Efficient palladium-catalyzed cross-coupling reaction of alkynyl halides with organoboronic acids under aerobic conditions

Article abstract of DOI:10.1055/s-0031-1290159

Ligand-free palladium-catalyzed cross-coupling reaction of alkynyl halides with organoboronic acids under aerobic conditions has been developed. In the presence of bis(dibenzylideneacetone)palladium(0) and cesium carbonate, a variety of alkynyl halides (I, Br, and Cl) underwent the Suzuki-Miyaura cross-coupling reaction with organoboronic acids at room temperature to afford the corresponding unsymmetrical diarylalkynes in moderate to good yields. It is noteworthy that this is first report on the reaction of alkynyl chlorides with arylboronic acids. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0031-1290159

PAPER
541
Efficient Palladium-Catalyzed Cross-Coupling Reaction of Alkynyl Halides
with Organoboronic Acids under Aerobic Conditions
P
alladium
i
-Cataly
a
ze
d
Cross-
C
oupling Re
a
ction un
S
de
r
A
erobic
Ch
onditions eng Tang,*a,b Mi Tian,a Wen-Bing Sheng,a Can-Cheng Guo*a
a
College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P. R. of China
Fax +86(731)88821488; E-mail: ccguo@hnu.edu.cn
b
Mathematics and Science Department, Hunan First Normal University, Changsha 410205, P. R. of China
Fax +86(731)82841056; E-mail: hnyztjs@163.com
Received 12 November 2011; revised 12 December 2011
Pd(dba)2, Cs2CO3
MeOH, r.t., air
R2 B(OH)2
R1
X
R1
R2
Abstract: Ligand-free palladium-catalyzed cross-coupling reaction
of alkynyl halides with organoboronic acids under aerobic condi-
tions has been developed. In the presence of bis(dibenzylideneace-
tone)palladium(0) and cesium carbonate, a variety of alkynyl
halides (I, Br, and Cl) underwent the Suzuki–Miyaura cross-
coupling reaction with organoboronic acids at room temperature to
afford the corresponding unsymmetrical diarylalkynes in moderate
to good yields. It is noteworthy that this is first report on the reaction
of alkynyl chlorides with arylboronic acids.
+
R1 = aryl, heteroaryl, aliphatic R2 = aryl, alkenyl
X = I, Br, Cl
Scheme 1 Palladium-catalyzed synthesis of unsymmetrical diaryl-
alkynes
nyl halides (I, Br, and Cl) with organoboronic acids under
aerobic and ligand-free conditions (Scheme 1).
Key words: palladium, alkynyl halides, organoboronic acids,
cross-coupling reaction, alkynes
The reaction between (iodoethynyl)benzene (1a) and 4-
methoxyphenylboronic acid (2a) was chosen as a model
reaction to screen the optimal reaction conditions, and the
results are summarized in Table 1. Initially, the effect of
the palladium catalyst was examined. The results showed
that treatment of iodoalkyne 1a with 2a using 0.1 mol%
palladium catalyst and two equivalents of cesium carbon-
ate in methanol under air atmosphere for 12 hours afford-
ed the desired product 3 in 78, 60, 48, 83, and 90% yield,
respectively (Table 1, entries 1–5). Pd(dba)2 turned out to
be the best catalyst in terms of yields, and the amount of
Pd(dba)2 also affected the yield to some extent (entries 5
and 6). No cross-coupling product was generated in a con-
trol experiment without the palladium catalyst (entry 7). A
set of bases, such as cesium carbonate, potassium carbon-
ate, potassium acetate, sodium methoxide, potassium
phosphate, and triethylamine were then investigated, and
cesium carbonate gave the best result (entries 5 and 8–12).
Finally, some solvents, including methanol, ethanol, iso-
propanol, tetrahydrofuran, N,N-dimethylformamide, and
acetonitrile were also tested, and methanol provided the
highest yield (entries 5 and 13–17).
The acetylenic subunit is a useful building block in organ-
ic synthesis and a commonly found motif in many natural
products.1 Among the methods for the synthesis of
alkynes, the traditional Sonogashira cross-coupling reac-
tion has proven to be the most commonly used tool.2 How-
ever, it does not work well for electron-poor alkynes.
