Tandem suzuki-miyaura cross-coupling/dehydrobromination of 1,1-dibromoalkenes to alkynes with a cyclobutene-1,2-diylbis(imidazolium) salt as catalyst precursor

Article abstract of DOI:10.1055/s-0029-1218848

A cyclobutene-1,2-bis(imidazolium) salt proved to be an efficient catalyst precursor for one-pot tandem Suzuki-Miyaura/dehydrobromination reactions for the synthesis of alkynes starting from 1,1-dibromoalkenes and palladium(II) acetate, aryl boronic acids, and potassium tert-butoxide in toluene. Starting materials were prepared from aldehydes under Corey-Fuchs conditions. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0029-1218848

PAPER
2621
Tandem Suzuki–Miyaura Cross-Coupling/Dehydrobromination of
1,1-Dibromoalkenes to Alkynes with a Cyclobutene-1,2-diylbis(imidazolium)
Salt as Catalyst Precursor
Synthesis of
A
lkyn
l
es from
i
1,1-
D
r
ibromoa
e
lkenes za Rahimi, Andreas Schmidt*
Clausthal University of Technology, Institute of Organic Chemistry, Leibnizstr. 6, 38678 Clausthal-Zellerfeld, Germany
Fax +49(5323)723861; E-mail: schmidt@ioc.tu-clausthal.de
Received 17 February 2010; revised 12 April 2010
enes,10 and internal alkynes.11 In addition, the Suzuki–
Abstract: A cyclobutene-1,2-bis(imidazolium) salt proved to be an
efficient catalyst precursor for one-pot tandem Suzuki–Miyaura/
dehydrobromination reactions for the synthesis of alkynes starting
from 1,1-dibromoalkenes and palladium(II) acetate, aryl boronic
Miyaura reaction of boronic esters with dibromides to
alkynes has been reported.12 In organic synthesis, the
Stille coupling of 1,1-dibromoalk-1-enes for the prepara-
acids, and potassium tert-butoxide in toluene. Starting materials tion of alkynes13 plays an important role.14 In continuation
of our interest in N-heterocyclic carbenes15 we report here
were prepared from aldehydes under Corey–Fuchs conditions.
a new application of a cyclobutene-1,2-bis(imidazolium)
salt developed in our laboratory.16 This salt serves as cat-
alyst precursor for efficient one-pot tandem Suzuki–
Miyaura/dehydrobromination reactions for the synthesis
of alkynes starting from 1,1-dibromoalkenes, which were
prepared from aldehydes under Corey–Fuchs conditions.
Key words: imidazol-2-ylidene, N-heterocyclic carbene, biscar-
bene complex, Corey–Fuchs reaction
The alkyne moiety represents a functional group of high
energy, which is able to undergo a broad variety of reac-
tions. As a consequence numerous books,1 reference
works,2 and review articles3 dealing with the chemistry
and applications of alkynes have appeared. Whereas the
development of alkynes as starting materials in the re-
search laboratories to valuable intermediates in industrial
chemistry was initiated by Reppe in the 1940s, new syn-
thetic methods employing novel types of transition-metal
catalysts for the coupling of an alkyne moiety with almost
any other molecule were established in the 1970s. More
recently, considerable interest has focused on alkynes
from the viewpoint of materials chemistry, as they play
important roles in highly conjugated organic molecules,4
which are potentially useful or already applied in the areas
of photonics, optoelectronics, molecular electronics,
field-effect transistors, organic light-emitting diodes, so-
lar cells, and solid-state lasers.5 In addition, a plethora of
natural products with alkyne units have been reported.6
Solutions of the aldehydes 1a–h and tetrabromomethane
were treated with PPh3 at 0 °C to room temperature17 to
give the 1,1-dibromoalkenes 2a–h (Scheme 1). The tan-
dem Suzuki–Miyaura/dehydrobromination reaction for
the synthesis of the alkynes 3a–h proceeded in the pres-
ence of Pd(OAc)2, the title bis(imidazolium) salt 4, and
potassium tert-butoxide in the temperature range of 65–
90 °C in good to excellent yields. All results are summa-
rized in Table 1.
