Acrolein diethyl acetal: A three-carbon homologating reagent for the synthesis of β-arylpropanoates and cinnamaldehydes by heck reaction catalyzed by a Kaiser oxime resin derived palladacycle

Article abstract of DOI:10.1002/ejoc.200800047

A polymer palladacycle derived from Kaiser oxime resin was used as a source of palladium(0) in the chemoselective Heck reaction of acrolein diethyl acetal with aryl halides under ligand-free conditions. The use of typical Heck conditions afforded 3-arylpropionic esters, and the process can be directed to the synthesis of cinnamaldehydes under Cacchi conditions. These processes take place with rather low loading of the catalyst, which can be recovered by simple filtration and reused for at least five runs without competitive dehalogenation. This is the first time that a supported palladium complex has been reused under Cacchi conditions. ICP-OES analyses of the Pd content of the crude products in both transformations indicated lower leaching for the esters than for the aldehydes in the range up to 0.08 ppm for the esters and 0.8 ppm for the aldehydes. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800047

FULL PAPER
DOI: 10.1002/ejoc.200800047
Acrolein Diethyl Acetal: A Three-Carbon Homologating Reagent for the
Synthesis of β-Arylpropanoates and Cinnamaldehydes by Heck Reaction
Catalyzed by a Kaiser Oxime Resin Derived Palladacycle
Emilio Alacid[a] and Carmen Nájera*[a]
Keywords: Heck reaction / Palladacycles / Aldehydes / Esters / Polymers
A polymer palladacycle derived from Kaiser oxime resin was
used as a source of palladium(0) in the chemoselective Heck
reaction of acrolein diethyl acetal with aryl halides under li-
gand-free conditions. The use of typical Heck conditions af-
forded 3-arylpropionic esters, and the process can be di-
rected to the synthesis of cinnamaldehydes under Cacchi
conditions. These processes take place with rather low load-
ing of the catalyst, which can be recovered by simple fil-
tration and reused for at least five runs without competitive
dehalogenation. This is the first time that a supported palla-
dium complex has been reused under Cacchi conditions.
ICP-OES analyses of the Pd content of the crude products in
both transformations indicated lower leaching for the esters
than for the aldehydes in the range up to 0.08 ppm for the
esters and 0.8 ppm for the aldehydes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
for the preparation of cinnamaldehydes under Cacchi con-
ditions [DMF, KCl, tetra-n-butylammonium acetate
(TBAA), base, 110 °C], the catalyst could not be reused and
high dehalogenation rates were observed.
Introduction
The direct Heck reaction of aryl halides and acrolein is
not a general method for the synthesis of cinnamaldehyde
derivatives because of the problems associated with compet-
ing polymerization reactions[1] and the formation of β,β-
diarylated products.[2] However, the arylation of acrolein
acetals was found to be a much better alternative for the
synthesis of cinnamaldehydes and conjugate dienals.[1a,3] In
addition, Cacchi and coworkers described appropriate reac-
tion conditions to direct this arylation either to the synthe-
sis of cinnamaldehydes[4] or 3-arylpropionic esters[5] by
Heck reaction of acrolein diethyl acetal. Depending on the
reaction conditions it is possible to promote the regioselec-
tive elimination of one of the two β-hydrogens from the
carbopalladated intermediate (Scheme 1). Several soluble
catalysts, such as Pd(OAc)2,[4,5] the Herrmann’s palladacy-
cle,[2b] and [PdCl(C3H5)]2 with the tetraphosphane Ted-
icyp,[6] have been used for the chemoselective synthesis of
cinnamaldehydes or 3-arylpropionic esters. These methods
require high palladium loadings (2–5 mol-%) under ligand-
free conditions and only recently tetrakis(amine)palladium–
NaY zeolite {[Pd(NH3)4/NaY]} has been evaluated as a
heterogeneous catalyst in order to recover the palladium.[7]
Under classical Heck conditions (N-methyl-2-pyrrolidone,
base, 140 °C), 3-arylpropionic esters were obtained, and the
catalyst was stable only over the two first runs. However,
Scheme 1. Heck arylation of acrolein diethyl acetal.
