Palladium(II) oxide impregnated on magnetite as a catalyst for the synthesis of 4-arylcoumarins: Via a Heck-arylation/cyclization process

Article abstract of DOI:10.1039/c6ra01731b

Heck-arylation/cyclization was achieved using heterogeneous palladium(ii) oxide impregnated on magnetite catalyst (2.5 mol%) with a lower catalyst loading than that reported for similar processes. Ethanol was used as a non-toxic and bio-renewable solvent. Good yields were afforded using a broad range of substrates (40-98%). The catalyst could be partially recycled, and analyses confirmed the almost total reduction of palladium(ii) oxide to palladium(0) as well as the iodine poissoning effect, which is the main barrier to complete recyclability.

Full text of DOI:10.1039/c6ra01731b

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DOI: 10.1039/C6RA01731B
Journal Name
ARTICLE
Palladium(II) Oxide Impregnated on Magnetite as Catalyst for the
Synthesis of 4-Arylcoumarins via a Heck-arylation/cyclization
process
Received 00th January 20xx,
Accepted 00th January 20xx
Juana M. Pérez,a Rafael Cano,b Gerard P. McGlackenb and Diego J. Ramóna*
DOI: 10.1039/x0xx00000x
Heck-arylation/cyclization has been achieved using the heterogeneous palladium(II) oxide impregnated on magnetite
catalyst (2.5 mol%), using a lower catalyst loading than that reported for similar processes. Ethanol was used as non-
toxic and bio-renewable solvent. Good yields are afforded using a broad range of substrates (40-98 %). The catalyst
could be partially recycled and analyses confirmed the almost total reduction of palladium(II) oxide to palladium(0)
as well as iodine poissoning effect as the main barrier to complete recyclability.
www.rsc.org/
2005 using aryl halides in a molten
n-Bu4NOAc/n-Bu4NBr
mixture,12 later on the approach was modified by the use of
aryl diazonium salts in methanol.13 Finally, diaryliodonium(III)
salts have been successfully used to perform this
transformation using dimethylformamide as solvent.14 In all
cases the reaction was performed with the help of high
amounts of the homogeneous Pd(OAc)2 (5-10 mol%) catalyst,
giving moderate to good yields.
Introduction
The Heck reaction1 is a powerful and general synthetic method
used in Organic Chemistry to construct compounds by C-C
bond formation. Its synthetic flexibility and compatibility with
most organic functional groups makes it one of the most
explored reaction promoted by palladium.2 Some efforts have
been devoted to improving the efficiency of this reaction, and
recently, iodonium salts3 have been extensively studied as
arylation agent to replace aryl halides or triflates in the Heck
reaction. They are appealing coupling partners as they display
different reactivity profiles to halides, are highly reactive yet
air- and moisture-stable, and can be easily prepared in one
step from commercially available starting materials.4,5
Coumarins6 are important structural motifs in natural
compounds and exhibit broad biological activity. Particularly,
4-aryl derivatives constitute a subgroup of flavonoids that have
received considerable attention, as they display important
biological activities such as anti-HIV, antimalarial, antibacterial
and cytotoxic properties. Classical synthetic approaches for the
synthesis of 4-arylcoumarins are based on Knoevenagel
condensation,7 cross-coupling reactions,8 C-H bond activation,9
von Pechman condensation,10 among others.11 In many cases,
the reactions were performed under harsh reaction conditions
and high temperatures. The loading of transition metal was, in
many cases, very high (5-20 mol%).
As a continuation of our project on the arylation of
heterocycles,15 herein, we reported the synthesis of 4-
arylcoumarins using for the first time heterogeneous
palladium(II) oxide impregnated on magnetite catalyst for the
Heck-arylation/cyclization using diaryliodonium(III) salts.
Ethanol as a non-toxic and bio-renewable solvent was used
under mild reaction conditions.
Results and discussion
To start the study, (E)-ethyl 3-(2-hydroxyphenyl)acrylate (1a)
and diphenyliodonium tetrafluoroborate (2a), using palladium
impregnated on magnetite as catalyst,16 was selected as the
reaction model for the optimization (Table 1). Initially, the
reaction was performed using different equivalents of
compound 2a (entries 1-3). Full conversion of the starting
material was observed after 5 hours when 2 equivalents of the
salt were used. This result could not be improved by increasing
the amount of iodonium salt. After that, different loadings of
palladium catalyst were tested (entries 4-7). Good yields were
obtained with 2.5 mol% Pd, which could be slightly improved
using higher amounts of metal. Then, a study of the solvent
was performed (entries 8-15). A moderate yield was obtained
in H2O, but best results were observed in EtOH (entry 5). When
the reaction was performed without solvent (entry 16) only
traces of the product could be detected.
Another methodology to obtain 4-arylcoumarins, that has
been less studied, is the arylation/cyclization of
o-
hydroxylcinnamates. Initially, this approach was reported in
a. Instituto de Síntesis Orgánica (ISO), and Departamento de Química Orgánica,
Facultad de Ciencias, Universidad de Alicante, Apdo. 99, E-03080-Alicante, Spain.
b. Department of Chemistry and Analytical & Biological Chemistry Research Facility
(ABCRF), University College Cork, Ireland.
Electronic Supplementary Information (ESI) available: [TEM images, 1H-NMR and
13C-NMR]. See DOI: 10.1039/x0xx00000x
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Table 1. Optimization of the reaction conditions.a
Table 2. Optimization of the catalyst.a
View Article Online
DOI: 10.1039/C6RA01731B
CO2Et
Ph
Catalyst (mol%)
Ph2IBF4
+
EtOH (0.75 mL)
80 ºC, 5 h
O
O
OH
1a
2a
3a
Entry PdO-Fe3O4 (mol%) Solvent
T (ºC)
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
60
RT
80
Yield (%)b
Entry
1
Catalyst (mol%)
PdO-Fe3O4 (2.5)
-
Yield (%)b
1
10
10
10
1
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
Toluene
THF
99
54
99
46
86
90
99
0
99
0
2c
3d
4
2
3
Nano-Fe3O4 (129.9)
Micro-Fe3O4 (129.9)
CoO-Fe3O4 (2.83)
NiO-Fe3O4 (2.06)
Ru2O3-Fe3O4 (2.64)
Rh2O3-Fe3O4 (2.52)
Ag2O/Ag-Fe3O4 (2.50)
OsO2-Fe3O4 (2.05)
IrO2-Fe3O4 (2.10)
PtO/PtO2-Fe3O4 (2.15)
Au2O3/Au-Fe3O4 (2.26)
PdO/Cu-Fe3O4 (3.06/1.79)
NiO/Cu-Fe3O4 (1.82/1.76)
WO3-Fe3O4 (2.26)
CuO-Fe3O4 (2.34)
PdO (2.5)
11
10
17
0
4
5
2.5
5
5
6
6
7
7.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
7
25
25
4
8
8
9
0
9
10
11
12
13
14
15
16
17
H2O
64
0
10
11
12
13
14
15
16
17
18
19
8
Dioxane
DCM
CH3CN
DMF
DMSO
-
10
17
0
0
34
48
10
15
7
18
7
25
0
2.5
2.5
EtOH
EtOH
18
a
99
79
83
76
PdCl2 (2.5)
Reaction carried out using compounds 1a (0.25 mmol), 2a
b
(0.5 mmol). Yield determined by GC using 0.25 mmol of
c
tridecane as internal standard. Reaction carried out using
20
a
Pd(OAc)2 (2.5)
Reaction carried out using compounds 1a (0.25 mmol), 2a
b
d
compounds 1a (0.25 mmol), 2a (0.25 mmol).
Reaction (0.5 mmol). Yield determined by GC using 0.25 mmol of
tridecane as internal standard.
carried out using compounds 1a (0.25 mmol), 2a (0.75 mmol).
