Five-membered 2,3-dioxo heterocycles: LXI. Reaction of 3-aroyl-1H- pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with α-enamino esters. Crystalline and molecular structure of methyl 11-benzoyl-2-o-hydroxyphenyl-3,4, 10-trioxo-6,9-diphenyl-7-oxa-2,9-diazatr

Article abstract of DOI:10.1134/S1070428008080137

3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones react with methyl 4-aryl-2-arylamino-4-oxobut-2-enoate to give substituted methyl 7-aryl-4,9-bis(aroyl)-3-hydroxy-1-(2-hydroxyphenyl)-2,6-dioxo-1,7-diazaspiro[4. 4]nona-3,8-diene-8-carboxylates which

Full text of DOI:10.1134/S1070428008080137

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2008, Vol. 44, No. 8, pp. 1184–1189. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © N.L. Racheva, Z.G. Aliev, A.N. Maslivets, 2008, published in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 8, pp. 1197–1201.
Five-Membered 2,3-Dioxo Heterocycles:
LXI.* Reaction of 3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-
1,2,4-triones with α-Enamino Esters. Crystalline and Molecular
Structure of Methyl 11-Benzoyl-2-o-hydroxyphenyl-3,4,10-trioxo-
6,9-diphenyl-7-oxa-2,9-diazatricyclo[6.2.1.01,5]undec-5-ene-
8-carboxylate
N. L. Rachevaa, Z. G. Alievb, and A. N. Maslivetsa
a Perm State University, ul. Bukireva 15, Perm, 614990 Russia
e-mail: koh2@psu.ru
b Institute of Chemical Physics Problems, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia
Received January 9, 2008
Abstract—3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones react with methyl 4-aryl-2-arylamino-4-
oxobut-2-enoate to give substituted methyl 7-aryl-4,9-bis(aroyl)-3-hydroxy-1-(2-hydroxyphenyl)-2,6-dioxo-
1,7-diazaspiro[4.4]nona-3,8-diene-8-carboxylates which undergo thermal cyclization to methyl 9-aroyl-4,7-di-
aryl-1-(2-hydroxyphenyl)-2,3,8-trioxo-2,3,7,8-tetrahydro-1H,6H-6,8a-methanopyrrolo[2,3-e][1,3]oxazepine-6-
carboxylates. The crystalline and molecular structures of methyl 9-benzoyl-1-(2-hydroxyphenyl)-2,3,8-trioxo-
4,7-diphenyl-2,3,7,8-tetrahydro-1H,6H-6,8a-methanopyrrolo[2,3-e][1,3]oxazepine-6-carboxylate was studied
by X-ray analysis.
DOI: 10.1134/S1070428008080137
Substituted 4-acyl-2,3-dihydro-1H-pyrrole-2,3-di-
ones, including those fused at the [a] side to nitrogen-
containing heterocycles (hetareno[a]pyrrole-2,3-di-
ones), are capable of reacting with difunctional nu-
cleophiles to produce a broad spectrum of fused and
spiro-fused heterocyclic systems [2, 3]. We previously
showed that 4-acyl-2,3-dihydro-1H-pyrrole-2,3-diones
fused to a 1,4-benzoxazine fragment, namely 3-aroyl-
1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones react
with acyclic enamino ketones and β-enamino esters as
1,3-C,N-binucleophiles according to a scheme includ-
ing successive attacks by the β-CH and NH groups of
the enamine on the C3a and C4 atoms of pyrrolobenz-
oxazinetrione, respectively. These reactions are accom-
panied by opening of the 1,4-oxazine ring at the C4–O5
bond and lead to the formation of substituted 4-aroyl-
3-hydroxy-1-(o-hydroxyphenyl)-1,7-diazaspiro[4.4]-
nona-3,8-diene-2,6-diones and alkyl 4-aroyl-3-hy-
droxy-1-(2-hydroxyphenyl)-2,6-dioxo-1,7-diazaspiro-
[4.4]nona-3,8-diene-9-carboxylates [4, 5].
