New reaction of 1H-pyrazoles with selenium dioxide: One-pot synthesis of bis(1H-pyrazol-4-yl)selenides

Article abstract of DOI:10.1016/j.tet.2010.08.071

A novel reaction between 3- and 3,5-substituted pyrazoles with selenium dioxide proceeds with formation of bis(3R,5R′-1H-pyrazol-4-yl)selenides in high yield. On this basis, an efficient one-pot synthetic procedure has been developed. In the case of the unsubstituted pyrazole a selenonium compound has been obtained. The identity and structure of the isolated selenium derivatives have been confirmed by spectral methods and their molecular structures investigated by X-ray analysis.

Full text of DOI:10.1016/j.tet.2010.08.071

Tetrahedron 66 (2010) 8772e8777
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New reaction of 1H-pyrazoles with selenium dioxide: one-pot synthesis
of bis(1H-pyrazol-4-yl)selenides
,
b
c
d
Maksym Seredyuk a, Igor O. Fritskya , Roland Kramer , Henryk Koz1owski , Matti Haukka ,
*
€
Philipp Gütlich e
a Department of Chemistry, National Taras Shevchenko University, Volodymyrska Str. 64, 01601 Kiev, Ukraine
b
€
Anorganisch-Chemisches-Institut, Universitat Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
c Faculty of Chemistry, University of Wrocław, F.Joliot-Curie 14, 50-383 Wrocław, Poland
d Department of Chemistry, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland
e
€
Institut für Anorganische und Analytische Chemie, Johannes Gutenberg Universitat Mainz Staudinger Weg 9, 55122 Mainz, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 May 2010
Received in revised form 6 August 2010
Accepted 31 August 2010
Available online 9 September 2010
A novel reaction between 3- and 3,5-substituted pyrazoles with selenium dioxide proceeds with for-
mation of bis(3R,5R0-1H-pyrazol-4-yl)selenides in high yield. On this basis, an efficient one-pot synthetic
procedure has been developed. In the case of the unsubstituted pyrazole a selenonium compound has
been obtained. The identity and structure of the isolated selenium derivatives have been confirmed by
spectral methods and their molecular structures investigated by X-ray analysis.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Organoselenium compounds
One-pot synthesis
Crystal structure
Nucleophiles
Heterocycles
Reaction mechanisms
1. Introduction
‘hard’ and ‘soft’ binding sites for creation of supramolecular
frameworks.4
Diaryl selenides are central reagents in organoselenium
chemistry.1 They have long proved to be valuable intermediates
and useful synthons in organic synthesis as selenium atoms can
readily be removed from organic molecules. Also, diaryl and
dihetaryl selenides attract considerable attention due to their
remarkable biological activity and their potential as efficient
antioxidants,2 antitumor and anti-infective agents,2b,c enzyme
inhibitors,2b,c glutathione peroxidase mimics,2a,c and immuno-
modulators.2b Moreover, diaryl selenides themselves are key
intermediates in synthesis of a variety of biologically and
pharmaceutically important organoselenium compounds such
as selenonium salts, selenoxides, selenimines, and selenide
dihalides.1,2b,3 Dihetalryl selenides have rarely been studied and
apart from the evident pharmacological interest, these com-
pounds are promising multidentate ligand systems having both
Traditional preparative methods for diaryl selenides include
the reactions of metal selenides or selenocyanates with aryl
halides, the conversion of aryl halides to the corresponding
aryllithium, -magnesium or -tin compounds, and subsequent
reaction with diaryl diselenides,1,2b,5 formation of selenides via
diazonium intermediates,1 the cross-coupling reactions of aryl
halides with aryl selenols,6 or the oxidation of selenols or sele-
nolates.1,2b In many cases these methods are laborious and
involve multi-step syntheses or have significant limitations or
disadvantages. Therefore, in spite of the versatility of available
synthetic pathways, there is a high demand for development of
convenient and straightforward methods for the synthesis of
diaryl selenides.
