Novel synthetic approach to pyrrolo[1,2-b]cinnolines

Article abstract of DOI:10.1007/s10593-020-02770-w

[Figure not available: see fulltext.] Straightforward method for the synthesis of pyrrolo[1,2-b]cinnolines starting from 2-nitrobenzaldehydes and 2-methylfurans has been elaborated. The key steps of the process are oxidative furan ring opening with diazon

Full text of DOI:10.1007/s10593-020-02770-w

DOI 10.1007/s10593-020-02770-w
Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Novel synthetic approach to pyrrolo[1,2-b]cinnolines
Anastasia T. Plieva1*, Petrakis N. Chalikidi1, Andrey V. Gutnov1, Anatolij M. Turiev1,
Oleg P. Demidov2, Nicolai A. Aksenov2, Taimuraz T. Magkoev1, Vladimir T. Abaev1*
1 Department of Chemistry, North Ossetian State University named after K. L. Khetagurov,
46 Vatutina St., Vladikavkaz 362025, Russia; e-mail: plieva_nastya@mail.ru, hampazero@mail.ru
2 Department of Chemistry, North Caucasus Federal University,
1a Pushkina St., Stavropol 355009, Russia
Submitted March 20, 2020
Accepted after revision July 15, 2020
Published in Khimiya Geterotsiklicheskikh Soedinenii,
2020, 56(8), 1030–1041
Straightforward method for the synthesis of pyrrolo[1,2-b]cinnolines starting from 2-nitrobenzaldehydes and 2-methylfurans has been
elaborated. The key steps of the process are oxidative furan ring opening with diazonium cation and intramolecular alkylation of azo
group of the resulted cinnoline with secondary allyl alcohol.
Keywords: aza-heterocycles, cinnolines, pyrrolo[1,2-b]cinnolines, furan ring opening.
In the last decade, pyrrolo[1,2-b]pyridazines enjoy ever-
growing use in medicine due to the wide spectrum of
biological activity they possess including anticancer,1
antibacterial,2 antioxidant,3–5 anti-inflammatory,6 Janus
kinase (JAKs)7–9 and IRAK4 inhibiting activity.10 No less
attention is paid to the photophysical properties of this
class of compounds. Their fluorescent properties made
them popular materials in the constructing different optical
devices, lasers, OLED screens.11–15 Some representatives of
pyrrolo[1,2-b]cinnolines display prominently high lumines-
cence level with quantum efficiencies up to 90%.12
General methods of assembling pyrrolo[1,2-b]pyridazine
framework are numerous and mainly based on conden-
sation and cycloaddition approaches.16,17 The number of
synthetic routes to access pyrrolo[1,2-b]cinnolines is
considerably lower. Thus, the first derivative of rare
pyrrolo[1,2-b]cinnoline ring system was reported by Ames
in 1975.18 The corresponding 2-aminovalerophenone was
diazotized under conditions of Borsche–Koelsch cinnoline
synthesis, and resulting 3-methoxypropylcinnolinone was
refluxed with concentrated HBr (Scheme 1). Later on
pyrrolo[1,2-b]cinnolinone derivative was prepared from
2-benzoyl-1H-pyrrol-1-ylcarbamate employing aromatic
nucleophilic substitution.19 Methylation with diazomethane
produced O-methyl ether and further reaction with
benzylamine allowed for obtaining 10-amino derivative of
pyrrolo[1,2-b]cinnoline. Pyrrolo[1,2-b]cinnoline derivative
accompanied anticipated product of the Hantzsch
1,4-dihydropyridine Vilsmeier formylation. Its formation
was rationalized by unusual dihydropyridine ring recycli-
zation (Scheme 1).20 In 2003, the synthesis of pyrrolo[1,2-b]-
cinnolines directly from cinnolines under the action of
dimethyl acetylenedicarboxylate (DMAD) in MeOH at low
temperature was developed. Alternatively, cinnolines were
N-alkylated with tert-butyl bromoacetate before the
reaction with DMAD.12
We developed a novel approach for the synthesis of
pyrrolo[1,2-b]cinnolines starting from o-nitrobenz-
aldehydes or o-azidobenzhydrols.
Cinnolines 4a–h,l which were employed as precursors
for the synthesis of pyrrolo[1,2-b]cinnolines were easily
obtained from 2-nitrobenzaldehydes 1a–h,l (Scheme 2) as
was reported earlier.21–30 At the first step, condensation of
benzaldehydes with 2-methylfuran in the presence of HClO4
gave rise to the corresponding difurylmethanes 2a–h,l
which were reduced with NaBH4 in the presence of
palladium on charcoal. Diazotisation under mild conditions
with tert-butyl nitrite in MeCN resulted in electrophilic
attack of diazonium cation onto furan ring, its opening and
furnished the desired cinnolines 4a–h,l in good yields.
0009-3122/20/56(8)-1030©2020 Springer Science+Business Media, LLC
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Scheme 1. Reported synthetic approaches
to pyrrolo[1,2-b]cinnoline ring system
Table 1. Synthesis of pyrrolo[1,2-b]cinnolines 6a–l
from (Z)-4-(cinnolin-3-yl)but-3-en-2-ones 4a–j,l
Ames et al., 197518
O
O
N
aq HBr
N
, 1.5 h
79%
N
N
H
OMe
Hamer et al., 198819
O
O
N
O
KOH
HN
Cl
N
EtOH–H2O
, 1 h
OEt
Com-
Isolated
yield, %
Cl
N
H
R1
R2
R3
R4
R5
pound
98%
Cl
H
H
H
OMe
H
H
OMe
H
H
H
5-MeFu
5-MeFu
5-MeFu
5-MeFu
5-MeFu
5-MeFu
5-MeFu
H
68
64
72
62
65
68
70
61
73
74
98
–
6a
Bn
1. CH2N2
THF, rt, 48 h
46%
NH
6b
6c
6d
6e
6f
OMe
H
OMe
OMe
OMe
Br
N
2. BnNH2
Cl
N
H
H
Hg(OAc)2
55°C, 2 h
92%
OMe
OMe
OMe
H
Me
H
OMe
OMe
OMe
Cl
H
Flitsch et al., 199020
H
Cl
6g
6h
6i
EtO2C
Me
CO2Et
OMe
H
H
N
N
O
H
H
Ph
H
OMe
H
OMe
H
H
Ph
6j
EtO2C
Me
CO2Et
Me2NCHO
POCl3
(32%)
+
H
OH
H
5-MeFu
5-MeFu
6k
6l
N
N
Me
H
NO2
H
CH2Cl2
rt, 48 h
EtO2C
N
N
Scheme 2. Synthesis of starting (Z)-4-(cinnolin-3-yl)but-
3-en-2-ones 4a–j,l
CO2Et
(0.7%)
Cinnolines with phenyl substituent in position 4 4i,j were
obtained from the corresponding amines 3i,j which were
available via condensation of 2-azidobenzhydrols with
sylvan and subsequent Staudinger reaction followed by
hydrolysis.
Having a set of cinnolines 4a–j,l in hand, we reduced
carbonyl group with NaBH4 to get alcohols 5a–j,l.
Interestingly that during workup, initial cinnoline cis-
enones 4a–j,l underwent complete isomerization and
alсohols 5a–j,l were obtained exclusively in the trans form.
