Synthesis of perfluoroalkyl-substituted 4,5-dihydro-3H-pyrazolo[4,3-a] phenazines and tetrahydroimidazo[4,5-e]indazoles

Article abstract of DOI:10.1134/S1070428013030184

Oxidation of 1-aryl-3-perfluoroalkyl-6,7-dihydro-1H-indazol-4(5H)-ones with selenium dioxide in the presence of sulfuric acid in glacial acetic acid, followed by treatment of 6,7-dihydro-1H-indazole-4,5-diones thus obtained with an equimolar amount of o-phenylenediamine in ethanol or with a mixture of 4-fluorobenzaldehyde and ammonium acetate in acetic acid, gave 3-aryl-1-perfluoroalkyl-4,5-dihydro-3H-pyrazolo-[4,3-a]phenazines and 6-aryl-2-(4-fluorophenyl)-8-perfluoroalkyl-1(3),4,5,6-tetrahydroimidazo[4,5-e] indazoles, respectively.

Full text of DOI:10.1134/S1070428013030184

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 3, pp. 421–427. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © T.S. Khlebnikova, Yu.A. Piven’, A.V. Baranovskii, F.A. Lakhvich, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49,
No. 3, pp. 433–439.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on her jubilee
Synthesis of Perfluoroalkyl-Substituted
4,5-Dihydro-3H-pyrazolo[4,3-a]phenazines and Tetrahydro-
imidazo[4,5-e]indazoles
T. S. Khlebnikova, Yu. A. Piven’, A. V. Baranovskii, and F. A. Lakhvich
Institute of Bioorganic Chemistry, National Academy of Sciences of Belarus,
ul. Akademika Kuprevicha 5/2, Minsk, 220141 Belarus
e-mail: khlebnicova@iboch.bas-net.by
Received January 16, 2013
Abstract—Oxidation of 1-aryl-3-perfluoroalkyl-6,7-dihydro-1H-indazol-4(5H)-ones with selenium dioxide in
the presence of sulfuric acid in glacial acetic acid, followed by treatment of 6,7-dihydro-1H-indazole-4,5-di-
ones thus obtained with an equimolar amount of o-phenylenediamine in ethanol or with a mixture of 4-fluoro-
benzaldehyde and ammonium acetate in acetic acid, gave 3-aryl-1-perfluoroalkyl-4,5-dihydro-3H-pyrazolo-
[4,3-a]phenazines and 6-aryl-2-(4-fluorophenyl)-8-perfluoroalkyl-1(3),4,5,6-tetrahydroimidazo[4,5-e]in-
dazoles, respectively.
DOI: 10.1134/S1070428013030184
Indazole ring system and other fused pyrazole
systems constitute structural fragments of many com-
pounds that are base components of modern antiviral,
antitumor, and anti-inflammatory drugs, as well as of
agrochemicals [1]. Introduction of fluorine atoms or
fluoroalkyl groups into heterocyclic structures pro-
vides an important tool for optimization of their bio-
logical activity and extension of the spectrum of their
physiological effects [2]. The most promising synthetic
approach to fluorinated heterocyclic compounds is
based on the use of polyfunctional fluorine-containing
building blocks. We recently synthesized 3-polyfluoro-
alkyl-6,7-dihydro-1H-indazol-4(5H)-ones I [3] which
can be used as starting compounds for the preparation
of a number of biologically active polyfluoroalkyl-sub-
stituted heterocyclic systems. For example, 3-poly-
fluoroalkyl-7-(1H-1,2,3-triazol-1-yl)-6,7-dihydro-1H-
indazol-4(5H)-ones were obtained by 1,3-dipolar cy-
cloaddition of alkynes to 7-azido derivatives of I [4],
and the Ritter reaction afforded 4-acylaminotetrahy-
droindazoles [5]. Heterocyclic compounds containing
phenazine or imidazole fragment are also known to
exhibit a broad spectrum of biological activity, in
particular antiproliferative, antiviral, analgesic, anti-
inflammatory, etc. [6]. Therefore, incorporation of
such pharmacophoric fragments into the structure of
polyfluoroalkyl-substituted indazolones could enhance
their biological potential.
The goal of the present work was to synthesize
potentially biologically active perfluoroalkyl-substitut-
ed 4,5-dihydro-3H-pyrazolo[4,3-a]phenazines and
tetrahydroimidazo[4,5-e]indazoles. Cyclic α-diketones
are widely used in the synthesis of various fused nitro-
gen-containing heterocyclic systems [7]. We propose
to obtain the target compounds via transformation of
perfluoroalkyl-substituted 6,7-dihydro-1H-indazol-
4(5H)-ones Ia–If into α-diketones IIa–IIf, followed by
reaction of the latter with o-phenylenediamine or
4-fluorobenzaldehyde and ammonium acetate in acetic
acid (as source of ammonia).
The oxidation of Ia–If in acetic acid with 1.5 equiv
of finely ground selenium dioxide in the presence of
sulfuric acid according to [8] (5 days, room tempera-
ture) gave 6,7-dihydro-1H-indazole-4,5-diones IIa–IIf
in 54–71% yield. By heating compounds IIa–IIf with
an equimolar amount of o-phenylenediamine in boiling
ethanol for 4 h we obtained 76–82% of 4,5-dihydro-
3H-pyrazolo[4,3-a]phenazines IIIa–IIIf. 6,7-Dihydro-
1H-indazole-4,5-diones IIa–IIf reacted with 1 equiv of
421

KHLEBNIKOVA et al.
422
Scheme 1.
X
X
4'
5'
5'
Me
3'
X
Me
N
6'
4
6'
4'
3'
SeO2, H2SO4
AcOH
2'
1'
5
N
C6H4(NH2)2-o
Me
Me
Me
Me
7
3
6
1'
N
1N
7
4
N
N2
2'
6
5
8
N
N2
1
11
3
O
9
10
RF
IIIa–IIIf
Me Me
RF
RF
O
O
Ia–If
IIa–IIf
Me Me
H3
N
5''
3''
6''
N
4-FC6H4CHO
NH4OAc, AcOH
4
5
5'
2
4''
6'
F
F
4'
1''
X
X
IIa–IIf
6
N
N
N
2''
N
1'
1
H
3'
8
2'
N7
N
RF
RF
IVa–IVf
I– IV, X = H: RF = CF3 (a), C2F5 (b), C3F7 (c); X = F: RF = CF3 (d), C2F5 (e), C3F7 (f).