Direct synthesis of organic selenides from selenium dioxide may
be considered as a reasonable alternative approach but is poorly
studied. All reported organic selenides prepared from SeO2 are
collected in Table 1. As seen, in several cases this method provides
reasonable yields, but mostly selenides are formed only as minor
products often requiring laborious separation from precipitated
selenium and main products. Among reported direct syntheses of
* Corresponding author. Tel./fax: +38 044 239 33 93; e-mail address: ifritsky@
univ.kiev.ua (I.O. Fritsky).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.08.071

M. Seredyuk et al. / Tetrahedron 66 (2010) 8772e8777
8773
Table 1
dihetaryl selenides the most investigated is the family of indole
derivatives, which form different types of selenides depending on
the substituents,7 while reports on other classes of organic com-
pounds are sporadic.8 To the best of our knowledge, except our
recent studies,9 pyrazole derivatives were not explored in this type
of reaction, however one-step synthesis of pyrazole selenides is
attractive in view of their high efficiency toward suppression of
carcinoma cells reproduction combined with low toxicity for
mammal organisms.10 Herein, we report the remarkably facile
formation of bis(3R,5R0-1H-pyrazol-4-yl)selenides by the reaction
of pyrazoles with selenium dioxide.
Reported selenides synthesized accordingly to the equation: RHþSeO2/R2Se
R
Yield Ref.
(%)
R
Yield Ref.
(%)
OH
22
44
7a
7b
d
8b
8b
HN
Cl
COOH
N
HO
2. Results and discussion
d
HN
Despite the fact that direct conversion of selenium dioxide to
organic selenides was found to be inefficient in most reported
cases, reaction with some substituted 1H-pyrazole derivatives is an
exception to the rule; we have found that it proceeds without se-
lenium sedimentation and results in formation of corresponding
selenides in stable high yields.
O
The initial impetus for an upsurge interest in the reaction was
found during an attempt to oxidize the methyl group in
3-methyl-5-(2-pyridyl)-1H-pyrazole by SeO2 in pyridine (taken
in 1:1.5 M ratio) to generate a corresponding carboxylic acid.
Surprisingly, no acid was formed under these conditions, unlike
in the case of 1-methyl-3-(2-pyridyl)-benzene11 and 4-methyl-6-
(2-pyridyl)-pyrimidine,12 but only the bis(3-methyl-5-(pyridin-2-
yl)-1H-pyrazol-4-yl)selenide (1a) as the sole reaction product
was isolated in 64% yield (Table 2). Using the same experimental
protocol (1 mol equiv of pyrazole per 1.5 equiv of SeO2 in
refluxing pyridine), the reactivity of a series of pyrazole derivates
has been studied (Table 2). The results allowed us to elaborate
the general synthetic procedure for bispyrazolyl selenides, in
particular for 1bef (see Table 2 for the chemical formulas), and to
elucidate differences in the conversion of different pyrazole
derivates. It should be noted, that the chosen ratio between
the starting reagents with an excess of SeO2 was found to be
crucial for the formation of the target selenides. Different pyra-
zole to SeO2 ratios have been checked in the range from 2:1 to
1:2 and found that the 1:1.5 ratio is optimal. For example, in the
case of 1:1 ratio the corresponding selenides were formed in
a poor yield.
O
d
7c
d
8b
NH
O
N
t-Bu
t-Bu
OH
7
7d
25
8c
HN
O
O
O
O
31
7e
16
8d
NH
4-BrC6H4
CHO
In all the studied cases the corresponding reaction mixtures and
crude products have been subjected to TLC, ESIMS, 1H, and 13C NMR
control. Identity and structure of the isolated selenides were con-
firmed by a variety of analytical and spectral methods; the molec-
ular structures of 1aed were investigated by X-ray analysis and are
depicted in Fig. 1.
O
O
O
35
7e
d
8e
O
NH
CHO
Ph
Although we did not conduct any specific studies to elucidate
the mechanism of the reaction, on the basis of the obtained
structural and ESIMS data we can tentatively propose a reaction
pathway from a pyrazole to its selenide depicted in Scheme 1.
