Reactions of selenourea with benzoyl- and 2-thienoylbromoacetylenes: synthesis of 1,3-diselenetanes and 1,4-diselenafulvenes

Article abstract of DOI:10.1016/j.tetlet.2007.12.016

A novel reaction of selenourea with benzoylbromoacetylene and 2-thienoylbromoacetylene is described. The reaction proceeds in the presence of triethylamine at -30 to 0 °C to afford new 4- and 5-membered heterocycles.

Full text of DOI:10.1016/j.tetlet.2007.12.016

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 974–976
Reactions of selenourea with benzoyl- and 2-thienoylbromoacetylenes:
synthesis of 1,3-diselenetanes and 1,4-diselenafulvenes
a,
a
a
*
Svetlana V. Amosova , Valentina N. Elokhina , Anatoly S. Nakhmanovich ,
Lyudmila I. Larina a, Alexander V. Martynov a, Barry R. Steele b, Vladimir A. Potapov a,*
a A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Division of the Russian Academy of Sciences, 1 Favorsky Str., 664033 Irkutsk, Russia
b National Hellenic Research Foundation, The Institute of Organic and Pharmaceutical Chemistry, Vas. Constantinou 48, 116 35 Athens, Greece
Received 2 October 2007; revised 23 November 2007; accepted 5 December 2007
Available online 8 December 2007
Abstract
A novel reaction of selenourea with benzoylbromoacetylene and 2-thienoylbromoacetylene is described. The reaction proceeds in the
presence of triethylamine at À30 to 0 °C to afford new 4- and 5-membered heterocycles.
Ó 2007 Elsevier Ltd. All rights reserved.
Diselenetanes and ditelluretanes are a relatively rare
class of compounds. A number of 1,3-dithietanes have been
synthesised,1,2 whereas only a few representatives of the
1,3-diselenetanes and 1,3-ditelluretanes are known.3,4
In comparison to 1,3-diselenetanes, 1,4-diselenafulvenes
are better known compounds, and have received much
attention from scientists, inter alia as starting materials
for the synthesis of tetraselenafulvalenes.5 The latter com-
pounds are used for the preparation of ‘organic metals’,
ion radical salts and charge transfer complexes exhibiting
conductivity.6 Efficient methods for the preparation of
1,4-dichalcogenafulvenes have also been reported.7
lurafulvene by the reaction of elemental tellurium with
acetylene using the system HMPA/KOH/reducing agent.9
In the course of our systematic study of reactions of
various selenium reagents with acetylenes, we have investi-
gated a novel reaction of selenourea with benzoylbromo-
acetylene and 2-thienoylbromoacetylene. We found that
the reaction of selenourea with benzoylbromoacetylene
proceeded in the presence of triethylamine at À30 to 0 °C
to afford the 4- and 5-membered heterocycle, E-2,4-
bis(benzoylmethylene)-1,3-diselenetane (1) (23% yield)
and E- and Z-3,5-dibenzoyl-1,4-diselenafulvene (2 and 3)
(60% yield, E/Z = 3/2) (Scheme 1).11
The synthesis of chalcogen-containing heterocycles is a
field of continued interest to us.1,8–10 We have found that
the reaction of elemental selenium with phenylacetylene
in the system HMPA/KOH/SnCl2/H2O provided 2,6-
diphenyl-1,4-diselenafulvene in 70% yield.8 Under similar
conditions the reaction of tellurium with phenylacetylene
gave 2,6-diphenyl-1,4-ditellurafulvene.8,9 We have also
obtained previously unknown 1,4-ditellurin and 1,4-ditel-
Compound 1 and the mixture of E- and Z-isomer 2 and
3 were separated by column chromatography. It is also
*
Corresponding authors. Tel.: +7 3952 425885; fax: +7 3952 419346
(V.A.P.).
E-mail addresses: amosova@irioch.irk.ru (S. V. Amosova), v.a.
Scheme 1.
potapov@mail.ru (V. A. Potapov).
