Decarboxylative olefination of potassium benzoates via bimetallic catalysis strategy

Article abstract of DOI:10.1007/s00706-018-2267-y

Abstract: A novel synthesis of styrene derivatives through decaroxylative olefination of potassium benzoates with alkynes using Pd₂dba₃/CuBr as catalyst system has been developed. The protocol proceeded smoothly and in most cases Z-alkene was the main product. Electron-rich potassium benzoates reacted more efficiently than those of electron-deficient substrates. Heteroaromatic and electron-deficient aryl alkynes were not consistent with this transformation. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s00706-018-2267-y

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ORIGINAL PAPER
Decarboxylative olefination of potassium benzoates via bimetallic
catalysis strategy
Mehdi Khalaj1
Majid Ghazanfarpour-Darjani1 Saeed Taheri1 Sajjad Sedaghat2 Seyed Jalal Hoseyni1
•
•
•
•
Received: 28 January 2018 / Accepted: 1 July 2018
Ó Springer-Verlag GmbH Austria, part of Springer Nature 2018
Abstract
A novel synthesis of styrene derivatives through decaroxylative olefination of potassium benzoates with alkynes using
Pd2dba3/CuBr as catalyst system has been developed. The protocol proceeded smoothly and in most cases Z-alkene was the
main product. Electron-rich potassium benzoates reacted more efficiently than those of electron-deficient substrates.
Heteroaromatic and electron-deficient aryl alkynes were not consistent with this transformation.
Graphical abstract
Keywords Bimetallic catalysis Á Decarboxylation Á Hydrometalation Á Benzoic acid Á Alkyne
Introduction
decarboxylative olefination of benzoic acids by Meyers [7],
extensive studies have been conducted to form C–C bonds
via this strategy [8–12]. Moreover, Gooßen and co-workers
have developed an outstanding decarboxylation reaction to
form biaryl structures using bimetallic strategy [13]. In
2010, Gooßen and co-workers reported a decarboxylative
reaction for the synthesis of biaryl compounds with Ag/Pd
catalyst system [14]. The same group described a modular,
decarboxylative coupling of a-ketocarboxylates, amines,
and aryl halides catalysis in copper/palladium [15]. Cahiez
developed an efficient decarboxylation reaction for the
synthesis of simple arenes [16]. Ge and co-workers
reported a room temperature decarboxylative ortho-acyla-
tion of acetanilides with a-oxocarboxylic acids [17]. The
use of cheap and readily available carboxylic acids as the
source of active aryl instead of costly preformed reagents
(e.g., aryl iodide) makes this procedure very attractive from
economic and environmental points of view. However,
using this strategy for direct olefination of aryl carboxylic
acids is a challenging goal.
The introduction of new and efficient routes for the syn-
thesis of organic skeletons serves as one of the most
interesting topics in organic chemistry [1–3]. In this con-
text, metal-catalyzed cross-coupling reactions have pro-
foundly changed the protocols for the construction of
organic compounds and led to the formation of compounds
from simpler starting materials. However, these catalytic
reactions still suffer from the fundamental drawbacks
[4–6]. Since the report of
a
palladium-catalyzed
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s00706-018-2267-y) contains
supplementary material, which is available to authorized
users.
& Mehdi Khalaj
khalaj_mehdi@yahoo.com
1
Department of Chemistry, Buinzahra Branch, Islamic Azad
University, Buinzahra, Iran
The introduction of alkenyl group into aromatic ring has
long been a fundamental transformation within the field of
2
Department of Chemistry, Faculty of Science, Shahr-e-Qods
Branch, Islamic Azad University, Tehran, Iran
123

M. Khalaj et al.
organic chemistry. The seminal research of Fujiwara,
Mizoroki, and Heck demonstrated that cross-coupling
reactions can offer a general approach for substitution on
sp2-C atoms. In recent years, a variety of catalytic methods
have been developed for the construction of styrene
skeletons [18–23]. An alternative strategy to the synthesis
of aryl-olefin bond involves hydroarylation of C–C multi-
ple bonds using a low-valent transition metal catalyst
[24–27].
entries 14–17). Reduction of the loading of ligand deliv-
ered a slightly lower yield and stereoselectivity (Table 1,
entry 18). Lowering the reaction temperature proved to be
detrimental, and the yield of the product decreased as the
temperature was lowered (Table 1, entry 19). Upon short-
ening the reaction time, lower yield was obtained (Table 1,
entry 20). Reaction conducted in the absence of 1,10-
phenanthroline as a r-donor ligand formed a lower yield of
the product (Table 1, entry 21). Unfortunately, the reaction
with cheaper benzoate salt like sodium benzoate resulted in
formation of the desired product in lower yield (Table 1,
entry 22).
