Selective synthesis of cyclic triperoxides from 1,1′-dihydroperoxydi(cycloalkyl)peroxides and acetals using SnCl4

Article abstract of DOI:10.1007/s11172-019-2555-7

A method for the synthesis of 1,2,4,5,7,8-hexaoxonanes by the reaction of 1,1′-dihydroperoxydi(cycloalkyl)peroxides with acetals using SnCl₄ has been developed. For the first time, it was shown that SnCl₄ can serve as an effective reagent for the synthesis of cyclic organic peroxides. The proposed method allows obtaining 9-membered cyclic triperoxides selectively and in the yields of up to 90% based on the isolated product.

Full text of DOI:10.1007/s11172-019-2555-7

Russian Chemical Bulletin, International Edition, Vol. 68, No. 6, pp. 1289—1292, June, 2019
1289
Brief Communications
Selective synthesis of cyclic triperoxides
from 1,1´-dihydroperoxydi(cycloalkyl)peroxides and acetals using SnCl4
P. S. Radulov,a,b Yu. Yu. Belyakova,a A. A. Demina,c G. I. Nikishin,а I. A. Yaremenko,a,b,d and A. O. Terent´eva,b,d
аN. D. Zelinsky Institute of Organic Chemistry of the Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
E-mail: terentev@ioc.ac.ru
bAll-Russia Research Institute for Phytopathology,
5 ul. Institut, Bolshie Vyazyomy, Odintsovo District, 143050 Мoscow Region, Russian Federation.
cM. V. Lomonosov Moscow State University,
1-3 Leninskiye Gory, 119991 Moscow, Russian Federation.
dD. I. Mendeleev University of Chemical Technology of Russia,
9 Miusskaya pl., 125047 Moscow, Russian Federation
A method for the synthesis of 1,2,4,5,7,8-hexaoxonanes by the reaction of 1,1´-dihydro-
peroxydi(cycloalkyl)peroxides with acetals using SnCl4 has been developed. For the first time,
it was shown that SnCl4 can serve as an effective reagent for the synthesis of cyclic organic
peroxides. The proposed method allows obtaining 9-membered cyclic triperoxides selectively
and in the yields of up to 90% based on the isolated product.
Key words: triperoxides, hexaoxonanes, tin tetrachloride, peroxidation, acetals.
Triperoxides such as 1,2,4,5,7,8-hexaoxonanes have
found application as polymerization initiators1—5, starting
compounds in the synthesis of macrocyclic ketones and
lactones by the Story reaction,6—10 as well as in the syn-
thesis of unsymmetric tetraoxanes.11 Data on high anti-
malarial,12—16 antischistosomal,17—20 fungicidal18 activ-
ities and cytotoxicity of related organic peroxides towards
cancer cells21—25 suggest that macrocyclic peroxides can
be of interest in view of developing compounds having
useful applied properties. A number of works on studying
properties of such cyclic peroxides and proposed methods
of their analysis has been published. 26—32
Hexaoxonanes are generally obtained by an acid-
catalyzed reaction between hydrogen peroxide and ke-
tones26,33—37, condensation of 1,1´-dihydroperoxydi-
(cycloalkyl)peroxides with ketones38 and acetals39,40
,
condensation of geminal bis-hydroperoxides with ke-
tones41, as well as by ozonolysis of alkenes42—44. The main
drawbacks of these methods include low selectivity and
challenges in the synthesis of hexaoxonanes bearing bulky
substituents. Condensation of 1,1´-dihydroperoxydi-
* Dedicated to Academician of the Russian Academy of Sciences
O. N. Chupakhin on the occasion of his 85th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1289—1292, June, 2019.
1066-5285/19/6806-1289 © 2019 Springer Science+Business Media, Inc.

1290
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 6, June, 2019
Radulov et al.
Table 1. Synthesis of hexaoxonane 4b from acetal 1b and
peroxide 2ba
(cycloalkyl)peroxides with ketones provides moderate
yields and is limited to α-unsubstituted С5- and С6-cyclic
ketones. Condensations of ketones with the ring size of
С8 or larger or bearing a substituent adjacent to the carb-
onyl group are mostly unsuccessful and only in some cases
the 40% yields are attained.45 Condensation of 1,1´-di-
hydroperoxydi(cycloalkyl)peroxides with acetals catalyzed
by BF3•Et2O proved to be the most promising approach
to obtain 1,2,4,5,7,8-hexaoxonanes.40
In the present work, SnCl4 was for the first time shown
to be the most effective reagent in the synthesis of cyclic
triperoxides. The studies are known wherein SnCl4 was
used in the synthesis of geminal bis-hydroperoxides,
geminal hydroxy hydroperoxides via the reaction of per-
oxidation of ketones and aldehydes respectively;46 in the
synthesis of vicinal hydroxy hydroperoxides via the reac-
tion of an oxirane ring opening in the presence of hydro-
gen peroxide,47 as well as in the synthesis of a cyclic
tetraperoxide from acetone and H2O2 (see Ref. 48).
