A new and convenient route to 2,2′-dipyridyl diselenide/ditelluride and some of their alkyl/aryl derivatives through BF3-complexed pyridyl carbanion

Article abstract of DOI:10.1081/SCC-120003627

Synthesis of 2,2′-dipyridyl diselenide/ditelluride and some alkyl/aryl pyridyl selenide/telluride is reported.

Full text of DOI:10.1081/SCC-120003627

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A NEW AND CONVENIENT ROUTE TO 2,2′-DIPYRIDYL
DISELENIDE/DITELLURIDE AND SOME OF THEIR ALKYL/
ARYL DERIVATIVES THROUGH BF -COMPLEXED PYRIDYL
3
CARBANION
a
a
a
a
a
a
K. K. Bhasin , B. S. Bhandal , J. Singh , N. Singh , K. N. Singh & P. Singh
a
Department of Chemistry, Centre of Advanced Studies in Chemistry, Panjab University,
Chandigarh, 160 014, India
Published online: 17 Aug 2006.
To cite this article: K. K. Bhasin , B. S. Bhandal , J. Singh , N. Singh , K. N. Singh & P. Singh (2002): A NEW AND CONVENIENT
ROUTE TO 2,2′-DIPYRIDYL DISELENIDE/DITELLURIDE AND SOME OF THEIR ALKYL/ARYL DERIVATIVES THROUGH BF -COMPLEXED
3
PYRIDYL CARBANION, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 32:9, 1319-1325
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SYNTHETIC COMMUNICATIONS, 32(9), 1319–1325 (2002)
A NEW AND CONVENIENT ROUTE TO
2
0
,2 -DIPYRIDYL DISELENIDE/
DITELLURIDE AND SOME OF THEIR
ALKYL/ARYL DERIVATIVES THROUGH
BF -COMPLEXED PYRIDYL CARBANION
3
K. K. Bhasin,* B. S. Bhandal, J. Singh,
N. Singh, K. N. Singh, and P. Singh
Department of Chemistry and Centre of
Advanced Studies in Chemistry,
Panjab University, Chandigarh-160014, India
ABSTRACT
0
Synthesis of 2,2 -dipyridyl diselenide/ditelluride and some
alkyl/aryl pyridyl selenide/telluride is reported.
Key Words: Chalcogens; Organic; Selenium; Tellurium;
Pyridine
Organoselenium and organotellurium compounds have become
1
increasingly important as reagents and intermediates in organic synthesis
,2
3
apart from proving promising donor molecules for conductive and photo-
4
conductive organic molecules. Although there exists a variety of methods
for the introduction of selenium/tellurium into organic molecules, research
continues on the development of new selenium or tellurium transfer reagents
5
,6
and methods. It is curious to note that compared to the chemistry of alkyl,
aryl or mixed alkyl aryl chalcogenides, the corresponding chemistry of pyr-
*
Corresponding author. Fax: +91-172-545074. E-mail: kkbhasin@pu.ac.in
319
1
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