Therefore, the development of a novel cross-coupling al-
ternative to these alkynes synthesis is of interest.3–5 Re-
cently, Sun and co-workers reported a palladium(II)
chloride catalyzed cross-coupling reaction of arylalkyne
iodides with arylboronic acids to afford moderate to good
yields of the corresponding products.5b However, the re-
action required a high loading of palladium(II) chloride
(1–5 mol%), and no reactions involving the synthesis of
arylalkyne analogues were reported. Subsequently, Wang
and co-workers extended the scope to organoboronic
acids using a magnetic-nanoparticle-supported palladi-
um(II) and only examples of alkynyl bromides were de-
scribed.5d Very recently, we also reported a modified
protocol for the synthesis of internal alkynes, such as N,3-
diarylphenylpropiolamides, by palladium(II) acetate cata-
lyzed Suzuki–Miyaura cross-coupling reaction of alkynyl
iodides with arylboronic acids.5c To the best of our knowl-
edge, no reactions involving the synthesis of alkynyl chlo-
rides with arylboronic acids have been reported. As an
extension of our work, we report here a simple system
With the optimal reaction conditions in hand, the scope of
alkynyl halides with organoboronic acids was investigat-
ed (Table 2). Initially, a variety of organoboronic acids
2b–j were investigated by reacting with (iodoethy-
nyl)benzene (1a) (Table 2, entries 1–9). The results dem-
onstrated that the optimal conditions were general for
arylboronic acids and styrylboronic acid, and compatible
with several functional groups, including methyl, meth-
oxy, chloro, acetyl, nitro, and cyano groups on the aryl
moiety. For example, phenylboronic acid (2b) or the
methyl-substituted arylboronic acids 2c–e smoothly un-
derwent the reaction with substrate 1a, 0.1 mol%
Pd(dba)2, and two equivalents of cesium carbonate under
air atmosphere in good yields, although the ortho-substi-
such
as
bis(dibenzylideneacetone)palladium(0)
[Pd(dba)2] and cesium carbonate for the general Suzuki–
Miyaura cross-coupling reaction of a wide range of alky-
SYNTHESIS 2012, 44, 541–546
x
x
.x
x
.2
0
1
2
Advanced online publication: 16.01.2012
DOI: 10.1055/s-0031-1290159; Art ID: H105711SS
© Georg Thieme Verlag Stuttgart · New York

542
J.-S. Tang et al.
PAPER
Table 1 Screening Optimal Conditionsa
Pd
I
+ MeO
B(OH)2
OMe
1a
2a
3
Entry
1
Pd catalyst
Pd(OAc)2
PdCl2
Base
Solvent
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
EtOH
Yield (%)b
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
K2CO3
KOAc
NaOMe
K3PO4
Et3N
78
60
48
83
90
47
0
2
3
PdCl2(MeCN)2
Pd(PPh3)4
Pd(dba)2
Pd(dba)2
–
4
5
6c
7
8
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
61
32
59
36
32
88
32
11
25
19
9
10
11
12
13
14
15
16
17
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
i-PrOH
THF
DMF
MeCN
a Reaction conditions: 1a (0.3 mmol), 2a (0.36 mmol), Pd catalyst (0.1 mol%), base (2 equiv), solvent (2 mL), 12 h, r.t., air atmosphere.
b Yield of isolated product.
c Pd catalyst (0.01 mol%), for 60 h; the conversion of 1a was 62% (determined by GC analysis).
tution on the arene ring decreased the substrates activity acids were also proceeded efficiently to give the corre-
(entries 1–4). The optimal conditions were compatible sponding cross-coupled products in moderate to good
with chloro-substituted substrate 2f (entry 5). Gratifying- yields (entries 17–21). For example, treatment of 1h with
ly, substrates 2g–i with the activation group, such as arylboronic acids 2a, 2b, and 2c gave the corresponding
acetyl, nitro, or cyano group, was tolerated well (entries products 3, 4, and 5 in 92, 91, and 91% yield, respectively
6–8). Alkenylboronic acid 2j was also a suitable substrate (entries 17–19). A moderate yield of the desirable product
providing moderate yield (entry 9). Subsequently, a num- 12 was isolated from the reaction of substrate 1h with alk-
ber of alkynyl iodides, were examined in the presence of enyl boronic acid 2j (entry 20). The reaction of heteroaryl
arylboronic acid, Pd(dba)2, and cesium carbonate (entries bromoalkyne 1i with phenylboronic acid (2b) also pro-
10–16). Substituted iodoalkynes 1b–d successfully react- ceeded smoothly to produce 94% yield of the correspond-
ed with phenylboronic acid (2b) in moderate to good ing product 15 under the same conditions (entry 21). It is
yields (entries 10, 11, 13). Using heteroaryl iodoalkyne worth mentioning that the system was still effective for
(1e), a good yield of the product was achieved under the the coupling of the alkynyl chlorides, including activated
same conditions (entry 14). Although the activity was re- and deactivated alkynyl chlorides. In the presence of 0.1
duced for the reaction, aliphatic iodoalkynes 1f and 1g mol% Pd(dba)2 and two equivalents of cesium carbonate,
were also suitable substrates leading to the desired prod- treatment of 1j with phenylboronic acid (2b) by prolong-
ucts 16 and 17 smoothly in moderate yields (entries 15 ing the reaction time to 36 hours afforded the desired
and 16).
