Prenylation of 4-Methylphenol

Article abstract of DOI:10.1134/S1070363220030032

Abstract: Organoaluminum (aluminum phenolate and aluminum isopropylate) and acidicheterogeneous catalysts (zeolites C-10, C-100 and ZSM, clay KSF, sulfonic cationexchangers Fiban K-1 and Amberlist 36 Dry) were studied in the alkylation of4-methylphenol wi

Full text of DOI:10.1134/S1070363220030032

ISSN 1070-3632, Russian Journal of General Chemistry, 2020, Vol. 90, No. 3, pp. 335–340. © Pleiades Publishing, Ltd., 2020.
Russian Text © The Author(s), 2020, published in Zhurnal Obshchei Khimii, 2020, Vol. 90, No. 3, pp. 346–352.
Prenylation of 4-Methylphenol
I. Yu. Chukichevaa,*, I. V. Fedorovaa, Т. А. Kolegovaa, and A.V. Kutchina
a Institute of Chemistry, of the Komi Scientific Centre of the Ural Branch of the Russian Academy of Sciences,
Syktyvkar, 167000 Russia
*е-mail: chukichevaiy@mail.ru
Received July 25, 2019; revised July 25, 2019; accepted August 6, 2019
Abstract—Organoaluminum (aluminum phenolate and aluminum isopropylate) and acidic heterogeneous catalysts
(zeolites C-10, C-100 and ZSM, clay KSF, sulfonic cation exchangers Fiban K-1 and Amberlist 36 Dry) were
studied in the alkylation of 4-methylphenol with prenol. Effective catalysts and conditions for the synthesis of
4-methyl-2-prenylphenol, 2,6-diprenyl-4-methylphenol, and chromane were revealed.
Keywords: 4-methylphenol, prenol, catalysts, alkylation
DOI: 10.1134/S1070363220030032
Prenylated phenols form a group of natural compounds
and are involved in many biological processes. They
exhibit a wide range of pharmacological activity, including
anti-inflammatory, antitumor, antifungal, anti-HIV, as
well as are strong phytoestrogens [1–4].
improvement of the environmental characteristics of the
processes compared to homogeneous catalysts, which is
important for the further development of the technology.
Herein, a comparative study of various types of
catalysts was carried out in order to identify the most
effective and selective ones for the synthesis of 4-methyl-
prenylphenols or chromane through the alkylation
of 4-methylphenol 1 with prenol (3-methyl-2-buten-
1-ol) 2 (Scheme 1). For this purpose, a number of
heterogeneous acid catalysts (zeolites C-10, C-100 and
ZSM, montmorillonite KSF, sulfocationionites Fiban K-1
andAmberlist 36 Dry) and organoaluminum compounds
[aluminum cresolate (4-MeC6H4O)3Al and (i-PrO)3Al)]
in catalytic and equimolar amounts were screened
(Table 1).
As a rule, ortho-phenylated phenols can be synthesized
by Friedel–Crafts alkylation, Claisen rearrangement,
anionic alkylation, direct ortho-metalation, and metal–
halogen exchange reaction [5–10]. For the synthesis
of prenylated compounds, strong Brønsted acids,
Lewis acids, including in an ionic liquid medium, clay,
mesoporous aluminosilicates are used as catalysts. In
the presence of these catalysts, the selective formation
of 4-methyl-2-prenylphenol (69–88%) and chromane
(benzopyran) derivatives (78%) is possible, however,
their preparation requires a long reaction time or complex
catalytic systems [6–9].
The reaction products 3–8 were isolated by preparative
column chromatography. Structure of the synthesized
compounds was established using spectral methods.
Previously, we have reported the alkylation of phenol
and dihydroxybenzenes with prenol in the presence of
organoaluminum catalysts such as aluminum phenolate
(PhO)3Al and aluminum isopropylate (i-PrO)3Al
[11, 12]. The optimal conditions for the efficient
production of the corresponding chromanes (56–87%)
and prenylphenols (52–65%) have been revealed. It is
known that organoaluminum homogeneous catalysts
have a high selectivity in ortho-alkylation of phenols, and
aluminum phenolate is one of the most active [13–15].
