Synthesis of Arylated Pyrazoles by site-selective suzuki-miyaura reactions of tribromopyrazoles

Article abstract of DOI:10.1055/s-0030-1258489

The first Suzuki-Miyaura reactions of N-protected tribromopyrazoles are reported. Their reaction with three, two, or one equivalents of arylboronic acids afforded 3,4,5-triarylpyrazoles, 3,5-diaryl-4-bromopyrazoles, or 5-aryl-3,4-dibromopyrazoles, respect

Full text of DOI:10.1055/s-0030-1258489

LETTER
1923
Synthesis of Arylated Pyrazoles by Site-Selective Suzuki–Miyaura Reactions
of Tribromopyrazoles
Synthesis of
Aryl
a
atedPyrazo
s
les heed Ahmad Khera,a Asad Ali,a Munawar Hussain,a Jovana Tatar,a Alexander Villinger,a Peter Langer*a,b
a
Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
Fax +49(381)4986412; E-mail: peter.langer@uni-rostock.de
b
Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
Received 31 March 2010
aryl-3,4-dibromopyrazoles, are of considerable pharma-
cological relevance.9 Previous syntheses of these mole-
cules are not straightforward and mainly include
derivatives containing one and the same type of aryl moi-
ety.9
Abstract: The first Suzuki–Miyaura reactions of N-protected tri-
bromopyrazoles are reported. Their reaction with three, two, or one
equivalents of arylboronic acids afforded 3,4,5-triarylpyrazoles,
3,5-diaryl-4-bromopyrazoles, or 5-aryl-3,4-dibromopyrazoles, re-
spectively. All reactions proceeded with very good site-selectivity.
Key words: pyrazoles, catalysis, Suzuki–Miyaura reaction, regio-
selectivity, palladium
N-Benzyltribromopyrazole (2a) was prepared from com-
mercially available tribromopyrazole by modification of a
known procedure (Scheme 1).10 Instead of benzylchlo-
ride, which was used in the original procedure, benzylbro-
mide was employed. N-Vinyltribromopyrazole (2b) was
prepared, following a reported procedure,8 by reaction of
commercially available tribromopyrazole with dibromo-
ethane.
Pyrazoles represent important synthetic building blocks
and are important lead structures in medicinal chemistry.
Pharmacological properties include activity as nicotinic
acid receptor agonists1a and excitatory amino acid antago-
nists, respectively.1b Ethyl 5-propyl-1H-pyrazole-3-car-
boxylate is a key intermediate for the synthesis of viagra.1c
Celecoxib represents a clinically used COX-2 inhibitor
which exhibits promising anti-inflammatory and analge-
sic activity.1d,e Nicolaou et al.1f reported that a pyrazole-
substituted epothilone derivative shows a strong antitu-
mor activity. In fact, it is considered to be the most potent
epothilone derivative reported to date.
Br
Br
4
3
5
N
Br
2
N
Br
1
Ph
i
Ph
Br
Br
2a (82%)
Br
N
N
Br
4
ii
Br
Pyrazoles are available by cycloaddition of diazoalkanes
with alkynes.2 Other syntheses rely on the cyclization of
hydrazines with 1,3-diketones or a,b-unsaturated ke-
tones.3 An interesting approach to pyrazoles relies on the
cyclization of hydrazone dianions, generated by means of
n-BuLi, with esters, acid chlorides, nitriles, a-haloke-
tones, propiolates, Weinreb amides, and diethyl oxalate.4
The reaction of hydrazines with 4-aryl-2,4-dioxoesters af-
forded 5-arylpyrazole-3-carboxylates which were trans-
formed into potent and selective COX-1 and COX-2
inhibitors.5
H
5
3
Br
1
Br
N
Br
N
2
1
2b (78%)
Scheme 1 Synthesis of 2a,b. Reagents and conditions: (i) 1 (1.0
equiv), benzylbromide (1.0 equiv), Et3N (1.1 equiv), CH2Cl2 (5 mL/
mmol of 1), 20 °C, 4 h; (ii) 1 (1.0 equiv), DCE (1.2 equiv), Et3N (5
mL/mmol), MeCN (5 mL/mmol of 1), 70 °C, 7 h.