Obviously, this thermodynamically driven process occurs
via reversible addition to enone double bond of nucleo-
phile, more likely hydroxide ion. Alternatively, isomeriza-
tion can be self-catalyzed and cinnoline ring can act as
nucleophile by analogy with 4-dimethylaminopyridine in
the related isomerization process in acylvinylindoles.27
Next, pyrrolocinnolines 6a–j were obtained by the intra-
molecular alkylation with BF3·Et2O which appeared to be
an appropriate reagent. Depending on the nature of the
substituents cyclization was completed in 4–8 h in
refluxing dichloroethane in 62–73% yields (Table 1).
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Figure 1. Molecular structure of compound 6b with atoms repre-
sented as thermal vibration ellipsoids of 50% probability.
Unfortunately, conjugation of cinnoline azo fragment with
nitro group retarded the reaction and precluded the
formation of pyrrolocinnoline 6l.
For the unambiguous proof of structure of obtained
compounds, a single crystal of representative compound 6b
was grown from the EtOAc – petroleum ether mixture and
characterized using X-ray structural analysis (Fig. 1).
As it is known from the literature data, benzannulation
enhances aromaticity of pyrrolopyridazine which is
evidenced by increased bond equalization.12 Thus, the
length of N–N bond equals to 1.375 Å in 3-ethyl 1,2-di-
methyl pyrrolo[2,1-a]phthalazine-1,2,3-tricarboxylate (PPH),
while in trimethyl pyrrolo[1,2-b]cinnoline-1,2,3-tricarboxy-
late (PC) it is much shorter: 1.343 Å. Meanwhile the N=C
double bond in PPH (1.294 Å) is sufficiently shorter than
N=C bond in PC (1.343 Å) (Fig. 2).12
For the synthesized compound 6b, N–N and N=C bond
lengths equal to 1.353 аnd 1.323 Å, respectively, which are
medium values between PPH and РС. As can be seen from
Figure 3, the π-planes of the molecules do not stack up
unlike PPH, PP, and РС where π-stacking interactions are
reflected in the distances between π-planes: 3.39, 3.34, and
3.31 Å, respectively.
Figure 3. π-Stacking diagram of compound 6b.
From another point of view (Fig. 4), the relatively small
distance of 3.892 Å between centroids of furan and
pyridazine rings may be indicative of their donor–acceptor
interaction.
Next, optical properties of the synthesized compounds
were studied. The absorption spectra of compounds 6a–i
were recorded in DMSO, MeOH, CH2Cl2, and hexane
solutions at room temperature.
Figure 4. Plane centroid – plane centroid distance for compound 6b.
Figure 2. Structures of PP, PPH, and PC.
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Table 2. Absorption spectra of compounds PC, 6a–i (λmax, nm)
Solvent
Compound
DMSO
MeOH
СН2Сl2
Hexane
РС12
6a
6b
6c
437
550
529
543
550
546
577
494
534
435
547
522
539
547
545
570
494
531
440
549
525
539
541
547
572
495
534
448
548
517
536
547
542
564
497
535
6d
6e
6f
6h
6i
Figure 5. The UV absorption spectra of compounds 6a,b,c,d,e in
CH2Cl2.
known tool for measurement of reduction and oxidation
potentials of organic compounds, which correlate with
HOMO and LUMO energies, constituting substantial
interest in prediction of stabilities of materials for opto-
electronic devices.
As it can be seen from Figure 5 and Table 2, absorption
peaks of compounds 6a–i are sufficiently shifted to long
wave region in comparison with РС – displaying a
difference of 100 nm in hexane and even more (113 nm) in
more polar DMSO.
In the paper published in 2003 on the synthesis and
properties of high fluorescent pyrrolopyridazine deriva-
tives,12 electrochemical behavior of pyrrolo[1,2-b]cinnoline
containing various electron-withdrawing substituents in the
pyrrole ring was described. Along with noted surprisingly
large red shift (about 100 nm), its HOMO and LUMO
energy levels are characterized as ideally appropriate for
the employment in the development of materials for optical
devices.31–34 With the series of synthesized pyrrolo[1,2-b]-
cinnolines incorporating electron-donating substituents in
hand, we were interested in their electrochemical properties
evaluation for revealing high signal reversibility in the
cathode region, similarly to PC. All of the explored
compounds possess high electrochemical activity, though
the nature of the redox processes is in direct accordance
with the presence of R1–4 substituents. The cyclic
voltammetry reduction and oxidation potentials for the
examined pyrrolo[1,2-b]cinnolines are given in Table 3.
Figure 6 depicts voltammetric curves for pyrrolo[1,2-b]-
cinnoline 6a, without R1–4 substituents on the aryl ring.
In general, if substituents R1–4 in pyrrolo[1,2-b]-
cinnolines bearing 5-methylfuryl as R5 substituent are
methoxy groups then absorption peaks are shifted to blue
region (compounds 6b,c,d,e), and oppositely, in the case of
acceptor bromine substituent in R4 position of compound
6f, absorption peaks shifted red in comparison to
unsubstituted compound 6a (Table 2).
Noteworthy that the π-system extension with furan
(compound 6a) or benzene ring (compound 6i) as R5
substituent in comparison with compound 6h, lacking R5
substituent is in accordance with electrochemical data
below. For compound 6h, strong shift to blue region is
observed (497 nm), then follows absorption peak of
compound 6i (535 nm), and finally red-shifted absorbance
band of compound 6a (548 nm). Although here λmax are
presented for hexane, the same tendency was observed for
other solvents.
Further, electrochemical studies of the synthesized
compounds were performed. Cyclic voltammetry is well-
Figure 6. Cyclic voltammograms of compound 6a at a glassy carbon disk electrode with a) negative and b) positive scan directions;
1 mM solution in MeCN containing 0.1 M TBAP; v 0.2 V/s.
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Table 3. Electrochemical properties of compounds 6a–k*
Reduction
Epk, V Epa,V
Oxidation
Epa, V
Compound
Epk,V
–1.51 (А)** –0.61 (A'')
+0.72 (C)
+1.08 (D)
+1.95
–
–
6a
–2.09 (В)
–1.42 (A')
–2.19
–1.67
–2.24
–0.80
+0.52
–
–
–
–
–
6b
–1.61
+0.86
–2.31
+1.76
+1.88
+2.23
–1.56
–2.25
–0.59
–1.47
–2.22
+0.69
+0.94
+1.71
+2.15
–
–
–
–
6c
–1.60
–2.24
–0.71
–1.47
–2.27
+0.63
+0.99
+1.84
+1.98
+2.29
–
–
–
–
–
6d
Figure 7. Cyclic voltammograms of compounds 6a,g,k at a glassy
carbon disk electrode with negative and positive scan directions;
1 mM solution in MeCN containing 0.1 M TBAP; v 0.2 V/s.
–1.53
–2.12
–0.63
–1.43
–1.91
+0.75
+1.01
+1.39
+1.75
+2.10
+0.74
+0.97
+1.75
+2.09
–
–
–
–
–
–
–
–
–
6e
6f
–1.49
–1.67
–2.27
–0.62
–0.78
–1.37
–1.64
–2.27
–1.40
–1.96
–0.54
–1.31
–1.98
+0.72
+0.95
+1.72
+2.06
+0.66
+0.92
+1.78
+2.28
+2.45
+0.84
+1.08
+1.67
+2.17
+0.75
+0.97
+1.64
+1.82
+2.33
+0.82
+1.10
+1.67
+1.94
+0.61
–
6g
6h
–
–
–
–1.80
–1.04
–1.68
–
–
–
–
–
–1.55
–2.06
–0.59
–1.47
–1.67
–
6i
6j
–
–
–
–1.72
–2.22
–0.64
–1.61
–1.96
–
–
–
–
–
–1.35
–1.88
–0.08
–0.38
–1.86
–
6k
–
–
–
Fc***
–
–
+0.47
* Solvent: MeCN, containing 0.1 M TBAP; v 0.2 V/s.
