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15Calixarenes Каликсарены
МаКрОГЗТЭрОЦИКЛЫ
http://macroheterocycles.isuct.ru
Paper Статья
DOI: 10.6060/mhc214097b
One-pot Synthesis of Mono-substituted Quaternized p- tert-Butylthiacalix[4]arenes
Bulat Kh. Gafiatullin,a Ilya V. Paskevich,a Vladimir A. Burilova@
b э.
Svetlana E. Solovieva and Igor S. Antipin
aKazan Federal University, 420008Kazan, Russian Federation
bArbuzov Institute of Organic and Physical Chemistry, FRC Kazan Scientific Center, Russian Academy of Sciences, 420088 Kazan, Russian Federation @Corresponding author E-mail: [email protected]
The possibility of one-pot synthesis of mono-substituted quaternized derivatives of p-tert-butylthiacalix[4]arene was demonstrated for the first time by the reaction of distally di-bromopropyl substituted p-tert-butyl thiacalix[4]arene with several nitrogen-containing nucleophiles. The structure and composition of the reaction products were analyzed by modern physical methods, including two-dimensional NMR spectroscopy and high-resolution mass spectrometry. A detailed analysis of the reaction mixtures made it possible to reveal the dealkylation mechani sm, which consists in the nucleophilic attack of the bromide ion on the O-CH2 carbon atom, followed by the formation of a bromine-containing adduct, detected by mass spectrometry. Dealkylation does not occur when the classical di-bromopropyl substituted p-tert-butyl calix[4]arene is used as a substrate - the bis-quaternized imidazolium calix[4]arene salt is formed in a high yield. Such a difference in the reactivity of two macrocycles is associated with the difference in the sizes of the macrocycles: in the case of di-substituted thiacalixarene, which has a large size, two unsubstituted hydroxyl groups form a hydrogen bond with only one alkoxy group, while in the classical calix[4]arene, two paired hydrogen bonds are formed. As a result, one of the two alkoxy groups of the thiacalixarene is more accessible for nucleophilic attack; formed thereafter thiacalixarene nucleofuge-anion is stabilized by two hydrogen bonds at once.
Keywords: Thiacalix[4]arenes, N-heterocyclic carbene precursors, dealkylation.
Однореакторный синтез моно-замещенных кватернизированных производных п- трет-бутилтиакаликc[4]арена
Б. Х. Гафиатуллин ,a И. В. Паскевич ,а В. А. Бурилов ,а@ С. Е. Соловьева,13 И. С. Антипина
aКазанский (Приволжский) федеральный университет, 420008 Казань, Республика Татарстан, Россия ьИнститут органической и физической химии им. А.Е. Арбузова ФИЦ Казанский научный центр РАН, 420088 Казань, Республика Татарстан, Россия @E-mail: [email protected]
Впервые путем реакции дистально ди-бромпропил замещенного п-трет-бутилтиакаликс[4]арена с рядом азот-содержащих нуклеофилов продемонстрирована возможность однореакторного синтеза моно-замещенных кватернизированных производных п-трет-бутилтиакаликс[4]арена. Структура и состав продуктов реакций проанализированы комплексом современных физических методов исследования, включающих двумерную ЯМР спектроскопию и масс -спектрометрию высокого разрешения. Детальный анализ реакционных смесей позволил выявить механизм деалкилирования, заключающийся в нуклеофильной атаке бромид-иона на O-CH2 атом углерода c последующим формированием бром-содержащего аддукта, зафиксированного масс-спектрометрией. При использовании в качестве субстрата классического ди -бромпропил замещенного п-трет-бутилкаликс[4]арена деалкилирования не происходит — формируется бис-кватернизированная имидазолиевая соль с высоким выходом. Подобная разница в реакционной способности двух макроциклов связана с разницей в размерах макроциклов, в результате чего, в случае тиакаликсарена, обладающего большим размером, в ди -замещенных производных две незамещенные гидроксильные группы
образуют водородную связь лишь с одной алкокси-группой, в то время как в классическом каликс[4]арене образуются две парные водородные связи. Вследствие этого, одна из двух алкокси -групп тиакаликсарена оказывается более доступной для нуклеофильной атаки, а сформированный тиакаликсареновый нуклеофуг стабилизируется также сразу двумя водородными связями.
