Synthetic transformations of higher terpenoids: XXV.* cross coupling of phlomisoic acid methyl ester with alkenes in the presence of oxidants

Article abstract of DOI:10.1134/S107042801104021X

The reaction of phlomisoic acid methyl ester with styrene, catalyzed by Pd(OAc)₂, in the presence of Cu(OAc)₂ and 1,4-benzoquinone in a mixture of propionic acid with diethyl ether gave the corresponding 15,16-distyryl derivative and

Full text of DOI:10.1134/S107042801104021X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 4, pp. 602–605. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © Yu.V. Kharitonov, E.E.Shul’ts, M.M. Shakirov, G.A. Tolstikov, 2011, published in Zhurnal Organicheskoi Khimii, 2011, Vol. 47,
No. 4, pp. 597–600.
Synthetic Transformations of Higher Terpenoids:
XXV.* Cross Coupling of Phlomisoic Acid Methyl Ester
with Alkenes in the Presence of Oxidants
Yu. V. Kharitonov, E. E.Shul’ts, M. M. Shakirov, and G. A. Tolstikov
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: schultz@nioch.nsc.ru
Received September 22, 2010
Abstract—The reaction of phlomisoic acid methyl ester with styrene, catalyzed by Pd(OAc)2, in the presence
of Cu(OAc)2 and 1,4-benzoquinone in a mixture of propionic acid with diethyl ether gave the corresponding
15,16-distyryl derivative and only traces of 15- and 16-monosubstituted furanolabdanoids. Oxidative coupling
of the title compound with methyl acrylate under analogous conditions afforded a mixture of 15-mono-, 16-
mono-, and 15,16-dialkenylation products whose ratio changed during the process. The reaction was stereo-
selective, and the exocyclic double bond in the products had exclusively E configuration.
DOI: 10.1134/S107042801104021X
Plant labdanoids are natural compounds possessing
versatile pharmacological activity [2]. We previously
described the synthesis of phlomisoic acid (I) [3] and
its methyl ester II [4] from lambertianic acid which
is an accessible metabolite of Siberian pine (Pinus
sibirica). With a view to obtain diterpenoid derivatives
with alkenyl substituents in the furan ring we ex-
amined oxidative coupling (Heck oxidative reaction)
[5] of phlomisoic acid methyl ester (II) with alkenes.
Oxidative coupling of 2-methylfuran with activated
alkenes in the presence of a stoichiometric amount of
palladium compounds was reported in [6]. In addition,
there are published data on catalytic alkenylation of
furans in the presence of catalytic systems containing
palladium complexes and copper(II) salts [7], in partic-
ular palladium acetate–tert-butyl hydroperoxide–ben-
zoquinone [8], palladium acetate–molybdovanado-
phosphoric acid [9], and palladium acetate–copper
acetate–benzoquinone [10].
The reaction of phlomisoic acid methyl ester (II)
with styrene (2 equiv), catalyzed by Pd(OAc)2
(0.1 equiv), in the presence of Cu(OAc)2 (0.5 equiv)
and 1,4-benzoquinone (0.1 equiv) in a 1:1 mixture of
propionic acid with diethyl ether (35°C, 10 h) in
an oxygen atmosphere resulted in the formation of
(E)-15,16-distyryl-15,16-epoxylabdatrienoate III in
63% yield, the conversion being 90%. Increase of the
reaction time until complete conversion of the initial
compound did not improved the yield of III. When the
reaction was performed using an equimolar amount of
styrene, other conditions being equal, the product was
15,16-distyryl derivative III as well (yield 32%, con-
version 40%). In the presence of 0.05 equiv of
Pd(OAc)2 the yield of III was 23% (conversion 57%).
In these cases, only trace amounts of monosubstituted
furanolabdanoids IV and V were detected. Interesting-
ly, the reaction of II with 1 equiv of styrene in di-
oxane–propionic acid (5:1) in the presence of a stoi-
chiometric amount of palladium acetate at 100°C
(10 h) also afforded (E)-15,16-distyryllabdatrienoate
III as the only product (yield 19%, conversion 57%)
and was accompanied by considerable tarring.
