Synthesis and properties of 2-(2-furyl)-and 2-(2-Thienyl)-1,3-benzoxazoles

Article abstract of DOI:10.1134/S1070428010060205

Condensation of o-aminophenol with furoyl and thenoyl chlorides in 1-methylpyrrolidin-2-one gave, respectively, 2-(2-furyl)- and 2-(2-thienyl)-1,3-benzoxazoles in which the furan and thiophene rings showed no acidophobic properties. Reactions of 2-(2-fury

Full text of DOI:10.1134/S1070428010060205

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2010, Vol. 46, No. 6, pp. 898–902. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © A.A. Aleksandrov, E.V. Vlasova, M.M. El’chaninov, 2010, published in Zhurnal Organicheskoi Khimii, 2010, Vol. 46, No. 6,
pp. 902–905.
Synthesis and Properties of 2-(2-Furyl)-
and 2-(2-Thienyl)-1,3-Benzoxazoles
A. A. Aleksandrov, E. V. Vlasova, and M. M. El’chaninov
Southern Russian State Technical University (Novocherkassk Polytechnical Institute),
ul. Prosveshcheniya 132, Novocherkassk, 346428 Russia
e-mail: aaanet1@yandex.ru
Received June 1, 2009
Abstract—Condensation of o-aminophenol with furoyl and thenoyl chlorides in 1-methylpyrrolidin-2-one
gave, respectively, 2-(2-furyl)- and 2-(2-thienyl)-1,3-benzoxazoles in which the furan and thiophene rings
showed no acidophobic properties. Reactions of 2-(2-furyl)- and 2-(2-thienyl)-1,3-benzoxazoles with electro-
philic reagents (acylation, bromination, nitration, and sulfonation) afforded products of hydrogen replacement
in both hetaryl and benzene rings, depending on the conditions.
DOI: 10.1134/S1070428010060205
of Ia and IIa with dilute nitric acid (d = 1.32 g/cm3)
In continuation of our studies aimed at synthesizing
new biologically active compounds and organic
luminophores in the series of 2-hetaryl-substituted
benzazoles, in the present work we made an attempt to
develop a convenient procedure for the preparation of
2-(2-furyl)- and 2-(2-thienyl)-1,3-benzoxazoles Ia and
IIa, examine their relative reactivity, and elucidate
mutual effect of the aromatic benzoxazole system and
fundamental π-excessive heterocycles of the pyrrole
series, linked together through a single C–C bond.
was performed.
We previously showed [3, 4] that the effect of
benzazol-2-yl substituent on pyrrole type heterocycles
leads to general reduction of electron density in the
latter and its redistribution over aromatic fragment
fused to the azole ring. As a result, the hetaryl groups
lose their acidophobic character, so that they can be
involved in chemical transformations under a broader
range of conditions, including strongly acidic medium,
elevated temperature, etc. Like other electron-with-
drawing groups, the presence of benzoxazol-2-yl sub-
stituent favors reduced equilibrium concentration of
protonated furan species and its reduced reactivity,
which minimizes the contributions of oligomerization
processes and addition of various nucleophiles.
Compound Ia was synthesized previously in 34%
yield by heating a mixture of o-aminophenol, 2-furoic
acid, and boric acid in boiling xylene [1]. Hetarylbenz-
oxazoles Ia and IIa were later prepared via photo-
chemical and thermal aromatization of the correspond-
ing Schiff bases (yield 35 and 45%, respectively) [2].
The best results were obtained by us by carrying out
the condensation of o-aminophenol with 2-furoyl and
2-thenoyl chlorides in 1-methylpyrrolidin-2-one. In
this case, the yields of 2-(2-furyl)- and 2-(2-thienyl)-
1,3-benzoxazoles Ia and IIa were 76 and 88%, re-
spectively. Compounds Ia and IIa were then brought
into reactions with electrophilic reagents, namely with
a mixture of nitric and polyphosphoric (PPA) acids,
bromine in 1,2-dichloroethane, hexamethylenetetra-
amine in PPA, acetic anhydride in the presence of an-
hydrous magnesium perchlorate, benzoic acid in PPA,
and sulfuric acid in PPA. In addition, radical nitration
Heating of compounds Ia and IIa in boiling dilute
nitric acid (d = 1.32 g/cm3) resulted in the formation of
2-(5-nitrofuran-2-yl)- and 2-(5-nitrothiophen-2-yl)-1,3-
benzoxazoles Ib and IIb, respectively. It is known that
under the above conditions the nitration follows radical
mechanism. Compounds Ib and IIb were also formed
in the nitration of Ia and IIb with fuming nitric acid
(d = 1.51 g/cm3) in PPA at 20°C. At 95°C compound
Ia underwent tarring, whereas thienylbenzoxazol IIa
was converted into dinitro derivative IIc (Scheme 1).
