Intermolecular cyclocondensation of arylchloropyruvates in the synthesis of 2,3-dihydrofuran-3,5-dicarboxylic acid derivatives

Article abstract of DOI:10.1007/s11172-015-1239-1

Methyl arylchloropyruvates undergo intermolecular self-condensation in the presence of a catalytic amount of a base under high-temperature conditions (~250°C) with the formation of 3,4-diaryl-2-oxo-2,3-dihydrofuran-3,5-dicarboxylic acid derivatives.

Full text of DOI:10.1007/s11172-015-1239-1

Russian Chemical Bulletin, International Edition, Vol. 64, No. 12, pp. 2865—2868, December, 2015
2865
Intermolecular cyclocondensation of arylchloropyruvates
in the synthesis of 2,3ꢀdihydrofuranꢀ3,5ꢀdicarboxylic acid derivatives
V. A. Mamedov,a,b E. A. Khafizova, A. I. Zamaletdinova, A. B. Dobrynin,a
a,b
a,b
a
a,b
I. A. Litvinov, and O. G. Sinyashin
aA. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy of Sciences,
8
ul. Akad. Arbuzova, 420088 Kazan, Russian Federation.
Fax: +7 (843) 273 2253. Eꢀmail: mamedov@iopc.ru
Kazan National Research Technological University,
b
6
8 ul. K. Marksa, 420015 Kazan, Russian Federation.
Fax: +7 (843) 238 5694
Methyl arylchloropyruvates undergo intermolecular selfꢀcondensation in the presence of
o
a catalytic amount of a base under highꢀtemperature conditions (~250 C) with the formation of
3
,4ꢀdiarylꢀ2ꢀoxoꢀ2,3ꢀdihydrofuranꢀ3,5ꢀdicarboxylic acid derivatives.
Key words: furanones, γꢀbutyrolactones, arylchloropyruvates, Darzens condensation, Xꢀray
diffraction analysis.
Substituted dihydrofuranones (or γꢀbutyrolactones) are
important synthetic intermediate products in organic synꢀ
thesis and usually are encountered as structural parts of
natural biologically active compounds, receptors, and
medicines.1 Apart from that, compounds containing
a γꢀbutyrolactone fragment have a long history of pharꢀ
tion of reaction products by distillation in vacuo using an
9,10
oil pump (0.01—0.02 Torr)
or by column chromatogꢀ
9
raphy on silica gel.
It was found9 that a prolonged heating during vacuꢀ
um distillation using a waterꢀjet pump (12—16 Torr)
of crude arylchloropyruvates 1a—d isolated from the reꢀ
action mixtures led to a partial intermolecular selfꢀconꢀ
densation with the formation of furanꢀ5ꢀones 2a—d
(Scheme 1).
,10
2
macological activity, including muscarinic (pilocarpine)
3
and antimuscarinic action (Kaiser lactones), convulsive
(
picrotoxin, βꢀsubstituted γꢀbutyrolactones) and anticonꢀ
4
vulsive activities (αꢀalkylꢀsubstituted γꢀbutyrolactones),
carcinogenic and antiꢀtumor activities, as well as the
ability to modulate sensory thresholds in the body.
5
6
7
Scheme 1
Though such furanones can be synthesized by a numꢀ
3
,8
ber of described methods, the multiꢀstep character of
the processes, poor availability of starting reagents, and
low yields of final products make impossible their use for
the synthesis of functionally substituted derivatives or limit
their application.
Earlier, we have shown that the reaction of dichloroꢀ
acetates with aromatic aldehydes under the Darzens conꢀ
densation conditions in the presence of a base proceeded,
depending on the character of substituents in the aromatic
ring of benzaldehyde, with the formation of either arylꢀ
chloroglycidates, or arylchloropyruvates 1, or a mixture of
these products.9,10 As a rule, a standard treatment of these
reaction mixtures included the washing with the concenꢀ
trated solution of NaCl, extraction with toluene or chloroꢀ
Ar = Ph (a), 4ꢀClC6H4 (b), 4ꢀBrC6H4 (c), 4ꢀFC6H4 (d)
Conditions: i. ~250 °C, 2 h.
form, drying the organic layer with MgSO , and purificaꢀ
4
The formation of furanꢀ5ꢀones 2a—d was indicated by
the presence in the H NMR spectrum of two singlets
1
*
Dedicated to Academician of the Russian Academy of Sciences
from the methyl protons of the ester groups. The IR spectrum
exhibited the bands for three carbonyl groups in the region
N. S. Zefirov on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2865—2868, December, 2015.
066ꢀ5285/15/6412ꢀ2865 © 2015 Springer Science+Business Media, Inc.
