Thermal and acid-catalyzed transformations of 3H-pyrazoles obtained from diphenyldiazomethane and methyl phenylpropiolate

Article abstract of DOI:10.1134/S1070428007020145

Reaction of diphenyldiazomethane with methyl phenylpropiolate in diethyl ether alongside the expected methyl triphenyl-3H-pyrazole-4-and-5-carboxylates (I and II) (38 and 24%) gave rise also to 8% of methyl 3,5-diphenyl-1-(1- ethoxyethyl)-1H-pyrazole-4-ca

Full text of DOI:10.1134/S1070428007020145

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 2, pp. 231−240. © Pleiades Publishing, Ltd. 2007.
Original Russian Text © A.A. Fedorov, Sh.E. Duisenbaev, V.V. Razin, M.A. Kuznetsov, E. Linden, 2007, published in Zhurnal Organicheskoi
Khimii, 2007, Vol. 43, No. 2, pp. 239−248.
Thermal andAcid-Catalyzed Transformations of 3H-Pyrazoles
Obtained from Diphenyldiazomethane and Methyl Phenylpropiolate
A. A. Fedorova, Sh. E. Duisenbaeva, V. V. Razina, M. A. Kuznetsova, and E. Lindenb
aSt. Petersburg State University, St. Petersburg, 19850 Russia
e-mail: vvrazin@mail.ru
bInstitut fur Organische Chemie, Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
Received March 5, 2006
Abstract—Reaction of diphenyldiazomethane with methyl phenylpropiolate in diethyl ether alongside the expected
methyl triphenyl-3H-pyrazole-4- and -5-carboxylates (I and II) (38 and 24%) gave rise also to 8% of methyl 3,5-
diphenyl-1-(1-ethoxyethyl)-1H-pyrazole-4-carboxylate. The main thermolysis product obtained from 4-methoxy-
carbonyl derivative I was methyl 1,3,5-triphenyl-1H-pyrazole-4-carboxylate, whereas from regioisomer II formed
predominantly methyl 4,4,5-triphenyl-4H-pyrazole-3-carboxylate and 1-methoxycarbonyl-2,3,3-triphenylcycloprop-
ene that was a minor product of 3H-pyrazole I thermolysis. Addition of concn. H2SO4 to the solutions of methyl
triphenyl-3H-pyrazole-4- and -5-carboxylates inAcOH resulted in fast regioselective isomerization of the 3H-pyr-
azole derivatives into the corresponding 4H-pyrazoles.
DOI: 10.1134/S1070428007020145
..
Alphen−Huttel rearrangement of two isomeric 3H-pyr-
azoles I and II distinguished by positions of substituents
at C4 and C5 atoms. Beside the purely thermal reaction
we investigated transformations of compounds I and II
at the treatment with a strong acid.
3H-Pyrazoles rearrangement with the migration of
substituents around the ring has been discovered more
than half-century ago and since that time is known as
van Alphen−Huttel rearrangement [1, 2]. Much later it
was interpreted in the framework of Woodward–Hoff-
mann rule as resulting from a suprafacial 1,5-sigmatropic
shift [3]. Depending on the direction of the substituent
migration from C3 atom this sigmatropic rearrangement
of a substituted 3H-pyrazole A can yield either aromatic
1H-pyrazole B (shift to N2 atom), or nonaromatic 4H-
pyrazole C (shift to C4 atom) [4]. Yet due to subsequent
1,5-shifts 4H-pyrazole C can finally also transform into
aromatic 1H-pyrazole of B type, but with another position
of the substituents [4–7].
We applied to the preparation of initial 3H-pyrazoles I
and II the known reaction of diphenyldiazomethane with
methyl phenylpropiolate [8–13]. In the first report on this
reaction [8] vanAlphen succeeded in isolation of a single
3H-pyrazole that further was considered [9] to have
structure I as a product of cycloaddition against the
Auwers rule. The formation of a single adduct I was
also described later in [10, 11], but then practically
simultaneously [12, 13] the reaction was found to yield
both possible isomers of 3H-pyrazole I and II, and in
[13] their structural assignment was proved by photo-
chemical denitration into isomeric indenes. We carried
out a reaction of 1.5 equiv. of diphenyldiazomethane with
methyl phenylpropiolate in ethyl ether (unlike [12, 13]
where no solvent had been used) at room temperature
(18–23°C) and in keeping with the data of [12, 13] we
obtained both 3H-pyrazoles I and II that were separated
by column chromatography on silica gel. However
alongside the expected products, 3H-pyrazoles I (38%),
II (24%), and benzophenone azine we isolated from the
reaction mixture 8% of previously unknown 1H-pyrazole
R3
R3
R4
R3
R4
R4
R1
R2
~R1
~R1
R2
R1
N
N
N
R2
N
R1
N
N
B
A
C
At the same time the effect of the nature and position
of substituents in the 3H-pyrazoles on the migration direc-
tion is not yet clearly understood and therefore requires
further investigations. We carried out in this study a van
231

FEDOROV et al.
232
Ph
Ph
(C2H5)2O
N2
Ph
CO2CH3
18_23oC
100 days
H3CO2C
Ph
Ph
CO2CH3
H3CO2C
Ph
Ph
(Ph2C=N)2
Ph
Ph
Ph
Ph
N
N
N
N
N
N
O
III
I
II
In the 13C NMR spectra of both 3,3-diphenyl-3H-pyr-
azoles I and II the chemical shift δ of C3 atom ~110 ppm
is characteristic (cf. [14]).
III containing only two phenyl groups instead of three,
and a fragment of the solvent.
The ratio of 3H-pyrazoles I and II obtained is well
consistent with the data of [12] (62:38) and [13] (~2:1),
and their structure is additionally confirmed by the features
The prevalence of pyrazole I, the product of anti-
Auwers addition, is likely due to steric factors: since the
efficient volume of the phenyl group is considerably larger
than that of the ester group, regioisomer II should suffer
stronger destabilization caused by its repulsion from the
gem-diphenyl moiety at C3 atom (cf. the discussion on
the regioselectivity of diazoalkanes cycloaddition to
unsymmetrical alkynes in [15]).