16
12
13
O
11
20
Me
15
14
9
Me17
1
2
3
8
10
5
7
In the reaction of phlomisoic acid methyl ester (II)
with methyl acrylate, the complete conversion was
attained in 80 h. The products were 15,16-bis(3-me-
thoxy-3-oxoprop-1-en-1-yl)-, 16-(3-methoxy-3-oxo-
prop-1-en-1-yl)-, and 15-(3-methoxy-3-oxoprop-1-en-
4
6
H
19
Me COOH
18
I
* For communication XXIV, see [1].
602

SYNTHETIC TRANSFORMATIONS OF HIGHER TERPENOIDS: XXV.
603
Scheme 1.
R
2'
1'
O
O
Pd(OAc)2 (5–10 mol %)
BQ (20 mol %), Cu(OAc)2 (50 mol %)
Et2O, EtCOOH, O2, 35°C
Me
Me
Me
Me
+
R
R
CH2
H
H
Me COOMe
Me COOMe
II
III, VI
R
O
O
Me
H
Me
Me
Me
+
+
R
H
Me COOMe
Me COOMe
IV, VII
V, VIII
III–V, R = Ph; VI–VIII, R = MeOCO; BQ = 1,4-benzoquinone.
1-yl)-15,16-epoxy-8(9),13(16),14-labdatrien-18-oic
acid methyl esters VI–VIII (27, 17, and 7%, respec-
tively; Scheme 1). Pure compounds VI and VII were
isolated by column chromatography. According to the
16-H protons resonated as singlets at δ 6.49 and
7.24 ppm, respectively.
To conclude, oxidative coupling of phlomisoic acid
methyl ester with alkenes can be used for the synthesis
of furanolabdanoids having alkenyl substituents in the
α-positions of the furan ring.
1
data of H NMR monitoring, the ratio of compounds
VI, VII, and VIII in the reaction mixture changed
during the process. It was 1:7:8 in 10 h and 1:2:1 in
30 h. These findings indicate that monoalkenyl-substi-
tuted labdanoids VII and VIII are formed initially as
the major products.
EXPERIMENTAL
1
The H and 13C NMR spectra were recoded on
The structure of the products was confirmed by
their IR, UV, NMR, and mass spectra. The presence of
alkenyl groups in the furan ring of labdanoids III,
VI, and VII gives rise to absorption bands in the elec-
tronic absorption spectra with their maxima at λ 286,
387 (III), 251, 336 (VI), and 315 nm (VII).
Bruker AV-300 (300.13 and 75.47 MHz, respectively)
and Bruker DRX-500 spectrometers (500.13 and
125.76 MHz, respectively). Multiplicity of signals in
the 13C NMR spectra was determined using standard
J-modulation techniques with off-resonance decou-
pling from protons. The mass spectra were obtained on
a Thermo Scientific DFS high-resolution mass spec-
trometer. The optical rotations [α]D20 were determined
on a PolAAr 3005 polarimeter at room temperature
(20–23°C). The IR spectra were recorded in KBr on
a Bruker Vector-22 instrument. The UV spectra were
measured on an HP 8453 UV-Vis spectrophotometer
from solutions in ethanol (c = 10–4 M). The progress
of reactions and the purity of products were monitored
by TLC on Silufol UV-254 plates using chloroform–
ethanol (3:1) and petroleum ether–ethyl acetate (10:1)
as eluents; the chromatograms were developed by
spraying with a 10% aqueous solution of H2SO4,
followed by heating to 100°C, or by UV irradiation.
1
The H and 13C NMR spectra of the obtained com-
pounds were consistent with the assumed structures;
they contained one set of signals typical of the furano-
diterpene fragment and the corresponding substituent.
Protons at the exocyclic double bond (1′-H, 2′-H) reso-
nated as doublets at δ 7.10–7.45 and 6.24–6.90 ppm,
and the coupling constant 3J1′,2′ (16.1 Hz for compound
III and 15.6 Hz for methyl acrylate derivatives VI–
VIII) indicated trans orientation of these protons. Sub-
stitution at C16 of the furan ring leads to downfield
1
shift of the 14-H and 15-H signals in the H NMR
spectrum of VII (δ 6.38 and 7.39 ppm, respectively,
3J14,15 = 1.9 Hz). In the spectrum of VIII, the 14-H and
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 4 2011

KHARITONOV et al.