We recently described the use of commercially available
oxime-derived palladacycles 1 and 2 (Figure 1) as catalysts
for C–C bond forming reactions,[8] such as the Heck,[9]
Suzuki,[10] Hiyama,[11] Ullmann,[10b] Sonogashira,[12] and
Glaser[12b] reactions, and for the acylation of alkynes.[13] By
using these catalysts in the arylation of acrolein diethyl ace-
tal[9g] with aryl bromides for the synthesis of 3-arylpro-
pionic esters under Heck conditions [N,N-dimethylacet-
amide (DMAc)/H2O, Cy2NMe, 120 °C], the loading of Pd
could be reduced down to 0.1 mol-%. When Cacchi condi-
[a] Departamento de Química Orgánica, Facultad de Ciencias and
Instituto de Síntesis Orgánica (ISO), Universidad de Alicante,
Apdo. 99, 03080 Alicante, Spain
Fax: +34-965-903-549
E-mail: cnajera@ua.es
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Acrolein Diethyl Acetal: a Three-Carbon Homologating Reagent
tions [DMAc, KCl, TBAA, K2CO3, 120 °C] were employed Table 1. Synthesis of ethyl 3-arylpropanoates by arylation of acro-
lein diethyl acetal.[a]
for the synthesis of cinnamaldehydes, aryl iodides, bro-
mides, and chlorides were employed as arylating reagents
with the use of 1 mol-% of Pd. Recently, we showed that
the palladacycle derived from Kaiser oxime resin 3,[9h,9i,9j]
can be used as reusable catalyst in Heck reactions, both in
organic and aqueous solvents. In this contribution, we re-
port for the first time the use of polymeric catalyst 3 as a
reusable immobilized complex for the chemoselective Heck
reaction of acrolein diethyl acetal with aryl halides under
ligand-free conditions.
Figure 1. Oxime-derived palladacycles.
[a] Reaction conditions: aryl halide (1 mmol), acrolein diethyl ace-
tal (1.5 mmol), catalyst (0.1 mol-% Pd), Cy2NMe (1.5 mmol),
TBAB (1 mmol), solvent (5 mL) heated (see column) in a pressure
Results and Discussion
tube. [b] Determined by GC of the crude product. [c] Determined
by 1H NMR spectroscopy by using diphenylmethane as an internal
Following our previous work[9g] on the arylation of acro-
standard for product 4. Yield of product 4 after flash chromatog-
raphy is in parentheses. [d] Ratio 4:1. [e] Without TBAB. [f] Ref.[9g]
lein diethyl acetal, the typical Heck conditions using pallad-
acycles 1 and 3 followed by acid hydrolysis were applied to
the synthesis of ethyl 3-arylpropanoates 4 (Scheme 2 and
Table 1). The reaction of aryl halides with 1.5 equiv. of
acrolein diethyl acetal was performed with a Pd loading of
0.1 mol-% by using (dicyclohexyl)methylamine as the base.
The reaction of an activated aryl halide such as 4-chlo-
roiodobenzene could be performed by using polymer 3 as a
catalyst at 90 °C in aqueous DMAc with good chemoselec-
tivity, and product 4a was isolated in higher yield than that
obtained when palladacycle 1 was used[9g] (Table 1, En-
tries 1 and 2). The reaction could be performed in DMF
with similar results to those obtained in aqueous DMAc
(Table 1, compare Entries 1 and 3).
coupling with 4-bromobenzonitrile took place with high
chemoselectivity in both aqueous DMAc and DMF in 3
and 4 h, respectively (Table 1, Entries 7 and 9). Pallada-
cycles 3 and 1 both afforded compound 4c with the same
yields (Table 1, compare Entries 7 and 8). In the case of
3-bromoquinoline, both catalysts gave the same selectivity,
which was also observed with the use of {[Pd(NH3)4/NaY]}
as the catalyst.[7] Product 4d was obtained in good yield
with a lower loading of Pd (Table 1, Entries 10 and 11),
whereas deactivated 9-bromoanthracene required a longer
reaction time to give mainly product 4e in good yield
(Table 1, Entries 12 and 13). It can be concluded that both
catalytic systems provided similar yields and selectivities
and that aqueous DMAc was a better solvent that DMF
for aryl bromides.
