Microwave assisted synthesis of 3-(2,2′-bipyridine-4-yl)-2-propenoic acid ethyl ester

Article abstract of DOI:10.1007/s00706-016-1908-2

Abstract: 3-(2,2′-Bipyridine-4-yl)-2-propenoic acid ethyl ester which may be used for the introduction of metal coordination sites in polyacrylates is synthesized by an improved synthetic route to the key intermediate 4-bromo-2,2′-bipyridine working under microwave conditions, which leads to drastic shortening of reaction times, as well as to the reduction of reaction steps. In addition, a synthetic procedure to formyl-bipyridines that is not based on reductive or oxidative reaction conditions could be applied. Starting from the formyl-bipyridine derivative the title compound may be effectively generated using modified Horner–Wadsworth–Emmons reaction conditions to yield the new ligand. Graphical abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s00706-016-1908-2

Monatsh Chem (2017) 148:991–998
DOI 10.1007/s00706-016-1908-2
ORIGINAL PAPER
Microwave assisted synthesis of 3-(2,20-bipyridine-4-yl)-2-
propenoic acid ethyl ester
Katharina Heintz1 Wolfgang Imhof1
2
•
•
¨
Helmar Gorls
Received: 13 October 2016 / Accepted: 30 December 2016 / Published online: 19 April 2017
Ó Springer-Verlag Wien 2017
Abstract 3-(2,20-Bipyridine-4-yl)-2-propenoic acid ethyl
ester which may be used for the introduction of metal
coordination sites in polyacrylates is synthesized by an
improved synthetic route to the key intermediate 4-bromo-
2,20-bipyridine working under microwave conditions,
which leads to drastic shortening of reaction times, as well
as to the reduction of reaction steps. In addition, a synthetic
procedure to formyl-bipyridines that is not based on
reductive or oxidative reaction conditions could be applied.
Starting from the formyl-bipyridine derivative the title
compound may be effectively generated using modified
Horner–Wadsworth–Emmons reaction conditions to yield
the new ligand.
Introduction
Polyacrylates are known for their variable properties and
their numerous industrial applications [1]. According to
material development it is of general interest to create even
more applications for polyacrylates by functionalization of
side chains. Therefore, a new synthetic route was designed
that allows to prepare 2,20-bipyridines with acrylate related
side chains, thus creating a substituent with a polymeriz-
able double bond. 2,20-Bipyridines modified this way might
be used as co-monomers in the synthesis of polyacrylates
as a potential pathway to integrate coordination sites for
transition metals into the surfaces of polymer
nanoparticles.
Graphical abstract
The synthetic route was drastically improved concerning
reaction periods and reaction rates by application of labo-
ratory microwave technology [2]. Additionally, a new
synthesis of 4-formyl-2,20-bipyridine (6) was developed on
the basis of a metal-halogen-exchange reaction. In the last
step a Horner–Wadsworth–Emmons reaction (HWE reac-
tion) was applied to 2,20-bipyridinecarbaldehyde under
microwave irradiation. The title compound 7 as well as the
intermediate 4-nitro-2-(pyridin-2-yl)pyridine 1-oxide (3)
were also characterized by X-ray diffraction.
Keywords Bromination Á Microwave assisted synthesis Á
Ligands Á Wittig reaction Á Crystal structure
Results and discussion
Scheme 1 shows the complete synthetic pathway produc-
ing the title compound 7. The synthesis of the intermediate
4-bromo-2,20-bipyridine (4) is a known synthesis and for
example published in [3]. This synthesis is characterized by
long-lasting reaction times, harmful side products as, e.g.
nitrous or bromine fumes and moderate reproducibility. In
general, the reduction of reaction times may be achieved by
an increase of temperature. Nevertheless, in this case the
& Wolfgang Imhof
Imhof@uni-koblenz.de
1
Institute of Integrated Natural Sciences, University
¨
Koblenz-Landau, Universitatsstr. 1, 56070 Koblenz,
Germany
2
Institute of Inorganic and Analytical Chemistry,
Friedrich-Schiller University Jena, Humboldtstr. 8,
07743 Jena, Germany
123

992
K. Heintz et al.
Scheme 1
yield of the desired product 4 decreases and the amount of
unrequested side products increases. significant
Molecular structures of 4-nitro-2-(pyridin-2-yl)pyridine-
1-oxide (3) and 3-(2,20-bipyridine-4-yl)-2-propenoic acid
ethyl ester (7) in the solid state were analyzed by single-
crystal X-ray diffraction. Crystal data and structure
refinement parameters for 3 and 7 are collected in Table 1.