1
320
BHASIN ET AL.
7
,8
idyl chalcogenides has not been developed. In continuation of our work,
on the chemistry of organoselenium and organotellurium compounds, we
0
wish to report a new and convenient method for the preparation of 2,2 -
dipyridyl diselenide/ditelluride and some of their 2-pyridyl selenium/tellur-
ium derivatives.
9
,10
It has recently been reported by two of us
BF -complexed pyridine can be conveniently accomplished at the 2-position
that deprotonation of
3
1
with the highly hindered base lithium tetramethyl piperidine (LTMP) in
ꢀ
ether at À78 C. The usefulness of the methodology has now been extended
towards the preparation of several versatile pyridyl selenium/tellurium com-
pounds which are not only difficult to prepare in respectable yields but also
require longer hours. Elemental selenium/tellurium when added to the
ꢀ
BF -complexed 2-lithiopyridine solution at À78 C and allowing the reaction
3
to come to room temperature affords a deep red coloured solution 2 with
the complete dissolution of metals. Elemental selenium dissolves readily in
20min whereas elemental tellurium takes about 45 min to dissolve almost
completely. It is probably because the commercially available tellurium is
1
1
known to exhibit low chemical reactivity due to its surface oxidation.
0
Aerial oxidation of 2 after usual work up affords 2,2 -dipyridyl di-
selenide/ditelluride in nearly quantitative yields. The present method for
the preparation of 2,2 -dipyridyl diselenide has several advantages over
the existing methods in terms of easy work up and requires only 2 h com-
1
pared to 23–92 h reported in the literature. In addition it avoids the use
0
4
14a
1
4c
and in situ evolution
0
of highly toxic hydrogen selenide gas. Whereas
in case of 2,2 -dipyridyl ditelluride it gives maximum yield when compared
1
5
to reported methods.
Alkylation of the deep red coloured solution of BF -complexed 2-
3
seleno/telluropyridyl carbanion solution 2 as prepared above was carried
Scheme. Methodology for the synthesis. Reagents and conditions: i) BF ꢀEt O,
3
2
ꢁ
ꢁ
ꢁ
0
iv) hydrolysis and aerial oxidation at room temperature for 30min.
C, 15 min, ether, ii) LTMP, ꢂ 78 C, 15 min, ether, iii) E ¼ Se/Te, ꢂ 78 C, 30min.

BF
3
-COMPLEXED PYRIDYL CARBANION
1321
ꢀ
out by a variety of alkylating agents at À78 C. After warming to about
ꢀ
À20 C, and allowing to come to room temperature followed by usual
work up afforded high yields of alkyl pyridyl selenide/telluride indicating
clearly that lithium 2-pyridyl selenolate/tellurolate or a chemically equiva-
lent specie is cleanly formed when elemental selenium/tellurium reacts with
2-lithiated pyridine. This procedure describes the preparation of 2-methyl-
selenopyridine and 2-(n)-butyltelluropyridine starting from cheaply and
conveniently available pyridine. It requires less time with better yields and
compares favourably with those reported in the literature starting from 2-
1
4(a,b),16,17
bromopyridine.
Quenching of the BF -complexed lithiated 2-pyridine 1 with diphenyl
3
diselenide and dibenzyl diselenide resulted in the reductive cleavage of
heteroatom-heteroatom bond with the formation of phenylpyridyl selenide
and benzyl pyridyl selenide respectively in good yields.
EXPERIMENTAL
All manipulations must be carried out under a dry oxygen-free nitro-
gen atmosphere to prevent the oxidation of oxygen sensitive selenium and
tellurium intermediates.
Elemental selenium and tellurium was stored in a desiccator prior to
1
2
13
use. Diphenyl diselenide and dibenzyl diselenide was prepared by the
literature methods. Methyl iodide (Sisco) n-butyl bromide (Sisco) and
2,2,2-trifluoroethyl iodide (Aldrich), were purified by distillation and were
subsequently deoxygenated with a stream of nitrogen. The H NMR spectra
1
were recorded in CDCl , relative to TMS using a Varian EM 390operated
3
1
3
at 90MHz. C NMR spectra were recorded on Jeol FX90Q FT NMR spec-
trometer operating at 22.49 MHz with an internal deuterium lock. Infrared
spectra were recorded as neat liquid between AgCl plates on a Perkin-Elmer
1
1
430spectrophotometer. The EI mass spectra were obtained on a VG 7 05 ,
1-2503 mass spectrometer at 70 eV. C, H and N were estimated on a
Perkin-Elmer 2400 CHN elemental analyzer.
General Procedure for the Generation of BF -Complexed
3
2
-Pyridyl Seleno/Telluro Carbanion Followed by the Aerial
0
Oxidation for the Preparation of 2,2 -Dipyridyl
Diselenide/Ditelluride
Into a flame dried two necked round bottomed flask equipped with a
stir bar and septum cap was placed a solution of pyridine (0.23 g, 0.24 ml,