For studying the reuse of polymeric catalyst 3 and the
Pd leaching, the Heck reaction of 4-bromobenzonitrile and
acrolein diethyl acetal was chosen (Table 2). Thus, under
Scheme 2. Synthesis of ethyl 3-arylpropanoates 4.
The Heck reaction with aryl bromides needed the pres- the optimized reaction conditions and by using 0.1 mol-%
ence of 1 equiv. of tetra-n-butylammonium bromide of Pd, the reaction was heated at 120 °C for 5 h, and when
(TBAB) as an additive for the stabilization of the palladacy- the reaction was finished, the polymer was filtered off,
cle-generated Pd nanoparticles.[9h,9j] When an activated bro- washed, and dried under vacuum. The recycled polymer
mide such as 4-nitrobromobenzene was allowed to react was then used in the next run. The reaction time was be-
with acrolein diethyl acetal in aqueous DMAc at 120 °C the tween 5 and 14 h and the yield was maintained between 92
corresponding ester 4b was obtained with high chemoselec- and 86% after four runs. In the fifth cycle, the yield de-
tivity and good yield (Table 1, Entry 4). Concerning the cat- creased to 65% and the reaction time increased to 24 h,
alyst, a similar yield was observed with polymer 3 and di- probably not only due to Pd0 leaching but also to partial
meric palladacycle 1[9g] (Table 1, Entries 4 and 5). However, loss of the polymer during the successive manipulations.
this arylation needed longer reaction times in DMF than in The selectivity of the reaction over the five runs was main-
aqueous DMAc (Table 1, compare Entries 4 and 6). The tained between 92 and 86%. Inductively coupled plasma-
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E. Alacid, C. Nájera
FULL PAPER
optical emission spectrometry (ICP-OES) of the crude Table 3. Synthesis of cinnamaldehydes by arylation of acrolein di-
ethyl acetal.[a]
product during the first cycles gave a Pd content of ca.
0.18 mg/g of product. These results are better than those
described with the use of {[Pd(NH3)4/NaY]} as the cata-
lyst,[7] which gave 65% conversion in the third run and
Ͻ5% in the fifth run by using a larger loading of Pd (2 mol-
%).
Table 2. Recycling experiments of the Heck reaction of acrolein
diethyl acetal and 4-bromobenzonitrile: Synthesis of ethyl 4-cyano-
propanoate 4c.[a]
[a] Reaction conditions: 4-bromobenzonitrile (1 mmol), acrolein di-
ethyl acetal (1.5 mmol), 3 (0.1 mol-% Pd), Cy2NMe (1.5 mmol),
TBAB (1 mmol), DMAc/H2O (4:1) (5 mL), heated at 120 °C in a
pressure tube. [b] Determined by GC of the crude product. [c] De-
1
termined by H NMR spectroscopy by using diphenylmethane as
an internal standard for product 4c. [d] Determined by ICP-OES
of the crude product.
[a] Reaction conditions: aryl halide (1 mmol), acrolein diethyl ace-
The Cacchi conditions (K2CO3 as base and TBAA and
tal (1.5 mmol), catalyst (1 mol-% Pd), K2CO3 (1.5 mmol), TBAA
(2 mmol), KCl (1 mmol), DMAc/H2O (5 mL) or DMAc(4 mL)
KCl as additives at 120 °C), previously described with the
use of palladacycle 1[9g] were used for the synthesis of cinna-
heated at 120 °C in a pressure tube. [b] Determined by GC of the
1
crude product. [c] Determined by H NMR spectroscopy by using
diphenylmethane as an internal standard for product 5. Yield of
product 5 after flash chromatography is in parentheses. [d] Ratio
4:1. [e] Ref.[9g]
maldehydes 5 (Scheme 3 and Table 3). Initial studies of 4-
chloroiodobenzene with catalyst 3 (1 mol-% Pd) in aqueous
DMAc afforded a 3:1 mixture of products 5a and 4a
(Table 3, Entry 1). However, total selectivity was observed
with polymer 3 and dimer 1[9g] in DMAc (Table 3, Entries 2
and 3). Again, the same influence of the solvent in the selec-
tivity was obtained with 4-iodoanisole, which provided 4-
methoxycinnamaldehyde (5f) (Table 3, Entries 4–6).