Ключевые слова: Каликс[4]арены, NHC прекурсоры, деалкилирование.
Introduction
In the last decade the attention of many research groups has been focused on the synthesis ofN-heterocy clic carbene (NHC) transition metal complexes on a macrocyclic platform. [1>2] The fixation of NHC fragments on the macrocyclic platform allows a significant change in the microenvironment of the metal, opens the opportunity for the varying the number of NHC fragments to give both mono and bis-NHC complexes. The presence of a molecular cavity in the macrocycle allows highly selective metalloenzyme-like transformations due to the possibility of selective inclusion of reagents into the reaction "pocket". Among the variety ofmacrocycles, a special place is occupied by calix[4]arens and their analogues - thiacalix[4]arens as well as pillar[n]arens.[3-6] These molecules have a number of advantages to build NHC complexes of various structures and compositions on their platform. Modification of both the upper rim of the macrocycles as well as their phenolic hydroxyl groups can be used for introduction of NHC fragments and additional lipophilic fragments to obtain complexes with an amphiphilic architecture. Recently we obtained bis-NHC complexes of palladium(II) on the p-tert-butylthiacalix[4]arene platform in the 1,3-alternate stereoisomer^ form.[7] The resulting complexss showed activity both in the Suzuki coupling reaction as well as in the model hydrogenation reaction of p-nitrophenol. Continuing research towards the creation of precursors of NHC thiacalix[4]arene complexes, this work presents a new one-pot method for the synthesis of mono-substituted quaternized derivatives of p-tert-butylthiacalix[4]arene based on the reaction of available distal-disubstituted O-bromoalkyl derivatives of p-tert-butylthiacalix[4]arene with nitrogen containing nucleophiles .
Experimental
The solvents were purified according to known literature methods.'8' All reagents were commercially available from Sigma Aldrich or Alfa-Aesar catalogues. Sy nthesis of the starting 5,11,17,23-tetra-tert-bwy-25,27-dihydroxy-26,28-di-3-bromopropoxy-2,8,14,20-tetrathiacalix[4]arene (1) and 5,11,17,23-tetra-tert-bwtyl-25,27-dihydroxy-26,28-di-3-bromopropoxy-2,8,14,20 tetracalix[4]arene (5) was carried out according to the literature methods.[9,10]
The purity of the substances was controlled by thin layer chromatography, which was carried out using silica gel coated plates manufactured by Merck (HX68558954) with Vilber Lourmat VL-6.LC UV lamp control at 254 nm. NMR spectra were recorded at 25 oC on a Bruker Nanobay spectrometer (400 MHz for 'H and 101 MHz for 13C). Chemical shifts were corrected relative to the signals of residual protons of deuterated solvents CDCl3 (for *H 7.26 ppm; for 13C 77.36 ppm). IR spectra of the compounds were recorded on an IR Fourier spectrometer Bruker Vector-22 in the range of 400-4000 cm-1. Samples were prepared using suspending in mineral oil or as thin films, obtained from
chloroform solutions dried on the surface of the KBr tablet. Highresolution mass spectra with electrospray ionization (HRESI MS) were obtained on an Agilent iFunnel 6550 Q-TOF LC/MS. Carrier gas - nitrogen, temperature 300 °C, carrier flow rate 12 L/min, nebulizer pressure 275 kPa, funnel voltage 3500 V, capillary voltage 500 V, total ion current recording mode, 100-3000 m/z mass range, scanning speed 7 spectra/s. The melting points of the substances were determined on an OptiMelt MPA100 automatic heating table (Oxford Instruments, USA). Elemental analysis was performed on a EuroVector EA 3000 CHN analyzer.