product in good yield whereas the reactions of alkynyl
chloride 1k with arylboronic acids 2a–c were conducted
smoothly in moderate yields (entries 23–25).
Under the same reaction conditions, the couplings of alky-
nyl bromide and heteroaryl bromoalkyne with arylboronic
Synthesis 2012, 44, 541–546
© Thieme Stuttgart · New York

PAPER
Palladium-Catalyzed Cross-Coupling Reaction under Aerobic Conditions
543
Table 2 Palladium-Catalyzed Cross-Coupling Reaction of Alkynyl Halides 1 with Organoboronic Acids 2a
Pd(dba)2, Cs2CO3
R2 B(OH)2
R1
X
R1
R2
+
MeOH, r.t., 12 h
1
2
Entry
1
Alkynyl halide 1
Organoboronic acid 2
Yield (%)b (Product)
1a
2b
90 (4)
94 (5)
I
I
B(OH)2
2
3
1a
1a
2c
B(OH)2
B(OH)2
B(OH)2
2d
84 (6)
76 (7)
I
I
4
1a
2e
5
6
1a
1a
2f
83 (8)
80 (9)
Cl
B(OH)2
I
I
O
2g
B(OH)2
B(OH)2
7
8
9
1a
1a
1a
2h
78 (10)
84 (11)
68 (12)
I
I
I
O2N
2i
NC
B(OH)2
B(OH)2
2j
I
10
1b
1c
2b
2b
80 (7)
B(OH)2
11
12
82 (10)
91 (13)
O2N
I
I
B(OH)2
1c
2a
O2N
MeO
B(OH)2
13
1d
2b
74 (14)
B(OH)2
I
14
15
16
17
18
19
1e
1f
2b
2b
2b
95 (15)
63 (16)
68 (17)
92 (3)
I
B(OH)2
B(OH)2
B(OH)2
S
n-C6H13
n-C5H11
I
1g
1h
1h
1h
I
2a
Br
Br
Br
MeO
B(OH)2
2b
2c
91 (4)
B(OH)2
91 (5)
B(OH)2
© Thieme Stuttgart · New York
Synthesis 2012, 44, 541–546

544
J.-S. Tang et al.
PAPER
Table 2 Palladium-Catalyzed Cross-Coupling Reaction of Alkynyl Halides 1 with Organoboronic Acids 2a (continued)
Pd(dba)2, Cs2CO3
R2 B(OH)2
R1
X
R1
R2
+
MeOH, r.t., 12 h
1
2
Entry
20
Alkynyl halide 1
Organoboronic acid 2
Yield (%)b (Product)
B(OH)2
1h
2j
67 (12)
Br
Br
21
1i
2b
2b
94 (15)
78 (10)
56 (3)
54 (4)
55 (5)
B(OH)2
S
22c
23c
24c
25c
1j
O2N
Cl
B(OH)2
1k
1k
1k
2a
Cl
Cl
Cl
MeO
B(OH)2
2b
2c
B(OH)2
B(OH)2
a Reaction conditions: 1 (0.3 mmol), 2 (0.36 mmol), Pd(dba)2 (0.1 mol%), Cs2CO3 (2 equiv), MeOH (2 mL), 12 h, r.t., air atmosphere.
b Isolated yield.
c Reaction performed for 36 h.
(Na2SO4), and evaporated in vacuum. The residue was purified by
flash column chromatography on silica gel (hexane–EtOAc) to af-
ford the desired product (Table 2).
In summary, we have developed a mild, efficient, and
general protocol for the synthesis of unsymmetrical diaryl-
alkynes by palladium-catalyzed Suzuki–Miyaura cross-
coupling reaction of alkynyl halides with organoboronic
acids under aerobic and ligand-free conditions. The proto-
col can provide good yields for alkynyl bromides and
alkynyl iodides containing different functional groups us-
ing a relatively lower loading of palladium catalysts and
is also extended to deactivated alkynyl chlorides with
moderate to good yields. Currently, further efforts to ap-
ply these methods in other transformations are underway
in our laboratory.
