Copper(II) oxide catalyzed ligand-free coupling reaction of heteroarenes with bromoalkynes

Article abstract of DOI:10.1055/s-0030-1258403

The coupling reaction of imidazoles and pyrazoles with bromoacetylenes has efficiently been carried out under ligand-free conditions in the presence of copper(II) oxide as the catalyst using potassium hydroxide in 1,4-dioxane at 80 C. The method is a simpler access to N-alk-1-ynyl- and/or N-(2-bromovinyl)- substituted heteroarenes. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0030-1258403

816
PAPER
Copper(II) Oxide Catalyzed Ligand-Free Coupling Reaction of Heteroarenes
with Bromoalkynes1
C
opper(II)-Cataly
i
z
ed Co
s
upling of
w
Heteroarenes
w
ith
a
Bromoalk
n
ynes ath Das,* Gandolla Chinna Reddy, Penagaluri Balasubramanyam, N. Salvanna
Organic Chemistry Division-1, Indian Institute of Chemical Technology, Hyderabad 500607, India
Fax +91(40)27160512; E-mail: biswanathdas@yahoo.com
Received 26 November 2010; revised 29 November 2010
Initially the reaction of imidazole with bromo- and io-
Abstract: The coupling reaction of imidazoles and pyrazoles with
bromoacetylenes has efficiently been carried out under ligand-free
conditions in the presence of copper(II) oxide as the catalyst using
potassium hydroxide in 1,4-dioxane at 80 °C. The method is a sim-
do(phenyl)acetylenes was studied under ligand-free con-
ditions using various copper sources and different bases as
well as solvents (Table 1). Bromo(phenyl)acetylene was
pler access to N-alk-1-ynyl- and/or N-(2-bromovinyl)-substituted found to undergo C–N coupling reaction with imidazole
heteroarenes.
to form 1-(phenylethynyl)-1H-imidazole (entries 1–10)
while iodo(phenyl)acetylene was almost inactive (entries
11 and 12). The reaction was carried out at 80 °C; no prod-
uct was isolated at room temperature. Various copper cat-
alysts were examined for the reaction of
bromo(phenyl)acetylene with imidazole, copper(II) oxide
gave the best yields (cf. entry 5 vs. entries 4, 8, and 10). It
is noteworthy that copper(I) iodide was used as the cata-
lyst in earlier cases of the reaction of imidazoles with bro-
moalkynes,8 however, under the present conditions its
Key words: coupling reaction, ligand-free conditions, copper(II)
oxide, N-alkynylheteroarene, N-(2-bromovinyl)heteroarene
N-Alkynylheteroarenes are valuable intermediates in or-
ganic synthesis2 as well as in medicinal chemistry.3 They
are also known to possess important biological3,4 and pho-
toconductive properties.5 However, these compounds
have not yet been properly explored, possibly, due to the
unavailability of mild and general methods for their syn-
thesis.6 Earlier methods for the preparation of N-alkynyl-
Table 1 Optimization of Reaction Conditionsa
heteroarenes,
including
the
elimination
of
N
haloenamines,7a coupling of alkynyliodonium salts,7b and
isomerization of the propargyl group,7c require several
steps. These compounds have also been prepared using
ligand-assisted copper(I) iodide as the catalyst and micro-
wave irradiation.8 Herein, we report a ligand-free efficient
synthesis of N-alkynylheteroarenes.
N
Cu source, base
+
X
Ph
N
solvent
80 °C
10 h
N
H
Ph
Entry
X
Cu Source
Solvent
Base
Yieldb
(%)
In continuation of our work9 on the development of useful
synthetic methodologies, we have discovered that the
treatment of heteroarenes with bromoalkynes in the pres-
ence of a catalytic amount of copper(II) oxide with potas-
sium hydroxide as the base in 1,4-dioxane afforded the
corresponding N-alkynyl- and/or N-(2-bromovinyl)-sub-
stituted heteroarenes at 80 °C (Scheme 1).