Recently, Han and co-workers have reported an out-
standing work on selective hydrogenation of alkynes with
formic acid in the presence of palladium salts [28]. Tunge
developed a polymer-supported rhodium(I) catalyst for the
addition of boronic acid to internal alkyne [29]. Norton
reported that the reaction between activated alkynes and
benzene using CpCr(CO)3H affords styrene derivatives in
good yields [30]. Based on this finding and in continuation
of valuable researches that have been published in
bimetallic catalysis [31–34], the efficacy of potassium
benzoates and acetylenic esters for the synthesis of styrene
derivatives was examined.
With the optimized conditions in hand, we began to
examine the scope of the reaction with various potassium
benzoates (Table 2). Besides the model substrate, alkyl-
substituted potassium benzoates like 2b–2d were all com-
petent substrates in the reaction, and they all gave the
products in good yields (Table 2, entries 2–4). It should be
emphasized that steric hindrance of substrates adversely
affects the yield as potassium 2-methylbenzoate (2e)
affords a moderate yield and potassium 2-(tert-butyl)ben-
zoate (2f) only affords the product in traces amounts
(Table 2, entries 5 and 6). In addition, potassium benzoates
bearing chloride in the ortho- and para-positions were also
reliable reaction partners with 2a (Table 2, entries 7 and 8).
Potassium 4-methoxybenzoate (1i) provided a lower yield
of the product than 1a (Table 2, entry 9). A possible reason
is that the methoxy group might impede the reaction by
binding to palladium or interfering in decarboxyation step.
Additionally, electron-deficient substrates gave the corre-
sponding products in low yields (Table 2, entries 10–12).
Surprisingly, an excellent yield of the product was
achieved when potassium furan-2-carboxylate (1m) was
used as the substrate, an outcome we attribute to the
facilitating the transmetallation step by coordination of
heteroatom to the hydropalladiated intermediate (Table 2,
entry 13). Potassium cinnamate (1n) was proven to be a
good substrate in this reaction (Table 2, entry 14). In
general, the reaction favored by lack of hindrance on
substrates which is consistent with conditions promotes
transmetallation step in bimetallic catalysis. It should be
noted that aliphatic carboxylic salt such as potassium
acetate (1o) did not participate in this transformation
(Table 2, entry 15).
Results and discussion
We initially examined the reaction of potassium benzoate
(1a) with dimethyl acetylenedicarboxylate (2a) as a model
reaction to assess the reaction efficiency. When a mixture
of 1a (1.2 mmol) and 1b (1.0 mmol) was stirred in dioxane
in reflux condition for 24 h using Pd(Ph3P)4 (3 mol%), 1,4-
bis(diphenylphosphino)butane
(12 mol%),
Cu2O
(10 mol%), 1,10-phenanthroline (5 mol%), and acetic acid
(4.0 mmol), 3a was obtained in 29% yield (Table 1, entry
1). Our studies were followed by attempting the reaction
under different catalyst systems, solvents, and reaction
temperatures (Table 1). Control experiments revealed that
palladium and copper metallic source were necessary for
this reaction, and the reaction was totally halted if either of
them was absent (Table 1, entries 2 and 3). Among palla-
dium precatalyst examined, the use of Pd2dba3 led to the
formation of 3a in a higher yield (Table 1, entries 1, 4, and
5). The choice of ligand also has great impact for the high
productivity and stereoselectivity (Table 1, entries 5–8).