The first step of the reaction includes a double nucleophilic at-
tack by the C-4 pyrazole carbon on the selenium atom7b to afford
a selenoxide (i), which is also detected in some of the reaction
mixtures (Table S1). Further transformation of the oxide includes
addition of pyrazole or pyridine with formation of unstable
selenonium ions R2XSeþ [R, X¼3,5-disubstituted-1H-pyrazol-4-yl
(ii0) or X¼pyridyl (ii00)] (Scheme 1, Table S1), which disappear
after drying. Instead, the organic selenide (iii) and bispyrazolyl
(iv0) and pyrazolylpyridine (iv00) byproducts are formed as follows
from ESIMS spectra of the reaction mixtures. The proposed
reaction pathway is confirmed indirectly by the fact that neither
selenonium ions nor bispyrazolyl byproduct are formed by
treating a bispyrazolyl selenide with pyrazole under the reaction
O
70
8a
45
8f
O
OH
OH
OH
Cl
8g
O
d
8b
9
N

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M. Seredyuk et al. / Tetrahedron 66 (2010) 8772e8777
Table 2
Isolated bis(3R,5R0-1H-pyrazol-4-yl)selenides 1ae1f and tris(1H-pyrazol-4-yl)selenonium ethylselenite (2g) synthesized accordingly to the equation: PzHþSeO2/Pz2Se
(Pz3Seþ), where Pz is pyrazole derivative
Entry
Substrate
Isolated
Selenide
Yield (%)
Entry
Substrate
Isolated
Selenide
Yield (%)
Selenonium
Selenonium
2-Py
HN
N
HN
N
1
1a
1b
1c
1d
d
64
7
d
2g
37
CF3
Ph
HN
N
HN
N
2
3
4
5
d
d
d
67
52
62
8
ea
ea
ea
ea
d
d
d
d
d
d
d
d
CF3
COOH
Ph
HN
9
HN
N
N
COOH
COOEt
Et
HN
N
HN
N
10
11
Et
COOEt
Ph
HN
N
HN
1e
1f
d
50
55
N
Ph
6
HN
N
d
a
No organoselenium species were detected in the reaction mixture.
conditions. Furthermore, the ESIMS spectrum of the reaction
mixture of bis(3,5-dimethyl-1H-pyrazolyl) selenoxide13 with 3,5-
dimethyl-1H-pyrazole after boiling in pyridine for 6 h contains
peaks of pyrazolylpyridine and 1e confirming that the selenoxide
might be a precursor of ii and iii, however a more comprehensive
study is required to clarify the details of the reaction pathway.
We also would like to stress that according to the proposed
mechanism the highest yield of the selenide is limited to near
50e67%, with respect to pyrazole.
Earlier two groups reported on aryl selenonium salts synthe-
sized from selenium dioxide in concentrated mineral acids.8a,b,14
In case of the unsubstituted pyrazole the symmetrical seleno-
nium salt with ethylselenite anion (2g) is also a sole product
isolated after ethanolic workup, which was investigated by X-ray
analysis (Fig. 1), but interestingly no selenonium compounds of
3-methylpyrazole and 3,5-methylpyrazole could be isolated in the
solid state. To our opinion differences in the stability of the
selenonium compounds in this series might be explained in terms
of sterical repulsion between the methyl groups, increasing
number of which might cause geometrical distortion of the
selenonium ions that make them more inclined toward degra-
dation to selenides.
case of 3,5-bis(trifluoromethyl)-1H-pyrazole no organo-
selenium species were detected (Table 2), however its struc-
tural analog 3,5-dimethyl-1H-pyrazole, gave 1e. Similarly, 1H-
pyrazole-3,5-dicarboxylic acid, its diethyl ester and 3,5-bi-
phenyl-1H-pyrazole are inactive in this reaction (see Table 2). In
these four cases ESIMS control of the reaction mixtures
revealed the presence of the starting compounds as the only
pyrazole-containing species.
The influence of hydrochloric or hydrobromic acid was
expected to force the conversion of reagents to higher yield.