1

2
866
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Mamedov et al.
of 1733—1813 cm , one of which (1805—1813 cm–1
–
1
)
The formation of furanꢀ5ꢀones 2 can be presumably
represented by the scheme of intermolecular condensaꢀ
tion including a cascade of reactions (Scheme 2): 1) the
nucleophilic substitution of a chlorine atom in one of
the molecules with the carbon atom C(3) of the other
molecule of arylchloropyruvate with the formation of
compound A, 2) first, the closure of the fiveꢀmemꢀ
bered and, then, the threeꢀmembered rings with the
belonging to the lactone carbonyl fragment.11
Heating the individual compounds 1a—d at 200—250 °C
for 3 h does not lead to the formation of furanꢀ5ꢀones 2a—d.
Only in the case of compound 1a, a desired compound 2a
was isolated in low yield. Carrying out the selfꢀcondensaꢀ
tion of arylchloropyruvates 1a—d at the same temperaꢀ
tures, but in the presence of a small amount of a base, gave
the corresponding furanꢀ5ꢀones 2a—d in higher yields than
in the case of selfꢀcondensation of crude arylchloropyruꢀ
vates 1a—d observed in the course of distillation. Carrying
out the reaction in the presence of an equimolar amount
of a base at high temperature (above 200 °C) leads to
a difficult to separate mixtures of products, whereas at
1
6,17
formation of compound B,
3) the migration of the
ester group as a result of several intramolecular rearranꢀ
1
8,19
gements involving the intermediate compounds
C,
D, and E.
Scheme 2
relatively low temperatures (0—65 °C), as it was shown
earlier, to different condensation products,1
2—14
including
those of intermolecular selfꢀcondensation, depending on
the character of a base and reaction conditions.15
The structure of the selfꢀcondensation products was
also confirmed by Xꢀray diffraction studies of furanone 2a
(
Fig. 1).
Compound 2a crystallizes in the centrosymmetric
space group P2 /n, the independent part of the unit cell
1
contains one molecule. The fiveꢀmembered oxygenꢀ
containing (dihydrofuran) heterocycle is planar (within
0
.027(4) Å), the acetyl substituent at carbon atom C(5)
lies in the plane of the heterocycle (the torsion angle
O(1)—C(5)—C(51)—O(52) is 7.2(5)°). The phenyl subꢀ
stituent at atom C(4) is turned from the plane of the heteroꢀ
cycle (the torsion angle C(5)—C(4)—C(41)—C(46) is
5
7.4(6), the dihedral angle between the planes of the rings
is 58.3(2)°), the acetyl and the phenyl substituents at atom
C(3) are also turned relative to the plane of the heterocycle
(
the dihedral angles between their planes and the plane of
the fiveꢀmembered ring are 83.8(3) and 77.4(2)°, respecꢀ
tively). The presence of bulky substituents at the atoms of
heterocycle does not lead to the distortion of the main
geometric parameters of the molecule: its bond distances
lie within the standard values for this type of the bonds.
O(31)
C(41)
Note that compounds 2a,b have been synthesized earꢀ
lier20,21 from arylchloropyruvates 1a,b, but under more
complex experimental conditions. The authors prepared
C(46)
O(51)
20
O(32)
these compounds using copper salts (CuCl , CuBr ) on
C(5)
C(3)
2
2
C(4)
a SiO support in chlorobenzene at 130 °C, as well as obꢀ
C(51)
2
tained compound 2a by the reaction of CuCl with cyanoꢀ
2
epoxide in acetonitrile at low temperatures. Lactone 2a
C(2)
2
1
O(1)
was obtained by photooxidation of 2,5ꢀdi(methoxyꢀ
carbonyl)ꢀ3,4ꢀdiphenylcyclopentadienone with subseꢀ
quent dehydration.
O(52)
O(2)
Fig. 1. Molecular geometry of 2a in crystal.

Cyclocondensation of arylchloropyruvates
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015 2867
The found by us thermal intermolecular selfꢀcondenꢀ
sation of arylchloropyruvates opens the access to 3,4ꢀdiꢀ
arylꢀ2ꢀoxoꢀ2,3ꢀdihydrofuranꢀ3,5ꢀdicarboxylic acid derivꢀ
atives without application of metal catalysts and other
expensive reagents.