The molecular structure of 3 is depicted in Fig. 1, the
crystal structure showing the supramolecular hydrogen
bond network is presented in Fig. 2. The most significant
bond lengths and angles are shown in Table 2. The pyr-
idine subunits in 3 are arranged in an s-trans configuration
with respect to the central carbon–carbon bond. A CSD
search for crystallographically characterized non-coordi-
nated 2,20-bipyridine derivatives with a R-value below 5%
gave only four hits, in which the arrangement of the pyr-
idine subunits is s-cis [5–8], whereas in 134 hits the same s-
trans configuration was reported that we also observed for
3 and 7 [9]. The nitrogen atom trans to the nitro substituent
is oxidized and there is a weak intramolecular interaction
between the hydrogen atom at C4 and O1. The nitro group
is perfectly coplanar with the respective pyridine ring,
whereas the pyridine rings enclose a dihedral angle of
29.98(4)°.
A
improvement of reaction conditions may be obtained by
microwave technology [2]. The application of closed
microwave vessels prevents the emission of harmful side
products. At the same time a definite temperature increase
can be performed so that reaction times decrease.
The common nitration of 2,2-bipyridine-N-oxide (2) to
produce 4-nitro-2-(pyridin-2-yl)pyridine 1-oxide (3) takes
about 72 h [3]. In contrast, microwave assisted synthesis
only takes about 2 h (cf. Experimental Part). The yields are
comparable if the same work-up procedure is applied.
Moreover, microwave assisted synthesis in this case
leads to the omission of one reaction step which can be
seen as another positive side effect. According to literature
procedures bromination of 3 leads to the intermediate
formation of 4-bromo-2,20-bipyridine-N-oxide which then
has to be reduced by phosphorus tribromide to synthesize
4-bromo-2,20-bipyridine (4) with an overall yield of 62%
[3]. Under microwave conditions bromination and reduc-
tion take place simultaneously, therefore, allowing the one-
pot synthesis of 4 directly from 3 in 75% yield.
Synthesis of 6 is achieved by a one-pot reaction at
-78 °C first exchanging the bromo substituent in (4)
against lithium followed by the reaction with DMF which
then is stopped by the addition of hydrochloric acid.
Microwave assisted synthesis positively affects the
HWE reaction as well. The commonly applied synthetic
conditions in a round flask lasts at least about 48 h [4].
Completion of the same reaction assisted by microwave
irradiation requires about 2 h.
The crystal structure of 3 is determined by weak non-
classical hydrogen bond interactions of the C–H–O type
with oxygen atoms of the nitro substituents, as well as of
the pyridine-N-oxide function acting as hydrogen bond
acceptor sites [10]. Due to the dihedral angle between the
pyridine rings of the bipyridine core an infinite waved layer
is formed in the bc plane of the unit cell (Fig. 2). These
layers are again linked by additional hydrogen bonds to
produce a 3D supramolecular structure.
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Microwave assisted synthesis of 3-(2,20-bipyridine-4-yl)-2-propenoic acid ethyl ester
993
Table 1 Selected bond lengths/
pm and angles/° of 3
N1–C1
133.3(3)
148.4(3)
137.0(3)
120.8(2)
120.6(2)
N1–C5
135.8(3)
138.0(3)
129.6(3)
118.6(2)
C5–C6
N2–C6
N2–C10
C6–N2–O1
C6–N2–C10
Hydrogen bonds
H9–O1
N2–O1
C10–N2–O1
222.2
245.7
265.5
247.0
C9–H9–O1
C7–H7–O1
C1–H1–O2
C3–H3–O2
152.8
126.2
137.5
168.6
H7–O1
H1–O2
H3–O2
Fig. 1 Molecular structure of
4-nitro-2-(pyridin-2-yl)pyridine
1-oxide (3)
The molecular structure of 7 is presented in Fig. 3,
which shows one of the independent molecules present in
the asymmetric unit of 7. Selected bond lengths and angles
of the respective molecule are summarized in Table 3. The
crystal structure showing the supramolecular hydrogen
bonding system is depicted in Fig. 4.
infinite chains by bifurcated hydrogen bonds between the
carbonyl oxygen atom and one aromatic and one olefinic
hydrogen atom.