Nevertheless, the reaction between 3,5-dimethylpyrazole and
selenium dioxide in concentrated hydrochloric acid according
to the described procedure8b,c led to 1f with a comparable
yield (46%). In contrast, an attempt to obtain 1a from 3-methyl-
5-(2-pyridyl)-1H-pyrazole in this media was met with no
success.
Finally, as well as their mentioned interest for medicine, bis-
pyrazolyl selenides can also be used as ligands for supramolecular
networks, in which a molecule of the ligand serves as a bidentate
bent connector forming polynuclear complexes. The presence of
a soft selenium atom in synthesized selenides could allow the co-
ordination to a soft 4d- of 5d-metal ion and, on the other hand,
nitrogen atoms of the pyrazole moieties are good donors for the
3d-transition metals.9
The course of the reaction is influenced to great extent by
electronic nature of the 3,5-substituents. For example, in the

M. Seredyuk et al. / Tetrahedron 66 (2010) 8772e8777
8775
Fig. 1. Molecular structures and numbering schemes for 1ae2g (50% probability ellipsoids). Solvent molecules and inorganic anions are omitted for clarity.

8776
M. Seredyuk et al. / Tetrahedron 66 (2010) 8772e8777
NH
N
R
R'
R'
HN
R
Se
R
R
NH
HN
N
NH
N
N
N
R
R'
ii'
O
pz
py
R
N
R'
HN
R
N
R'
N
R'
R'
R
Se
Se
SeO2
iv'
R
R'
NH
NH
HN
+
N
NH
N
N
R
R'
R
R'
N
3R,5R'-1H-pyrazole
iii
i
HN
N
R'
HN
R
N
Se
R'
NH
iv"
N
R
R'
ii"
Scheme 1. A proposed reaction pathway from pyrazole to bis(3R,5R0-1H-pyrazol-4-yl)selenide.
3. Conclusion
free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Summarizing, we have reported a new reaction of 1H-pyr-
azole and its 3- and 3,5-disubstituted pyrazoles with selenium
dioxide and established that in the case of dialkyl- or alkylaryl-
derivatives it results in the formation of bis(3R,5R0-1H-pyrazol-
4-yl)selenides as the main reaction products in good yields,
which enhances the pool of available methods for this class of
compounds and should find further application in organic syn-
thesis. The obtained compounds appear to be valuable synthetic
intermediates for preparation of various heterocylic and orga-
noselenium compounds of pharmaceutical interest, and polynu-
cleating ligands applicable in crystal engineering and molecular
magnetism, and the study of reactivity of bispyrazolyl selenides
is currently underway in our laboratories. We also are in the
process of expanding the scope of this reaction to other hetero-
cyclic systems.
4.1.1. Bis(3-methyl-5-(pyridin-2-yl)-1H-pyrazol-4-yl)selenide
(1a$MeOH). Mixture of 2-(3-methyl-1H-pyrazol-3-yl)pyridine16
(15.92 g, 0.10 mol), selenium dioxide (16.70 g, 0.15 mol) and pyri-
dine (50 mL) was refluxed 6 h, after that pyridine was distilled off
under reduced pressure. Syrup-like yellow-to-brown residue was
treated with 20 mL of NaOH (6.0 g, 0.15 mol) aqueous solution. The
obtained yellowish precipitate was filtered off and washed twice
with distilled water and recrystallized from hot methanol. Mp:
212e214 ꢁC. ESIMS (rel int.): m/z 396.7 [MþH, 80Se]þ (100%); 1H
NMR (DMSO-d6, 400 MHz):
d 11.95 (1H br s, NH pz), 8.60 (1H, ddd,
J¼0.9, 1.5, 4.9 Hz, pyH), 7.97 (1H, d, J¼7.5 Hz, pyH), 7.75 (1H, td,
J¼1.5, 7.5 Hz, pyH), 7.32 (1H, ddd, J¼0.9, 4.9, 7.5 Hz, pyH), 1.86 (3H, s,
CH3); 13C NMR (DMSO-d6, 100 MHz):
d 152.5, 150.8, 148.7, 138.4,
125.8, 124.5, 123.3, 102.3, 13.3; FTIR (KBr, cmꢀ1): 3300 (m), 3124 (s),
2919 (s), 1592 (s), 1463 (s), 1150 (s), 1061 (s), 998 (s), 787 (s), 623 (s),
515 (s). C19H20N6OSe requires C, 53.4, H, 4.7, N, 19.7. Found C, 53.5,
H, 4.6, N, 19.5.