To complete the optimization, different temperature were The corresponding product was obtained with a 39 % yield
tried (entries 17-18). Only traces of product were detected at after the first cycle indicating that the catalytic activity of the
room temperature and full conversion of the starting material catalyst has been affected by the first reaction.
was observed at 80 °C.
As a consequence of the non-recyclability of the catalyst, some
Once the optimal conditions were determined, the reaction investigative studies were performed. X-Ray Photoelectron
was submitted to a variety of catalysts, prepared by a simple Spectroscopy (XPS) analyses of the catalyst showed a change in
impregnation protocol17 (Table 2). The reaction without the oxidation state [palladium(II) oxide to palladium(0)] after
catalyst did not give any product (entry 2). The partial completion of the reaction.
inactivity of the support was confirmed (entries 3 and 4), the
role of magnetite is only to facilitate the easy separation of the
reaction media through magnetic decantation.18 Then,
normal recycle
different metal oxides impregnated on magnetite (entries 5-
17) were evaluated as catalyst, but the high activity displayed
regeneration of catalyst with O2
100
by the palladium catalyst could not be surpassed. With these
80
results in hand, the reaction was carried out using different
60
sources of palladium, (entries 18-20). All catalysts tested
40
(homogeneous, as well as heterogeneous) failed to give similar
20
or improved activities relative to palladium on magnetite
(entry 1).
0
In order to establish the reusability of the catalyst, the
standard reaction was repeated (Figure 1). When the reaction
was completed, the catalyst was retained in the reaction vessel
using a magnet and washed several times with ethanol. The
0
1
2
Cycle
vessel was then charged with a new set of reagents and the Figure 1. Recycling of the PdO-Fe3O4 catalyst.
standard conditions were applied.
2 | J. Name., 2012, 00, 1-3
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30
25
Before reaction
11900
9900
7900
5900
3900
1900
-100
20
15
10
5
Fit
3d 5/2 PdO
3d 3/2 PdO
0
330
335
340
345
Particle size (nm)
Binding energy (eV)
Figure 3. Particle size distribution of fresh catalyst.
After reaction
Fit
2950
2450
1950
1450
950
3d 5/2 Pd
3d 3/2 Pd
3d 5/2 Pd
3d 3/2 Pd
3d 5/2 PdO
3d 3/2 PdO
The TPR and TPO analyses of Fe3O4, fresh and recycled catalyst
were carried out (see Supporting Information). Previously to
analyses, the samples were pre-treated by heating at 200 ºC
under Argon atmosphere to be sure that all the organic
material was removed. Then, the samples were heated to 900
ºC at 10 ºC/min in the corresponding atmosphere [TPR was
performed with a mixture Ar/H2 (1.8 %), and TPO with a
mixture Ar/O2 (3%)].
450
-50
In the case of differential thermogravimetric analysis under
reductive atmosphere (Figure 4a), when the temperature
reached 100 ºC only the fresh catalyst sample showed a
consumption of hydrogen and an emergence of H2O, what it
could be assigned to the reduction from PdO to Pd(0).
330
335
340
345
Binding energy (eV)
Figure 2. XPS of the fresh and recycled palladium catalyst.
At 300 ºC a new consumption of H2 could be observed and it
seems to be due to the reduction of superficial magnetite. In
the case of both magnetite support and recycled catalyst, only
this last consumption of hydrogen was detected. It should be
pointed out that in the case of the supported catalyst the
reduction of superficial magnetite took places at lower
temperatures, probably by the influence of the supported
palladium. From the data of differential thermogravimetric
analysis under reductive atmosphere it could be calculated the
expected weight losing due to a PdO to Pd(0) transformation,
with this figure being slightly higher than the nominal
palladium. This could be due to the reduction through a spill-
over of hydrogen to the support of magnetite units that are in
intimate contact with palladium.
The XPS spectra of the post-reaction sample showed, after
deconvolution, four peaks at 334.9, 335.7, 340.3 and 341.3 eV,
which correspond to the binding energies of Pd 3d5/2 and Pd
3d3/2, and two more peaks that have the same binding energy
than the starting palladium(II) oxide nanoparticles, with a
relative area of 4% (Figure 2). Furthermore, Transmission
Electron Microscopy (TEM) analyses were carried out. We
observed a high sinterization of the palladium nanoparticles as
well dissociation of the palladium from the support after
completion of the reaction (see Supporting Information). The
initial size range of the starting PdO nanoparticles was 2-4 nm
(Figure 3) but increased to 14-16 nm after the reaction. The
phenomenon of leaching was studied by inductively coupled
plasma mass spectrometry (ICP-MS). Here, the reaction
mixture was filtered at high temperature after completion of
the reaction and the homogeneous solution was tested. Only
3.64 % of the initial palladium was present in solution. More
importantly, no progress of the reaction was observed in the
filtrate after the filtration, providing further evidence of the
heterogeneous nature of the reaction.
In the case of differential thermogravimetric analysis under
oxidative atmosphere, only the recycled sample showed a
weight losing at about 400 ºC (Figure 4b). The mass analysis
showed the loss of CO2 and then iodine in the case of recycled
catalyst (Figure 5). The emergence of CO2 should be associated
to organic compounds strongly bounded to the catalyst
surface; meanwhile the emergence of iodine could be a
hindered proof of the poisoning of palladium species by this
element.
Finally, a modified hot filtration test was performed. Thus after
the standard reaction, the mixture was decanted with the aid
of a magnet, while hot, and a mixture of 1c (0.25 mmol) and 2a
(0.5 mmol) dissolved in 0.75 mL of ethanol, was added to the
filtrate. After five hours at 80 °C, starting reagents 1c and 2a
were recovered unchanged.
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The use of substituted acrylates and diVaireywliAortdicolenOinulimne
tetrafluoroborates gave very good yieDldOsI: 1in0.10a3ll9/Cth6ReA0c1a7s3e1Bs
(entries 9-11). To finish with the study, different
diaryliodonium trifluoromethanesulfonates were tested, which
gave moderate to good results (entries 12-14). In the case of
phenyl(2,4,6-triisopropylphenyl)iodonium
0,00245
a)
Fe3O4
Fresh PdO-Fe3O4
Recycled PdO-Fe3O4
0,00195
0,00145
0,00095
0,00045
-0,00005
trifluoromethanesulfonate (entry 12) the expected product 3a
was obtained with a lower yield than that obtained with the
previously tested diphenyliodonium tetrafluoroborate (entry
1). Others aryl sources were ineffective in similar reactions.19
Once the scope of the reaction was evaluated, the possible
pathway of the process was studied. The reaction could occur
through a cyclization reaction followed by arylation20 or
through a Heck-arylation reaction and subsequent cyclization.
To check if the reaction took place following the first process,
0
200
400
600
800
1000
T (ºC)
Fe3O4
b)
6,00E-04
3,00E-04
0,00E+00
-3,00E-04
-6,00E-04
-9,00E-04
Fresh PdO-Fe3O4
Recycled PdO-Fe3O4
the
cyclization
reaction
of
(
E)-ethyl
3-(2-
hydroxyphenyl)acrylate (1a) using ethanol at 80 °C was tested.
Here the starting material was recovered unchanged. We
0
100
200
300
400
500
T (ºC)
600
700
800
gained access to the cyclised product using an
mediated reaction.6 When the resulting 2
n-Bu3P
H
-chromen-2-one
was treated with salt 2a and PdO-Fe3O4 under standard
conditions, only starting chromenone was recovered. These
results suggest that the cyclization/arylation pathway is
unlikely. To further study if the Heck-arylation reaction took
place first, followed by cyclization (Scheme 1), some acrylates
Figure 4. Differential thermogravimetric curves of Fe3O4
support, fresh and recycled catalyst with: a) reductive cyclisation, were tested under the optimal reaction conditions
atmosphere, b) oxidative atmosphere. (Table 4). Using two equivalents of 2a, a 3:1 mixture of the
4, no longer possessing the required –OH group needed for
mono- and di-substituted products
5
were obtained in good
Guided by the previously mentioned XPS, as well as TPR and yield (entry 1).