Conclusions
Both molecules of 7 in the asymmetric unit show a s-
trans conformation of the bipyridine system with respect to
the central carbon–carbon bond. In addition, the carbon–
carbon double bond in the substituent in both molecules
exhibits a trans-conformation. Bond lengths and angles in
both crystallographically independent molecules are almost
identical. The only significant difference concerning both
molecules of 7 in the asymmetric unit is the dihedral angle
between the two pyridine subunits, which is 7.2(8)° and
1.9(8)°, respectively.
From Fig. 4 it gets obvious that the two molecules in the
asymmetric unit are connected into dimers by non-classical
C–H–O hydrogen bonds of the oxygen atom connected to
the ethyl group of the ester towards an aromatic C–H
function [10]. These dimers are then linked to produce
A synthetic procedure yielding 3-(2,20-bipyridine-4-yl)-2-
propenoic acid ethyl ester which may be used for the
introduction of metal coordination sites in polyacrylates is
presented herein. The reaction sequence proceeds via an
improved synthetic route to the key intermediate 4-bromo-
4,40-bipyridine (4) working under microwave conditions
which leads to drastic shortening of reaction times as well
as to the reduction of reaction steps. In addition, a synthetic
procedure to formyl-bipyridines that is not based on
reductive or oxidative reaction conditions could be applied.
Starting from the respective formyl-bipyridine derivative,
the title compound may be effectively generated using
modified HWE reaction conditions to yield the new
ligands.
123

994
K. Heintz et al.
Fig. 2 Supramolecular structure of 4-nitro-2-(pyridin-2-yl)pyridine 1-oxide (3)
All other hydrogen atoms were included at calculated
positions with fixed thermal parameters. The crystal of 7
was a non-merohedral twin. The twin law was determined
by PLATON to (0.179 -0.081 0.740) (-1.179 -0.919
-0.740) (1.179 -0.081 -0.260). The contribution of the
main component was refined to 0.774(5) [15]. Molecular
illustrations were drawn using the programs ORTEP-3 for
Windows and Mercury [16, 17].
Experimental
Reagents and solvents were purchased from Aldrich, Carl
Roth, and Laachner and used without further purification.
Diethyl ether, THF, and toluene were dried over sodium/
benzophenone. Silica gel 60 from Machery-Nagel was used
for column chromatography. Nitrogen was used as inert gas
if needed.
Crystallographic data deposited at the Cambridge
Crystallographic Data Centre under CCDC-1446087 for 3
and CCDC-1446088 for 7 contain the supplementary
crystallographic data excluding structure factors; this data
can be obtained free of charge via http://www.ccdc.cam.ac.
uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge CB2
1EZ, UK; fax: (?44) 1223-336-033; or deposit@
ccdc.cam.ac.uk).
For microwave assisted reactions a MLS Ethos Lab
microwave oven with pressure vessels in a monorack and
internal ATC-FO sensor was used.
Melting points were determined with a Melting Point
Meter MPM-HV2, GC–MS spectra were recorded with a
Finnigan Mat GCQ. IR spectra were recorded with a Shi-
madzu IR Prestige-21 FTIR spectrometer, UV–Vis data
were obtained with a WTW photolab 6600 UV–Vis spec-
trometer. NMR data were recorded on a Bruker DRX 400
spectrometer (1H: 400.13 MHz; 13C: 100.62 MHz; CDCl3
as internal standard).
Compounds 2, 3, 4, and 6 have already been reported in
the literature [3, 18]. We report here modified procedures
to obtain the respective compounds which are identified by
comparison of their melting points with those reported
earlier and additionally by MS.
Intensity data were collected on a Nonius KappaCCD
diffractometer, using graphite-monochromated Mo-Ka
radiation. Data were corrected for Lorentz and polarization
effects; absorption was taken into account on a semi-em-
pirical basis using multiple scans [11–13]. The structure
was solved by direct methods (SHELXS) and refined by
full-matrix least squares techniques against Fo2 (SHELXL-
97) [14]. The hydrogen atoms of compound 3 were located
by difference Fourier synthesis and refined isotropically.