Br
CBr4, Ph3P, CH2Cl2
0 °C (30 min), then r.t., 1 h
R
Br
RCHO
1a–h
2a–h
(HO)2B Ar
Pd(OAc)2 (3.0 mol%)
salt 4 (3.0 mol%)
KOt-Bu (3.0 equiv)
toluene, 2.5–5 h
Elimination strategies are useful for the synthesis of
alkynes, and these involve 1,2- as well as 1,1-elimina-
tions.7 The conversion of an aldehyde by chain extension
into a 1,1-dibromovinyl derivative, which gives an alkyne
on treatment with strong bases such as BuLi is known as
the Corey–Fuchs reaction.8 A modification has been re-
ported in which the 1,1-dibromoalkene is treated with 1,8-
diazabicyclo[5.4.0]undec-7-ene in DMSO to yield 1-bro-
moalkynes, which are valuable starting materials for
Cadiot–Chodkiewicz couplings.9 1,1-Dibromoalkenes are
also known to react under Suzuki–Miyaura conditions
with a broad variety of boronic acids to tri- and tetrasub-
stituted alkenes, (Z)-1-aryl- or (Z)-alkenyl-1-bromoalk-1-
Ar
Br
R
Me
Cl
Cl
N
N+
Cl
Cl
–
2 BF4
– HBr
Ar
N+
N
Me
R
4
3a–h
Scheme 1
SYNTHESIS 2010, No. 15, pp 2621–2625
x
x.
x
x
.
2
0
1
0
Advanced online publication: 25.06.2010
DOI: 10.1055/s-0029-1218848; Art ID: T03910SS
© Georg Thieme Verlag Stuttgart · New York

2622
A. Rahimi, A. Schmidt
PAPER
Table 1 Alkyne Syntheses by the Title Reaction
Entry Aldehyde 1
1,1-Dibromoalkene 2 Yield
Boronic acid
Alkyne 3
Time Temp Yield
(h)
(%)a of 2
(°C) (%)a of 3
Br
Br
CHO
a
79
2.5
65
65
70
80
81
73
(HO)2B
Br
Br
CHO
p-Tol
b
81
77
3
4
(HO)2B
(HO)2B
p-Tol
Br
Br
CHO
c
Br
MeO
CHO
Br
d
e
71
63
5
90
65
71b
(HO)2B
MeO
Ph
MeO
Br
Br
N
CHO
3.5
83
(HO)2B
N
N
Ph
Br
CHO
Ph
Br
f
77
5
70
74
(HO)2B
(HO)2B
(HO)2B
Ph
Br
Ph
Br
CHO
Cl
Cl
Cl
g
63
89
5
80
65
69
79
N
N
N
O
O
O
TMS
TMS
TMS
o-Tol
Br
Br
CHO
h
3.5
a Yields refer to isolated products characterized by spectroscopic and analytical data (1H and 13C NMR, EIMS, IR, CHN analyses).
b Four mol% of Pd(OAc)2 were used.
The Suzuki–Miyaura reaction between 3-(2,2-dibromovi- 65 °C and required a reaction time of 17 hours. After that
nyl)pyridine and phenylboronic acid (Table 1, entry e) is time, Bu4NOH was added to the mixture to perform the
literature known. This reaction was performed with dehydrobromination within one additional hour. 3-(Phe-
Pd2dba3, tri(2-furyl)phosphine, and Cs2CO3 in water at nylethynyl)pyridine was finally isolated in 67% yield.11
Synthesis 2010, No. 15, 2621–2625 © Thieme Stuttgart · New York

PAPER
Synthesis of Alkynes from 1,1-Dibromoalkenes
2623
(E)-1,1-Dibromo-4-phenylbuta-1,3-diene (2f)
Our system gave 83% yield in 3.5 hours at the same tem-
perature. To the best of our knowledge, all other com-
pounds of Table 1 have been prepared for the first time by
a one-pot tandem Suzuki–Miyaura/dehydrobromination
reaction.
Yield: 77%; colorless solid; mp 51–53 °C (Lit.20 mp 45 °C).
5-Chloro-3-(2,2-dibromovinyl)-1-(2-trimethylsilylethoxymeth-
yl)indole (2g)
Protection of NH: 5-Chloroindole-3-carboxaldehyde (0.75 g, 4.1
mmol) was dissolved in DMF (15 mL) at 0 °C under N2, and then
NaH (60%, 0.2 g, 5 mmol) and SEMCl (0.736 g, 4.2 mmol) were
added subsequently. The reaction mixture was stirred for 1 h, then
quenched with sat. aq NH4Cl (10 mL). The product was extracted
with CH2Cl2 (3 × 40 mL). The combined organic layers were sub-
sequently washed with H2O (100 mL) and brine (50 mL), and dried
(Na2SO4). The solvent was then evaporated and the residue was pu-
rified by flash column chromatography (PE–EtOAc, 2:1) to give
1.05 g (81%) of 5-chloro-3-formyl-1-(2-trimethylsilylethoxymeth-
yl)indole as a colorless solid, mp 97–98 °C.