Run
SnCl4 : 2b
mol/mol
Solventb
τ/hс
Yc (%)
1
2
3
4
5
6
0.5
1.0
0.5
1.0
0.5
0.1
Et2O
Et2O
THF
THF
THF
THF
8
8
8
8
4
4
10
10
82
83
69
27
а Synthesis conditions are given in the Experimental part.
b The solvent volume is 5 mL.
с The reaction time.
d Yield on the basis of the isolated product.
a solvent in use, and the reaction time on the yield of
peroxide 4b has been studied (Table 1). The 1.5 : 1.0 ac-
etal 1b : peroxide 2b molar ratio was chosen. Condens-
ation of 1,1´-dihydroperoxydi(cyclododecyl)peroxide (2b)
with 1,1-dimethoxycycloheptane (1b) was carried out at
20—25 °С in argon atmosphere without access of air.
Condensation of 1,1´-dihydroperoxydi(cyclododecyl)
peroxide (2b) with 1,1-dimethoxycycloheptane (1b) within
8 h in diethyl ether at 0.5 : 1.0 or 1.0 : 1.0 molar ratio of
SnCl4 : peroxide 2b, afforded no desired hexaoxonane 4b
even in trace amounts (see Table 1, runs 1 and 2). Using
THF as a solvent and 0.5 : 1.0 molar ratio of SnCl4 : per-
oxide 2b, the yield of the desired hexaoxonane 4b was 82%
based on the isolated product (see Table 1, run 3). With
equimolar amount of SnCl4 relatively to peroxide 2b the
yield of peroxide 4b changed negligibly (see Table 1, run 4).
Decreasing the reaction time for condensing 1,1´-dihydro-
peroxydi(cyclododecyl)peroxide (2b) with 1,1-dimeth-
oxycycloheptane (1b) as well as using a lesser amount of
SnCl4 resulted in a reduced yield of the desired peroxide
(see Table 1, runs 5 and 6). Based on these data, the reac-
tion conditions of run 4 with an excess of SnCl4 have been
chosen as optimal conditions to synthesize hexaoxonane
4b to ensure the success even in the case of partial hydro-
lysis of SnCl4.
Results and Discussion
In the present study, a synthetic procedure to obtain
1,2,4,5,7,8-hexaoxonanes based on the reaction between
acetals and 1,1´-dihydroperoxydi(cycloalkyl)peroxides in
the presence of SnCl4 as a Lewis acid has been proposed
(Scheme 1). Using tin tetrachloride and acetals as starting
compounds instead of ketones makes it possible to
perform the synthesis of hexaoxonanes from С6—С8 and
С12-cycloalkanones.
Scheme 1
To find the application and reliability limits of the
procedure under optimal conditions (see Table 1, run 4),
a series of hexaoxonanes 4a—d were obtained at 20—25 °С.
In the case of hexaoxonanes 3a—d condensation of
acetals 1a—d with 1,1´-dihydroperoxydi(cyclohexyl)-
peroxide (2a) was carried out at 0—5 °С. By the example
of synthesis of peroxide 3a it was found that the yield of
peroxide 3a at 0—5 °С is 20% higher than at 20—25 °С.
All peroxides were obtained in high yields of up to 90%
based on the isolated product: 80% (3a), 90% (3b), 74%
(3c), 88% (3d), 70% (4a), 83% (4b), 72% (4c), and 72%
(4d). The yields of the desired peroxides were higher than
using BF3•Et2O40 as a catalyst; e.g., the yields of peroxides
1: R1—R2 = (CH2)5 (a), (CH2)6 (b), (CH2)7 (c), (CH2)11 (d)
2—4: n = 2 (2a, 3a—d), 8 (2b, 4a—d)
Reagents and conditions: SnCl4, THF, 0—25 °C, 4—8 h.