1
2
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
CuI
toluene
KOH
50
45
48
22
80
68
72
25
trace
30
CuI
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
toluene
Cs2CO3
K3PO4
K3PO4
KOH
3
CuI
4
Cu(OTf)2
CuO
5
A
A
A
6
CuO
KOH
R1
B
R1
B
R1
CuO, KOH
B
R2
+
and/or
Br
N
N
1,4-dioxane
80 °C
10–14 h
7
CuO
1,4-dioxane
1,4-dioxane
1,4-dioxane
Cs2CO3
KOH
N
Br
2
H
R2
8
Cu(OAc)2
Cu(OTf)2
A = N, B = CH
A = CH, B = N
R2
9
KOH
63–85%
21–38%
1
3
4
10
11
12
CuSO4·5 H2O 1,4-dioxane
KOH
Scheme 1
c
CuI
toluene
Cs2CO3
KOH
–
c
I
CuO
1,4-dioxane
–
a Reaction conditions: imidazole (1.0 mmol), haloalkyne (1.0 mmol),
copper source (2.0 mol%), base (2.0 equiv), solvent (3 mL), 80 °C, 10
SYNTHESIS 2011, No. 5, pp 0816–0820
Advanced online publication: 11.01.2011
DOI: 10.1055/s-0030-1258403; Art ID: Z29810SS
© Georg Thieme Verlag Stuttgart · New York
x
x
.
x
x
.2
0
1
1
h.
b Isolated yield.
c No reaction.

PAPER
Copper(II)-Catalyzed Coupling of Heteroarenes with Bromoalkynes
817
activity was not impressive (entries 1–3). Next examining 16). The conversion was complete within 10–14 hours
the solvent showed that 1,4-dioxane gave superior yields and the N-alkynylimidazoles 3 were formed in high yields
to toluene (entry 5 vs. entry 6). Finally potassium hydrox- (67–85%).
ide and cesium carbonate were examined as the base, po-
tassium hydroxide gave a better yield (80% vs. 72%, entry
5 vs. entry 7). The optimal conditions were using the bro-
moacetylene as substrate with copper(II) oxide as the cat-
alyst, potassium hydroxide as the base, and 1,4-dioxane as
the solvent at 80 °C.
When 4-phenyl-1H-imidazole was treated with bro-
mo(phenyl)acetylene, a mixture of 1,4- and 1,5-regioiso-
mers of 3g were produced in the ratio of 3:2 (entry 7).
However, reaction of 4-phenyl-1H-imidazole with bro-
mo(4-pentylphenyl)acetylene (entry 8) or with bromo(6-
methoxy-2-naphthyl)acetylene (entry 9) gave only the
A series of N-alkynylimidazoles 3 were prepared 1,4-regioisomers. The reaction of 2-ethyl-1H-imidazole
(Table 2) using the optimized conditions (Scheme 1). with bromo(phenyl)acetylene under these conditions
Various substituted imidazoles, including benzimida- yielded 2-ethyl-1-(phenylethynyl)-1H-imidazole (3l) as
zoles, were employed (entries 1–13). Both aromatic and the major product (71%) together with the minor product
aliphatic bromoacetylenes underwent the conversion 1-(2-bromo-1-phenylvinyl)-2-ethyl-1H-imidazole
(4l)
smoothly. Even bromo(6-methoxy-2-naphthyl)acetylene (22%) (entry 12). A similar result was also observed when
afforded the corresponding products (entries 3, 6, 9, and benzimidazole was treated with bromo(6-methoxy-2-
Table 2 C–N Coupling of Bromoalkynes with Imidazoles and Pyrazolesa,b
A
A
R1
A
B
R1
CuO, KOH
B
R2
+
R1
Br
B
+
N
1,4-dioxane
80 °C
10–14 h
N
Br
N
H
1
2
R2
4
R2
3
Entry
Imidazole/Pyrazole 1 R2
Time (h)
Product
Yieldc (%) of 3 Yieldc (%) of 4
1
2
3
Ph
4-Me(CH2)4C6H4
6-methoxy-2-naphthyl
10
12
14
3a
3b
3c
80
78
73
–
–
–
N
N
H
4
5
6
Ph
11
12
13
3d
4e
3f/4f
76
–
67
–
38
24
N
4-Me(CH2)4C6H4
6-methoxy-2-naphthyl
N
H
7
8
9
Ph
10
13
13
14
3g
3h
3i
81d
82
85
78
–
–
–
–
Ph
N
4-Me(CH2)4C6H4
6-methoxy-2-naphthyl
(CH2)5Me
N
H
10
3j
N
11
12
13
Ph
Ph
Ph
10
12
13
3k
68
71
79
–
N
H
N
3l/4l
3m
22
–
N
H
N
N
H
14
15
16
Ph
10
11
14
3n
3o/4o
3p
69
63
72
–
21
–
N
N
4-Me(CH2)4C6H4
6-methoxy-2-naphthyl
N
H
17
Ph
12
3q
69
–
N
H
a Reaction conditions: imidazole/pyrazole (1.0 mmol), haloalkyne (1.0 mmol), CuO (2.0 mol%), KOH (2.0 equiv), 1,4-dioxane (3 mL), 80 °C.