The 1H and 13C NMR spectra were recorded on Bruker Avance 400
and Avance DPX-200 spectrometers. Chemical shifts d are reported
in ppm relative to TMS as the internal standard. FT-IR spectra were
obtained using a Bruker Vektor 22 spectrometer in the range of 400
to 4000 cm–1. Solids were recorded as pellets (2.5%) in KBr and oils
as films between NaCl plates. The mass spectra were recorded on a
Hewlett Packard HP 5989 spectrometer. The electrospray ioniza-
tion mass spectra (ESIMS) were obtained using an Agilent LCMSD
series HP 1100 with APIES. Melting points are uncorrected and
were determined in an apparatus according to Dr. Tottoli (Büchi).
Yields were not optimized. Petroleum ether (PE) used refers to the
fraction boiling in the range 60–70 °C.
IR (KBr): 3105, 3047, 2952, 2919, 2812, 1650, 1537, 1398, 1082,
830 cm–1.
1H NMR (400 MHz, CDCl3): d = 10.04 (s, 1 H), 8.35 (d, J = 2.0 Hz,
1 H), 7.84 (s, 1 H), 7.49 (d, J = 8.7 Hz, 1 H), 7.35 (dd, J = 8.7, 2.0
Hz, 1 H), 5.56 (s, 2 H), 3.55 (t, J = 8.0 Hz, 2 H), 0.96 (t, J = 8.0 Hz,
2 H), 0.00 (s, 9 H).
13C NMR (100 MHz, CDCl3): d = 186.1, 140.2, 136.9, 130.8, 128.0,
126.3, 123.2, 119.8, 113.3, 76.4, 68.2, 19.1, 0.0.
MS (70 eV): m/z = 309 [M+].
1,1-Dibromoalkenes 2; General Procedure
To a solution of the corresponding aldehyde 1 (7.2 mmol) and CBr4
(7.2 mmol) in CH2Cl2 (15 mL) at 0 °C was added a solution of PPh3
(14.4 mmol) in CH2Cl2 (10 mL). The reaction mixture was main-
tained for 30 min at this temperature. Then, the ice bath was re-
moved and the stirring was continued for 1 h. Petroleum ether (10
mL) was then added to the reaction mixture, which was filtered
through a short column of silica gel to remove the Ph3PO, and
washed with n-hexane (2 × 30 mL). The solvent was evaporated and
the residue was finally purified by flash column chromatography
(silica gel; PE–EtOAc, 20:1).
Anal. Calcd for C15H20ClNO2Si: C, 58.14; H, 6.51; N, 4.52. Found:
C, 58.31; H, 6.65; N, 4.39.
Corey–Fuchs Reaction: The conditions described in the general
procedure were applied to give 2.0 g (63%) of 2g as a viscous yel-
low oil.
1,1-Dibromo-2-phenylethene (2a)18
Yield: 79%; light yellow oil.
IR (film): 3128, 3016, 2953, 2893, 1527, 1469, 1354, 1249, 1086,
857, 836, 813 cm–1.
1H NMR (400 MHz, CDCl3): d = 8.03 (s, 1 H), 7.65 (d, J = 7.4 Hz,
1 H), 7.47 (d, J = 8.6 Hz, 1 H), 7.29 (d, J = 8.6 Hz, 1 H), 5.52 (s, 2
H), 3.53 (t, J = 8.0 Hz, 2 H), 0.95 (t, J = 8.0 Hz, 2 H), 0.00 (s, 9 H).
1,1-Dibromo-2-(4-methylphenyl)ethane (2b)18
Yield: 81%; colorless oil.
13C NMR (100 MHz, CDCl3): d = 133.9, 128.9, 128.5, 127.7, 126.9,
123.5, 118.1, 111.4, 111.4, 85.8, 76.2, 66.2, 17.6, –1.5.
1,1-Dibromo-2-cyclopentylethene (2c)
Yield: 77%; light yellow oil.