TPO analysis, we attribute the deactivation of the catalyst to
an almost complete reduction of the nanoparticles of
palladium(II) oxide to palladium(0), the associated
morphologic changes and the poisoning by iodine species.
CO2
Thus in an attempt to recycle the catalyst, post reaction
particles of palladium(II) were subjected to oxygen (bubbling
O2) (see Figure 1). Using this protocol, the results obtained for
the recycling of the catalyst were improved but did not reach
the initial catalyst activity. Other oxidants tested (e.g.
or I2) gave poorer results.
t-BuOOH
Once the best conditions were established, the scope of the
reaction was evaluated (Table 3). Moderate yields could be
obtained using symmetrical bis(4-fluorophenyl)iodonium
tetrafluoroborate (entry 2). Better results were observed, with
symmetrical bis(4-methoxyphenyl)iodonium tetrafluoroborate
0
200
400
600
800
1000
T (ºC)
Iodine
giving 77
%
yield (entry 3). Chemoselective Heck-
arylation/cyclization reactions were performed by introducing
a non-transferable aryl group such as 1,3,5-triisopropylphenyl
(TRIP). Good results were observed with substrates bearing
electron-withdrawing and sterically hindered electron-
donating groups (entries 4 and 5).
Then various substituted
tested (entries 6-8). Better results were found with the
sterically hindered )-ethyl 3-(3,5-di-tert-butyl-2-
hydroxyphenyl)acrylate. The presence of electron-withdrawing
groups at 5-position in the aromatic ring of the acrylate Figure 5. MS analysis of CO2 and iodine on recycled PdO-Fe3O4
o-hydroxyphenylacrylates were
0
200
400
600
800
1000
(
E
T (ºC)
seemed to negatively affect the reaction.
catalyst.
4 | J. Name., 2012, 00, 1-3
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Table 3. Scope of the reactiona
Entry
1
R1
H
R2
H
X
Ar1
Ar2
Nº
3a
3b
3c
3d
3e
3f
Yield (%)b
98
BF4
BF4
BF4
BF4
BF4
BF4
BF4
BF4
BF4
BF4
BF4
OTf
OTf
OTf
Ph
Ph
2
H
H
4-FC6H4
4-MeOC6H4
4-ClC6H4
2-MeC6H4
Ph
4-FC6H4
4-MeOC6H4
TRIP
40
3
H
H
77
4
H
H
64
5
H
H
TRIP
55
6
F
H
Ph
72
7
tBu
Br
F
tBu
OMe
H
Ph
Ph
3g
3h
3i
97
8
Ph
Ph
56
9
4-MeOC6H4
4-FC6H4
4-FC6H4
Ph
4-MeOC6H4
4-FC6H4
4-FC6H4
TRIP
70
10
11
12
13
14
tBu
Br
H
tBu
OMe
H
3j
79
3k
3a
3l
95
66
H
H
4-MeC6H4
4-MeC6H4
52
Br
OMe
4-MeC6H4
4-MeC6H4
3m
91
aReaction carried out using compounds 1 (0.25 mmol) and 2 (0.5 mmol). bIsolated yield after column chromatography.
With these results in hand, the reaction was repeated with Table 4. Heck-arylation reactiona
only one equivalent of the salt 2a. A lower amount of the di-
substituted product 5b was obtained, along with concomitant
improvement in the yield of 5a (entry 2). Then, methyl
cinnamate (4b) was tested and a 68 % yield of 5c was obtained
(entry 3). To finish with the study of the Heck-arylation,
different substituents at the 4-possition of the aromatic ring of
starting cinnamate were used, obtaining a ca. mixture 1:1 of
Z/E isomers in good yields (entries 4 and 5).
PdO-Fe3O4
(2.5 mol%)
O
R
O
Ph2IBF4
+
R
OR'
Ph
OR'
EtOH (0.75 mL)
80 ºC, 5h
4
2a
5
Entry
R
R’
Et
Et
Et
Nº
5a
5a
5b
Yield (%)b
76 (23)c
86 (13)c
1
H
2d
3
H
Ph
68
4
4-MeC6H4
Me
Me
5c
71 (Z/E 0.95/1)
69 (Z/E 1/0.8)
5
4-MeOC6H4
5d
aReaction carried out using compounds
4 (0.25 mmol) and 2a
(0.5 mmol). bIsolated yield after bulb-to-bulb distillation.
cIsolated yield of compound 5b. Reaction carried out using
d
compounds 4 (0.25 mmol) and 2a (0.25 mmol).
Experimental
General
Solvents and reagents were used as obtained from commercial
1
sources and without purification. H NMR (400 MHz) spectra
and 1H NMR (300 MHz) spectra were recorded on Bruker
Avance 400 and Bruker Avance 300 NMR spectrometers
respectively in proton coupled mode. 13C NMR (150 MHz)
spectra and 13C NMR (75.5 MHz) spectra were recorded on
Bruker Avance 400 and Bruker Avance 300 NMR
Scheme 1. Possible mechanism of the reaction.
spectrometers respectively in proton decoupled mode at 20 °C
in deuterated chloroform using tetramethylsilane as internal
standard; chemical shifts are given in δ (parts per million) and
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coupling constants (
J) in Hertz. Low-resolution mass spectra mL) was added ethyl 2-(diethoxyphosphoryl)acetate (5.2 mmol) and
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DOI: 10.1039/C6RA01731B
were recorded on a Waters Quattro Micro triple quadropole DBU (5.1 mL). The solution was stirred at room temperature
instrument in electrospray ionisation (ESI) mode using 50 % overnight. The resulting mixture was quenched with water and
acetonitrile-water containing 0.1 % formic acid as eluent; extracted with AcOEt (3 × 5 mL). The organic phases were dried
samples were made up in acetonitrile. High resolution precise over MgSO4, followed by evaporation under reduced pressure to
mass spectra (HRMS) were recorded on a Waters LCT Premier remove the solvent. The product was usually purified by
Tof LC-MS instrument in electrospray ionisation (ESI) mode chromatography on silica gel (hexane/ethyl acetate) to give the
using 50 % acetonitrile-water containing 0.1 % formic acid as corresponding products 1. Physical and spectroscopic data follow:
(E)-Ethyl 3-(2-hydroxyphenyl)acrylate (1a).13 White solid; m.p. =
eluent; samples were made up in acetonitrile. Infrared spectra
were measured as pressed potassium bromide (KBr) for solids
83-86 ºC (Hexane/AcOEt); IR (ATR): ν 3375, 1675, 1601, 1459, 1249,
1036 cm-1; 1H-NMR (300 MHz, CDCl3): δ 1.36 (3H, t, J = 7.1 Hz), 4.30
or thin films on sodium chloride plates for liquids on a Perkin-
Elmer FT-IR spectrometer. Melting points were obtained with a
(2H, q, J = 7.1 Hz), 6.62 (1H, d, J = 16.2 Hz), 6.85-6.95 (3H, m), 7.20-
7.25 (1H, m), 7.45-7.50 (1H, m), 8.02 (1H, d, J = 16.2 Hz); 13C-NMR
Reichert Thermovar apparatus. XPS analyses were carried out
on a VG-Microtech Mutilab. TEM images were obtained on a
(75 MHz, CDCl3): δ 14.3, 60.8, 116.4, 118.1, 120.5, 121.6, 129.2,
131.4, 140.9, 155.6, 168; MS (EI) m/z (%): 192 (M+, 7), 147 (15), 146
JEOL, model JEM-2010 equipped with an X-ray detector
OXFORD INCA Energy TEM 100 for microanalysis (EDS). XRF
(69), 118 (100), 91 (20), 90 (18), 89 (21).