By the example of condensation between 1,1´-dihydro-
peroxydi(cyclododecyl)peroxide (2b) with 1,1-dimeth-
oxycycloheptane (1b), the effect of the amount of SnCl4,

SnCl4 in the synthesis of triperoxides
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 6, June, 2019
1291
δ: 1.33—1.91 (m, 30 H, 15 CH2). NMR 13C (CDCl3), δ: 22.7
(CH2), 25.7 (CH2), 30.7 (CH2), 107.7 (C).
3b and 4d rised from 65% to 88%, and from 40% to 72%,
respectively.
7,8,15,16,24,25-Hexaoxatrispiro[5.2.59.2.617.26]penta-
cosane (3b)40. White crystals, m.p. 55—56 °С (cf. Ref. 40: m.p.
55—56 °С). Rf = 0.29 (TLC, PE—EA, 30 : 1). NMR 1Н (CDCl3),
δ: 1.35—1.93 (m, 30 H, 15 CH2); 2.12—2.24 (m, 2 H, CH2).
NMR 13C (CDCl3), δ: 22.8 (CH2), 22.9 (CH2), 25.7 (CH2), 30.1
(CH2), 30.7 (CH2), 30.9 (CH2), 32.8 (CH2), 107.6 (C), 112.9 (C).
7,8,15,16,25,26-Hexaoxatrispiro[5.2.59.2.717.26]hexaco-
sane (3c)40. Yellow oil. Rf = 0.42 (TLC, PE—EA, 20 : 1). NMR
1Н (CDCl3), δ: 1.35—1.95 (m, 34 H, 17 CH2). NMR 13C
(CDCl3), δ: 22.1 (CH2), 22.8 (CH2), 25.2 (CH2), 25.6 (CH2),
28.1 (CH2), 28.6 (CH2), 30.6 (CH2), 30.8 (CH2), 107.6 (C),
111.9 (C).
To summarize, the method of the selective synthesis
of 9-membered cyclic peroxides, namely, 1,2,4,5,7,8-hexa-
oxonanes in high yields has been developed. For the first
time it was shown that SnCl4 in THF is an effective reagent
in the synthesis of cyclic organic peroxides, which ap-
plication provided condensation of acetals with 1,1´-di-
hydroperoxydi(cycloalkyl)peroxides.
Experimental
7,8,15,16,29,30-Hexaoxatrispiro[5.2.59.2.1117.26]triacon-
tane (3d)40. White crystals, m.p. 57—59 °С (hexane) (cf. Ref. 40:
NMR 1Н and 13С spectra were recorded on a Bruker AM-300
spectrometer (300.13 and 75.48 MHz, respectively) in СDCl3.
Plates Macherey-Nagel Alugram UV254 were used for TLC.
Column chromatography was performed on silica gel 0.060—
0.200 mm, 60 Å, CAS 7631-86-9. Melting points were determined
on a Kofler heating stage.
1
m.p. 57—59 °С). Rf = 0.45 (TLC, PE—EA, 20 : 1). NMR Н
(CDCl3), δ: 1.17—1.94 (m, 42 H, 21 CH2). NMR 13C (CDCl3),
δ: 19.5 (CH2), 22.1 (CH2), 22.3 (CH2), 22.9 (CH2), 25.7 (CH2),
26.1 (CH2), 26.3 (CH2), 26.8 (CH2), 30.5 (CH2), 107.7 (C),
111.7 (C).
Cyclohexanone, cycloheptanone, cyclooctanone, cyclodo-
decanone, trimethylorthoformate, SnCl4, p-TsOH, BF3•Et2O,
LiAlH4 (Acros) are commercially available and were used as
purchased. H2SO4 (98%), H2O2 (35% aqueous solution), MgSO4,
NaHCO3 were of national production. Diethyl ether (Et2O),
methanol, petroleum ether (PE) (40/70), ethyl acetate (EA) were
distilled before use. Tetrahydrofurane was distilled over LiAlH4.
The starting 1,1´-dihydroperoxydi(cyclohexyl)peroxide (2a) and
1,1´-dihydroperoxydi(cyclododecyl)peroxide (2b) were synthe-
7,8,21,22,35,36-Hexaoxatrispiro[5.2.119.2.1123.26]hexa-
triacontane (4a)40. White crystals, m.p. 160—162 °С (MeOH).