2,20-Bipyridine-N-oxide (2) (modified literature procedure
[3])
2,20-Bipyridine (1, 4.0 g, 25 mmol) was dissolved in
20.0 cm3 trifluoroacetic acid and cooled to 10 °C in an
ice bath. Over a period of 15 min 4.0 cm3 of 30% H2O2
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Microwave assisted synthesis of 3-(2,20-bipyridine-4-yl)-2-propenoic acid ethyl ester
995
Table 2 Crystal data and structure refinement for 3 and 7
Identification code
3
7
Empirical formula
Formula weight
Temperature/K
C10H7N3O3
217.19
C15H14N2O2
254.28
133 (2)
133 (2)
˚
Wavelength/A
0.71073
0.71073
Triclinic
Crystal system
Space group
Orthorhombic
P212121
ꢀ
P1
Unit cell dimensions
˚
a/A
6.9940 (1)
10.4261 (2)
12.8786 (3)
90
9.6491 (4)
˚
b/A
12.1557 (5)
12.9902 (5)
103.317 (2)
105.541 (2)
110.931 (2)
1277.90 (9), 4
1.322
˚
c/A
a/°
b/°
c/°
90
90
3
˚
Volume/A , Z
939.11 (3), 4
1.536
Density (calc.)/Mg m-3
Absorption coefficient/mm-1
Crystal size/mm3
0.117
0.089
0.06 9 0.06 9 0.05
2.51–27.46
-9 B h B 9
-11 B k B 13
-16 B 1 B 16
6511
0.12 9 0.01 9 0.09
3.0.3–26.37
-12 B h B 11
-15 B k B 14
-15 B 1 B 16
11599
H range for data collection/°
Limiting indices
Reflections collected
Independent reflections
Completeness
2144 (Rint = 0.0641)
100.0%
5157 (Rint = 0.0656)
98.6%
Absorption correction
Max. and min. transmission
Refinement method
none
Semi-empirical from equivalents
0.7456 and 0.6512
Full-matrix least-squares on F2
5157/0/346
–
Full-matrix least-squares on F2
2144/0/174
1.080
Data/restrains/parameters
Goodness-of-fit on F2
Final R indices [I [ 2r(I)]
1.097
R1 = 0.0509
wR2 = 0.1134
R = 0.0571
wR2 = 0.1177
0.376, -0.270
R1 = 0.0992
wR2 = 0.2002
R indices (all data)
R = 0.1533
wR2 = 0.2292
-3
˚
Largest diff. peak and hole/eA
0.348, -0.370
(31 mmol) were added dropwise. The solution was allowed
to warm to room temperature and was stirred overnight.
The solution was then mixed with 35 cm3 CH2Cl2 and was
carefully washed three times with 30 cm3 of 3 N NaOH.
The aqueous phase was extracted with 20 cm3 of CH2Cl2.
The combined organic layers were dried over sodium
sulfate, filtered, and evaporated. The product was obtained
as a pale yellow oil which solidified at room temperature
after about 24 h. Yield: 93% (4.1 g, 23.8 mmol); m.p.:
53–54 °C; MS (EI): m/z (%) = 172.0 (60) [M?], 173.0
(20) [M??H?], 172.2 (100) [M?-H?], 156.2 (10) [M?-O],
145.4 (30) [M?–C2H2], 144.2 (98) [M?–C2H2 ? H?],
143.2 (35) [M?–C2H2-H?].
4-Nitro-2,20-bipyridine-N-oxide (3)
(a) Classical synthesis [3]
Potassium nitrate (12.0 g, 119 mmol) was dissolved under
cooling in 30 cm3 concentrated sulfuric acid, 4.1 g of 2
(23.8 mmol) were added and the solution was heated to
70 °C for 72 h. For the purification procedure, see below.