4-fluorobenzaldehyde and excess ammonium acetate
in boiling acetic acid (3 h) to produce tetrahydro-
imidazo[4,5-e]indazoles IVa–IVf in 67–88% yield.
proton in the imidazole ring. The presence of two
signals [intensity ratio ~(0.93–0.95):(0.07–0.05), 1H
in total] indicated that compounds IVa–IVf in DMSO
exist as mixtures of 3H- and 1H-tautomers.
The structure of compounds II–IV was confirmed
1
by their elemental compositions and IR and H, 13C,
In order to refine the structures of the synthesized
compounds and completely assign signals in their
NMR spectra, two-dimensional NMR experiments
were performed with compounds IIIc, IVa, and IVb.
Specific attention was given to the assignment of
signals from quaternary carbon atoms since identifica-
tion of protonated carbon atoms involved no dif-
ficulties. We also intended to localize the NH group in
the molecules of IVa and IVb which were shown to
exist as mixtures of tautomers, one tautomer strongly
prevailing. Quaternary carbon atoms were identified
by analysis of the HMBC spectra. It should be noted
that we observed neither NH proton signal nor signals
19
19
and F NMR spectra. The F NMR spectra of II–IV
contained a signal at δF –60.0 to –63.6 ppm due to
trifluoromethyl group, and perfluoroethyl and per-
fluoropropyl derivatives displayed signals in the regions
δF –82.4 to –83.4 (CF3), –109.1 to –112.1 ppm (CF2)
and δF –79.9 to –80.4 (CF3), –107.6 to –110.2 (CF2),
–124.8 to –126.0 ppm (CF2), respectively. In the IR
spectra of IIa–IIf we observed strong absorption bands
at 1705 and 1695 cm–1 belonging to stretching vibra-
tions of two carbonyl groups, methylene protons on C7
resonated in their 1H NMR spectra at δ 3.17–3.21 ppm,
and signals from the carbonyl carbon atoms appeared
13
1
in the C NMR spectra at δC 173.5–174.2 and 198.7–
from C3a and C8b in the H and 13C NMR spectra of
199.0 ppm. The IR spectra of phenazine derivatives
IIIa–IIIf lacked carbonyl absorption in the region
1705–1695 cm–1, but bands typical of C=N bonds were
present at 1615–1580 cm–1. Correspondingly, no
signals were observed in the region δC 173.5–
199.0 ppm of the 13C NMR spectra, but those typical
of C=N carbon atoms were located at δC 141.2–
157.6 ppm. The 1H NMR spectra of tetrahydroimidazo-
[4,5-e]indazoles IVa–IVf in DMSO-d6 contained
signals from protons in the methyl and methylene
groups and benzene rings, and signals at δ ~11.74–
12.03 and 12.32–12.35 ppm were assigned to NH
IVa in acetone-d6, and we succeeded in localizing
these signals only by very weak interactions with
methyl protons in the HMBC spectrum. However,
these signals were readily distinguishable in the
spectra recorded from DMSO-d6 solution. Analysis of
the HMBC spectra of IVa and IVb was necessary to
assign signals from C2, C3a, C5a, C8a, and C8b, while the
other carbon signals can readily be assigned on the
basis of one-dimensional spectra. The C8a signal ap-
peared in a strong field [9] and displayed a cross peak
with the 5-H proton. The C2 signal was identified by
couplings with ortho-protons in the aromatic ring and
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SYNTHESIS OF PERFLUOROALKYL-SUBSTITUTED 4,5-DIHYDRO-3H-PYRAZOLO[4,3-a]...
423
NH proton, and the C3a nucleus showed cross peaks
with protons of the methyl and methylene groups and
NH proton. A strong cross peak was observed between
C8b and proton on N3 in the imidazole ring, while the
cross peak of the same carbon nucleus with methylene
protons was weak. The C5a nucleus was coupled only
with the methylene protons. The HMBC data in com-
bination with the NOESY spectrum allowed us to
determine the position of the NH proton in the imid-
azole ring. As noted above, the NH proton showed
a strong coupling with C8b, whereas its cross peaks
with C2 and C3a had similar intensities. If that proton
were attached to N1, the stronger cross peak would be
observed with C3a. This conclusion is supported by the
presence of a weak cross peak between N3H and
methyl protons in the NOESY spectrum.
We failed to unambiguously assign C6a and C10a
signals in the HMBC spectrum of IIIc because of
overlap by signals from aromatic protons on C7–C10.
The C3a, C5a, C11a, and C11b signals were assigned on
the basis of the following considerations. As in the
spectra of IVa and IVb, the C11b nucleus in IIIc
resonated in a strong field and was coupled only with
protons on C4. The C3a and C5a nuclei showed cross
peaks with both methyl and methylene protons, but the
coupling of C5a with methyl protons was much
stronger. A weak cross peak was observed for C11a and
protons on C4. Signals from the other quaternary
carbon atoms were identified on the basis of their
couplings with fluorine nuclei.
The elemental analyses were obtained on a Euro-
Vector EA3000 CHNS-O analyzer. The progress of
reactions and purity of products were monitored by
TLC on Silufol UV–254 plates using ethyl acetate–
hexane as eluent. Column chromatography was per-
formed on silica gel (70–230 mesh; eluent ethyl
acetate–hexane). Polyfluoroalkyl-substituted indazol-
ones Ia–If were synthesized according to the proce-
dure described in [3].
Oxidation of indazolones Ia–If (general proce-
dure). Water, 1.5 mmol (0.03 g, 0.03 ml), was added to
1.5 mmol (0.17 g) of finely powdered selenium(IV)
oxide, 3 mmol (0.29 g, 0.16 ml) of concentrated sul-
furic acid was added, the mixture was stirred for
20 min, and a solution of 1 mmol of indazolone Ia–If
in 10 ml of glacial acetic acid was added to the
resulting suspension. The mixture was left to stand for
5 days at room temperature with intermittent shaking.
It was then treated with a mixture of 40 ml of 25%
aqueous ammonia and 20 g of ice and extracted with
chloroform (3×20 ml), the organic phase was separat-
ed, dried over anhydrous MgSO4, and filtered, the
solvent was removed under reduced pressure, and the
residue was subjected to column chromatography to
isolate indazole-4,5-diones IIa–IIf as colorless crystal-
line substances.