(cf. Ref. 40: m.p. 160—162 °С). Rf = 0.84 (TLC, PE—EA, 20 :
1). NMR 1Н (CDCl3), δ: 1.22—1.85 (m, 54 H, 27 CH2). NMR
13C (CDCl3), δ: 19.4 (CH2), 22.1 (CH2), 22.2 (CH2), 22.9 (CH2),
25.7 (CH2), 26.1 (CH2), 26.3 (CH2), 26.7 (CH2), 30.8 (CH2),
107.5 (C), 111.6 (C).
8,9,22,23,36,37-Hexaoxatrispiro[6.2.1110.2.1124.27]hepta-
triacontane (4b)40. White crystals, m.p. 193—195 °С (MeOH).
(cf. Ref. 40: m.p. 193—195 °С). Rf = 0.83 (TLC, PE—EA, 20 :
1). NMR 1Н (CDCl3), δ: 1.20—1.83 (m, 54 H, 27 CH2);
2.07—2.22 (m, 2 H, CH2). NMR 13C (CDCl3), δ: 19.4 (CH2),
22.1 (CH2), 22.3 (CH2), 22.9 (CH2), 26.1 (CH2), 26.3 (CH2),
26.7 (CH2), 26.8 (CH2), 30.0 (CH2), 32.8 (CH2), 111.6 (C),
112.6 (C).
sized according to the known procedure40
.
Synthesis of 1,2,4,5,7,8-hexaoxonanes 3a—d (general pro-
cedure). To a stirred solution of peroxide 2а (0.200 g, 0.74 mmol)
in THF (5 mL), acetal 1а—d (0.161—0.255 g, 1.12 mmol) was
added at 20—25 °С. The reaction mixture was cooled to 0—5 °С,
SnCl4 (0.086 mL, 0.193 g, 0.74 mmol, 1.0 mol SnCl4/1.0 mol 2а)
was added thereto, and the resulting mixture was stirred for 4 h
at 0—5 °С. The mixture was diluted with petroleum ether (30 mL),
washed with 5% aqueous NaHCO3 (20 mL), water (2×20 mL),
dried over MgSO4, and filtered. The solvent was removed in vacuo
on a rotary evaporator. 1,2,4,5,7,8-Hexaoxonanes 3a—d were
isolated in an individual state by column chromatography on
SiO2 using PE—Et2O mixture as an eluent with Et2O gradient
from 0 to 5 vol.%.
9,10,23,24,37,38-Hexaoxatrispiro[7.2.1111.2.1125.28]octa-
triacontane (4c)40. White crystals, m.p. 198—200 °С (MeOH).
(cf. Ref. 40: m.p. 198—200 °С). Rf = 0.86 (TLC, PE—EA, 20 : 1).
NMR 1Н (CDCl3), δ: 1.20—1.84 (m, 58 H, 29 CH2). NMR 13
C
(CDCl3), δ: 19.5 (CH2), 22.1 (CH2), 22.3 (CH2), 25.1 (CH2),
26.1 (CH2), 26.3 (CH2), 26.8 (CH2), 26.9 (CH2), 28.2 (CH2),
28.3 (CH2), 111.5 (C), 111.7 (C).
13,14,27,28,41,42-Hexaoxatrispiro[11.2.1115.2.1129.212
]
Synthesis of 1,2,4,5,7,8-hexaoxonanes 4a—d (general pro-
cedure). To a stirred solution of peroxide 2b (0.200 g, 0.46 mmol)
in THF (5 mL), acetal 1а—d (0.100—0.158 g, 0.69 mmol) was
added at 20—25 °С. The reaction mixture was cooled to 0—5 °С,
SnCl4 (0.054 mL, 0.120 g, 0.46 mmol, 1.0 mol SnCl4/1.0 mol 2b)
was added thereto and the resulting mixture was stirred for 8 h
at 20—25 °С. Then, Et2O (10 mL) and dried K2CO3 (0.5 g) were
added, the mixture was stirred for 30 min and filtered. The solvent
was removed in vacuo on a rotary evaporator, methanol (10 mL)
was added to the resulting residue to give sticky white solid, to
which Et2O was added dropwise until homogenization. Et2O was
removed in vacuo on a rotary evaporator until precipitation began;
the residue was cooled to 0÷–5 °С for 20 min. The precipitated
crystals of 4a—d were filtered and rinsed with МеОН (2×3 mL)
at 0 °С, and dried.
dotetracontane (4d)40. White crystals, m.p. 218—220 °С (MeOH).
(cf. Ref. 40: m.p. 218—220 °С). Rf = 0.76 (TLC, PE—EA, 20 : 1).