Colorless crystals, m.p. 167—168 °C, C20H16O6, M = 352.33
monoclinic, at 296 K a = 9.386(3), b = 9.657(3), c = 19.198(6) Å,
3
β = 99.584(5)°, V = 1715.8(9) Å , Z = 4, space group P2 /n,
1
dcalc = 1.364 g cm–3, μ = 0.101 mm , F(000) = 736. Parameters
of unit cell and experimental data were obtained at T = 296 K on
a Bruker Smart APEX II CCD automated diffractometer
–1
(
λ(MoꢀKα) = 0.71073 Å, ωꢀscan technique), 2θ < 54°, Rint = 0.034.
Experimental
From 13744 measured reflections, 3701 were independent, the
number of observed reflections with I > 2σ(I) was 1754. Absorpꢀ
2
2
Melting points were determined on Boetius heating stage.
IR spectra for all the compounds were recorded on a Bruker
Vectorꢀ22 Fourierꢀtransform spectrometer in KBr pellets. Elecꢀ
tron ionization mass spectra were obtained on a ThermoQuest/
Finnigan Trace MS quadrupole mass spectrometer, the samples
were injected through a system of direct injection with water
cooling; highꢀprecision mass spectra were obtained on a Finniꢀ
tion was included using the SADABS program. The structure
2
3
was solved by direct method using the SIR program and
refined by the fullꢀmatrix leastꢀsquares method using the
SHELXL97 program. . Hydrogen atoms were calculated geoꢀ
metrically and refined using a riding model. All the calculations
were carried out using the WinGX and APEX2 programs.
The final Rꢀfactor values: R 0.0748, wR 0.2284, GOOF = 1.01,
number of refined parameters 238. Crystallographic data for the
structure 1 were deposited with the Cambridge Crystallographic
Data Center (http://www.ccdc.cam.ac.uk; CCDC 1407989).
Dimethyl 3,4ꢀbis(4ꢀchlorophenyl)ꢀ2ꢀoxoꢀ2,3ꢀdihydrofuranꢀ
3,5ꢀdicarboxylate (2b). A. Compound 2b (0.44 g, 21%) was obꢀ
tained from 4ꢀchlorobenzaldehyde (1.40 g, 10.0 mmol) accordꢀ
ing to the described procedure.
B. Compound 2b (1.02 g, 64%) was obtained from 1b9,10
(2.00 g, 8.1 mmol) according to the procedure described above.
White crystals. M.p. 113—114 °C (Ref. 20: m.p. 120 °C). IR
(KBr), ν/cm– : 3444, 2952, 1805, 1750, 1731, 1648, 1594, 1495,
1435, 1403, 1337, 1260, 1242, 1209, 1188, 1124, 1098, 1015.
996, 976, 919, 904, 823, 799, 768, 758, 741, 727, 621, 509. 499,
2
4
2
5
26
2
1
gan MAT 212 highꢀprecision mass spectrometer. H NMR specꢀ
tra were recorded on Bruker AVANCE 400 and Bruker AVANCE
5
00 spectrometer. Chemical shifts are given relative to the signals
of the solvents used.
Synthesis of 2,3ꢀdihydrofuranꢀ3,5ꢀdicarboxylic acid derivaꢀ
tives (2) (general procedure). A. Potassium tertꢀbutoxide (10 mmol)
was slowly added to a mixture of an equimolar amount of the
corresponding dichloroacetate (10 mmol) and an aromatic aldeꢀ
hyde (10 mmol) in anhydrous toluene (30 mL) with stirring at
0
—10 °C under dry argon. The reaction mixture was allowed to
1
stand at room temperature for 14 h and quenched with a 25%
aqueous solution of NaCl (20 mL). After thorough shaking, the
organic layer was separated, the aqueous layer was extracted
with toluene (2×15 mL). The combined organic extracts were
1
482. H NMR (CDCl ), δ: 3.82 (s, 3 H, OCH ); 3.83 (s, 3 H,
3
3
dried with MgSO , the solvent was evaporated. The residue was
heated at ~250—270 °C for 2 h and cooled. Then, the reaction
OCH ); 7.04 (d, 2 H, J = 8.4 Hz); 7.22 (d, 2 H, J = 8.4 Hz); 7.28
(d, 2 H, J = 8.4 Hz); 7.34 (d, 2 H, J = 8.4 Hz). H NMR
4
3
1
mixture was diluted with diethyl ether (10 mL), the crystals
formed were filtered and recrystallized from Pr OH.