analyses were obtained on a PHILIPS MAGIX PRO (PW2400) X-
(E)-Ethyl 3-(5-fluoro-2-hydroxyphenyl)acrylate (1b).21 White solid;
ray spectrometer equipped with a rhodium X-ray tube and a
m.p. = 114-115 ºC (Hexane/AcOEt); IR (KBr): ν 3431, 1685, 1629,
beryllium window. BET isotherms were carried out on an
1508, 1445, 1372, 1335, 1264, 1199 cm-1; 1H-NMR (300 MHz,
AUTOSORB-6 (Quantachrome), using N2. The chromatographic
CDCl3): δ 1.35 (3H, t, J = 7.1 Hz), 4.30 (2H, q, J = 7.1 Hz), 6.59 (1H, d,
analyses (GLC) were determined with a Hewlett Packard HP-
3
4
J = 16.2 Hz), 6.82 (1H, dd, J(H,H) = 8.9 Hz, J(H,F) = 4.6 Hz), 6.94 (1H,
ddd, 3J(H,H) = 8.8 Hz, 3J(H,F) = 7.8 Hz, 4J(H,H) = 8.8 Hz), 7.10-7.20 (2H, m),
8.03 (1H, d, J = 15.7 Hz); 13C-NMR (75 MHz, CDCl3): δ 14.2, 61.0,
5890 instrument equipped with a flame ionization detector
and 12 m HP-1 capillary column (0.2 mm diam, 0.33 mm film
thickness, OV-1 stationary phase), using nitrogen (2 mL/min)
as a carrier gas, Tinjector = 275 ºC, Tdetector = 300 ºC, Tcolumn = 60
2
3
2
114.3 (d, J(C,F)= 23.3 Hz), 117.4 (d, J(C,F)= 8.0 Hz), 118.1 (d, J(C,F)
=
3
4
23.5 Hz), 119.1, 122.6 (d, J(C,F)= 7.5 Hz), 139.8 (d, J(C,F)= 2.2 Hz),
ºC (3 min) and 60-270 ºC (15 ºC/min),
P = 40 kPa. Thin layer
4
1
151.7 (d, J(C,F)= 1.9 Hz), 156.7 (d, J(C,F)= 238.4 Hz), 168.5; 19F NMR
chromatography (TLC) was carried out on Schleicher & Schuell
F1400/LS 254 plates coated with a 0.2 mm layer of silica gel;
(282 MHz, CDCl3): δ -123.9 (m).
detection by UV254 light, staining with phosphomolybdic acid (E)-Ethyl 3-(3,5-di-tert-butyl-2-hydroxyphenyl)acrylate (1c).14 Pale
[25 g phosphomolybdic acid, 10 g Ce(SO4)2 4 H2O, 60 mL of yellow solid; m.p. = 120-122 ºC (Hexane/AcOEt); IR (ATR): ν 1684,
concentrated H2SO4 and 940 mL H2O]. Column 1621, 1471, 1441, 1289, 1186 cm-1; 1H-NMR (300 MHz, CDCl3): δ
chromatography was performed using silica gel 60 of 40-63 1.30 (9H, s), 1.33 (3H, t, J = 7.1 Hz), 1.44 (9H, s), 4.27 (2H, q, J = 7.1
mesh. The ICP-MS analyses were carried out on a Thermo Hz), 5.84 (1H, br s), 6.44 (1H, d, J = 15.8 Hz), 7.33 (1H, d, J = 2.4 Hz),
Elemental VGPQ-ExCell spectrometer. TG-DTA analysis were 7.36 (1H, d, J = 2.4 Hz), 8.09 (1H, d, J = 15.8 Hz); 13C-NMR (75 MHz,
carried out on a METTLER TOLEDO equipment, model CDCl3): δ 14.3, 29.9 (3C), 31.4 (3C), 34.3, 34.8, 60.7, 118.7, 121.8,
TGA/SDTA851e/LF/1600, and EM analysis on a PFEIFFER 122.3, 126.6, 136.5, 140.6, 142.7, 151.4, 167.5; MS (EI) m/z (%): 304
VACUUM, model THERMOSTAR GSD301T.
(M+, 7), 244 (16), 243 (100).
(E)-Ethyl 3-(5-bromo-2-hydroxy-3-methoxyphenyl)acrylate (1d).
White solid; m.p. = 97-99 ºC (Hexane/AcOEt); IR (ATR): ν 1734,
1701, 1630, 1359, 1260, 1172 cm-1; 1H-NMR (300 MHz, CDCl3): δ
1.33 (3H, t, J = 7.1 Hz), 3.91 (3H, s), 4.26 (2H, q, J = 7.1 Hz), 6.11 (1H,
s), 6.55 (1H, d, J = 16.2 Hz), 6.95 (1H, d, J = 2.2 Hz), 7.22 (1H, d, J =
2.2 Hz), 7.85 (1H, d, J = 16.2 Hz); 13C-NMR (75 MHz, CDCl3): δ 14.3,
56.4, 60.5, 111.5, 114.8, 120.3, 122.2, 123.0, 137.9, 144.3, 147.4,
167.1; MS (EI) m/z (%): 302 (M++2, 18), 300 (M+, 21), 281 (18), 257
(17), 256 (100), 255 (24), 254 (98), 226 (16), 208 (69), 148 (16), 133
(13), 105 (27), 77 (15), 76 (11); HRMS calcd. (%) for C12H13BrO4:
299.9997; found: 299.9990.
Synthetic procedures
General procedure for the preparation of impregnated palladium
on magnetite catalyst: To a stirred solution of PdCl2 (177 mg, 1
mmol), KCl (1 g, 13 mmol, to increase the palladium solubility) in
deionized water (120 mL) was added Fe3O4 (4 g, 17 mmol, powder
<5 mm, BET area: 9.86 m2/g). After 10 min at room temperature,
the mixture was slowly basified with NaOH (1 M) until pH around
13. The mixture was stirred during 1 day at room temperature in
air. After that, the catalyst was filtered and washed with deionized
water (3 x 10 mL). The solid was dried at 100 ºC during 24 h in a
standard glassware oven, obtaining the expected catalyst:
incorporation of palladium of 3.0 % according to XRF; by XPS the
palladium on the surface was determined as 24.8 %; the BET area
surface was 13.6 m2/g. The molar ratio of catalyst PdO:Fe3O4 was
6.3:100.
General prodecure for the preparation of the diaryliodonium salts:
The diaryliodonium salts were prepared following the procedures
previously described.4,5
Diphenyliodonium tetrafluoroborate (2a).5b m-CPBA (24 mmol,
5.120 g) was dissolved in CH2Cl2 (80 mL). To the solution was added
iodobenzene (21.6 mmol, 2.48 mL) followed by slow addition of
General procedure for the preparation of acrylates: To a solution
of the corresponding 2-hydroxybenzaldehyde (5 mmol) in THF (30
6 | J. Name., 2012, 00, 1-3
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BF3·OEt2 (54.4 mmol, 6.8 mL) at room temperature. The resulting solution was stirred for 1 h at room temperature after which 1,3,5-
View Article Online
DOI: 10.1039/C6RA01731B
yellow solution was stirred at room temperature for 30 min and triisopropyl benzene (6.5 mmol, 1.32 mL) was added and the
then cooled to 0 ºC and PhB(OH)2 (24 mmol, 2.960 g) was added. solution cooled to 0 ºC. Tetrafluoroboric acid (50 % aqueous, 10
After 15 min of stirring at room temperature, the crude mixture was mmol, 1.25 mL) was added over 15 min via syringe pump and the
applied on a silica plug (20 g) and eluted with CH2Cl2 (2 x 100 mL) solution stirred at 0 ºC for 30 min before being allowed to warm to
followed by CH2Cl2/MeOH (2 x 100 mL). The latter solution was rt. After 6 h the solution was recooled to 0 ºC and water (100 mL)
concentrated and diethyl ether (40 mL) was added to the residue to was slowly added with fast stirring. The solution was extracted with
induce precipitation. The solution was allowed to stir for 15 min, CH2Cl2 (2 x 50 ml) and the combined organic extracts dried (MgSO4)
and then the solid was filtered and washed several times with and evaporated. The pure iodonium tetrafluoroborate salts were
diethyl ether and then dried in vacuo. White solid; m.p. = 133-135 precipitated with Et2O from a concentrated solution of hot CH2Cl2
1
ºC (Et2O); IR (KBr): ν 1560, 1471, 1444, 1287, 1053, 985 cm-1; H- and obtained by filtration followed by washed with generous
NMR (300 MHz, DMSO-d6): δ 7.54 (4H, t, J = 7.6 Hz), 7.68 (2H, t, J = amounts of Et2O on the filter.
