Rearrangements of 3H-Pyrazoles—Adducts of Dimethyl Acetylenedicarboxylate with Diphenyldiazomethane and 9-Diazofluorene

Article abstract of DOI:10.1134/S1070428018060118

Structurally related 3H-pyrazoles resulting from 1,3-dipolar cycloaddition of diphenyldiazomethane and 9-diazofluorene to dimethyl acetylenedicarboxylate undergo van Alphen–Hüttel rearrangement on heating in a polar solvent (methanol, ethanol, acetic acid

Full text of DOI:10.1134/S1070428018060118

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2018, Vol. 54, No. 6, pp. 892–900. © Pleiades Publishing, Ltd., 2018.
Original Russian Text © V.A. Vasin, V.V. Razin, E.V. Bezrukova, Yu.A. Popkova, N.V. Somov, 2018, published in Zhurnal Organicheskoi Khimii, 2018,
Vol. 54, No. 6, pp. 890–897.
Rearrangements of 3H-Pyrazoles—Adducts of Dimethyl
Acetylenedicarboxylate with Diphenyldiazomethane
and 9-Diazofluorene
V. A. Vasin†a, V. V. Razinb, E. V. Bezrukovaa,* Yu. A. Popkovaa, and N. V. Somovc
a Ogarev Mordovian State University, ul. Bol’shevistskaya 68, Saransk, 430005 Russia
*e-mail: tadaakiyattsu@gmail.com
b St. Petersburg State University, Universitetskii pr. 26, St. Petersburg, 198504 Russia
c Lobachevskii Nizhny Novgorod State University, pr. Gagarina 23, Nizhny Novgorod, 603950 Russia
Received June 14, 2017
Abstract—Structurally related 3H-pyrazoles resulting from 1,3-dipolar cycloaddition of diphenyldiazomethane
and 9-diazofluorene to dimethyl acetylenedicarboxylate undergo van Alphen–Hüttel rearrangement on heating
in a polar solvent (methanol, ethanol, acetic acid). In the first case, the rearrangement involves strictly
regioselective 1,5-phenyl migration toward the carbon atom with the formation of relatively stable 4H-pyra-
zole. Post-rearrangement of the product on heating at 180°C in toluene gives a mixture of methyl 1H-pyrazole-
1-carboxylates via successive migrations of the CO2Me group. In the second case, the aryl substituent
concurrently migrates both to nitrogen atom with the formation of 1H-pyrazole structure (phenanthridine
derivative) and to carbon atom with subsequent rearrangement of unstable 4H-pyrazole to 3H-pyrazole fused to
phenanthrene fragment. Heating of dimethyl acetylenedicarboxylate adducts (3H-pyrazoles) in an aprotic
solvent (benzene, toluene) leads to the corresponding denitrogenation products. This process is especially facile
for the spirocyclic 3H-pyrazole derived from 9-diazofluorene, and it yields cyclopropene derivative. Some
previous errors in the structure determination of the rearrangement products have been corrected.
DOI: 10.1134/S1070428018060118
Two structurally related compounds 1 and 2 synthe-
sized via 1,3-dipolar cycloaddition of diphenyldiazo-
methane and 9-diazofluorene to dimethyl acetylenedi-
carboxylate [1, 2] have become the first and important
subjects of studies which have led to the discovery of
thermal transformations of 3H-pyrazoles currently
known as van Alphen–Hüttel rearrangement [3].
Interest in such transformations of 3H-pyrazoles per-
sists so far, and more complete interpretation of the
Alphen–Hüttel rearrangement has been proposed
[4–7]. Furthermore, its useful applications for organic
synthesis have been revealed [6–8].
In keeping with the modern concepts, the van
Alphen–Hüttel rearrangement of 3,3-disubstituted
3H-pyrazoles is considered as 1,5-sigmatropic shift of
substituent from the 3-position. The 3-substituent is
capable of migrating in two directions, with the forma-
tion of N-substituted 1H-pyrazole derivative or
4H-pyrazole; in some cases, the rearrangement in one
or another direction was highly regioselective [8, 9].