In the case of 3-bromopyridine, the reaction needed longer
reaction times and afforded product 5k with lower selectiv-
ity and moderate yields (Table 3, Entries 17 and 18). The
activated aryl chloride 4-chloro-1-(trifluoromethyl)benzene
gave exclusively 4-(trifluoromethyl)cinnamaldehyde (5l) in
good yield (Table 3, Entries 19 and 20).
Two representative examples for the synthesis of cinnam-
aldehydes were selected for recycling studies (Table 4). In
the arylation of acrolein diethyl acetal with 4-chloroiodo-
benzene, the reaction time was increased from 2.5 h in the
Scheme 3. Synthesis of cinnamaldehydes 5.
The arylation with aryl bromides were performed in first run to 24 h in the sixth, and the yield of product 5a
DMAc to afford cinnamaldehydes 5 with very good selec- was maintained between 96 and 86% over five runs and
tivity (Table 3, Entries 7–18). In the case of 4-bromoanisole started to decrease in the sixth run to 62%. Similar results
and 1-bromonaphthalene, only the formation of 4-meth- were observed in the case of 1-bromonaphthalene, which
oxycinnamaldehyde (5f) and 5g, respectively, was observed afforded product 5g in 92 to 74% yield over five runs. The
with both catalysts (Table 3, Entries 7–10). However, 2-bro- selectivity remained high and was 96:4 in all cycles for both
monaphthalene provided product 5h in lower selectivity examples. The Pd leaching in product 5g was rather low
(Table 3, Entries 11 and 12). Deactivated 4-(dimethylamino) (0.154–0.257 mg Pd/g of product). The role of polymer 3 as
phenyl bromide and 3-benzyloxybromobenzene gave exclu- a precatalyst and source of Pd0 nanoparticles is supported
sively the corresponding products 5i and 5j, respectively, in by the following experiments: After XPS analyses of the
high yields either by using polymer 3 or dimer 1 (Table 3, recycled polymer, only PdII was detected.[9h] Furthermore,
Entries 13–16). 4-(Dimethylamino)cinnamaldehyde (5i) is 6–8-nm sized Pd nanoparticles were found in solution by
an important unit for nonlinear optics[4] and 3-(benzyloxy)- TEM analyses (Figure 2). In addition, when Hg0 (300 equiv.
cinnamaldehyde (5j) possess a potent inhibitory activity with respect to Pd) was added to the reaction mixture, the
against cyclin-dependent kinases, especially D1-CDK4.[14] Heck reaction stopped.
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Acrolein Diethyl Acetal: a Three-Carbon Homologating Reagent
Table 4. Recycling experiments of the Heck reaction of acrolein case, very low amounts of palladium were found in the
diethyl acetal for the synthesis of cinnamaldehydes 5a and 5g.[a]
product (0.47–0.81 ppm) without competitive dehalogena-
tion. These are the first examples in which the catalyst has
been recycled, because when {[Pd(NH3)4/NaY]} was used
as the catalyst,[7] mainly dehalogenation was observed.
Experimental Section
General Remarks: The reagents and solvents were obtained from
commercial sources and were generally used without further purifi-
cation. Melting points were determined with a Reichert Thermovar
hot plate apparatus and are uncorrected. Only the structurally most
important peaks of the IR spectra (recorded with a Nicolet 510 P-
FT) are listed. 1H (300 MHz) and 13C NMR (75 MHz) spectra
were obtained with a Bruker AC-300 by using CDCl3 as the solvent
and TMS as an internal standard, unless otherwise stated. Low-
resolution electron impact (EI) mass spectra were obtained at 70 eV
with a Shimadzu QP-5000. Analytical TLC was performed on
Schleicher & Schuell F1400/LS silica-gel plates, and the spots were
visualized under UV light (λ = 254 nm). For flash chromatography
we employed Merck silica gel 60 (0.040–0.063 mm). The catalysts
were weighed in an electronic microscale (Sartorius, XM1000P)
with precision of 1 µg. ICP-OES analyses were performed with a
Perkin–Elmer Optima 4300 spectrometer (1% aqueous HNO3 solu-
tion). Palladacycle 1 and Kaiser oxime resin are commercially avail-
able. Palladacycle 3 was prepared as described in ref.[9i]
[a] Reaction conditions: aryl halide (1 mmol), acrolein diethyl ace-
tal (1.5 mmol), (1 mol-% Pd), K2CO3 (1.5 mmol), TBAA
(2 mmol), KCl (1 mmol), DMAc (4 mL), heated at 120 °C in a pres-
3
sure tube. [b] Determined by GC of the crude product. [c] Deter-
1
mined by H NMR spectroscopy by using diphenylmethane as an
internal standard for product 5. [d] Determined by ICP-OES of the
crude product.