In addition, compounds Ib and IIb were obtained by
independent synthesis implying ipso substitution of the
898

SYNTHESIS AND PROPERTIES OF 2-(2-FURYL)- AND 2-(2-THIENYL)-1,3-...
899
Scheme 1.
HNO3–PPA
or dilute HNO3
NO2
N
X
X
X
O
R
R
Ib, IIb, IIc
Br
N
X
N
Br2, 1,2-Cl2C2H4
O
O
Ia, IIa
Ic, Id, IId, IIe
O
PhCOOH–(CH2)6N4
Ac2O–PPA
N
R
O
Ie–Ig, IIf–IIh
I, X = O; II, X = S; Ib, Ic, Ie, IIb, IId, IIf, R = H; IIc, R = O2N; Id, IIe, R = Br; If, IIg, R = Me; Ig, IIh, R = Ph.
bromine atom by nitro group in 2-(5-bromofuran-2-yl)-
and 2-(5-bromothiophen-2-yl)benzoxazoles Ic and IId.
Likewise, the bromination of Ia and IIa with molec-
ular bromine in 1,2-dichloroethane resulted in substitu-
tion of hydrogen in position 5 of the hetaryl ring by
bromine. Further replacement in the benzoxazole frag-
ment occurred upon prolonged heating of 5-bromo
derivatives Ic and IId with 3 equiv of bromine.
While searching for most appropriate conditions and
taking into account successful benzoylation of analo-
gous benzimidazoles [6], we applied Gardner’s proce-
dure for the acylation of phenols and phenyl ethers [7].
According to [7], compounds Ia and IIa were treated
with benzoic acid in PPA at 140–150°C. In this case,
5-benzoyl derivatives Ig and IIh were smoothly
formed in good yield.
It is known that 2-(2-hetaryl)-1,3-benzothiazoles
give rise to the corresponding formyl derivatives by
the action of Vilsmeier reagent [5]. However,
2-(2-thienyl)-1,3-benzothiazole (IIa) failed to react
under these conditions. Therefore, we used a different
procedure, which was shown previously to be success-
ful in the formylation of hetarylbenzimidazoles. In
fact, the reaction of benzoxazoles Ia and IIa with
hexamethylenetetraamine in PPA gave the correspond-
ing aldehydes Ie and IIf in 30 and 45% yield.
In contrast to structurally related benzimidazoles
[6], we failed to isolate products of sulfonation of
2-hetarylbenzoxazoles Ia and IIa, although their
formation was detected by TLC. During the process,
the spot of initial compound Ia or IIa disappeared,
whereas attempts to isolate free sulfonic acids resulted
in hydrolytic elimination of the sulfo group (Scheme 2).
Presumably, the corresponding sulfonic acids exist as
inner salts whose stability depends on the basicity of
the benzoxazole fragment, which is known to be the
lowest among benzazoles [8].
Unlike analogous benzimidazoles, we succeeded in
obtaining acetyl derivatives of compounds Ia and IIa
in 48 and 33% yield by heating them in boiling acetic
anhydride in the presence of a catalytic amount of
anhydrous magnesium perchlorate. Different versions
of benzoylation of Ia and IIa were unsuccessful.
It is known that, like benzimidazole and benzo-
thiazole derivatives, some 2-hetarylbenzoxazoles ex-
hibit antiparasitic activity. Study on their biological
activity revealed strong antihelminthic effect of 5-nitro
derivatives [9].
Scheme 2.
H
N
SO3
N
X
X
H2O
H2SO4, PPA
–H2O
Ia, IIa
–H2SO4
O
O
Ia, IIa
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 6 2010

ALEKSANDROV et al.
previously synthesized by condensation of o-amino-
900
EXPERIMENTAL
phenol with 5-nitrothiophene-2-carbaldehyde in acetic
acid at 70°C in the presence of lead tetraacetate [9].