b Compounds 3a, 3d, 3g, 3j, 3k, 3n are known.8
c Isolated yield.
d Ratio of 1,4- to 1,5-regioisomeric products was (3:2).
Synthesis 2011, No. 5, 816–820 © Thieme Stuttgart · New York

818
B. Das et al.
PAPER
1-[(6-Methoxy-2-naphthyl)ethynyl]-1H-imidazole (3c)
naphthyl)acetylene (entry 6). However, when benzimida-
zole was treated with bromo(4-pentylphenyl)acetylene,
1-[2-bromo-1-(4-pentylphenyl)vinyl]-1H-benzimidazole
(4e) was formed as the sole product, though its yield was
low (38%) (entry 5). The olefinic double bond in all the N-
(2-bromovinyl) products was in the Z-configuration as the
olefinic proton did not show any NOESY correlation with
the protons of the imidazole core.
IR (KBr): 2309, 1638, 1498, 1389, 1216 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.98 (s, 1 H), 7.88 (s, 1 H), 7.72
(d, J = 8.0 Hz, 2 H), 7.49 (d, J = 8.0 Hz, 1 H), 7.28–7.05 (m, 4 H),
3.92 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 159.2, 132.0, 129.7, 129.5, 128.9,
127.3, 122.1, 120.0, 106.1, 78.8, 69.0, 55.4.
MS (ESI): m/z = 249 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C16H13N2O: 249.1027; found:
249.1019.
The above reaction was also successfully applied to the
C–N coupling of bromoalkynes with pyrazoles
(Scheme 1) to produce a series of N-alkynylpyrazoles (en-
tries 14–17); the products were formed in good yields
(63–72%) within 10–14 h. The reaction of pyrazole with
bromo(4-pentylphenyl)acetylene afforded both N-alky-
nylpyrazole 3o (major, 63%) and N-(2-bromovinyl)pyra-
zole 4o (minor, 21%) (entry 15). The structures of all the
products were established from their spectral (IR, 1H and
13C NMR, ESIMS and HRESIMS) data.
1-[2-Bromo-1-(4-pentylphenyl)vinyl]-1H-benzimidazole (4e)
IR (KBr): 2310, 1644, 1456 cm–1.
1H NMR (200 MHz, CDCl3): d = 8.01 (m, 1 H), 7.82 (m, 1 H), 7.36–
7.01 (m, 7 H), 6.92 (s, 1 H), 2.59 (t, J = 7.0 Hz, 2 H), 1.71–1.52 (m,
2 H), 1.40–1.24 (m, 4 H), 0.88 (t, J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 146.6, 141.0, 139.0, 135.5, 129.6,
129.0, 126.1, 124.1, 122.9, 120.6, 111.8, 103.7, 36.0, 31.8, 31.1,
22.8, 14.2.
MS (ESI): m/z = 369, 371 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C20H22BrN2: 369.0966; found:
In conclusion, we have developed a simple and efficient
coupling reaction of heteroarenes with bromoacetylenes
using copper(II) oxide (as a catalyst) and potassium hy-
droxide in 1,4-dioxane to prepare N-alk-1-ynyl- and/or N-
(2-bromovinyl)-substituted heteroarenes under ligand-
free conditions. Fourteen new compounds have been pre-
pared.
369.0960.