The Suzuki–Miyaura reaction of 2a and 2b with arylbo-
ronic acids 3a–e (1.0 equiv) afforded the 5-aryl-3,4-dibro-
mopyrazoles 4a–e in 66–73% yield (Table 1,
Scheme 2).11,12 A good yield was obtained even for the
sterically hindered boronic acid 3d. During the optimiza-
tion, the best yields were obtained when Pd(PPh3)4 was
used as the catalyst (3 mol%) and when K3PO4 (1.5 equiv)
was used as the base. The use of Pd(OAc)2 in the presence
of XPhos13 or of PdCl2(PPh3)2 proved to be less efficient
in terms of yield. The use of exactly one equivalent of the
boronic acid proved to be important to avoid multiple cou-
pling. The reactions were carried out in a 4:1 mixture of
dioxane and water. The employment of toluene was less
efficient because of the low solubility of the boronic acids.
The temperature (100 °C) and the reaction time (12 h) also
The development of site-selective cross-coupling reac-
tions of polyhalogenated heterocycles is of considerable
current interest.6,7 Palladium-catalyzed cross-coupling re-
actions of polyhalogenated pyrazoles have, to the best of
our knowledge, not been reported to date. Recently, met-
al-halide exchange reactions of N-vinyl-tribromopyrazole
have been reported.8 Herein, we report our preliminary re-
sults related to the first Suzuki–Miyaura reactions of N-vi-
nyl- and N-benzyltribromopyrazole. The products,
triarylpyrazoles, 3,5-diaryl-4-bromopyrazoles, and 5-
SYNLETT 2010, No. 13, pp 1923–1926
x
x
.x
x
.2
0
1
0
Advanced online publication: 09.07.2010
DOI: 10.1055/s-0030-1258489; Art ID: G10210ST
© Georg Thieme Verlag Stuttgart · New York

1924
R. A. Khera et al.
LETTER
Br
Br
played an important role. The yields decreased when the
reaction mixture was stirred for a shorter period of time
(no complete conversion) or when the reaction time was
extended. The conversion was not complete when the re-
action was cariied out at lower temperature. The forma-
tion of 4a–e proceded, like the metal–halide exchange,8
with excellent site-selectivity in favour of position 5. The
configuration of the products was unambiguously con-
firmed by 2D NMR experiments (NOESY, HMBC,
HMQC). Inspection of the crude product mixture showed
that a small amount of pyrazole derived from double and
triple Suzuki reaction were formed. In addition, some bi-
aryl formation (by dimerization of the boronic acid) was
detected.
ArB(OH)2
3c–f
Br
Ar
Br
Ar
i
N
N
N
N
R
R
2a,b
5a–d
Scheme
3
Synthesis of 5-aryl-3,4-dibromopyrazoles 5a–d.
Reagents and conditions: (i) 2a,b (1.0 equiv), ArB(OH)2 (2.0 equiv),
K3PO4 (3.0 equiv), Pd(PPh3)4 (5 mol%), 1,4-dioxane–H2O (4:1), 100
°C, 12 h.
Table 2 Synthesis of 5a–d
2
3
5
R
Ar
Yield of 5
(%)a
b
b
b
a
c
d
f
a
b
c
vinyl
vinyl
vinyl
Bn
4-MeOC6H4
60
62
74
66
Br
Br
ArB(OH)2
3a–e
Br
Br
2,6-(MeO)2C6H3
3,5-(MeO)2C6H3
4-FC6H4
Br
Ar
N
i
N
N
N
R
R
e
d
2a,b
4a–e
a Yields of isolated compounds.
Scheme
2
Synthesis of 5-aryl-3,4-dibromopyrazoles 4a–e.
Reagents and conditions: (i) 2a,b (1.0 equiv), ArB(OH)2 (1.0 equiv),
K3PO4 (1.5 equiv), Pd(PPh3)4 (3 mol%), 1,4-dioxane–H2O (4:1), 100
°C, 12 h.
Table 1 Synthesis of 4a–e
2
b
b
b
b
a
3, 4
a
R
Ar
Yield of 4 (%)a
vinyl
vinyl
vinyl
vinyl
Bn
4-MeC6H4
2-MeOC6H4
4-MeOC6H4
66
69
73
b
c
d
2,6-(MeO)2C6H3 71
4-FC6H4 68
Figure 1 Crystal structure of 5a
e
a Yields of isolated compounds.
important to use 10 mol% of the catalyst and an excess of
the boronic acid (3.5 equiv) and of the base (4.5 equiv).