Seemingly, the results of rearrangement of com-
pounds 1 and 2 have been determined long ago and are
reliable. However, our recent studies on the isomeriza-
tion of structurally related 3H-pyrazoles [10–12]
prompted us to revise the results of thermal trans-
formations of pyrazoles 1 and 2. One of the reasons
was recently increased interest in so-called van
Alphen–Hüttel post-rearrangement. This process in-
volves further transformations of one product of the
E
E
N
N
N
N
E
E
1
2
†
Deceased.
Hereinafter, E = CO2Me.
892

REARRANGEMENTS OF 3H-PYRAZOLES
893
isomerization of 3H-pyrazole, 4H-pyrazole derivative.
Completely substituted 3H-pyrazole and 4H-pyrazole
are isomeric conjugated systems, so that a rearrange-
ment analogous to the rearrangement of 3H-pyrazole
may be quite admissible for 4-H-pyrazole. However,
available data on thermal transformations of 4H-pyra-
zoles are incommensurably poorer than the data on
analogous transformations of 3H-pyrazoles [9, 13].
The results of thermolysis of pyrazole 1 [1] were
rechecked for the first time by Baumes et al. [14]. It
was shown experimentally that 4H-pyrazole 3 is the
only product of the reaction in glacial acetic acid at
100°C. The authors revealed that van Alphen errone-
ously assigned the 1H-pyrazole structure 4 to the prod-
uct of thermolysis of compound 1. The data given in
[15], which seemingly confirmed van Alphen’s conclu-
sions, were in fact erroneous, as we reported in [12].
The results of [14] have aroused a keen interest in
the van Alphen–Hüttel rearrangement, and the forma-
tion of 4H-pyrazole derivatives, often together with
N-substituted 1H-pyrazoles, in the thermolysis of other
3H-pyrazoles was confirmed in a number of publica-
tions [16–33]. More recent studies on this topic were
reviewed in [8, 9] and reported in [34–41].
We reproduced the experiment described in [14]
and, in fact, obtained 4H-pyrazole 3 as the only prod-
uct on heating compound 1 in acetic acid (Scheme 1).
In our previous study [12], the thermolysis of 3H-pyr-
azole 1 in boiling toluene afforded compound 3 in
a mixture with a comparable amount of indene 5.
When the thermolysis was carried out in ethanol, the
amount of 5 was insignificant.
Taking into account that indene 5 (together with
isomeric cyclopropene derivative 6) can be synthesized
by photolysis of 3H-pyrazole 1 [42, 43], we repro-
duced the described procedure. By varying the tem-
perature, we found conditions under which not only
compounds 3 and 5 but also cyclopropene 6 were
13
detected by C NMR among the thermolysis products
of pyrazole 1 in benzene (~65–70°C). Special experi-
ment showed that cyclopropene 6 is quantitatively
converted to indene 5 on heating in boiling toluene. No
other thermolysis products, including hypothetical
N-phenyl-1H-pyrazole A (product of phenyl group
migration to nitrogen), were detected. We were the
first to observe thermal fragmentation of compound 1,
though analogous fragmentation accompanying van
Alphen–Hüttel rearrangement of other 3,3-diphenyl-
3H-pyrazoles was described previously [25, 28, 34,
41]. Thermal 3-phenylcyclopropene–indene isomeriza-
tion is also well known [34, 44–46].
We then studied for the first time high-temperature
transformations of 4H-pyrazole 3. This compound
turned out to be considerably more stable than 3H-pyr-
azole 1. The complete conversion of 3 was achieved
only on heating in toluene at 180°C in a microwave
furnace, and a mixture of N-methoxycarbonyl-1H-
pyrazoles 4 and 7 was formed; after heating in boiling
p-xylene for 10 h, the conversion of pyrazole 3 did not
exceed 12%.
Scheme 1.
E
N
∆
N
E
Ph
Ph
A
E
E
E
E
E
E
EtOH
80°C
PhMe
180°C
N
N
N
N
N
∆
H
Et2NH
1
E
N
N
N
N
N
Ph
Ph
E
Ph
Ph
Ph
Ph
E
Ph
Ph
Ph
Ph
3
B
7
4
8
Ph
Ph
Ph
∆, PhH
E
E
E
E
H
6
5
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

VASIN et al.