The IR spectra were recorded on a Specord 75IR
spectrometer from samples dispersed in mineral oil.
The 1H NMR spectra were measured on a Varian Unity
300 instrument at 300 MHz, using CDCl3 as solvent
and tetramethylsilane as internal reference. The prog-
ress of reactions was monitored by TLC on aluminum
oxide of activity grade II according to Brockmann
using methylene chloride or chloroform as eluent;
development with iodine vapor. The elemental com-
positions were determined on a Perkin–Elmer 2400
analyzer. The melting points were measured in capil-
laries on a PTP melting point apparatus.
2-(5-Nitrofuran-2-yl)-1,3-benzoxazole (Ib). Yield
(20%), mp 218–219°C. IR spectrum: ν 1370 cm–1
(NO2). 1H NMR spectrum, δ, ppm: 7.44 t (1H, 6-H, J =
6.7 Hz), 7.48 t (1H, 5-H, J = 6.7 Hz), 7.62 d (1H, 3′-H,
J = 4.0 Hz), 7.74 d (1H, 7-H, J = 7.9 Hz), 7.78 d (1H,
4′-H, J = 4.0 Hz), 7.80 d (1H, 4-H, J = 7.6 Hz). Found,
%: C 57.77; H 3.02; N 11.92. C11H6N2O4. Calculated,
%: C 57.40; H 2.63; N 12.17.
2-(5-Nitrothiophen-2-yl)-1,3-benzoxazole (IIb).
Yield (27%), mp 205–206°C. IR spectrum: ν 1370 cm–1
1
(NO2). H NMR spectrum, δ, ppm: 7.41–7.45 m (2H,
2-(2-Furyl)-1,3-benzoxazole (Ia). Furan-2-carbon-
yl chloride, 1.31 g (10 mmol), was added to a solution
of 1.09 (10 mmol) of o-aminophenol in 10 ml of
1-methylpyrrolidin-2-one. The mixture was heated for
2 h under reflux, cooled, and poured into 50 ml of cold
water, and the precipitate was filtered off, thoroughly
washed with cold water, and recrystallized from
5-H, 6-H), 7.58–7.62 m (1H, 7-H), 7.78–7.80 m (1H,
4-H), 7.80 d (1H, 3′-H, J = 4.2 Hz), 7.97 d (1H, 4′-H,
J = 4.2 Hz). Found, %: N 10.54. C11H6N2O3S. Calcu-
lated, %: N 10.81.
6-Nitro-2-(5-nitrothiophen-2-yl)-1,3-benzoxazole
(IIc). Nitric acid (d = 1.51 g/cm3), 1.25 ml (30 mmol),
was added to a solution of 2.01 g (10 mmol) of ben-
zoxazole IIa in 40 g of polyphosphoric acid, the mix-
ture was heated for 3 h at 90–95°C under continuous
stirring, poured into 200 ml of water, and neutralized
with a 25% solution of ammonia, and the precipitate
was filtered off. Yield 24%, mp 213–214°C. IR spec-
1
ethanol. Yield 76%, mp 86–87°C. H NMR spectrum,
δ, ppm: 6.62–6.64 m (1H, 4′-H), 7.28 d (1H, 3′-H, J =
3.5 Hz), 7.34–7.37 m (2H, 5-H, 6-H), 7.55–7.58 m
(1H, 7-H), 7.67 d (1H, 5′-H, J = 1.0 Hz), 7.74–7.77 m
(1H, 4-H). Found, %: C 70.98; H 4.03; N 7.74.
C11H7NO2. Calculated, %: C 71.35; H 3.81; N 7.56.
1
trum: ν 1370 cm–1 (NO2). H NMR spectrum, δ, ppm:
2-(2-Thienyl)-1,3-benzoxazole (IIa) was synthe-
sized in a similar way. Yield (88%), mp 106–107°C.
1H NMR spectrum, δ, ppm: 7.20 t (1H, 4′-H, J =
4.4 Hz), 7.33–7.36 m (2H, 5-H, 6-H), 7.52–7.58 m
(1H, 7-H), 7.56 d (1H, 3′-H, J = 4.2 Hz), 7.72–7.77 m
(1H, 4-H), 7.92 d (1H, 5′-H, J = 4.9 Hz). Found, %:
C 65.97; H 3.82. C11H7NOS. Calculated, %: C 65.65;
H 3.51.