General Method for the Synthesis of Ethyl 3-Arylpropanoates 4: A
solution of aryl halide (1 mmol), acrolein diethyl acetal (1.5 mmol,
0.229 mL), (dicyclohexyl)methylamine (1.5 mmol, 0.321 mL), tetra-
n-butylammonium bromide (1 mmol, 322 mg, only for aryl bro-
mides), palladium catalyst (0.1 mol-% Pd) in N,N-dimethylacet-
amide (4 mL) and water (1 mL) was stirred at 90 °C (aryl iodides)
or at 120 °C (aryl bromides) (bath temperature) in a pressure tube.
Upon completion of the reaction (GC), the resulting solution was
cooled to room temperature, poured into ethyl acetate (20 mL), and
washed successively with HCl (2 , 2ϫ20 mL) and H2O (20 mL).
The organic layer was dried with MgSO4, and the solvent was evap-
orated (15 Torr); the residue was purified by flash chromatography
to afford product 4.
Figure 2. TEM images of the reaction solution after Heck reaction
of acrolein diethyl acetal with 4-chloroiodobenzene.
Conclusions
General Method for the Synthesis of Cinnamaldehydes 5: A suspen-
sion of aryl halide (1 mmol), acrolein diethyl acetal (1.5 mmol,
0.229 mL), potassium carbonate (1.5 mmol, 207 mg), tetra-n-butyl-
ammonium acetate (2 mmol, 602 mg), potassium chloride (1 mmol,
75 mg), palladium catalyst (1 mol-% Pd), and N,N-dimethylacet-
amide (4 mL) was stirred at 120 °C (bath temperature) in a pressure
tube. Upon completion of the reaction (GC), the solution was co-
oled and an aqueous solution of HCl (2 , 10 mL) was added
slowly. The mixture was stirred at room temperature for 10 min.
Then, the reaction crude was poured into ethyl acetate (20 mL) and
washed successively with HCl (2 , 20 mL) and H2O (2ϫ20 mL).
The organic layer was dried with MgSO4, and the solvent was evap-
orated (15 Torr); the resulting residue was purified by flash
chromatography to provide compounds 5.
The polymer-anchored palladacycle derived from Kaiser
oxime resin has shown similar catalytic efficiency in the
chemoselective Heck reaction of acrolein diethyl acetal with
aryl halides than the unsupported dimeric 4-hydroxyace-
tophenone oxime palladacycle. The arylation with aryl
iodides and bromides took place in short reaction times
under Heck conditions (Cy2NMe, TBAB, DMAc/H2O,
120 °C) to afford ethyl 3-arylpropanoates with very low cat-
alyst loading (0.1 mol-% Pd). This polymeric complex can
be reused for at least five cycles; it also acts as a palladium
reservoir and leaches a very low amount of palladium
nanoparticles (0.06–0.08 ppm) into the solution. When
Cacchi reaction conditions (K2CO3, TBAA, KCl, DMAc,
120 °C) were used, aryl iodides, bromides, and chlorides can
be coupled with acrolein diethyl acetal to provide cinnamal-
dehydes in short reaction times with 1 mol-% loading of Pd.