1H-Pyrazole 7 in toluene at 180°C was largely con-
894
C7
C8
C13
verted to isomer 4. Under the same conditions, only
≤10% of pure 1H-pyrazole 4 isomerized to 7. Thus,
1H-pyrazoles 4 and 7 are thermally interconvertible
via 1,5-sigmatropic rearrangement [47]. We believe
that the primary isomerization product of 4H-pyrazole
3 is 1H-pyrazole 7 which is transformed to more stable
isomer 4 under thermolysis conditions.
C14
C9
C6
C15
C12
C11
C4
C5
O4
C10
C3
C2
Frampton et al. [36] reported two products of
thermolysis of compound 9 (3,3-dimethyl analog of 1)
in benzene at 160°C. The major product was 1H-pyra-
zole 10 (an analog of 7) whose structure was reliably
proved by X-ray analysis. The other product was
assigned the structure of N-methyl-1H-pyrazole 11,
though, in our opinion, there were no sufficient
grounds for this assignment. We believe that the
second product was in fact compound 12, an analog of
4 (Scheme 2).
Thus, van Alphen [1] erroneously assigned the
structure of the thermolysis product of 3H-pyrazole 1
on the basis of indirect evidences, namely easy frag-
mentation of 1H-pyrazole 4 to monoester 8 by the
action of concentrated sulfuric acid [1]; as follows
from our results, analogous fragmentation of 4H-pyra-
zole 3 is also possible.
Now let us proceed with a spirocyclic analog of
3H-pyrazole 1, compound 2. According to van Alphen
[2], 3H-pyrazole 2 in acetic acid at 100°C is converted
to 1H-pyrazole 13, and fragmentation of 2 on treat-
ment with hot concentrated sulfuric acid gives 1H-pyr-
azole 14 (Scheme 3). It was also noted that compound
14 is not formed from 13. Reimlinger [48] later
reported that heating of 3H-pyrazole 2 in boiling ben-
zene leads only to denitrogenation with the formation
of cyclopropene 15. Mataka and Tashiro [32] deter-
mined the composition of the thermolysis products of
compound 2 in different solvents (methanol, ethanol,
acetonitrile, benzene, toluene). Cyclopropene deriva-
tive 15 was formed in an aprotic nonpolar solvent
(benzene or toluene), which confirmed the data of [48].
However, the thermolysis of 2 in polar solvents gave
compound 15 and three other nitrogen-containing com-
pounds which were identified as 3H-pyrazole 16 and
1H-pyrazoles 14 and 17.
C17
O1
N1
C1
C16
O3
C18
N2
O2
C19
Fig. 1. Structure of the molecule of dimethyl 4,5-diphenyl-
1H-pyrazole-1,3-dicarboxylate (7) according to the X-ray
diffraction data.
Pure compounds 4 and 7 were isolated from their
mixture by flash chromatography on silica gel. Com-
pound 7 was a crystalline solid, and isomer 4 was
liquid under normal conditions. Their structure was
confirmed by IR and H and 13C NMR spectra. The
1
structure of 7 was unambiguously determined by X-ray
analysis of its single crystal (Table 1, Fig. 1). Com-
pounds 4 and 7 can be regarded as carbamate deriva-
tives; they are relatively readily converted to known
1H-pyrazole 8 [12] by keeping at 20°C in diethyl ether
solution containing a small excess of diethylamine [6].
To rationalize the results of thermal isomerization
of 4H-pyrazole 3, we presumed that the methoxy-
carbonyl group, being more labile than phenyl substit-
uent [6], migrates from the 4-position to C5 rather
than C3 (1,5-sigmatropic shift) with the formation of
3H-pyrazole B. By analogy with the isomerization of
related 3H-pyrazoles [12], the observed regioselec-
tivity in the migration of the CO2Me group is likely
to be determined by the directing effect of the other
ester group on C3 [36]. We failed to detect presumed
intermediate B.
Scheme 2.
E
E
E
E
E
N
N
N
N
or
N
N
N
N
Me
E
Me
E
Me
E
Me
Me
Me
Me
11
Me
10
12
9
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

REARRANGEMENTS OF 3H-PYRAZOLES
895
Scheme 3.