1-Methoxy-4-(phenylethynyl)benzene (3)2j
Yield starting from alkynyl iodide 1a: 56.2 mg (90%), from alkynyl
bromide 1h: 57.4 mg (92%), from alkynyl chloride 1k: 34.9 mg
(56%); white solid; mp 57.1–59.2 °C.
1H NMR (500 MHz, CDCl3): d = 7.51 (d, J = 2.0 Hz, 2 H), 7.50 (d,
J = 1.0 Hz, 2 H), 7.35–7.29 (m, 3 H), 6.87 (d, J = 9.0 Hz, 2 H), 3.82
(s, 3 H).
13C NMR (125 MHz, CDCl3): d = 159.6, 133.0, 131.4, 128.3, 127.9,
123.6, 115.4, 114.0, 89.4, 88.1, 55.3.
MS (EI, 70 eV): m/z (%) = 208 (100, [M]+).
All chemicals were purchased from commercial suppliers (Aldrich,
USA, and Changsha Chemical Company, China) and used without
purification prior to use. Alkynyl halides 1 were respectively syn-
thesized via iodination, bromination, or chlorination of terminal
alkynes according to the literature.5a,6,7 NMR spectroscopy was per-
formed on a Bruker 500 spectrometer operating at 500 MHz (1H
NMR) and 125 MHz (13C NMR). TMS was used an internal stan-
dard and CDCl3 as the solvent. Mass spectrometric analysis was
performed on GC-MS analysis (Shimadzu GCMS-QP2010 plus).
Melting points were measured on a Kolfler micromelting point hot
stage apparatus and are uncorrected.
1, 2-Diphenylethyne (4)2j
Yield starting from alkynyl iodide 1a: 48 mg (90%), from alkynyl
bromide 1h: 48.6 mg (91%), from alkynyl chloride 1k: 28.8 mg
(54%); white solid; mp 59.4–60.3 °C.
1H NMR (500 MHz, CDCl3): d = 7.54–7.52 (m, 4 H), 7.34 (d,
J = 6.5 Hz, 6 H).
13C NMR (125 MHz, CDCl3): d = 131.6, 128.3, 128.2, 123.3, 89.4.
MS (EI, 70 eV): m/z (%) = 178 (100, [M]+).
1-Methyl-4-(phenylethynyl)benzene (5)2j
Yield starting from alkynyl iodide 1a: 54.1 mg (94%), from alkynyl
bromide 1h: 52.4 mg (91%), from alkynyl chloride 1k: 31.7 mg
(55%); white solid; mp 70.1–72.2 °C.
Palladium-Catalyzed Suzuki–Miyaura Cross-Coupling Reac-
tion of Alkynyl Halides 1 with Organoboronic Acids 2; General
Procedure
1H NMR (500 MHz, CDCl3): d = 7.53–7.51 (m, 2 H), 7.42 (d,
J = 8.0 Hz, 2 H), 7.35–7.31 (m, 3 H), 7.15 (d, J = 8.0 Hz, 2 H), 2.36
(s, 3 H).
13C NMR (125 MHz, CDCl3): d = 138.4, 131.6, 131.5, 129.1, 128.3,
128.0, 123.5, 120.2, 89.6, 88.7, 21.5.
Alkynyl halide 1 (0.3 mmol), organoboronic acid 2 (0.36 mmol),
Pd(OAc)2 (0.1 mol%), Cs2CO3 (2 equiv), and MeOH (2 mL) were
successively added to a Schlenk tube. Then, the mixture was stirred
at r.t. for the indicated time (12 h) until complete consumption of
starting material was observed [reaction monitored by TLC (eluent:
hexane–EtOAc, 60:1) and GC-MS analysis]. The mixture was
washed with brine (3 × 3 mL), extracted with Et2O (3 × 5 mL), dried
MS (EI, 70 eV): m/z (%) = 192 (100, [M]+).
Synthesis 2012, 44, 541–546
© Thieme Stuttgart · New York

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Palladium-Catalyzed Cross-Coupling Reaction under Aerobic Conditions
545
1-Methyl-3-(phenylethynyl)benzene (6)3b
Yield: 48.4 mg (84%); white solid; mp 71.1–73.4 °C.