6,6-Dimethyl-1-phenyl-3-trifluoromethyl-6,7-
dihydro-1H-indazole-4,5-dione (IIa). Yield 68%,
mp 56–58°C. IR spectrum, ν, cm–1: 1705, 1695, 1505.
1H NMR spectrum, δ, ppm: 1.35 s (6H, CH3), 3.20 s
13
(2H, 7-H), 7.51–7.60 m (5H, Harom). C NMR spec-
trum, δC, ppm: 24.7 (6-CH3), 36.5 (C6), 46.2 (C7),
EXPERIMENTAL
1
117.9 (C3a), 120.0 q (CF3, JCF = 270 Hz), 124.6
The 1H, 19F, and 13C NMR spectra were recorded at
293 K on a Bruker Biospin Avance 500 spectrometer at
500.13, 470.59, and 125.77 MHz, respectively, using
a 5-mm QNP Z-gradient probe; chloroform-d was used
(Carom), 130.0 (Carom), 130.1 (Carom), 137.2 (Carom),
2
141.6 q (C3, JCF = 41 Hz), 149.5 (C7a), 174.3 (C4),
199.0 (C5). 19F NMR spectrum: δF –63.6 ppm (CF3).
Found, %: C 59.57; H 4.01; N 8.63. C16H13F3N2O2.
Calculated, %: C 59.63; H 4.07; N 8.69.
1
as solvent (unless otherwise stated); the H chemical
shifts were determined relative to tetramethylsilane
(CDCl3) or residual proton signal of the solvent
(acetone-d5, δ 2.05 ppm; DMSO-d5, δ 2.50 ppm); the
13C signals were measured relative to the solvent signal
(CDCl3, δC 77.16 ppm; acetone-d6, δC 29.84 ppm;
DMSO-d6, δC 39.52 ppm); α,α,α-trifluorotoluene was
6,6-Dimethyl-3-perfluoroethyl-1-phenyl-6,7-
dihydro-1H-indazole-4,5-dione (IIb). Yield 74%,
mp 46–48°C. IR spectrum, ν, cm–1: 1705, 1695, 1500.
1H NMR spectrum, δ, ppm: 1.34 s (6H, CH3), 3.21 s
13
(2H, 7-H), 7.52–7.59 m (5H, Harom). C NMR spec-
trum, δC, ppm: 24.6 (6-CH3), 36.5 (C6), 46.0 (C7),
19
1
2
used as external reference for F (δF –63 ppm). Two-
110.1 t.q (CF2, JCF = 253 Hz, JCF = 39 Hz), 118.7 q.t
(CF3, JCF = 287 Hz, JCF = 36 Hz), 119.1 (C3a), 124.6
1
2
dimensional shift correlation experiments (HSQC,
COSY, HMBC, NOESY) were performed according to
standard Bruker–Biospin procedures. The IR spectra
were recorded on a Bomem Michelson 100 instrument
from samples pelleted with KBr. The melting points
were determined on a Boetius melting point apparatus.
(Carom), 130.0 (Carom), 130.1 (Carom), 137.2 (Carom),
2
140.7 t (C3, JCF = 30 Hz), 149.6 (C7a), 173.9 (C4),
19
199.1 (C5). F NMR spectrum, δF, ppm: –83.4 (CF3),
–112.1 (CF2). Found, %: C 54.91; H 3.55; N 7.56.
C17H13F5N2O2. Calculated, %: C 54.84; H 3.52; N 7.52.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

KHLEBNIKOVA et al.
424
6,6-Dimethyl-3-perfluoropropyl-1-phenyl-6,7-
(6-CH3), 36.3 (C6), 45.9 (C7), 109.7 t.m (CF3CF2,
1
2
1JCF = 266 Hz), 110.0 t.t (3-CF2, JCF = 269 Hz, JCF
=
dihydro-1H-indazole-4,5-dione (IIc). Yield 71%,
mp 39–42°C. IR spectrum, ν, cm–1: 1705, 1695, 1500.
1H NMR spectrum, δ, ppm: 1.33 s (6H, CH3), 3.21 s
2
31), 117.2 d (C3′, C5′, JCF = 23 Hz), 117.8 q.t (CF3,
1JCF = 288 Hz, 2JCF = 34 Hz), 119.4 (C3a), 126.7 d (C2′,
13
3
4
(2H, 7-H), 7.52–7.61 m (5H, Harom). C NMR spec-
C6′, JCF = 9 Hz), 133.2 d (C1′, JCF = 2 Hz), 140.7 t
trum, δC, ppm: 24.5 (6-CH3), 36.4 (C6), 45.9 (C7),
(C3, JCF = 30 Hz), 149.6 (C7a), 163.2 d (C4′, JCF
=
2
1
252 Hz), 173.7 (C4), 198.8 (C5). 19F NMR spectrum,
δF, ppm: –80.4 (CF3), –109.7 (4′-F), –110.2 (CF2),
–126.0 (CF2). Found, %: C 49.17; H 2.79; N 6.40.
C18H12F8N2O2. Calculated, %: C 49.10; H 2.75; N 6.36.
1
108.9 t.m (CF3CF2, JCF = 266 Hz), 112.6 t.t (3-CF2,
2
1
1JCF = 255 Hz, JCF = 32), 118.0 q.t (CF3, JCF
=
288 Hz, 2JCF = 34 Hz), 119.3 (C3a), 124.6 (Carom), 130.0
(Carom), 130.1 (Carom), 137.1 (Carom), 140.6 t (C3, 2JCF
=
31 Hz), 149.6 (C7a), 173.8 (C4), 199.1 (C5). F NMR
spectrum, δF, ppm: –80.4 (CF3), –110.2 (CF2), –126.0
(CF2). Found, %: C 51.26; H 3.15; N 6.69.
C18H13F7N2O2. Calculated, %: C 51.19; H 3.10; N 6.63.
19
Pyrazolo[4,3-a]phenazines IIIa–IIIf (general
procedure). o-Phenylenediamine, 1 mmol (0.11 g), was
added to a solution of 1 mmol of α-diketone IIa–IIf in
20 ml of ethanol, and the mixture was heated for 4 h
under reflux. The solvent was removed under reduced
pressure, and the residue was purified by column
chromatography. Compounds IIIa–IIIf were isolated
as colorless crystals.
