Nitropyridines: X.* Palladium-catalyzed cross-coupling of 2-bromo-5-nitropyridine with terminal acetylenes

Article abstract of DOI:10.1134/S1070428010120109

Substituted 5-nitro-2-ethynylpyridines were synthesized by the Sonogashira reaction of 2-bromo-5-5-nitropyridine with terminal acetylenes. Desilylation, oxidative decarbonylation, and the retro-Favorskii reaction of the cross-coupling products of 2-bromo-5-nitropyridine with trimethylsilylacetylene, prop-2-ynyl alcohol, and 2-methylbut-3-yn-2-ol, respectively, gave 2-ethynyl-5-nitropyridine. The hydration of 2-ethynyl-5-nitropyridine and 5-nitro-2-(phenylethynyl)pyridine according to Kucherov afforded 2-acetyl-5-nitropyridine and 5-nitro-2-phenacylpyridine, respectively. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S1070428010120109

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 12, pp. 1830–1834. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © G.P. Sagitullina, M.A. Vorontsova, A.K. Garkushenko, N.V. Poendaev, R.S. Sagitullin, 2010, published in Zhurnal Organicheskoi
Khimii, 2010, Vol. 46, No. 12, pp. 1820–1823.
Nitropyridines: X.* Palladium-Catalyzed Cross-Coupling
of 2-Bromo-5-nitropyridine with Terminal Acetylenes
G. P. Sagitullina, M. A. Vorontsova, A. K. Garkushenko, N. V. Poendaev, and R. S. Sagitullin†
Dostoevskii Omsk State University, pr. Mira 55a, Omsk, 644077 Russia
e-mail: Sagitullina@orgchem.univer.omsk.su
Received September 16, 2009
Abstract—Substituted 5-nitro-2-ethynylpyridines were synthesized by the Sonogashira reaction of 2-bromo-5-
5-nitropyridine with terminal acetylenes. Desilylation, oxidative decarbonylation, and the retro-Favorskii reac-
tion of the cross-coupling products of 2-bromo-5-nitropyridine with trimethylsilylacetylene, prop-2-ynyl
alcohol, and 2-methylbut-3-yn-2-ol, respectively, gave 2-ethynyl-5-nitropyridine. The hydration of 2-ethynyl-5-
nitropyridine and 5-nitro-2-(phenylethynyl)pyridine according to Kucherov afforded 2-acetyl-5-nitropyridine
and 5-nitro-2-phenacylpyridine, respectively.
DOI: 10.1134/S1070428010120109
Most nitropyridines reported so far have been syn-
thesized by direct nitration of 2(4)-hydroxy- and
2(4)-aminopyridines [2]. The simplicity of replace-
ment of 2(4)-hydroxy and 2(4)-amino groups in the
corresponding 3(5)-nitropyridines by halogen deter-
mines accessibility of halonitropyridines and their pos-
sible wide application in the synthesis of ethynylpyri-
dines via cross-coupling reaction [3–9]. Interest in new
ethynylnitropyridines is stimulated by their potential
biological activity [10–12]. Some alkynylpyridines are
also used for the preparation of organic materials pos-
sessing nonlinear optical properties, organic semicon-
ductors and conducting polymers, liquid crystals, and
photoluminophores [13–18]. The most convenient
procedure for the synthesis of substituted ethynylpyri-
dines is based on the Sonogashira reaction [19, 20].
drawing substituents are present in the pyridine ring
[20]. Up to now only a few examples of the Sonoga-
shira reaction involving halonitropyridines and termi-
nal acetylenes have been reported [13, 18, 21–23].
In this article we describe the synthesis of a series
of substituted 2-ethynyl-5-nitropyridines and their
transformation into difficultly accessible 2-acetyl-5-
nitropyridine and 5-nitro-2-phenacylpyridine. Initial
2-bromo-5-nitropyridine (II) was prepared by reaction
of 5-nitropyridin-2(1H)-one (I) with tetrabutylammo-
nium bromide in the presence of phosphorus penta-
oxide (Scheme 1) according to the convenient proce-
dure proposed previously [9] for pyridinones having
no electron-withdrawing substituents.
Cross-coupling of 2-bromo-5-nitropyridine (II)
with terminal alkynes was performed under argon in
the presence of Pd(PPh3)2Cl2–CuI as catalytic system.
In the reaction of 2-bromo-5-nitropyridine (II) with
It is known that electron-deficient halopyridines
fairly readily undergo cross-coupling reaction and that
their reactivity considerably increases if electron-with-
Scheme 1.
HC
R (IIIa–IIId)
Bu4NBr, P2O5
benzene
Pd(PPh3)2Cl2, CuI
Et3N (a) or KOAc (b–d)
O2N
O2N
O2N
O2N
N
O
N
Br
N
N
H
CH
R
I
II
IVa–IVd
V
R = Me3Si (a), HOCH2 (b), Me2C(OH) (c), Ph (d).
* For communication IX, see [1].
†
Deceased.
1830