604
Phlomisoic acid methyl ester (II) was synthesized
according to the procedure reported in [4]. Palladium
(II) acetate was prepared as described in [11].
(20), 103 (19), 91 (27), 77 (14), 41 (11), 28 (13), 18
(11). Found: m/z 534.3126 [M]+. C37H42O3. Calculated:
M 534.3129.
Reaction of phlomisoic acid methyl ester (II)
with methyl acrylate. Phlomisoic acid methyl ester
(II), 1.00 g (3.03 mmol), was dissolved in a mixture of
4 ml of propionic acid and 4 ml of diethyl ether, and
0.27 ml (3.03 mmol) of methyl acrylate, 0.046 g
(0.15 mmol) of Pd(OAc)2, 0.275 g (1.51 mmol) of
Cu(OAc)2, and 0.033 g (0.30 mmol) of 1,4-benzo-
quinone were added in succession under stirring. The
mixture was stirred for 80 h at 35°C in a stream of
oxygen, an additional portion (0.13 ml) of methyl
acrylate being added every 10 h. The mixture was then
poured into 30 ml of water and extracted with chloro-
form (3×40 ml), the extracts were combined, washed
with water (3×50 ml), and dried over MgSO4, the
solvent was distilled off under reduced pressure, and
the residue was subjected to chromatography on silica
gel using petroleum ether–diethyl ether (10 :1) as
eluent to isolate (in order of elution) 0.30 g (24%) of
a mixture of compounds VII and VIII and 0.40 g
(27%) of compound VI.
Methyl (1S,4aS,8aR)-5-(2-{2,5-bis[(E)-styryl]-
furan-3-yl}ethyl)-1,4a,6-trimethyl-1,2,3,4,4a,7,8,8a-
octahydronaphthalene-1-carboxylate (III). Phlomi-
soic acid methyl ester (II), 1.00 g (3.03 mmol), was
dissolved in a mixture of 4 ml of propionic acid and
4 ml of diethyl ether, and 0.70 ml (6.06 mmol) of
styrene, 0.046 g (0.15 mmol) of Pd(OAc)2, 0.275 g
(1.51 mmol) of Cu(OAc)2, and 0.033 g (0.30 mmol) of
1,4-benzoquinone were added in succession under
stirring. The mixture was stirred for 10 h at 35°C in
a stream of oxygen, cooled, poured into 30 ml of
water, and extracted with chloroform (3×40 ml). The
extracts were combined, washed with water (3×50 ml),
and dried over MgSO4, the solvent was distilled off
under reduced pressure, and the residue was subjected
to chromatography on silica gel using petroleum ether–
diethyl ether (10:1) as eluent. The product was addi-
tionally purified by recrystallization from diethyl ether.
Yield 1.02 g (63%), light yellow substance, mp 62–
64°C, [α]D20 = +49.59° (c = 1.36, CHCl3). IR spectrum,
ν, cm–1: 695, 753, 846, 955, 973, 1154, 1232, 1379,
1464, 1602, 1723, 2872, 2928, 2959, 3432. UV spec-
Methyl (1S,4aS,8aR)-5-(2-{2,5-bis[(E)-3-methoxy-
3-oxoprop-1-en-1-yl]furan-3-yl}ethyl)-1,4a,6-tri-
methyl-1,2,3,4,4a,7,8,8a-octahydronaphthalene-
1-carboxylate (VI). Oily substance, [α]D20 = +53.54°
(c = 0.99, CHCl3). IR spectrum, ν, cm–1: 618, 1013,
1064, 1084, 1103, 1122, 1152, 1195, 1254, 1349, 1437,