1
of H and 13C NMR spectra. For instance, the most
downfield signal in the 1H NMR spectrum of pyrazole I
at 8.1 ppm, removed from the multiplets of the other
aromatic protons by ~0.6 ppm, belongs to the ortho
protons of the phenyl ring on the C5 atom. Its downfield
shift is caused by the contiguous N=N group, and also by
the possibility of coplanarity of the phenyl substituent and
the heterocycle, and then its ortho-protons should occur
in the deshielding region of the π system of 3H-pyr-
azole. Unlike that, in regioisomer II the phenyl ring
attached to C4 atom should by steric reasons be located
virtually normally to the plane of the five-membered ring.
Therewith its ortho-protons are shielded by two
neighboring phenyl groups and give a signal at 7.04 ppm.
Azines formation is a frequent event in diazoalkanes
reactions [13], whereas the unusual for these processes
product III is far more interesting. Its composition was
confirmed by elemental anaysis, and the signals of all
fragment of the molecule clearly appeared in the 1H and
13C NMR spectra. We failed to observe the molecular
ion peak of pyrazole III in its mass spectrum, but the
main fragment ions are in good agreement with the
assumed structure. The position of the substituents in the
five-membered ring was established from the nuclear
Overhauser effect: the irradiation of the methoxy protons
resulted in enhanced intensity of all the free aromatic
signals, revealing that the ester group is adjacent to both
phenyls. The structure of compound III was finally
proved by X-ray diffraction analysis (see the figure).
С18
С19
С14
С17
С16
С8
O6
O7
С4
С3
С6
С5
С15
С21
N2
N1
С9
С22
The way of 1H-pyrazole III formation is not clear,
but presumably the process is of a radical character.
Taking into account the similar position of substituents at
the carbon atoms of compounds I and III it may be
concluded that substance III originates from the
secondary transformations of pyrazole I. However we
failed to obtain it from pyrazole I. 1H-Pyrazole III was
neither obtained by keeping the solution of compound I
in ethyl ether at 18–23°C for ~3 months, nor by heating
at 90°C in a sealed ampule for 3 h the ether solution of
3H-pyrazole I with a catalytic amount of benzoyl peroxide.
С20
С23
С10
O11
С25
С24
С12
С13
Structure of 1H-pyrazole III according to X-ray diffraction
anlysis (ORTEPprojection [16]; arbitrary numbering of atoms;
ellipsoids of displacement are given in 50% probability).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

THERMAL AND ACID-CATALYZED TRANSFORMATIONS OF 3H-PYRAZOLES
233
H3CO2C
Ph
H3CO2C
Ph
Ph
Ph
Ph
H+
Δ
C6H6
VI
I
N
Ph
N
Ph
N
N
Ph
CO2CH3
Ph
IV
VI
VIII
Ph
CO2CH3
Ph
CO2CH3
H+
Δ
C6H6
Ph
Ph
VIII
VII
II
N
Ph
N
N
N
Ph
V
VII
The thermolysis of 3H-pyrazoles I and II was carried
out in benzene solution in a thick-walled sealed ampule.
In both cases after 90 min at 135°C we observed
complete disappearance of the initial compounds and
formation of products of phenyl substituent migration to
the adjacent nitrogens (1H-pyrazoles IV and V) and
carbons (4H-pyrazoles VI and VII), and also of denitra-
tion product, cyclopropene VIII. The thermolysis of
3H-pyrazole I gave a mixture of 1H-pyrazole IV,
4H-pyrazole VI, and cyclopropene VIII in a ratio
~75:20:5, and of 3H-pyrazole II, a mixture of 1H-pyrazole
V, 4H-pyrazole VII, and cyclopropene VIII in a ratio
~10:50:40.
1H-Pyrazole V was identified with an authentic
compound prepared from methyl 2,4 dioxo-3,4-diphenyl-
butanoate and phenylhydrazine.
CH3
CO2CH3
Ph
N
Ph
N
IX
Ph
Ph
Ph
Ph
COCO2CH3
PhNHNH2
V
N
H3CO2C
O
N
CH3OH, Δ
Ph
X
Cyclopropene VIII was identified by comparison with
an authentic sample that we had described previously
[17]. The structure of thermolysis products of 3H-pyrazole
I, compounds IV and VI, was established in [10, 11] and
was additionally confirmed in our study by 13C NMR
spectra. Besides 1H-pyrazole IV was identified by its
1H NMR spectrum with a published spectrum of a com-
pound synthesized by another method [18]. Individual
samples of 4H-pyrazoles VI and VII we isolated in the
experiments on acid isomerization of 3H-pyrazoles I and
II (see further); the structure of previously unknown
compound VII was proved by the combination of its
spectral data, in particular, by their comparison with those
of its already known methyl analog IX [19]. Chromo-
phore Ph–C=N–N=C–CO2CH3 common for these
compounds results in the presence in their UV spectra
of a strong long-wave absorption band: for pyrazole VII
The identity of this obtained by us condensation product
with 1H pyrazole V and not with its regioisomer X [20]
follows even from the comparison of the melting points
of our sample and compound X (the latter melts 74°C
lower [20]). The final proof of the structure of 1H-pyr-
azole V and assignment of the signals in its NMR spectra
1
we carried out using 2D NMR experiments (1H− H- and
13
1H− C-COSY, COLOC, 2D-NOESY). The decisive
confirmation of structure V is the Overhauser effect
between the ortho-protons of one of the phenyl rings
(m, 7.01 ppm) and the protons of two other phenyl
substituents: ortho-protons of the second phenyl ring
(m, ~7.29 ppm), and protons of the third one appearing
as a singlet at 7.33 ppm. This fact shows that all the
three phenyl groups are close in space, impossible for
structure X.
13C NMR spectrum of 1H-pyrazole V registered
without decoupling from protons provided a possibility to
identify three downfield signals of quaternary carbon
atoms at 142.2, 140.9, and 139.3 ppm. The first one is
a triplet (J 3.3 Hz) and therefore belongs to C5 atom
attached to a phenyl ring (C4 atom in 1H-pyrazoles
λ
max 303 nm (log ε 4.22), for compound IX λmax 300 nm
(log ε 4.11) [19]. It is also significant that the chemical
shifts of C3 and C5 atoms of 4H-pyrazoles VII and IX in
the 13C NMR spectra virtually coincide (with clearly
different chemical shifts of C4atoms).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

FEDOROV et al.