7.4 Hz), 8.25 (4H, d, J = 7.3 Hz); 13C-NMR (75 MHz, DMSO-d6): δ
(4-Chlorophenyl)(2,4,6-triisopropylphenyl)iodonium
116.4 (2C), 131.7 (4C), 132.0 (2C), 135.1 (4C); 19F NMR (282 MHz,
tetrafluoroborate (2d).16 White solid; m.p. = 180-181 ºC (Et2O); IR
(KBr): ν 1585, 1570, 1471, 1389, 1369, 1087, 1011, 817 cm-1; 1H-
DMSO-d6): δ -148.2 (br. s), -148.3 (dd, . J = 2.3, 1.2 Hz).
Bis(4-methoxyphenyl)iodonium tetrafluoroborate (2b).5b m-CPBA NMR (300 MHz, CDCl3): δ 1.26 (12H, d, J = 6.8 Hz), 1.29 (6H, d, J =
(6 mmol, 1.280 g) was dissolved in CH2Cl2 (20 mL). To the solution 7.0 Hz), 2.79 (1H, hept, J = 6.9 Hz), 3.26 (2H, hept, J = 6.7 Hz), 7.20
was added 1-iodo-4-methoxybenzene (5.4 mmol, 1.264 g). The (2H, s), 7.42 (2H, d, J = 8.9 Hz), 7.64 (2H, d, J = 8.9 Hz); 13C-NMR (75
mixture was placed then on a pre-heated oil bath at 80 ºC and MHz, CDCl3): δ 23.6 (2C), 24.3 (4C), 32.4, 39.7 (2C), 108.6, 119.7,
stirred for 10 min. The mixture was cooled at -78 ºC. A 0 ºC cooled 125.5 (2C), 132.6 (2C), 133.9 (2C), 139.0, 152.7 (2C), 156.1; 19F NMR
mixture of BF3·OEt2 (13.6 mmol, 1.7 mL) and 4- (282 MHz, CDCl3): δ -146.7 (br. s), -146.8 (dd, J = 3.3, 1.6 Hz).
methoxybenzeneboronic acid (6 mmol, 912 mg) in 20 mL of CH2Cl2
o-Tolyl(2,4,6-trisiopropylphenyl)iodonium tetrafluoroborate (2e).
was added dropwise. The resulting solution was stirred at -78 ºC for
White solid; m.p. = 154-155 ºC (Et2O); IR (KBr): ν 1586, 1572, 1560,
1
1467, 1426, 1058, 979 cm-1; H-NMR (300 MHz, DMSO-d6): δ 1.21
30 min Then was allowed to warm to room temperature and was
applied on a silica plug (12 g) and eluted with CH2Cl2 (2 x 50 mL)
(18H, 2 x d, J = 6.7 and 6.9 Hz, respectively), 2.63 (3H, s), 2.98 (1H,
followed by CH2Cl2/MeOH (2 x 50 mL). The latter solution was
hept, J = 6.9 Hz), 3.31 (2H, hept, J = 6.9 Hz), 7.25-7.35 (3H, m), 7.50-
7.60 (2H, m), 7.77 (1H, d, J = 7.9 Hz); 13C-NMR (75 MHz, DMSO-d6):
concentrated and diethyl ether (40 mL) was added to the residue to
induce precipitation. The solution was allowed to stir for 15 min,
δ 23.5 (2C), 24.0 (4C), 24.4, 33.3, 38.9 (2C), 119.4, 123.0, 124.8 (2C),
129.6, 132.0, 132.3, 135.4, 140.4, 151.1 (2C), 154.2. 19F NMR (282
and then the solid was filtered and washed several times with
diethyl ether and then dried in vacuo. Grey solid; m.p. = 177-180 ºC
MHz, DMSO-d6): δ -148.3 (br. s), -148.3 (dd, J = 2.3, 1.1 Hz); HRMS
calcd. (%) for C22H30I+: 421.1287; found: 421.1368.
(Et2O); IR (KBr): ν 1572, 1487, 1441, 1406, 1302, 1258, 1177, 1062,
1
1022, 825 cm-1; H-NMR (300 MHz, DMSO-d6): δ 3.80 (6H, s), 7.07
(4H, d, J = 9.2 Hz), 8.13 (4H, d, J = 9.1 Hz); 13C-NMR (75 MHz, DMSO-
Phenyl(2,4,6-triisopropylphenyl)iodonium
trifluoromethanesulfonate (2f).4a 1,3,5-triisopropylbenzene (10
d6): δ 55.7 (2C), 105.9 (2C), 117.3 (4C), 136.8 (4C), 161.8 (2C); 19F
mmol, 2.38 mL) was added to a solution of iodobenzene (9 mmol, 1
NMR (282 MHz, DMSO-d6): δ -148.2 (br. s), -148.3 (dd, J = 2.3, 1.1
Hz).
mL) and m-CPBA (10 mmol, 2.64 g) in CH2Cl2 (40 mL). The solution
was cooled to 0ºC. Trifluoromethanesulfonic acid (15 mmol, 1.31
Bis(4-fluorophenyl)iodonium tetrafluoroborate (2c).14 m-CPBA (2.9
mL) was added dropwise over 5 min and the mixture allowed to
mmol, 610 mg) was dissolved in CH2Cl2 (10 mL). To the solution was
slowly warm to room temperature over 2 hours. The latter solution
added 1-fluoro-4-iodobenzene (2.6 mmol, 300 μL) followed by slow
was concentrated and diethyl ether (40 mL) was added to the
addition of BF3·OEt2 (6.5 mmol, 802 μL) at room temperature. The
residue to induce precipitation. The solution was allowed to stir for
resulting solution was stirred at room temperature for 30 minutes
15 min, and then the solid was filtered and washed several times
and then cooled at 0 ºC, and 4-(fluorophenyl)boronic acid (2.9
with diethyl ether and then dried in vacuo. White solid; m.p. = 169-
mmol, 406 mg) was added. After 15 min of stirring at room
170 ºC (Et2O); IR (KBr): ν 1580, 1588, 1566, 1465, 1279, 1240, 1162,
1029, 881, 756 cm-1; 1H-NMR (300 MHz, DMSO-d6): δ 1.15-1.25
temperature, the crude mixture was applied on a silica plug (20 g)
and eluted with CH2Cl2 (2 x 100 mL) followed by CH2Cl2/MeOH (2 x
(18H, m), 2.90-3.05 (1H, m), 3.35-3.45 (2H, m), 7.32 (2H, s), 7.54
(2H, t, J = 7.5 Hz), 7.64 (1H, t, J = 7.4 Hz), 7.93 (2H, d, J = 7.3 Hz); 13C-
100 mL). The latter solution was concentrated and diethyl ether (40
mL) was added to the residue to induce precipitation. The solution
NMR (75 MHz, DMSO-d6): δ 23.4 (2C), 23.9 (4C), 33.3, 38.6 (2C),
was allowed to stir for 15 min, and then the solid was filtered and
114.9, 123.0, 124.6 (2C), 131.7, 131.9 (2C), 133.9 (2C), 151.2 (2C),
154.2; 19F NMR (282 MHz, DMSO-d6): δ -77.8 (br. s), -148.3 (dd, . J =
washed several times with diethyl ether and then dried in vacuo.