1
322
BHASIN ET AL.
3
.0mmol) in dry ether (15 ml) under oxygen-free nitrogen atmosphere.
ꢀ
The solution was cooled to 0 C in ice bath, and BF ÁEt O (0.46 g, 0.41 ml,
3
2
ꢀ
3
1
.3 mmol) added to it. The resulting white suspension was stirred at 0 for
ꢀ
5 min. The temperature was lowered to À78 C and LTMP (Lithium tetra-
methyl piperidine), prepared by stirring TMP (0.46 g, 0.56 ml, 3.3 mmol) in
dry ether (10ml) and n-BuLi (2.2 ml, 1.5 N, 3.3 mmol) at À10 C, was added
ꢀ
slowly via cannula under nitrogen atmosphere. The resulting brown solution
ꢀ
was stirred for 15 min at À78 C. Elemental selenium/tellurium (3.0mmol)
was added and temperature was raised slowly until complete dissolution of
selenium/tellurium took place. At this stage the supply of nitrogen was
discontinued and the reaction mixture was hydrolyzed followed by exposing
to aerial oxidation for 30min. The aqueous layer was extracted with diethyl
ether (4 Â 10ml), organic layer was washed with water, brine and dried over
anhydrous sodium sulphate. The solvent was removed on a rotary evapora-
tor to afford the crude product which was purified by column chromatog-
0
raphy as yellow needles in case of 2,2 -dipyridyl diselenide and as red
0
crystals in case of 2,2 -dipyridyl ditelluride.
14
0 ꢀ ꢀ
2
,2 -Dipyridyl diselenide: (88% yield) m.p. 48–49 C (lit. 48 C).
1
1
H NMR (CDCl ) d 6.95 (m, 2H), 7.41 (m, 2H), 7.69 (m, 2H), 8.34 (m, 2H).
3
3
C NMR (CDCl ) d 120.6, 122.8, 136.7, 148.8 and 153.6. MS (EI): m/z 316
3
þ
þ
(
M ); 236 (M -Se).
0
ꢀ
15
,2 -Dipyridyl ditelluride: (80% yield) m.p. 51–52 C (lit. 50–51.5 C).
ꢀ
2
1
H NMR (CDCl ) d 7.02–8.02 (m, 6H), 8.45 (d, 2H). MS (EI): m/z 416
3
þ þ
(
M ); 286 (M -Te).
General Procedure for the Preparation of
-Alkylseleno/Telluropyridine
2
Alkyl halide {methyl iodide, n-butyl bromide or 2,2,2-trifluoroethyl
iodide (3.0mmol)} was added dropwise over a period of 30min to the
cooled solution of BF -complexed seleno/telluro pyridyl carbanion
3
ꢀ
ꢀ
(
3.0mmol) at À78 C prepared as described above. After stirring further
for 20min at À78 C, the temperature was gradually allowed to rise to
room temperature and quenched with deoxygenated water (20ml). The
aqueous layer was extracted with diethyl ether (4 Â 10ml). The organic
layer was washed with water, brine and dried over anhydrous sodium sul-
phate. The solvent was removed on a rotary evaporator to afford the crude
product which was purified by column chromatography/vacuum distillation
to afford analytically pure 2-alkylseleno/telluro pyridine.
ꢀ
2
-Methylselenopyridine: Pale yellow oil (90% yields), b.p. 50–52 C/
ꢀ
1
6a
1
3
0torr (lit.
43–44 C/25 mm torr). H NMR (CDCl ) d 2.45 (s, 3H),
3