234
removed from nitrogens resonate far upfield). The signal
at 140.9 ppm remains singlet and consequently can
originate only from C3 atom. The latter signal is split into
a multiplet indicating that it belongs to Ci of the phenyl
substituent, and the large chemical shift shows the
contiguity of a nitrogen atom. In the COLOC-experiment
appears a cross-peak between the most upfield signal of
the two aromatic protons (m, 7.01 ppm) and a signal of
C5 atom of the five-membered ring (142.2 ppm). There-
fore the signal at 7.01 ppm should be assigned to the
ortho-protons of the phenyl ring at C5 atom in agreement
with the data on the Overhauser effect. One more impor-
tant cross-peak is found between the narrow 5-protons
singlet at 7.33 ppm and the signal of Ci substituent at
a nitrogen atom (139.3 ppm). This is the only cross-peak
for the latter signal, and we are thus enabled to assign
this singlet at 7.33 ppm to all the five protons of the
phenyl ring linked to N1 atom. This assignment was
melt at ~100°C gave a mixture of pyrazoles IV and VI in
a ratio 3.6:1 [10], and at the thermolysis of its solution in
o-xylene at 135°C [11] alongside the mixture of com-
pounds IV and VI, 6:1, also 8% of cyclopropene VIII
was obtained. Our data are in agreement with the results
of [10, 11] and confirm the formation in thermolysis of
3H-pyrazole I of cyclopropene VIII that once has been
considered unexpected [21].
The comparison of thermolysis results for isomeric
3H-pyrazoles I and II reveals considerable difference
in their behavior. The main thermolysis product of
4-methoxycarbonyl derivative I is aromatic 1H-pyrazole
IV whereas regioisomer II undergoes predominantly
migration of a phenyl group to a carbon atom leading to
the formation of 4H-pyrazole VII. The formation of
cyclopropene VIII competes successfully with the latter
process, but in the thermolysis of pyrazole I cyclopropene
VIII is a minor product.
1
13
confirmed by the H− C COSY spectrum whose
The presence of a mineral acid is known to accelerate
1
analysis in combination with the spectra 1H− H COSY
..
significantly the vanAlphen–Huttel rearrangement [22].
and 2D-NOESY permitted unambiguous assignment of
practically all signals in the 1H and 13C NMR spectra of
1H-pyrazole V.
We showed that adding concn. H2SO4 to a solution of
3H-pyrazoles I and II in acetic acid already at 20°C
resulted in their regioselective isomerization (and
exclusively in isomerization!) into 4H-pyrazoles VI and
VII respectively. Formerly at heating 3H-pyrazole I in
acetic acid solution at 80–90°C for 3 h was obtained
a mixture of pyrazoles IV and VI in a ratio 1:1.25 [11],
quite different in composition both from the products of
the pure thermolysis and the acid-catalyzed process; the
reaction under the above conditions presumably followed
both routes.
In the 1H NMR spectra of obtained methoxycarbonyl-
lpyrazoles a clear dependence of the chemical shift of
the protons from the COOCH3 was observed on its
position in the hetero ring. In compounds I, III, IV, and
VI where it is linked to C4 and therewith from the both
sides it is shielded by the phenyl substituents the cor-
responding singlet appears in the region δ 3.52–3.68 ppm.
In pyrazoles V, VII, and IX the OCH3 group occurs in
the deshielding field of the C=N bond, and the respective
signal suffers a downfield shift to δ 3.79–3.88 ppm. The
maximum value of 3.94 ppm the chemical shift of these
protons attains in the neighborhood of the N=N bond in
3H-pyrazole II.
Now we should focus on the discussion of results of
thermal and acid-catalyzed transformations of 3H-pyr-
azoles I and II. We applied to the interpretaion of the
regioselectivity of their thermal isomerization regarded
as 1,5-sigmatropic rearrangement the approach of M.
Dewar who considered the transition state of this peri-
cyclic reaction as topologically equivalent to the aromatic
system of bicyclo-[3.1.0]hexatriene [23]. Since the
system is nonalternating, it is polarized with electrons
transfer from the three-membered to the five-membered
ring, and it may be regarded as a combination of an allyl
anion and cyclopropenylium cation [24].
An unambiguous identification of 4H-pyrazoles VI and
VII was based on their 13C NMR spectra where the
characteristic signal was that of C4 atom at 76.2 (VI)
and 77.9 (VII) ppm. Sharp reduction of the number of
signals in the spectrum of compounds VI and double
intensity of some among them confirm its symmetrical
structure. Note also that the signals of C3 and C5 atoms
in the spectrum of 4-phenyl-1H-pyrazole V appear at
141.0 and 142.2 ppm respectively, whereas in going to
4-methoxycarbonyl-1H-pyrazoles III and IV the signals
suffer downfeld shift to ~147 and 153 ppm.
The data on thermolysis were published only for 3H-
pyrazole I [10, 11]. It was reported that the heating of its
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

THERMAL AND ACID-CATALYZED TRANSFORMATIONS OF 3H-PYRAZOLES
235
In keeping with above in the transition state atoms 1,
5, and 6 are charged positively, atoms 2 and 4 possess
a negative charge, and the charge in position 3 is virtually
zero. Then the introduction of electron-withdrawing
substituents into positions 2 and 4 should enhance the
stability of the bicyclo[3.1.0]hexatriene system, into
positions 1 and 5, cause its destabilization, and substituent
in position 3 should not notably affect the process.
tially more numerous [26, 27], but the photolytic denitration
of 3H-pyrazoles had been discovered earlier [28] and
was better studied [4]. The photolysis of 3H-pyrazoles
was shown to start with the ring opening into vinyl-
diazomethane derivatives that then eliminate a nitrogen
molecule turning into vinylcarbenes. The latter further
either isomerize into cyclopropenes (1,3-cyclization), or
take part in other reactions [4]. In particular, the photolysis
of 3H-pyrazoles I and II [13] proceeds through unsaturat-
ed diazo XI and XII leading in both cases to the formation
of mixtures of the same cyclopropene VIII and indenes
XIII and XIV corresponding to 1,5-cyclization of the
respective vinylcarbenes.
In the framework of this model the transition states
for migration of 3-phenyl substituent in 3H-pyrazoles I
and II to atoms C4 and N2 are as follows.
I, XI, XIII, R = Ph, R' = CO2Me; II, XII, XIV, R = CO2Me,
R' = Ph
As seen, the transition state TS II(C) is more stable
than TS I(C), and TS I(N) is more favorable, than TS
II(N). Therefore we may expect that in the thermolysis
products of 3H-pyrazole II the fraction of 4H-pyrazole
would be greater, and that of 1H-pyrazole, smaller, than
in the isomerization of 3H-pyrazole I as is found
experimentally.