1H NMR (500 MHz, CDCl3): d = 7.53–7.51 (m, 2 H), 7.36–7.30 (m,
5 H), 7.22 (t, J = 7.5 Hz, 1 H), 7.13 (d, J = 7.5 Hz, 1 H), 2.34 (s, 3
1H NMR (500 MHz, CDCl3): d = 7.47–7.45 (m, 2 H), 7.40 (d,
J = 8.0 Hz, 2 H), 7.33–7.23 (m, 6 H), 7.08 (d, J = 16.0 Hz, 1 H),
6.38 (d, J = 16.0 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 141.2, 136.3, 131.5, 128.7, 128.6,
128.3, 126.3, 123.4, 91.8, 88.9.
H).
13C NMR (125 MHz, CDCl3): d = 138.0, 132.2, 131.6, 129.1, 128.7,
MS (EI, 70 eV): m/z (%) = 204 (100, [M]+).
128.3, 128.2, 128.1, 123.4, 123.1, 89.6, 89.0, 21.2.
1-Methoxy-4-[(4-nitrophenyl)ethynyl]benzene (13)9
Yield: 69.0 mg (91%); yellow solid; mp 120.5–122.2 °C.
MS (EI, 70 eV): m/z (%) = 192 (100, [M]+).
1-Methyl-2-(phenylethynyl)benzene (7)2j
Yield starting from alkynyl iodide 1a: 43.8 mg (76%), from alkynyl
bromide 1b: 46 mg (80%); colorless oil.
1H NMR (500 MHz, CDCl3): d = 8.20 (d, J = 6.0 Hz, 2 H), 7.62 (d,
J = 11.0 Hz, 2 H), 7.60 (d, J = 10.5 Hz, 2 H), 6.90 (d, J = 10.5 Hz,
2 H), 3.84 (s, 3 H).
1H NMR (500 MHz, CDCl3): d = 7.53 (d, J = 7.5 Hz, 2 H), 7.50 (d,
J = 7.5 Hz, 1 H), 7.35–7.32 (m, 3 H), 7.22 (d, J = 4.0 Hz, 2 H),
7.22–7.14 (m, 1 H), 2.51 (s, 3 H).
13C NMR (125 MHz, CDCl3): d = 140.2, 131.8, 131.5, 129.4, 128.3,
128.3, 128.1, 125.6, 123.6, 123.0, 88.3, 20.7.
13C NMR (125 MHz, CDCl3): d = 160.4, 146.7, 134.0, 133.4, 132.0,
123.6, 114.2, 114.1, 95.1, 86.6, 55.3.
MS (EI, 70 eV): m/z (%) = 253 (100, [M]+).
1-(Phenylethynyl)naphthalene (14)5d
Yield: 50.6 mg (74%); colorless oil.
MS (EI, 70 eV): m/z (%) = 192 (100, [M]+).
1H NMR (500 MHz, CDCl3): d = 8.36 (d, J = 8.0 Hz, 1 H), 7.88–
7.86 (m, 2 H), 7.85–7.82 (m, 1 H), 7.77–7.75 (m, 2 H), 7.73 (d,
J = 7.0 Hz, 1 H), 7.66–7.64 (m, 1 H), 7.59–7.58 (m, 1 H), 7.45–7.34
(m, 3 H).
13C NMR (125 MHz, CDCl3): d = 133.2, 133.1, 131.7, 130.4, 129.3,
128.4, 128.3, 127.2, 126.9, 126.4, 126.1, 125.3, 123.4, 120.9, 94.3,
87.5.
1-Chloro-4-(phenylethynyl)benzene (8)5d
Yield: 52.8 mg (83%); white solid; mp 80.1–81.5 °C.
1H NMR (500 MHz, CDCl3): d = 7.62–7.58 (m, 4 H), 7.54–7.53 (m,
2 H), 7.38–7.36 (m, 3 H).
13C NMR (125 MHz, CDCl3): d = 134.3, 132.8, 131.6, 128.7, 128.5,
128.4, 123.0, 121.8, 90.3, 88.2.
MS (EI, 70 eV): m/z (%) = 212 (100, [M]+).
MS (EI, 70 eV): m/z (%) = 228 (100, [M]+).
2-(Phenylethynyl)thiophene (15)10
Yield starting from alkynyl iodide 1e: 52.4 mg (95%), from alkynyl
bromide 1i: 51.9 mg (94%); white solid; mp 49.1–50.5 °C.
1H NMR (500 MHz, CDCl3): d = 7.52–7.49 (m, 2 H), 7.34–7.31 (m,
3 H), 7.26–7.24 (m, 2 H), 6.98–6.97 (m, 1 H).
13C NMR (125 MHz, CDCl3): d = 131.8, 131.4, 128.4, 128.3, 127.2,
127.0, 123.3, 122.9, 93.0, 82.6.