However, carrying out acid-catalyzed reactions on solid
catalysts is notable for the subsequent work-up and the
The alkylation of 4-methylphenol 1 with prenol 2 in
the presence of catalytic amounts of (4-MeC6H4O)3Al
took place at a temperature ≥160°C. The reaction of
4-methylphenol 1 with prenol 2 under these conditions
for 1 h with incomplete conversion of 4-methylphenol
(60%) led to the predominant formation of 4-methyl-
2-prenylphenol 8a (38%) (Table 1). In addition, ether 6
and dialkylated phenol 7a were isolated (29 and 12%,
respectively). An increase in the reaction time (2–
5 h) makes it possible to increase the conversion of the
starting reagents up to 98%. After 2 h, the total yield of
335

336
CHUKICHEVA et al.
Scheme 1.
OH
+
OH
2
1
10
11
2
2
Ra
OH
1
1
3
4
O
1
OH
O
O
8a
8a
R
2
R
6
R
Ra
4a
cat
2
3
8
8
4a
Ra
Ra
O
5
4
6
9
7
3
4
5
6
7
8
4'
3'
5'
4'
1'
3'
1'
(a),
(b).
R =
5'
2'
2'
prenylphenols 7 and 8 was 82%, while the amount of ether
6 decreased to 15%. A further increase in the reaction
time to 5 h contributed to the intramolecular cyclization
of the ortho-prenyl substituent. As a result, chromane 4
(91%) was produced with high selectivity. Alkylation of
4-methylphenol 1 with a twofold excess of prenol 2 in
the presence of catalytic amounts of (4-MeC6H4O)3Al
proceeded with low selectivity to form a mixture of O-
and C-alkylation products.
a decrease in the reaction selectivity and an increase in
the yield of dialkylated phenols 7a and 7b.
Prenylation of 4-methylphenol 1 in the presence of
heterogeneous clay catalysts montmorillonite KSF and
sulfocationic Amberlyst 36 Dry, Fiban K-1 proceeded
with high conversion (84–98%). Heating in methylene
chloride (40°C) led to the formation of 4-methyl-2-
prenylphenol 8a with a yield of up to 62% in the case of
KSF, 46% with Amberlyst 36 Dry and 38% with Fiban
K-1. Raising the temperature to 70 or 100°C resulted in
the intramolecular cyclization of the prenyl substituent
and preferential formation of chromane type ethers 4 and
5 with a total yield of up to 90%. Fiban K-1 sulfocationite
was used in a 10% amount, which was sufficient for a
high conversion reaction to take place. In the presence
of 10% Amberlyst 36 Dry, the reaction took place with
heating at ≥100°C.
In the presence of equimolar amounts of
(4-MeC6H4O)3Al and a twofold excess of prenol at
120°C, 4-methyl-2-prenylphenol 8a was obtained in 45%
yield. However, in addition to ether 6 and dialkylphenols
7a and 7b, a rather large number of polymerization and
oxidation products were formed (18%).
It should be noted that in the presence of
(4-MeC6H4O)3Al, the isomerization of the starting prenol
was not affected by the catalyst amount. Perhaps this is
due to the high temperature of the reaction mixture and
the significant chemical activity of the prenyl carbocation.
For the reaction of phenol 1 with prenol 2 in the
presence of zeolites, it is optimal to heat the reaction
mixture at 100°C. Zeolite C-10 (100 wt% with respect
to the starting 4-methylphenol) show low selectivity:
phenols 7 and 8, as well as chromane ethers 4 and 5,
were formed as a result of prenylation. A similar result
was obtained when using equimolar amount of zeolite
C-100 under the same conditions.
The use of aluminum isopropylate as a catalyst made it
possible to reduce the temperature of the reaction mixture
to 120–140°С. Regardless of the (i-PrO)3Al amount,
4-methyl-2-prenylphenol 8a was formed in 36% yield.