0040-4039/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.12.016

S. V. Amosova et al. / Tetrahedron Letters 49 (2008) 974–976
975
possible to isolate compound 1 using the differences in sol-
ubility of the products. In contrast to diselenafulvenes 2
and 3, compound 1 exhibits low solubility in chloroform
and therefore can be isolated as a solid simply by washing
a sample with this solvent.
We were unable to separate the E- and Z-isomer 2 and 3
using column chromatography due to an isomerisation
process. For example, when we tried to chromatograph a
fraction enriched with the Z-isomer we were only able to
isolate fractions enriched with the E-isomer. This indicates
that the Z-isomer undergoes isomerisation to the more
stable E-isomer on the column.
also more stable thermodynamically than the Z-isomer,
leads to negligible formation of the latter isomer.
The reaction of selenourea with 2-thienoylbromoacetyl-
ene gives E-2,4-bis(2-thienoylmethylene)-1,3-diselenetane
(4) (40% yield) as the major product12 and Z-2,4-bis(2-thi-
enoylmethylene)-1,3-diselenetane (5) (6% yield) as the
minor product (Scheme 2).
The structural assignment of the E- and Z-isomer, 4 and
1
5, was made by H, 13C and 77Se NMR spectroscopy and
mass spectrometry. In particular, the 77Se spectrum of
product 4 exhibits one signal indicating the E-isomer,
which has two chemically equivalent selenium atoms. Heat-
ing the E-isomer 4 for 1.5 h at 120 °C in HMPA led to
isomerisation13 and formation of a mixture of the Z- and
E-isomer, 4 and 5 (Z/E = 45/55).
The structural assignment of compounds 1, 2 and 3 was
1
made by H, 13C and 77Se NMR spectroscopy and mass
spectrometry. In the mass spectra of compounds 1, 2 and
3, the molecular ions (M+Å 420) were observed, but the
spectra differed in their fragmentation pattern. The mass
spectrum of diselenetane 1 showed a maximum peak for
the phenyl group ion (77, Ph+) and a peak (209) which is
suggested to correspond to the selenoketene ion,
[PhC(O)C@C@Se]+. The mass spectrum of the diselenaful-
venes 2 and 3 exhibited a maximum peak (105) for the frag-
ment [PhC(O)]+.
According to the mass spectra, the reaction mixture con-
tains two other compounds with the same molecular ion as
selenetanes 4 and 5. We suggest that these compounds
are likely to be the Z- and E-isomer of the corresponding
Compound 1 demonstrated one signal for an olefinic
1
proton in the H NMR spectrum and one signal for sele-
nium in the 77Se NMR spectrum indicating a symmetric
heterocycle. Another symmetric 6-membered compound
with the same molecular formula, that is, 2,5-dibenzoyl-
1,4-diselenin, would also contain one olefinic proton signal
1
in the H NMR spectrum and one signal for selenium in
the 77Se NMR spectrum, but the observed value of the cou-
pling constant JSeH (11.2 Hz) corresponds to a vicinal posi-
tion for the proton and the selenium atom and thus
indicates structure 1. The value of the geminal coupling
Scheme 2.
2
constant JSeH in selenium-containing heterocycles10 is
about 50–55 Hz, and therefore product 1 was not 2,5-
dibenzoyl-1,4-diselenin. The choice between the structures
of the Z- and E-isomer of 1,3-diselenetane 1 was made
based on the 77Se spectrum, which contained only one
signal. The selenium atoms are chemically equivalent in
the E-isomer, which gives one signal in the 77Se spectrum,
whereas the Z-isomer having two chemically inequivalent
selenium atoms would show two signals in the 77Se
spectrum.
The assignment of the E- and Z-isomer, 2 and 3, was
5
made based on the coupling constants JHH. The value of
this coupling constant in the E-isomer was about 0.7 Hz,
whereas in the Z-isomer this value was close to zero.
Similar trends have been used to assign the structures of
the Z- and E-isomer of 1,4-selenasilafulvenes.10
We did not isolate the isomer of compound 1, Z-2,4-
bis(benzoylmethylene)-1,3-diselenetane, from the reaction
1
mixture, but the H NMR and mass spectral data indicate
that this compound is present in the reaction mixture in
only a tiny amount. We postulate that the reaction pro-
ceeds via dimerisation of selenoketenes to give the E-isomer
directly. This, coupled with the fact that the E-isomer is
Scheme 3.