MS (EI, 70 eV): m/z (%) = 184 (100, [M]+).
1-(4-(Phenylethynyl)phenyl)ethanone (9)5c
Yield: 52.8 mg (80%); pale yellow solid; mp 99.2–101.6 °C.
1H NMR (500 MHz, CDCl3): d = 7.93 (d, J = 8.5 Hz, 2 H), 7.59 (d,
J = 7.5 Hz, 2 H), 7.56–7.54 (m, 2 H), 7.36 (d, J = 3.5 Hz, 3 H), 2.60
(s, 3 H).
13C NMR (125 MHz, CDCl3): d = 197.2, 136.2, 131.7, 131.6, 128.8,
128.4, 128.3, 128.2, 122.6, 92.7, 88.6, 26.5.
MS (EI, 70 eV): m/z (%) = 220 (100, [M]+).
Oct-1-ynylbenzene (16)3a
Yield: 35.2 mg (63%); colorless oil.
1H NMR (500 MHz, CDCl3): d = 7.39–7.38 (m, 2 H), 7.27–7.25 (m,
3 H), 2.43 (t, J = 3.5 Hz, 5 H), 2.27–2.24 (m, 2 H), 1.73–1.69 (m, 6
1-Nitro-4-(phenylethynyl)benzene (10)2j
Yield starting from alkynyl iodide 1a: 52.2 mg (78%), from alkynyl
bromide 1c: 54.9 mg (82%), from alkynyl chloride 1j: 52.2 mg
(78%); yellow solid; mp 120.3–122.6 °C.
H).
1H NMR (500 MHz, CDCl3): d = 8.21 (d, J = 9.0 Hz, 2 H), 7.66 (d,
J = 8.5 Hz, 2 H), 7.57–7.55 (m, 2 H), 7.41–7.36 (m, 3 H).
13C NMR (125 MHz, CDCl3): d = 131.5, 128.2, 127.5, 123.9, 94.2,
84.1, 27.7, 27.7, 27.6, 27.6, 20.4, 18.0.
13C NMR (125 MHz, CDCl3): d = 147.0, 132.3, 131.8, 130.3, 129.3,
128.5, 123.6, 122.1, 94.7, 87.5.
MS (EI, 70 eV): m/z (%) = 186 (100, [M]+).
MS (EI, 70 eV): m/z (%) = 223 (100, [M]+).
1-(Hept-1-ynyl)-4-methylbenzene (17)5c
Yield: 37.9 mg (68%); colorless oil.
4-(Phenylethynyl)benzonitrile (11)8
Yield: 51.2 mg (84%); white solid; mp 108.4–110.6 °C.
1H NMR (500 MHz, CDCl3): d = 7.52 (t, J = 4.0 Hz, 2 H), 7.46 (t,
J = 9.0 Hz, 2 H), 7.35–7.31 (m, 5 H).
13C NMR (125 MHz, CDCl3): d = 132.0, 131.9, 131.7, 129.1, 128.5,
128.2, 122.2, 118.4, 111.4, 93.7, 87.7.
MS (EI, 70 eV): m/z (%) = 203 (100, [M]+).
1H NMR (500 MHz, CDCl3): d = 7.28 (d, J = 8.0 Hz, 2 H), 7.07 (d,
J = 8.0 Hz, 2 H), 2.38 (t, J = 7.5 Hz, 2 H), 2.31 (s, 3 H), 1.60 (t,
J = 7.5 Hz, 2 H), 1.44–1.41 (m, 4 H), 0.92 (t, J = 7.5 Hz, 3 H).
13C NMR (125 MHz, CDCl3): d = 137.3, 131.4, 128.9, 121.0, 89.6,
80.5, 31.1, 28.5, 22.2, 21.3, 19.4, 14.0.
MS (EI, 70 eV): m/z (%) = 186 (33, [M]+), 157 (33), 142 (38),
131(69), 129 (100).
(E)-But-1-en-3-yne-1,4-diyldibenzene (12)9
Yield starting from alkynyl iodide 1a: 41.6 mg (68%), from alkynyl
bromide 1h: 41 mg (67%); light yellow solid; mp 97.1–98.6 °C.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synthesis.
© Thieme Stuttgart · New York
Synthesis 2012, 44, 541–546

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J.-S. Tang et al.
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Synthesis 2012, 44, 541–546
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