BF
3
-COMPLEXED PYRIDYL CARBANION
1323
þ
6
9
.9 (m, 1H), 7.4 (m, 1H); 7.2 (m, 1H); 8.4 (m, 1H). MS (EI): m/z 173 (M );
þ
3 (M -Se).
2
1
7
1
-(n)Butyltelluoropyridine: Yellow oil (85% yield). H NMR (CDCl )
3
d 0.92–0.89 (m, 3H), 1.46–1.41 (m, 2H), 1.93–1.88 (m, 2H), 3.15–3.10 (t, 2H);
6
.99–6.97 (m, 1H), 7.30–7.29 (m, 1H), 7.45–7.39 (m, 1H), 8.47–8.46 (d, 1H).
C NMR (CDCl ) d 9.28, 13.4, 25.1, 1, 33.8, 120.8, 131.5, 135.2, 141.1 and
1
3
3
þ
þ
1
50.6. MS (EI): m/z 265 (M ); 135 (M -Te).
,2,2-Trifluoroethyltelluoropyridine: Light yellow oil (85% yield).
H NMR (CDCl ) d 4.10–3.7 (q, 2H), 7.50–7.39 (m, 3H), 8.61–8.60 (d,
2
1
3
1
9
1
1
4
H). F NMR d 58.5 (t, CH CF ). IR (neat): 3060, 2976, 2928, 1631,
2
3
590, 1568, 1472, 1432, 1290, 1260, 1246, 1151, 1050, 990, 863, 575, 537,
À1
þ
þ
61 cm . MS (EI): m/z 291 (M ); 161 (M -Te). Anal. calcd for
C H NF Te: C, 28.86; H, 2.06; N, 4.81. Found: C, 28.72; H, 2.01; N, 4.92.
3
7
6
General Procedure for the Preparation of 2-Phenylselenopyridine
Diphenyl diselenide (3.0mmol) dissolved in 20ml THF was added
dropwise over a period of 20min to the cooled solution of BF -complexed
3
ꢀ
2
-pyridyl carbanion (3.0mmol) at À78 C as described above in the typical
ꢀ
preparation. After stirring for 20min at À78 C, the temperature was grad-
ually allowed to rise to room temperature and quenched with deoxygenated
water (20ml). It was subjected to usual work up as described above and
afforded the crude product, which was purified by flash chromatography to
give analytically pure 2-phenylselenopyridine in 46% yield as pale yellow
1
6a 1
oil.
8
1
H NMR d 7.0–6.8 (m, 2H), 7.4–7.1 (m, 4H), 7.70–7.50 (m, 2H),
.4–8.26 (m, 1H); C NMR (CDCl ) d 120.2, 124.0, 127.5, 128.6, 129.4,
35.9, 136.4, 149.6 and 158.5. MS (EI) 234 (M ); 154 (M -Se).
13
3
þ
þ
2-Benzylselenopyridine: 2-Benzylselenopyridine was prepared similarly
using dibenzyl diselenide. It was purified by column chromatography over
silica gel. Elution with hexane–ethylacetate (8 : 2) afforded the pure viscous
1
13
oil in 45% yield. H NMR d 4.4 (s, 2H); 7.0–7.6 (m, 8H), 8.4–8.6 (d, 1H),
C
(
IR (neat): 3080, 3060, 2969, 2938, 1637, 1571, 1556, 1453, 1437, 1260, 1034,
CDCl ) d 29.2, 120.4, 125.3, 126.8, 128.4, 128.9, 135.9, 139.0, 149.9, 155.5.
3
À1 þ þ
982, 808, 503, 470 cm . MS (EI) 249 (M ); 168 (M -SeH). Anal. calcd for
C H NSe: C, 57.83; H, 4.41; N, 5.62. Found: C, 57.75; H, 4.23; N, 5.60.
In summary, the present one flask procedure provides a new path for
1
2
11
0
the synthesis of 2,2 -dipyridyl diselenide/ditelluride and their derivatives and
constitutes an important addition to the synthetic methodology starting
from pyridine. In addition, it has advantages of mild conditions, simple
operation and good yields over the existing methods in the literature.

1
324
BHASIN ET AL.
ACKNOWLEDGMENTS
Research grant from CSIR, New Delhi, India is gratefully
acknowledged.
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BF
3
-COMPLEXED PYRIDYL CARBANION
1325
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Received in Japan January 29, 2001