** Letters A–D correspond to the peaks on Figures 6–8.
*** Ferrocene was used as an internal reference redox electrode.
It is legitimate that the lowest first-stage reduction
potentials (Table 3) belong to bromo 6f (–1.49 V), chloro
6g (–1.40 V), and hydroxy derivatives 6k (–1.35 V), which
is accounted by the presence of an electron-withdrawing
substituent (Fig. 7). Apparently in the case of compound 6k
the negative inductive effect of the hydroxy group oxygen
at R4 position tends to be stronger than the positive
mesomeric effect. Compounds 6b,c,d,e,h having electron-
donating substituents in the benzene ring are capable of
adding electrons at more negative potentials in contrast to
compound 6a (Fig. 8).
Figure 8. Cyclic voltammograms of compounds 6a,b,h,i at a glassy
carbon disk electrode with a) negative and b) positive scan direc-
tions; 1 mM solution in MeCN containing 0.1 M TBAP; v 0.2 V/s.
As it is evident from Figures 6–8, the electrochemical
reduction of the synthesized pyrrolo[1,2-b]cinnolines
proceeds in two steps, with the first one being reversible to
large extent, while the second is only partially reversible. It
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
is also worth noting that the first reduction signal on the E
be observed if one compares the redox behavior of
compounds 6c, 6d, and 6e. All of the three compounds
have more positive Eox magnitudes compared to that of
compound 6b (+0.52 V): +0.69, +0.63, and +0.75 V,
respectively. Most likely, the presence of donating groups
at positions 8 and 9 obstructs the first step of oxidation.
Note that the current description is generally in a good
agreement with the data in literature; oxidation of 1,2-di-
methoxybenzene is known to be impeded in contrast to that
of 1,4-dimethoxybenzene.35
For elongation of conjugation and modulation of
photophysical properties of pyrrolo[1,2-b]cinnolines, few
test reactions were performed. First we considered that
electrophilic activation of the ring should lead to enhanced
acidity of pyrrole-bound methyl group rendering it suitable
for condensation with benzaldehydes. Unexpectedly,
treatment of pyrrolocinnoline 6c with benzaldehydes 7а,b
gave rise to dihetarylmethanes 8a,b rather than styryl
compounds (Scheme 4). Structure of compound 8a has
been proved by X-ray crystallography (Fig. 9). The crystal
of compound 8a contains two nonequivalent molecules
which differ in the side chain conformation (methoxy
group) and the relative angles of aromatic cycles around a
pseudoasymmetric carbon atom.
curve produces an extra peak А'' (Figs. 6, 7, and 8). We
assume the formation of a stable anion radical at the first
step (peak A), which upon addition of an electron is
converted to a dianion (peak B), capable of being oxidized
at negative potentials (Scheme 3). Seemingly, from the two
anion radicals a dimer-dianion is chemically formed with
the involvement of one of R1–4 positions. Peak А' is
considered the dimer-dianion oxidation signal. The
existence of some correlation between the dimer-dianion
stability and the height of the peak А'' is also presumed. As
Figure 6 indicates, the maximal magnitude of this signal is
observed for compound 6a in which the electron density of
the pyrrolocinnoline nucleus is additionally stabilized by
the furan ring. For compound 6h which is lacking an
additional stabilizing factor, such a signal is absent.
Scheme 3. Electrochemical reduction of compounds 6a–k
at a glassy carbon disk electrode
R1 R5
R1 R5
R2
R3
R2
R3
+e-
N
N
N
N
R4
Me
R4
Me
6a–k
Scheme 4. Synthesis of dihetarylmethanes 8a,b
R1 R5
+e-
R2
N
R3
N
R4
Me
The influence of
a more extended π-system in
comparison to PC can be conveniently viewed considering
examples 6a,i involving a 5-methylfuryl and phenyl groups
at position 10, and compound 6h, which is unsubstituted at
this position. As the data from Table 3 and Figure 6
implies, the strongest stabilizing effect on the anion radical
formed at the first stage is provided by the methylfuryl
substituent in compound 6a (–1.51 V), while the potential
for the first stage of reduction of compound 6i is slightly
more negative (–1.55 V). In the case of absence of
substituents at position 10, the signal shifts to the region of
more negative magnitudes and is –1.80 V for compound
6h. The effect of the extended π-system on the reversibility
of signals of the first stage of oxidation is lower, than it is
for reduction. All the synthesized compounds have
significantly lower oxidation potentials than PC. First stage
of oxidation proceeds with the greatest facility in the case
of compound 6b (+0.52 V), which incorporates methoxy
substituents at positions 7, 8 and the methylfuryl group at
position 10. It may also be outlined that, in general, the
presence of an electron-accepting halogen substituent at
position 6, compensated in terms of electronic effects by
the presence of two donating methoxy substituents at
positions 8 and 9, has no considerable influence on the Eox
magnitude: it equals to +0.72 V for the model compound
6a, +0.74 V and +0.72 V for compounds 6f and 6g,
respectively. An interesting effect of the influence of
donating substituent position on the first stage potential can
Figure 9. Molecular structure of compound 8a with atoms repre-
sented as thermal vibration ellipsoids of 50% probability.
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Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Eleven new heterocycles, based on the pyrrolo[1,2-b]-
132.7; 130.8; 121.3; 111.2; 109.0 (2C); 106.2 (2C); 56.4;
39.6; 30.9; 13.6. Found, m/z: 350.0999 [M+Na]+.
C18H17NNaO5. Calculated, m/z: 350.1008.
Preparation of compounds 3c–g (General method).
The compounds were prepared according to the literature
method.29,30
2-[Bis(5-methylfuran-2-yl)methyl]-3,6-dimethoxyaniline
(3c). Yield 2.61 g (88%), beige solid, mp 147–149°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 6.70 (1H, d,
J = 8.7, H-5 Ar); 6.30 (1H, d, J = 8.7, H-4 Ar); 6.19 (1H, s,
CH); 6.05 (2H, d, J = 2.8, H-3 furan); 5.91 (2H, d, J = 2.8,
H-4 furan); 4.17 (2H, br. s, NH2); 3.82 (3H, s, OCH3); 3.80
(3H, s, OCH3); 2.28 (6H, s, 2CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 152.0; 151.6 (2C); 151.3 (2C); 142.3;
137.0; 112.4; 108.8; 108.1 (2C); 106.0 (2C); 99.0; 56.5;
55.9; 34.9; 13.8 (2C). Found, m/z: 350.1363 [M+Na]+.
C19H21NNаO4. Calculated, m/z: 350.1352.
cinnoline unit, have been prepared and their electro-
chemical properties, as well as their crystal structures, have
been studied. We have shown that the molecules of the
synthesized pyrrolo[1,2-b]cinnolines, which involve two
nucleophilic fragments – furan and pyrrole rings – possess
strongly polarized character, which is demonstrated by
their condensation reactions with suitable benzaldehydes,
where pyrrolo[1,2-b]cinnolines act as donor aromatic
compounds.
Experimental
1H and 13C NMR spectra were recorded on a Bruker
Avance HD 400 (400 and 101 MHz, respectively)
spectrometer at room temperature in CDCl3 or DMSO-d6.
