Microwave enhancement of arylation of activated olefins with 4-bromoacetophenone

Full text of DOI:10.1134/S1070428010030280

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 3, pp. 455–456. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © R.N. Shakhmaev, A.R. Chanysheva, A.U. Ishbaeva, S.S. Vershinin, V.V. Zorin, 2010, published in Zhurnal Organicheskoi Khimii,
2
010, Vol. 46, No. 3, pp. 459–460.
SHORT
COMMUNICATIONS
Microwave Enhancement of Arylation of Activated Olefins
with 4-Bromoacetophenone
R. N. Shakhmaev, A. R. Chanysheva, A. U. Ishbaeva, S. S. Vershinin, and V. V. Zorin
Ufa State Petroleum Technological University, ul. Kosmonavtov 1, Ufa, 450062 Bashkortostan, Russia
e-mail: biochem@rusoil.net
Received November 5, 2008
DOI: 10.1134/S1070428010030280
Palladium-catalyzed arylation and vinylation of
configuration of the double bond. Ketone I reacted
with styrene IV in a similar way, yielding exclusively
1-{4-[(E)-2-phenylvinyl]phenyl}ethan-1-one (V).
olefins (Heck reaction) are important reactions in
organic synthesis [1, 2]. In most cases, under classical
conditions (closed system, no solvent, temperature
At temperatures below 100°C the reactions oc-
curred at a low rate, and the yields were almost quan-
titative (calculated on the reacted compound I). The re-
action rate considerably increased when the tempera-
ture was raised above 110°C, but the selectivity of the
process simultaneously decreased. Above 140°C, side
processes became predominating. Thus the optimal
temperature in the classical procedure is ~100°C; it en-
sures high yields of the target products and acceptable
reaction time.
1
00–120°C) complete substrate conversion is attained
in several hours to several days [3]. Attempts to carry
out the reaction at a higher temperature resulted in
decomposition of the catalytic system and formation of
by-products. In the recent time, examples of successful
application of microwave irradiation to accelerate Heck
reactions in polar solvents have been reported [4–8].
We compared the results of arylation of some
activated olefins with 4-bromoacetophenone (I) under
classical solvent-free conditions and under microwave
irradiation. The reaction mixtures were heated in
a thermostat (temperature range 85–140°C) and in the
active zone of a microwave furnace (40–300 W). The
reaction of 4-bromoacetophenone (I) with methyl
acrylate (II) in both cases gave methyl (2E)-3-(4-ace-
tylphenyl)acrylate (III) as the only product. The spin–
spin coupling for the olefinic protons in III was larger
than 16 Hz, which unambiguously indicated trans
By varying the microwave irradiation power and
other conditions we succeeded in considerably shorten-
ing the reaction time, the high selectivity being re-
tained, without using polar solvents. At an MW power
of 140 W, the complete conversion of 4-bromoaceto-
phenone (I) was attained in all cases within 10 min,
and the yields of products III and V were comparable
with those obtained under conventional heating at
1
00°C over a period of 15 h.
O
Arylation of activated olefins with 4-bromo-
acetophenone (general procedure). A 10-ml thick-
walled ampule was charged with 1.990 g (10 mmol) of
4-bromoacetophenone (I), 12.5 mmol of methyl
acrylate (II) or styrene (IV), 1.265 g (12.5 mmol) of
triethylamine, 0.105 g (0.4 mmol) of triphenylphos-
phine, and 0.0225 g (0.1 mmol) of palladium(II) ace-
tate. The ampule was purged with argon, sealed, and
placed into a reactor charged with isooctane and
equipped with a reflux condenser. The reactor was sub-
jected to microwave irradiation at a power of 140 W
over a period of 10 min. When the substrate conver-
Me
+
H C
R
2
Br
I
II, IV
O
Pd(OAc) , Ph P, Et N, MW
2
3
3
Me
R
III, V
II, III, R = COOMe; IV, V, R = Ph.
4
55

4
56
SHAKHMAEV et al.
sion was complete, the ampule was cooled to room
temperature and opened, 5 ml of water and 5 ml of
chloroform were added, and the mixture was trans-
ferred to a separatory funnel. The organic phase was
separated, the aqueous phase was extracted with
chloroform (3×5 ml), and the extracts were combined
with the organic phase, dried over Na SO , and con-
centrated. The product was isolated by column chro-
matography on neutral silica gel L 40/100 using hex-
ane–diethyl ether (5:1) as eluent.
(2C, Carom), 128.88 (2C, Carom), 131.44 (CH=), 135.93
(Carom), 136.68 (Carom), 141.99 (Carom), 197.48 (CH CO).
3
+
Mass spectrum, m/z (I , %): 223 (19) [M + 1] , 222
rel
+
+
(85) [M] , 207 (100) [M – CH ] , 179 (35), 178 (56),
3
152 (12), 89 (22).
Microwave-assisted reactions were performed
using a Microdigest M 301 single mode microwave
furnace (operating frequency 2450 MHz). The IR spec-
tra were recorded from samples dispersed in mineral
oil on a Shimadzu Prestige-21 spectrometer with
2
4
1
13
Methyl (2E)-3-(4-acetylphenyl)prop-2-enoate
Fourier transform. The H and C NMR spectra were
(
III). Yield 1.753 g (86%), mp 107–108°C. IR spec-
measured from solutions in CDCl on a Bruker AM-
3
–
1
trum, ν, cm : 3069, 3024, 2949, 2928, 2916, 2853,
3
00 instrument at 300 and 75.47 MHz, respectively,
1
1
715 (C=O, ester), 1672 (C=O, ketone), 1636 (C=C),
using tetramethylsilane as internal reference. Gas chro-
matographic–mass spectrometric analysis was per-
formed using a Khromatek Kristall 5000 instrument
coupled with a Finnigan DSQ mass-selective detector
603, 1456, 1439, 1412, 1362, 1329, 1265, 1200,
1
1177, 1007, 966, 849, 827. H NMR spectrum, δ, ppm:
2
.58 s (3H, CH CO), 3.78 s (3H, CH O), 6.49 d (1H,
3 3
=CHCO, J = 16.2 Hz), 7.57 d (2H, Harom, J = 8.3 Hz),
(
electron impact, 70 eV).
7
.67 d (1H, =CHC H , J = 16.2 Hz), 7.93 d (2H, Harom,
6 4
1
3
J = 8.3 Hz). C NMR spectrum, δ , ppm: 26.59
C
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(
CH CO), 51.80 (OCH ), 120.21 (=CHCOO), 128.05
3 3
(
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4
3
1
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(
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+
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3
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7
7
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3
.95 d (2H, Harom, J = 8.4 Hz). C NMR spectrum,
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3
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 3 2010