E
E
E
N
N
N
13
E
H
N
E
E
N
N
N
N
E
E
N
N
E
2
C
16
17
14
E
E
15
We studied the thermolysis of 2 in acetic acid, as
well as its transformation in glacial acetic acid at 20°C
in the presence of a catalytic amount of concentrated
sulfuric acid. In the first case, we obtained three prod-
ucts, compounds 13, 14, and 17. Poorly soluble in-
dazole 14 was separated by filtration (yield 29%), and
The structure of 3H-pyrazole 16 was confirmed by
spectral data which were consistent with the data of
[32]. Unfortunately, we failed to isolate pure 1H-pyra-
zole 17 by chromatographic separation of its mixture
with 13 because of isomerization to 14. Therefore,
1
the H and 13C NMR spectra of 17 were obtained by
1
the filtrate contained (according to the H NMR data)
exclusion of signals belonging to 13 from the spectra
of their mixture (ratio 17:13 1:3).
compounds 13 and 17 at a ratio of 3:1, which were
difficult to separate. In the second case, the only prod-
uct was indazole 14 which was likely to be formed as
a result of hydrolysis of 17 during the isolation proce-
dure. Indazole 14 was also reported as the only product
of thermolysis of 2 in acetic acid at 100°C [20]. The
structure of 14 was confirmed by spectral data.
C13
C12
C14
C15
C5
C6
C7
C11
C10
C4
N1
When 3H-pyrazole 2 was heated in boiling metha-
nol, a mixture of four compounds was formed. Inda-
zole 14 precipitated from the reaction mixture and was
separated by filtration (yield 32%). According to the
13C NMR data, the filtrate contained cyclopropene
derivative 15 identical to a sample obtained by
thermolysis in benzene. The remaining two products
were isolated in the pure state by flash chroma-
tography. One of them was 3H-pyrazole 16 (in agree-
ment with the data of [32]), and the second had the
C3
N2
C1
C9
O1
C18
C8
C19
C2
O3
C16
O2
O4
1
13
C17
melting point and H and C NMR spectra coinciding
with those given in [32] for compound 17; however,
in fact, it was 1H-pyrazole 13 whose structure was
determined by X-ray analysis of its single crystal
(Table 1, Fig. 2).
Fig. 2. Structure of the molecule of dimethyl pyrazolo[1,5-f]-
phenanthridine-2,3-dicarboxylate (13) according to the X-ray
diffraction data.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

VASIN et al.
896
Scheme 4.
E
E
N
E
E
E
E
E
E
190°C
to N2
190°C
to C4
E
N
N
N
E
N
N
N
N
N
N
19
18
20
Thus, unlike compound 1, the van Alphen–Hüttel
rearrangement of 3H-pyrazole 2 follows two alter-
native paths. 1,5-Sigmatropic shift toward the N2 atom
gives thermally stable phenanthridine derivative 13,
whereas the shift toward C4 leads to the formation of
thermally unstable 4H-pyrazole C which undergoes
post-rearrangement via 1,5-migration of the methoxy-
carbonyl group, yielding new 3H-pyrazole 16. Pre-
sumably, apart from the high mobility of the CO2Me
group, the low thermal stability of 4H-pyrazole C and
its fast rearrangement to 3H-pyrazole 16 are deter-
mined by stabilizing effect due to formation of aro-
matic phenanthrene system. Compound 16 undergoes
partial fragmentation to monoester 14, seemingly
through 1H-pyrazole 17 which is unstable in boiling
methanol.
reference (CHCl3, δ 7.26 ppm; CDCl3, δC 77.16 ppm).
The IR spectra were recorded in KBr on an InfraLYuM
FT-02 spectrometer with Fourier transform. The ele-
mental analyses were obtained with a Vario MICRO
CHNS analyzer. Sorbfil plates were used for analytical
TLC (light petroleum ether–acetone, 4:1); spots were
visualized by treatment with iodine vapor. Flash
chromatography was performed on Merck 60 silica gel
(0.040–0.063 mm); eluent light petroleum ether–
acetone, 7:1 to 3:1. Dimethyl acetylenedicarboxylate
was commercial product (from Aldrich).
Thermolysis of 3H-pyrazole 1 in benzene. A solu-
tion of 0.5 g (1.5 mmol) of 3H-pyrazole 1 [12] in
12 mL of anhydrous benzene was refluxed for 1 h.