We believed that bulky ligands exhibiting a large cone
angle destabilize hydrometalated intermediate and disfa-
vored subsequent transmetallation step. Screening of the
catalysts for the decarboxylation path also revealed that
CuBr was the best choice (Table 1, entries 9–12). How-
ever, catalyst screen indicated that Pd2dba3 and AgBF4 also
afforded the product (Table 1, entry 13). Although the
reaction proceeded acceptably in dioxane, we felt that a
better coordinative solvent may facilitate the decarboxy-
lation step and hereby improve the overall yield (Table 1,
In addition, we examined the reaction with different
alkynes (Table 3). The investigation disclosed that ali-
phatic terminal alkynes afforded the products in accept-
able yields; however, the Z/E selectivities were not
satisfactory (Table 3, entries 1 and 2). Phenyl acetylene
(2d) afforded the product in good yield and selectivity
(Table 3, entry 3). Other acetylenic esters also proved to be
good substrates for the current transformation (Table 3,
entries 4–6). Internal aryl alkyne was also successfully
123

Decarboxylative olefination of potassium benzoates via bimetallic catalysis strategy
Table 1 Optimization of the reaction conditions
Entry
Pd system
Cu system
Solvent
Yield of 3a/%, (E/Z)a
1
Pd(Ph3P)4/dppb
–
Cu2O/phen
Cu2O/phen
–
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
DMA
29 (64/36)
–
2
3
Pd(Ph3P)4/dppb
Pd(OAc)2/dppb
Pd2dba3/dppb
Pd2dba3/dppp
Pd2dba3/P(2-Fur)3
Pd2dba3/PtBu3
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Pd2dba3/dppb
Traces
4
Cu2O/phen
Cu2O/phen
Cu2O/phen
Cu2O/phen
Cu2O/phen
CuCl/phen
CuBr/phen
CuPF6/phen
CuBF4/phen
AgBF4
16
5
51 (90/10)
44 (81/19)
16
6
7
8
Traces
9
36 (88/12)
64 (95/5)
51 (85/15)
27 (67/33)
40b (68/32)
71 (99/1)
61 (97/3)
70 (97/3)
56 (94/6)
57c (77/23)
28d (99/1)
60e (97/3)
36 (95/5)
35 (95/5)
10
11
12
13
14
15
16
17
18
19
20
21
22
CuBr/phen
CuBr/phen
CuBr/phen
CuBr/phen
CuBr/phen
CuBr/phen
CuBr/phen
CuBr
DMF
NMP
DMSO
DMA
DMA
DMA
DMA
CuBr/phen
DMA
Reaction conditions: 1a (1.2 mmol), 2a (1.0 mmol), Pd precatalyst (3 mol%), ligand (12 mol%), Cu salt (10 mol%), ligand (5 mol%), acetic
acid (4.0 mmol), and 3.0 cm3 solvent were stirred at 120 °C for 24 h, under a N2 atmosphere
Phen 1,10-phenanthroline, dppp 1,4-bis(diphenylphosphino)butane
aDetermined by GC
b20 mol% of AgBF4 was used
c6 mol% of dppb was used
dThe reaction conducted at 100 °C
eThe mixture was stirred for 18 h
reduced to 3u with excellent stereoselectivity (Table 3,
entry 7). Heteroaromatic alkynes like 2-ethynylfuran (2j)
and electron-deficient aryl alkynes like 1-ethynyl-4-ni-
trobenzene (2k) were completely inconsistent with this
transformation (Table 3, entries 8 and 9). This represents
one of the major limitations of this reaction, which should
be improved in further studies.
carbon dioxide (Scheme 1). By considering this proposed
mechanism, the role of a r-donor ligand like 1,10-
phenanthroline would be to favor the oxidative addition of
the C–C bond. In a parallel path, hydrometalation proceeds
via the reaction of an alkyne coordinated Pd(0) complex 6,
followed by generating intermediate 7 by the act of acetic
acid. On the basis of Hou’s findings [28], the current
reduction of an alkyne to a Z-alkene with acetic acid can be
clearly rationalized to take place via a catalytic cycle
involving hydropalladation of the triple bond with acetic
acid to produce alkenenylpalladium species 7. Subsequent
The mechanism of the reaction is not clear. However, as
suggested in previous reports [35, 36], the complexation of
carboxylate 1 by salt metathesis with copper-bromide gives
4, followed by generating an arylcopper intermediate 5 and
123

M. Khalaj et al.
competent substrates in the reaction, but heteroaromatic
and electron-deficient aryl-substituted terminal alkynes and
alkyl carboxylic salts were incompatible with the reaction
conditions. A possible mechanism was proposed and dis-
tinctive transmetallation of hydropalladated intermediate
with decarboxylated intermediate was proposed to be
involved.