Solvent signals were used as internal standard (CDCl3:
1
7.26 ppm for Н nuclei, 77.2 ppm for 13C nuclei; DMSO-d6:
1
2.50 ppm for Н nuclei, 39.5 ppm for 13C nuclei). Mass
2-[Bis(5-methylfuran-2-yl)methyl]-6-methoxyaniline
(3d). Yield 2.58 g (87%), beige solid, mp 71–73°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 6.78 (2H, d,
J = 4.2, H-3,5 Ar); 6.65–6.58 (1H, m, H-4 Ar); 5.96 (2H, d,
J = 2.3, H-3 furan); 5.92 (2H, s, H-4 furan); 5.51 (1H, s,
CH); 4.29 (2H, br. s, NH2); 3.87 (3H, s, OCH3); 2.27 (6H,
s, 2CH3). 13C NMR spectrum (CDCl3), δ, ppm: 151.7;
151.5 (2C); 148.0; 148.1; 121.1; 119.0; 118.7; 109.1 (2C);
108.7 (2C); 106.1 (2C); 55.7; 40.6; 13.7 (2C). Found, m/z:
296.1292 [M–H]–. C18H18NO3. Calculated, m/z: 296.1295.
2-[Bis(5-methylfuran-2-yl)methyl]-3,6-dimethoxy-
4-methylaniline (3e). Yield 2.68 g (82%), pale-yellow
spectra were recorded on a Bruker UHR-TOF Maxis™
Impact mass spectrometer (ESI). Melting points were
determined with a Stuart SMP 30 and are uncorrected.
All the reactions were carried out using freshly distilled
and dry solvents from solvent stills.
The starting 2-nitrobenzaldehyde (1a), 2-methylfuran,
benzaldehydes 7a,b were commercial reagents. Other
aldehydes were synthesized according to the published
procedures.21–24 5,5'-[(2-Nitrophenyl)methylene]bis(2-methyl-
furan)
methylene]bis(2-methylfuran) (2b),25 5,5'-[(3,6-dimethoxy-
2-nitrophenyl)methylene]bis(2-methylfuran)
(2c),25
(2a),25
5,5'-[(4,5-dimethoxy-2-nitrophenyl)-
1
solid, mp 111–114°C. H NMR spectrum (CDCl3), δ, ppm
5,5'-[(2,5-dimethoxy-3-methyl-6-nitrophenyl)methylene]bis-
(2-methylfuran) (2e),25 5,5'-[(3-bromo-5,6-dimethoxy-
2-nitrophenyl)methylene]bis(2-methylfuran) (2f),25 5,5'-[(3-
chloro-5,6-dimethoxy-2-nitrophenyl)methylene]bis(2-methyl-
furan) (2g),25 (4,5-dimethoxy-2-nitrophenyl)(5-methylfuran-
(J, Hz): 6.58 (1H, s, H-5 Ar); 6.07 (2H, d, J = 2.6, H-3
furan); 6.06 (1H, s, CH); 5.90 (2H, d, J = 2.6, H-4 furan);
4.01 (2H, br. s, NH2); 3.81 (3H, s, OCH3); 3.70 (3H, s,
OCH3); 2.28 (3H, s, CH3); 2.26 (6H, s, 2CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 151.3 (4С); 150.3; 143.8;
134.5; 118.1; 117.2; 111.5; 108.3 (2С); 106.0 (2С); 61.2;
55.7; 36.1; 16.0; 13.7 (2С). Found, m/z: 342.1700 [M+H]+.
C20H24NO4. Calculated, m/z: 342.1699.
2-yl)methanone
(phenyl)methyl]-5-methylfuran (2i),27 2-[(2-azido-4,5-di-
methoxyphenyl)(phenyl)methyl]-5-methylfuran
(2j),27
(2h),26
2-[(2-azido-5-chlorophenyl)-
5,5'-[(2-azido-5-nitrophenyl)methylene]bis(2-methylfuran)
(2l),27 2-[bis(5-methylfuran-2-yl)methyl]aniline (3a),28
2-[bis(5-methylfuran-2-yl)methyl]-4,5-dimethoxyaniline (3b),29
4,5-dimethoxy-2-[(5-methylfuran-2-yl)methyl]aniline (3h)26
were prepared according to the published procedures.
2-[Bis(5-methylfuran-2-yl)methyl]-6-bromo-3,4-di-
methoxyaniline (3f). Yield 3.41 g (84%), yellow solid,
mp 89–91°C. 1H NMR spectrum (CDCl3), δ, ppm (J, Hz):
7.04 (1H, s, H-5); 6.19 (1H, s, CH); 6.09 (2H, d, J = 2.7,
H-4 furan); 5.92 (2H, d, J = 2.7, H-3 furan); 4.12 (2H, br. s,
NH2); 3.83 (3H, s, OCH3); 3.82 (3H, s, OCH3); 2.27 (6H, s,
2CH3). 13C NMR (CDCl3), δ, ppm: 151.5; 150.5 (2C);
147.5; 145.1; 137.9; 119.7; 116.4; 108.5 (2C); 106.1 (2C);
104.7 (2C); 61.2; 56.6; 36.1; 13.7 (2C). Found, m/z: 428.0468
[M+Na]+. C19H20BrNNаO4. Calculated, m/z: 428.0489.
2-[Bis(5-methylfuran-2-yl)methyl]-6-chloro-3,4-di-
methoxyaniline (3g). Yield 3.1 g (86%), yellow solid,
2,2'-[(3-Methoxy-2-nitrophenyl)methanediyl]bis(5-methyl-
furan) (2d). HClO4 (0.1 ml) was added to a solution of
o-nitrobenzaldehyde 1d (10 mmol) and 2-methylfuran
(3 ml, 33.4 mmol) in 1,4-dioxane (15 ml). The reaction
mixture was stirred overnight, poured into H2O, and
extracted with warm PhH (3×30 ml). Combined organic
fractions were dried over Na2SO4 and concentrated
in vacuo. The oily residue was dissolved in hot hexane,
passed through a thin pad of Al2O3, and left overnight. The
crystalline product was filtered off and dried on air. Yield
2.68 g (82%), white solid, mp 129–132°C. 1H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 7.37 (1H, t, J = 8.2,
H Ar); 6.97–6.93 (2H, m, H Ar); 5.96 (2H, d, J = 2.9,
H Ar); 5.90 (2H, d, J = 2.1, H Ar); 5.45 (1H, s, CH); 3.89
(3H, s, OCH3); 2.25 (6H, s, 2CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 152.0 (2C); 150.8; 150.1 (2C); 141.0;
1
mp 85–87°C. H NMR spectrum (CDCl3), δ, ppm (J, Hz):
6.89 (1H, s, H-5 Ar); 6.17 (1H, s, CH); 6.09 (2H, d, J = 2.7,
H-3 furan); 5.92 (2H, d, J = 2.7, H-4 furan); 4.08 (2H, br. s,
NH2); 3.83 (3H, s, OCH3); 3.82 (3H, s, OCH3); 2.27 (6H, s,
2CH3). 13C NMR spectrum (CDCl3), δ, ppm: 151.6 (2C);
150.5 (2C); 146.8; 144.8; 136.7; 119.7; 114.7; 113.3; 108.5
(2C); 106.1 (2C); 61.3; 56.5; 36.0; 13.7 (2C). Found, m/z:
384.0973 [M+Na]+. C19H20ClNNaO4. Calculated, m/z:
384.0971.
1036

Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
Preparation of compounds 3i,j (General method). PPh3
Found, m/z: 279.1128 [M+H]+. C17H15N2O2. Calculated, m/z:
279.1122.