A mixture of 4H-pyrazole 3 and indene 5 at a ratio of
1.6:1 was formed. By flash chromatography on silica
gel (petroleum ether–ethyl acetate, 4:1) we isolated
0.29 g (58%) of 3 and 0.18 g (36%) of 5. The melting
According to [40], the thermolysis of bicyclic
3H-pyrazole 18 (an analog of 2) in benzene at 190°C
(60 min) leads to the formation of compounds 19 and
20 (Scheme 4) which are analogous to 13 and 17.
1
points and H and 13C NMR spectra of the isolated
compounds coincided with those given in [12].
The pronounced tendency to fragmentation of
3H-pyrazole 2 during the thermolysis in benzene (in
comparison to pyrazole 1) may be explained by the
greater stability of diazo compound D which mediates
the denitrogenation process [29] due to the presence of
9-fluorenyl anion fragment (cf. structure E derived
from 1). No cyclopropene derivatives were detected
in the thermolysis of 3H-pyrazole 18 and 3,3-dialkyl
analogs of 1 [36], for which the corresponding
denitrogenation intermediates are less stable than not
only structure D but also E.
By heating 3H-pyrazole 1 in benzene at 65–70°C
for 1 h we obtained a mixture of compounds 1, 3, 5,
and 6 at a ratio of 0.5:1.8:1:0.3.
Thermolysis of 3H-pyrazole 1 in acetic acid.
A solution of 0.3 g (0.9 mmol) of 3H-pyrazole 1 in
8 mL of glacial acetic acid was heated for 1 h at
100°C. The mixture was cooled, diluted with 10 mL of
water, and extracted with diethyl ether (3×15 mL).
The extract was washed with an aqueous solution of
sodium hydrogen carbonate and water and dried over
MgSO4, and the solvent was removed on a rotary
evaporator to isolate 0.19 g (63%) of 4H-pyrazole 3.
Thermal isomerization of cyclopropene deriva-
tive 6. A solution of 0.1 g (0.3 mmol) of compound 6
[43] in 10 mL of anhydrous toluene was refluxed for
3 h (until the initial compound disappeared according
to the TLC data). Crystallization from light petroleum
ether gave 84 mg (84%) of 5.
E
E
N
N
N
N
E
E
D
E
Thermolysis of 4H-pyrazole (3). A solution of
0.1 g (0.3 mmol) of 4H-pyrazole 3 in 4 mL of anhy-
drous toluene was heated for 2 h at 180°C in a micro-
wave reactor. The solvent was removed under reduced
pressure, and the residue was a mixture of 1H-pyra-
EXPERIMENTAL
The H and 13C NMR spectra were recorded on
a Jeol JNM-ECX400 spectrometer at 400.1 and
100.6 MHz, respectively, using CDCl3 as solvent and
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

REARRANGEMENTS OF 3H-PYRAZOLES
897
Table 1. Crystallographic data, parameters of X-ray diffrac-
tion experiments, and structure refinement parameters for
compounds 7 and 13
zoles 4 and 7 at a ratio of 2 :1 (according to the
1H NMR data). The product mixture was separated by
flash chromatography on silica gel.
Dimethyl 3,4-diphenyl-1H-pyrazole-1,5-dicar-
boxylate (4). Yield 59 mg (60%), colorless oily mate-
rial. IR spectrum, ν, cm–1: 1763 v.s (C=O), 1740 v.s
(C=O), 1466 v.s, 1447 s, 1350 v.s, 1320 s, 1269 s,
1219 v.s, 1181 m, 1065 s, 980 m, 965 m, 760 m, 698 s.
1H NMR spectrum, δ, ppm: 3.84 s (3H, OMe), 4.04 s
(3H, OMe), 7.24–7.27 m (3H, Harom), 7.28–7.33 m
Parameter
Formula
Molecular weight
Appearance
7
13
C19H16N2O4
336.34
C19H14N2O4
334.32
Needles
Prisms
Crystal dimensions,
0.238×0.151× 0.514×0.334×
mm
0.115
0.152
Monoclinic
P21/c
13
(5H, Harom), 7.40–7.43 m (2H, Harom). C NMR spec-
Crystal system
Space group
Temperature, K
Z
a, Å
b, Å
c, Å
α, deg
β, deg
Triclinic
trum, δC, ppm: 53.4 (OMe), 55.6 (OMe), 124.4 (C4),
128.41 (CHarom), 128.44 (2C, Carom), 128.6 (2C, Carom),
128.8 (2C, Carom), 129.2 (CHarom), 129.6 (Carom),
129.7 (2C, Carom), 130.8 (Carom), 135.6 (C3), 149.7 (C5),
153.8 (C=O), 161.8 (C=O). Found, %: C 67.97;
H 4.71; N 8.42. C19H16N2O4. Calculated, %: C 67.85;
H 4.79; N 8.33.