1
trum, λmax, nm (logε): 286 (4.22), 387 (4.12). H NMR
spectrum, δ, ppm: 0.80 s (3H, C20H3), 1.06 d.t (1H,
3-H, J = 13.4, 4.1 Hz), 1.22 s (3H, C19H3), 1.28 m (1H,
1-H), 1.37 d.d (1H, 5-H, J = 13.0, 1.5 Hz), 1.59 m (1H,
2-H), 1.70 s (3H, C17H3), 1.75 d.d (1H, 6-H, J = 12.3,
5.3 Hz), 1.80–1.92 m (1H, 2-H), 1.94–2.01 m (3H,
1-H, 6-H, 7-H), 2.04–2.16 m (2H, 7-H, 11-H), 2.22–
2.27 m (2H, 3-H, 11-H), 2.53 m (2H, 12-H), 3.63 s
(3H, OCH3), 6.34 s (1H, 14-H), 6.85 d (1H, 2′-H, J =
16.1 Hz), 6.90 d (1H, 2′-H, J = 16.1 Hz), 7.10 d (1H,
1′-H, J = 16.1 Hz), 7.12 d (1H, 1′-H, J = 16.1 Hz),
7.23 m (2H, p-H), 7.35 m (4H, m-H), 7.49 m (4H, o-H,
J = 7.9 Hz). 13C NMR spectrum, δC, ppm: 17.41 q
(C20), 19.27 t (C2), 19.55 q (C17), 20.46 t (C6), 25.32 t
(C12), 28.06 q (C19), 28.99 t (C11), 33.93 t (C7), 36.94 t
(C1), 37.34 t (C3), 39.26 s (C10), 43.52 s (C4), 50.73 q
(OCH3), 53.12 d (C5), 111.87 d (C14), 113.76 d (C1′),
115.74 d (C1′), 125.28 d (C2′), 125.75 d and 125.94 d
(Co), 126.48 s (C13), 126.78 d (C2′), 126.92 d (Cp),
127.15 d (Cp), 127.25 s (C8), 128.31 d and 128.34 d
(Cm), 136.71 s (Ci), 137.08 s (Ci), 138.16 s (C9),
147.91 s (C15), 151.84 s (C16), 177.65 s (C18). Mass
spectrum, m/z (Irel, %): 534 (35), 286 (39), 285 (100),
212 (27), 189 (20), 181 (12), 179 (100), 175 (12), 173
(13), 165 (16), 157 (12), 153 (12), 141 (13), 133 (13),
131 (38), 129 (13), 119 (15), 115 (13), 107 (10), 105
1459, 1634, 1705, 2860, 2945, 3524. UV spectrum,
1
λ
max, nm (logε): 251 (3.84), 336 (3.84). H NMR spec-
trum, δ, ppm: 0.74 s (3H, C20H3), 1.01 d.t (1H, 3-H,
J = 13.4, 4.6 Hz), 1.18 s (3H, C19H3), 1.22 m (1H,
1-H), 1.32 d.m (1H, 5-H, J = 13.0 Hz), 1.50–1.56 m
(1H, 2-H), 1.60 s (3H, C17H3), 1.65–1.79 m (2H, 2-H,
6-H), 1.81–1.96 m (3H, 1-H, 6-H, 7-H), 1.98–2.06 m
(2H, 7-H, 11-H), 2.16–2.22 m (2H, 3-H, 11-H), 2.50 m
(2H, 12-H), 3.60 s (3H, OCH3), 3.77 s (6H, OMe),
6.34 d (1H, 2′-H, J = 15.6 Hz), 6.38 d (1H, 2′-H, J =
15.6 Hz), 6.56 s (1H, 14-H), 7.33 d (1H, 1′-H, J =
15.6 Hz), 7.40 d (1H, 1′-H, J = 15.6 Hz). 13C NMR
spectrum, δC, ppm: 17.64 q (C20), 19.41 t (C2), 19.76 q
(C17), 20.62 t (C6), 24.55 t (C12), 28.26 q (C19), 28.32 t
(C11), 34.13 t (C7), 37.17 t (C1), 37.50 t (C3), 39.43 s
(C10), 43.72 s (C4), 50.99 q (OCH3), 51.61 q (OCH3),
51.66 q (OCH3), 53.26 d (C5), 115.66 d (C14), 117.22 d
(C1′), 117.46 d (C1′), 128.05 d (C2′), 128.06 s (C8),
130.15 d (C2′), 132.84 s (C13), 137.79 s (C9), 148.10 s
(C15), 151.52 s (C16), 167.01 s (C=O), 167.29 s (C=O),
177.88 s (C18). Mass spectrum, m/z (Irel, %): 498
(0.34), 330 (16), 255 (10), 250 (13), 249 (11), 235
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 4 2011

SYNTHETIC TRANSFORMATIONS OF HIGHER TERPENOIDS: XXV.