Table 2 Reaction scope for potassium carboxylate
Entry
1
R1
Yield of 3/%, (Z/E)a
Experimental
1
1a
1b
1c
1d
1e
1f
Ph
3a, 71 (99/1)
3b, 82 (99/1)
3c, 76 (98/2)
3d, 85 (99/1)
3e, 47 (95/5)
3f, traces
2
4-Me-C6H4
3-Me-C6H4
3,5-Me-C6H4
2-Me-C6H4
2-t-Bu-C6H4
2-Cl-C6H4
4-Cl-C6H4
4-MeO-C6H4
4-CH3OCO-C6H4
4-NO2-C6H4
3-CF3-C6H4
2-Furyl
Regents, compounds, catalyst, and solvents were obtained
from commercial sources and were used without further
purification. All reactions were carried out in oven-dried
Schlenk tubes under N2 atmosphere. Dry solvents were
obtained by purification according to the standard methods.
Reagents were used as received unless otherwise noted.
Column chromatography was performed using Silica gel 60
(particle size 63–200 lm) (Merck, item number 7734-3).
TLC was performed using Silica gel 60 (Merck, item
number 116835). Melting points: Electrothermal-9100
3
4
5
6
7
1g
1h
1i
3g, 56 (95/5)
3h, 80 (98/23)
3i, 59 (78/22)
3j, 53 (89/11)
3k, 28 (99/1)
3l, 61 (97/3)
3m, 81 (99/1)
3n, 68 (92/8)
–
8
9
10
11
12
13
14
15
1j
1k
1l
1
apparatus. IR Spectra: Shimadzu IR-460 spectrometer. H
and 13C NMR spectra: Bruker DRX-500 AVANCE
instrument; in CDCl3 at 500.1 and 125.7 MHz, resp; d in
ppm, J in Hz. EI-MS (70 eV): Finnigan-MAT-8430 mass
spectrometer. Elemental analyses (C, H, N) were per-
formed with a Heraeus CHN-O-Rapid analyzer. The results
agreed favorably with the calculated values. Gas chro-
matographic (GC) analysis was acquired on a Shimadzu
GC-2010 Series GC System equipped with a flame-ion-
ization detector. GC–MS analysis was performed on Shi-
madzu GCMS-QP2010 Plus Gas Chromatograph/Mass
Spectrometer.
1m
1n
1o
PhCHCH
Me
Reaction conditions:
1 (1.2 mmol), 2a (1.0 mmol), Pd2dba3
(3 mol%), dppb (12 mol%), CuBr (10 mol%), phen (5 mol%), acetic
acid (4.0 mmol), and 3.0 cm3 DMA were stirred at 120 °C for 24 h,
under a N2 atmosphere
aDetermined by GC
transmetallation of 7 with intermediated 5 affords inter-
mediate 8 and regenerates LCuBr. Finally, a reductive
elimination of intermediate 8 gives the Z-products 3 and
regenerates the palladium active catalyst (Scheme 1). No
styrene derivative was obtained when the reaction repeated
with benzene instead of potassium benzoate. It could be
deduced that benzene intermediate did not involve in this
transformation (see Supplementary Material, Scheme 1). It
is worth mentioning that the reaction conducted in the
absence of acetic acid resulted in formation of biphenyl in
91% yield (see Supplementary Material, Scheme 2). As
such, the path involved the nucleophilic attack of car-
boxylate ion on complex 6 to form styrene derivatives
could be overstated. Moreover, the reaction conducted with
benzoic acid instead of benzoate salt afforded vinyl ben-
zoate and dimeric alkene in low yields (see Supplementary
Material, Scheme 3).
General procedure for synthesis of compound 3
An oven-dried and nitrogen-flushed Schlenk tube equipped
with a mechanical stirrer was charged with potassium
carboxylate (1.2 mmol), copper(I) bromide (10 mol%),
Phen (5 mol%), and 3.0 cm3 DMA. The resulting mixture
was stirred at 120 °C for 2 h. Afterwards, the mixture was
charged with Pd2(dba)3 (3 mol%), dppb (12 mol%), and
alkynes (1.0 mmol). The Schlenk tube was sealed and then
evacuated and backfilled with Ar (3 cycles). After stirring
the mixture at room temperature for 15 min, AcOH
(4.0 mmol) was injected and the reaction was heated to
120 °C for 22 h. The mixture was cooled to room tem-
perature and filtered through Celite. The solid was rinsed
with 50 cm3 ethyl acetate and the resulting filtrate was
concentrated under vacuum. The residues were purified by
column chromatography on silica gel (eluent: petroleum
ether/ethyl acetate, gradient 20:1 to 5:1) furnishing 3.