The use of Pd(OAc)2 in the presence of XPhos or of
PdCl2(PPh3)2 resulted in a decrease of the yield. The best
results were again obtained when the reaction was carried
out at 100 °C for 12 hours. The yields slightly decreased
for products 6b,g derived from the electron-poor boronic
acids 3f,j. Inspection of the crude product mixture showed
that a small amount of biaryls were formed. It is surprising
that the yields of products 6a–g were in the same range as
the yields of products 4a–e and 5a–d. This might be ex-
plained by increasing steric hindrance during the triple
Suzuki reaction, dimerization of the arylboronic acid, and
decomposition.
The Suzuki–Miyaura reaction of 2a and 2b with arylbo-
ronic acids 3c–f (2.0 equiv) afforded the 3,5-diaryl-4-bro-
mopyrazoles 5a–d in 40–74% yield (Table 2,
Scheme 3).11,14 A good yield was obtained even for the
sterically hindered boronic acid 3d. A slightly increased
amount of the catalyst (5 mol%), exactly two equivalents
of the boronic acid, and the double amount of base (3.0
equiv) were employed. The use of Pd(OAc)2/XPhos or
PdCl2(PPh3)2 resulted in a decrease of the yield. The
yields decreased when the temperature or the reaction
time was decreased. Inspection of the crude product mix-
ture showed that a small amount of pyrazole derived from
mono and triple Suzuki reaction were formed. The struc-
ture of 5a was independently confirmed by X-ray crystal
structure analysis (Figure 1).15
In conclusion, we have reported the first Suzuki–Miyaura
reactions of N-protected tribromopyrazoles. Their reac-
tion with three, two, or one equivalents of arylboronic
acids afforded triarylpyrazoles, 3,5-diaryl-4-bromo-
pyrazoles, or 5-aryl-3,4-dibromopyrazoles, respectively.
The products are not readily available by other methods.
All reactions proceed with very good site-selectivity.
The Suzuki–Miyaura reaction of 2a and 2b with an excess
of arylboronic acids 3a,e–j (3.5 equiv) afforded the 3,4,5-
triarylpyrazoles 6a–g in 50–76% yield (Table 3,
Scheme 4).11,16 During the optimization, it proved to be
Synlett 2010, No. 13, 1923–1926 © Thieme Stuttgart · New York

LETTER
Synthesis of Arylated Pyrazoles
1925
(4) For a review of cyclization reactions of dianions in organic
synthesis, see: (a) Langer, P.; Freiberg, W. Chem. Rev.
2004, 104, 4125. For original papers, see: (b) Matsumura,
N.; Kunigihara, A.; Yoneda, S. Tetrahedron Lett. 1983, 24,
3239. (c) Matsumura, N.; Kunigihara, A.; Yoneda, S.
Tetrahedron Lett. 1984, 25, 4529. (d) Duncan, D. C.;
Trumbo, T. A.; Almquist, C. D.; Lentz, T. A.; Beam, C. F.
J. Heterocycl. Chem. 1987, 24, 555. (e) Beam, C. F.;
Reames, D. C.; Harris, C. E.; Dasher, I. W.; Hollinger,
W. M.; Shealy, N. L.; Sandifer, R. M.; Perkins, M.; Hauser,
C. R. J. Org. Chem. 1975, 40, 514. (f) Persson, T.; Nielsen,
J. Org. Lett. 2006, 8, 3219. (g) Dang, T. T.; Dang, T. T.;
Reinke, H.; Fischer, C.; Langer, P. Tetrahedron 2008, 64,
2207.
(5) Ranatunge, R. R.; Augustyniak, M.; Bandarage, U. K.; Earl,
R. A.; Ellis, J. L.; Garvey, D. S.; Janero, D. R.; Letts, L. G.;
Martino, A. M.; Murty, M. G.; Richardson, S. K.; Schroeder,
J. D.; Shumway, M. J.; Tam, S. W.; Trocha, A. M.; Young,
D. V. J. Med. Chem. 2004, 47, 2180.
(6) For reviews of cross-coupling reactions of polyhalogenated
heterocycles, see: (a) Schröter, S.; Stock, C.; Bach, T.
Tetrahedron 2005, 61, 2245. (b) Schnürch, M.; Flasik, R.;
Khan, A. F.; Spina, M.; Mihovilovic, M. D.; Stanetty, P. Eur.
J. Org. Chem. 2006, 3283.
Br
Ar
ArB(OH)2
3a, e–j
Br
Ar
Br
Ar
i
N
N
N
N
R
2a,b
R
6a–g
.