(10 mmol) was added to a solution of compound 2i,j
(10 mmol) in THF (30 ml). The reaction mixture was
stirred at room temperature for 2 h, after which H2O (8 ml)
and AcOH (2 ml) were added, followed by stirring at 50°С
for 4 h (TLC control, petroleum ether – EtOAc, 4:1).
4-Chloro-2-[(5-methylfuran-2-yl)(phenyl)methyl]aniline
(3i). Yield 2.44 g (82%), pale-yellow solid, mp 95–97°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.41–7.25 (3H,
m, H Ph); 7.21 (2H, d, J = 7.0, H Ph); 7.07 (1H, dd, J = 8.4,
J = 2.3, H-5 Ar); 6.77 (1H, d, J = 2.2, H-3 furan); 6.63 (1H,
d, J = 8.4, H-6 Ar); 5.92 (1H, d, J = 1.9, H-3 Ar); 5.78 (1H,
d, J = 2.8, H-4 furan); 5.35 (1H, s, CH); 3.55 (2H, br. s,
NH2); 2.30 (3H, s, CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 152.9; 152.1; 142.8; 139.7; 129.1; 128.8 (4C);
127.6 (2C); 127.3; 123.6; 117.5; 109.8; 106.2; 46.3; 13.7.
Found, m/z: 320.0821. [M+Na]+. C18H16ClNNaO. Calcu-
lated, m/z: 320.0818.
(E)-4-[6,7-Dimethoxy-4-(5-methylfuran-2-yl)cinnolin-
3-yl]but-3-en-2-one (4b). Yield 2.90 g (86%), yellow-
1
orange solid, mp 150–152°C. H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 7.93 (2H, s, H-8 Ar, CH=); 7.91 (1H, d,
J = 15.7, CH=); 7.69 (1H, d, J = 15.7, H-7 Ar); 7.51 (1H, s,
H-5 Ar); 6.76 (1H, d, J = 3.1, H-3 furan); 6.36 (1H, d,
J = 3.1, H-4 furan); 4.16 (3H, s, OCH3); 4.04 (3H, s,
OCH3); 2.51 (3H, s, CH3); 2.42 (3H, s, CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 198.2; 155.8; 154.4; 154.1;
147.1; 145.3; 144.3; 137.3; 131.0; 124.2; 121.5; 117.8;
108.8; 106.5; 102.3; 56.8; 56.3; 29.2; 14.0. Found, m/z:
339.1339 [M+H]+. C19H19N2O4. Calculated, m/z: 339.1329.
(E)-4-[5,8-Dimethoxy-4-(5-methylfuran-2-yl)cinnolin-
3-yl]but-3-en-2-one (4c). Yield 2.70 g (80%), yellow solid,
mp 95–97°C. 1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.78
(2H, s, H-6,7 Ar); 7.11 (1H, d, J = 15.2, CH=); 7.03 (1H, d,
J = 15.2, CH=); 6.38 (1H, d, J = 2.7, H-3 furan); 6.21 (1H, d,
J = 2.7, H-4 furan); 4.15 (3H, s, OCH3); 3.70 (3H, s, OCH3);
2.42 (3H, s, CH3); 2.39 (3H, s, CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 198.5; 153.3; 150.6; 148.8; 148.7; 144.9;
142.6; 136.9; 131.8; 123.1; 118.4; 113.0; 111.6; 109.3;
107.2; 56.9; 56.6; 28.7; 13.7. Found, m/z: 361.1159
[M+Na]+. C19H18N2NаO4. Calculated, m/z: 361.1141.
4,5-Dimethoxy-2-[(5-methylfuran-2-yl)(phenyl)methyl]-
aniline (3j). Yield 2.68 g (83%), pale-yellow oil. 1H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 7.37–7.20 (5H, m,
H Ph); 6.38 (1H, s, H-6 Ar); 6.31 (1H, s, H-3 Ar); 5.91
(1H, s, H-3 furan); 5.77 (1H, d, J = 2.5, H-4 furan); 5.38
(1H, s, CH); 3.84 (3H, s, OCH3); 3.68 (3H, s, OCH3); 3.36
(2H, s,); 2.28 (3H, s, CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 154.1; 151.7; 148.7; 141.9; 140.8; 138.1; 128.8
(2C); 128.6 (2C); 127.0; 118.7; 114.2; 109.3; 106.0; 101.6;
56.6; 55.8; 46.0; 13.7. Found, m/z: 346.1414 [M+Na]+.
C20H21NNaO3. Calculated, m/z: 346.1411.
(E)-4-[8-Methoxy-4-(5-methylfuran-2-yl)cinnolin-3-yl]-
but-3-en-2-one (4d). Yield 2.59 g (84%), yellow-green
1
solid, mp 175–177°C. H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.98 (1H, d, J = 15.6, CH=); 7.84–7.75 (2H, m,
H-7 Ar, CH=); 7.71 (1H, t, J = 8.1, H-6 Ar); 7.18 (1H, d,
J = 7.6, H-5 Ar); 6.73 (1H, d, J = 3.0, H-3 furan); 6.34 (1H,
d, J = 3.0, H-4 furan); 4.21 (3H, s, OCH3); 2.51 (3H, s,
CH3); 2.45 (3H, s, CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 198.5; 156.6; 155.6; 146.5; 144.1; 142.6; 137.8;
132.6; 131.7; 125.0; 124.0; 117.7; 116.9; 108.8; 108.5; 56.5;
28.9; 14.0. Found, m/z: 331.1053 [M+Na]+. C18H16N2NaO3.
Calculated, m/z: 331.1055.
2-[Bis(5-methylfuran-2-yl)methyl]-4-nitroaniline (3l).
Yield 2.68 g (86%), yellow solid, mp 153–155°C. 1H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 8.04 (1H, dd, J = 8.8,
J = 2.5, H-5 Ar); 7.86 (1H, d, J = 2.5, H-3 Ar); 6.66 (1H, d,
J = 8.8, H-4 Ar); 6.00 (2H, d, J = 2.9, H-3 furan); 5.96 (2H,
d, J = 2.9, H-4 furan); 5.34 (1H, s, CH); 4.45 (2H, br. s,
NH2); 2.29 (6H, s, 2CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 152.4; 150.6; 149.7; 139.3; 132.2; 132.1; 128.6;
128.5; 126.0; 124.8; 123.6; 115.1; 109.4; 106.5; 41.0; 13.7
(2C). Found, m/z: 335.1002 [M+Na]+. C17H16N2NaO4.
Calculated, m/z: 335.0998.
(E)-4-[5,8-Dimethoxy-6-methyl-4-(5-methylfuran-2-yl)-
cinnolin-3-yl]but-3-en-2-one (4e). Yield 2.78 g (84%),
1
yellow-green solid, mp 134–137°C. H NMR spectrum
Preparation of compounds 4a–j,l(General method).29
Me3SiCl (2 ml, 16 mmol) and t-BuONO (1.1 ml, 11 mmol)
were added to a solution of compound 3a–j,l (10 mmol) in
MeCN (15 ml). The mixture was stirred for 30 min, poured
into H2O (200 ml), and neutralized with dry NaHCO3. The
product was extracted with EtOAc (3×50 ml), combined
organic fractions were dried over Na2SO4 and concentrated
in vacuo. The product was isolated by column chromato-
graphy, eluent petroleum ether – EtOAc, 4:1.