In continuation of our studies on reactions of het-
arene-fused pyrrole-2,3-diones with binucleophiles in
the present work we examined reactions of 3-aroyl-
1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones Ia
and Ib with methyl 4-aryl-2-arylamino-4-oxobut-2-
enoates IIa–IIc as potential 1,3-C,N-binucleophiles
(α-enamino esters). Compounds Ia and Ib reacted with
esters IIa–IIc at a ratio of 1:1 in boiling anhydrous
benzene to give in 20–25 min (the dark violet color
typical of initial pyrrolobenzoxazinetriones I disap-
peared) substituted methyl 7-aryl-4,9-bisaroyl-3-hy-
droxy-1-(2-hydroxyphenyl)-2,6-dioxo-1,7-diazaspiro-
[4.4]nona-3,8-diene-8-carboxylates IIIa–IIId in high
yield (Scheme 1). Attempted recrystallization of com-
pounds IIIa–IIId from ethyl acetate resulted in their
cyclization to methyl 9-aroyl-4,7-diaryl-1-(2-hydroxy-
phenyl)-2,3,8-trioxo-2,3,7,8-tetrahydro-1H,6H-6,8a-
methanopyrrolo[2,3-e][1,3]oxazepine-6-carboxylates
IVa–IVd whose structure was proved by X-ray anal-
ysis of a single crystal of IVb.**
* For communication LX, see [1].
** For preliminary communication, see [6].
1184

FIVE-MEMBERED 2,3-DIOXO HETEROCYCLES: LXI.
1185
Scheme 1.
COAr2
O
N
O
O
O
N
O
NHAr3
O
O
Ar2
COAr1
COOMe
+
OMe
Ar1
O
N
·
·
·
H
Ar3
O
O
OH
Ia, Ib
IIa–IIc
Ar3
N
Ar3
N
O
COOMe
COAr2
O
O
COOMe
COAr2
[1,5]-H, Δ
N
N
HO
HO
OH
O
COAr1
O
OH
IIIa–IIId
Ar1
V
Ar3
N
O
COOMe
COAr2
O
N
HO
O
Ar1
O
IVa–IVd
I, Ar1 = Ph (a), 4-BrC6H4 (b); II, Ar2 = Ph, Ar3 = 4-MeC6H4 (a); Ar2 = Ar3 = Ph (b); Ar2 = 4-EtOC6H4, Ar3 = 4-MeC6H4 (c); III, IV,
Ar1 = Ar2 = Ph, Ar3 = 4-MeC6H4 (a); Ar1 = Ar2 = Ar3 = Ph (b); Ar1 = Ph, Ar2 = 4-EtOC6H4, Ar3 = 4-MeC6H4 (c); Ar1 = 4-BrC6H4,
Ar2 = 4-EtOC6H4, Ar3 = 4-MeC6H4 (d).
Compounds IIIa–IIId are light yellow crystalline
substances which melt at high temperature with de-
composition; they are readily soluble in dimethylform-
amide and dimethyl sulfoxide, poorly soluble in com-
mon organic solvents, and insoluble in saturated hy-
drocarbons and water. Compounds IIIa–IIId showed
a positive test (cherry color) for enolic and phenolic
hydroxy groups on treatment with an alcoholic solu-
tion of iron(III) chloride.
droxy proton (δ 9.80–9.84 ppm), and a broadened
singlet from the enolic proton (δ 12.50–12.60 ppm).
The spectral parameters of compounds IIIa–IIId re-
semble those reported for analogous 4-aroyl-3-hy-
droxy-1-(o-hydroxyphenyl)-1,7-diazaspiro[4.4]nona-
3,8-diene-2,6-diones [4, 5] and substituted spiro[in-
dole-3,2′-pyrroles] [1] whose structure was proved by
X-ray analysis.
Compounds IVa–IVd are colorless crystalline sub-
stances with high decomposition points; they are
readily soluble in dimethylformamide and dimethyl
sulfoxide, poorly soluble in common organic solvents,
and insoluble in saturated hydrocarbons and water.