In summary, we have developed a catalytic reaction for
the olefination of potassium carboxylate with accept-
able catalyst and additive loading. Aryl and heteroaryl
potassium carboxylate and a decent range of alkynes were
123

Decarboxylative olefination of potassium benzoates via bimetallic catalysis strategy
Table 3 Reaction scope for alkynes
Entry
2
R2
R3
Yield of 3/%, (Z/E)a
1
2
3
4
5
6
7
8
9
2b
2c
2d
2e
2f
n-Bu
H
3o, 62 (75/25)
3p, 60 (78/22)
3q, 73 (89/11)
3r, 79 (99/1)
3s, 65 (98/2)
3t, 83 (99/1)
3u, 84 (99/1)
–
n-Pr
H
Ph
H
CO2Et
Ph
CO2Et
CO2Et
H
2g
2h
2j
CO2Et
Ph
Ph
2-Furyl
4-NO2-C6H4
H
2k
H
–
Reaction conditions: 1a (1.2 mmol), 2 (1.0 mmol), Pd2dba3 (3 mol%), dppb (12 mol%), CuBr (10 mol%), phen (5 mol%), acetic acid
(4.0 mmol), and 3.0 cm3 DMA were stirred at 120 °C for 24 h, under a N2 atmosphere
aDetermined by GC
Dimethyl 2-phenylmaleate (3a) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
4/1, Rf = 0.32) affording 0.16 g (73%) of 3a. Spectroscopic
data were consistent with that reported in Ref. [30].
Dimethyl 2-(o-tolyl)maleate (3e) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
3/1, Rf = 0.46) affording 0.11 g (47%) of 3e. Spectroscopic
data were consistent with that reported in Ref. [38].
Dimethyl 2-(p-tolyl)maleate (3b) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
4/1, Rf = 0.35) affording 0.19 g (82%) of 3b. Spectro-
scopic data were consistent with that reported in Ref. [37].
Dimethyl 2-(2-chlorophenyl)maleate (3g, C12H11ClO4) The
crude product was purified by column chromatography
(SiO2; hexane/EtOAc 3/1, Rf = 0.34) affording 0.14 g
(56%) of 3 g. IR (KBr): vꢀ = 3046, 2981, 1728, 1718, 1634,
1
1466, 1357, 1087 cm-1; H NMR (500.1 MHz, CDCl3):
Dimethyl 2-(m-tolyl)maleate (3c) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
4/1, Rf = 0.46) affording 0.18 g (76%) of 3c. Spectroscopic
data were consistent with that reported in Ref. [37].
d = 3.58 (3H, s, OCH3), 3.90 (3H, s, OCH3), 6.65 (1H, s,
3
CH), 7.15 (1H, t, J = 6.9 Hz, CH), 7.30-7.38 (2H, m, 2
CH), 7.65 (1H, d, 3J = 6.9 Hz, CH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 54.1 (OCH3), 56.8 (OCH3),
102.6 (CH), 128.7 (CH), 129.3 (CH), 131.2 (CH), 131.7
(CH), 134.2 (C), 137.1 (C), 149.4 (C), 165.7 (C=O), 168.1
(C=O) ppm; EI-MS (70 eV): m/z (%) = 256 ([M ? 2]?,
12), 254 (M?, 4), 223 (16), 195 (41), 193 (51), 136 (62),
111 (100), 85 (49).