General procedurefor the quatemization reaction: 0.18 mmol of dibromopropyloxy derivative of p-tert-butyl(thia)calix[4]arene (1 or 5) and 1.8 mmol of tertiary amine (pyridine, 1-methylimi-dazole, N-methylmorpholine) were placed into the glass autoclave 'GlassChem' (CEM ® corporation) and dissolved in 3 mL of dry acetonitrile. The reactions were carried out in an inert nitrogen atmosphere. The reaction mixture was heated to 130 °C for 16-60 hours. The progress of the reaction was monitored by TLC (petroleum ether: ethyl acetate 1:4, the resulting salts have Rf = 0). To isolate the target products, the solvent was evaporated to give precipitate, which was dried in vacuo for 8 hours. The product was additionally purified by column chromatography (eluent metha-nol:methylene chloride 1:7).
5,n,17,23-Tetm-tert-butyl-25,26,27-trihydroxy-28-(3-(3-N-met-hylimidazoliwm)propoxy)-2,8,14,20-tetrathiaoalix[4]arene bromide, 2. Yield: 0.14 g (88%). HRESI MS: m/z [M-Br] + calcd. C47H59N2O4S4+ 843.3353, found: 843.3345. Tm (decomp) = 245 oC. IR (KBr) Vmax cm-1: 1261 (CAr -O), 1571 (C = N), 2869 (CH2), 2961 (CH3). *H NMR (CDCl3, 363 K) Sh ppm: 0.67 (9H, s, C(CH3)3), 1.21 (9H, s, C(CH3>), 1.29 (18H, s, C(CH3)3), 2.48 (2H, p, CH2, J = 5.7 Hz), 4.11 (3H, s, CH3), 4.57 (2H, t, CH2O, J = 5.7 Hz), 4.94 (2H, br.t, CH2N, J = 5.7 Hz), 6.83 (2H, s, ArH), 7.20 (2H, br.s, ImdH), 7.55 (2H, s, ArH), 7.58 (2H, d, ArH, J = 2.5 Hz), 7.63 (2H, d, ArH, J = 2.5 Hz), 10.43 (1H, s, HImd). 13C NMR (CDCl3) S ppm: 30.56, 31.05, 31.68, 37.09, 47.42, 68.75, 122.12, 122.84, 122.95, 123.45, 123.65, 129.83, 131.32, 134.43, 134.98, 136.26, 139.58, 147.19, 156.69, 158.84.
5,n,17,23-Tetm-tert-butyl-25,26,27-trihydroxy-28-(3-(1-pyridi-nium)propoxy)-2,8,14,20-tetrathiacalix[4]arene bromide, 3. Yield: 0.13 g (76%). HRESI MS: m/z [M-Br]+ calcd. for C48H58NO4S4+ 840.3244, found 840.3247. Tm (decomp) = 200 oC. IR (KBr) Vmax cm-1: 1251 (CAr -O), 1633 (C = N), 2869 (CH2), 2962 (CH3). NMR (CDCl3, 363 K) Sh ppm: 0.64 (9H, s, C (CH3)3), 1.21 (9H, s, C (CH3)3), 1.30 (9H, s, C (CH3)3) 2.75(2H, p, CH2, J = 5.1 Hz), 4.55 (2H, t, CH2O, J = 5.1 Hz), 5.29 (2H, br.t, CH2N,J = 5.1 Hz), 6.80 (2H, s, HAr), 7.56 (2H, s, HAr), 7.60 (2H, br.d, HAr), 7.64 (2H, br.d, HAr), 8.07-8.13 (2H, m, PyH), 8.17-8.23 (1H, m, PyH), 10.00 (2H, m, PyH). 13C NMR (CDCl3) S ppm: 30.57, 31.70, 34.16, 59.37, 67.96, 122.07, 123.36, 123.58, 128.61, 129.97, 131.37, 134.50, 135.03, 136.31, 141.26, 144.36, 146.94, 147.50, 156.40, 158.66.