(CDCl3), δ, ppm (J, Hz): 7.75 (1H, d, J = 15.7, CH=); 7.66
(1H, d, J = 15.7, CH=); 6.99 (1H, s, C-7 Ar); 6.45 (1H, d,
J = 3.0, H-3 furan); 6.22 (1H, d, J = 2.2, H-4 furan); 4.15
(3H, s, OCH3); 3.30 (3H, s, OCH3); 2.48 (3H, s, CH3); 2.43
(3H, s, CH3); 2.38 (3H, s, CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 198.5; 153.5; 152.7; 149.1; 145.8; 144.7;
142.2; 137.0; 135.5; 132.0; 122.2; 121.1; 113.2; 112.5;
107.2; 61.5; 56.5; 28.6; 17.3; 13.7. Found, m/z: 353.1496
[M+H]+. C20H21N2O4. Calculated, m/z: 353.1493.
4(E)-4-[4-(5-Methylfuran-2-yl)cinnolin-3-yl]but-3-en-
2-one (4a). Yield 2.30 g (83%), yellow-green solid, mp 94–
(E)-4-[8-Bromo-5,6-dimethoxy-4-(5-methylfuran-2-yl)-
cinnolin-3-yl]but-3-en-2-one (4f). Yield 3.58 g (86%),
1
1
96°C. H NMR spectrum (CDCl3), δ, ppm (J, Hz): 8.61
yellow-green solid, mp 183–185°C. H NMR spectrum
(1H, d, J = 8.4, H-8 Ar); 8.27 (1H, d, J = 8.4, H-5 Ar); 8.01
(1H, d, J = 15.6, CH=); 7.89 (1H, t, J = 7.6, H-6 Ar); 7.87–7.81
(2H, m, H-7 Ar, CH=); 6.75 (1H, d, J = 3.2, H-3 furan);
6.35 (1H, d, J = 2.7, H-4 furan); 2.52 (3H, s, CH3); 2.45
(3H, s, CH3). 13C NMR spectrum (CDCl3), δ, ppm: 198.4;
155.9; 149.9; 145.8; 144.0; 137.6; 131.9; 131.5; 130.8;
130.5; 125.8; 124.2; 123.6; 118.0; 108.6; 29.1; 14.0.
(CDCl3), δ, ppm (J, Hz): 7.99 (1H, s, H-7 Ar); 7.80 (1H, d,
J = 15.7, CH=); 7.68 (1H, d, J = 15.7, CH=); 6.43 (1H, d,
J = 2.6, H-4 furan); 6.21 (1H, d, J = 2.6, H-4 furan); 4.07
(3H, s, OCH3); 3.54 (3H, s, OCH3); 2.41 (3H, s, CH3); 2.37
(3H, s, CH3). 13C NMR spectrum (CDCl3), δ, ppm: 198.3;
153.6; 153.7; 148.3; 144.2; 142.8; 141.9; 136.3; 132.3;
122.7; 122.3; 121.9; 112.9 (2C); 107.2; 61.4; 57.0; 28.8;
1037

Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
13.7. Found, m/z: 417.0444 [M+H]+. C19H18BrN2O4. Calcu-
compound 4a–j,l (10 mmol) in EtOH (30 ml). The reaction
mixture was stirred at room temperature for 2 h until the
full conversion of the starting material (TLC control,
petroleum ether – EtOAc, 2:1). The reaction mixture was
poured into H2O (150 ml), extracted with EtOAc (3×50 ml),
combined organic fractions were dried over Na2SO4 and
concentrated in vacuo. The obtained compounds were used
further without purification.
lated, m/z: 417.0443.
(E)-4-[8-Chloro-5,6-dimethoxy-4-(5-methylfuran-2-yl)-
cinnolin-3-yl]but-3-en-2-one (4g). Yield 3.31 g (89%),
1
yellow-green solid, mp 126–128°C. H NMR spectrum
(CDCl3), δ, ppm (J, Hz): 7.77 (1H, s, H-7 Ar); 6.85 (1H, d,
J = 15.7, CH=); 6.46–6.39 (2H, m, H-3 furan, CH=); 6.19
(1H, d, J = 3.0, H-4 furan); 4.07 (3H, s, OCH3); 3.53 (3H,
s, OCH3); 2.41 (3H, s, CH3); 2.39 (3H, s, CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 202.4; 153.5; 153.1; 150.0;
144.9; 142.0; 140.9; 135.4; 131.8; 130.2; 122.5; 120.2;
119.0; 113.1; 107.0; 61.4; 56.9; 30.6; 13.7. Found, m/z:
373.0950 [M+H]+. C19H18ClN2O4. Calculated, m/z: 373.0964.
(E)-4-(6,7-Dimethoxycinnolin-3-yl)but-3-en-2-one (4h).
(E)-4-[6,7-Dimethoxy-4-(5-methylfuran-2-yl)cinnolin-
3-yl]but-3-en-2-ol (5b). Yield 3.33 g (98%), beige solid,
mp 149–151°C. 1H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.71 (1H, s, H-8 Ar); 7.50 (1H, s, H-8 Ar); 6.75–
6.68 (2H, m, H-3 furan, CH=); 6.29 (1H, s, H-4 furan);
6.14 (1H, dd, J = 11.6, J = 7.4, CH=); 4.76–4.67 (1H, m,
CH–OH); 4.11 (3H, s, OCH3); 4.02 (3H, s, OCH3); 2.48
(3H, s, CH3); 1.44 (3H, d, J = 6.4, CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 154.7; 154.1; 153.1; 148.4;
147.3; 145.2; 141.4; 126.8; 122.2; 121.4; 116.9; 108.2;
106.9; 101.9; 63.4; 56.4; 56.2; 22.4; 13.9. Found, m/z:
341.1496 [M+H]+. C19H21N2O4. Calculated, m/z: 41.1485.
Preparation of compounds 6a–j,l (General method).
1
Yield 2.0 g (78%), white solid, mp 215–218°C. H NMR
spectrum (CDCl3), δ, ppm (J, Hz): 7.83 (1H, d, J = 16.5,
CH=); 7.80 (1H, s, H-4 Ar); 7.73 (1H, s, H-8 Ar); 7.33
(1H, d, J = 16.4, CH=); 6.98 (1H, s, H-5 Ar); 4.10 (3H, s,
OCH3); 4.06 (3H, s, OCH3); 2.46 (3H, s, CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 198.4; 154.1; 148.9; 148.4;
140.3; 129.8; 123.2; 122.3; 121.0; 107.1; 103.2; 56.6; 56.5;
28.1. Found, m/z: 259.1077 [M+H]+. C14H15N2O3. Calcu-
lated, m/z: 259.1077.
.
BF3 OEt2 (1.10 ml) was added dropwise to a solution of
compound 5a–j,l (3 mmol) in 1,2-dichloroethane (20 ml).
The reaction mixture was stirred at 60°С for 4–8 h until the
full conversion of the starting material (TLC control,
petroleum ether – EtOAc, 4:1), poured into H2O (100 ml),
and extracted with 1,2-dichloroethane (3×50 ml). Combined
organic fractions were dried over Na2SO4 and concentrated
in vacuo. The products were isolated by column chromato-
graphy, eluent petroleum ether – EtOAc, 9:1.
(E)-4-(6-Chloro-4-phenylcinnolin-3-yl)but-3-en-2-one
(4i). Yield 2.53 g (82%), yellow solid, mp 198–200°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 8.57 (1H, d,
J = 9.0, H-8 Ar); 7.81 (1H, d, J = 15.7, CH=); 7.79 (1H, dd,
J = 8.9, J = 2.1, H-7 Ar); 7.65–7.61 (3H, m, H-2,4,6 Ph);
7.58 (1H, d, J = 1.7, H-5 Ar); 7.49 (1H, d, J = 15.6, CH=);
7.35 (2H, dd, J = 6.5, J = 2.9, H-3,5 Ph); 2.33 (3H, s, CH3).