The stability of this polymeric complex under these reaction
conditions was remarkable, and it could be reused over five
General Method for Recycling Experiments: The reaction was per-
formed under any previous described conditions: aromatic halide
(1 mmol), acrolein diethyl acetal (0.229 mL, 1.5 mmol), base
(1.5 mmol), 1 (0.1–1 mol-%, 8.2–82 mg), solvent (5 mL DMA/H2O,
4:1 or 4 mL DMA) and TBAB (322 mg, 1 mmol) for aryl bromides,
heating at corresponding temperature. Upon completion of the re-
action, the catalyst was filtered off in a porous plate 4 (1 cm dia-
cycles with the use of aryl iodides and bromides. In this meter and 8 cm height), washed with ethyl acetate, and dried under
Eur. J. Org. Chem. 2008, 3102–3106
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3105

E. Alacid, C. Nájera
FULL PAPER
vacuum for 20 min. Workup of the crude product was performed
as was previously described.
solider INGENIO 2010 CSD2007-00006), the Generalitat Valenci-
ana (GV05/157), and the University of Alicante. E. A. thanks the
Ministerio de Educación y Ciencia of Spain for a predoctoral fel-
lowship.
Ethyl 3-(4-chlorophenyl)propanoate (4a),[15] ethyl 3-(4-nitrophenyl)-
propanoate (4b),[9g] ethyl 3-(4-cyanophenyl)propanoate (4c),[16] 4-
chlorocinnamaldehyde (5a),[4] 4-methoxycinnamaldehyde (5f),[4]
(E)-3-(1-naphthyl)propenal (5g),[9g] (E)-3-(naphthalen-2-yl)prope-
nal (5h),[17] 4-(dimethylamino)cinnamaldehyde (5i),[4] 3-(benzyl-
oxy)cinnamaldehyde (5j),[14] (E)-3-(pyridin-3-yl)propenal (5k),[18]
and 4-(trifluoromethyl)cinnamaldehyde (5l)[19] are known com-
pounds.
[1] a) T. C. Zebovitz, R. F. Heck, J. Org. Chem. 1977, 42, 3907–
3909; b) T. Jefferey, J. Chem. Soc., Chem. Commun. 1984, 1287–
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[2] a) A. Nejjar, C. Pinel, L. Djakovitch, Adv. Synth. Catal. 2003,
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[3] a) B. A. Patel, J. I. Kim, D. D. Bender, L.-C. Kao, R. F. Heck,
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Ethyl 3-(Quinolin-3-yl)propanoate (4d): Yellow oil, 153 mg (67%).
R = 0.36 (n-hexane/ethyl acetate, 3:2). IR (film): ν = 1194, 1161,
˜
f
1375, 1502, 1575, 1729, 2860, 2924, 2978, 3051 cm–1. 1H NMR
(300 MHz, CDCl3): δ = 1.21 (t, J = 7.2 Hz, 3 H, CH3), 2.72 (t, J
= 7.6 Hz, 2 H, CH2CH2O), 3.13 (t, J = 7.6 Hz, 2 H, CH2O), 4.12
(q, J = 7.2 Hz, 2 H, OCH2), 7.51 (dt, J = 7.9 and 1.1 Hz, 1 H,
ArH), 7.65 (dt, J = 8.4 and 1.4 Hz, 1 H, ArH), 7.75 (d, J = 8.1 Hz,
1 H, ArH), 7.94 (d, J = 1.2 Hz, 1 H, ArH), 8.08 (d, J = 8.4 Hz, 1
H, ArH), 8.80 (d, J = 2.2 Hz, 1 H, ArH) ppm. 13C NMR (75 MHz,
CDCl3): δ = 14.1 (CH3), 28.2, 35.3, 60.6 (CH2), 126.7 127.4
(ArCH), 127.9 (ArC), 128.8, 129.1 (ArCH), 133.2 (ArC), 134.4
(ArCH), 146.9 (ArC), 151.6 (ArCH), 172.3 (COO) ppm. MS (EI):
m/z (%) = 230 (14) [M + 1]+, 229 (80) [M]+, 185 (48), 184 (24), 158
(70), 157 (11), 156 (44), 155 (100), 154 (31), 142 (77), 128 (23),
127 (13), 115 (24). HRMS: calcd. for C14H15NO2 229.1103; found
229.1113.
[4] G. Battistuzzi, S. Cacchi, G. Fabrizi, Org. Lett. 2003, 5, 777–
780.
[5] G. Battistuzzi, S. Cacchi, G. Fabrizi, R. Bernini, Synlett 2003,
1133–1136.
[6] M. Lemhadri, H. Doucet, M. Santelli, Tetrahedron 2004, 60,
11533–11540.
[7] S. Nöel, C. Luo, C. Pinel, L. Djakovitch, Adv. Synth. Catal.