–
P1
297(2)
297(2)
2
4
09.6641(4)
10.3573(4)
10.5328(5)
117.634(4)
110.058(4)
094.538(3)
840.65(7)
1.329
12.653(3)0
07.2325(5)
23.507(4)0
90
132.96(3)
90
1574.2(7)
1.411
0.101
Dimethyl 4,5-diphenyl-1H-pyrazol-1,3-dicarbox-
ylate (7). Yield 32 mg (30%), colorless crystals,
mp 194–195°C (from diethyl ether). IR spectrum, ν,
cm–1: 1775 v.s (C=O), 1732 v.s (C=O), 1466 m,
1447 m, 1435 m, 1343 m, 1308 v.s, 1204 s, 1173 m,
g, deg
V, Å3
d
calc, g/cm3
1
1142 m, 992 m, 845 m, 768 m, 706 m. H NMR spec-
μ, mm–1
0.095
trum, δ, ppm: 3.88 s (3H, OMe), 3.98 s (3H, OMe),
7.13–7.15 m (2H, Harom), 7.19–7.24 m (5H, Harom),
7.29–7.35 m (3H, Harom). 13C NMR spectrum, δC, ppm:
52.5 (OMe), 55.4 (OMe), 126.8 (C4), 127.8 (CHarom),
127.9 (2C, Carom), 128.1 (2C, Carom), 129.05 (Carom),
129.14 (CHarom), 129.9 (Carom), 130.0 (2C, Carom), 130.4
(2C, Carom), 144.01 (C3), 145.4 (C5), 149.8 (C=O),
162.0 (C=O). Found, %: C 67.89; H 4.88; N 8.27.
C19H16N2O4. Calculated, %: C 67.85; H 4.79; N 8.33.
Correction for absorption, Multiscan [55], Multiscan [55],
T
min/Tmax
0.82336/1
352
2.31–30.506 3.573–30.739
–13 ≤ h ≤ 13
–14 ≤ k ≤ 14
–15 ≤ l ≤ 15
0.451/1
696
F(000)
Range of θ, deg
Reflection indices
–16 ≤ h ≤ 16
–9 ≤ k ≤ 9
–31 ≤ l ≤ 31
Total number of
reflections
32735
55024
3908
2960
Mutual transformations of 1H-pyrazoles 4
and 7. a. A solution of 50 mg (0.15 mmol) of
1H-pyrazole 4 in 4 mL of anhydrous toluene was
heated at 180°C for 30 min. The product was a mixture
of compounds 4 and 7 at a ratio of 9:1.
Number of independent
5110
reflections
Number of reflections
3568
with I > 2σ(I)
b. A solution of 50 mg (0.15 mmol) of 1H-pyrazole
7 in 4 mL of anhydrous toluene was heated at 180°C
for 40 min. The solvent was removed. According to the
1H NMR data, the residue contained 1H-pyrazoles 4
and 7 at a ratio of 35:65.
Reaction of 1H-pyrazoles 4 and 7 with diethyl-
amine. A mixture of 1H-pyrazoles 4 and 7 (1.8:1),
0.1 g (0.3 mmol), and 67 mg (0.9 mmol) of diethyl-
amine in 5 mL of anhydrous diethyl ether was stirred
at 20°C for 20 h. Volatile components were removed
under reduced pressure (water-jet pump) to isolate
63 mg (77%) of 1H-pyrazole 8 as colorless crystals.