It is presumable that the thermal denitration of 3H
pyrazoles occurs in the same fasion. It should be however
taken into consideration that their isomerization into
vinyldiazomethane derivatives is strongly endothermic
(the enthalpy change for unsubstituted 3H-pyrazole is
estimated at 26.8 kcal mol−1 [27]), and during the
thermolysis with this process competes thermally
permitted 1,5-sigmatropic shift. It is therefore
understandable why the denitration of 3H pyrazoles under
thermolysis occurs only in event they contain substituents
capable to strongly stabilize the intermediate diazo
compound (for instance, two phenyl groups attached to
C3 atom) [25–27].
This approach provides also an understanding of the
regioselectivity of the acid-catalyzed isomerization of
3H-pyrazoles I and II. Inasmuch as the protonation of
compounds I and II occurs likely at the lone pair of the
terminal nitrogen of the conjugation system (cf. [25]) it
should lead in the corresponding pyrazolium cations to
the stabilization of the structures TS I(C) and TS II(C)
and in contrast to a strong destabilization of TS I(N) and
TS II(N) due to the appearance of a positive charge in
the cyclopropenyl fragment. Thus the prevalence of the
1,5-sigmatropic shift of the phenyl group to the carbon
atom, i.e., of the formation of the corresponding 4H-pyr-
azole, sharply increases.
The comparison of thermolysis results of 3H-pyrazoles
I and II and with photolysis results of these compounds
revealed two interesting facts. Firstly, the ratio of the
denitration product to the products of rearrangement is
quite different for compounds I and II. Secondly, unlike
the photochemical denitration the thermal process yielded
exclusively cyclopropene VIII. We failed to find indenes
XIII or XIV in the corresponding reaction mixtures either
by TLC or 1H NMR spectroscopy.
The thermal rearrangement of 3H-pyrazoles I and II
suffers a competition with their denitration to cyclo-
propene VIII. The first scanty examples of 3H-pyrazoles
denitration under thermolysis [11, 25] then turned essen-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

FEDOROV et al.
236
The considerably higher yield of cyclopropene VIII
EXPERIMENTAL
in the thermolysis of 3H-pyrazole II than in reaction of
its isomer I may be considered as indication of the higher
rate of ring opening of compound II into the corresponding
vinyldiazo compound XII caused by additional stabiliza-
tion of the latter by the electronegative substituent
(CO2Me) at the carbon atom of the diazo group. Yet this
assumption requires that the summary rates of the
concurrent 1,5-sigmatropic rearrangements be nearly the
same for pyrazoles I and II.
Elemental analyses were performed on a C2H2N-
analyzer Hewlett-Packard 185Β. H (300 MHz) and
1
13C (75.4 MHz) NMR spectra of solutions in CDCl3 were
registered on a spectrometer Bruker DPX-300 (if not
indicated otherwise) using as internal references for
1H NMR spectra the residual chloroform signal
(δ 7.26 ppm), and for 13C NMR spectra, the solvent
resonance (δ 77.0 ppm). IR spectra were recorded on
a spectrophotometer Perkin Elmer-1600 FT-IR, mass
spectra were measured on Finnigan MAT-90 instrument
in the electron impact mode (ionizing electrons energy
70 eV) and in the chemical ionization mode (reactant gas
ammonia). UV spectrum of pyrazole VII in hexane was
taken on a spectrophotometer Perkin Elmer M-402.
Melting points were measured on Buchi Melting point B-
540 instrument. The separation and purification of
substances was carried out by column chromatography
on silica gel L 5/40 (Chemapol). The composition of
reaction mixture and fractions obtained by their separation,
and also the purity of compounds isolated were
determined by TLC on Silufol UV-254 plates (eluent
heptane–ether, 1:1).
We believe that the second distinction is due to the
possibility of a singlet-triplet transition in the course of
the photochemical generation of vinylcarbene which is
forbidden in thermolysis. Here we proceed from the
assumption [13] on allowable 1,3-bonding into cyclo-
propene for a singlet vinylcarbene and favorable
1,5-cyclization for a triplet styrylcarbene.
The discoverers of vanAlphen–Huttel rearrangement
reported [1, 2] as the final product of 3H-pyrazole I trans-
formations methyl-3,4,5-triphenyl-1H-pyrazole-1-carb-
oxylate (XV). Since in our experiments we did not find it
at all, it was presumable that the compound was a product
of secondary transformations of the nonaromatic 4H-pyr-
azole VI under more stringent conditions. Although
4H-pyrazole VI was stated to be stable at 200°C [11],
the heating of its benzene solution to 185°C for 2 h resulted
in complete disappearance of the initial compound and in
formation of 1 methyl-3,4,5-triphenyl-1H-pyrazole (XVI)
and 3,4,5-triphenyl-1H-pyrazole (XVII) in a ratio ~2 : 1.
Diphenyldiazomethane [29], methyl phenylpropiolate
[13], and methyl 2,4-dioxo-3,4-diphenylbutanoate [30]
were obtained by published procedures.
X-ray diffraction analysis*. The single crystal of
1H-pyrazole III was obtained by slow evaporation of its
solution in a mixture of ethyl ether and hexane, 1:1. The
structural measurements were carried out on
diffractometer Nonius KappaCCD [31]. The set of
experimental reflections from the single crystal was
Ph
Ph
Ph
°
185oC, 2 h
C6H6
obtained by ω-scanning on the MoKα (λ 0.71073 A)
VI
N
radiation with graphite monochromator at cooling with
Oxford Cryosystems Cryostream 700. The data treatment
was performed as suggested in [32]. The structure was
solved by the direct method using software [33] and was
refined by least-squares method in a full-matrix
approximation by F2. The atomic amplitudes for neutral
nonhydrogen atoms were taken from [34], for hydrogens,
from [35]. The effect of abnormal dispersion was taken
N
CO2CH3
XV
Ph
Ph
Ph
Ph
Ph
N
Ph
N
N
N
H
into account in Fc [36], the values used for f ' and f ''
CH3
XVI
XVII
were from [37], the values of mass decrease factors,
from [38]. The calculations were performed applying
software package SHELXL97 [40].
Possibly compounds XVI and XVII are the products
of further transformations of the intermediately arising
1H-pyrazole XV. However since we failed to find the
latter we cannot prove or disprove this assumption.