Scheme 4 Synthesis of 3,4,5-triarylpyrazoles 6a–g. Reagents and
conditions: (i) 2a,b (1.0 equiv), ArB(OH)2 (3.5 equiv), K3PO4 (4.5
equiv), Pd(PPh3)4 (10 mol%), 1,4-dioxane–H2O (4:1), 100 °C, 12 h.
Table 3 Synthesis of 6a–g
2
3
6
R
Ar
Yield of 6
(%)a
a
a
b
b
b
b
a
a
e
f
a
b
c
d
e
f
Bn
4-MeC6H4
4-FC6H4
70
63
57
76
72
74
50
Bn
vinyl
vinyl
vinyl
vinyl
Bn
3,5-(MeO)2C6H3
4-t-BuC6H4
4-EtC6H4
g
h
i
(7) For studies from our laboratory, see: (a) Dang, T. T.; Dang,
T. T.; Ahmad, R.; Reinke, H.; Langer, P. Tetrahedron Lett.
2008, 49, 1698. (b) Dang, T. T.; Villinger, A.; Langer, P.
Adv. Synth. Catal. 2008, 350, 2109. (c) Hussain, M.;
Nguyen, T. H.; Langer, P. Tetrahedron Lett. 2009, 50, 3929.
(d) Tengho Toguem, S.-M.; Hussain, M.; Malik, I.;
Villinger, A.; Langer, P. Tetrahedron Lett. 2009, 50, 4962.
(e) Dang, T. T.; Dang, T. T.; Rasool, N.; Villinger, A.;
Langer, P. Adv. Synth. Catal. 2009, 351, 1595.
3,5-Me2C6H3
4-ClC6H4
j
g
a Yields of isolated compounds.
Acknowledgment
(8) Iddon, B.; Toender, J. E.; Hosseini, M.; Begtrup, M.
Tetrahedron 2007, 63, 56.
Financial support from the State of Pakistan (HEC scholarship for
M.H.), from the DAAD (scholarships for A.A. and R.A.K.), from
the State of Mecklenburg-Vorpommern (scholarships for M.H. and
J.T.), and from the Friedrich-Irmgard-Harms-Stiftung (scholarship
for A.A.) is gratefully acknowledged. Partial financial support by
the Ministry of Science of the Republic of Serbia, Grant No.
142007, is gratefully acknowledged.
(9) For pharmacologically relevant 3,4,5-triarylpyrazoles, see:
(a) Meanwell, N. A.; Rosenfeld, M. J.; Wright, J. J. K.;
Brassard, C. L.; Buchanan, J. O. J. Med. Chem. 1992, 35,
389. For pharmacological relevant 3,5-diaryl-4-bromo-
pyrazoles, see: (b) Bondavalli, F.; Bruno, O.; Ranise, A.;
Schenone, P.; Donnoli, D. Farmaco 1989, 44, 655.
(c) Bondavalli, F.; Bruno, O.; Ranise, A.; Schenone, P.;
Addonizio, P. Farmaco 1988, 43, 725. Only very few
5-aryl-3,4-dibromopyrazoles have been reported so far:
(d) Trofimenko, S.; Yap, G. P. A.; Jove, F. A.; Claramunt,
R. M.; Garcia, M. A.; Santa Maria, M. D.; Alkorta, I.;
Elguero, J. Tetrahedron 2007, 63, 8104.
References and Notes
(1) (a) van Herk, T.; Brussee, J.; van den Nieuwendijk,
A. M. C. H.; van der Klein, P. A. M.; Ijzerman, A. P.;
Stannek, C.; Burmeister, A.; Lorenzen, A. J. Med. Chem.
2003, 46, 3945. (b) Varano, F.; Catarzi, D.; Colotta, V.;
Filacchioni, G.; Galli, A.; Costagli, C.; Carlà, V. J. Med.
Chem. 2002, 45, 1035. (c) Clayden, J.; Geeves, N.; Warren,
S. Organic Chemistry; Oxford University Press: Oxford,
2000. (d) Dannhardt, G.; Laufer, S. Curr. Med. Chem. 2000,
71101. (e) Carty, T. J.; Marfat, A. Curr. Opin. Anti-Inflamm.
Immunomod. Invest. Drugs 1999, 1, 89. (f) Nicolaou, K. C.;
Pratt, B. A.; Arseniyadis, S.; Wartmann, M.; O’Brate, A.;
Giannakakou, P. ChemMedChem 2006, 1, 41.