B. An equimolar amount of a base (5% aqueous solution of
КOH (5.6 mL) was added to methyl 3ꢀarylꢀ3ꢀchloroꢀ2ꢀoxoproꢀ
pionate (5 mmol), the reaction mixture was extracted with toluene
(DMSOꢀd ), δ: 3.76 (s, 3 H, OCH ); 3.87 (s, 3 H, OCH ); 7.18
6
3
3
i
(d, 2 H, J = 8.6 Hz); 7.40 (d, 2 H, J = 8.6 Hz); 7.44 (d, 2 H,
J = 8.6 Hz); 7.54 (d, 2 H, J = 8.6 Hz). MS, m/z (I (%)): 422 (36),
+
421 (10), [M] 420 (48), 378 (23), 377 (9), 376 (33), 363 (16),
362 (11), 361(23), 335 (70), 334 (23), 333 (84), 307 (71), 306
(22), 305 (84), 273 (19), 264 (66), 263 (22), 262 (84), 246 (73),
212 (46), 199 (60), 191 (70), 176 (68), 150 (55), 149 (78), 139 (100),
125 (63).
(
2×25 mL). The organic layer was washed with water (2×25 mL)
and dried with MgSO , the solvent was evaporated. The residue
4
was heated at a high temperature (250—270 °C) for 2 h. After
cooling, the reaction mixture was treated with diethyl ether to
isolate crystals.
Dimethyl 2ꢀoxoꢀ3,4ꢀdiphenylꢀ2,3ꢀdihydrofuranꢀ3,5ꢀdicarꢀ
boxylate (2a). A. (0.51 g, 29%) was obtained from benzaldehyde
Dimethyl 3,4ꢀbis(4ꢀbromophenyl)ꢀ2ꢀoxoꢀ2,3ꢀdihydrofuranꢀ
3,5ꢀdicarboxylate (2c) was obtained according to the procedure
B described above from compound 1c9 (2.00 g, 6.9 mmol).
The yield of compound 2c was 1.05 g (60%).
,10
(
1.06 g, 10.0 mmol) according to the procedure described above.
Light brown crystals. M.p. 99—100 °C. IR (KBr), ν/cm–1
:
B. Compound 2a (1.06 g, 64%) was obtained from arylchloꢀ
2953, 1814, 1766, 1737, 1589, 1488, 1436, 1398, 1334, 1274,
1204, 1174, 1115, 1071, 1011, 964, 931, 824, 758, 508. H NMR
ropyruvate 1a9 (2.00 g, 9.4 mmol) according to the procedure
,10
1
described above.
(DMSOꢀd ), δ: 3.72 (s, 3 H, OCH ); 3.83 (s, 3 H, OCH ); 7.07
(d, 2 H, J = 8.8 Hz); 7.29 (d, 2 H, J = 8.4 Hz); 7.54 (d, 2 H,
J = 8.4 Hz); 7.63 (d, 2 H, J = 8.8 Hz).
6
3
3
i
White crystals. M.p. 167—168 °C (Pr OH) (Ref. 21: m.p.
1
1
1
71 °C). IR (KBr), ν/cm–1: 3443, 2997, 2953, 1805, 1752, 1733,
651, 1498, 1441, 1335, 1260, 1242, 1205, 1191, 1127, 1018,
002, 979, 927, 772, 748, 709, 699, 691, 609. H NMR (CDCl ),
Dimethyl 3,4ꢀbis(4ꢀfluorophenyl)ꢀ2ꢀoxoꢀ2,3ꢀdihydrofuranꢀ
3,5ꢀdicarboxylate (2d) was obtained by method B from comꢀ
1
3
2
7
δ: 3.80 (s, 3 H, OCH ); 3.82 (s, 3 H, OCH ); 7.07—7.09 (m, 2 H,
Ph); 7.28—7.37 (m, 8 H, Ph). H NMR (DMSOꢀd ), δ: 3.73 (s,
pound 1d (2.00 g, 8.7 mmol). The yield of compound 2d was
1.21 g (72%).