605
(16), 189 (75), 175 (25), 149 (28), 147 (20), 133 (34),
121 (19), 119 (34), 109 (20), 107 (22), 105 (26), 97
(18), 95 (23), 91 (23), 85 (64), 83 (100), 81 (26), 71
(38), 69 (28), 67 (19), 59 (21), 57 (55), 55 (49), 43
(59), 41 (44), 27 (24). Found: m/z 498.2606 [M]+.
C25H34O5. Calculated: M 498.2612.
51.03 q (OCH3), 51.23 q (OCH3), 53.13 d (C5),
114.60 d (C14), 115.66 d (C1′), 127.23 s (C8), 130.97 d
(C2′), 130.98 s (C13), 138.14 s (C9), 144.17 d (C16),
146.28 s (C15), 167.21 s (C=O), 177.96 s (C18).
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 08-03-00340).
Methyl (1S,4aS,8aR)-5-(2-{2-[(E)-3-methoxy-3-
oxoprop-1-en-1-yl]furan-3-yl}ethyl)-1,4a,6-trimeth-
yl-1,2,3,4,4a,7,8,8a-octahydronaphthalene-1-car-
boxylate (VII) was isolated by repeated chromatog-
raphy of mixture VII/VIII. Oily substance. IR spec-
trum, ν, cm–1: 973, 1041, 1165, 1193, 1235, 1306,
1377, 1436, 1464, 1637, 1723, 1772, 2952, 3432. UV
REFERENCES
1. Antimonova, A.N., Uzenkova, N.V., Petrenko, N.I.,
Shakirov, M.M., Shul’ts, E.E., and Tolstikov, G.A.,
Russ. J. Org. Chem., 2011, vol. 47, p. 589.
2. Tolstikov, G.A., Tolstikova, T.G., Shults, E.E., Soroki-
na, I.V., Chernov, S.V., and Kharitonov, Y.V., Oxygen
and Sulfur-Containing Heterocycles, Kartsev, V.G.,
Moscow: IBS, 2003, vol. 1, p. 94; Gonzalez-Colo-
ma, A., Guadano, A., Tonn, C.E., and Sosa, M.E.,
Z. Naturforsch., Tile C, 2005, vol. 60, p. 855; Su, C.-R.,
Ueng, Y.-F., Dung, N.X., Reddy, M.V.B., and Wu, T.-S.,
J. Nat. Prod., 2007, vol. 70, p. 1930; Prisinzano, T.E.
and Rothman, R.B., Chem. Rev., 2008, vol. 108,
p. 1732.
3. Mironov, M.E., Kharitonov, Yu.V., Shul’ts, E.E., Sha-
kirov, M.M., Bagryanskaya, I.Yu., and Tolstikov, G.A.,
Khim. Prirodn. Soedin., 2010, Vol. 46, p. 194.
4. Kharitonov, Yu.V., Shul’ts, E.E., Shakirov, M.M., and
Tolstikov, G.A., Russ. J. Org. Chem., 2008, vol. 44,
p. 516.
5. Shilov, E. and Shul’pin, G.V., Chem. Rev., 1997, vol. 97,
p. 2879; Dyker, G., Angew. Chem., 1999, vol. 111,
p. 1808; Jia, C., Kitamura, T., and Fujiwara, Y., Acc.
Chem. Res., 2001, vol. 34, p. 633; Ritleng, V., Sinlin, C.,
and Pfeffer, M., Chem. Rev., 2002, vol. 102, p. 1731;
Beccalli, E.M., Broggini, G., Martinelli, M., and Sotto-
cornala, S., Chem. Rev., 2007, vol. 107, p. 5318.
6. Asano, P., Moritani, I., Fujiwara, Y., and Teranishi, H.,
Bull. Chem. Soc. Jpn., 1973, vol. 46, p. 663; Fuji-
wara, Y., Maruyama, O., Yoshidomi, M., and Tani-
guchi, H., J. Org. Chem., 1981, vol. 46, p. 851.