5,n,17,23-Tetm-tert-butyl-25,26,27-tnhydroxy-28-(3-(3-N-met-hylmorphdimwn)pmpoxy)-2,8,14,20-tetrathiacaUx[4]arene bromide, 4. Yield: 0.14 g (84%). HRESI MS m/z [M-Br]+ calcd. for C48H64NO5S4+ 862.3663, found: 862.3662; Tm (decomp) = 200 oC. IR (KBr) Vmax cm-1: 1260 (CAr -O), 1570 (C-N), 2869 (CH2), 2962 (CH3). NMR (CDCl3, 363 K) Sh ppm: 0.46 (9H, s, C(CH3)3), 1.19 (9H, s, C(CH3)3), 1.31 (18H, s, C(CH3)3), 2.44-2.65 (2H, m, CH2), 3.50 (3H, s, CH3), 3.67-3.73 (4H, m, CH2N), 3.97-4.12 (4H, m, CH2O), 4.34 (4H, br.t, CH2O), 4.75 (4H, br.t, CH2N+), 6.54 (2H, s,
V. A. Burilov et al.
ArH), 7.49 (2H, s, ArH), 7.58 (4H, s, ArH). 13C NMR (CDCI3) 5 ppm 23.89, 29.85, 30.32, 34.19, 47.27, 60.48, 61.07, 121.91, 123.82, 124.14, 129.28, 130.68, 134.14, 134.81, 136.29, 141.42, 147.52, 155.53, 157.79.
5,11,17,23-Tetra-tert-butyl-25,27-dihydroxy-26,28-bis (3-(3-N-methylimidazolium)propoxy)-2,8,14,20-calix[4]arene dibromide, 6. Yield: 0.16 g (85%). HRESI MS m/z [M-2Br]2+ calcd. for C58H78N4O42+ 447.3006, found 447.3008. Tm (decomp) = 235 oC. IR (KBr) Vmax cm-1: 1240 (CAr -O), 1573 (C = N), 2869 (CH2), 2962 (CH3). 'H NMR (CDCI3, 363 K) 5h ppm: 0.97 (18H, s, C (CH3)3), 1.28 (18H, s, C (CH3)3), 2.68 (4H, p, CH2, J = 7.0 Hz), 3.36 (4H, d, CH2, J = 13.0 Hz), 4.05-4.15 (14H, m, CH2, OCH2, CH3), 4.84 (4H, t, CH2N, J= 6.9 Hz), 6.83 (4H, s, ArH), 7.07 (4H, s, ArH), 7.47 (2H, s, OH), 7.53 (2H, br.s, ImdH), 7.85 (2H, br.s, ImdH), 10.26 (2H, s, ImdH). 13C NMR (CDCI3) 5 ppm: 31.07, 31.78, 31.96, 34.03, 34.13, 37.11, 46.79, 72.08, 122.67, 124.09, 125.56, 125.98, 127.82, 132.33, 137.85, 142.74, 147.84, 149.32, 149.99.
Results and Discussion
In order to obtain new precursors for bis-NHC complexes on the platform of p-tert-butylthiacalix[4]arene and classical p-tert-butylcalix[4]arene, the reaction of dibromopropyl-substituted calix[4]arenes with N-methylimidazole was carried out. For this purpose, the initial distal-disubstituted O-bromopropyl-containing macrocycles 1 and 5 were obtained according to the literature methods[9-10] by the Mitsunobu reaction of the initial thia- or classic calix[4]arenes with bromopropanol. The obtained macrocycles 1 and 5 were used in Menshutkin's reaction with
1-methylimidazole according to Scheme 1. The reactions were carried out in acetonitrile in a 'GlassChem' autoclave (CEM® corporation) at 130 °C with the thin lay er chromatography control of the reaction.