However, increasing the temperature up to 160°C led to
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 3 2020

PRENYLATION OF 4-METHYLPHENOL
337
Table 1. Prenylation of 4-methylphenol
Alkylation product, %
Conversion,
1 : 2 : саt Reaction conditionsa
7
8
3
4
5
6
otherb
%
a
b
a
b
(4-МеС6Н4O)3Al
1 : 1 : 0.1
160°С, 1 h
160°С, 2 h
60
98
6
3
−
−
−
−
29
15
12
14
−
38
−
6
9
38
30
−
−
19
−
160°С, 5 h
160°С, 2 h
120°С, 4 h
98
97
98
−
10
−
91
−
−
−
−
2
2
28
7
−
−
5
−
1 : 2 : 0.1
1 : 2 : 1
−
20
16
23
14
−
45
18
(i-PrO)3Al
1 : 2 : 0.1
1 : 2 : 1
140°С, 6 h
160°С, 4 h
120°С, 3.5 h
160°С, 1 h
99
99
95
98
5
5
3
−
−
−
−
−
25
21
10
−
11
23
42
42
−
3
−
−
36
21
36
13
9
−
−
−
14
27
5
−
4
15
KSF
−
17
13
1 : 2 : 1
40°С, 2 h
70°С, 2 h
100°С, 2 h
84
96
97
−
−
−
−
6
−
−
16
7
−
−
−
62
3
−
−
−
16
10
10
67
67
13
23
−
−
Amberlist 36 Dry
1 : 2 : 1
40°С, 1 h
98
98
90
95
−
−
−
−
30
11
6
3
−
−
−
5
−
3
2
−
−
−
−
46
−
−
−
−
−
5
7
5
5
70°С, 1 h
87
100°С, 0.5 h
100°С, 3 h
74
2
16
1
1 : 2 : 0.1
1 : 2 : 0.1
90
Fiban K-1
32
2
40°С, 2 h
70°С, 1 h
100°С, 2 h
93
97
98
6
−
−
3
15
8
3
−
−
11
9
−
−
−
38
−
−
−
−
7
8
6
68
85
1
−
Zeolite C-100
16
1 : 2 : 0.1
40°С, 24 h
70°С, 8 h
100°С, 7 h
100°С, 2 h
48
74
83
92
−
23
16
13
−
20
17
16
23
−
−
−
−
38
36
45
26
−
−
−
−
−
8
23
−
−
6
−
7
9
3
−
1 : 2 : 1
1 : 2 : 1
30
12
Zeolite C-10
32
−
−
−
100°С, 2 h
90
13
−
24
25
6
Zeolite ZSM
2
−
−
1
−
−
−
1 : 2 : 0.1
1 : 2 : 0.2
1 : 2 : 1
100°С, 10 h
100°С, 5 h
100°С, 5 h
26
40
45
5
−
−
−
3
−
−
9
90
14
47
−
−
8
48
8
25
1
13
26
a Solvent at 40°С was СН2Сl2, 70°С (hexane), 100°С (heptane).
b Polymerization and oxidation products.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 3 2020

338
CHUKICHEVA et al.
When using 10 wt% zeolite C-100, the alkylation with
used (4-MeC6H4O)3Al (prepared in situ), (i-PrO)3Al (Alfa
Aesar), zeolites (C-10, C-100 and ZSM), montmorillonite
KSF (Acros Organics), Fiban K-1 (sulfonic acid cation
exchange resin) provided by the Institute of Physical
and Organic Chemistry of the NAS of Belarus. Zeolites
(C-10, C-100 and ZSM) were pre-dried. The quantitative
composition of the alkylation products is presented in
Table 1.
prenol proceeded with incomplete conversion (48–83%)
and low selectivity regardless of the reaction temperature
(Table 1). Only heating the reaction mixture to 100°C led
to the predominant formation of 4-methyl-2-prenylphenol
8a (45%).