1
spectrum: λmax 315 nm (logε 4.02). H NMR spectrum,
δ, ppm: 0.75 s (3H, C20H3), 1.03 d.t (1H, 3-H, J = 13.4,
4.3 Hz), 1.20 s (3H, C19H3), 1.25 m (1H, 1-H), 1.34 d.d
(1H, 5-H, J = 12.6, 1.9 Hz), 1.53–1.57 m (1H, 2-H),
1.63 s (3H, C17H3), 1.69–1.76 m (1H, 6-H), 1.82–
1.89 m (1H, 2-H), 1.92–1.97 m (3H, 1-H, 6-H, 7-H),
2.00–2.10 m (2H, 7-H, 11-H), 2.18–2.23 m (2H, 3-H,
11-H), 2.53 m (2H, 12-H), 3.62 s (3H, OCH3), 3.76 s
(3H, OCH3), 6.24 d (1H, 2′-H, J = 15.6 Hz), 6.38 d
(1H, 14-H, J = 1.9 Hz), 7.39 d (1H, 15-H, J = 1.9 Hz),
7.45 d (1H, 1′-H, J = 15.6 Hz). 13C NMR spectrum, δC,
ppm: 17.65 q (C20), 19.46 t (C2), 19.79 q (C17), 20.67 t
(C6), 25.54 t (C12), 28.32 q (C19), 28.94 t (C11), 34.17 t
(C7), 37.16 t (C1), 37.56 t (C3), 39.46 s (C10), 43.77 s
(C4), 51.03 q (OCH3), 51.50 q (OCH3), 53.32 d (C5),
113.03 d and 113.46 d (C14, C1′), 127.86 s (C8),
129.08 d (C2′), 130.98 s (C13), 138.09 s (C9), 144.17 d
(C15), 146.28 s (C16), 167.76 s (C=O), 177.96 s (C18).
Methyl (1S,4aS,8aR)-5-(2-{5-[(E)-3-methoxy-3-
oxoprop-1-en-1-yl]furan-3-yl}ethyl)-1,4a,6-trimeth-
yl-1,2,3,4,4a,7,8,8a-octahydronaphthalene-1-car-
1
boxylate (VIII). Characteristic H and 13C NMR sig-
nals were identified in the spectra of a mixture of com-
1
pounds VIII and VII at a ratio of 2:1. H NMR spec-
trum, δ, ppm: 0.75 s (3H, C20H3), 1.03 d.t (1H, 3-H,
J = 13.4, 4.3 Hz), 1.19 s (3H, C19H3), 1.25 m (1H,
1-H), 1.34 d.d (1H, 5-H, J = 12.6, 1.9 Hz), 1.53–
1.57 m (1H, 2-H), 1.61 s (3H, C17H3), 1.69–1.76 m
(1H, 6-H), 1.82–1.89 m (1H, 2-H), 1.92–1.97 m (3H,
1-H, 6-H, 7-H), 2.00–2.10 m (2H, 7-H, 11-H), 2.18–
2.23 m (2H, 3-H, 11-H), 2.53 m (2H, 12-H), 3.62 s
(3H, OCH3), 3.76 s (3H, OCH3), 6.24 d (1H, 2′-H, J =
15.6 Hz), 6.49 s (1H, 14-H), 7.24 s (1H, 16-H), 7.35 d
(1H, 1′-H, J = 15.6 Hz). 13C NMR spectrum, δC, ppm:
17.34 q (C20), 19.46 t (C2), 19.79 q (C17), 20.67 t (C6),
25.17 t (C12), 28.32 q (C19), 28.94 t (C11), 34.17 t (C7),
36.85 t (C1), 37.32 t (C3), 39.46 s (C10), 43.77 s (C4),
7. Tsuji, J. and Nagashima, H., Tetrahedron, 1984, vol. 40,
p. 2699.
8. Jia, C., Lu, W., Kitamuro, T., and Fujiwara, Y., Org.
Lett., 1999, vol. 1, p. 2097.
9. Yokota, T., Tani, M., Sakaguchi, S., and Ishii, Y., J. Am.
Chem. Soc., 2003, vol. 125, p. 1476; Tani, M., Sakagu-
chi, S., and Ishii, Y., J. Org. Chem., 2004, vol. 69,
p. 1221.
10. Aouf, C., Thiery, E., Le Bras, J., and Muzart, J., Org.
Lett., 2009, vol. 11, p. 4096.
11. Shul’pin, G.B., Organicheskie reaktsii, kataliziruemye
kompleksami metallov (Organic Reactions Catalyzed by
Metal Complexes), Moscow: Nauka, 1988, p. 275.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 4 2011