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[8] For accounts, see: a) E. Alacid, D. A. Alonso, L. Botella, C.
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D. A. Alonso, L. Botella, C. Nájera, M. C. Pacheco, Synthesis
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[9] a) D. A. Alonso, C. Nájera, M. C. Pacheco, Org. Lett. 2000, 2,
1823–1826; b) D. A. Alonso, C. Nájera, M. C. Pacheco, Adv.
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2008, viii, 50–67.
Ethyl 3-(Anthracen-9-yl)propanoate (4e): Yellow oil, 192 mg (69%).
R = 0.49 (n-hexane/ethyl acetate, 5:1). IR (film): ν = 1175, 1362,
˜
f
1441, 1616, 1730, 2978, 3044 cm–1. 1H NMR (300 MHz, CDCl3):
δ = 1.24 (t, J = 7.1 Hz, 3 H, CH3), 2.75 (t, J = 8.5 Hz, 2 H,
CH2CH2O), 3.94 (t, J = 8.5 Hz, 2 H, CH2O), 4.17 (q, J = 7.1 Hz,
2 H, OCH2), 7.43 (t, J = 7.0 Hz, 2 H, ArH), 7.50 (dt, J = 7.6 and
1.3 Hz, 2 H, ArH), 7.96 (d, J = 8.2 Hz, 2 H, ArH), 8.24 (d, J =
8.8 Hz, 2 H, ArH), 8.31 (s, 1 H, ArH) ppm. 13C NMR (75 MHz,
CDCl3): δ = 14.3 (CH3), 23.4 (CH2), 35.4 (CH2), 60.7 (OCH2),
124.0 (2ϫArCH), 125.0 (2ϫArCH), 126.0 (2ϫArCH), 126.4
(ArCH), 129.4 (2ϫArCH), 129.6 (2ϫArC), 131.6 (2ϫArC), 132.5
(ArC), 173.2 (COO) ppm. MS (EI): m/z (%) = 279 (10) [M + 1]+,
278 (51) [M]+, 204 (12), 203 (15), 192 (16), 191 (100). HRMS: calcd.
for C19H18O2 278.1307; found 278.1301.
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181; b) D. A. Alonso, C. Nájera, M. C. Pacheco, J. Org. Chem.
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(E)-3-(Quinolin-3-yl)propenal (5h): Yellow solid, m.p. 81–83 °C. Rf
= 0.24 (n-hexane/ethyl acetate, 3:2). IR (KBr): ν = 1129, 1335,
˜
1376, 1491, 1560, 1618, 1681, 2820, 2912, 2963, 3050 cm–1. 1H
NMR (300 MHz, CDCl3): δ = 6.95 (dd, J = 16.1 and 7.5 Hz, 1 H,
CH) = 7.62 (dt, J = 8.0 and 1.1 Hz, 1 H, ArH), 7.64 (d, J =
16.1 Hz, 1 H, CH), 7.80 (dt, J = 8.4 and 1.4 Hz, 1 H, ArH), 7.89
(d, J = 8.1 Hz, 1 H, ArH), 8.14 (d, J = 8.4 Hz, 1 H, ArH), 8.31 (d,
J = 2.0 Hz, 1 H, ArH), 9.10 (d, J = 2.2 Hz, 1 H, ArH), 9.79 = (d,
J = 7.5 Hz, 1 H, CHO) ppm. 13C NMR (75 MHz, CDCl3): δ =
126.9, 127.5 (ArC) = 127.7, 128.6, 129.5, 129.9, 131.3 (ArCH),
136.0 (CH), 148.8 (ArCH), 149.0 (ArC), 149.2 (CH), 193.1 (CHO)
ppm. MS (EI): m/z (%) = 184 (12) [M + 1]+, 183 (100) [M]+, 155
(24), 154 (94), 129 (27), 128 (13), 127 (25). HRMS: calcd. for
C12H9NO 183.0684; found 183.0672.
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This work was financially supported by the Dirección General de
Investigación of the Ministerio de Educación y Ciencia of Spain
(Grants CTQ2004-00808/BQU, CTQ2007-62771/BQU, and Con-
Received: January 15, 2008
Published Online: April 29, 2008
3106
www.eurjoc.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 3102–3106