Compounds IVa–IVd showed a positive test (cherry
color) for phenolic hydroxy group on treatment with
an alcoholic solution of iron(III) chloride. In the IR
spectra of IVa–IVd, stretching vibrations of the O–H
group appeared as a broad band at 3220–3241 cm–1,
the ester carbonyl group gave rise to absorption at
1767–1776 cm–1, one or two peaks in the region 1721–
The IR spectra of IIIa–IIId contained absorption
bands due to stretching vibrations of hydroxy groups
(a broad band at 3150–3170 cm–1), ester (1760–
1772 cm–1) and lactam carbonyl groups (two peaks in
the region 1723–1737 cm–1), and acetyl and aroyl
carbonyl groups (two peaks in the region 1620–
1
1675 cm–1). In the H NMR spectra of solutions of
IIIa–IIId in DMSO-d6 we observed signals from
protons in the aromatic rings and substituents attached
thereto, a singlet from the ester methoxy group
(δ 3.20–3.34 ppm), a singlet from the phenolic hy-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008

RACHEVA et al.
1186
C18
O4
the latter at the C4–O5 bonds yields 2,3′-spiro-fused bi-
O3
C17
C15
C16
C3
pyrroles III. Intramolecular cyclization of compounds
III to bridged structures IV on attempted recrystalliza-
tion from ethyl acetate involves addition of the enolic
hydroxy group in hydroxymethylidene tautomer V at
the C5 atom of the neighboring pyrrole ring. We
believe that the presence of an electron-withdrawing
methoxycarbonyl group in position 8 of 1,7-diaza-
spiro[4.4]nona-3,8-diene-8-carboxylates III enhances
electrophilicity of C8 as compared to structurally
related compounds reported by us previously [1, 4, 5],
thus favoring intramolecular nucleophilic attack by the
enolic hydroxy group.
C19
C7
C8
N2
C20
C23
O2
O6
C9
H5
C6
C10
C21
O5
C22
C24
C25
C14
C5
C31
C4
O1
C27
C13
C11
H6
N1
C30
C12
C26
O2
C1
O8
O7
C28
C32
C35
C34
C29
C33
The described reaction is the first example of intra-
molecular cyclization of 1,7-diazaspiro[4.4]nona-3,8-
diene-8-carboxylates with selective formation of diffi-
cultly accessible bridged 6,8a-methanopyrrolo[2,3-e]-
[1,3]oxazepine system.
Structure of the molecule of methyl 9-benzoyl-1-(2-hydroxy-
phenyl)-2,3,8-trioxo-4,7-diphenyl-2,3,7,8-tetrahydro-1H,6H-
6,8a-methanopyrrolo[2,3-e][1,3]oxazepine-6-carboxylate
(IVb) according to the X-ray diffraction data.
EXPERIMENTAL
1756 cm–1 corresponded to the lactam and ketone
(C3=O) carbonyl groups, and the band at 1700–
1709 cm–1 was assigned to the aroyl carbonyl group.
The IR spectra were recorded on an FSM-1201
spectrometer from samples dispersed in mineral oil.
1
The H and 13C NMR spectra were measured on
1
Compounds IVa–IVd displayed in the H NMR spec-
1
tra (DMSO-d6) signals from aromatic protons and pro-
tons in the substituents at the aromatic rings; protons
of the ester methoxy group resonated as a singlet at
δ 3.22–3.34 ppm, the 9-H signal appeared as a singlet
at δ 5.15–5.29 ppm, and the OH proton gave a singlet
at δ 9.91–10.01 ppm. The 13C NMR spectrum of IVd
in DMSO-d6 contained the following signals, δC, ppm:
189.11 (COC6H4), 176.95 (C4=O), 167.87 and 163.07
(C8=O, C2=O), 159.80 (COOMe), 154.07 (C4a), 137.68–
106.49 (Carom), 92.44 (C6), 65.29 (C8a), 63.72 (C9), 53.76
(OCH2), 44.52 (OCH3), 20.49 (CH3), 14.40 (CH2CH3).
a Bruker AM-400 instrument (at 400 MHz for H)
from solutions in DMSO-d6 using tetramethylsilane as
internal reference. The purity of the products was
checked by TLC on Silufol plates using ethyl acetate
or ethyl acetate–benzene (1:5) as eluent; spots were
visualized by treatment with iodine vapor.