13C NMR spectrum (CDCl3), δ, ppm: 198.1; 147.0; 138.3;
136.2 (2C); 134.6; 132.0 (2C); 131.8; 131.7; 129.9 (2C);
129.7; 129.2 (2C); 124.5 (2C); 29.0. Found, m/z: 331.0609
[M+Na]+. C18H13ClN2NaO. Calculated, m/z: 331.0607.
(E)-4-(6,7-Dimethoxy-4-phenylcinnolin-3-yl)but-3-en-
2-one (4j). Yield 2.94 g (88%), brown solid, mp 225–227°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.92 (1H, s,
H-8 Ar); 7.69 (1H, d, J = 15.6, CH=); 7.64–7.58 (3H, m,
H-2,4,6 Ph); 7.45 (1H, d, J = 15.6, CH=); 7.38–7.34 (2H,
m, H-3,5 Ph); 6.75 (1H, s, H-5 Ar); 4.15 (3H, s, OCH3);
3.84 (3H, s, OCH3); 2.31 (3H, s, CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 198.2; 154.2; 154.1; 147.3; 145.9; 136.7;
132.8; 130.7; 129.7 (2C); 129.4; 129.1 (2C); 122.9; 106.6;
101.9; 56.8; 56.3; 31.0; 28.9. Found, m/z: 335.1390 [M+H]+.
C20H19N2O3. Calculated, m/z: 335.1318.
3-Methyl-10-(5-methylfuran-2-yl)pyrrolo[1,2-b]cinnoline
(6a). Yield 0.53 g (68%), purple solid, mp 72–74°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 8.19 (1H, d,
J = 8.9, H-6 Ar); 7.76 (1H, d, J = 9.0, H-9 Ar); 7.41 (1H,
br. dd, J = 9.0, J = 6.8, H-8 Ar); 7.15 (2H, s, H-7 Ar, H-1 Ar);
7.08–7.05 (2H, m, H-2 Ar, H-3 furan); 6.33 (1H, d, J = 2.5,
H-4 furan, H-2 Ar); 2.82 (3H, s, CH3); 2.55 (3H, s, CH3).
13C NMR spectrum (CDCl3), δ, ppm: 154.6; 147.1; 146.0;
129.0; 125.8; 125.1 (3C); 124.1; 122.3; 117.0; 116.1;
113.1; 108.3; 99.6; 14.1; 12.0. Found, m/z: 263.1179
[M+H]+. C17H15N2O. Calculated, m/z: 263.1190.
7,8-Dimethoxy-3-methyl-10-(5-methylfuran-2-yl)pyrrolo-
[1,2-b]cinnoline (6b). Yield 0.61 g (64%), purple-red
1
solid, mp 150–152°C. H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.44 (1H, s, H-6 Ar); 7.01 (1H, d, J = 3.0, H-3
furan); 6.96–6.97 (2H, m, H Ar); 6.93 (1H, d, J = 4.4, H-2
Ar); 6.32 (1H, d, J = 3.0, H-4 furan); 4.04 (3H, s, OCH3);
3.97 (3H, s, OCH3); 2.74 (3H, s, CH3); 2.52 (3H, s, CH3).
13C NMR spectrum (CDCl3), δ, ppm: 153.8; 153.2; 148.2;
147.5; 144.4; 124.3; 123.1; 122.6; 114.9; 114.6; 110.0; 108.2;
101.7; 101.6; 97.5; 56.1; 55.7; 14.0; 11.9. Found, m/z:
323.1390 [M+H]+. C19H19N2O3. Calculated, m/z: 323.1391.
6,9-Dimethoxy-3-methyl-10-(5-methylfuran-2-yl)pyrrolo-
[1,2-b]cinnoline (6c). Yield 0.69 g (72%), purple solid,
mp 165–167°C. 1H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.08 (1H, d, J = 4.5, H-8 Ar); 6.86 (1H, d, J = 4.5,
H-7 Ar); 6.65 (1H, d, J = 3.1, H-3 furan); 6.59 (1H, d, J = 8.2,
H-1 Ar); 6.24–6.20 (2H, m, H-2 Ar, H-4 furan); 4.05 (3H, s,
OCH3); 3.70 (3H, s, OCH3); 2.84 (3H, s, CH3); 2.44 (3H, s,
(E)-4-[4-(5-Methylfuran-2-yl)-6-nitrocinnolin-3-yl]but-
3-en-2-one (4l). Yield 2.52 g (78%), yellow solid, mp 205–
1
207°C. H NMR spectrum (CDCl3), δ, ppm (J, Hz): 9.25
(1H, d, J = 1.8, H-5 Ar); 8.69 (1H, d, J = 9.2, H-8 Ar); 8.51
(1H, dd, J = 9.2, J = 2.0, H-7 Ar); 7.97 (1H, d, J = 15.5,
CH=); 7.77 (1H, d, J = 15.5, CH=); 6.82 (1H, d, J = 3.3,
H-3 furan); 6.36 (1H, d, J = 3.1, H-4 furan); 2.49 (3H, s,
CH3); 2.40 (3H, s, CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 198.0; 157.7; 149.8; 148.6; 146.8; 143.2; 136.4;
132.8; 132.6; 124.6; 124.1; 123.7; 122.6; 120.1; 109.6;
29.4; 14.2. Found, m/z: 346.0798 [M+Na]+. C17H13N3NaO4.
Calculated, m/z: 346.0760.
Preparation of compounds 5a–j,l (General method).
NaBH4 (10 mmol) was added in portions to a suspension of
1038

Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
CH3). 13C NMR spectrum (CDCl3), δ, ppm: 152.6; 150.0;
127.0; 123.0; 122.1; 114.8; 113.6; 103.2; 101.2; 96.8; 56.1;
55.9; 11.8. Found, m/z: 243.1128 [M+H]+. C14H15N2O2.
Calculated, m/z: 243.1125.
147.6; 146.6; 140.3; 127.4; 125.3 (2C); 117.1; 111.6;
109.0; 107.0; 105.0; 99.9; 99.2; 56.2; 56.0; 13.8; 11.9.
Found, m/z: 323.1390 [M+H]+. C19H19N2O3. Calculated, m/z:
323.1383.
8-Chloro-3-methyl-10-phenylpyrrolo[1,2-b]cinnoline
(6i). Yield 0.64 g (73%), red-pink solid, mp 118–121°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.69 (1H, d,
J = 9.5, H-6 Ar); 7.55–7.47 (5H, m, H Ph); 7.40 (1H, d,
J = 2.1, H-9 Ar); 7.23 (1H, dd, J = 9.5, J = 2.1, H-7 Ar);
7.03 (1H, s, H-1 Ar); 6.57 (1H, s, H-2 Ar); 2.73 (3H, s,
CH3). 13C NMR spectrum (CDCl3), δ, ppm: 144.1; 137.2;
133.8; 130.9; 129.9 (2C); 129.3; 128.8 (2C); 127.6; 127.2;
126.2; 125.3; 123.8; 118.1; 114.6; 100.5; 12.0. Found, m/z:
293.0840 [M+H]+. C18H14ClN2. Calculated, m/z: 293.0835.