IR (film): 2959, 2869, 1794, 1716, 1450, 1290, 966 cm–1.
MS (70 eV): m/z = 465 [M+].
1H NMR (400 MHz, CDCl3): d = 6.31 (d, J = 9.0 Hz, 1 H), 2.72–
2.62 (m, 1 H), 1.93–1.85 (m, 2 H), 1.71–1.54 (m, 4 H), 1.35–1.26
(m, 2 H).
Anal. Calcd for C16H20Br2ClNOSi: C, 41.27; H, 4.33; N, 3.01.
Found: C, 41.08; H, 4.21; N, 3.13.
13C NMR (100 MHz, CDCl3): d = 143.7, 87.2, 44.0, 32.0, 25.1.
MS (70 eV): m/z = 254 [M+].
9-(2,2-Dibromovinyl)anthracene (2h)
Yield: 89%; yellow crystals; mp 141–142 °C (Lit.18 mp 140 °C).
Alkynes 3 by Suzuki–Miyaura/Dehydrobromination Reaction;
General Procedure
Anal. Calcd for C7H10Br2: C, 33.11; H, 3.97. Found: C, 33.34; H,
3.78.
A flame-dried two-necked flask was charged with salt 4 (3.0
mol%), arylboronic acid, Pd(OAc)2, and base, capped with a rubber
septum, and then evacuated and backfilled with N2. To the flask
were sequentially added the gem-dibromoalkene 2 and toluene via
a syringe. Bromides, which were solid at r.t., were added during the
initial charge, prior to the evacuation/backfill. Then, the reaction
mixture was stirred at the mentioned temperature for the indicated
period of time (Table 1). Filtration and flash column chromatogra-
phy gave the corresponding alkynes.
Dibromo-2-(2¢-methyl-4¢-methoxyphenyl)ethane (2d)
Yield: 71%; yellow oil.
IR (film): 3047, 2961, 1633, 1527, 1216, 1017, 837 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.58 (m, 2 H), 7.48 (s, 1 H), 7.33
(s, 1 H), 3.84 (s, 3 H), 2.51 (s, 3 H).
13
C NMR (100 MHz, CDCl3): d = 156.5, 142.3, 133.2, 131.8,
129.0, 123.9, 114.5, 91.6, 54.8, 20.8.
MS (70 eV): m/z = 306 [M+].
Diphenylacetylene (3a)
Anal. Calcd for C10H10Br2O: C, 39.25; H, 3.29. Found: C, 39.37; H,
3.44.
Phenylboronic acid (146.5 mg, 1.20 mmol), 1,1-dibromo-2-phe-
nylethene (262 mg, 1.0 mmol), KOt-Bu (336.6 mg, 3.0 mmol),
Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg, 0.03 mmol) in
toluene (5 mL) were used. Flash column chromatography was per-
formed on silica gel (PE) to provide 143 mg (80%) of the title com-
pound as a colorless solid; mp 58–59 °C (Lit.21 mp 58–60 °C).
3-(2,2-Dibromoethenyl)pyridine (2e)
Yield: 63%; light brown solid; mp 54–56 °C (Lit.19 mp 57–59 °C).
Synthesis 2010, No. 15, 2621–2625 © Thieme Stuttgart · New York

2624
A. Rahimi, A. Schmidt
PAPER
IR (KBr): 3024, 1605, 1490, 756 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.54–7.51 (m, 2 H), 7.34–7.32 (m,
3 H).
13C NMR (100 MHz, CDCl3): d = 131.7, 128.4, 128.3, 123.3, 89.4.
MS (70 eV): m/z = 178 [M+].
1H NMR (400 MHz, CDCl3): d = 8.76 (s, 1 H), 8.52 (d, J = 5.0 Hz,
1 H), 7.78 (dt, J = 7.8, 2.0 Hz, 1 H), 7.56–7.52 (m, 2 H), 7.37–7.33
(m, 3 H), 7.29 (d, J = 7.8 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 152.2, 148.4, 138.3, 131.6, 128.7,
128.3, 123.0, 122.4, 120.3, 92.5, 85.9.
MS (70 eV): m/z = 179 [M+].
Anal. Calcd for C14H10: C, 94.34; H, 5.66. Found: C, 94.47; H, 5.51.
Anal. Calcd for C13H9N: C, 87.12; H, 5.06; N, 7.82. Found: C,
87.31; H, 4.89; N, 7.73.