4. Experimental section
4.1. General
The same method was used for the preparation of 1bef starting
from the corresponding substituted pyrazoles.
All starting materials were purchased from Aldrich or Fluka and
used as received.
4.1.2. Bis(3-methyl-5-phenyl-1H-pyrazol-4-yl)selenide
(1b$MeOH). Recrystallized from methanol as white crystalline
powder. Mp: substance has no definite mp, it begins to soften at
130 ꢁC. ESIMS (rel int.): m/z 395.1 [MþH, 80Se]þ (100%); 1H NMR
ESIMS measurements were done on a Finnagan TSQ 700 mass
spectrometer. 1H (400 MHz) and 13C (100.63 MHz) NMR spectra
were recorded on a Bruker AC-400 spectrometer at 293 K;
d-values
(CDCl3, 400 MHz):
d
7.53 (2H, dd, J1¼1.4 Hz, J2¼2.7 Hz, 3,5H Ph), 7.27
are expressed in parts per million relative to an internal reference.
FTIR spectra were recorded on a PerkineElmer 983 G spectropho-
tometer, nmax in cmꢀ1 (range 400e4000). CHN analysis was done on
a PerkineElmer 2400 CHN.
(3H, m, 2,4,6-H Ph), 1.84 (3H, s, CH3); 13C NMR (CDCl3, 100 MHz):
d
151.7, 143.8, 133.4, 129.5, 128.1, 127.1, 100.4, 12.7; FTIR (KBr, cmꢀ1):
3159 (br), 3058 (br), 2921 (s), 2821 (s), 2000e1650 (m),1562 (s),1451
(m), 1272 (s), 1038 (s), 966 (s), 774 (s), 695 (s), 520 (s). C21H22N4OSe
requires: C, 59.3, H, 5.2, N, 13.2. Found C, 58.8, H, 4.9, N, 13.2.
X-ray data collection was done on a Bruker AXS CCD Smart 1000
diffractometer with refinement using SHELXL-97.15 Crystals of 1a,
1b, 1d, 1f were obtained in the form of salt with inorganic anions by
dissolving of the corresponding selenide in a small amount of the
corresponding concentrated aqueous acid and further disposal of
the obtained solution in a fridge at 4 ꢁC for several days. Crystals of
1c and 1e were grown by slow diffusion of ethereal vapors into
a vessel with alcoholic solutions of corresponding selenides over
one week. Crystals of 2g were obtained upon dissolving of dried
reaction mixture in ethanol and further cooling of the solution in
a fridge at 4 ꢁC overnight.
4.1.3. Bis(3-phenyl-1H-pyrazol-4-yl)selenide (1c$0.25C2H5OH). Rec-
rystallized from ethanol as white powder. Mp: 201e203 ꢁC. ESIMS
(rel int.): m/z 367.1 [MþH, 80Se]þ (100%); 1H NMR (C2D5OD,
400 MHz):
d 7.76 (s, 1H, PzH), 7.67 (m, 2H, 3,5-H Ph), 7.36 (m, 3H,
2,4,6-H Ph); 13C NMR (C2D5OD, 100 MHz):