As a result of the quaternization reaction between dibromo-substituted thiacalix[4]arene 1 with 1-methylimidazole, after 30 hours of stirring monosubstituted adduct 2 was isolated in high yield (88%) instead of the expected di-substituted product. The structure of the adduct 2 was proved by NMR, IR spectroscopy, high-resolution electrospray mass spectrometry (HRESI MS). Dealkylation during quaternization is unambiguously evidenced by the data of both one-dimensional and two-dimensional 1H-1H NOESY NMR spectroscopy and HRESI MS experiments. Thus, the 1H NMR spectrum of the macrocycle 2 (Figure 1) exhibits a typical signal pattern of mono-substituted thiacalixarenes (two singlets and two doublets of signals for aromatic protons 7, 9, 8, and 8 ', as well as three signals for protons of tert-butyl groups 10, 11 and 12 as singlets with a ratio of 1:2:1). In the 2D (1H-1H) NOESY NMR spectrum of compound 2, there are the cross-peaks between the signals of N-CH-N protons of the imidazolium fragment 1 (5 = 10.41 ppm) and methylene protons of the propyl linker 4-6 (5 = 4.91, 2.47 and 4.57 ppm) and also between the signals of the N-CH3 protons of fragment 2 (5 = 4.06 ppm) and the nearby imidazolium protons 3, 3 'and 1 (5 = 7.21 and 10.41 ppm). The presence of cross peaks between the protons of neighboring tert-butyl groups (5 = 1.20 and 0.63; 1.29 and 0.65 ppm) indicates the "cone" stereoisomers form of macrocycle 2.
R
130°C, MeCN
Scheme 1. Synthesis of imidazolium salts based onp-ferf-butyl(thia)calix[4]arene. Макрогетероцикnbl/Macroheterocycles 2022 75(1) 53-58
9
IU 12 J
11
5 -
2 ■
64-
8,8
1
7
3,3'
UL
V 12
■f7.S5 /
A {7.64,1.29} {7.58,1.29}
^{10.41,2.47}
^{10.42,4.06} {10.40,4.57} •^{10.41,4.91} {7.21,4. 06}
{7.64,6.80}^ o*
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10.
-4
E
5 12
h5 TT
{1. é1 20,0 29,0 / 63} .65}
i. c s c
p
0
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 1.30 1.20
ppm ppm
Figure 1. Fragments of the 2D ('H-'H)NOESY NMR spectrum of compound 2 (CDCI3, 25 oC).
IT j c a) h r c c c ^ a b) I c> « c « e .. i,i c) « ( ( f r: d) 0 0 c f> c a - (O CD o o 6 o M I . I. L ... L, . . ,. .. e) I ( rm CM CN O) o m . I........
600 800 1000 m/z 600 800 1000 m/z 500 80j> 1000 400 450 500 m/z 200 250 300 350 400 450 500 550 600 650 700 750 800 850 m/z
Figure 2. Fragments of HRESI mass spectia of compounds 2 (a), 3 (b), 4 (c), 6 (d), as well as reaction mixture 1 with pyridine after 10 hours of heating (e).
The reaction with other nucleophiles (pyridine and N-methylmorpholine) proceeds in a similar way - as the only product, monosubstituted salts 3 and 4 were also isolated in high yields. The structure of all compounds was also confirmed by HRESI MS. The mass spectrum (Figure 2) of compound 2 showed a peak [M-Br]+ with m/z = 843.3345 (calculated for C47H59№O4S4+ 843.3353), similar peaks of the molecular ion [M-Br]+ were recorded for compound 3: m/z = 840.3247 (calculated for C4sH58NO4S4+ 840.3244) and 4: m/z = 862.3662 (calculated for C4sH54NO5S4+862.3663).
To reveal the mechanism of the observed dealkylation, the reaction mixture of 1 with pyridine was analyzed by HRESI MS after 10 hours of reflux According to the data obtained (Figure 2e), the mixture contains a peak [M-2Br]2+
of di-quaternized product 7 with m/z = 480.2022 (calculated for C56H5sN2O4S42+ 480.2026) (Scheme 2) and mono-quarter-nized product 3. In addition to these signals, the spectrum contains [M-Br]+ signal of the adduct 8 with m/z = 200.0066 (calculated for CsHiiBrN+ 200.0070).