NITROPYRIDINES: X.
1831
Scheme 2.
O2N
H2O, Hg2+
R = H
Me
O2N
N
O
VI
N
O2N
R
O
IVd, V
H2O, Hg2+
R = Ph
N
N · ·
O
·
H
O2N
A
VII
B
trimethylsilylacetylene, triethylamine was used as base
and solvent, and in the other cases the reactions were
carried out in anhydrous acetonitrile at room tempera-
ture using potassium acetate as base. Cross-coupling
products, 2-ethynyl-5-nitropyridines IVa–IVd were
isolated in high yields (Scheme 1). It should be noted
that 5-nitro-2-(2-trimethylsilylethynyl)pyridine (IVa)
was reported previously [23], but its melting point was
not given, and the position of the SiMe3 singlet in the
1H NMR spectrum (δ 1.56 ppm) was doubtful.
served in the 13C NMR spectrum (APT pulse se-
quence) at δC 47.98 ppm. Enol tautomer B was charac-
terized by the vinyl proton signal at δ 6.24 ppm and
1
hydroxy proton signal at δ 15.00 ppm in the H NMR
spectrum. The 13C NMR spectrum (APT) contained
signals at δC 168.57 (=COH) and 94.65 ppm (–CH=).
Tautomerism of 2-, 3-, and 4-phenacylpyridines having
no nitro group in the pyridine ring was studied previ-
ously. It was found that 2-phenacylpyridine can exist
as three tautomers, the third tautomer being enamino
ketone; its concentration depended on the solvent
polarity [24–28].
Substituted ethynylnitropyridines IVa–IVc were
used as starting compounds for the synthesis of
2-ethynyl-5-nitropyridine (V). Desilylation of 5-nitro-
2-(2-trimethylsilylethynyl)pyridine (IVa) by the action
of potassium fluoride in ethanol (method a) gave
2-ethynyl-5-nitropyridine (V) in 90% yield. Oxidative
decarbonylation of pyridine IVb with manganese
dioxide in the presence of alkali (method b) afforded
42% of compound V. Taking into account high cost of
trimethylsilylacetylene, method b deserves attention.
Ethynylpyridine V was also synthesized by the retro-
Favorskii reaction of pyridine IVc (method c), but the
yield was as poor as 15%.
The structures of the newly synthesized compounds
1
were confirmed by their IR and H and 13C NMR
spectra and elemental analyses.
EXPERIMENTAL
The IR spectra of compounds IVb–IVd and V were
recorded on a Specord IR-75 spectrometer from solu-
tions in chloroform, and the spectrum of VII was
recorded on an Infralum FT-801 instrument from both
solution in chloroform and crystalline sample using an
attenuated total internal reflectance (ATR) adapter. The
1H NMR spectra were measured on a Bruker AC-200
spectrometer at 200.13 MHz using tetramethylsilane as
Kucherov hydration of pyridines IVd and V led to
the formation of difficultly accessible 2-acetyl-5-nitro-
pyridine (VI) and 5-nitro-2-phenacylpyridine (VII).
The reaction followed the Markovnikov rule, and
pyridines VI and VII were obtained in good yields
(Scheme 2).
1
internal reference. The H and 13C NMR spectra of
compound VII were obtained on a Bruker Avance
DRX-400 spectrometer at 400.13 and 100.62 MHz,
respectively. The elemental compositions were deter-
mined on a Perkin–Elmer analyzer. The progress of
reactions and the purity of products were monitored by
TLC on Silufol UV-254 plates; spots were visualized
under UV light.
1
The H and 13C NMR spectra of 5-nitro-2-phen-
acylpyridine (VII) contained signals assignable to
ketone and enol tautomers A and B at a ratio of 1:3.
The enol structure of VII predominates due to addi-
tional stabilization by intramolecular hydrogen bond.
Ketone tautomer A showed in the 1H NMR spectrum
a signal at δ 4.65 ppm from protons in the methylene
group, and the corresponding carbon signal was ob-
5-Nitropyridin-2(1H)-one (I) was synthesized as
described in [29], and tetrabutylammonium bromide
was prepared according to the procedure reported in
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 12 2010