d 151.7, 143.8, 133.4,
129.5, 127.1, 100.4, 12.7. C74H62N16OSe4 requires C, 59.0; H, 4.2; N,
14.9. Found C 58.8, H, 4.3, N, 14.8.
4.1.4. Bis(3,5-diethyl-1H-pyrazol-4-yl)selenide (1d). Recrystallized
from ethanol as white powder. Mp: 217e218 ꢁC. ESIMS (rel int.):
m/z 326.2 [MþH, 80Se]þ (100%); 1H NMR (DMSO-d6, 400 MHz):
The presented crystallographic data are deposited under CCDC
numbers 299920e299924, 773478, 773479 and can be obtained

M. Seredyuk et al. / Tetrahedron 66 (2010) 8772e8777
8777
d
2.52 (2H, q, J¼7.5 Hz, CH2) 1.00 (3H, t, J¼7.5 Hz, CH3); 13C NMR
Supplementary data
(DMSO-d6, 100 MHz):
d
152.7, 100.9, 21.2, 15.5; FTIR (KBr, cmꢀ1):
3167(br), 3086(m), 3021(s), 2970(s), 2935(s), 2870(s), 1561(s), 1461
(m), 1277(s), 1036(s), 796(m), 498(s). C14H22N4Se requires C, 51.6, H,
6.8, N, 17.2. Found C, 51.3, H, 6.7, N, 17.2.
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.tet.2010.08.071. These include
ESIMS and crystallographic data for 1ae2g.
4.1.5. Bis(3,5-dimethyl-1H-pyrazol-4-yl)selenide (1e$H2O). Recryst-
allized from methanol as yellowish precipitate. Mp: 232e233 ꢁC.
ESIMS ESI (rel int.): m/z 271.0 [MþH, 80Se]þ (100%); 1H NMR
References and notes
1. (a) Klayman, D. L. Organic Selenium Compounds, Their Chemistry and Biology;
John Wiley: New York, NY, 1973; (b) Krief, A. Organoselenium Chemistry;
Springer: Berlin, 1988; (c) Krief, A. In Comprehensive Organometallic Chemistry
II; Abel, E. V., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: New York, NY, 1995;
(d) Wirth, T. Top. Curr. Chem. 2000, 208.
2. (a) Mugesh, G.; Singh, H. B. Chem. Soc. Rev. 2000, 29, 347e357; (b) Mugesh, G.;
du Mont, W.-W.; Sies, H. Chem. Rev. 2001, 101, 2125e2179; (c) Nogueira, C. W.;
Zeni, G.; Rocha, J. B. T. Chem. Rev. 2004, 104, 6255e6285.
(DMSO-d6, 400 MHz):
100 MHz):
d
2.17 (s, CH3); 13C NMR (DMSO-d6,
d
146.6, 101.5, 12.3; FTIR (KBr, cmꢀ1): 3400 (br), 3173 (s),
3086 (s), 2970 (m), 2870 (s), 1562 (s), 1414 (s), 1297 (s), 1095 (s),
1033 (s), 849 (br), 764 (s), 461 (s). C10H16N4OSe requires: C, 41.8, H,
5.6, N, 19.5. Found C, 41.5, H, 5.8, N, 19.6.
3. (a) Magdesieva, N. N. Russ. Chem. Rev. 1988, 57, 161e173; (b) Freudendahl, D. M.;
Shahzad, S. A.; Wirth, T. Eur. J. Org. Chem. 2009, 1649e1664.
4. Janiak, C. Dalton Trans. 2003, 2781e2804.
5. Beletskaya, I. P.; Sigeev, A. S.; Peregudov, A. S.; Petrovskii, P. V. Tetrahedron Lett.
4.1.6. Bis(3-methyl-1H-pyrazol-4-yl)selenide (1f$2H2SO4). Recryst-
allized from ethanol with several drops of sulfuric acid to
obtain colorless well formed crystals. Mp: 280e281 ꢁC
(decomp.). ESIMS (rel int.): m/z 243.0 [MþH, 80Se]þ (100%); 1H
2003, 44, 7039e7041.
6. Gujadhur, R. K.; Venkataraman, D. Tetrahedron Lett. 2003, 44, 81e84.
7. (a) Bergman, J. Acta Chem. Scand. 1968, 22, 1883e1887; (b) Minakata, S.; Itoh, S.;
Komats, M.; Ohshiro, Y. Bull. Chem. Soc. Jpn. 1992, 65, 2992e2997; (c) Khan, M. A.;
Raees, H. Z. Naturforsch., B 1996, 51,1779e1780; (d) Abele, E.; Popelis, J.; Shestakova,
I.; Domracheva, I.; Arsenyan, P.; Lukevics, E. Chem. Heterocycl. Compd. 2004, 40,
742e746; (e) Jones, A. W.; Wahyuningsih, T. D.; Pchalek, K.; Kumar, N.; Black, D. S.