*
Free access to crystallographic data on compound III (CCDC-
286780) is available from Cambridge Crystallographic Data Centre:
www.ccdc.cam.ac.uk/data_request/cif.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

THERMAL AND ACID-CATALYZED TRANSFORMATIONS OF 3H-PYRAZOLES
237
X-ray diffraction data for pyrazole III. C21H22N2O3.
M 350.42, colorless plates, crystal dimensions 0.07×0.17 ×
0.30 mm, orthorhombic crystal system, space group
Pca21, Z 4, a 16.5694(9),
Methyl 3,5-diphenyl-1-(1-ethoxyethyl)-1H-pyr-
azole-4-carboxylate (III). mp 123–123.8°C. IR
spectrum, cm–1: 3008 w, 2973 w, 2940 w, 2903 w, 2879 w,
1715 s, 1485 m, 1459 m, 1436 m, 1377 m, 1316 m, 1234 m,
1197 m, 1146 m, 1119 s, 1043 m, 765 m, 697 m. 1H NMR
spectrum (spectrometer Bruker DPX-600, 600 MHz), δ,
ppm: 7.73–7.71 m (2Harom), 7.50–7.49 m (3Harom), 7.43–
7.27 m (5Harom), 5.38 q (1H, CH–O, J 6.0 Hz), 3.52 s
°
°
b 8.4759(4), c 13.5010(6) A, V 1896.1(2) A3,
DX 1.194 g/cm3, μ(MoKα) 0.203 mm–1, T 160 K, ϕ and ω
scanning, transmission factors (min, max) 0.908, 0.974,
2θmax 55°, total measured 26432 reflexions, independent
reflexions 1739, reflexions with I > 2σ(I) 1563, 1739
reflexions were used in refining, 239 refined parameters,
restrictions 1, R [for F, I > 2σ(I) reflexions] 0.0381,
2
3
(3H, MeO), 3.31 d.q (1H, J 14.1, J 7.1 Hz) and
2
3
3.22 d.q (1H, J 14.1, J 7.1 Hz) OCHAHΒ; 1.7 d (3H,
CHCH3, J 6.0 Hz), 1.08 t (3H, CH2CH3, J 7.0 Hz).
13C NMR spectrum, δ, ppm: 164.0 (C=O), 152.8 and
147.4 (C3), 132.9, 130.0, 129.3, 129.2, 129.0, 128.9, 128.3,
128.2, 127.8 (12Carom, C4), 84.3 (OCH), 63.4 (OCH2),
51.0 (MeO), 21.2 (CHCH3), 14.7 (CH2CH3). Mass
spectrum, electron impact m/z (Irel,%): 278 (22) [M –
CH(Me)OEt], 247 (19) [M – CH(Me)OEt, – OMe]+,
104 (10) [C(NH)Ph], 77 (18), 73 (35) [CH(Me)OEt],
45 (100) (OEt). Found, %: C 72.08; H 6.31; N 7.95.
C21H22N2O3. Calculated, %: C 71.98; H 6.33; N 7.99.
2
2
wR(F2) (for all reflexions) 0.947 {w = [σ (Fo ) +
(0.0527P)2 ++ 0.2766P]–1, γdε P = (Fo + 2Fc2)/3}, quality
2
factor 1.062, secondary extinction factor 0.014(2),
Δ
max/σ 0.001, ΔC (max/min) = 0.16/–0.15 eA–3.
Reaction of diphenyldiazomethane with methyl
phenylpropiolate. A solution of 1.45 g (7.5 mmol) of
diphenyldiazomethane and 0.80 g (5 mmol) of methyl
phenylpropiolate in 25 ml of anhydrous ethyl ether was
maintained in the dark at 10°C for 100 days in an air-
tight thick-walled vessel. Within this period the color of
the solution changed from dark-violet to pale pink. The
solvent was evaporated in a vacuum, the residue was
subjected to column chromatography on silica gel (eluent
heptane–ether, 1:1). We isolated 0.28 g (20%) of
benzophenone azine (Rf 0.79, mp 162–164°C [40]), 0.67
g (38%) of pyrazole I (Rf 0.56), 0.14 g (8%) of pyrazole
III (Rf 0.34), and 0.42 g (24%) of pyrazole II (Rf 0.26).
Attempts to obtain 1H-pyrazole III from 3H-
pyrazole I. A solution of 50 mg (140 μmol) of 3H-pyr-
azole I in 5 ml of anhydrous ethyl ether was kept at room
temperature (18–23°C) in the dark for 90 days. The
solvent was removed in a vacuum. The residue according
to 1H NMR spectrum and TLC data contained only initial
pyrazole I.
A solution of 50 mg (140 μmol) of pyrazole I and
5 mg (20 μmol) of benzoyl peroxide in 3 ml was heated
for 2 h in a thick-walled ampule at 90°C. The solvent
was removed in a vacuum. The residue according to
1H NMR spectrum contained initial pyrazole I with
admixture of its thermolysis products (see below), but no
compound III.
Methyl
3,3,5-triphenyl-3H-pyrazole-4-
carboxylate (I). mp 102.4–103.5°C [2]. IR spectrum,
cm–1: 3030 w, 2952 w, 1717 C, 1624 m, 1599 m, 1576 w,
1490 m, 1474 m, 1444 m, 1435 m, 1338 s, 1314 m, 1291
m, 1212 s, 1079 m, 1011 m, 970 m, 930 m, 754 m, 699 m.
1H NMR spectrum, δ, ppm: 8.11–8.09 m (2HO, 5-Ph),
7.54–7.52 m (3Harom), 7.37–7.35 m (6Harom), 7.30–7.28
m (4Harom), 3.68 s (3H, MεO). 13C NMR spectrum, δ,
ppm: 164.3 (C=O), 157.0 (C4), 138.7 (C5), 135.0, 130.6,
129.8 br, 128.5 br (in total 18Carom), 110.7 (C3), 52.2
(MεO). Mass spectrum, chemical ionization, m/z (Irel, %):
356 (24), 355 (100) [M + H]+.