1-(4-Fluorophenyl)-6,6-dimethyl-3-trifluoro-
methyl-6,7-dihydro-1H-indazole-4,5-dione (IId).
Yield 66%, mp 75–78°C. IR spectrum, ν, cm–1: 1705,
1
1695, 1510. H NMR spectrum, δ, ppm: 1.35 s (6H,
CH3), 3.17 s (2H, 7-H), 7.27 m (2H, Harom), 7.52 m
5,5-Dimethyl-3-phenyl-1-trifluoromethyl-4,5-
dihydro-3H-pyrazolo[4,3-a]phenazine (IIIa). Yield
82%, mp 188–190°C. IR spectrum, ν, cm–1: 1615,
(2H, Harom). 13C NMR spectrum, δC, ppm: 24.7
2
(6-CH3), 36.4 (C6), 46.1 (C7), 117.2 d (C3′, C5′, JCF
=
23 Hz), 117.9 (C3a), 119.9 q (CF3, JCF = 270 Hz),
1
1
1580, 1505. H NMR spectrum, δ, ppm: 1.49 s (6H,
126.7 (C2′, C6′, JCF = 9 Hz), 133.2 (C1′, JCF = 2 Hz),
3
4
CH3), 3.13 s (2H, 4-H), 7.51 m (1H, Harom), 7.56 m
(4H, Harom), 7.67 m (2H, Harom), 8.00 m (1H, Harom),
141.7 q (C3, JCF = 40 Hz), 149.6 (C7a), 162.9 (C4′,
2
1JCF = 251 Hz), 174.1 (C4), 198.9 (C5). 19F NMR spec-
trum, δF, ppm: –63.6 (CF3), –109.7 (4′-F). Found, %:
C 56.40; H 3.51; N 8.19. C16H12F4N2O2. Calculated,
%: C 56.48; H 3.55; N 8.23.
13
8.08 m (1H, Harom). C NMR spectrum, δC, ppm: 27.8
(5-CH3), 36.0 (C4), 39.7 (C5), 116.1 (C11b), 121.3 q
1
(CF3, JCF = 269 Hz), 124.3 (Carom), 129.0 (Carom),
129.1 (Carom), 129.4 (Carom), 129.7 (Carom), 138.1
(Carom), 140.1 q (C1, 2JCF = 39 Hz), 141.0 (Carom), 141.4
(Carom), 142.5 (C11a), 144.0 (C3a), 157.7 (C5a). 19F NMR
spectrum: δF –62.4 ppm (CF3). Found, %: C 66.52;
H 4.28; N 14.17. C22H17F3N4. Calculated, %: C 67.00;
H 4.34; N 14.21.
1-(4-Fluorophenyl)-6,6-dimethyl-3-perfluoro-
ethyl-6,7-dihydro-1H-indazole-4,5-dione (IIe). Yield
64%, mp 119–120°C. IR spectrum, ν, cm–1: 1705,
1
1695, 1515. H NMR spectrum, δ, ppm: 1.34 s (6H,
CH3), 3.18 s (2H, 7-H), 7.28 m (2H, Harom), 7.53 m
(2H, Harom). 13C NMR spectrum, δC, ppm: 24.6
5,5-Dimethyl-1-perfluoroethyl-3-phenyl-4,5-
dihydro-3H-pyrazolo[4,3-a]phenazine (IIIb). Yield
76%, mp 111–113°C. IR spectrum, ν, cm–1: 1615,
1
(6-CH3), 36.3 (C6), 45.9 (C7), 109.8 t.q (CF2, JCF
=
253 Hz, 2JCF = 39 Hz), 117.2 d (C3′, C5′, 2JCF = 23 Hz),
1
2
1
118.6 q.t (CF3, JCF = 286 Hz, JCF = 36 Hz), 119.0
1580, 1505. H NMR spectrum, δ, ppm: 1.49 s (6H,
(C3a), 126.7 d (C2′, C6′, JCF = 9 Hz), 133.2 d (C1′,
3
CH3), 3.13 s (2H, 4-H), 7.50 m (1H, Harom), 7.56 m
(4H, Harom), 7.68 m (2H, Harom), 8.00 m (1H, Harom),
4JCF = 2 Hz), 140.8 t (C3, JCF = 32 Hz), 149.7 (C7a),
2
163.2 d (1JCF = 252 Hz), 173.8 (C4), 198.9 (C5).
19F NMR spectrum, δF, ppm: –83.4 (CF3), –109.7
(4′-F), –112.1 (CF2). Found, %: C 52.25; H 3.16;
N 7.12. C17H12F6N2O2. Calculated, %: C 52.32;
H 3.10; N 7.18.
13
8.07 m (1H, Harom). C NMR spectrum, δC, ppm: 27.7
1
(5-CH3), 36.0 (C4), 39.6 (C5), 111.3 t.q (CF2, JCF
=
253 Hz, JCF = 39 Hz), 117.6 (C11b), 119.4 q.t (CF3,
2
1JCF = 286 Hz, JCF = 36 Hz), 124.3 (Carom), 128.9
2
(Carom), 129.0 (Carom), 129.1 (Carom), 129.4 (Carom),
129.5 (Carom), 129.7 (Carom), 138.1 (Carom), 139.0 t (C1,
2JCF = 30 Hz), 140.9 (Carom), 141.4 (Carom), 142.5
(C11a), 143.9 (C3a), 157.8 (C5a). 19F NMR spectrum, δF,
ppm: –82.4 (CF3), –109.7 (CF2). Found, %: C 62.23;
H 3.90; N 12.64. C23H17F5N4. Calculated, %: C 62.16;
H 3.86; N 12.61.
1-(4-Fluorophenyl)-6,6-dimethyl-3-perfluoro-
propyl-6,7-dihydro-1H-indazole-4,5-dione (IIf).
Yield 54%, mp 46–49°C. IR spectrum, ν, cm–1: 1705,
1
1695, 1520. H NMR spectrum, δ, ppm: 1.34 s (6H,
CH3), 3.17 s (2H, 7-H), 7.28 m (2H, Harom), 7.53 m
(2H, Harom). 13C NMR spectrum, δC, ppm: 24.6
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

SYNTHESIS OF PERFLUOROALKYL-SUBSTITUTED 4,5-DIHYDRO-3H-PYRAZOLO[4,3-a]...