7.90 d (1H, 7-H, J = 8.8 Hz), 7.92 d (1H, 3′-H, J =
4.3 Hz), 8.01 d (1H, 4′-H, J = 4.3 Hz), 8.39 d (1H,
5-H, J = 8.8 Hz,), 8.53 d (1H, 4-H, J = 2.1 Hz). Found,
%: C 44.97; H 2.03; N 14.59. C11H5N3O5S. Calculated,
%: C 45.36; H 1.73; N 14.43.
2-(5-Bromohetaren-2-yl)-1,3-benzoxazoles Ic and
IId (general procedure). Bromine, 1.06 ml (20 mmol),
was added to a solution of 10 mmol of compound Ia or
IIa in 50 ml of 1,2-dichloroethane, the mixture was
heated for 4 h under reflux and evaporated in air, and
the residue was recrystallized from alcohol.
2-(5-Nitrohetaren-2-yl)-1,3-benzoxazoles Ib and
IIb (general procedure). a. A solution of 10 mmol
of compound Ia or IIa in 50 ml of nitric acid (d =
1.32 g/cm3) was heated for 0.5 h at the boiling point.
The mixture was cooled and poured into 250 ml of
cold water, and the precipitate was filtered off and
washed with 2–3 small portions of cold water.
2-(5-Bromofuran-2-yl)-1,3-benzoxazole (Ic).
1
Yield 84%, mp 101–102°C. H NMR spectrum, δ,
ppm: 6.55 d (1H, 4′-H, J = 3.6 Hz), 7.22 d (1H, 3′-H,
J = 3.6 Hz), 7.35–7.38 m (2H, 5-H, 6-H), 7.55–7.58 m
(1H, 7-H), 7.74–7.77 m (1H, 4-H). Found, %: C 50.33;
H 2.37; N 5.47. C11H6BrNO2. Calculated, %: C 50.03;
H 2.29; N 5.30.
b. Sodium nitrite, 2.08 g (30 mmol), was added to
a solution of 10 mmol of compound Ic or IId in 30 ml
of acetic acid, the mixture was heated for 1 h at the
boiling point, cooled, and poured into 100 ml of water,
and the precipitate was filtered off and washed with
2–3 small portions of cold water. Samples of Ib and
IIb obtained according to methods a and b were
identical in melting point (no depression of the melting
point was observed on mixing). Compound IIb was
2-(5-Bromothiophen-2-yl)-1,3-benzoxazole (IId).
1
Yield 80%, mp 110–110.5°C. H NMR spectrum, δ,
ppm: 7.15 d (1H, 4′-H, J = 3.8 Hz), 7.32–7.38 m (2H,
5-H, 6-H), 7.52–7.56 m (1H, 7-H), 7.64 d (1H, 3′-H,
J = 3.8 Hz), 7.7–7.74 m (1H, 4-H). Found, %: C 46.82;
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 6 2010

SYNTHESIS AND PROPERTIES OF 2-(2-FURYL)- AND 2-(2-THIENYL)-1,3-...
901
H 1.97; N 5.13. C11H6BrNOS. Calculated, %: C 47.16;
H 2.16; N 5.00.
2-(5-Acetylhetaren-2-yl)-1,3-benzoxazoles If and
IIg (general procedure). Compound Ia or IIa,
10 mmol, was dissolved in 30 ml of acetic anhydride,
a catalytic amount of anhydrous magnesium perchlo-
rate, 0.01 g (0.04 mmol), was added, and the mixture
was heated for 1 h under reflux. The mixture was then
treated with 50 ml of water, neutralized with a con-
centrated solution of ammonia, and extracted with
methylene chloride. The product was purified by col-
umn chromatography on aluminum oxide using meth-
ylene chloride as eluent.
6-Bromo-2-(5-bromohetaren-2-yl)-1,3-benzoxa-
zoles Id and IIe (general procedure). Bromine,
1.59 ml (30 mmol), was added to a solution of
10 mmol of compound Ic or IId in 50 ml of 1,2-di-
chloroethane, and the mixture was heated for 8 h under
reflux. The mixture was evaporated, and the residue
was dissolved in methylene chloride and subjected to
column chromatography on aluminum oxide (15×
2.5 cm) using methylene chloride as eluent.