Thermolysis of 3H-pyrazoles I and II. A solution
of 355 mg (1 mmol) of an appropriate 3H-pyrazole in 15
ml of benzene was maintained in a thick-walled ampule
at 135°C for 50–90 min. TLC monitoring after 50 min
indicated the presence in the reaction mixture of still
considerable amounts of initial compounds, but within 90
min they completely disappeared. The solvent was
removed in a vacuum, yields of reaction products were
estimated from the intensity ratio of the corresponding
methoxy protons in the 1H NMR spectra. As a result of
thermolysis of 3H-pyrazole I a mixture was obtained of
pyrazoles IV and VI and cyclopropene VIII in a ratio ~
75:20:5, and a mixture obtained from pyrazole II
contained pyrazoles V and VII and cyclopropene VIII
in a ratio ~ 10:50:40. By means of column chromato-
Methyl
3,3,4-triphenyl-3H-pyrazole-5-
1
carboxylate (II). mp 103°C (99–100°C[13]). H NMR
spectrum, δ, ppm: 7.67–7.22 m (9Harom), 7.17–7.15
doublet-like multiplet (4H, 3-Ph, H°, J 7.3 Hz), 7.06–
7.03 doublet-like multiplet (2H, 4-Ph, H°, J 7.3 Hz), 3.94
s (3H, MεO). 13C NMR spectrum, δ, ppm: 164.0, 162.1
(C=O and C5), 143.2 (C4), 133.2, 130.5, 130.1, 129.0,
128.8 br, 128.6 br, 128.0 (in total 18Carom), 109.2 (C3),
52.5 (MeO).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

FEDOROV et al.
238
7.29 m (9Harom), 3.63 s (3H, MeO). 13C NMR spectrum,
δ, ppm: 174.4 (C3,5), 166.9 (C=O), 131.5, 131.3, 129.4,
128.8 br, 128.6, 128.5, 127.1 (8Carom), 76.2 (C4), 53.4
(MeO).
graphy we isolated in an individual state the main
thermolysis product of compound I and two principal
thermolysis products of compound II. The minor
components of the reaction mixture were identified by
comparison with authentic substances by TLC and the
position of the methoxy protons in the 1H NMR spectra.
Methyl 4,4,5-triphenyl-4H-pyrazole-3-carboxy-
late (VII). mp 179.3–180.3°C, Rf 0.20. UV spectrum,
max, nm (log ε): 303 (4.22). IR spectrum, cm–1: 3059 w,
Methyl 1,3,5-triphenyl-1H-pyrazole-4-carboxy-
late (IV). Rf 0.50, mp 139–140°C [2]. 1H NMR spectrum,
δ, ppm: 7.82–7.80 doublet-like multiplet (2Harom), 7.49–
7.47 m (3Harom), 7.40–7.31 m (10Harom), 3.63 s (3H,
MεO). 13C NMR spectrum, δ, ppm: 164.2 (C=O), 153.2,
146.3 (C3, C5), 139.1 (Cand, 1-Ph), 132.7, 130.3, 129.0,
λ
2946 w, 1729 C, 1598 w, 1551 w, 1514 m, 1493 m,
1441 m, 1339 s, 1194 m, 1144 s, 1034 w, 989 w, 952 w,
808 w, 773 m, 753 m, 699 s. 1H NMR spectrum, δ, ppm:
7.80 d (2Harom, J 7.3 Hz), 7.38–7.24 m (13Harom), 3.79 s
(3H, MεO). 13C NMR spectrum, δ, ppm: 181.3 (C5),
171.7 (C=O), 160.3 (C3), 132.7, 131.9, 129.7, 129.0, 128.6,
128.5 br, 128.4, 128.3 (18Carom), 77.9 (C4), 52.7 (MeO).
Mass spectrum, electron impact, m/z (Irel, %): 327 (16),
326 (61), 312 (12), 311 (33), 294 (18), 268 (14), 267 (30),
266 (8), 265 (13), 252 (8), 251 (13), 219 (8), 207 (15),
193 (15), 192 (58), 191 (18), 190 (20), 166 (28), 165 (100),
164 (9), 105 (17), 103 (13). Found, %: C 77.73; H 5.16;
N 7.83. C23H18N2O2. Calculated, %: C 77.95; H 5.12;
N 7.90.
128.7 br, 128.5, 128.3, 128.0, 127.9, 127.8, 125.4 (17Carom
,
C4), 51.2 (MeO).
Methyl 1,4,5-triphenyl-1H-pyrazole-3-carboxy-
late (V). A solution of 100 mg (0.35 mmol) of methyl
2,4-dioxo-3,4-diphenylbutanoate and 76 mg (0.7 mmol)
of phenylhydrazine in 15 ml of methanol was heated at
reflux for 92 h. The reaction mixture was kept for half
a year, then the formed precipitate was separated and
washed with methanol (2×10 ml). Yield 49.5 mg (40%),
mp 180.6–182.4°C, Rf 0.33. IR spectrum, cm–1: 3059 w,
2953 w, 1730 s, 1599 m, 1499 m, 1444 m, 1368 m,
1324 m, 1243 m, 1199 s, 1161 s, 1093 m, 1011 m, 784 m,
763 m, 701 s. 1H NMR spectrum, δ, ppm: 7.33 s (5H,
1-Ph), 7.29–7.23 m (6H; 5H, 4-Ph; Hp, 5-Ph), 7.21–
7.16 m (2Hm, 5-Ph), 7.02–6.99 m (2Ho, 5-Ph), 3.88 s
(3H, MeO). 13C NMR spectrum, δ, ppm: 162.7 q (C=O,
J 4.2 Hz), 142.2 t (C5, J 3.3 Hz), 141.0 C (C3), 139.3 m
(Ci, 1-Ph), 131.4 m (Ci, 5-Ph), 130.5 d.m (Co 4-Ph),
130.3 d.m (Co, 5-Ph), 128.8 d.m (Cm, 1-Ph), 128.4 d.m
(Cp, 5-Ph), 128.2 d.m (Cm, 5-Ph), 128.1 d.m (Cp, 1-Ph),
127.6 d.m (Cm, 4-Ph), 127.1 d.m (Cp, 4-Ph), 125.6 d.m
(Co, 1-Ph), 124.9 m, 51.9 q (MeO, J 147.6 Hz). The
multiplicity of signals and coupling values were obtained
from the 13C NMR spectrum registered without
decoupling from protons. The values of direct coupling
constants 1JCH in the phenyl substituents were ~160 Hz.