Methyl 4,9-dibenzoyl-3-hydroxy-1-(2-hydroxy-
phenyl)-7-(4-methylphenyl)-2,6-dioxo-1,7-diaza-
spiro[4.4]nona-3,8-diene-8-carboxylate (IIIa). A so-
lution of 1.0 mmol of compound Ia and 1.0 mmol of
ester IIa in 10 ml of anhydrous benzene was heated for
25 min under reflux (the mixture turned colorless). The
mixture was cooled, and the precipitate was filtered
off, and washed with ethyl acetate (2×1 ml) and hex-
ane (5 ml). Yield 85%, mp 184–185°C. IR spectrum, ν,
cm–1: 3170 br (OH), 1760 (COOMe), 1732 (C6=O),
1727 (C2=O), 1675 and 1625 (4-C=O, 9-C=O).
1H NMR spectrum, δ, ppm: 3.23 s (3H, OMe), 2.25 s
(3H, Me), 6.92–7.97 m (18H, Harom), 9.84 s (1H, OH,
phenol), 12.50 br.s (1H, OH, enol). Found, %: C 70.32;
H 4.16; N 4.58. C36H26N2O8. Calculated, %: C 70.35;
H 4.26; N 4.56.
The structure of molecule IVb is shown in figure.
All double bonds in structure IVb are localized. The
bond lengths and bond angles do not differ from the
corresponding standard values. Molecules IVb in
crystal are linked to centrosymmetric dimers through
intermolecular hydrogen bonds O5–H5 ···O3 (–x + 1,
–y, –z + 1) with the following parameters O5–H5 0.880,
H5···O3 1.846, O5···O3 2.704 Å, ∠O5H5O3 164.68°.
Presumably, the reaction follows a scheme analo-
gous to that proposed by us previously [1, 4, 5]. In the
first step, the activated β-CH group of the enamino
fragment in ester II adds at the C3a carbon atom of
pyrrolobenzoxazinetrione I. The subsequent Z–E iso-
merization, pyrrole ring closure via intramolecular
attack by the free amino group on the lactone carbonyl
carbon atom in the benzoxazine ring, and cleavage of
Compound IIIb–IIId were synthesized in a similar
way.
Methyl 4,9-dibenzoyl-3-hydroxy-1-(2-hydroxy-
phenyl)-2,6-dioxo-7-phenyl-1,7-diazaspiro[4.4]-
nona-3,8-diene-8-carboxylate (IIIb). Yield 87%,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 44 No. 8 2008

FIVE-MEMBERED 2,3-DIOXO HETEROCYCLES: LXI.
1187
mp 200–202°C. IR spectrum, ν, cm–1: 3152 br (OH),
IR spectrum, ν, cm–1: 3227 br (OH), 1776 (COOMe),
1751 (C2=O), 1721 (C3=O, C8=O), 1707 (COPh).
1H NMR spectrum, δ, ppm: 3.22 s (3H, OMe), 5.29 s
(1H, 9-H), 6.94–7.98 m (19H, Harom), 10.01 s (1H,
OH). Found, %: C 69.89; H 4.07; N 4.70. C35H24N2O8.
Calculated, %: C 69.92; H 4.03; N 4.66.
1770 (COOMe), 1737 (C6=O), 1724 (C2=O), 1672 and
1
1620 (4-C=O, 9-C=O). H NMR spectrum, δ, ppm:
3.20 s (3H, OMe), 7.10–7.98 m (19H, Harom), 9.80 s
(1H, OH, phenol), 12.60 br.s (1H, OH, enol). Found,
%: C 70.10; H 4.00; N 4.55. C35H24N2O8. Calculated,
%: C 70.00; H 4.03; N 4.66.