Yield: 70% (3.6 g, 16.6 mmol); m.p.: 183 °C; MS (EI): m/
z (%) = 216.9 (35) [M?], 201.0 (23) [M?-O], 171.1 (60)
[M?–NOÁ2], 155.2 (88) [M?–NOÁ2, –O, ?H?].
b) Microwave assisted synthesis
Potassium nitrate (6.0 g, 59.5 mmol) was dissolved under
cooling in 15 cm3 concentrated sulfuric acid, 2.0 g of 2
123

996
K. Heintz et al.
Fig. 3 Molecular structure of
3-(2,20-bipyridine-4-yl)-2-
propenoic acid ethyl ester (7)
Table 3 Selected bond lengths/
pm and angles/° of 7
N1a-C1a
133.9(5)
N1a-C5a
133.5(5)
C5a-C6a
148.2(5)
134.1(5)
131.5(6)
117.4(4)
120.1(4)
121.7(4)
N2a-C6a
134.9(5)
147.0(6)
147.5(6)
122.4(4)
125.9(4)
N2a-C10a
C8a-C11a
C11a-C12a
C12a-C13a
C7a-C8a-C11a
C8a-C11a-C12a
C7a-C8a-C9a
C9a-C8a-C11a
C11a-C12a-C13a
Hydrogen bonds
H2aa–O2b
263.2
248.9
250.2
C2a-H2aa—O2b
C11b-H11b—O1a
C9b-H9ba—O1a
168.9
152.7
149.6
H11b–O1a
H9ba–O1a
Fig. 4 Supramolecular structure of 3-(2,20-bipyridine-4-yl)-2-propenoic acid ethyl ester (7)
(11.6 mmol) was added. The microwave vessel was sealed
and heated to 130 °C in a way that during a period of
30 min 130 °C had to be reached using a maximum power
of 1000 W. The reaction temperature then was maintained
for 90 min after which the vessel was allowed to cool
down to room temperature. For the purification procedure,
123

Microwave assisted synthesis of 3-(2,20-bipyridine-4-yl)-2-propenoic acid ethyl ester
997
anhydrous THF and stirred at room temperature for 15 min
before the suspension was refluxed for 20 min.
see below. Yield: 70% (1.75 g, 8.1 mmol); m.p.: 183 °C;
MS see above.
Purification procedure: the cooled solution was poured
onto ice and basified to pH 8–10 with sodium hydroxide
solution (6 N). The precipitate was filtered, washed with
cold water, and dried. It was used in the next reaction step
without further purification.
(a) Classical synthesis [4]
After cooling to room temperature 1.1 g of 6 (6.16 mmol)
in 2.0 cm3 anhydrous THF were added and the solution
then refluxed for 48 h.
(b) Microwave assisted synthesis
4-Bromo-2,20-bipyridine (4)
Compound 3 (1.7 g, 8.1 mmol) was dissolved in 20.0 cm3
glacial acetic acid. To this solution 3.0 cm3 acetyl
bromide (40.5 mmol) were added. The solution immedi-
ately turned yellow. The microwave vessel was sealed
and heated to 130 °C in a way that during a period of
10 min 130 °C had to be reached using a maximum
power of 1000 W. The reaction temperature then was
maintained for 2 h after which the vessel was allowed to
cool down to room temperature. After cooling, the
solution was poured onto ice and basified to pH 10–11
with sodium hydroxide solution (6 N). The aqueous phase
was extracted three times with CH2Cl2 (40 cm3 each).
The solvent was evaporated under reduced pressure. The
obtained light brown oil solidified at room temperature
overnight. The crude product was further purified by
distillation under reduced pressure to obtain a white solid.
Yield: 75% (1.6 g, 6.8 mmol); m.p.: 53–55 °C; MS (EI):
m/z (%) = 234.3 (85) [M?], 235.9 (83) [M?], 155.1 (100)
[M?–Br].
After cooling the suspension to room temperature, it was
transferred into a microwave vessel and 1.1 g of 6
(6.16 mmol) in 2.0 cm3 anhydrous THF were added. The
vessel was sealed and heated to 110 °C in a way that during
a period of 10 min 110 °C had to be reached using a
maximum power of 1000 W. The reaction temperature
then was maintained for 2 h after which the vessel was
allowed to cool down to room temperature.