Bis(4-methylphenyl)acetylene (3b)
4-Methylphenylboronic acid (163.2 mg, 1.20 mmol), 1,1-dibromo-
2-(4-methylphenyl)ethene (276 mg, 1.0 mmol), KOt-Bu (336.6 mg,
3.0 mmol), Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg,
0.03 mmol) in toluene (5 mL) were used; yield: 167 mg (81%); col-
orless solid, mp 127–129 °C (Lit.22 mp 127–128 °C).
(1E)-1,4-Diphenylbut-3-en-1-yne (3f)
Phenylboronic acid (146.5 mg, 1.20 mmol), (E)-1,1-dibromo-4-
phenylbuta-1,3-diene (288 mg, 1.0 mmol), KOt-Bu (336.6 mg, 3.0
mmol), Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg, 0.03
mmol) in toluene (5 mL) were used; yield: 151 mg (74%); colorless
solid; mp 92–94 °C (Lit.24 mp 95–96 °C).
IR (KBr): 3023, 2210, 1605, 1493, 1412, 817 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.34 (dd, J = 7.8, 1.8 Hz, 2 H),
7.07 (dd, J = 7.8, 1.8 Hz, 2 H), 2.29 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 138.1, 132.4, 130.4, 120.3, 88.9,
20.6.
IR (KBr): 3027, 1967, 1604, 1495, 1430, 1175, 774 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.47–7.28 (m, 10 H), 7.03 (d,
J = 15.5 Hz, 1 H), 6.37 (d, J = 15.5 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 141.2, 136.3, 131.5, 128.7, 128.6,
128.3, 128.1, 126.3, 123.4, 108.1, 91.7, 88.9.
MS (70 eV): m/z = 206 [M+].
MS (70 eV): m/z = 204 [M+].
Anal. Calcd for C16H14: C, 93.16; H, 6.84. Found: C, 93.34; H, 6.67.
Anal. Calcd for C16H12: C, 94.08; H, 5.92. Found: C, 94.21; H, 5.83.
Cyclopentylphenylacetylene (3c)
Phenylboronic acid (146.5 mg, 1.20 mmol), 1,1-dibromo-2-cyclo-
pentylethene (254 mg, 1.0 mmol), KOt-Bu (336.6 mg, 3.0 mmol),
Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg, 0.03 mmol) in
toluene (5 mL) were used; yield: 124 mg (73%); colorless oil.
5-Chloro-3-(phenylethynyl)-1-(2-trimethylsilylethoxymeth-
yl)indole (3g)
Phenylboronic acid (146.5 mg, 1.20 mmol), 5-chloro-3-(2,2-dibro-
movinyl)-1-(2-trimethylsilylethoxymethyl)indole (466 mg, 1.0
mmol), KOt-Bu (336.6 mg, 3.0 mmol), Pd(OAc)2 (7.5 mg, 0.03
mmol), and salt 4 (16.8 mg, 0.03 mmol) in toluene (5 mL) were
used; yield: 263 mg (69%); light yellow solid; mp 77–79 °C.
IR (film): 2967, 2876, 2227, 1495, 823 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.53–7.51 (m, 2 H), 7.39–7.35 (m,
2 H), 7.29–7.25 (m, 1 H), 2.77–2.73 (m, 1 H), 1.95–1.88 (m, 2 H),
1.71–1.68 (m, 4 H), 1.64–1.61 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 131.6, 128.8, 127.2, 124.2, 94.6,
80.1, 34.0, 30.9, 25.1.
IR (KBr): 3059, 2954, 2925, 1660, 1470, 1448, 1278, 1125, 919,
799 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.87 (s, 1 H), 7.64 (d, J = 8.7 Hz,
1 H), 7.55 (d, J = 8.7 Hz, 1 H), 7.31 (s, 1 H), 7.17–7.11 (m, 5 H),
5.31 (s, 2 H), 3.26 (t, J = 8.0 Hz, 2 H), 0.85 (t, J = 8.0 Hz, 2 H), 0.00
(s, 9 H).
MS (70 eV): m/z = 170 [M+].
Anal. Calcd for C13H14: C, 91.71; H, 8.29. Found: C, 91.57; H, 8.43.
13C NMR (100 MHz, CDCl3): d = 144.8, 139.7, 138.6, 133.9, 128.9,
128.5, 127.7, 126.9, 123.5, 118.1, 111.4, 111.3, 92.3, 83.2, 76.3,
66.2, 17.6, –1.0.