White solid; m.p. = 97-98 ºC (Et2O); IR (ATR): ν 1576, 1479, 1232,
2.3, 1.2 Hz).
1034, 996, 827 cm-1; 1H-NMR (300 MHz, DMSO-d6): δ 7.40-7.45 (4H,
Di-p-tolyliodonium trifluoromethanesulfonate (2g).5a m-CPBA
m), 8.30-8.35 (4H, m); 13C-NMR (75 MHz, DMSO-d6): δ 111.2 (2C),
2
3
(1.65 mmol, 285 mg) and 1-iodo-4-methylbenzene (1.5 mmol, 327
mg) were dissolved in CH2Cl2 (7 mL). Toluene (1.65 mmol, 176 μL)
was added to the solution at room temperature followed by
dropwise addition of TfOH (2 equiv.). The reaction mixture was
119.36 (4C, d, J(C,F) = 22.8 Hz), 138.00 (4C, d, J(C,F) = 9.0 Hz), 163.99
(2C, d, 1J(C,F) = 251.4 Hz).
The appropriate iodoarene (5 mmol) was added to a stirred solution
of m-CPBA (7.5 mmol, 1.6 g) in acetic anhydride (10 ml) and the
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stirred at room temperature during 10 minutes and subsequently 4-(o-Tolyl)-2H-chromen-2-one (3e).14 Colourless oil; IR (KBr): ν
View Article Online
-1
1
concentrated under vacuum. Et2O was added and the mixture was 1731, 1604, 1564, 1483, 1451, 1365, 1276, 1D2O54I:,1902.1903c9m/C6;RAH0-1N7M31BR
stirred at room temperature for 10 minutes to precipitate out an (300 MHz, CDCl3): δ 2.16 (3H, s), 6.32 (1H, s), 7.07 (1H, dd, J = 7.9
4
off-white solid. To ensure complete precipitation, the flask was Hz, J = 1.6 Hz), 7.15-7.20 (2H, m), 7.30-7.35 (2H, m), 7.35-7.45 (2H,
4
stored in the freezer for at least 30 minutes before the solid was m), 7.53 (1H, ddd, J = 8.6, 7.2 Hz, J = 1.6 Hz); 13C-NMR (75 MHz,
filtered off, washed with Et2O and dried under vacuum. Grey solid; CDCl3): δ 19.7, 115.7, 117.1, 119.4, 124.3, 126.1, 126.9, 128.4,
m.p. = 121-123 ºC (Et2O); IR (ATR): ν 1481, 1242, 1156, 1024, 812, 129.2, 130.5, 131.9, 134.7, 135.3, 153.8, 156.1, 160.8; HRMS calcd.
796 cm-1; 1H-NMR (300 MHz, DMSO-d6): δ 2.33 (6H, s), 7.30-7.35 (%) for C16H13O2: 237.0916; found: 237.0908.
(4H, m), 8.05-8.10 (4H, m); 13C-NMR (75 MHz, DMSO-d6): δ 20.8
6-Fluoro-4-phenyl-2H-chromen-2-one (3f).22 White solid; m.p. =
(2C), 113.0 (2C), 132.3 (4C), 135.0 (4C), 142.4 (2C).
127-129 ºC (Hexane/AcOEt); IR (KBr): ν 1732, 1564, 1481, 1446,
1
1428, 1360, 1263, 1247, 1179, 971, 826 cm-1; H-NMR (300 MHz,
CDCl3): δ 6.42 (1H, s), 7.10-7.20 (1H, m), 7.20-7.30 (1H, m), 7.35-
General procedure for the synthesis of products 3: To a stirred
7.50 (3H, m), 7.50-7.60 (3H, m); 13C-NMR (75 MHz, CDCl3): δ 112.5
solution of the corresponding acrylate 1 (0.25 mmol) in ethanol
2
3
2
(d, J(C,F)= 25.2 Hz), 116.0, 118.8 (d, J(C,F)= 8.4 Hz), 119.3 (d, J(C,F)
=
(0.75 mL) were added the corresponding diaryliodonium salt 2 (2
equiv) and PdO-Fe3O4 (25 mg, 2.5 mol% Pd). The mixture was
stirred at 80 ºC for 5 h. The catalyst was removed by a magnet and
the solvent was evaporated under reduced pressure. The
corresponding products 3 were usually purified by chromatography
on silica gel (hexane/ethyl acetate).
3
24.5 Hz), 119.9 (d, J(C,F)= 8.6 Hz), 128.2 (2C), 129.0 (2C), 129.9,
4
4
134.6, 150.3 (d, J(C,F)= 2.0 Hz), 154.7 (d, J(C,F)= 2.7 Hz), 158.6 (d,
1J(C,F)= 243.9 Hz), 160.2; 19F NMR (282 MHz, CDCl3): δ -116.9 (m);
HRMS calcd. (%) for C15H10O2F: 241.0665; found: 241.0668.
6,8-Di-tert-butyl-4-phenyl-2H-chromen-2-one (3g).14 White solid;
4-Phenyl-2H-chromen-2-one (3a).14 White solid; m.p. = 98-100 ºC
(Hexane/AcOEt); IR (KBr): ν 1737, 1607, 1558, 1444, 1367, 1247,
1181, 1115, 941, 884, 773, 744, 699 cm-1; 1H-NMR (300 MHz,
CDCl3): δ 6.38 (1H, s), 7.20-7.30 (1H, m), 7.35-7.60 (8H, m); 13C-NMR
(75 MHz, CDCl3): δ 115.1, 117.3, 118.9, 124.1, 127.0, 128.4 (2C),
128.8 (2C), 129.6, 131.9, 135.2, 154.2, 155.6, 160.7; MS (EI) m/z (%):
222 (M+, 100), 221 (M+-1, 50), 194 (89), 166 (11), 165 (69), 164 (13),
m.p. = 181-183 ºC (Hexane/AcOEt); IR (ATR): ν 1720, 1568, 1362,
1
1250, 869, 766, 704 cm-1; H-NMR (300 MHz, CDCl3): δ 1.26 (9H, s),
1.56 (9H, s), 6.35 (1H, s), 7.32 (1H, d, J = 2.3 Hz), 7.40-7.45 (2H, m),
7.50-7.55 (3H, m), 7.61 (1H, d, J = 2.3 Hz); 13C-NMR (75 MHz, CDCl3):
δ 30.0 (3C), 31.3 (3C), 34.7, 35.2, 114.4, 118.6, 121.5, 127.1, 128.4
(2C), 128.7 (2C), 129.4, 136.1, 137.5, 146.1, 150.9, 156.8, 160.6; MS
(EI) m/z (%): 334 (M+, 22), 320 (23), 319 (100), 207 (55).
163 (10), 139 (11); HRMS calcd. (%) for C15H11O2: 223.0759; found: 6-Bromo-8-methoxy-4-phenyl-2H-chromen-2-one (3h). White
223.0762.
solid; m.p. = 181-183 ºC (Hexane/AcOEt); IR (ATR): ν 1726, 1554,
1
1461, 1443, 1358, 1259, 1209, 1167, 1085, 865, 699 cm-1; H-NMR
4-(4-Fluorophenyl)-2H-chromen-2-one (3b).14 White solid; m.p. =
(300 MHz, CDCl3): δ 3.98 (3H, s), 6.40 (1H, s), 7.16 (1H, d, J = 2.3 Hz),
7.20 (1H, d, J = 2.3 Hz), 7.40-7.45 (2H, m), 7.50-7.55 (3H, m). 13C-
NMR (75 MHz, CDCl3): δ 56.6, 116.4, 116.5, 116.8, 120.6, 120.7,
128.3 (2C), 129.0 (2C), 129.9, 134.8, 143.1, 148.3, 154.8, 159.4; MS
(EI) m/z (%): 332 (M++2, 91), 331 (M++1, 19), 330 (M+, 92), 304 (32),
302 (35), 281 (29), 208 (22), 207 (100), 163 (12), 152 (83), 151 (24),
150 (15), 102 (17), 76 (23), 73 (10); HRMS calcd. (%) for C16H11BrO3:
329.9892; found: 329.9883.