1-[(6-Methoxy-2-naphthyl)ethynyl]-1H-benzimidazole (3f)
IR (KBr): 2265, 1617, 1528, 1489, 1245 cm–1.
1H NMR (200 MHz, CDCl3): d = 8.20 (s, 1 H), 8.02 (s, 1 H), 7.88
(d, J = 8.0 Hz, 1 H), 7.80–7.66 (m, 3 H), 7.58 (d, J = 8.0 Hz, 1 H),
7.50–7.33 (m, 2 H), 7.28–7.12 (m, 2 H), 3.94 (s, 3 H).
TLC used silica gel F254 plates; the spots were examined under UV
light and then developed by I2 vapor. Column chromatography was
performed with silica gel (BDH 100–200 mesh). Solvents were pu-
rified according to standard procedures. The spectra were recorded
with the following instruments; IR: Perkin-Elmer RX FT-IR spec-
trophotometer; NMR: Varian Gemini 200 MHz (1H) and 50 MHz
(13C) spectrometer; ESIMS: VG-Autospec micromass. Organic ex-
tracts were dried over anhyd Na2SO4.
13C NMR (50 MHz, CDCl3): d = 159.0, 144.0, 132.2, 129.5, 129.2,
128.6, 128.5, 127.3, 127.2, 125.1, 124.4, 121.1, 120.0, 116.2, 110.9,
105.8, 77.8, 74.2, 55.3.
MS (ESI): m/z = 299 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C20H15N2O: 299.1184; found:
299.1170.
1-[2-Bromo-1-(6-methoxy-2-naphthyl)vinyl]-1H-benzimida-
zole (4f)
N-Alkynylation of Imidazoles and Pyrazoles; General Proce-
dure
IR (KBr): 2267, 1620, 1505, 1272 cm–1.
To a soln of bromoacetylene 2 (1.0 mmol) in anhyd 1,4-dioxane (3
mL) were added imidazole or pyrazole 1 (1.0 mmol), KOH (2.0
equiv), and CuO (2.0 mol%). The mixture was heated in an oil bath
at 80 °C for 10–14 h. The reaction was monitored by TLC. Upon
completion, the mixture was cooled to r.t., the solvent was evapo-
rated, and the mixture was diluted with cold H2O (10 mL). This was
extracted with EtOAc (2 × 10 mL). The combined organic layers
were dried (anhyd Na2SO4), concentrated in vacuo, and purified by
column chromatography (silica gel, Merck, 60–120 mesh, 1–4%
EtOAc–hexane) to afford pure product(s).
1H NMR (200 MHz, CDCl3): d = 8.19 (s, 1 H), 7.91 (d, J = 8.0 Hz,
1 H), 7.74–7.61 (m, 2 H), 7.52 (s, 1 H), 7.40–7.01 (m, 7 H), 3.91 (s,
3 H).
13C NMR (50 MHz, CDCl3): d = 159.4, 135.1, 130.2, 128.7, 128.2,
126.2, 124.0, 123.8, 123.2, 120.2, 120.0, 111.9, 106.0, 104.1, 55.2.
MS (ESI): m/z = 379, 381 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C20H16BrN2O: 379.0445;
found: 379.0435.
1-[(4-Pentylphenyl)ethynyl]-1H-imidazole (3b)
1-[(4-Pentylphenyl)ethynyl]-4-phenyl-1H-imidazole (3h)
IR (KBr): 2264, 1677, 1482, 130 cm–1.
IR (KBr): 2250, 1605, 1485, 1413 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.79 (s, 1 H), 7.39 (d, J = 8.0 Hz,
2 H), 7.18 (s, 1 H), 7.12 (d, J = 8.0 Hz, 2 H), 7.05 (s, 1 H), 2.60 (t,
J = 7.0 Hz, 2 H), 1.70–1.51 (m, 3 H), 1.38–1.29 (m, 3 H), 0.90 (t,
J = 7.0 Hz, 3 H).