3-Methyl-4-(phenylethynyl)anisole (3d)
Phenylboronic acid (146.5 mg, 1.20 mmol), dibromo-2-(2¢-methyl-
4¢-methoxyphenyl)ethene (306 mg, 1.0 mmol), KOt-Bu (336.6 mg,
3.0 mmol), Pd(OAc)2 (10 mg, 0.04 mmol), and salt 4 (22.4 mg, 0.04
mmol) in toluene (5 mL) were used; yield: 158 mg (71%); colorless
solid; mp 73–74 °C (Lit.23 mp 78–79 °C).
MS (70 eV): m/z = 381 [M+].
Anal. Calcd for C22H24ClNOSi: C, 69.18; H, 6.33; N, 3.67. Found:
C, 69.31; H, 6.47; N, 3.51.
IR (KBr): 3017, 2983, 2824, 1492, 1157, 853 cm–1.
1H NMR (400 MHz, CDCl3): d = 7.57 (d, J = 7.8 Hz, 2 H), 7.46 (d,
J = 8.2 Hz, 1 H), 7.43–7.33 (m, 3 H), 6.82 (d, J = 2.0 Hz, 1 H), 6.75
(dd, J = 8.2, 2.0 Hz, 1 H), 3.82 (s, 3 H), 2.54 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 159.5, 142.0, 133.1, 131.3, 128.3,
127.8, 123.9, 115.2, 115.0, 111.2, 91.9, 88.3, 55.2, 21.0.
9-(o-Tolylethynyl)anthracene (3h)
2-Methylphenylboronic acid (163.2 mg, 1.20 mmol), 9-(2,2-dibro-
movinyl)anthracene (362 mg, 1.0 mmol), KOt-Bu (336.6 mg, 3.0
mmol), Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg, 0.03
mmol) in toluene (5 mL) were used; yield: 230 mg (79%); yellow
solid; mp 87–88 °C.
MS (70 eV): m/z = 222 [M+].
IR (KBr): 3049, 2963, 1622, 1485, 1453, 1262, 1098, 1024, 884,
803, 755 cm–1.
1H NMR (400 MHz, CDCl3): d = 8.67 (dd, J = 8.7, 0.7 Hz, 2 H),
8.41 (s, 1 H), 8.00 (d, J = 8.5 Hz, 2 H), 7.75 (dd, J = 7.6, 1.6 Hz, 1
H), 7.60–7.56 (m, 2 H), 7.51–7.47 (m, 2 H), 7.33–7.25 (m, 3 H),
2.73 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 140.0, 132.6, 132.2, 131.3, 129.7,
128.8, 128.6, 127.7, 126.8, 126.7, 125.8, 125.7, 123.6, 117.7, 99.8,
90.2, 21.4.
Anal. Calcd for C16H14O: C, 86.45; H, 6.35. Found: C, 86.32; H,
6.50.
3-(Phenylethynyl)pyridine (3e)
Phenylboronic acid (146.5 mg, 1.20 mmol), 3-(2,2-dibromoethen-
yl)pyridine (263 mg, 1.0 mmol), KOt-Bu (336.6 mg, 3.0 mmol),
Pd(OAc)2 (7.5 mg, 0.03 mmol), and salt 4 (16.8 mg, 0.03 mmol) in
toluene (5 mL) were used; yield: 149 mg (83%); mp 53–54 °C
(Lit.23 mp 48–50 °C).
IR (KBr): 3042, 2198, 1567, 1473, 1395, 784 cm–1.
MS (70 eV): m/z = 292 [M+].
Anal. Calcd for C23H16: C, 94.48; H, 5.52. Found: C, 94.31; H, 5.67.
Synthesis 2010, No. 15, 2621–2625 © Thieme Stuttgart · New York

PAPER
Synthesis of Alkynes from 1,1-Dibromoalkenes
2625
(11) (a) Chelucci, G.; Capitta, F.; Baldino, S.; Pinna, G. A.
Acknowledgment
Tetrahedron Lett. 2007, 48, 6514. (b) Chelucci, G.; Capitta,
F.; Baldino, S. Tetrahedron 2008, 64, 10250.
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The Deutsche Forschungsgemeinschaft (DFG) is gratefully
acknowledged for financial support.
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