Rint
0.0385
290
1.069
0.0597
260
1.025
Number of variables
Goodness of fit
R [F2 > 2σ(F2)]
R1 = 0.0494
R1 = 0.0457
wR2 = 0.1399 wR2 = 0.1124
R (all reflections)
R1 = 0.0745
R1 = 0.0628
wR2 = 0.1509 wR2 = 0.1206
Residual electron density –0.235/0.299
–0.175/0.22
(min/max), ē/A3
Software
SHELX2014 [50],
WINGX [51], CrysAlisPro [52]
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

VASIN et al.
898
1
The melting point and NMR spectra of 8 coincided
1219 v.s, 1142 m, 1069 m, 760 s. H NMR spectrum,
δ, ppm: 4.04 s (3H, OMe), 4.05 (3H, OMe), 7.49–
7.56 m (2H, Harom), 7.61 br.t (2H, Harom, J = 7.8 Hz),
8.28–8.31 m (2H, Harom), 8.46 d (1H, Harom, J =
8.0 Hz), 8.61 d (1H, Harom, J = 8.2 Hz). 13C NMR spec-
trum, δC, ppm: 52.9 (OCH3), 53.0 (OCH3), 110.4,
117.4 (CHarom), 122.0, 122.6, 122.8 (CHarom), 123.3
(CHarom), 125.7 (CHarom), 126.8 (CHarom), 127.7, 128.6
(CHarom), 129.6 (CHarom), 129.8 (CHarom), 132.7, 136.2,
143.7, 162.8 (C=O), 165.5 (C=O). Found, %: C 58.39;
H 4.34; N 8.31. C19H14N2O4. Calculated, %: C 68.26;
H 4.22; N 8.38.
with those reported in [12].
Dimethyl spiro[fluorene-9,3′-pyrazole]-4′,5′-di-
carboxylate (2) was synthesized according to the
procedure described in [2]. Yield 86%, mp 124–125°C;
published data [2]: mp 110°C (decomp.). IR spectrum,
ν, cm–1: 1740 v.s (C=O), 1628 m, 1451 m, 1339 m,
1273 s, 1142 m, 1107 m, 995 m, 822 m, 756 m.
1H NMR spectrum, δ, ppm: 3.56 (OMe), 4.08 (OMe),
6.82 d (2H, Harom, J = 7.6 Hz), 7.26 t (2H, Harom, J =
7.5 Hz), 7.48 t (2H, Harom, J = 7.4 Hz), 7.81 d (2H,
H
arom, J = 7.5 Hz). 13C NMR spectrum, δC, ppm: 53.13
(OMe), 53.36 (OMe), 109.8 (C3), 121.2 (2C, CHarom),
123.9 (2C, CHarom), 128.5 (2C, CHarom), 130.6 (2C,
CHarom), 132.7 (2C, Carom), 143.7 (2C, Carom), 148.57
(Carom), 148.72 (Carom), 160.3 (C=O), 161.8 (C=O).
Methyl 1(2)H-dibenzo[e,g]indazole-3-carbox-
ylate (14). Yield 0.13 g (32%), colorless crystals,
mp 294–295°C; published data: mp 298°C [2], 297–
298°C [20]. IR spectrum, ν, cm–1: 3191 w.br (NH),
1717 v.s (C=O), 1439 w, 1277 w, 1134 m, 1088 w,
Dimethyl spiro[cycloprop-2-ene-1,9′-fluorene]-
2,3-dicarboxylate (15) was synthesized according to
[32] by heating 0.4 g (1.2 mmol) of 3H-pyrazole 2 in
15 mL of benzene for 1 h under reflux. The product
was isolated by crystallization from methanol. Yield
0.27 g (74%), yellowish crystals, mp 150–151°C; pub-
lished data: mp 151–154°C (from EtOH) [48]; 146°C
[49]. IR spectrum, ν, cm–1: 1855 w (C=C, cyclo-
propene), 1732 v.s (C=O), 1435 m, 1265 s, 1130 w.