1H NMR (200 MHz, CDCl3): d = 7.81–7.70 (m, 3 H), 7.42–7.30 (m,
5 H), 7.24 (t, J = 8.0 Hz, 1 H), 7.12 (d, J = 8.0 Hz, 2 H), 2.62 (t,
J = 7.0 Hz, 2 H), 1.70–1.52 (m, 3 H), 1.39–1.22 (m, 3 H), 0.89 (t,
J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 144.2, 140.0, 132.1, 129.3, 129.0,
13C NMR (50 MHz, CDCl3): d = 144.2, 142.0, 140.1, 133.0, 131.9,
128.9, 127.7, 125.6, 118.2, 117.0, 77.7, 71.0, 36.1, 31.2, 30.8, 22.5,
13.8.
MS (ESI): m/z = 315 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C22H23N2: 315.1861; found:
122.1, 118.5, 77.9, 70.8, 36.1, 31.7, 31.2, 22.8, 14.1.
MS (ESI): m/z = 239 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C16H19N2: 239.1548; found:
239.1559.
315.1854.
Synthesis 2011, No. 5, 816–820 © Thieme Stuttgart · New York

PAPER
Copper(II)-Catalyzed Coupling of Heteroarenes with Bromoalkynes
819
1-[(6-Methoxy-2-naphthyl)ethynyl]-4-phenyl-1H-imidazole (3i)
1H NMR (200 MHz, CDCl3): d = 7.74 (m, 1 H), 7.67 (m, 1 H), 7.12
(d, J = 8.0 Hz, 2 H), 7.01 (d, J = 8.0 Hz, 2 H), 6.62 (s, 1 H), 6.42 (m,
1 H), 2.01 (t, J = 7.0 Hz, 2 H), 1.69–1.52 (m, 2 H), 1.39–1.21 (m, 4
H), 0.90 (t, J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 145.0, 141.1, 133.4, 131.8, 128.9,
128.8, 126.3, 106.2, 100.6, 35.8, 31.2, 30.7, 22.3, 14.0.
MS (ESI): m/z = 319, 321 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C16H20BrN2: 319.0809; found:
IR (KBr): 2254, 1622, 1493, 1383, 1263 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.99 (s, 1 H), 7.90 (s, 1 H), 7.82
(d, J = 8.0 Hz, 2 H), 7.73 (d, J = 8.0 Hz, 2 H), 7.52–7.35 (m, 4 H),
7.31–7.10 (m, 3 H), 3.92 (s, 3 H).
13C NMR (50 MHz, CDCl3): d = 159.0, 140.1, 131.9, 129.6, 129.0,
127.9, 127.1, 125.1, 119.9, 119.8, 117.2, 117.0, 105.9, 78.0, 71.2,
55.5.
MS (ESI): m/z = 325 [M + H]+.
319.0810.
HRMS (ESI): m/z [M + H]+ calcd for C22H17N2O: 325.1340; found:
325.1326.
1-[(6-Methoxy-2-naphthyl)ethynyl]-1H-pyrazole (3p)
IR (KBr): 2235, 1628, 1458, 1388, 1261 cm–1.
2-Ethyl-1-(phenylethynyl)-1H-imidazole (3l)
1H NMR (200 MHz, CDCl3): d = 8.01 (s, 1 H), 7.83–7.69 (m, 4 H),
7.52 (d, J = 8.0 Hz, 1 H), 7.21–7.09 (m, 2 H), 6.40 (m, 1 H), 3.91 (s,
3 H).
13C NMR (50 MHz, CDCl3): d = 155.7, 143.9, 139.0, 131.9, 129.3,
129.1, 127.1, 119.2, 106.0, 76.2, 68.9, 55.7.
IR (KBr): 2264, 1681, 1503, 1428 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.56–7.47 (m, 2 H), 7.43–7.32 (m,
3 H), 7.12 (s, 1 H), 6.93 (s, 1 H), 2.91 (q, J = 7.0 Hz, 2 H), 1.40 (t,
J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 146.9, 131.8, 129.0, 128.8, 127.9,
MS (ESI): m/z = 249 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C16H13N2O: 249.1027; found:
121.5, 78.0, 73.4, 20.7, 11.3.
MS (ESI): m/z = 197 [M + H]+.
249.1028.
HRMS (ESI): m/z [M + H]+ calcd for C13H13N2: 197.1078; found:
197.1086.