NMR 1Н (CDCl3), δ: 1.17—1.84 (m, 66 H, 33 CH2). NMR 13
C
(CDCl3), δ: 19.4 (CH2), 22.1 (CH2), 22.3 (CH2), 26.0 (CH2),
26.1 (CH2), 26.8 (CH2), 111.5 (C).
The study was financially supported by the Russian
Science Foundation (Project No. 17-73-10364).
References
1. W. C. Sheng, J. Y. Wu, G. R. Shan, Z. M. Huang, Z. X. Weng,
J. Appl. Polym. Sci., 2004, 94, 1035.
2. R. M. Torenbeek, J. A. Hogt, H. G. Bekendam, WO 9603397,
1996.
3. J. M. Van der Schuur, J. Nuysink, R. C. J. Millet, B. Fischer,
WO 2015135865, 2015.
7,8,15,16,23,24-Hexaoxatrispiro[5.2.59.2.517.26]tetra-
cosane (3a)40. White crystals, m.p. 88—90 С (cf. Ref. 40: m.p.
88—90 °С). Rf = 0.41 (TLC, PE—EA, 20 : 1). NMR 1Н (CDCl3),

1292
Russ. Chem. Bull., Int. Ed., Vol. 68, No. 6, June, 2019
Radulov et al.
4. B. Fischer, J. Meijer, R. H. Van Den Berg, J. Nuysink,
WO 2004052877, 2004.
5. A. Deckers, W. Weber, F.-O. Maehling, L. Wittkowski,
EP 1134237, 2001.
6. P. R. Story, D. D. Denson, C. E. Bishop, B. C. Clark, J. C.
Farine, J. Am. Chem. Soc., 1968, 90, 817.
7. J. R. Sanderson, K. Paul, P. R. Story, D. D. Denson, J. A.
Alford, Synthesis-Stuttgart, 1975, 3, 159.
8. J. R. Sanderson, K. Paul, P. R. Story, Synthesis-Stuttgart,
1975, 4, 275.
9. J. R. Sanderson, P. R. Story, K. Paul, J. Org. Chem., 1975,
40, 691.
10. E. K. Starostin, A. V. Aleksandrov, A. V. Ignatenko, G. I.
Nikishin, Izv. AN SSSR, Ser. Khim., 1982, 141 [Bull. Acad.
Sci. USSR, Div. Chem. Sci. (Engl. Transl.), 1982, 31, 133].
11. P. R. Story, P. I. Busch, in Advances in Organic Chemistry,
Ed. E. C. Taylor, Wiley, New York, 1972, 8, pp. 67—95.
12. L. C. Fisher, M. A. Blackie, Mini-Rev. Med. Chem., 2014,
14, 123.
25. I. A. Yaremenko, M. A. Syroeshkin, D. O. Levitsky, F. Fleury,
A. O. Terent'ev, Med. Chem. Res., 2017, 26, 170.
26. F. Dubnikova, R. Kosloff, J. Almog, Y. Zeiri, R. Boese,
H. Itzhaky, A. Alt, E. Keinan, J. Am. Chem. Soc., 2005,
127, 1146.
27. C. Denekamp, L. Gottlieb, T. Tamiri, A. Tsoglin, R. Shilav,
M. Kapon, Org. Lett., 2005, 7, 2461.
28. D. Muller, A. Levy, R. Shelef, S. Abramovich-Bar, D. So-
nenfeld, T. Tamiri, J. Forensic Sci., 2004, 49, 935.
29. R. Schulte-Ladbeck, P. Kolla, U. Karst, Anal. Chem., 2003,
75, 731.
30. I. Yavari, M. R. Hosseini-Tabatabaei, F. Nasiri, J. Mol. Struc-
Theochem., 2001, 538, 239.
31. L. Widmer, S. Watson, K. Schlatter, A. Crowson, Analyst,
2002, 127, 1627.
32. A. B. Fialkov, A. Amirav, Rapid Commun. Mass Sp., 2003,
17, 1326.
33. K. Zmitek, S. Stavber, M. Zupan, D. Bonnet-Delpon, J. Iskra,
Tetrahedron, 2006, 62, 1479.
13. C. W. Jefford, Curr. Top. Med. Chem., 2012, 12, 373.
14. D. M. Opsenica, B. A. Šolaja, J. Serb. Chem. Soc., 2009,
74, 1155.