(2) (a) The Chemistry of Heterocyclic Compounds, Part 1, Vol.
49; Grunanger, P.; Vita-Finzi, P., Eds.; John Wiley: New
York, 1991. (b) Aggarwal, V. K.; de Vincente, J.; Bonnert,
R. V. J. Org. Chem. 2003, 68, 5381. (c) Deng, X.; Mani,
N. S. Org. Lett. 2006, 8, 3505.
(3) (a) Handbook of Heterocyclic Chemistry; Katritzky, A. R.;
Pozharskii, A. F., Eds.; Pergamon: Oxford, 2000.
(b) Heller, S. T.; Natarajan, S. R. Org. Lett. 2006, 8, 2675.
(c) Humphries, P. A.; Finefield, J. M. Tetrahedron Lett.
2006, 47, 2443. (d) Bishop, B. C. Synthesis 2004, 43.
(e) Ahmed, S. M.; Kobayashi, K.; Mori, A. Org. Lett. 2005,
7, 4487.
(10) Grandberg, A. J. Gen. Chem. USSR (Engl. Transl.) 1963, 33,
503; Zh. Obshch. Khim. 1963, 33, 511.
(11) General Procedure for Suzuki–Miyaura Coupling
Reactions
To a 1,4-dioxane solution (4 mL) of 2a,b (152 mg, 0.5
mmol) was added Pd(PPh3)4 (3–10 mol%) at 20 °C under
argon atmosphere. After stirring for 30 min, the arylboronic
acid (1.0–1.2 equiv per bromine atom of the substrate),
K3PO4 (1.5 equiv per bromine atom of the substrate), and
H2O (1.0 mL) were added. The mixture was heated for 12 h
at 100 °C. After cooling to 20 °C, the mixture was diluted
with H2O, extracted with CH2Cl2 (3 × 25 mL), dried
(Na2SO4), and filtered. The solvent of the filtrate was
concentrated in vacuo and the residue was purified by
column chromatography (heptanes–EtOAc).
(12) 3,4-Dibromo-5-(4-methoxyphenyl)-1-vinyl-1H-pyrazole
(4c)
Starting with 2b (165 mg, 0.50 mmol), Pd(PPh3)4 (18 mg, 3
mol%), 1,4-dioxane–H2O (4:1, 5 mL), K3PO4 (159 mg, 0.75
mmol), and 4-methoxyphenylboronic acid (76 mg, 0.50
mmol), 4c was isolated as a white solid (131 mg, 73%). 1H
Synlett 2010, No. 13, 1923–1926 © Thieme Stuttgart · New York

1926
R. A. Khera et al.
LETTER
NMR (300 MHz, CDCl3): d = 3.80 (s, 3 H, OCH3), 4.77 (d,
1 H, J = 8.7 Hz, vinyl), 5.72 (d, 1 H, J = 15.2 Hz, vinyl), 6.70
(dd, 1 H, J = 15.2, 8.7 Hz vinylic CH), 6.95 (d, 2 H, J = 8.8
Hz, ArH), 7.25 (d, 2 H, J = 8.8 Hz, ArH). 13C NMR (75.5
MHz, CDCl3): d = 55.4 (OCH3), 98.2 (C), 102.7 (CH2),
114.3 (CH), 119.0 (C), 129.7 (CH), 130.5 (C), 131.5 (CH),
142.4, 160.7 (C). IR (KBr): 3002, 2936, 2835, 1730 (w),
1641 (m), 1574 (w), 1488 (s), 1432 (m), 1392 (w), 1355 (m),
1332 (s), 1290 (m), 1249 (s), 1196 (w), 1174 (s), 1110 (m),
1030, 984 (s), 888 (m), 833 (s), 801 (m), 725 (w), 602 (m),
551 (m) cm–1. GC-MS (EI, 70 eV): m/z (%) = 358 (81Br, 100)
[M]+, 343 (13), 327 (22), 277 (39), 246 (22), 198 (23).
HRMS (EI, 70 eV): m/z calcd for C12H10N2Br2O [M]+ (79Br):
355.91544; found: 355.91535.
1207 (m), 1250, 1178 (s), 1161, 1111 (m), 1029 (s), 1114
(m), 975 (s), 943 (m), 834 (s), 795 (w), 736 (m), 635 (w), 528
(m) cm–1. GC-MS (EI, 70 eV): m/z (%) = 384 (79Br, 3) [M]+,
365 (8), 332 (7), 281 (13), 207 (100), 175 (09), 135 (04) cm–1.