The assignment of signals was based on the data of 2D
Methyl 2,3,3-triphenylcyclopropene-1-carboxy-
1
late (VIII). mp 127–128°C [19], Rf 0.71. H NMR
spectrum, δ, ppm: 7.93–7.91 m (2Harom), 7.50–7.48 m
(3Harom), 7.37–7.33 m (4Harom), 7.31–7.22 m (6Harom),
3.95 s (3H, MeO). 13C NMR spectrum, δ, ppm: 161.1
(C=O), 143.9 (C1), 133.3 (C2), 131.7, 131.5, 129.4,
128.3 br, 126.4, 125.9 (18Carom), 109.9 (C3), 52.4 (MeO).
Methyl 4-methyl-4,5-diphenyl-4H-pyrazole-3-
carboxylate (IX). The sample was obtained in [19].
1
mp 104–105°C. H NMR spectrum, δ, ppm: 7.75 d
(2Harom, J 7.2 Hz), 7.42–7.30 m (6Harom), 7.22–7.17 m
(2Harom), 3.84 s (3H, OCH3), 1.96 s (3H, CH3). 13C NMR
spectrum, δ, ppm: 181.9 (C3), 172.1 (C=O), 160.0 (C5),
132.7, 131.9, 129.3, 128.9, 128.6, 128.3, 128.1, 125.7
(Carom), 67.1 (C4), 52.5 (OCH3), 18.9 (CH3).
Acid-catalyzed isomerization of 3H-pyrazoles I
and II. To a solution of 100 mg (0.28 mmol) of 3H-pyr-
azole I or II in 10 ml of glacial acetic acid was added
0.1 ml (2 mmol) of concn. H2SO4, and the reaction mixture
was left standing at room temperature (18–23°C).
According to TLC 2 h later the initial pyrazoles disappear-
ed, and in each case a single reaction product was
obtained. The reaction was stopped by diluting the mixture
with water, the products were extracted into ether
(3×10 ml), the organic solution was washed with
NaHCO3 solution till the end of gas liberation, and then it
was dried with MgSO4. The residue after evaporating
1
1
13
NMR spectroscopy (1H− H- and H− C COSY,
COLOC, 2D-NOESY). Mass spectrum, electron impact,
m/z (Irel, %): 355 (27), 354 (100) [M]+, 323 (23), 321
(18), 296 (18), 295 (18), 180 (17), 77 (14). Found, %:
C 77.90; H 5.10; N 7.84. C23H18N2O2. Calculated, %:
C 77.95; H 5.12; N 7.90. M 354.41.
Methyl 3,4,5-triphenyl-4H-pyrazole-4-carboxy-
late (VI). mp 196–198°C (198–201°C [10]), Rf 0.26.
1H NMR spectrum, δ, ppm: 7.88 d (4Harom, J 6.5 Hz),
7.54–7.52 doublet-like multiplet (2Harom, J 6.5 Hz), 7.39–
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

THERMAL AND ACID-CATALYZED TRANSFORMATIONS OF 3H-PYRAZOLES
239
and Katritzky, A.R., Adv. Heterocycl. Chem., 1983, vol. 34,
p. 1.
5. Bramley, R.K., Grigg, R., Guilford, G., and Milner, P.,
Tetahedron, 1973, vol. 29, p. 4159.
6. Frampton, C.S., Majchrzak, M.W., andWarkentin, J., Canad.
J. Chem., 1991, vol. 69, p. 373.
7. Yen, Y.P., Chen, S.F., Heng, Z.C., Huang, J.C., Kao, L.C.,
Lai, C.C. and Liu, R.S.H., Heterocycles, 2001, vol. 55,
p. 1859.
the solvent was virtually pure product (TLC data). After
recrystallization we obtained from compound I 60 mg
(60%) of 4H-pyrazole VI, and from compound II 55 mg
(55%) of 4H-pyrazole VII.
Thermolysis of 4H-pyrazole VI. A solution of
100 mg (0.28 mmol) of 4H-pyrazole VI in 6 ml of benzene
was heated for 2 h at 185°C in a thick-walled ampule.
The reaction mixture became colorless solution with
a white precipitate.According to TLC the initial pyrazole
disappeared, and two thermolysis products were present.
After separation on a column charged with 15 g of silica
gel (eluent a mixture hexane–ethyl ether, 2:1) we obtained
53 mg (61%) of pyrazole XVI and 22 mg (26%) of
pyrazole XVII.
8. VanAlphen, J., Rec. Trav. Chim., 1943, vol. 62, p. 485.
..
9. Huttel, R., Riedl, J., Martin, H., and Franke, K., Chem. Ber.,
1960, vol. 93, p. 1425.
10. Abbott, P.J., Acheson, R.M., Flowerday, R.F., and
Brown, G.W., J. Chem. Soc., Perkin, Trans. 1, 1974, p. 1177.
11. Komendantov, M.I. and Bekmukhametov, R.R., Khim.
Geterotsikl. Soedin., 1975, p. 79.
1-Methyl-3,4,5-triphenyl-1H-pyrazole (XVI).
mp 189.8–190.2°C (191–192°C [41]). H NMR spec-
12. Aspart-Pascot, L. and Bastide, M.J., C.r., 1971, vol. 273C,
p. 1772.
1
13. Leach, C.L. and Wilson, J.W., J. Org. Chem., 1978, vol. 43,
p. 4880.
14. Sharp, J.T., Findlay, R.H., and Thorogood, P.B., J. Chem.
Soc., Perkin, Trans. 1, 1975, p. 102.
15. Domnin, I.N., Zhuravleva, E.F., Serebrov, V.L., and
Bekmukhametov, R.R., Khim. Geterotsikl. Soedin., 1978,
p. 1091; Padwa,A. and Kennedy, G.D., J. Org. Chem., 1984,
vol. 49, p. 4344.
16. Johnson, C.K., ORTEPII Report ORNL-5138, Oak Ridge
National Laboratory, Oak Ridge, Tennessee, 1976.
17. Razin, V.V. and Gupalo, V.I., Zh. Org. Khim., 1974, vol. 10,
p. 2342.
18. Fliege, W., Huisgen, R., Clovis, J.S., and Knupfer, H., Chem.
Ber., 1983, vol. 116, p. 3062.