In the presence of catalytic amounts (10%) of ZSM
zeolite, the selective formation of compound 8a occurred,
but the conversion of the starting 4-methylphenol was
very small (26%). An increase in the catalyst amount to
20 wt% led to the predominant formation of chromanes 4
and 5 with moderate conversion. When using equimolar
amount of ZSM zeolite, 4-methyl-2-prenylphenol 8a was
obtained as the main product (47%).
Alkylation of 4-methylphenol with prenol
in the presence of (4-MeC6H4O)3Al (catalytic
method). To 4-methylphenol heated to 160°С (0.48 g,
4.5 mmol) aluminum chips were added in small portions
(0.0038 g, 0.14 mmol). After complete dissolution of
aluminum in 4-methylphenol, the solution was cooled
to 40°C, then 0.39 g (4.5 mmol) of prenol was added.
The reaction mixture was carried stirred at 160°C until
complete conversion of prenol. The reaction progress
was monitored by TLC (petroleum ether : Et2O = 3 : 1,
developing with vanillin). After the reaction completed,
the reaction mixture was cooled, and diluted with Et2O.
Next, a 50% HCl solution was added to the catalyst
consumption, then the mixture was washed with a 5%
NaOH solution and water until neutral. The organic layer
was dried with anhydrous Na2SO4. After removal of the
solvent, the reaction products were separated by column
chromatography.
In summary, effective heterogeneous catalysts were
revealed that are not inferior in selectivity to the action
of homogeneous organoaluminum compounds. The
catalysts and optimal conditions for the selective synthesis
of the target 4-methyl-2-prenylphenol, 2,6-diprenyl-
4-methylphenol and 3,4-dihydro-2,2,6-trimethyl-2H-
chroman were selected.
EXPERIMENTAL
1H and 13C NMR spectra were recorded on a
Bruker Avance II 300 spectrometer at frequencies of
300 (1H) and 75 MHz (13C) in CDCl3. The signals
assignment was performed using 13C NMR spectra
recorded in the J-modulation mode, as well as using
two-dimensional NMR spectroscopy (COSY, NOESY,
and HSQC experiments). IR ATR spectra were recorded
on a Shimadzu IR Prestige 21 Fourier transform IR
spectrometer from a thin layer. Elemental analysis was
performed on a vario Micro cube automated analyzer in
CHNS mode.
3-Methyl-1-(3-methylbut-2-enyloxy)but-2-ene (3).
Yellow oil. The spectral characteristics correspond to the
data reported in [1].
3,4-Dihydro-2,2,6-trimethyl-2H-chromane (4).
Colorless oil. IR spectrum, ν, cm–1: 2974, 2927, 1496
and 1375 (СН3, СН2), 1618, 1585 (Аr), 1157 and 1122
(C−O−C), 814 (=С−Н). 1Н NMR spectrum, δ, ppm: 1.40 s
(6Н, CH310, CH311), 1.86 t (2H, H3, J = 6.6 Hz), 2.33 s
9
(3H, CH3 ), 2.81 t (2H, H4, J = 6.6 Hz), 6.76 d (1H, H8,
Thin layer chromatography (TLC) was performed
on Sorbfil plates. Detection was performed by treating
the plates with a KMnO4 solution of (15 g of KMnO4,
300 mL of H2O, 0.5 mL of conc. H2SO4), as well as a
vanillin solution (1 g of vanillin, 100 mL of 95% ethanol,
5 mL of conc. sulfuric acid), followed by heating up to
100–150°С.
J = 8.1 Hz), 6.95–6.98 m (2H, Н5, H7). 13С NMR
spectrum, δС, ppm: 73.90 (C2), 32.98 (C3), 22.51 (C4),
120.58 (C4a), 127.95 (C5), 128.70 (C6), 129.81 (C7),
117.03 (C8), 151.75 (C8a), 20.50 (С9), 26.88 (C10, 11). The
spectral characteristics correspond to the data reported
in [16].
The reaction products were isolated using column
chromatography on silica gel (Alfa Aesar, 70/230μ),
eluent – petroleum ether–Et2O with an increase in the
fraction of the latter.
