 (s, 6H), 7.12 (d, J = 8.1 Hz, 4H), 7.39 (d, J = 8.1 Hz,
4H); 13C NMR (75 MHz, CDCl3) δ 21.9, 73.6, 81.7, 119.0, 129.4, 132.6,
139.7; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m, Agilent
Technologies) carrier gas flow rate = He gas, 1 mL/min, initial column
temp = 273 K, final column temp = 573 K, progress rate = 20 deg/min,
retention time = 11.7 min; MS (EI) m/z (%) 230.8 (100%) [Mþ].
1,4-Bis(4-methoxyphenyl)buta-1,3-diyne (4c):23 1H NMR
(300 MHz, CDCl3) δ 3.80 (s, 6H), 6.83 (d, J = 8.7 Hz, 4H), 7.43 (d,
J = 8.7 Hz, 4H); 13C NMR (75 MHz, CDCl3) δ 55.5, 73.1, 81.4, 114.1,
114.3, 134.3, 160.4; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m,
Agilent Technologies) carrier gas flow rate = He gas, 1 mL/min, initial
column temp = 273 K, final column temp = 573 K, progress rate = 20
deg/min, retention time = 14.1 min; MS (EI) m/z (%) 262.5 (100%)
[Mþ].
1,4-Di(pyridin-3-yl)buta-1,3-diyne (4k):23 1H NMR (300
MHz, CDCl3) δ 7.24-7.29 (m, 2H), 7.79 (dt, J = 7.8, 1.5 Hz, 2H),
8.56-8.58 (m, 2H), 8.74 (br, 2H); 13C NMR (75 MHz, CDCl3) δ 76.6,
79.2, 118.9, 123.1, 139.4, 149.5, 153.2; GC (HP-5MS capillary column,
0.32 mm ꢀ 60 m, Agilent Technologies) carrier gas flow rate = He gas,
1 mL/min, initial column temp = 273 K, final column temp = 573 K,
progress rate = 20 deg/min, retention time = 10.8 min; MS (EI) m/z
(%) 204.8 (100%) [Mþ].
1
4,40-(Buta-1,3-diyne-1,4-diyl)diphenol (4d): H NMR (300
MHz, CD3OD) δ 3.39 (br, 2H), 6.79 (d, J = 8.4 Hz, 4H), 7.37 (d, J = 8.4
Hz, 4H); 13C NMR (75 MHz, CD3OD) δ 73.3, 82.1, 113.9, 116.8,
135.2, 160.1; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m, Agilent
Technologies) carrier gas flow rate = He gas, 1 mL/min, initial column
temp = 273 K, final column temp = 573 K, progress rate = 20 deg/min,
retention time = 15.3 min; MS (EI) m/z (%) 234.8 (100%) [Mþ].
4,40-(Buta-1,3-diyne-1,4-diyl)ethyl benzoate (4e):23 1H
NMR (300 MHz, CDCl3) δ 1.38 (t, J = 6.9 Hz, 6H), 4.36 (q, J = 6.9
Hz, 4H), 7.56 (dd, J = 6.9, 1.5 Hz, 4H), 8.00 (dd, J = 6.6, 1.5 Hz, 4H); 13C
NMR (75 MHz, CDCl3) δ 14.5, 61.5, 76.4, 82.1, 126.2, 129.7, 131.1,
132.6, 165.9; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m, Agilent
Technologies) carrier gas flow rate = He gas, 1 mL/min, initial column
temp = 273 K, final column temp = 573 K, progress rate = 20 deg/min,
retention time = 18.8 min; MS (EI) m/z (%) 346.5 (100%) [Mþ].
1,4-Bis(4-fluorophenyl)buta-1,3-diyne (4f):23 1H NMR (300
MHz, CDCl3) δ 6.99-7.05 (m, 4H), 7.47-7.51 (m, 4H); 13C NMR
(75 MHz, CDCl3) δ 73.5, 80.4, 115.8, 116.1, 117.78, 117.84, 134.5,
134.6, 161.4, 164.7; GC (HP-5MS capillary column, 0.32 mm ꢀ 60 m,
Agilent Technologies) carrier gas flow rate = He gas, 1 mL/min, initial
column temp = 273 K, final column temp = 573 K, progress rate = 20
deg/min, retention time = 10.0 min; MS (EI) m/z (%) 238.5 (100%)
[Mþ].
’ ASSOCIATED CONTENT
S
Supporting Information. Spectroscopic data for all com-
b
pounds. This material is available free of charge via the Internet at
http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Phone: þ82-52-259-2339. Fax: þ82-52-259-2348. E-mail:
insukim@ulsan.ac.kr.
’ ACKNOWLEDGMENT
This work was supported by the National Research Founda-
tion of Korea (No. 2010-0002465) and the Priority Research
Centers Program (No. 2009-0093818) through the National
Research Foundation of Korea funded by the Ministry of
Education, Science and Technology.
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1,4-Bis(3-methoxyphenyl)buta-1,3-diyne (4g):24 1H NMR
(300 MHz, CDCl3) δ 3.82 (s, 6H), 6.93-6.97 (m, 2H), 7.06 (br, 2H),
7.13-7.16 (m, 2H), 7.26-7.29 (m, 2H); 13C NMR (75 MHz, CDCl3)
δ 55.5, 73.8, 81.7, 116.3, 117.3, 122.9, 125.3, 129.8, 159.5; GC (HP-5MS
capillary column, 0.32 mm ꢀ 60 m, Agilent Technologies) carrier gas
flow rate = He gas, 1 mL/min, initial column temp = 273 K, final column
temp = 573 K, progress rate = 20 deg/min, retention time = 13.5 min;
MS (EI) m/z (%) 262.8 (100%) [Mþ].
2218
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