Dimethyl 2-(3,5-dimethylphenyl)maleate (3d, C14H16O4) The
crude product was purified by column chromatography
(SiO2; hexane/EtOAc 5/1, Rf = 0.42) affording 0.21 g
(85%) of 3d. IR (KBr): vꢀ = 3028, 2965, 1738, 1727, 1644,
1
1451, 1316, 1102 cm-1; H NMR (500.1 MHz, CDCl3):
d = 2.35 (6H, s, 2 CH3), 3.56 (3H, s, OCH3), 3.80 (3H, s,
OCH3), 6.60 (1H, s, CH), 7.17 (2H, s, 2 CH), 7.25 (1H, s,
CH) ppm; 13C NMR (125.7 MHz, CDCl3): d = 25.6 (2
CH3), 53.5 (OCH3), 56.6 (OCH3), 107.2 (CH), 126.9 (2
CH), 131.4 (CH), 134.8 (C), 139.6 (2 C), 149.5 (C), 165.3
(C=O), 167.0 (C=O) ppm; EI-MS (70 eV): m/z (%) = 248
(M?, 2), 217 (16), 189 (32), 187 (46), 142 (56), 105 (100),
81 (79).
Dimethyl 2-(4-chlorophenyl)maleate (3h) The crude pro-
duct was purified by column chromatography (SiO2; hex-
ane/EtOAc 4/1, Rf = 0.21) affording 0.20 g (80%) of 3h.
Spectroscopic data were consistent with that reported in
Ref. [41].
Dimethyl 2-(4-methoxyphenyl)maleate (3i) The crude
product was purified by column chromatography (SiO2;
hexane/EtOAc 3/1, Rf = 0.38) affording 0.15 g (59%) of
123

M. Khalaj et al.
Scheme 1
3i. Spectroscopic data were consistent with that reported in
Ref. [37].
(SiO2; hexane/EtOAc 3/1, Rf = 0.26) affording 0.18 g
(61%) of 3 l. IR (KBr): vꢀ = 3043, 2978, 1729, 1718, 1671,
1
1453, 1361, 1182 cm-1; H NMR (500.1 MHz, CDCl3):
Dimethyl 2-[4-(methoxycarbonyl)phenyl]maleate (3j, C14H14O6)
The crude product was purified by column chromatography
(SiO2; hexane/EtOAc 3/1, Rf = 0.56) affording 0.15 g
(53%) of 3j. IR (KBr): vꢀ = 3018, 2960, 1736, 1725, 1710,
d = 3.55 (3H, s, OCH3), 3.76 (3H, s, OCH3), 7.02 (1H, s,
CH), 7.19-7.30 (2H, m, 2 CH), 7.44 (1H, d, J = 6.9 Hz,
3
CH), 7.59 (1H, s, CH) ppm; 13C NMR (125.7 MHz,
CDCl3): d = 54.1 (OCH3), 57.9 (OCH3), 114.4 (CH), 125.1
1638, 1466, 1314, 1094 cm-1 1H NMR (500.1 MHz,
;
3
3
(CH, q, J = 3.9 Hz), 126.2 (CH, q, J = 3.9 Hz), 128.7
(CF3, q, 1J = 273.1 Hz), 129.5 (CH), 131.2 (C, q,
2J = 31.9 Hz), 133.2 (CH), 135.8 (C), 151.1 (C), 166.1
(C=O), 169.2 (C=O) ppm; EI-MS (70 eV): m/z (%) = 288
(M?, 11), 268 (12), 171 (38), 120 (58), 105 (100), 77 (60).
CDCl3): d = 3.69 (3H, s, OCH3), 3.81 (3H, s, OCH3), 3.94
(3H, s, OCH3), 6.92 (1H, s, CH), 7.52 (2H, d, 3J = 7.0 Hz,
3
2 CH), 7.80 (2H, d, J = 7.0 Hz, 2 CH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 53.1 (OCH3), 55.0 (OCH3), 56.2
(OCH3), 111.6 (CH), 130.1 (2 CH), 133.5 (C), 134.6 (2
CH), 138.2 (C), 153.1 (C), 165.7 (C=O), 165.9 (C=O),
167.1 (C=O) ppm; EI-MS (70 eV): m/z (%) = 278 (M?, 6),
247 (13), 219 (34), 217 (30), 160 (48), 129 (69), 105 (100).