425
5,5-Dimethyl-1-perfluoropropyl-3-phenyl-4,5-
dihydro-3H-pyrazolo[4,3-a]phenazine (IIIc). Yield
80%, mp 133–135°C. IR spectrum, ν, cm–1: 1615,
N 12.09. C23H16F6N4. Calculated, %: C 59.74; H 3.49;
N 12.12.
3-(4-Fluorophenyl)-5,5-dimethyl-1-perfluoro-
1
1580, 1505. H NMR spectrum, δ, ppm: 1.48 s (6H,
propyl-4,5-dihydro-3H-pyrazolo[4,3-a]phenazine
(IIIf). Yield 87%, mp 105–106°C. IR spectrum, ν,
CH3), 3.13 s (2H, 4-H), 7.51 m (1H, Harom), 7.56 m
(4H, Harom), 7.66 m (2H, Harom), 8.01 m (2H, Harom).
13C NMR spectrum, δC, ppm: 27.6 (5-CH3), 36.0 (C4),
39.6 (C5), 109.3 t.m (CF3CF2, 1JCF = 267 Hz), 113.2 t.t
1
cm–1: 1615, 1580, 1510. H NMR spectrum, δ, ppm:
1.49 s (6H, CH3), 3.09 s (2H, 4-H), 7.26 m (2H, Harom),
7.55 m (2H, Harom), 7.68 m (2H, Harom), 8.02 m (2H,
1
2
(1-CF2, JCF = 255 Hz, JCF = 31), 117.9 (C11b),
Harom). 13C NMR spectrum, δC, ppm: 27.5 (5-CH3),
1
2
118.3 q.t (CF3, JCF = 288 Hz, JCF = 34 Hz), 124.4
(Carom), 128.9 (Carom), 129.1 (Carom), 129.4 (Carom),
129.5 (Carom), 129.7 (Carom), 138.1 (Carom), 139.0 t (C1,
2JCF = 30 Hz), 140.9 (Carom), 141.3 (Carom), 142.5
(C11a), 144.0 (C3a), 157.8 (C5a). 19F NMR spectrum, δF,
ppm: –80.4 (CF3), –107.8 (CF2), –124.8 (CF2). Found,
%: C 58.38; H 3.50; N 11.39. C24H17F7N4. Calculated,
%: C 58.30; H 3.47; N 11.33.
1
35.8 (C4), 39.4 (C5), 109.3 t.m (CF3CF2, JCF
=
1
2
267 Hz), 113.2 t.t (1-CF2, JCF = 255 Hz, JCF = 32),
116.6 d (C3′, C5′, JCF = 23 Hz), 117.8 (C11b), 118.3 q.t
2
(CF3, JCF = 288 Hz, JCF = 34 Hz), 126.2 d (C2′, C6′,
1
2
3JCF = 9 Hz), 128.8 (Carom), 129.0 (Carom), 129.3 (Carom),
134.1 d (C1′, JCF = 2 Hz), 138.9 t (C1, JCF = 29 Hz),
4
2
140.7 (Carom), 141.2 (Carom), 142.1 (C11a), 143.9 (C3a),
157.5 (C5a), 162.5 d (C4′, JCF = 250 Hz). 19F NMR
1
3-(4-Fluorophenyl)-5,5-dimethyl-1-trifluoro-
methyl-4,5-dihydro-3H-pyrazolo[4,3-a]phenazine
(IIId). Yield 78%, mp 159–161°C. IR spectrum, ν,
spectrum, δF, ppm: –80.4 (CF3), –107.8 (CF2), –111.7
(4′-F), 124.8 (CF2). Found, %: C 56.33; H 3.19;
N 10.98. C24H16F8N4. Calculated, %: C 56.26; H 3.15;
N 10.93.
1
cm–1: 1615, 1580, 1510. H NMR spectrum, δ, ppm:
1.49 s (6H, CH3), 3.09 s (2H, 4-H), 7.26 m (2H, Harom),
7.54 m (2H, Harom), 7.68 m (2H, Harom), 8.00 m (1H,
Tetrahydroimidazo[4,5-e]indazoles IVa–IVf
(general procedure). α-Diketone IIa–IIf, 1 mmol, was
dissolved in 10 ml of acetic acid, 1 mmol (0.12 g) of
4-fluorobenzaldehyde and 5 g of ammonium acetate
were added, and the mixture was heated for 3 h under
reflux. The mixture was cooled to room temperature
and poured into a mixture of 40 ml of 25% aqueous
ammonia and 20 g of ice. The precipitate was filtered
off and purified by column chromatography. Com-
pounds IVa–IVf were isolated as light brown crystal-
line substances.
H
arom), 8.08 m (1H, Harom). 13C NMR spectrum, δC,
ppm: 27.8 (5-CH3), 36.0 (C4), 39.7 (C5), 116.2 (C11b),
116.8 (C3′, C5′, JCF = 23 Hz), 121.3 q (CF3, JCF
=
2
1
269 Hz), 126.3 d (C2′, C6′, JCF = 9 Hz), 129.0 (Carom),
129.1 (Carom), 129.4 (Carom), 129.5 (Carom), 134.2 d (C1′,
4JCF = 2 Hz), 140.2 q (C1, 2JCF = 39 Hz), 141.0 (Carom),
141.4 (Carom), 142.4 (C11a), 144.0 (C3a), 157.6 (C5a),
3
162.6 d (C4′, JCF = 252 Hz). 19F NMR spectrum, δF,
1
ppm: –62.4 (CF3), –111.8 (4′-F). Found, %: C 64.01;
H 3.87; N 13.55. C22H16F4N4. Calculated, %: C 64.08;
H 3.91; N 13.59.