3
3
1
6
3
7
H, OCH ); 3.84 (s, 3 H, OCH ); 7.13—7.15 (d, 2 H, J = 7.0 Hz);
.31—7.38 (m, 5 H, Ph); 7.43—7.44 (m, 3 H, Ph). MS, m/z
Brown crystals. M.p. 119—121 °C. IR (KBr), ν/cm–1: 3440,
2958, 1805, 1750, 1733, 1603, 1511, 1436, 1339, 1261, 1241,
3
3
+
1
(
(
I (%)): 353 (10), [M] 352 (31), 308 (28) 265 (44), 237 (48), 233
20), 194 (55), 178 (100), 176 (48), 166 (35), 165 (35), 152 (350,
1165, 1126, 1016, 1002, 836, 592, 536. NMR H NMR (CDCl ),
3
δ: 3.82 (s, 3 H, OCH ); 3.83 (s, 3 H, OCH ); 6.99 (dd, 2 H,
3
3
1
51 (33), 150 (25), 126 (22), 115 (41), 91 (40).
Crystals of compound 2a suitable for Xꢀray diffraction studies
J = 8.6 Hz, J = 8.6 Hz); 7.06 (dd, 2 H, J = 8.6 Hz, J = 8.6 Hz);
7.09 (dd, 2 H, J = 9.0 Hz, J = 5.3 Hz); 7.27 (dd, 2 H, J = 9.0 Hz,
J = 5.3 Hz).
were obtained by recrystallization from isopropyl alcohol.

2
868
Russ.Chem.Bull., Int.Ed., Vol. 64, No. 12, December, 2015
Mamedov et al.
This work was financially supported by the Russian
11. L. A. Kazitsyna, N. B. Kupletskaya, Primenenie UFꢀ, IKꢀ i
YaMRꢀspektroskopii v organicheskoi khimii [Application of UV,
IR, and NMRꢀspectroscopy in Organic Chemistry], Vysshaya
shkola, Moscow, 1971, 264 pp. (in Russian).
Science Foundation (Priority Direction of Studies "Funꢀ
damental Scientific Studies and Scientific Search by the
Personal of Existing Research Laboratories (Departꢀ
ments)" (Project No. 14ꢀ23ꢀ00073).
1
2. V. A. Mamedov, I.A. Litvinov, I. A. Nuretdinov, Bull. Russ.
Acad. Sci., Div. Chem. Sci. (Engl. Transl.), 1990, 39, 2226
[
Izv. Akad. Nauk SSSR, Ser. Khim., 1990, 2454].
References
13. V. A. Mamedov, I. A. Litvinov, A. T. Kh. Lenstra, Yu. Ya.
Efremov, V. A. Naumov, I. A. Nuretdinov, Bull. Russ. Acad.
Sci., Div. Chem. Sci. (Engl. Transl.), 1991, 40, 1267 [Izv.
Akad. Nauk SSSR, Ser. Khim., 1991, 1427].
1
. (a) X. Wu, H. Chen, Tetrahedron, 2008, 64, 10331; (b) T. Ok,
H. Lee, J. Org. Chem., 2009, 72, 7390; (c) V. V. Shchepin,
A. E. Korzun, N. V. Bronnikova, Russ. J. Org. Chem.
Engl. Transl.), 2004, 40, 999 [Zh. Org. Khim., 2004, 40,
040]; (d) T. Hiroki, U. Yasuhiro, M. Takefumi, J. Org.
Chem., 1995, 60, 5628; (e) P. L. Creger, J. Org. Chem., 1972,
7, 1907; (f) K. Mori, Tetrahedron, 1983, 39, 3107; (g) L. J.
Theodore, W. L. Nelson, J. Org. Chem., 1987, 52, 1309.
. H. R. Rang, M. M. Dale, J. M. Ritter, P. Moore, In Pharmaꢀ
cology, Ed. L. Hunter, 5th ed., London, Churchill Livingꢀ
stone, 2003, p 144.
. C. Kaiser, L. NoronhaꢀBlob, J. Med. Chem. 1992, 35, 4415.
. M. I. Konaklieva, B. J. Plotkin, MiniꢀRev. Med. Chem., 2005,
1
4. V. A. Mamedov, A. T. Gubaidullin, I. A. Litvinov, S. Tsubꢀ
oi, Heterocycles, 2000, 52, 1385.