128-130 ºC (Hexane/AcOEt); IR (ATR): ν 1724, 1605, 1507, 1190,
1
1158, 943, 840, 830 cm-1; H-NMR (300 MHz, CDCl3): δ 6.37 (1H, s),
7.20-7.30 (3H, m), 7.40-7.50 (4H, m), 7.57 (1H, ddd, J = 8.6, 7.3, 1.6
Hz respectively); 13C-NMR (75 MHz, CDCl3): δ 115.3, 116.1 (2C, d,
3
2J(C,F)= 21.8 Hz), 117.4, 118.9, 124.2, 126.7, 130.4 (2C, d, J(C,F)= 8.4
4
Hz), 131.2 (d, J(C,F)= 3.5 Hz), 132.0, 154.1, 154.6, 160.5, 163.5 (d,
1J(C,F)= 250.2 Hz); MS (EI) m/z (%): 241 (M++1, 11), 240 (M+, 72), 239
(10), 213 (15), 212 (100), 207 (27), 184 (13), 183 (82).
6-Fluoro-4-(4-methoxyphenyl)-2H-chromen-2-one (3i).23 White
solid; m.p. = 162-164 ºC (Hexane/AcOEt); IR (KBr): ν 1718, 1610,
1565, 1510, 1478, 1431, 1361, 1253, 1176, 1120, 1036, 824 cm-1;
1H-NMR (300 MHz, CDCl3): δ 3.90 (3H, s), 6.39 (1H, s), 7.06 (2H, d, J
= 8.8 Hz), 7.20-7.30 (2H, m), 7.35-7.45 (3H, m with d at 7.40, J = 8.8
4-(4-Methoxyphenyl)-2H-chromen-2-one (3c).14 White solid; m.p. =
123-126 ºC (Hexane/AcOEt); IR (KBr): ν 1731, 1605, 1509, 1451,
1367, 1296, 1245, 1176, 1030, 929, 831, 752 cm-1; 1H-NMR (300
MHz, CDCl3): δ 3.90 (3H, s), 6.35 (1H, s), 7.00-7.05 (2H, m), 7.20-7.30
(1H, m), 7.35-7.45 (3H, m), 7.50-7.60 (2H, m); 13C-NMR (75 MHz,
CDCl3): δ 55.4, 114.3 (2C), 114.6, 117.3, 119.2, 124.1, 127.0, 127.5,
129.9 (2C), 131.8, 154.2, 155.3, 160.8, 160.9; HRMS calcd. (%) for
C16H13O3: 253.0865; found: 253.0863.
2
Hz); 13C-NMR (75 MHz, CDCl3): δ 55.4, 112.6 (d, J(C,F)= 25.2 Hz),
3
2
114.5 (2C), 115.5, 118.8 (d, J(C,F)= 8.4 Hz), 119.2 (d, J(C,F)= 24.5 Hz),
3
4
120.1 (d, J(C,F)= 8.5 Hz), 126.9, 129.8 (2C), 150.3 (d, J(C,F)= 2.0 Hz),
154.5 (d, J(C,F)= 2.7 Hz), 158.6 (d, J(C,F)= 243.4 Hz), 160.5, 161.0; 19
4
1
F
4-(4-Chlorophenyl)-2H-chromen-2-one (3d).14 White solid; m.p. =
NMR (282 MHz, CDCl3): δ -117.1 (m); HRMS calcd. (%) for C16H12O3F:
271.0770; found: 271.0758.
180-182 ºC (Hexane/AcOEt); IR (KBr): ν 1733, 1606, 1557, 1482,
1
1445, 1404, 1365, 1253, 1191, 1093, 945, 842, 750 cm-1; H-NMR
6,8-Di-tert-butyl-4-(4-fluorophenyl)-2H-chromen-2-one (3j). White
solid; m.p. = 112-114 ºC (Hexane/AcOEt); IR (ATR): ν 1727, 1601,
1507, 1223 cm-1; 1H-NMR (300 MHz, CDCl3): δ 1.26 (9H, s), 1.56 (9H,
s), 6.33 (1H, s), 7.20-7.30 (3H, m), 7.40-7.50 (2H, m), 7.61 (1H, d, J =
2.3 Hz); 13C-NMR (75 MHz, CDCl3): δ 30.0 (3C), 31.3 (3C), 34.8, 35.3,
(300 MHz, CDCl3): δ 6.36 (1H, s), 7.15-7.30 (1H, m), 7.35-7.45 (4H,
m), 7.50-7.60 (3H, m). 13C-NMR (75 MHz, CDCl3): δ 115.4, 117.4,
118.7, 124.3, 126.7, 129.2 (2C), 129.8 (2C), 132.1, 133.6, 136.0,
154.2, 154.4, 160.4; HRMS calcd. (%) for C15H10O2Cl: 257.0369;
found: 257.0371.
2
114.6, 115.9 (d, J(C,F)= 21.8 Hz, 2C), 118.6, 121.2, 127.3, 130.4 (d,
4
3J(C,F)= 8.3 Hz, 2C), 132.1 (d, J(C,F)= 3.1 Hz), 137.7, 146.2, 150.9,
8 | J. Name., 2012, 00, 1-3
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155.7, 160.4, 163.3 (d, J(C,F)= 250.0 Hz); MS (EI) m/z (%): 330 (M+, 128.0, 128.2 (2C), 128.3 (2C), 129.1 (2C), 129.3, 139.0V,i1ew40Ar.t8ic,le1O5n6l.in4e,
+
+
+
DOI: 10.1039/C6RA01731B
23), 338 (23), 337 (100); HRMS calcd. (%) for C23H25FO2: 352.1839; 166.1; MS (EI) m/z (%): 253 (M +1, 15), 252 (M , 83), 251 (M -1, 18),
found: 352.1830.
223 (15), 211 (28), 208 (12), 207 (73), 180 (45), 179 (60), 178 (100),
177 (16), 176 (21), 165 (20), 152 (27), 151 (13), 105 (18), 77 (18).
6-Bromo-4-(4-fluorophenyl)-8-methoxy-2H-chromen-2-one (3k).
White solid; m.p. = 178-180 ºC (Hexane/AcOEt); IR (ATR): ν 1719, (E/Z)-Methyl 3-phenyl-3-(p-tolyl)acrylate (5c).2 Pale yellow oil; IR
1601, 1558, 1507, 1262, 1091, 835 cm-1; 1H-NMR (300 MHz, CDCl3): (ATR): ν 1721, 1608, 1509, 1492, 1263, 1160, 1150, 815 cm-1; 1H-
δ 3.98 (3H, s), 6.39 (1H, s), 7.11 (1H, d, J = 2.0 Hz), 7.21 (1H, d, J = NMR (300 MHz, CDCl3): δ 2.35 (3H, s), 2.39 (3H, s), 3.60 (3H, s), 3.63
2.0 Hz), 7.25-7.30 (2H, m), 7.40-7.45 (2H, m); 13C-NMR (75 MHz, (3H, s), 6.32 (1H, s), 6.35 (1H, s), 7.10-7.40 (18H, m); 13C-NMR (75
2
CDCl3): δ 56.6, 116.2 (2C, d, J(C,F)= 21.9 Hz), 116.5, 116.6, 116.9, MHz, CDCl3): δ 21.2, 21.3, 51.2 (2C), 115.8, 116.4, 127.8 (2C), 128.0,
3
4
120.3, 120.6, 130.3 (2C, d, J(C,F)= 8.4 Hz), 130.7 (d, J(C,F)= 3.5 Hz), 128.1, 128.8 (2C), 128.3 (2C), 128.4 (2C), 128.6 (2C), 129.0 (4C),
1
143.1, 148.3, 153.7, 159.2, 163.6 (d, J(C,F)= 250.7 Hz); MS (EI) m/z 129.1 (2C), 129.4, 135.7, 137.9, 138.1, 139.0, 139.7, 141.1, 157.1,
(%): 351 (M++3, 18), 350 (M++2, 100), 349 (M++1, 21), 348 (M+, 99), 157.4, 166; MS (EI) m/z (%): 253 (M++1, 17), 252 (M+, 100), 251 (M+-
323 (10), 322 (45), 321 (10), 320 (43), 279 (10), 277 (12), 184 (14), 1, 35), 222 (16), 221 (97), 194 (13), 193 (29), 192 (14), 191 (19), 189
181 (11), 171 (11), 170 (94), 169 (22), 120 (21), 85 (19); HRMS calcd. (15), 179 (16), 178 (57), 165 (17), 115 (23).