SAGITULLINA et al.
1832
[30]. Trimethylsilylacetylene (IIIa), prop-2-yn-1-ol
(IIIb), and 2-methylbut-3-yn-2-ol (IIIc) were com-
mercial products (from Fluka) and were used without
additional purification. Phenylacetylene (IVd) was
synthesized as described in [31].
3-(5-Nitropyridin-2-yl)prop-2-yn-1-ol (IVb).
Reaction time 30 min, eluent chloroform–ethyl acetate
(1:1). Yield 66%, mp 125–126°C (from toluene). IR
spectrum, ν, cm–1: 3390 (OH); 2220 (C≡C); 1580,
1
1360 (NO2). H NMR spectrum (DMSO-d6), δ, ppm:
4.41 d (2H, CH2, J = 5.9 Hz), 5.60 t (1H, OH, J =
2-Bromo-5-nitropyridine (II). A mixture of 1.53 g
(10.94 mmol) of 5-nitropyridin-2(1H)-one (I), 4.1 g
(12.71 mmol) of tetrabutylammonium bromide, and
3.71 g (26.1 mmol) of P2O5 in 29 ml of benzene was
heated for 1 h with stirring under reflux. The mixture
was cooled to room temperature, the upper layer was
separated by decanting, and the bottom layer was
ground with benzene (3 ×6 ml). The extracts were
combined with the organic phase, washed with a satu-
rated solution of NaHCO3 and NaCl, and dried over
MgSO4. The solvent was distilled off under reduced
pressure, and the residue was recrystallized from petro-
leum ether (bp 40–70°C). Yield 1.7 g (48%), mp 138–
139°C [6].
3
5.9 Hz), 7.78 d (1H, 3-H, J = 8.8 Hz), 8.59 d.d
3
4
(1H, 4-H, J = 8.8, J = 2.4 Hz), 9.34 d (1H, 6-H,
4J = 2.4 Hz). Found, %: C 54.24; H 3.35; N 15.47.
C8H6N2O3. Calculated, %: C 53.94; H 8.39; N 15.73.
2-Methyl-4-(5-nitropyridin-2-yl)but-3-yn-2-ol
(IVc). Reaction time 30 min, eluent benzene–ethyl
acetate (5:1). Yield 98%, mp 85–86°C (from ethanol).
IR spectrum, ν, cm–1: 3390 (OH); 2220 (C≡C); 1580,
1
1360 (NO2). H NMR spectrum (CDCl3), δ, ppm:
1.67 s (6H, Me), 3.22 s (1H, OH), 7.60 d (1H, 3-H,
3J = 8.3 Hz), 8.47 d.d (1H, 4-H, 3J = 8.3, 4J = 2.4 Hz),
4
9.40 d (1H, 6-H, J = 2.4 Hz). Found, %: C 59.43;
H 4.97; N 12.60. C10H10N2O3. Calculated, %: C 58.25;
H 4.89; N 13.59.
5-Nitro-2-(2-trimethylsilylethynyl)pyridine
(IVa). A suspension of 0.5 g (2.5 mmol) of 2-bromo-5-
nitropyridine (II) in 7.8 ml of triethylamine was cooled
to 0–5°C, 0.010 g (0.05 mmol) of copper(I) iodide and
0.039 g (0.055 mmol) of Pd(Ph3P)2Cl2 were added
under stirring in a stream of argon, argon flow was
terminated, the flask was tightly capped (Suba-Seal™
septum, Aldrich), and 0.35 ml (2.47 mmol) of trimeth-
ylsilylacetylene (IIIa) was added with a syringe. The
mixture was stirred for 1 h on cooling and for 2 h at
room temperature, diluted with diethyl ether, and
filtered. The ether layer was washed with a saturated
solution of NaCl and dried over MgSO4, the solvent
was distilled off, and the residue was purified by chro-
matography on silica gel using diethyl ether–petroleum
ether (1:1) as eluent. Yield 0.44 g (80%), mp 110–
5-Nitro-2-(2-phenylethynyl)pyridine (IVd). Reac-
tion time 90 min, eluent benzene. Yield 90%, mp 164–
165°C (from petroleum ether, bp 70–100°C). IR spec-
trum, ν, cm–1: 2215 (C≡C); 1580, 1360 (NO2). 1H NMR
spectrum (CDCl3), δ, ppm: 7.39–7.66 m (5H, Ph),
3
3
7.68 d (1H, 3-H, J = 8.7 Hz), 8.45 d.d (1H, 4-H, J =
8.7, 4J = 2.5 Hz), 9.42 d (1H, 6-H, 4J = 2.5 Hz). Found,
%: C 69.63; H 3.64; N 12.55. C13H8N2O2. Calculated,