2-(4-Fluorophenyl)-4,4-dimethyl-8-trifluoro-
methyl-6-phenyl-3,4,5,6-tetrahydroimidazo[4,5-e]-
indazole (IVa). Yield 78%, mp 295–296°C. IR spec-
3-(4-Fluorophenyl)-5,5-dimethyl-1-perfluoro-
ethyl-4,5-dihydro-3H-pyrazolo[4,3-a]phenazine
(IIIe). Yield 80%, mp 144–147°C. IR spectrum, ν,
1
trum, ν, cm–1: 1635 br, 1600, 1530, 1505. H NMR
1
cm–1: 1615, 1580, 1510. H NMR spectrum, δ, ppm:
spectrum (DMSO-d6), δ, ppm: 1.31 s (6H, CH3), 3.01 s
(2H, CH2), 7.31 m (2H, Harom), 7.53 m (1H, Harom),
7.61 m (4H, Harom), 8.03 m (2H, Harom), 12.03 s (0.07H,
NH), 12.35 s (0.93H, NH). 13C NMR spectrum
(DMSO-d6), δC, ppm: 27.4 (4-CH3), 33.0 (C4), 36.9
(C5), 113.4 (C8a), 115.6 d (C3″, C5″, JCF = 22 Hz),
1.49 s (6H, CH3), 3.09 s (2H, 4-H), 7.26 m (2H, Harom),
7.54 m (2H, Harom), 7.68 m (2H, Harom), 8.01 m (1H,
H
arom), 8.07 m (1H, Harom). 13C NMR spectrum, δC,
ppm: 27.7 (5-CH3), 36.0 (C4), 39.6 (C5), 111.2 t.q
(CF2, JCF = 253 Hz, JCF = 39 Hz), 116.8 d (C3′, C5′,
1
2
1
121.9 q (CF3, JCF = 269 Hz), 124.1 (C2′, C6′), 127.0 d
2JCF = 23 Hz), 117.7 (C11b), 119.3 q.t (CF3, JCF
=
1
3
(C2′′, C6″, JCF = 8 Hz), 127.5 (C1″), 128.5 (C8b), 128.6
287 Hz, JCF = 37 Hz), 126.3 d (C2′, C6′, JCF = 9 Hz),
2
3
(C4′), 129.6 (C3′, C5′), 134.4 q (C8, 2JCF = 38 Hz), 134.8
(C3a), 138.2 (C1′), 139.4 (C5a), 144.4 (C2), 161.9 d (C4″,
1JCF = 245 Hz). 19F NMR spectrum (DMSO-d6), δF,
129.0 (Carom), 129.2 (Carom), 129.4 (Carom), 129.5
4
2
(Carom), 134.3 d (C1′, JCF = 2 Hz), 139.2 t (C1, JCF
=
31 Hz), 141.0 (Carom), 141.4 (Carom), 142.4 (C11a), 144.0
1
1
(C3a), 157.6 (C5a), 162.7 d (C4′, JCF = 250 Hz).
ppm: –60.0 (CF3), –114.4 (4″-F). H NMR spectrum
19F NMR spectrum, δF, ppm: –82.5 (CF3), –109.7
(CF2), –111.8 (4′-F). Found, %: C 59.69; H 3.46;
(acetone-d6), δ, ppm: 1.34 s (6H, CH3), 3.02 s (2H,
CH2), 7.18 m (2H, Harom), 7.51 m (1H, Harom), 7.59 m
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 3 2013

KHLEBNIKOVA et al.
426
(4H, Harom), 8.07 m (2H, Harom). 13C NMR spectrum
2,6-Bis(4-fluorophenyl)-4,4-dimethyl-8-trifluoro-
methyl-3,4,5,6-tetrahydroimidazo[4,5-e]indazole
(IVd). Yield 67%, mp 273–277°C. IR spectrum, ν,
(acetone-d6), δC, ppm: 27.7 (4-CH3), 34.2 (C4), 38.2
2
(C5), 114.0 br.s (C8a), 116.2 (C3″, C5″, JCF = 22 Hz),
1
123.0 q (CF3, JCF = 268 Hz), 125.0 (C2′, C6′), 128.0 d
1
cm–1: 1635 br, 1600, 1530, 1505. H NMR spectrum
3
(C2″, C6″, JCF = 8 Hz), 128.5 (C1″), 129.4 (C4′), 130.3
(DMSO-d6), δ, ppm: 1.31 s (6H, CH3), 2.99 s (2H,
CH2), 7.31 m (2H, Harom), 7.44 m (2H, Harom), 7.67 m
(2H, Harom), 8.03 m (2H, Harom), 12.03 s (0.07H, NH),
2
(C1′), 137.0 q (C8, JCF = 38 Hz), 139.8 (C1′), 140.3
1
(C5a), 145.7 (C2), 163.4 d (C4″, JCF = 246 Hz).
19F NMR spectrum (acetone-d6), δF, ppm: –61.4 (CF3),
–115.8 (4-F). Found, %: C 64.73; H 4.22; N 13.10.
C23H18F4N4. Calculated, %: C 64.78; H 4.25; N 13.14.
13
12.34 s (0.93H, NH). C NMR spectrum (DMSO-d6),
δ, ppm: 27.4 (4-CH3), 33.0 (C4), 36.7 (C5), 113.4 (C8a),
115.6 d (C3″, C5″, 2JCF = 22 Hz), 116.4 d (C3′, C5′, 2JCF
=
23 Hz), 121.9 q (CF3, 1JCF = 268 Hz), 126.5 d (C2′, C6′,
2-(4-Fluorophenyl)-4,4-dimethyl-8-perfluoro-
ethyl-6-phenyl-3,4,5,6-tetrahydroimidazo[4,5-e]in-
dazole (IVb). Yield 88%, mp 246–248°C. IR spec-
3
3JCF = 9 Hz), 127.0 d (C2″, C6″, JCF = 8 Hz), 127.4
2
(C1″), 128.5 (C8b), 134.3 q (C8, JCF = 38 Hz), 134.6
(C1′), 134.8 (C3a), 139.7 (C5a), 144.4 (C2), 161.6 d (C4′,
1JCF = 246 Hz), 161.8 d (C4″, 1JCF = 245 Hz). 19F NMR
spectrum (DMSO-d6), δF, ppm: –60.0 (CF3), –113.3
(F), 114.4 (F). Found, %: C 62.11; H 3.84; N 12.57.
C23H17F5N4. Calculated, %: C 62.16; H 3.86; N 12.61.