(
1
1
5. V. A. Mamedov, S. Tsuboi, L. V. Mustakimova, H. Hamaꢀ
moto, A. T. Gubaidullin, I. A. Litvinov, Ya. A. Levin, Chem.
Heterocycl. Compd. (Engl. Transl.), 2000, 36, 911 [Khim.
Geterotsikl. Soedin., 2000, 8, 1042].
3
1
6. J. R. Cannon, V. A. Patrick, C. L. Raston, A. H. White, Aust.
J. Chem., 1978, 31, 6, 1265—1283.
2
1
1
7. W. Adam, K. Peters, M. Sauter, Synthesis, 1994, 1, 111.
8. W. Adam, L. Hadjiarapoglou, Th. Mosandl, C. R. Sahaꢀ
Möller, D. Wild, Angew. Chem., 1991, 103, 187.
9. Y. Kawase, S. Yamaguchi, H. Ochiai, H. Horita, Bull. Chem.
Soc. Jpn, 1974, 47, 2660.
3
4
1
5
, 73.
5
. (a) F. Dickens, H. E. H. Jones, Brit. J. Cancer, 1963, 17,
00; (b) F. Dickens, H. E. H. Jones, Brit. J. Cancer, 1965,
9, 392; (c) F. Dickens, H. E. H. Jones, H. B. Waynforth,
Brit. J. Cancer, 1966, 20, 134.
. (a) S. M. Kupchan, R. W. Britto, M. F. Ziegler, C. J.
Gilmore, R. J. Restivo, R. F. Bryan, J. Am. Chem. Soc.,
973, 95,1335; (b) S. M. Kupchan, M. Maruyama, R. J.
Hemingway, J. C. Hemingway, S. Shibuya, T. Fujita, J. Org.
Chem., 1973, 38, 2189.
. (a) J. Estephane, A. Doutheau, Bioorg. Med. Chem. Lett.,
008, 18, 4321; (b) G. D. Geske, H. E. Blackwell, Bioorg.
2
2
2
0. N. Brine, A. Foucaud, Bull. Soc. Chim. Fr., 1993, 130, 620.
1. G. Rio, B. Serkiz, Bull. Soc. Chim. Fr., 1976, 1491.
2. G. M. Sheldrick, SADABS. Bruker AXS Inc., Madison,
USA, 1997.
1
1
6
2
2
3. A. Altomare, G. Cascarano, C.Giacovazzo, D.Viterbo, Acta
Crystallogr. Sect. A, 1991, 47, 744.
4. G. M. Sheldrick, SHELXLꢀ97. Programꢀs for Crystal Strucꢀ
ture Analysis (Release 97ꢀ2). University of Göttingen, Götꢀ
tingen, 1997, Vols 1, 2.
1
7
8
2
2
5. L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
6. APEX2 (Version 2.1), SAINTPlus. Data Reduction and
Correction Programꢀ (Version 7.31A), Bruker Advanced
Xꢀray Solutions, Bruker AXS Inc., Madison, Wisconsin,
USA, 2006.
2
Med. Chem. Lett., 2008, 18, 5978.
. (a) M. Ito, T. Ikariya, Org. Lett., 2007, 9, 1821; (b) E. Abraꢀ
ham, A. D. Smith, Tetrahedron, 2007, 63, 5855; (c) M. M.
Kayser, C. M. Clouthier, J. Org. Chem. 2006, 71, 8424;
2
7. T. Hirayama, M. Okaniwa, T. Imada, A. Ohashi, M. Ohori,
K. Iwai, K. Mori , T. Kawamoto, A. Yokota, T. Tanaka,
T. Ishikawa, Bioorg. Med. Chem., 2013, 21, 5488.
(
d) D. Hoppe, Angew. Chem., Int. Ed. Engl., 1984, 23, 932.
9
. V. A. Mamedov, E. A. Berdnikov, S. Tsuboi, H. Hamamoto,
T. Komiyama, E. A. Gorbunova, A. T. Gubaidullin, I. A.
Litvinov, Russ. Chem. Bull. (Int. Ed.), 2006, 55, 1455 [Izv.
Akad. Nauk, Ser. Khim., 2006, 1402].
1
0. V. A. Mamedov, I. A. Nuretdinov, Bull. Russ. Acad. Sci.,
Div. Chem. Sci. (Engl. Transl.), 1992, 41, 1690 [Izv. Akad.
Nauk, Ser. Khim., 1992, 2159].
Received May 22, 2015;
in revised form October 22, 2015