Methyl 9-(4-ethoxybenzoyl)-1-(2-hydroxy-
phenyl)-7-(4-methylphenyl)-2,3,8-trioxo-4-phenyl-
2,3,7,8-tetrahydro-1H,6H-6,8a-methanopyrrolo-
[2,3-e][1,3]oxazepine-6-carboxylate (IVc). Yield
93%, mp 197–198°C (from ethyl acetate). IR spec-
trum, ν, cm–1: 3241 br (OH), 1775 (COOMe), 1756
Methyl 4-benzoyl-9-(4-ethoxybenzoyl)-3-hy-
droxy-1-(2-hydroxyphenyl)-7-(4-methylphenyl)-2,6-
dioxo-1,7-diazaspiro[4.4]nona-3,8-diene-8-carbox-
ylate (IIIc). Yield 86%, mp 189–190°C. IR spectrum,
ν, cm–1: 3152 br (OH), 1772 (COOMe), 1736 (C6=O),
1723 (C2=O), 1673 and 1622 (4-C=O, 9-C=O).
1H NMR spectrum, δ, ppm: 1.23 t (3H, CH3CH2, J =
6.9 Hz), 2.24 s (3H, Me), 3.34 s (3H, OMe), 3.52 q
(2H, OCH2, J = 6.9 Hz), 7.08–7.90 m (17H, Harom),
9.82 s (1H, OH, phenol), 12.60 br.s (1H, OH, enol).
Found, %: C 69.19; H 4.50; N 4.26. C38H30N2O9. Cal-
culated, %: C 69.29; H 4.59; N 4.25.
1
(C2=O, C3=O, C8=O), 1709 (COC6H4). H NMR spec-
trum, δ, ppm: 1.35 t (3H, CH3CH2, J = 7.0 Hz), 2.33 s
(3H, Me), 3.33 s (3H, OMe), 4.13 q (2H, OCH2, J =
7.0 Hz), 5.15 s (1H, 9-H), 6.89–7.92 m (17H, Harom),
9.91 s (1H, OH). Found, %: C 69.24; H 4.60; N 4.19.
C38H30N2O9. Calculated, %: C 69.29; H 4.59; N 4.25.
Methyl 4-(4-bromophenyl)-9-(4-ethoxybenzoyl)-
1-(2-hydroxyphenyl)-7-(4-methylphenyl)-2,3,8-tri-
oxo-2,3,7,8-tetrahydro-1H,6H-6,8a-methanopyrrolo-
[2,3-e][1,3]oxazepine-6-carboxylate (IVd). Yield
93%, mp 210–211°C (from ethyl acetate). IR spec-
trum, ν, cm–1: 3220 br (OH), 1767 (COOMe), 1753
(C2=O), 1721 (C3=O, C8=O), 1707 (COC6H4). 1H NMR
spectrum, δ, ppm: 1.34 t (3H, CH3CH2, J = 7.0 Hz),
2.25 s (3H, Me), 3.34 s (3H, OMe), 4.13 q (2H, OCH2,
J = 7.0 Hz), 5.15 s (1H, 9-H), 6.81–7.91 m (16H,
Harom), 9.91 s (1H, OH). 13C NMR spectrum
(DMSO-d6), δC, ppm: 189.11 (9-CO), 176.95 (C3),
167.87 and 163.07 (C8, C2O), 159.80 (COOMe),
154.07 (C3a), 137.68–106.49 (Carom), 92.44 (C6), 65.29
(C8a), 63.72 (C9), 53.76 (OCH2), 44.52 (OCH3), 20.49
(CH3C6H4), 14.40 (CH2CH3). Found, %: C 61.85;
H 3.94; Br 10.79; N 3.82. C38H29BrN2O9. Calculated,
%: C 61.88; H 3.96; Br 10.83; N 3.80.
Methyl 4-(4-bromobenzoyl)-9-(4-ethoxybenzoyl)-
3-hydroxy-1-(2-hydroxyphenyl)-7-(4-methylphen-
yl)-2,6-dioxo-1,7-diazaspiro[4.4]nona-3,8-diene-8-
carboxylate (IIId). Yield 86%, mp 209–210°C. IR
spectrum, ν, cm–1: 3150 br (OH), 1770 (COOMe),
1736 (C6=O), 1723 (C2=O), 1671 and 1620 (4-C=O,
1
9-C=O). H NMR spectrum, δ, ppm: 1.23 t (3H,
CH3CH2, J = 6.9 Hz), 2.24 s (3H, Me), 3.30 s (3H,
OMe), 3.50 q (2H, OCH2, J = 6.9 Hz), 7.17–7.87 m
(16H, Harom), 9.83 s (1H, OH, phenol), 12.60 br.s (1H,
OH, enol). Found, %: C 61.76; H 3.92; Br 10.84;
N 3.76. C38H29BrN2O9. Calculated, %: C 61.88; H 3.96;
Br 10.83; N 3.80.