The above HRESI MS data indicate that the mechanism of the dealkylation reaction involves a nucleophilic attack of the alpha-carbon atom of the ether group with a bromide ion, which leads to the cleavage of the carbon-oxygen bond, the formation of 1-(3-bromopropyl)pyridinium bromide 8 and the elimination of the nucleofuge - the anion of monosub-stituted calixarene 3, which is then protonated during the treating of the reaction mixture with water (Scheme 2). It is known that the high nucleophilicity of the bromide ion
V. A. Burilov et al.
+
S" i sl I i^s
o OH OH o
Br
Br
130°C, MeCN 10 h
i-Bu i-Bui-Bu i-Bu
i-Bu f-Bui-Bu Î"Bu
I I S
OH OH. O
Br.
№
Scheme 2.
Scheme 3.
allows cleavage of aryloxy-alkyl bonds with the release of the corresponding phenols in almost quantitative yield.[11] Dialkyl-substituted derivatives of p-tert-butyl-thiacalix[4]arene also undergo selective mono-dealkylation both in the presence of an excess of tetraalkylammonium halides[12] and in the presence of other nucleophiles (amines,[13] sodium azide[14]). It is noteworthy that no deal-kylation occurs during the quaternization of calix[4]arene 5 with 1-methylimidazole: after 16 hours of reflux, the distally disubstituted product 6 was isolated in a high yield (85%). The 1H NMR spectrum of compound 6 exhibits a classic pattern of signals characteristic of distally disubstituted calix[4]arenes: two singlets at 5 = 1.28 and 0.97 ppm, corresponding to the protons of tert-butyl groups, two singlets at 5 = 6.83 and 7.07 ppm, corresponding to the protons of the aromatic rings of calix[4]arene, as well as one signal of OH - protons at 7.47 ppm. According to HRESI MS data, the composition of compound 6 is fully consistent with the proposed structure - the peak [M-2Br]2+ with m/z = 447.3008 (calculated for C58H78N4O42+ 447.3006) is observed. This result clearly demonstrates the unique hydrolytic instability inherent in thiacalix[4]arenes compared to classical calix[4]arenes, as discussed earlier.[15] Due to the fact that the length of the bond between the carbons of the benzene ring and sulfur in the thiaca-lix[4]arene is 1.77 A, while in the classical calix[4]arene the bond between the carbons of the benzene ring and the methylene fragment is 1.54 A, the cavity of the thiaca-lix[4]arene is about 15% larger than that of calix[4]arene.[16] Such a cavity size difference leads to the different structures of distally disubstituted products as in the crystalline phase[17]
and in solution.[18] For thiacalix[4]arene, the most characteristic conformation is the "distorted cone", in which two hydrogens of phenolic hydroxyl groups form a hydrogen bond with only one alkyloxy fragment, while all oxygen atoms of classical calixarene are involved in the hydrogen bond (Scheme 3) and the most preferred conformation is the "flattened cone"
As a result of the distortion of the thiacalix[4]arene structure, one of the two substituents becomes more sterically available for nucleophilic attack. Stabilization of the nucleofuge is also important: in the case of thiaca-lix[4]arene, two hydrogen atoms of phenolic hydroxyl groups take part in the stabilization by a hydrogen bond (Scheme 3).
Conclusions
Convenient synthesis of mono-substituted quaternized salts by reaction of distal-dibromopropyl substituted derivatives of thiacalix[4]arene with nitrogen-containing nucleophiles was demonstrated for the first time. The reaction mechanism including nucleophilic attack of bromide ion to alpha-carbon atom of the ether group was evaluated by the HRESI MS method. It has been demonstrated that dealkylation occurs only with the participation of thiacalix[4]arene, while the expected di-substituted product is formed with the use of classical calix[4]arene.
Acknowledgements. This study was supported by the Russian Science Foundation (Grant No. 21-73-10062).
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Received 05.01.2022 Accepted 09.02.2022