1H NMR spectrum, δ, ppm: 3.72 s (6H, OMe), 7.27 d
(2H, Harom, J = 7.6 Hz), 7.34 t (2H, Harom, J = 7.4 Hz),
7.44 t (2H, Harom, J = 7.4 Hz), 7.84 d (2H, Harom, J =
1
1015 w, 810 w, 760 s, 725 w. H NMR spectrum
(DMSO-d6), δ, ppm: 4.01 s (3H, OMe), 7.59 t (1H,
Harom, J = 7.1 Hz), 7.61–7.74 m (3H, Harom), 8.57 d
(1H, Harom, J = 7.5 Hz), 8.72 br.t (2H, Harom, J =
6.6 Hz), 9.36 d (1H, Harom, J = 8.0 Hz). 13C NMR spec-
trum (DMSO-d6), δC, ppm: 51.95 (OMe), 115.7
(Carom), 121.4 br.s (Carom), 122.2 (CHarom), 123.6
(CHarom), 123.8 (CHarom), 126.00 (Carom), 126.02
(CHarom), 126.4 (CHarom), 127.3 (CHarom), 127.5
(CHarom), 127.7 (CHarom), 128.2 (Carom), 129.6 (Carom),
135.7 br.s (Carom), 139.5 br.s (Carom), 163.4 (C=O).
Found, %: C 73.77; H 4.47; N 10.01. C17H12N2O2.
Calculated, %: C 73.90; H 4.38; N 10.14.
13
7.5 Hz). C NMR spectrum, δC, ppm: 44.2 (C3′), 53.3
(2C, OMe), 120.3 (2C, CHarom), 121.0 (2C, Carom),
121.5 (2C, CHarom), 127.2 (2C, CHarom), 128.1 (2C,
CHarom), 140.6 (2C, Carom), 144.4 (C2=C3), 158.2
(2C, C=O).
Dimethyl 3H-dibenzo[e,g]indazole-3,3-dicarbox-
ylate (16). Yield 50 mg (10%), colorless crystals,
mp 174–175°C; published data [32]: mp 168–169°C.
IR spectrum, ν, cm–1: 1763 v.s, 1451 m, 1439 m,
1258 s, 1235 v.s, 1053 s, 752 m, 721 m. 1H NMR spec-
trum, δ, ppm: 3.81 s (6H, OCH3), 7.73 t (1H, Harom, J =
Thermolysis of 3H-pyrazole 2 in methanol. A so-
lution of 0.5 g (1.5 mmol) of 3H-pyrazole 2 in 20 mL
of methanol was refluxed for 3 h. The precipitate of
1H-pyrazole 14 was filtered off, the filtrate was diluted
with 20 mL of diethyl ether, and the precipitate of
phenanthridine 13 was filtered off. The residue was
subjected to flash chromatography on silica gel to
isolate pure indazole 15.
In an analytical experiment, the reaction mixture
obtained after thermolysis was evaporated under
reduced pressure (water-jet pump). According to the
1H NMR data, the residue contained compounds 13–16
at a ratio of 1.27:0.3:1:1.33.
7.1 Hz), 7.79–7.89 m (3H, Harom), 8.34 d (1H, Harom
,
J = 8.2 Hz), 8.76–8.80 m (2H, Harom), 9.09–9.13 m
(1H, Harom). 13C NMR spectrum, δC, ppm: 54.3 (2C,
OCH3), 104.5 (C3), 123.4 (CH), 123.8 (CHarom), 124.5,
124.7 (CHarom), 126.3, 128.2 (CHarom), 128.4 (CHarom),
128.8 (2C, CHarom), 129.1 (CHarom), 132.0, 132.52
(Carom), 132.54 (Carom), 153.9, 163.2 (2C, C=O).
Found, %: C 68.39; H 4.37; N 8.26. C19H14N2O4. Cal-
culated, %: C 68.26; H 4.22; N 8.38.
Thermolysis of 3H-pyrazole 2 in acetic acid.
A solution of 0.5 g (1.5 mmol) of 3H-pyrazole 2 in
15 mL of glacial acetic acid was heated for 2 h at
100°C. After cooling, the precipitate was filtered off,
washed with water, and dried under reduced pressure;
we thus isolated 145 mg (29%) of 14. The filtrate was
Dimethyl pyrazolo[1,5-f]phenanthridine-2,3-di-
carboxylate (13). Yield 0.21 g (41%), colorless crys-
tals, mp 153–154°C (from MeOH). IR spectrum, ν,
cm–1: 1724 s (C=O), 1543 m, 1447 m, 1277 m,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 54 No. 6 2018

REARRANGEMENTS OF 3H-PYRAZOLES
899
diluted with 15 mL of water and extracted with diethyl
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