1-[5-(1,3-Benzoxazol-2-yl)furan-2-yl]ethanone
(If). Yield 48%, mp 149–150°C. IR spectrum:
ν 1670 cm–1 (C=O). 1H NMR spectrum, δ, ppm: 2.64 s
(3H, CH3), 7.33 d (1H, 4-H, J = 3.7 Hz), 7.36 d (1H,
3-H, J = 3.7 Hz), 7.40–7.43 m (2H, 5′-H, 6′-H), 7.60–
7.63 m (1H, 7′-H), 7.80–7.83 m (1H, 4′-H). Found, %:
C 69.06; H 4.31; N 5.92. C13H9NO3. Calculated, %:
C 68.72; H 3.99; N 6.16.
6-Bromo-2-(5-bromofuran-2-yl)-1,3-benzoxazole
(Id). Yield 34%, mp 146–147°C. 1H NMR spectrum, δ,
ppm: 6.56 d (1H, 4′-H, J = 3.6 Hz), 7.23 d (1H, 3′-H,
J = 3.6 Hz), 7.49 d (1H, 5-H, J = 8.5 Hz), 7.61 d (1H,
7-H, J = 8.5 Hz), 7.72 d (1H, 4-H, J = 1.7 Hz). Found,
%: C 38.34; H 1.17; N 4.32. C11H5Br2NO2. Calculated,
%: C 38.52; H 1.47; N 4.08.
6-Bromo-2-(5-bromothiophen-2-yl)-1,3-benzoxa-
1-[5-(1,3-Benzoxazol-2-yl)thophen-2-yl]ethanone
(IIg). Yield 33%, mp 161–162°C. IR spectrum:
ν 1660 cm–1 (C=O). 1H NMR spectrum, δ, ppm: 2.63 s
(3H, CH3), 7.36–7.40 m (2H, 5′-H, 6′-H), 7.55–7.60 m
(1H, 7′-H), 7.73 d (1H, 4-H, J = 4.2 Hz), 7.75–7.79 m
(1H, 4′-H), 7.90 d (1H, 3-H, J = 4.2 Hz). Found, %:
C 63.87; H 4.08; N 5.39. C13H9NO2S. Calculated, %:
C 64.18; H 3.73; N 5.76.
1
zole (IIe). Yield 36%, mp 129–130°C. H NMR spec-
trum, δ, ppm: 7.16 d (1H, 4′-H, J = 4.0 Hz), 7.47 d
(1H, 5-H, J = 8.5 Hz), 7.58 d (1H, 7-H, J = 8.5 Hz),
7.64 d (1H, 3′-H, J = 4.0 Hz), 7.71 d (1H, 4-H, J =
1.8 Hz). Found, %: C 37.15; H 1.62; N 4.12.
C11H5Br2NOS. Calculated, %: C 36.80; H 1.40; N 3.90.
5-(1,3-Benzoxazol-2-yl)hetarene-2-carbalde-
hydes Ie and IIf (general procedure). Hexamethylene-
tetraamine, 5.6 g (40 mmol), was added to a mixture of
10 mmol of compound Ia or IIa and 40 g of PPA, and
the mixture was heated for 3 h at 80–90°C under
vigorous stirring. The mixture was then diluted with
100 ml of water and neutralized with a 25% solution of
ammonia, and the precipitate was filtered off and
recrystallized.
2-(5-Benzoylhetaren-2-yl)-1,3benzoxazoles Ig
and IIh (general procedure). A mixture of 10 mmol of
compound Ia or IIa, 40 g of PPA, and 3.6 g (30 mmol)
of benzoic acid was stirred for 8 h at 140–150°C. The
products were isolated as described above for acetyl
derivatives If and IIg.
