Synthesis and characterization of 2,5-bis(2-pyridyl)thiophene

Article abstract of DOI:10.1080/10426500211734

2-[2-(Trimethylsilyl)ethynyl] pyridine (6) was prepared in 95% yield by reaction of 2-bromopyridine with trimethylsilylacetylene in triethylamine in the presence of bis(triphenylphosphine)Palladium(II) chloride and Copper(I) iodide. Desilylation of (6) by refluxing with sodium hydroxide in methanol (yield 95%) of 2-ethynylpyridine (5). Oxidative coupling of (5) in pyridine by oxygen in the presence of Copper(I) chloride gives 70% yield of 1,4-bis(2-pyridyl)1,3-butadiyne (4). Reaction of 4 with sodium sulfide affords 100% of 2,5-bis(2-pyridyl) thiophene (1).

Full text of DOI:10.1080/10426500211734

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Synthesis and Characterization of 2,5-Bis(2-
pyridyl)thiophene
Samir A. Al-Taweel a
a Department of Chemistry, Mutah University, Karak, Jordan
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To cite this article: Samir A. Al-Taweel (2002): Synthesis and Characterization of 2,5-Bis(2-pyridyl)thiophene, Phosphorus,
Sulfur, and Silicon and the Related Elements, 177:5, 1041-1045
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:1041–1045
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DOI: 10.1080/10426500290092325
SYNTHESIS AND CHARACTERIZATION
OF 2,5-BIS(2-PYRIDYL)THIOPHENE
Samir A. Al-Taweel
Department of Chemistry, Mutah University, Karak, Jordan
(Received October 1, 2001; accepted November 6, 2001)
2-[2-(Trimethylsilyl)ethynyl] pyridine (6) was prepared in 95% yield
by reaction of 2-bromopyridine with trimethylsilylacetylene in triethy-
lamine in the presence of bis(triphenylphosphine)Palladium(II) chlo-
ride and Copper(I) iodide. Desilylation of (6) by refluxing with sodium
hydroxide in methanol (yield 95%) of 2-ethynylpyridine (5). Oxidative
coupling of (5) in pyridine by oxygen in the presence of Copper(I) chlo-
ride gives 70% yield of 1,4-bis(2-pyridyl)1,3-butadiyne (4). Reaction of
4 with sodium sulfide affords 100% of 2,5-bis(2-pyridyl) thiophene (1).
Keywords: 2,5-Bis(2-pyridyl)thiophene
2,20:50,200-Terthiophene is a biologically active natural product, it was
found in plants of family compositae. It shows nematicidal and fungi-
5
11
cidal activity.1 It was found that thiophene6,7 and pyridine8
are of
interest as repeating units for the construction of electroconductive
polymers, (2) and (3) respectively. Much of the research has been
focused on modification of the base monomers and oligomers, specif-
ically the alkyl derivatives which yield soluble polymers with im-
proved conductivity. Oligopyridines and mixed oligopyridylthiophenes
have resulted in a varity of new metal complexes. For example,
-sexipyridine12 forms a double helical complexe with Cd+2, 6-(200-
thienyl)-2,20-bipyridine13 exhibits a wide range of bond modes which
The author is grateful to Professor A. J. Ashe, III, University of Michigan, for his
limitless help running 1H, 13C-NMR and mass spectra.
Address correspondence to S. A. Al-Taweel, Department of Chemistry, Mutah Univer-
sity, Karak, Jordan. E-mail: s altawee@hotmail.com
1041

1042
S. A. Al-Taweel
include bidentate N,N-donor, terdentate N,N,S-donor, and cyclometa-
lated N,N,C-donor. Kumada14 introduced a convenient synthesis for
a varity of terheterocyclic compounds based on grignard compounds
in the presence of nickel catalyst. However, thienopyridines and
bipyridines were prepared in low yields. In view of the above, 2,5-
bis(2-pyridyl)thiophene (1) was prepared via sulfide cyclization of 1,4-
bis(pyridyl)-1,3-butadiyne. Herein, its synthesis and characterization
is described.
SYNTHESIS
The synthesis of 2-ethynylpyridines has been described in the
literature,15 but the method is tedious and the overall yield is low.
2-Ethynylpyridine (5) was prepared in 90%. This involves the coupling
of 2-bromopyridine with trimethylsilylacetylene16 in the presence of
bis(triphenylphosphine)Palladium(II)dichloride and copper(I) iodide in
triethylamine followed with desilylation17 with sodium hydroxide in
methanol (Scheme 1).
SCHEME 1