(E/Z)-Methyl 3-(4-methoxyphenyl)-3-phenylacrylate (5d).26 Pale
(%) for C16H10BrFO3: 347.9797; found: 347.9786.
4-(p-Tolyl)-2H-chromen-2-one (3l).14 Pale yellow solid; m.p. = 108- yellow oil; IR (ATR): ν 2843, 1719, 1601, 1509, 1247, 1160, 1147,
1
110 ºC (Hexane/AcOEt); IR (ATR): ν 3068, 1727, 1605, 1189, 940 cm- 1031, 831 cm-1; H-NMR (300 MHz, CDCl3): δ 3.60 (s, 3H), 3.64 (s,
1
1; H-NMR (300 MHz, CDCl3): δ 2.46 (3H, s), 6.36 (1H, s), 7.20-7.25 3H), 3.81 (s, 3H), 3.85 (s, 3H), 6.28 (s, 1H), 6.32 (s, 1H), 6.84 (d, J =
(1H, m), 7.35-7.45 (5H, m), 7.50-7.60 (2H, m); 13C-NMR (75 MHz, 8.9 Hz, 2H), 6.91 (d, J = 8.7 Hz, 2H), 7.15-7.40 (m, 14H); 13C-NMR (75
CDCl3): δ 21.3, 114.8, 117.3, 119.0, 124.0, 127.0, 128.4 (2C), 129.5 MHz, CDCl3): δ 51.2 (2C), 55.2, 55.4, 113.2, 113.8, 114.6, 116.2,
(2C), 131.8, 132.2, 139.9, 154.1, 155.7, 160.8; MS (EI) m/z (%): 237 127.9 (2C), 128.1 (2C), 128.3 (2C), 128.6 (2C), 129.0 (2C), 129.4 (2C),
(M++1, 10), 236 (M+, 92), 235 (M+-1, 26), 221 (54), 209 (17), 208 129.8 (2C), 130.9 (2C), 133.1, 139.0, 141.5, 153.9, 156.9, 157.1,
(100), 207 (25), 179 (14), 178 (30), 176 (10), 165 (35), 152 (13), 89 159.8, 160.8, 166.6 (2C); MS (EI) m/z (%): 269 (M++1, 12), 268 (M+,
(11), 76 (10), 63 (10).
100), 267 (M+-1, 13), 238 (13), 237 (71), 210 (16), 209 (15), 195 (11),
194 (16), 178 (10), 166 (16), 165 (50), 135 (21).
6-Bromo-8-methoxy-4-(p-tolyl)-2H-chromen-2-one (3m). White
solid; m.p. = 186-188 ºC (Hexane/AcOEt); IR (ATR): ν 1726, 1558,
1460, 1261, 1091 cm-1; H-NMR (300 MHz, CDCl3): δ 2.46 (3H, s),
1
Conclusions
3.98 (3H, s), 6.38 (1H, s), 7.15-7.30 (2H, m), 7.30-7.35 (4H, m); 13C-
NMR (75 MHz, CDCl3): δ 21.4, 56.6, 116.1, 116.4, 116.8, 120.7,
120.9, 128.3 (2C), 129.7 (2C), 131.9, 140.1, 143.1, 148.3, 154.9,
159.5; MS (EI) m/z (%): 347 (M++3, 24), 346 (M++2, 100), 345 (M++1,
17), 344 (M+, 95), 329 (13), 318 (32), 316 (36), 222 (12), 207 (22),
194 (10), 166 (35), 165 (56), 164 (13), 163 (10), 139 (10), 115 (16);
HRMS calcd. (%) for C17H13BrO3: 344.0048; found: 344.0029.
In conclusion, we have demonstrated that palladium(II) oxide
impregnated on magnetite is a cheap, selective, versatile and very
active catalyst for the Heck-arylation/cyclization reaction of o-
hydroxyphenylacrylates and diaryliodonium salts using ethanol, as
non-toxic and bio-renewable solvent. This is the first report of this
reaction using a heterogeneous palladium catalyst and with the
lowest amount ever used (2.5 mol%). The magnetic properties of
the catalyst allow its separation from the reaction media very
easily, not being possible the recyclability of the same, due to the
practically total reduction of the palladium(II) oxide, the
sinterization of the same particles on the surface of the magnetite
and iodine species poisoning.
General procedure for the synthesis of products 5: To a stirred
solution of the corresponding α,β-unsaturated ester 4 (0.25 mmol)
in ethanol (0.75 mL) was added the corresponding diaryliodonium
salt 2 (2 equiv) and PdO-Fe3O4 (25 mg, 2.5 mol% Pd). The mixture
was stirred at 80 ºC for 5 h. The catalyst was removed by a magnet
and the solvent was evaporated under reduced pressure. The
corresponding products 5 were usually purified by bulb-to-bulb
distillation.
Acknowledgements
The authors thank the Spanish Ministerio de Economía y
Competitividad (MICINN; CTQ2011-24151), University of
Alicante, Irish Research Council (RC) and Science Foundation
Ireland (SFI/12/IP/1315 and SFI/12/RC/2275). J.M.P. thanks
the MICINN (FPI program) for her fellowship.
Ethyl cinnamate (5a).24 Colorless oil; IR (ATR): ν 1707, 1637, 1450,
1
1165, 1036, 765 cm-1; H-NMR (300 MHz, CDCl3): δ 1.33 (3H, t, J =
7.1 Hz), 4.26 (2H, q, J = 7.1 Hz), 6.43 (1H, d, J = 16.0 Hz), 7.35-7.40
(3H, m), 7.50-7.55 (2H, m), 7.69 (1H, d, J = 16.0 Hz); 13C-NMR (75
MHz, CDCl3): δ 14.2, 60.4, 118.2, 127.9 (2C), 128.8 (2C), 130.1,
134.4, 144.5, 166.9; MS (EI) m/z (%): 176 (M+, 31), 148 (13), 147
(16), 132 (11), 131 (100), 103 (44), 102 (12), 77 (28), 51 (10).
Notes and references
Ethyl 3,3-diphenylacrylate (5b).25 Brown oil; IR (ATR): ν 1719, 1617,
1
(a) R. F. Heck, Acc. Chem. Res., 1979, 12, 146-151. (b) A.-L.
Lee, Org. Biomol. Chem., DOI: 10.1039/c5ob01984b
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1574 cm-1; H-NMR (300 MHz, CDCl3): δ 1.1 (3H, t, J = 7.1 Hz), 4.05
2
(2H, q, J = 7.1 H), 6.36 (1H, s), 7.20-7.40 (2H and 8H respectively,
2m); 13C-NMR (75 MHz, CDCl3): δ 13.9, 60.0, 117.5, 127.8 (2C),
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10 | J. Name., 2012, 00, 1-3
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