Tetrahedron 2005, 61 10490e10500.
NMR (D2O, 400 MHz):
NMR (D2O, 100 MHz):
d
d
7.94 (1H, s, PzH), 2.31 (3H, s, CH3); 13C
147.7, 138.6, 103.5, 9.7. C8H14N4O8S2Se
requires C, 22.0; H, 3.2; N, 12.8, S, 14.7; Found C 21.9, H 3.4, N,
13.1, S 14.5.
8. (a) Funk, H.; Weiss, W. J. Prakt. Chem. 1954, 1, 33e40; (b) Funk, H.; Papenroth,
W. J. Prakt. Chem. 1960, 4, 191e196; (c) Paine, T. K.; Weyhermüller, T.; Bothe, E.;
Wieghardt, K.; Chaudhuri, P. Dalton Trans. 2003, 3136e3144; (d) Engman, L.;
4.1.7. Tris(1H-pyrazol-4-yl)seleninium ethylselenite (2g). Mixture of
1H-pyrazole (6.80 g, 0.10 mol), selenium dioxide (16.70 g,
0.15 mol), and pyridine (50 mL) was heated to boiling that after
30 min led to the formation of colorless oil; refluxing was
continued for additional 5.5 h. After cooling the pyridine layer
was decanted and residual viscous oil was dissolved in ethanol
and subjected into a fridge overnight yielded yellowish crys-
talline hydroscopic precipitate of 2g. Mp: 250e251 ꢁC
(decomp.). ESIMS (rel int.): m/z 280.1 [M, 80Se]þ (100%); 1H NMR
€
Hellberg, J.; Ishag, C.; Soderholm, S. J. Chem. Soc., Perkin Trans. 1 1988,
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(D2O, 400 MHz):
d
7.99 (6H, s, 3,5-H Pz), 3.56 (2H, q, J¼6.4 Hz,
SeOCH2), 1.09 (3H, t, J¼6.4 Hz, SeOCH2CH3); 13C NMR (D2O,
100 MHz): 136.3 (C-3,5 Pz), 103.6 (CeSe), 57.2 (CH2), 16.5 (CH3);
FTIR (KBr, cmꢀ1): 3113 (m), 3028 (br), 2896 (m), 2846 (m), 2782
(m), 1532 (s), 1381 (s), 1156 (d), 1028 (s), 923 (d), 854 (s), 613 (s),
417 (s). C11H15N6O3Se2 requires C, 30.3, H, 3.2, N, 19.3. Found C,
30.1, H, 3.3, N, 19.2.
11. Sakamoto, T.; Sakasai, T.; Yamanaka, H. Chem. Pharm. Bull. 1980, 28, 571e577.
€
12. Strotmeyer, K. P.; Fritsky, I. O.; Ott, R.; Pritzkow, H.; Kramer, R. Supramol. Chem.
2003, 15, 529e547.
13. Obtained by treating bis(3,5-dimethyl-1H-pyrazolyl)selenide (1e) with hydro-
gen peroxide.
14. Epifanov, V. S.; Syskova, V. P.; Konyakhina, L. V.; Nosov, V. N.; Kulikova, L. Y.
Zh. Org. Khim. 1982, 28, 878e881.
15. Sheldrick, G. M. SHELXS97 and SHELXL97; University of Gottingen: Germany,
Acknowledgements
€
1997.
I.O.F. is grateful to the Deutsche Forschungsgemeinschaft (grant
16. Yu, W.-S.; Cheng, C.-C.; Cheng, Y.-M.; Wu, P.-C.; Song, Y.-H.; Chi, Y.; Chou, P.-T.
GZ: 436 UKR) for financial support.
J. Am. Chem. Soc. 2003, 125, 10800e10801.