Compounds IVa–IVd were obtained by recrystal-
lization of 1.0 mmol the corresponding compound
IIIa–IIId from ethyl acetate.
Methyl 9-benzoyl-1-(2-hydroxyphenyl)-7-(4-
methylphenyl)-2,3,8-trioxo-4-phenyl-2,3,7,8-tetra-
hydro-1H,6H-6,8a-methanopyrrolo[2,3-e][1,3]-
oxazepine-6-carboxylate (IVa). Yield 90%, mp 190–
191°C (from ethyl acetate). IR spectrum, ν, cm–1:
3230 br (OH), 1770 (COOMe), 1755 (C2=O), 1724
X-Ray diffraction data for compound IVb. Tri-
clinic crystals, C35H24N2O8, with the following unit
cell parameters: a = 11.162(2), b = 11.521(2), c =
12.389(3) Å; α = 103.37(3), β = 103.64(3), γ =
98.03(3)°; V = 1474.2(5) Å3; M 600.56; dcalc = 1.353 g×
cm–3; Z = 2; space group P-1. The experimental re-
flection intensities were measured on a KM-4 Kuma
Diffraction automatic four-circle diffractometer (χ-4
geometry, monochromatized MoKα irradiation, ω/2Θ
scanning, 2Θ ≤ 50.2°). Total of 5232 independent re-
flections were measured (Rint = 0.0289) with no correc-
tion for absorption (μ = 0.097 mm–1). The structure
was solved by the direct method using SIR92 program
[7] with subsequent calculation of the electron density
maps. Hydrogen atoms on O5 and C6 were localized by
1
(C3=O, C8=O), 1700 (COPh). H NMR spectrum, δ,
ppm: 2.24 s (3H, Me), 3.23 s (3H, OMe), 5.25 s (1H,
9-H), 6.92–7.97 m (18H, Harom), 10.01 s (1H, OH).
Found, %: C 70.28; H 4.21; N 4.49. C36H26N2O8. Cal-
culated, %: C 70.35; H 4.26; N 4.56.
Methyl 9-benzoyl-1-(2-hydroxyphenyl)-2,3,8-tri-
oxo-4,7-diphenyl-2,3,7,8-tetrahydro-1H,6H-6,8a-
methanopyrrolo[2,3-e][1,3]oxazepine-6-carboxylate
(IVb). Yield 92%, mp 201–203°C (from ethyl acetate).
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RACHEVA et al.
1188
3. Mashevskaya, I.V. and Maslivets, A.N., 2,3-Digidro-2,3-
pirroldiony, kondensirovannye s razlichnymi geterotsik-
lami storonoi [a], i ikh benzo[b]analogi: sintez, khimi-
cheskie svoistva, prakticheskoe primenenie (2,3-Dihydro-
pyrrole-2,3-diones Fused by the [a] Side to Various
Heterocycles and Their Benzo[b]-Fused Analogs), Perm:
Perm. Gos. Sel’skokhoz. Akad., 2003, p. 140.
4. Racheva, N.L., Aliev, Z.G., Belova, M.A., Mashev-
skaya, I.V., and Maslivets, A.N., Russ. J. Org. Chem.,
2008, vol. 44, p. 701.
difference synthesis of electron density, and positions
of the other hydrogen atoms were set on the basis of
geometry considerations. Full-matrix least-squares
anisotropic refinement of positions of non-hydrogen
atoms (SHELXL-97 [8]) was terminated at R1 =
0.0498 [2631 reflections with I ≥ 2σ(I)]; goodness of
fit 0.986.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 07-03-96036).
5. Racheva, N.L., Belova, M.A., and Maslivets, A.N., Russ.
J. Org. Chem., 2008, vol. 44, p. 582.
6. Racheva, N.L., Aliev, Z.G., and Maslivets, A.N., Russ. J.
Org. Chem., 2008, vol. 44, p. 1094.
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