Dimethyl 2-(furan-2-yl)maleate (3m, C10H10O5) The crude
product was purified by column chromatography (SiO2;
hexane/EtOAc 4/1, Rf = 0.47) affording 0.17 g (81%) of
3m. IR (KBr): vꢀ = 3058, 2982, 1739, 1728, 1654, 1461,
Dimethyl 2-(4-nitrophenyl)maleate (3k, C20H24N2O6) The
crude product was purified by column chromatography
(SiO2; hexane/EtOAc 2/1, Rf = 0.21) affording 0.08 g
(28%) of 3 k. IR (KBr): vꢀ = 3042, 2952, 1736, 1721, 1655,
1
1440, 1337, 1106 cm-1; H NMR (500.1 MHz, CDCl3):
d = 3.61 (3H, s, OCH3), 3.72 (3H, s, OCH3), 6.85-6.91
(2H, m, 2 CH), 7.31 (1H, d, 3J = 6.1 Hz, CH), 8.38 (1H, d,
3J = 6.2 Hz, CH) ppm; 13C NMR (125.7 MHz, CDCl3):
d = 53.9 (OCH3), 56.2 (OCH3), 113.3 (CH), 115.8 (CH),
116.2 (CH), 149.1 (CH), 150.3 (C), 150.8 (C), 166.3
(C=O), 168.0 (C=O) ppm; EI-MS (70 eV): m/z (%) = 210
(M?, 12), 179 (18), 151 (53), 149 (35), 92 (61), 67 (100).
1537, 1448, 1373, 1322, 1101 cm-1
;
1H NMR
(500.1 MHz, CDCl3): d = 3.72 (3H, s, OCH3), 3.90 (3H, s,
OCH3), 7.23 (1H, s, CH), 7.58 (2H, d, 3J = 6.8 Hz, 2 CH),
8.29 (2H, d, 3J = 6.8 Hz, 2 CH) ppm; 13C NMR
(125.7 MHz, CDCl3): d = 54.7 (OCH3), 56.8 (OCH3),
116.1 (CH), 127.4 (2 CH), 134.9 (2 CH), 140.1 (C), 148.2
(C), 152.5 (C), 166.9 (C=O), 169.7 (C=O) ppm; EI-MS
(70 eV): m/z (%) = 265 (M?, 1), 234 (11), 204 (39), 142
(100), 122 (51), 54 (63).
Dimethyl 2-[(E)-styryl]maleate (3n) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
5/1, Rf = 0.21) affording 0.17 g (68%) of 3n. Spectro-
scopic data were consistent with that reported in Ref. [30].
Dimethyl 2-[3-(trifluoromethyl)phenyl]maleate (3l, C13H11F3O4)
The crude product was purified by column chromatography
Hex-1-en-1-ylbenzene (3o) The crude product was puri-
fied by column chromatography (SiO2; hexane/EtOAc 7/1,
123

Decarboxylative olefination of potassium benzoates via bimetallic catalysis strategy
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Pent-1-en-1-ylbenzene (3p) The crude product was puri-
fied by column chromatography (SiO2; hexane/EtOAc 7/1,
Rf = 0.47) affording 0.09 g (60%) of 3p. Spectroscopic
data were consistent with that reported in Ref. [39].
Ethene-1,1-diyldibenzene (3q) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
6/1, Rf = 0.24) affording 0.13 g (73%) of 3q. Spectro-
scopic data were consistent with that reported in Ref. [43].
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Diethyl 2-phenylmaleate (3r) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
4/1, Rf = 0.38) affording 0.20 g (79%) of 3r. Spectroscopic
data were consistent with that reported in Ref. [40].
´
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21. Gordillo A, Ortun˜o MA, Lopez-Mardomingo C, Lledos A, Uja-
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Ethyl (Z)-2,3-diphenylacrylate (3s) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
5/1, Rf = 0.21) affording 0.16 g (65%) of 3s. Spectroscopic
data were consistent with that reported in Ref. [41].
24. Huang L, Biafora A, Zhang G, Bragoni V, Gooßen LJ (2016)
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13:10420
Ethyl 2-phenylacrylate (3t) The crude product was puri-
fied by column chromatography (SiO2; hexane/EtOAc 3/1,
Rf = 0.29) affording 0.15 g (83%) of 3t. Spectroscopic data
were consistent with that reported in Ref. [42].
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Ethene-1,1,2-triyltribenzene (3u) The crude product was
purified by column chromatography (SiO2; hexane/EtOAc
4/1, Rf = 0.36) affording 0.21 g (84%) of 3u. Spectro-
scopic data were consistent with that reported in Ref. [30].
Acknowledgements We thank Buinzahra Branch of Islamic Azad
University for additional unrestricted support.
34. Rudolphi F, Song B, Gooßen LJ (2011) Adv Synth Catal 353:337
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