19. Razin, V.V., Zh. Org. Khim., 1975, vol. 11, p. 1457.
20. Coutouli-Argyropoulou, E. and Thessalonikeos, E.,
J. Heterocycl. Chem., 1991, vol. 28, p. 1945.
21. Leigh, W.J. and Arnold, D.R., Canad. J. Chem., 1979,
trum, δ, ppm: 7.49–7.46 m (2Harom), 7.38–7.36 m (3Harom),
7.28–7.23 m (5Harom), 7.18–7.16 m (3Harom), 7.06–
7.03 m (2Harom), 3.88 s (3H, Me). 13C NMR spectrum,
δ, ppm: 133.4, 130.4, 130.2, 128.5, 128.1 br, 127.3, 126.3
(18Carom, C3, C4, C5), 37.4 (Me). Mass spectrum, electron
impact, m/z (Irel, %): 311 (24), 310 (100) [M]+, 309 (54),
294 (7), 267 (7), 166 (8), 147 (9), 118 (8), 77 (15). Found,
%: C 85.19; H 5.86; N 8.97. C22H18N2. Calculated, %:
C 85.13; H 5.85; N 9.02. M 310.40.
3,4,5-Triphenyl-1H-pyrazole (XVII). mp 267–
1
269°C (265–266°C [10]). H NMR spectrum, δ, ppm:
7.39–7.36 m (5Harom), 7.31–7.28 m (8Harom), 7.21–
7.20 m (2Harom). Mass spectrum, electron impact, m/z
(Irel, %): 297 (24), 296 (100) [M]+, 295 (67), 165 (22),
147 (9), 77 (8).
The authors are grateful to Associate Professor of
the Chemical Faculty of the St. Petersburg University
S.I. Selivanov for registering 2D NMR spectra.
A.A.Fedorov is thankful to Professor H.Heimgartner of
Zurich University for hospitality and possibility to use in
this study the facilities of his laboratory, and also to
Candidate of Sciences (Chemistry) N.V. Ulin for valuable
experimental suggestions.
vol. 57, p. 1186.
..
22. Durr, H. and Schmidt, W., Lieb. Ann., 1974, p. 1140;
Heydt, H. and Regitz, M., Lieb. Ann., 1977, p. 1766;
Schiess, P. and Stalder, H., Tetrahedron Lett., 1980, vol. 21,
p. 1413.
23. Dewar, M. and Dougherti, R., The PMO Theory of Organic
Chemistry, NewYork: Premium Press, 1975
24. Replogle, K.S. and Carpenter, B.K., J. Am. Chem. Soc., 1984,
vol. 106, p. 5751.
25. Durr, H., Schmidt, W., and Sergio, R., Lieb. Ann., 1974,
REFERENCES
..
1. VanAlphen, J., Rec. Trav. Chim., 1943, vol. 62, p. 491.
2. Huttel, R., Franke, K., Martin, H., Riedl, J., Chem. Ber., 1960,
vol. 93, p. 1433.
3. Woodward, R. B. and Hoffmann, R., The Conservation of
Orbital Symmetry, NewYork:Academic, 1970.
4. Spangler, C.W., Chem. Rev., 1976, vol. 76, p. 187;
Bekmukhametov, R.R., Sovr. Problemy Org. Khim., Izd.
Leningrad. Gos. Univ., 1976, vol. 5, p. 105; Sammes, M.P.
p. 1132.
26. Mataka, S., Takahashi, K., Ohshima, T., and Tashiro, M.,
Chem. Lett., 1980, p. 915; Mataka, S. and Tashiro, M.,
J. Org. Chem., 1981, vol. 46, p. 1929; Mataka, S., Ohshi-
ma, T., and Tashiro, M., J. Org. Chem., 1981, vol. 46, p. 3960;
Burger, W., Groβe, M., and Rewicki, D., Chem. Ber., 1982,
vol. 115, p. 309; Padwa, A. and Goldstein, S.I., Canad. J.
Chem., 1984, vol. 62, p. 2506.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007

FEDOROV et al.
240
27. Nakano, Y., Hamaguchi, M., and Nagai, T., J. Org. Chem.,
1989, vol. 54, p. 5912.
for Crystallography, Wilson,A.J.C., Ed., Dordrecht: Kluwer
Academic Publ., 1992.
28. Closs, G.L. and Boll, W.A., Angew. Chem., Int. Ed., 1963,
vol. 2, p. 399; Franck-Neumann, M. and Buchecker, C.,
Tetrahedron Lett., 1969, p. 15; Day,A.C. and Inwood, R.N.,
J. Chem. Soc. C, 1969, p. 1065; Schrader, L., Chem. Ber.,
1971, vol. 104, p. 941; Baron, W.J., Hendrick, M.E.,
and Jones, M., J. Am. Chem. Soc., 1973, vol. 95, p. 6286.
29. Miller, J.B., J. Org. Chem., 1959, vol. 24, p. 560.
30. Borsche, W. and Hahn, H., Lieb. Ann., 1939, vol. 537,
p. 219.
35. Stewart, R.F., Davidson, E.R., and Simpson, W.T., J. Chem.
Phys., 1965, vol. 42, p. 3175.
36. Ibers, J.A. and Hamilton, W.C., Acta Crystallogr., 1964,
vol. 17, p. 781.
37. Creagh, D.C. and McAuley, W.J., in Intern. Tables for Crys-
tallography, Wilson, A. J.C., Ed., Dordrecht: KluwerAca-
demic Publ., 1992.
38. Creagh, D.C., Hubbell, J.H., in Intern. Tables for Crystal-
lography, Wilson,A. J.C., Ed., Dordrecht: KluwerAcademic
Publ., 1992.
39. Sheldrick, G.M., SHELXL97. Program for the Refinement
of Crystal Structures, Germany: University of Gottingen,
1997.
40. Parham, W.E. and Hasek, W.R., J. Am. Chem. Soc., 1954,
vol. 76, p. 935.
31. Hooft, R., KappaCCD Collect Software Nonius BV Delft,
The Nederlands, 1999.
32. Macromolecular Crystallography, PartA., Carter, C.W. Jr.
and Sweet, R.M., New York:Academic, Press, 1997, p. 307.
33. Altomare,A., Cascarano, G., Giacovazzo, C., Guagliardi,A.,
Burla, M.C., Polidori, G., and Camalli, M., SIR92. J. Appl.
Crystallogr., 1994, vol. 27, p. 435.
41. Nagy, J., Nyitrai, J., Kolonits, P., Lempert, K., and Gerge-
ly,A., et al., J. Chem. Soc., Perkin Trans. 1, 1988, p. 3267.
34. Maslen, E.N., Fox,A.G., and O’Keefe, M.A., in Intern. Tables
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 2 2007