Thiophenes
1043
2,6-Bis(pyridyl)thiophene (1) was prepared in quantitative yield via
the interaction of sodium sulfide with 1,4-bis(2-pyridyl)-1,3-butadiyne
(4), it is a good method for preparing oligomers with an odd number
of thiophene rings. 4 was prepared in 70% yield from the oxidative
coupling of 2-ethynylpyridine (5) in the presence of copper(I) chloride
in pyridine shaken with oxygen bubbling (Scheme 1). Transition
metal complexes of 1 is in progress. Structures of new compounds
were based on elemental analysis data, 1H-NMR, 13C-NMR, and mass
spectrometry.
EXPERIMENTAL
Melting points were determined on electrothermal melting point ap-
paratus and are uncorrected. Proton magnetic resonance spectra were
recorded on Brucker AM-300 spectrometer for solution in CDCl3. The
1H-NMR spectra were calibrated by using signals from the solvent
referenced to (Me)4Si. The elemental analysis were determined by
M. H. W. laboratories (Phoenix, Arizona, U.S.A.). Mass spectra were
determined by Finnigan MAT 731 spectrometer at 70 ev. Triethy-
lamine and pyridine were dried over potassium hydroxide and were dis-
tilled before use. 2-Bromopyridine, dichloro[bis-(triphenylphosphine)]
Palladium(II), (Ph3P)2PdCl2 were purchased from Jansen Chemica.
Trimethylsilylacetylene was prepared according to the literature.16
Na2S.9H2O purchased from PSPARK Scientific Limited.
2-[2-(Trimethylsilyl)ethynyl]pyridine (6)17
Dichloro [bis(triphenylphosphine)]Palladium(II), 0.40 g and copper(I)
iodide, 0.27 g were added to a solution of 5.0 g (0.032 mmol) of 2-
bromopyridine and trimethylsilylacetylene 3.9 g (0.04 mmole) in dry
triethylamine (50 ml) under nitrogen atmosphere. The reaction mixture
was cooled in an ice bath for 1 h and allowed to stir at room temperature
overnight. Water was added and the mixture was extracted with ether
(4 50 ml), ether extract dried over anhydrous Na2SO4, filtered, and
concentrated to a brown oil. This material was passed over a silica gel
eluting with hexane, hexane was removed to afford colorless oil 5.32 g
(95%) yield. This product was used in the next step without farther pu-
rification. 1H-NMR (CDCl3): , 0.22 (S, 9H), 7.15–7.60 (m, 3H), 8.53 (d,
J = 6.0 Hz, 1H).
2-Ethynylpyridine (5)15
A solution of 5.0 g (0.028 mmole) of 2-[2-(Trimethylsilyl) ethynyl]
Pyridine (6) in methanol (50 ml) and 1N sodium hydroxide solution

1044
S. A. Al-Taweel
(30 ml) was stirred for 1 h at room temperature, acetic acid, 3.0 ml
(0.028 mmole) was added. The mixture was concentrated using rotatory
evaporator, the residue was extracted with ether (2
50 ml), ether
washed with water and brine, dried over anhydrous Na2SO4, ether was
removed to afford 2.5 g (90%) yield of brownish oil, vacuum distillation
(73 C/12 mmHg) afford colorless oil. 1H-NMR (CDCl3): , 3.15 (S, 1H),
7.17–7.78 (m, 3H), 8.58 (d, J = 6.0 HZ, 1H).
1,4-Bis(2-pyridyl)-1,3-butadiyne (4)18
Copper(I) chloride, 0.29
g was added to a solution of 2-
ethynylpyridine, 0.375 g (0.036 mmole) in dry pyridine (30 ml), and the
mixture bubbled with oxygen gas for 1 h; the color of the solution turned
black. The mixture was poured into water 300 ml, no precipitate was
formed. The reaction mixture was extracted with chloroform (3 40 ml),
the solution was dried over anhydrous calicum chloride, evaporation of
solvent using rotatory evaporator afford black oily product, evaporation
in fume hood overnight to remove residual pyridine afford black solid.
Crystallization from CCl4 using charcoal afford white shinny crystals,
2.4 g (70%), m.p. = 120 –121 C. 1H-NMR (CDCl3, 300 MHZ): , 7.27 (m,
1H), 7.52 (broad doublet, 1H), 7.67 (m, 1H), 8.60 (d, J = 5.0 Hz, 1H).
13C-NMR (CDCl3, 75 MHz): 73, 81, 124, 128, 136, 142, 150. Anal.
Calcd. For C14H8N2: C, 82.33, H, 3.95. Found: C, 81.55; H, 3.83. MS(EI)
[m/e (intensity)]: 205 (22), M+ 204 (100), 203 (26), 177 (11), 176 (11),
164 (2), 151 (12), 124 (4), 100 (4.5), 99 (8).
2,5-Bis(2-pyridyl)thiophene 1
A solution of 1,4-bis(2-pyridyl)-1,3-butadiyne 0.74 g (3.6 mmol) and
sodium sulfide nonahydrate, Na2S.9H2O in dry tetrahydrofuran (30 ml)
was refluxed overnight. THF was removed and the residue was ex-
tracted with hexane (2 20 ml), hexane was removed to afford light
golden crystals, 0.82 g (100%) yield m.p. 158–159 C. 1H-NMR (CDCl3,
300 MHz): 7.13 (m, 1H), 7.63 (S, 1H), 7.70 (m, 2H), 7.58 (d, J = 5.0 Hz,
2H). 13C-NMR (CDCl3, 75 MHz): 119, 122, 126, 127.8, 136.4, 149. Anal.
Calcd. for C14H10N2S: C, 70.56; H, 4.23. Found: C, 69.30; H, 4.20. MS
(EI) [m/e (intensity)]: 204 (7), 139 (18), M+ 238 (100), 237 (20), 205 (19),
160 (7), 78 (11).
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Thiophenes
1045
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