976
S. V. Amosova et al. / Tetrahedron Letters 49 (2008) 974–976
1
I.; Yarosh, O. G.; Voronkov, M. G. Khim. Geterotsikl. Soed. 2003,
634–635; Amosova, S. V.; Martynov, A. V.; Mahaeva, N. A.;
Belozerova, O. V.; Penzik, M. V.; Albanov, A. I.; Yarosh, O. G.;
Voronkov, M. G. J. Organomet. Chem. 2007, 692, 946–952.
1,4-diselenafulvene. The H NMR spectra contain signals
which can be attributed to the E- and Z-3,5-di(2-thi-
enoyl)-1,4-diselenafulvene. However, the amounts of these
compounds were very low and they were not isolated from
the reaction mixture.
11. Typical procedure for the preparation of diselenetane 1 and diselena-
fulvenes 2 and 3. A solution of triethylamine (0.7 ml) in absolute
methanol (5 ml) was added to a solution of selenourea (0.615 g,
5 mmol) in absolute acetonitrile (10 ml) under argon at 0 °C followed
by the addition of a solution of benzoylbromoacetylene (1.04 g,
5 mmol) in acetonitrile (10 ml). The reaction mixture was stirred for
2 h in an ice/water bath. The resulting yellow solid (1.32 g) was
filtered off, washed with absolute methanol and dried. The solid was
subjected to column chromatography (silica gel, chloroform/
The proposed reaction path involves the formation of
selenuronium salts, which generate selenoketenes and ethyne-
selenolates under the action of triethylamine (Scheme 3).
Selenoketenes are promising intermediates for the syn-
thesis of selenium-containing heterocycles and some of
them can be isolated at low temperature.3 Selenoketenes
are apt to both dimerisation and [1,3]-dipolar cycloaddi-
tion reaction with ethyneselenolates.14 We suggest that
selenoketene dimerisation leads to diselenetanes 1, 4 and
5, whereas a [1,3]-dipolar cycloaddition reaction of seleno-
ketenes and ethyneselenolates furnishes diselenafulvenes 2
and 3. It is noteworthy that dimerisation of thiocarbonyl
compounds to 1,3-dithietanes is a known reaction which
proceeds under various conditions, for example, in the
presence of bases and under irradiation.2
hexane = 1:10) to give diselenetane
1 (0.24 g, 23% yield) and
diselenafulvenes 2 and 3 (0.627 g, 60% yield) as a mixture of Z- and
E-isomer (E/Z = 3/2). Attempts to separate isomers 2 and 3 failed due
to Z-E-isomerisation during chromatography. Diselenetane 1 was
obtained as a yellow powder, mp 203–204 °C. 1H NMR (400 MHz,
HMPA-d18): d 8.92 (s, 2H, @CH), 8.16 (m, 4H, Hortho), 7.69 (m, 2H,
Hpara), 7.55 (m, 4H, Hmeta). 77Se NMR (76.3 MHz, HMPA-d18): d 993
(JSeH = 10.5 Hz). MS m/z
(
80Se): 420 (28) [M]+Å
,
209 (6)
[C6H5C(O)C2HSe]+, 105 (100) [C2HSe]+, 77 (80) [C6H5]+, 51 (18)
[C4H3]+. Anal. Calcd for C18H12O2Se2: C, 51.70; H, 2.89; Se, 37.76.
Found: C, 51.93; H, 3.02; Se, 38.17. The mixture of E- and Z-isomer 2
and 3 (E/Z = 3/2) was obtained as a yellow powder, mp 265–267 °C.