1-(3-Methylbut-2-enyloxy)-4-methylbenzene (6).
Pale yellow oil. 1Н NMR spectrum, δ, ppm: 1.77 s (3H,
5'
4'
7
CH3 ), 1.83 s (3H, CH3 ), 2.32 s (3H, CH3 ), 4.51 d
(2H, H1', J = 6.6 Hz), 5.55 t (1H, H2', J = 7.2 Hz), 6.85 d
(2H, H2, H6, J = 8.1 Hz), 7.11 d (2H, H3, H5, J = 8.1 Hz).
13С NMR spectrum, δС, ppm: 156.97 (C1), 64.80 (C1'),
119.93 (C2'), 114.51 (C2, С6), 129.85 (C3, С5), 137.94
3-Methyl-2-buten-1-ol (prenol) (AlfaAesar) was used
in the reactions without further purification; the solvents
and reagents were used freshly distilled. The catalysts
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 3 2020

PRENYLATION OF 4-METHYLPHENOL
339
(C3'), 132.00 (C4), 25.83 (C4'), 18.18 (С5'), 20.47 (С7).
Found, %: С 81.60; Н 9.77. C12H16O. Calculated, %: С
81.77; Н 9.15.
temperature (120, 140, and 160°C). The reaction mixture
work-up and isolation of reaction products were carried
out similarly to the procedure described above.
2,6-Bis(3-methylbut-2-en-1-yl)-4-methylphenol
(7a). Pale yellow oil. IR spectrum, ν, cm–1: 3445 (ОН),
2970, 2918, 1444 and 1377 (СН3, СН2), 1612 and 1504
(С=С), 854 (=С−Н). 1Н NMR spectrum, δ, ppm: 1.83 s
(12Н, CH3 , CH3 , CH3 , CH3 ), 2.30s(3Н, CH3 ), 3.37d
(4H, 2H1', 2Н1'', J = 7.2 Hz), 5.03 s (1H, OH), 5.37 t
(2H, H2', Н2'', J = 7.2 Hz), 6.84 s (2H, H3, Н5). 13С NMR
spectrum, δС, ppm: 152.00 (C1), 29.66 (C1', С1''), 126.97
(C2, С6), 122.33 (C2', С2''), 128.36 (C3, С5), 133.97 (C3',
С3''), 129.39 (C4), 25.79 (С4', С4''), 17.87 (С5', C5''), 20.52
(С7). Found, %: С 83.38; Н 10.08. C17H24O. Calculated,
%: С 83.55; Н 9.90.
3,4-Dihydro-2,2,6-trimethyl-8-(3-methyl-2-buten-
1-yl)-2H-1-benzopyran (5). Colorless oil. IR spectrum,
ν, cm–1: 2974, 2924, 1473 and 1375 (СН3, СН2), 1647
and 1595 (С=С), 1207 and 1157 (C−O−C), 852 (=С−Н).
1Н NMR spectrum, δ, ppm: 1.36 s (6Н, CH310, CH311),
4'
4''
5'
5''
7
4'
5'
1.77 s (6Н, CH3 , CH3 ), 1.82 t (2H, H3, J = 6.9 Hz),
9
2.28 s (3H, CH3 ), 2.78 t (2H, H4, J = 6.9 Hz), 3.29 d
(2H, H1', J = 7.2 Hz), 5.34 t (1H, H2', J = 7.2 Hz), 6.77 s
(1H, H7), 6.81 s (1H, H5). 13С NMR spectrum, δС, ppm:
28.55 (C1'), 73.67 (C2), 123.26 (C2'), 32.95 (C3), 132.00
(C3'), 22.68 (С4), 120.19 (C4a), 26.04 (С4'), 127.47 (C5),
17.83 (С5'), 129.53 (C6), 127.91 (C7), 128.05 (C8), 140.05
(C8a), 20.54 (C9), 27.14 (С10, С11). Found, %: С 83.09; Н
10.15. C17H24O. Calculated, %: С 83.55; Н 9.90.
2,6-Bis(2-methylbut-3-en-2-yl)-4-methylphenol
(7b). Pale yellow oil. IR spectrum, ν, cm–1: 3495 (ОН),
2972, 2927, 1496 and 1375 (СН3, СН2), 1618 and 1587
(С=С), 852 (=С−H). 1Н NMR spectrum, δ, ppm: 1.48 s
Acid-catalyzed prenylation of 4-methylphenol
(general procedure). Alkylation of 4-methylphenol
was carried out with a 2-fold excess of prenol. In the
case of Fiban K-1 sulfonic acid cation exchanger the
catalyst amount was 10 wt % with respect to the starting
4-methylphenol; montmorillonite KSF was taken in
a mass ratio of 1 : 1 relative to the amount of starting
phenol. Zeolites C-10, C-100, ZSM, and Amberlist 36
Dry sulfocationite were taken in amounts of 10 and
100 wt % relative to the starting 4-methylphenol. A
mixture of 4-methylphenol, prenol and catalyst was heated
at a given temperature. The reaction was carried out until
a significant conversion of the starting 4-methylphenol
(GLC and TLC control) was achieved, after which the
reaction mixture was dissolved in Et2O, and filtered. The
reaction products were isolated as described above. The
content of alkylation products is presented in Table 1.
4'
4''
5'
5''
7
(12H, CH3 , СH3 , СH3 , СH3 ), 2.33 s (3H, CH3 ),
5.31–5.41 m (4Н, 2Н3', 2Н3''), 5.69 s (Н, ОН), 6.23 d. d
(2Н, Н2', Н2'', J = 10.5, 17.7 Hz), 7.09 s (2Н, Н3, Н5).
NMR spectrum 13С, δС, ppm: 152.4 (C1), 40.27 (C1', С1''),
128.63 (C2, С6), 147.92 (C2', С2''), 117.55 (C3), 113.38
(C3', С3''), 129.77 (C4), 26.97 (С4', С4'', С5', С5''), 126.82
(C5), 20.56 (С7). Found, %: С 83.14; Н 10.39. C17H24O.
Calculated, %: С 83.55; Н 9.90.
4-Methyl-2-(3-methylbut-2-en-1-yl)phenol (8a).
Pale yellow oil. The spectral characteristics correspond
to the data reported in [6].
4-Methyl-2-(2-methylbut-3-en-2-yl)phenol (8b).
Pale yellow oil. IR spectrum, ν, cm–1: 3495 (ОН), 2973,
2929, 1496 and 1373 (СН3, СН2), 1615 and 1587 (С=С),
1
812 (=С−H). Н NMR spectrum, δ, ppm: 1.47 s (6H,
4'
5'
7
CH3 , CH3 ), 2.33 s (3H, CH3 ), 5.33 m and 5.36 m
(2Н, Н3'), 5.68 s (Н, ОН), 6.22 d. d (1Н, Н2', J = 10.5,
17.7 Hz), 6.77 d (1Н, Н6, J = 8.1 Hz), 7.00 d (1Н, Н5, J =
8.1 Hz), 7.09 s (1Н, Н3). 13С NMR spectrum, δС, ppm:
152.44 (C1), 40.27 (C1'), 127.00 (C2), 147.92 (C2'), 126.83
(C3), 113.38 (C3'), 129.69 (C4), 26.97 (С4', С5'), 128.63
(C5), 117.55 (C6), 20.84 (C7). Found, %: С 81.36; Н 9.38.
C12H16O. Calculated, %: С 81.77; Н 9.15.
FUNDING
This was financially supported by the Russian Founda-
tion for Basic Research (project no. 18-03-00950_a).
CONFLICT OF INTEREST
No conflict of interest was declared by the authors.