%: C 69.64; H 3.60; N 12.49.
2-Ethynyl-5-nitropyridine (V). a. Nitropyridine
IVa, 0.068 g (0.31 mmol), was added to a solution of
0.087 g (0.93 mmol) of KF·2H2O in 4 ml of ethanol,
the mixture was stirred for 30 min and filtered, the
filtrate was evaporated, and the residue was purified by
chromatography on silica gel (100–160 μm) using
chloroform–ethyl acetate (9:1) as eluent. Yield 0.04 g
(90%), mp 110–111°C (from petroleum ether, bp 70–
100°C). IR spectrum, ν, cm–1: 2215 (C≡C); 1525, 1360
1
111°C (from ethanol). H NMR spectrum (CDCl33), δ,
ppm: 0.25 s (9H, SiMe3), 7.55 d (1H, 3-H, J =
3
4
8.5 Hz), 8.38 d.d (1H, 4-H, J = 8.5, J = 2.5 Hz),
9.30 d (1H, 6-H, 4J = 2.5 Hz) [23].
1
(NO2). H NMR spectrum (CDCl3), δ, ppm: 3.48 s
Nitropyridines IVb–IVd (general procedure).
2-Bromo-5-nitropyridine II, 0.203 g (1 mmol), and
potassium acetate, 0.196 g (2 mmol), were dispersed in
7 ml of anhydrous acetonitrile, 0.007 g (0.01 mmol) of
Pd(Ph3P)2Cl2 and 0.002 g (0.01 mmol) of CuI were
added under stirring in a stream of argon, and a solu-
tion of 1.2 mmol of terminal alkyne IIIb–IIId in 7 ml
of acetonitrile was added dropwise. The mixture was
stirred at 40°C until the reaction was complete (TLC)
and filtered, the solvent was distilled off from the fil-
trate, and the residue was purified by column chroma-
tography on silica gel.
3
(1H, ≡CH), 7.68 d (1H, 3-H, J = 8.2 Hz), 8.49 d
3
(1H, 4-H, J = 8.2 Hz), 9.42 s (1H, 6-H). Found, %:
C 57.50; H 2.88; N 18.59. C7H4N2O2. Calculated, %:
C 56.76; H 3.72; N 18.91.
b. Nitropyridine IVb, 0.405 g (2.28 mmol), was
dissolved in 27 ml of anhydrous benzene, 0.128 g
(2.28 mmol) of powdered potassium hydroxide and
0.989 g (11.38 mmol) of manganese(IV) oxide were
added, and the mixture was stirred for 3 h at room tem-
perature. The mixture was cooled, the precipitate was
filtered off and washed with benzene, and the filtrate
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 12 2010

NITROPYRIDINES: X.
1833
was evaporated under reduced pressure. Yield
0.142 g (42%).
142.39 (C6), 162.99 (C2), 168.57 (=COH). Found, %:
C 64.68; H 4.12; N 11.65. C13H10N2O3. Calculated, %:
C 64.46; H 4.16; N 11.56.
c. Calcined potassium hydroxide, 1.52 g (2.71 mol),
was added to a solution of 0.540 g (2.62 mmol) of
nitropyridine IVc in 15.6 ml of benzene, and the mix-
ture was heated for 3 h under reflux in a stream of
argon. The mixture was filtered, the filtrate was evap-
orated, and the residue was purified by column chro-
matography. Yield 0.06 g (15%).
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 07-03-00783-a).
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1332 (NO2). H NMR spectrum (CDCl3), δ, ppm:
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(2H, C6H5), 8.46 d.d (1H, 4-H, J = 8.7, J = 2.6 Hz),
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9.39 d (1H, 6-H, J = 2.6 Hz); enol tautomer B: 6.24 s
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4-H, J = 9.0, J = 2.5 Hz), 9.20 d (1H, 6-H, J =
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128.56 (Co), 130.80 (Cp), 131.58 (C4), 134.92 (Ci),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 12 2010

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