Purification procedure: After cooling 20.0 cm3 of a 10%
potassium carbonate solution was added. The mixture was
extracted three times with 30 cm3 ethyl acetate. The
organic phase was dried over sodium sulfate and the sol-
vent was evaporated under reduced pressure. The
remaining triethyl phosphonoacetate was removed by dis-
tillation in vacuo. The crude product was purified by
column chromatography on silica gel using a diethyl ether:
light petroleum (40–60) 1: 1 mixture as the eluent. The
white crystalline product was then recrystallized from
ethanol/water by first dissolving the crude product in
ethanol and then adding water until the solution misted.
For crystallization the solution was placed in the refrig-
erator. Yield: 50% (0.78 g, 3.08 mmol, for both synthetic
procedures); m.p.: 51–52 °C; IR: vꢀ = 1711 vs, 1645 m,
1582 m, 1547 m, 1458 w, 1400 w, 1365 w, 1323 w,
1306 s, 1271 m, 1242 w, 1189 s, 1177vs, 1034 m, 997 s,
845 s, 789 vs, 743 s, 600 m, 571 m, 492 m cm-1; MS
(EI): m/z (%) = 254.1 (30) [M?], 225.2 (10) [M?–C2H5Á ],
210.2 (60) [M?–C2H4O], 182.4 (100) [M?–CO2C2HÁ5,
?H?]; 1H NMR (CDCl3, 600 MHz, 298 K): d = 1.34
(CH3, 3H, t, J = 7.1 Hz), 4.28 (CH2, 2H, q, J = 7.1 Hz),
6.72 (=CH, 1H, d, J = 15.9 Hz), 7.33 (=CHar, 1H, ddd,
J = 1.1 Hz, 4.7 Hz, 7.7 Hz), 7.36 (=CHar, 1H, dd,
J = 1.6 Hz, 4.9 Hz), 7.68 (=CH, 1H, d, J = 15.9 Hz),
7.81 (=CHar, 1H, ddd, J = 1.9 Hz, 7.7 Hz, 8.1 Hz), 8.40
(=CHar, 1H, d, J = 8.1 Hz), 8.53 (=CHar, 1H, s), 8.66–8.70
(=CHar, 2H, m) ppm; 13C NMR (CDCl3, 150.92 MHz,
298 K): d = 14.2 (CH3), 60.8 (CH2), 119.1 (=CHar), 121.1
(=CHar), 121.7 (=CHar), 123.0 (=CH), 124.0 (=CHar),
136.9 (=CHar), 141.8 (=CH), 142.6 (=Car), 149.2 (=CHar),
149.8 (=CHar), 155.5 (=CH), 157.0 (=CH), 166.1 (C=O)
ppm.
2,20-Bipyridine-4-carbaldehyde (6)
Compound 4 (1.8 g, 7.7 mmol) was dissolved in 20 cm3
anhydrous diethyl ether and 20 cm3 anhydrous toluene
under a nitrogen atmosphere at -78 °C. Butyl lithium in
hexane (4.0 cm3, 2.5 M) was added dropwise. The solution
was stirred at -78 °C for 90 min before 8.0 cm3 anhydrous
dimethyl formamide were added. The resulting solution
was then stirred for another 90 min at the same temper-
ature. To stop the reaction 50 cm3 of 2 N hydrochloric acid
were added at -78 °C and the solution was allowed to
reach room temperature. The organic phase was separated
and the aqueous phase was neutralized with diluted sodium
hydroxide solution. A smooth white precipitate was
formed. The aqueous phase was extracted three times with
CH2Cl2. The solvent was evaporated under reduced
pressure and a light brown oil that solidified to a light
brown solid was obtained. Yield: 80% (1.1 g, 6.16 mmol);
m.p.: 85–56 °C [18]; MS (EI): m/z (%) = 184.1 (80) [M?],
185.0 (10) [M??H?], 156.2 (100) [M?–CO?Á].
(E)-3-(2,20-Bipyridine-4-yl)-2-propenoic acid ethyl ester
(7, C15H14N2O2)
Dry potassium carbonate (1.3 g, 9.24 mmol) and 2.1 g
triethyl phosphonoacetate were suspended in 10 cm3 of
Acknowledgements K.H. gratefully acknowledges a Ph.D. Grant
from ‘‘Stiftung der Deutschen Wirtschaft’’.
123

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K. Heintz et al.
10. Desiraju GR, Steiner T (2001) The Weak Hydrogen Bond.
Oxford Science Publications
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