HRMS (EI, 70 eV): m/z calcd for C19H17N2BrO2 [M]+ (79Br):
384.04734; found: 384.04711.
(15) CCDC-777244 contains all crystallographic details of this
publication which are available free of charge at
www.ccdc.cam.ac.uk/conts/retrieving.html or can be
ordered from the following address: Cambridge
Crystallographic Data Centre, 12 Union Road, GB-
Cambridge CB21EZ; fax: +44 (1223)336033; or
deposit@ccdc.cam.ac.uk.
(16) 3,4,5-Tris(3,5-dimethylphenyl)-1-vinyl-1H-pyrazole (6f)
Starting with 2b (165 mg, 0.50 mmol), Pd(PPh3)4 (58 mg, 10
mol%), 1,4-dioxane–H2O (4:1, 5 mL), K3PO4 (477 mg, 2.25
mmol), and 3,5-dimethylphenylboronic acid (263 mg, 1.75
mmol), 6f was isolated as a white solid (165 mg, 74%). 1H
NMR (300 MHz, CDCl3): d = 2.06 (s, 6 H, 2 CH3), 2.10 (s,
6 H, 2 CH3), 2.15 (s, 6 H, 2 CH3), 4.69 (d, 1 H, J = 8.7 Hz,
vinyl), 5.78 (d, 1 H, J = 15.3 Hz, vinyl), 6.61–6.90 (m, 8 H),
7.09 (br s, 2 H, ArH). 13C NMR (75.5 MHz, CDCl3):
d = 21.1, 21.2, 21.3 (CH3), 100.5 (CH2), 120.5 (C), 126.2,
128.1, 128.2, 128.5 (CH), 129.2 (C), 129.3, 130.3, 130.4
(CH), 132.6, 133.0, 137.0, 137.4, 137.8, 141.8, 150.4 (C). IR
(KBr): 3002, 2915, 2859 (w), 1738, 1642 (m), 1600 (s), 1550
(w), 1444 (m), 1373 (s), 1303, 1268 (w), 1237 (s), 1203,
1154, 1110, 1096 (w), 1093 (m), 996, 900, 881 (w), 848 (s),
789 (w), 691 (m), 542 (w) cm–1. GC-MS (EI, 70 eV): m/z
(%) = 406 (100) [M]+, 391 (26), 375 (2), 259 (4), 203 (3),
180 (2), 132 (4). HRMS (EI, 70 eV): m/z calcd for C29H30N2
[M]+: 406.24090; found: 406.24057.
(13) Billingsley, K.; Buchwald, S. L. J. Am. Chem. Soc. 2007,
129, 3358; and references cited therein.
(14) 4-Bromo-3,5-bis(4-methoxyphenyl)-1-vinyl-1H-pyrazole
(5a)
Starting with 2b (165 mg, 0.50 mmol), Pd(PPh3)4 (29 mg, 5
mol%), 1,4-dioxane–H2O (4:1, 5 mL), K3PO4 (318 mg, 1.5
mmol), and 4-methoxyphenylboronic acid (152 mg, 1.0
mmol), 5a was isolated as a white crystalline solid (115 mg,
60%). 1H NMR (300 MHz, CDCl3): d = 3.79 (s, 3 H, OCH3),
3.81 (s, 3 H, OCH3), 4.75 (d, 1 H, J = 8.5 Hz, vinyl), 5.75 (d,
1 H, J = 15.4 Hz, vinyl), 6.78 (dd, 1 H, J = 8.8, 15.3 Hz,
vinylic CH), 6.92 (d, 2 H, J = 8.9 Hz, ArH), 6.96 (d, 2 H,
J = 8.8 Hz, ArH), 7.30 (d, 2 H, J = 8.8 Hz, ArH), 7.86 (d, 2
H, J = 8.9 Hz, ArH). 13C NMR (75.5 MHz, CDCl3):
d = 55.3, 55.4 (OCH3), 94.2 (C), 101.6 (CH2), 113.7, 114.2
(CH), 120.1, 124.5 (C), 129.4 (CH), 130.3, 131.7 (CH),
142.2, 149.3, 159.9, 160.4 (C). IR (KBr): 3090, 2996, 2834,
1789 (w), 1638 (m), 1574 (w), 1489 (s), 1436 (m), 1307 (w),
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