MS, m/z (80Se): 420 (20) [M]+Å, 343 (5) [MÀC6H5]+, 290 (10)
[MÀPhC(O)C2H]+Å, 158 (9) [C6H6Se]+Å, 133 (6) [C(O)C2HSe]+, 105
(84) [C2HSe]+, 77 (100) [C6H5]+, 51 (23) [C4H3]+. In the 1H NMR
spectrum (400 MHz, CDCl3), the mixture contains signals for the
E-isomer 2 [d 8.53 (d, JHH = 0.7 Hz, 1H, CHSe), 8.10 (d, JHH = 0.7,
1H, O@CCH)] and signals for the Z-isomer 3 [d 8.36 (s, 1H, CHSe),
8.02 (s, 1H, O@CCH)] along with multiplets due to the aromatic
protons. In the 77Se NMR spectrum (76.3 MHz, CDCl3), the mixture
contains signals for the E-isomer 2 [d 813 (2JSeH = 46.0, 3JSeH = 11.5,
@CHSe), 694 (3JSeH = 8.4, 3JSeH = 7.3, O@CCSe)] and signals for the
Thus, we have described the novel reaction of selenourea
with benzoylbromoacetylene and 2-thienoylbromoacetyl-
ene affording new 4- and 5-membered heterocycles.
References and notes
1. Nakhmanovich, A. S.; Glotova, T. E.; Skvortsova, G. G.; Sigalov, M.
V.; Komarova, T. N. Zh. Org. Khim. 1984, 20, 2145–2148; Nakhma-
novich, A. S.; Elokhina, V. N.; Shcherbinina, T. P.; Voronkov, M. G.
Izv. AN, Ser. Khim. 1976, 1631–1633.
3
Z-isomer 3 [d 772 (3JSeH = 10.5), 736 (2JSeH = 56.4, JSeH = 10.4)].
2. Pushkara Rao, V. Sulfur Rep. 1992, 12, 359–403.
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12. Synthesis of E-2,4-bis(2-thienoylmethylene)-1,3-diselenetane (4). Tri-
ethylamine (0.7 ml) was added to a solution of selenourea (0.615 g,
5 mmol) in absolute methanol (20 ml) under argon at À30 °C
followed by the addition of a solution of 2-thienoylbromoacetylene
(1.07 g, 5 mmol) in absolute methanol (15 ml). The reaction mixture
was stirred for 1.5 h at À30 °C. The resulting solid (0.46 g) was filtered
off, washed with absolute methanol and dried. Crystallisation of the
solid from 1,4-dioxane gave pure compound 4 (0.42 g, 40% yield), mp
274–275 °C (1,4-dioxane). 1H NMR (400 MHz, HMPA-d18): d 8.87 (s,
2H, @CHC@O) 8.55 (m, 4H, C3H, C5H), 7.39 (m, 2H, C4H). 13C
NMR (100.6 MHz, HMPA-d18): d 117.44 (–CH@) 128.25 (C4), 133.28
(C3), 136.40 (C5), 144.76 (@C–Se), 148.87 (C2), 181.57 (C@O). 77Se
NMR (76.3 MHz, HMPA-d18): d 696 (3JSeH = 11.5). MS, m/z, 80Se
(rel. int., %): 432 (18) [M]+Å, 296 (6) [MÀ2-ThC(O)C2H]+Å, 164 (10)
[2-ThSeH]+Å, 133 (12) [SeC(O)C2H]+, 111 (100) [2-ThC(O)]+, 83 (18)
[2-Th]+, 39 (26) [C3H4]+. Anal. Calcd for C14H8O2S2Se2: C, 39.08; H,
1.87; S, 14.90; Se, 36.70. Found: C, 39.09; H, 1.81; S, 14.86; Se, 36.18.
13. Thermal isomerisation of the E-isomer 4 to the Z-isomer 5. A solution
of the E-isomer 4 in HMPA-d18 was heated at 120 °C for 1.5 h. In the
1H NMR spectrum (400 MHz, HMPA-d18), the mixture contains
signals for the Z-isomer 5: d 8.75 s (2H, @CHC@O), 8.56 m (4H,
C3H, C4H), 8.36 m (2H, C5H). According to the 1H NMR data, the
yields of the Z-isomer 5 and the E-isomer 4 were 45% and 55%,
respectively.
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