15. B. A. Šolaja, N. Terzić, G. Pocsfalvi, L. Gerena, B. Tinant,
D. Opsenica, W. K. Milhous, L. C. Fisher, M. A. Blackie,
J. Med. Chem., 2002, 45, 3331.
34. N. A. Milas, A. Golubovic, J. Am. Chem. Soc., 1959, 81, 6461.
35. H. J. Liu, M. X. Sun, Y. Y. Su, D. Y. Deng, J. Y. Hu, Y. Lv,
Chem. Commun., 2018, 54, 7987.
36. E. Climent, D. Groninger, M. Hecht, M. A. Walter, R. Mar-
tinez-Manez, M. G. Weller, F. Sancenon, P. Amoros,
K. Rurack, Chem.-Eur. J., 2013, 19, 4117.
16. X. Wang, Y. Dong, S. Wittlin, S. A. Charman, F. C. K. Chiu,
J. Chollet, K. Katneni, J. Mannila, J. Morizzi, E. Ryan,
C. Scheurer, J. Steuten, J. Santo Tomas, C. Snyder, J. L.
Vennerstrom, J. Med. Chem., 2013, 56, 2547.
17. J. Keiser, K. Ingram, M. Vargas, J. Chollet, X. Wang, Y. Dong,
J. L. Vennerstrom, Antimicrob. Agents Chemother., 2012,
56, 1090.
37. Y. X. Dong, J. L. Vennerstrom, J. Heterocyclic Chem., 2001,
38, 463.
38. N. A. Milas, A. Golubović, J. Am. Chem. Soc., 1959, 81, 3361.
39. A. O. Terent´ev, M. M. Platonov, I. B. Krylov, G. I. Nikishin,
Russ. Chem. Bull. (Int. Ed.), 2009, 58, 335.
40. A. O. Terent´ev, M. M. Platonov, E. J. Sonneveld, R. Peschar,
V. V. Chernyshev, Z. A. Starikova, G. I. Nikishin, J. Org.
Chem., 2007, 72, 7237.
41. C. S. Neupane, S. K. Awasthi, Tetrahedron Lett., 2012,
53, 6067.
42. R. Criegee, Justus Liebigs Ann. Chem., 1953, 583, 1.
43. K. Griesbaum, W. S. Kim, J. Org. Chem., 1992, 57, 5574.
44. H. Keul, K. Griesbaum, Can. J. Chem., 1980, 58, 2049.
45. K. Paul, P. R. Story, P. Busch, J. R. Sanderson, J. Org. Chem.,
1976, 41, 1283.
18. V. A. Vil´, I. A. Yaremenko, A. I. Ilovaisky, A. O. Terent´ev,
Molecules, 2017, 22, 1881.
19. N. Cowan, I. A. Yaremenko, I. B. Krylov, A. O. Terent´ev,
J. Keiser, Bioorg. Med. Chem., 2015, 23, 5175.
20. K. Ingram, I. A. Yaremenko, I. B. Krylov, L. Hofer, A. O.
Terent´ev, J. Keiser, J. Med. Chem., 2012, 55, 8700.
21. A. A. Alagbala, A. J. McRiner, K. Borstnik, T. Labonte,
W. Chang, J. G. D'Angelo, G. H. Posner, B. A. Foster, J. Med.
Chem., 2006, 49, 7836.
22. D. Chaturvedi, A. Goswami, P. Pratim Saikia, N. C. Barua,
P. G. Rao, Y. Yuthavong, T. A. Shapiro, B. A. Foster, B. Foster,
J. Davis, A. P. Higson, E. Irving, G. H. Posner, P. M. O´Neill,
R. Daughenbaugh, Chem. Soc. Rev., 2010, 39, 435.
23. P. Coghi, I. A. Yaremenko, P. Prommana, P. S. Radulov,
M. A. Syroeshkin, Y. J. Wu, J. Y. Gao, F. M. Gordillo,
S. Mok, V. K. W. Wong, C. Uthaipibull, A. O. Terent´ev,
ChemMedChem, 2018, 13, 902.
46. D. Azarifar, K. Khosravi, F. Soleimanei, Synthesis-Stuttgart,
2009, 15, 2553.
47. X. Yan, C. H. Qiao, Z. W. Guo, Synlett, 2013, 24, 502.
48. H. Jiang, G. Chu, H. Gong, Q. D. Qiao, J. Chem. Res-S,
1999, 4, 288.
Received February 8, 2019;
in revised form March 7, 2019;
accepted March 13, 2019
24. D. M. Rubush, M. A. Morges, B. J. Rose, D. H. Thamm,
T. Rovis, J. Am. Chem. Soc., 2012, 134, 13554.