3-Methyl-1-(phenylethynyl)-1H-pyrazole (3q)
IR (KBr): 2263, 1558, 1454, 1411, 1281 cm–1.
1-(2-Bromo-1-phenylvinyl)-2-ethyl-1H-imidazole (4l)
1H NMR (200 MHz, CDCl3): d = 7.54–7.48 (m, 3 H), 7.39–7.30 (m,
3 H), 6.06 (m, 1 H), 2.49 (s, 3 H).
IR (KBr): 2309, 1648, 1435, 1281 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.40–7.31 (m, 3 H), 7.18–7.10 (m,
3 H), 7.07 (s, 1 H), 6.89 (s, 1 H), 2.48 (q, J = 7.0 Hz, 2 H), 1.21 (t,
J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 150.0, 141.5, 131.1, 130.0, 129.2,
127.9, 125.2, 119.8, 116.9, 20.2, 11.7.
13C NMR (50 MHz, CDCl3): d = 142.7, 131.5, 130.9, 128.8, 128.7,
128.6, 105.6, 79.9, 71.9, 11.3.
MS (ESI): m/z = 183 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C12H11N2: 183.0922; found:
183.0918.
MS (ESI): m/z = 277, 279 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C13H14BrN2: 277.0340; found:
277.0351.
Acknowledgment
The author thanks CSIR and UGC, New Delhi for financial assi-
stance.
2-Isopropyl-1-(phenylethynyl)-1H-imidazole (3m)
IR (KBr): 2263, 1500, 1426, 1253 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.52–7.45 (m, 2 H), 7.40–7.32 (m,
3 H), 7.10 (s, 1 H), 6.91 (s, 1 H), 3.32 (m, 1 H), 1.41 (d, J = 7.0 Hz,
6 H).
13C NMR (50 MHz, CDCl3): d = 157.0, 131.8, 129.1, 128.9, 127.9,
121.1, 78.1, 72.6, 27.0, 20.9.
MS (ESI): m/z = 211 [M + H]+.
HRMS (ESI): m/z [M + H]+ calcd for C14H15N2: 211.1235; found:
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IR (KBr): 2257, 1609, 1434, 1397, 1261 cm–1.
1H NMR (200 MHz, CDCl3): d = 7.68 (m, 1 H), 7.60 (m, 1 H), 7.35
(d, J = 8.0 Hz, 2 H), 7.09 (d, J = 8.0 Hz, 2 H), 6.29 (m, 1 H), 2.52
(t, J = 7.0 Hz, 2 H), 1.62–1.48 (m, 3 H), 1.33–1.14 (m, 3 H), 0.82 (t,
J = 7.0 Hz, 3 H).
13C NMR (50 MHz, CDCl3): d = 144.1, 142.2, 134.2, 131.8, 128.9,
118.2, 107.2, 77.3, 67.3, 36.0, 31.6, 31.0, 22.1, 13.5.
(6) (a) Mulder, J. A.; Kurtz, K. C. M.; Hsung, R. P. Synlett 2003,
1379. (b) Katritzky, A. R.; Jiang, R.; Singh, S. K.
Heterocycles 2004, 63, 1455.
MS (ESI): m/z = 239 [M + H]+.
(7) (a) Brandsma, L.; Mal’kina, A. G.; Trofimov, B. A. Synth.
Commun. 1994, 24, 2721. (b) Kitamura, T.; Tashi, N.;
Tsuda, K.; Chen, H.; Fujiwara, T. Heterocycles 2000, 52,
303. (c) Wei, L.; Mulder, J. A.; Xiong, H.; Zificsak, C. A.;
Douglas, C. J.; Hsung, R. P. Tetrahedron 2001, 57, 459.
HRMS (ESI): m/z [M + H]+ calcd for C16H19N2: 239.1548; found:
239.1552.
1-[2-Bromo-1-(4-pentylphenyl)vinyl]-1H-pyrazole (4o)
IR (KBr): 2309, 1652, 1616, 1512 cm–1.
Synthesis 2011, No. 5, 816–820 © Thieme Stuttgart · New York

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B. Das et al.
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Synthesis 2011, No. 5, 816–820 © Thieme Stuttgart · New York