1
trum, ν, cm–1: 1635 br, 1600, 1530, 1505. H NMR
spectrum (DMSO-d6), δ, ppm: 1.31 s (6H, CH3), 3.03 s
(2H, CH2), 7.32 m (2H, Harom), 7.54 m (1H, Harom),
7.61 m (4H, Harom), 8.03 m (2H, Harom), 11.80 s (0.05H,
NH), 12.33 s (0.95H, NH). 13C NMR spectrum
(DMSO-d6), δC, ppm: 27.4 (4-CH3), 32.9 (C4), 36.9
2,6-Bis(4-fluorophenyl)-4,4-dimethyl-8-per-
fluoroethyl-3,4,5,6-tetrahydroimidazo[4,5-e]inda-
zole (IVe). Yield 71%, mp 246–247°C. IR spectrum, ν,
1
2
(C5), 111.4 t.q (CF2, JCF = 250 Hz, JCF = 38 Hz),
114.9 (C8a), 115.6 d (C3″, C5″, JCF = 22 Hz), 119.0
2
1
2
(CF3, JCF = 286 Hz, JCF = 39 Hz), 124.1 (C2′, C6′),
127.0 d (C2″, C6″, 3JCF = 6 Hz), 127.5 (C1″), 128.6 (C8b),
128.7 (C4′), 129.6 (C3′, C5′), 133.2 t (C8, 2JCF = 30 Hz),
135.0 (C3a), 138.2 (C1′), 139.4 (C5a), 144.2 (C2),
1
cm–1: 1635 br, 1600, 1530, 1505. H NMR spectrum
(DMSO-d6), δ, ppm: 1.31 s (6H, CH3), 3.00 s (2H,
CH2), 7.31 m (2H, Harom), 7.44 m (2H, Harom), 7.66 m
(2H, Harom), 8.03 m (2H, Harom), 11.80 s (0.07H, NH),
161.9 d (C4″, JCF = 245 Hz). 19F NMR spectrum
1
13
12.34 s (0.93H, NH). C NMR spectrum (DMSO-d6),
δC, ppm: 27.4 (4-CH3), 32.9 (C4), 36.8 (C5), 111.4 t.q
(DMSO-d6), δF, ppm: –82.7 (CF3), –109.1 (CF2),
–114.4 (4″-F). Found, %: C 60.57; H 3.84; N 11.80.
C24H18F6N4. Calculated, %: C 60.51; H 3.81; N 11.76.
1
2
(CF2, JCF = 250 Hz, JCF = 38 Hz), 114.9 (C8a),
115.6 d (C3″, C5″, 2JCF = 22 Hz), 116.5 d (C3′, C5′, 2JCF
=
1
2
22 Hz), 119.0 (CF3, JCF = 286 Hz, JCF = 39 Hz),
119.0 (CF3, 1JCF = 286 Hz, 2JCF = 39 Hz), 126.5 d (C2′,
C6′, 3JCF = 9 Hz), 127.0 d (C2″, C6″, 3JCF = 8 Hz), 127.5
2-(4-Fluorophenyl)-4,4-dimethyl-8-perfluoro-
propyl-6-phenyl-3,4,5,6-tetrahydroimidazo[4,5-e]-
indazole (IVc). Yield 70%, mp 183–185°C. IR spec-
(C1″), 128.6 (C8b), 133.2 t (C8, JCF = 30 Hz), 134.6
2
1
trum, ν, cm–1: 1635 br, 1600, 1530, 1505. H NMR
(C1′), 135.0 (C3a), 139.7 (C5a), 144.3 (C2), 161.7 d (C4′,
1JCF = 246 Hz), 161.9 d (C4″, 1JCF = 245 Hz). 19F NMR
spectrum (DMSO-d6), δF, ppm: –82.7 (CF3), –109.2
(CF2), –113.2 (F), –114.4 (F). Found, %: C 58.36;
H 3.41; N 11.37. C24H17F7N4. Calculated, %: C 58.30;
H 3.37; N 11.33.
spectrum (DMSO-d6), δ, ppm: 1.30 s (6H, CH3), 3.02 s
(2H, CH2), 7.31 m (2H, Harom), 7.53 m (1H, Harom),
7.60 m (4H, Harom), 8.02 m (2H, Harom), 11.74 s (0.05H,
NH), 12.32 s (0.95H, NH). 13C NMR spectrum
(DMSO-d6), δC, ppm: 27.3 (4-CH3), 32.9 (C4), 36.9
1
(C5), 108.7 t.m (CF3CF2, JCF = 265 Hz), 113.2 t.t
1
2
(8-CF2, JCF = 255 Hz, JCF = 31 Hz), 115.3 (C8a),
2,6-Bis(4-fluorophenyl)-4,4-dimethyl-8-per-
fluoropropyl-3,4,5,6-tetrahydroimidazo[4,5-e]inda-
zole (IVf). Yield 69%, mp 162–165°C. IR spectrum, ν,
115.6 d (C3″, C5″, JCF = 22 Hz), 117.8 q.t (CF3, JCF
=
2
1
2
287 Hz, JCF = 34 Hz), 124.1 (C2′, C6′), 126.9 d (C2″,
C6″, JCF = 8 Hz), 127.6 (C1″), 128.6 (C8b), 128.7 (C4′),
cm–1: 1635 br, 1600, 1530, 1505. H NMR spectrum
3
1
129.6 (C3′, C5′), 133.1 t (C8, JCF = 29 Hz), 135.0
(DMSO-d6), δ, ppm: 1.30 s (6H, CH3), 3.00 s (2H,
CH2), 7.32 m (2H, Harom), 7.45 m (2H, Harom), 7.66 m
(2H, Harom), 8.01 m (2H, Harom), 11.74 s (0.07H, NH),
2
(C3a, JCF = 2 Hz), 138.2 (C1′), 139.4 (C5a), 144.2 (C2),
4
161.8 d (C4″, JCF = 245 Hz). 19F NMR spectrum
1
13
(DMSO-d6), δF, ppm: –79.9 (CF3), –107.6 (CF2),
–114.5 (4″-F), –125.7 (CF2). Found, %: C 57.09;
H 3.47; N 10.67. C25H18F8N4. Calculated, %: C 57.04;
H 3.45; N 10.64.
12.32 s (0.93H, NH). C NMR spectrum (DMSO-d6),
δC, ppm: 27.4 (4-CH3), 32.8 (C4), 36.7 (C5), 108.7 t.m
1
1
(CF3CF22, JCF = 265 Hz), 113.2 t.t (8-CF2, JCF
=
255 Hz, JCF = 31 Hz), 115.2 (C8a), 115.6 d (C3″, C5″,
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SYNTHESIS OF PERFLUOROALKYL-SUBSTITUTED 4,5-DIHYDRO-3H-PYRAZOLO[4,3-a]...
