Mendeleev Commun., 2012, 22, 37–38
Table 1 Geometrical parameters of hydrogen bonds in the crystal structure
C(25)
C(26)
C(21)
C(17)
C(24)
of compound 3.a
C(20)
C(18)
C(22)
N(4)
C(23)
C(28)
N(6)
C(27)
O(3) C(29)
Distance, Å
H···A
C(19)
D–H···A
angle/deg
D–H···A bond
O(2)
C(14)
N(5)
D–H
D···A
N(3)
C(30)
C(13)
C(15)
C(32)
O(2)–H(1AA)–O(3)
O(4)–H(2AA)–O(1)
N(2)–H(2B)–N(3) 1
N(6)–H(6A)–O(5) 2
1.01(2)
1.02(2)
0.96(2)
0.98(2)
1.49(2)
1.50(2)
1.89(2)
1.76(2)
2.493(2)
2.519(2)
2.827(2)
2.717(2)
174(2)
176(2)
168(2)
165(2)
C(31)
C(12)
C(16)
C(11)
C(36)
C(9)
C(35)
C(33)
C(10)
O(1)
C(8)
C(7)
N(2)
C(6)
N(7)
C(34)
a Symmetrical transformations of atoms: 1 (–x+3/2, y+1/2, –z+1/2); 2 (–x+1/2,
y–1/2, –z+1/2).
O(4)
C(42)
C(41)
N(8)
C(37)
N(1)
C(1)
C(5)
C(2)
C(38)
C(39)
C(40)
Ph
Ph
C(4)
C(3)
N
N
O
O
O
H
N
N
N
N
Figure 1 Molecular structure of compound 3.
i
i
Me
Me
H
Me
Me
1
3
H
The ethane moiety has standard C–C bond lengths and bond
angles. The torsion angles H(11)–C(11)–C(12)–H(12), C(10)–
C(11)–C(12)–C(13) and C(33)–C(11)–C(12)–C(32) are in the
range of –172 1°. The molecules have an antiperiplanar (trans
type) conformation. The azolyl substituents are pairwise located in
two tautomeric forms, namely, hydroxypyrazole and pyrazolinone
forms, which manifests itself in the different geometry of these
rings. In fact, the C–C bond lengths in the hydroxypyrazolyl
moiety are ~1.40 and 1.37 Å, which differ considerably from those
in the non-equivalent pyrazolinone (~1.36 and 1.43 Å, respec-
tively). The C–O bond lengths in the pyrazolyl moieties also
differ considerably: ~1.33 Å in the hydroxy form and ~1.26 Å
in the keto form. The spatial orientation of the azolyl moieties in
the molecule is determined by the existence of intramolecular
hydrogen bonds between the carbonyl and hydroxy groups of
these rings; the parameters of these bonds are presented in Table 1.
Molecules in a crystal have a layered packing; the layers are
arranged in parallel with plane (001). This packing results from
N
H
N
O
N
N
Ph
Ph
I1
4
I2
Scheme 2 Reagents: i, 2 equiv. of 3-methyl-1-phenylpyrazol-5-one.
the existence of intramolecular hydrogen bonds between the NH
groups of the azolyl moieties and between the DMF molecule
and the hydroxypyrazole ring.
We also obtained tetrapyrazolyl derivative 3 by an independent
synthesis, viz., the reaction of 3-methyl-1-phenylpyrazol-5-one
with glyoxal in DMSO in the presence of triethylamine. The
mechanism of tetrapyrazolylethane 3 formation apparently involves
the following steps: (a) nucleophilic addition of two 3-methyl-
1-phenylpyrazol-5-one molecules to the C=N bonds of quinoxaline
1 to form bis-adduct I1 (Scheme 2) and (b) cleavage of bis-adduct
I1 to give intermediate I2 followed by conversion of the latter to
tetrapyrazolylethane 3.
‡
The mass spectra were measured on a Bruker Daltonics MicrOTOF-Q II
mass spectrometer (Bremen, Germany) with an electrospray ionization
source, a 6-port divert valve and syringe pump kd Scientific with flow
rate 180 dm3 h–1. The instrument controls were performed with HyStar 3.2
and micrOTOFcontrol 2.3 patch 1 (Bruker Daltonics) software. The nominal
resolution of the instrument was 17500. The instrument was operated
in positive ion mode with an m/z range of 50–800. A 6-point external
instrument mass scale calibration was performed before each sequence
with lithium formate clusters by infusing 10 mm lithium hydroxide in
isopropanol/0.2% formic acid (1:1, v/v).
It is interesting that even short-term heating of product 3 in
DMF at 150°C results in dipyrazolylmethane 2. The same con-
version in the presence of iodine occurs even at room temperature.
Note that the formation of compound 2 was observed pre-
viously4 in the reaction of quinazoline with 3-methyl-1-phenyl-
pyrazol-5-one and resulted from the cleavage of two C=N hetero-
cycle bonds. However, the formation of compound 2 in reactions
of quinoxaline is due to the cleavage of C=N and C=C bonds.
In summary, quinoxaline acts the synthetic equivalent of glyoxal
serving as the donor of a one-carbon moiety in the reaction of
quinoxaline with 3-methyl-1-phenylpyrazol-5-one to furnish
dipyrazolylmethane 2. It should be, however, noted that cleavage
of the C=C bond of the pyrazine ring of quinoxaline results from
the homolytic cleavage of tetrapyrazolyl derivative 3, which is
formed initially, at the C–C bond of its ethane moiety.
§
Crystal data for compound 3. The X-ray diffraction study was performed
with an Xcalibur 3 single crystal X-ray diffractometer with a CCD detector
using the standard procedure [MoKa radiation, T = 295(2) K, w-scanning,
scanning step 1°]. The crystals dimensions were 0.25×0.20×0.15 mm,
monoclinic, space group P21/n, unit cell parameters: a = 16.6054(10),
b = 10.9650(6) and c = 23.7972(17) Å, b = 103.142(6)°, V = 4219.5(5) Å3,
Z = 4, dcalc = 1.247 g cm–3. The number of reflections collected in the
range of 2.67° < q < 28.29º was 26429, 10353 of these were independent
(Rint = 0.0365) and 3945 had I > 2s(I). The experiment completeness at
angles within q £ 26.0° was 99.3%. The structure was solved by the direct
method and refined by full-matrix least squares method with respect to F2
References
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Chupakhin, Mendeleev Commun., 2006, 26.
2 M. G. Ponizovskii, O. N. Chupakhin,V. N. Charushin and G. G.Aleksandrov,
Khim. Geterotsikl. Soedin., 1982, 1410 [Chem. Heterocycl. Compd. (Engl.
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using SHELXTL-97 software in anisotropic approximation for non-hydroge
n
atoms. No correction for absorption was introduced (m = 0.084 mm–1).
The final values of the refined parameters were R1 = 0.0413, wR2 = 0.0813
based on the reflections with I > 2s(I); R1 = 0.1236, wR2 = 0.0867 based on
all reflections; Q-factor S = 1.007. The NH and OH protons were localised
on the basis of spatial electron density peaks and refined independently.
The positions of the other hydrogen atoms were calculated geometrically
and included in the refinement based on a riding model.
CCDC 858777 contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cambridge
For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 2012.
Received: 27th July 2011; Com. 11/3771
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