[5-(1,3-Benzoxazol-2-yl)furan-2-yl]phenylmeth-
anone (Ig). Yield 32%, mp 114–115°C. IR spectrum:
ν 1640 cm–1 (C=O). 1H NMR spectrum, δ, ppm: 7.40 d
(1H, 4-H, J = 3.7 Hz), 7.42 d (1H, 3-H, J = 3.7 Hz),
7.40–7.43 m (2H, 5′-H, 6′-H), 7.56 t (3H, p-H, m-H,
J = 7.7 Hz), 7.60–7.63 m (1H, 7′-H), 7.80–7.83 m
(1H, 4′-H), 8.10 d (2H, o-H, J = 7.8 Hz). Found, %:
C 75.07; H 4.05. C18H11NO3. Calculated, %: C 74.73;
H 3.83.
5-(1,3-Benzoxazol-2-yl)furan-2-carbaldehyde
(Ie). Yield 30%, mp 130–131°C. IR spectrum:
ν 1680 cm–1 (C=O). 1H NMR spectrum, δ, ppm: 7.40 d
(1H, 4-H, J = 3.7 Hz). 7.42 d (1H, 3-H, J = 3.7 Hz),
7.40–7.43 m (2H, 5′-H, 6′-H), 7.61–7.64 m (1H, 7′-H),
7.80–7.84 m (1H, 4′-H), 9.86 s (1H, CHO). Found, %:
C 68.02; H 3.50; N 6.33. C12H7NO3. Calculated, %:
C 67.61; H 3.31; N 6.57.
[5-(1,3-Benzoxazol-2-yl)thiophen-2-yl]phenyl-
5-(1,3-Benzoxazol-2-yl)thiophene-2-carbalde-
methanone (IIh). Yield 29%, mp 127–128°C. IR spec-
1
trum: ν 1680 cm–1 (C=O). H NMR spectrum, δ, ppm:
hyde (IIf). Yield 45%, mp 137–138°C. IR spectrum:
1
ν 1670 cm–1 (C=O). H NMR spectrum, δ, ppm: 7.37–
7.40–7.43 m (2H, 5′-H, 6′-H), 7.54 t (3H, p-H, m-H,
J = 7.8 Hz), 7.60–7.63 m (1H, 7′-H), 7.70 d (1H, 4-H,
J = 4.0 Hz), 7.80–7.83 m (1H, 4′-H), 7.88 d (1H, 3-H,
J = 4.0 Hz), 8.12 d (2H, o-H, J = 7.8 Hz). Found, %:
C 71.19; H 3.39; N 4.29. C18H11NO2S. Calculated, %:
C 70.80; H 3.63; N 4.59.
7.40 m (2H, 5′-H, 6′-H), 7.56–7.60 m (1H, 7′-H),
7.72 d (1H, 4-H, J = 4.1 Hz), 7.77–7.80 m (1H, 4′-H),
7.92 d (1H, 3-H, J = 4.1 Hz), 9.88 s (1H, CHO).
Found, %: C 63.21; H 2.81; N 6.43. C12H7NO2S. Cal-
culated, %: C 62.87; H 3.08; N 6.11.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 6 2010

ALEKSANDROV et al.
5. Kornilov, M.Yu., Ruban, E.M., Fedchuk, V.N., Starin-
902
REFERENCES
skaya, E.V., and Buznik, M.V., Zh. Org. Khim., 1973,
vol. 9, p. 2577
1. Terashima, M., Ishi, M., and Kanaoka, Y., Synthesis,
1982, p. 484
6. El’chaninov, M.M., Simonov, A.M., and Oleiniko-
va, L.Ya., Khim. Geterotsikl. Soedin., 1983, p. 1311.
2. Tauer, E. and Grellmann, K.H., J. Org. Chem., 1981,
vol. 46, p. 4252
7. Gardner, P.D., J. Am. Chem. Soc., 1954, vol. 76, p. 4550.
3. Achkasova, A.A. and El’chaninov, M.M., Khim. Getero-
tsikl. Soedin., 2006, p. 191.
4. Mel’nikova, E.B., El’chaninov, M.M., Milov, A.A., and
Luk’yanov, B.S., Khim. Geterotsikl. Soedin., 2008,
p. 1331.
8. Pozharskii, A.F., Teoreticheskie osnovy khimii geterotsik-
lov (Theoretical Foundations of the Chemistry of Hetero-
cycles), Moscow: Khimiya, 1985, p. 126.
9. Dunn, G.L., Actor, P., and DiPasquo, V.J., J. Med. Chem.,
1966, vol. 9, p. 751.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 46 No. 6 2010