427
2JCF = 22 Hz), 116.5 d (C3′, C5′, 2JCF = 22 Hz), 117.8 q.t
4. Khlebnikova, T.S., Piven’, Yu.A., Baranovskii, A.V., and
Lakhvich, F.A., Russ. J. Org. Chem., 2012, vol. 48,
p. 411.
5. Turks, M., Strakova, I., Gorovojs, K., Belyakov, S.,
Piven, Yu.A., Khlebnicova, T.S., and Lakhvich, F.A.,
Tetrahedron, 2012, vol. 68, p. 6131.
1
2
(CF3, JCF = 287 Hz, JCF = 34 Hz), 126.5 d C2′, C6′,
3
3JCF = 9 Hz), 126.9 d (C2″, C6″, JCF = 8 Hz), 127.5
2
(C1″), 128.5 (C8b), 133.1 t (C8, JCF = 30 Hz), 134.6
(C1′), 135.0 (C3a), 139.6 (C5a), 144.2 (C2), 161.7 d (C4′,
1JCF = 246 Hz), 161.8 d (C4″, 1JCF = 245 Hz). 19F NMR
spectrum (DMSO-d6), δF, ppm: –79.9 (CF3), –107.7
(CF2), –113.2 (F), –114.4 (F), –125.7 (CF2). Found, %:
C 55.21; H 3.17; N 10.33. C25H17F9N4. Calculated, %:
C 55.15; H 3.15; N 10.29.
6. Rewcastle, G.W., Denny, W.A., and Baguley, B.C.,
J. Med. Chem., 1987, vol. 30, p. 843; Wang, W.,
Préville, P., Morin, N., Mounir, S., Cai, W., and Sid-
diqui, A., Bioorg. Med. Chem. Lett., 2000, vol. 10,
p. 1151; Soliman, A.M., Mohamed, S.K., El Ren-
maily, M.A.A., and Abdel-Ghany, H., Eur. J. Med. Chem.,
2012, vol. 47, p. 138; Gaba, M., Singh, D., Singh, S.,
Sharma, V., and Gaba, P., Eur. J. Med. Chem., 2010,
vol. 45, p. 2245; Wang, L., Woods, K.W., Li, Q.,
Barr, K.J., McCroskey, R.W., Hannick, S.M., Gherke, L.,
Credo, R.B., Hui, Y.-H., Marsh, K., Warner, R., Lee, J.Y.,
Zielinski-Mozng, N., Frost, D., Rosenberg, S.H., and
Sham, H.L., J. Med. Chem., 2002, vol. 45, p. 1697.
7. Gavara, L., Saugues, E., Debiton, E., Anizon, F., and
Moreau, P., Tetrahedron, 2011, vol. 67, p. 1633;
Gavara, L., Saugues, E., Alves, G., Debiton, E.,
Anizon, F., and Moreau, P., Eur. J. Med. Chem., 2010,
vol. 45, p. 5520; Strakov, A.Ya., Tonkikh, N.N., Petro-
va, M.V., and Strakova, I.A., Khim. Geterotsikl. Soedin.,
1997, p. 1669; Strakova, I.A., Strakov, A.Ya., and
Petrova, M.V., Latv. Khim. Zh., 1994, p. 773.
8. Gudrinietse, E.Yu., Strakov, A.Ya., Strakova, I.A.,
Zitsane, D.R., and Ievin’sh, A.F., Dokl. Akad. Nauk SSSR,
1974, vol. 216, p. 1293; Strakova, I.A., Strakov, A.Ya.,
and Petrova, M.V., Khim. Geterotsikl. Soedin., 2005,
p. 1829.
9. De Mendoza, J., Garcia-Ochoa, S., Prados, P., and
Parra, E., Tetrahedron, 1986, vol. 42, p. 2377; Al-
bright, T.A., Evans, S., Kim, C.S., Labaw, C.S., Rus-
siello, A.B., and Schweizer, E.E., J. Org. Chem., 1977,
vol. 42, p. 3691; Elguero, J., Martinez, A., Singh, S.P.,
and Kumar, D., J. Heterocycl. Chem., 1991, vol. 28,
p. 647.
REFERENCES
1. Thangadurai, A., Mini, M., Wakode, S., Agrawal, S., and
Narasimhan, B., Med. Chem. Res., 2012, vol. 21, p. 1509;
Cerecetto, H., Gerpe, A., González, M., Arán, V.J., and
de Ocárizi, C.O., Mini-Rev. Med. Chem., 2005, vol. 5,
p. 869; Lamberth, C., Heterocycles, 2007, vol. 71,
p. 1467.
2. Fluorinated Heterocyclic Compounds: Synthesis, Chem-
istry, and Applications, Petrov, V.A., Ed., Hoboken, NJ:
Wiley, 2009; Furin, G.G., Ftorsoderzhashchie geterotsikli-
cheskie soedineniya. Sintez i primenenie (Fluorine-
Containing Heterocyclic Compounds: Synthesis and Ap-
plication), Novosibirsk: Nauka, 2001; Claramunt, R.M.,
Lopez, C., Lopez, A., Perez-Medina, C., Perez-Tor-
ralba, M., Alkorta, I., Elguero, J., Escames, G., and
Acuna-Castroviejo, D., Eur. J. Med. Chem., 2011, vol. 46,
p. 1439; Jeschke, P., Chem. Bio. Chem., 2004, vol. 5,
p. 571; Kirsch, P., Modern Fluoroorganic Chemistry,
Weinheim: Wiley–VCH, 2004; Isakova, V.G., Khlebniko-
va, T.S., and Lakhvich, F.A., Usp. Khim., 2010, vol. 79,
p. 929.
3. Khlebnikova, T.S., Isakova, V.G., and Lakhvich, F.A.,
Dokl. Nats. Akad. Navuk Belarusi, 2007, vol. 51, no. 6,
p. 55; Khlebnikova, T.S., Isakova, V.G., Baranov-
skii, A.V., and Lakhvich, F.A., Russ. J. Gen. Chem., 2008,
vol. 78, p. 1954.
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