REFERENCES
Prenylation of 4-methylphenol in the presence
of (i-PrO)3Al (general procedure). A mixture of 0.5 g
(4.6 mmol) of 4-methylphenol, 0.79 g (9.2 mmol) of
prenol and (i-PrO)3Al [0.05 g (0.25 mmol) in the case of
the catalytic method or 0.95 g (4.6 mmol) using equimolar
amounts of catalyst] was heated at the appropriate
1. Bhargava, P., Grover, A., Nigam, N., Kaul, A., Doi, M.,
Ishida, Y., Kakuta, H., Kaul, S.C., Terao, K., and Wadh-
wa, R., Int. J. Oncol., 2018, vol. 52, no. 3, p. 925.
https://doi.org/10.3892/ijo.2018.4249
2. Wang, S., Dunlap, T.L., Howell, C.E., Mbachu, O.C.,
Rue, E.A., Phansalkar, R., Chen, S.-N., Pauli, G.F.,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 3 2020

340
CHUKICHEVA et al.
Dietz, B.M., and Bolton, J.L., Chem. Res. Toxicol.,
https://doi.org/10.1055/s-2004-830865
2016, vol. 29, no. 7, p. 1142.
https://doi.org/10.1021/acs.chemrestox.6b00112
10. Helesbeux, J.-J., Duval, O., Guilet, D., Séraphin, D.,
Rondeau, D., and Richomme, P., Tetrahedron,
2003, vol. 59, p. 5091.
3. Sansom, C.E., Larsen, L., Perry, N.B., Berridge, M.V.,
Chia, E.W., Harper, J.L., and Webb, V.L., J. Nat.
Prod., 2007, vol. 70, no. 12, p. 2042.
https://doi.org/10.1016/S0040-4020(03)00733-6
11. Chukicheva, I.Yu., Fedorova, I.V., Koroleva, A.A.,
and Kuchin, A.V., Chem. Nat. Compd., 2018, vol. 54,
no. 1, p. 1.
https://doi.org/10.1021/np070436t
4. Štulíková, K., Karabín, M., Nešpor, J., and Dostálek, P.,
Molecules, 2018, vol. 23, no. 3, p. 660.
https://doi.org/10.3390/molecules23030660
https://doi.org/10.1007/s10600-018-2245-y
12. Chukicheva, I.Yu., Fedorova, I.V., Nizovtsev, N.A., Ko-
roleva, A.A., Shevchenko, O.G., and Kuchin, A.V., Chem.
Nat. Compd., 2018, vol. 54, no. 5, p. 875.
https://doi.org/10.1007/s10600-018-2503-z
13. Kolka, A.J., Napolitano, J.P., and Ecke, G.G., J. Org.
Chem., 1956, vol. 21, no. 6, p. 712.
5. Hoarau, C. and Pettus Tomas, R.R., Synlett, 2003, vol. 1,
p. 127.
https://doi.org/10.1055/s-2003-36234
6. Varghese, S., Anand, C., Dhawale, D., Mane, G.P.,
Wahad, M.A., Mano, A., Raj, G.A.G., Naga-
rajan, S., and Vinu, A., ChemCatChem, 2013, vol. 5,
no. 4, p. 899.
https://doi.org/10.1021/jo01112a621
https://doi.org/10.1002/cctc.201200332
14. Gunko, V.M. and Roev, L.M., Teoret. Eksp. Khim., 1982,
p. 85.
7. Ricardo, С.L., Mo, X., McCubbin, J.A., and Hall, D.G.,
Chem. Eur. J., 2015, vol. 21, no. 11, p. 4218.
https://doi.org/10.1002/chem.201500020
15. Kuepper, F.-W. and Mueller, W., US Patent no. 5292970,
1991.
8. So Won, Youn, Synlett, 2007, vol. 19, p. 3050.
16. Yamamoto, Y. and Itonaga, K., Org. Lett., 2009,
vol. 11, no. 3, p. 717.
https://doi.org/10.1055/s-2007-990963
9. Dintzner, М.R., McClelland, K.M., Morse, K.M., and
Akroush, M.H., Synlett, 2004, vol. 11, p. 2028.
https://doi.org/10.1021/ol802800s
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 90 No. 3 2020