7,8-Dimethoxy-3-methyl-10-phenylpyrrolo[1,2-b]-
cinnoline (6j). Yield 0.70 g (74%), red solid, mp 126–128°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.65–7.54 (5H,
m, H Ph); 7.06 (1H, s, H-6 Ar); 6.92 (1H, s, H-9 Ar); 6.69
(1H, s, H-1 Ar); 6.45 (1H, s, H-2 Ar); 4.04 (3H, s, OCH3);
3.77 (3H, s, OCH3); 2.78 (3H, s, CH3). 13C NMR spectrum
(CDCl3), δ, ppm: 153.8; 147.9; 144.4; 135.1; 135.0; 129.7
(2C); 128.8; 128.7 (2C); 127.0; 123.5; 114.9; 111.4; 101.2;
101.1; 97.7; 56.2; 55.7; 11.9. Found, m/z: 319.1449 [M+H]+.
C20H19N2O2. Calculated, m/z: 319.1441.
6-Methoxy-3-methyl-10-(5-methylfuran-2-yl)pyrrolo-
[1,2-b]cinnoline (6d). Yield 0.54 g (62%), purple solid,
mp 131–133°C. 1H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.78 (1H, d, J = 8.7, H-9); 7.12 (2H, q, J = 4.7, H-7,8
Ar); 7.04 (1H, d, J = 3.3, H-3 furan); 6.98 (1H, dd, J = 9.0,
J = 7.4, H-1 Ar); 6.70 (1H, d, J = 7.4, H-2 Ar); 6.32 (1H, d,
J = 3.3, H-4 furan); 4.10 (3H, s, OCH3); 2.85 (3H, s, CH3);
2.53 (3H, s, CH3). 13C NMR spectrum (CDCl3), δ, ppm:
154.5; 152.3; 147.1; 139.8; 125.1; 124.9 (2C); 121.7; 117.8;
117.0; 116.2; 113.9; 108.3; 105.0; 99.4; 56.1; 14.0; 11.9.
Found, m/z: 315.1104 [M+Na]+. C18H16N2NaO2. Calculated,
m/z: 315.1107.
6,9-Dimethoxy-3,8-dimethyl-10-(5-methylfuran-2-yl)-
pyrrolo[1,2-b]cinnoline (6e). Yield 0.65 g (65%), purple
1
solid, mp 146–148°C. H NMR spectrum (CDCl3), δ, ppm
(J, Hz): 7.08 (1H, d, J = 4.5, H-1 Ar); 6.80 (1H, d, J = 4.5,
H-2 Ar); 6.69 (1H, d, J = 3.0, H-3 furan); 6.48 (1H, s,
H-7 Ar); 6.23 (1H, d, J = 3.0, H-4 furan); 4.06 (3H, s,
OCH3); 3.28 (3H, s, OCH3); 2.83 (3H, s, CH3); 2.46 (3H, s,
CH3); 2.33 (3H, s, CH3). 13C NMR spectrum (CDCl3),
δ, ppm: 152.8; 148.6; 147.3; 145.8; 140.0; 127.8; 124.6;
123.6; 121.5; 117.0; 112.3; 110.7; 108.7; 107.0; 99.0; 60.6;
56.2; 16.4; 13.9; 11.8. Found, m/z: 359.1366 [M+Na]+.
C20H20N2NаO3. Calculated, m/z: 359.1358.
3-Methyl-10-(5-methylfuran-2-yl)pyrrolo[1,2-b]cinnolin-
6-ol (6k). AlCl3 (665 mg) was added to a solution of
compound 6d (1 mmol) in 1,2-dichloroethane (5 ml). The
reaction mixture was stirred at 50°С for 6 h (TLC control,
petroleum ether – EtOAc, 4:1), poured into H2O (150 ml),
and extracted with EtOAc (3×15 ml). Combined organic
fractions were dried over Na2SO4 and concentrated
in vacuo. The product was separated by column chromato-
graphy, eluent petroleum ether – EtOAc, 50:1. Yield 0.27 g
(97%), purple solid, mp 90–92°C. 1H NMR spectrum
(DMSO-d6), δ, ppm (J, Hz): 9.59 (1H, s, OH); 7.64 (1H, d,
J = 8.9, H-9 Ar); 7.28–7.20 (2H, m, H-1 Ar, H-3 furan);
7.11 (1H, d, J = 4.5, H-2 Ar); 6.99 (1H, dd, J = 8.9, J = 7.4,
H-8 Ar); 6.79 (1H, d, J = 6.8, H-7); 6.51 (1H, d, J = 3.2,
H-4 furan); 3.33 (3H, s, CH3, overlapped with H2O); 2.75
6-Bromo-8,9-dimethoxy-3-methyl-10-(5-methylfuran-
2-yl)pyrrolo[1,2-b]cinnoline (6f). Yield 0.81 g (68%),
1
purple solid, mp 123–125°C. H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 7.74 (1H, s, H-7 Ar); 7.15 (1H, d, J = 4.5,
H-1 Ar); 6.83 (1H, d, J = 4.6, H-2 Ar); 6.67 (1H, d, J = 3.1,
H-3 furan); 6.23 (1H, d, J = 3.1, H-4 furan); 3.95 (3H, s,
OCH3); 3.57 (3H, s, OCH3); 2.82 (3H, s, CH3); 2.44 (3H, s,
CH3). 13C NMR spectrum (CDCl3), δ, ppm: 152.9; 146.9;
144.6; 142.8; 140.6; 128.3; 125.8; 125.0; 124.1; 118.2; 114.4;
111.8; 111.3; 107.0 (2C); 61.1; 58.1; 13.8; 11.7. Found, m/z:
401.0495 [M+H]+. C19H18BrN2O3. Calculated, m/z: 401.0512.
6-Chloro-8,9-dimethoxy-3-methyl-10-(5-methylfuran-
2-yl)pyrrolo[1,2-b]cinnoline (6g). Yield 0.75 g (70%),
1
(3H, s, CH3). H NMR spectrum (CDCl3), δ, ppm (J, Hz):
7.75 (1H, d, J = 9.0, H-9 Ar); 7.13 (1H, s, H-7 Ar); 7.11
(1H, d, J = 3.3, H-3 furan); 7.04 (1H, dd, J = 9.0, J = 7.2,
H-8 Ar); 6.94 (1H, d, J = 7.2, H-2 Ar); 6.35 (1H, d, J = 3.3,
H-4 furan); 2.80 (3H, s, CH3); 2.55 (3H, s, CH3). 13C NMR
spectrum (CDCl3), δ, ppm: 155.3; 148.0; 146.8; 137.7;
126.4; 125.7; 125.2; 123.0; 117.6; 117.4; 116.8; 113.1;
109.0; 108.7; 14.1; 12.1. Found, m/z: 279.1129 [M+H]+.
C17H15N2O2. Calculated, m/z: 279.1133.
1
purple solid, mp 121–123°C. H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 7.53 (1H, s, H-7 Ar); 7.15 (1H, d, J = 4.6,
H-1 Ar); 6.83 (1H, d, J = 4.6, H-2 Ar); 6.67 (1H, d, J = 3.6,
H-3 furan); 6.23 (1H, d, J = 3.6, H-4 furan); 3.95 (3H, s,
OCH3); 3.56 (3H, s, OCH3); 2.81 (3H, s, CH3); 2.45 (3H, s,
OCH3). 13C NMR spectrum (CDCl3), δ, ppm: 152.9; 147.0;
144.1; 142.1; 140.1; 128.2; 124.8; 124.4; 124.0; 122.0;
118.1; 111.8; 111.3; 107.0; 99.1; 61.1; 58.0; 13.8; 11.7.
Found, m/z: 357.1000 [M+H]+. C19H18ClN2O3. Calculated, m/z:
357.1003.
Preparation of compounds 8a,b (General method).
A solution of compound 6c (3 mmol) and benzaldehyde
7a,b (1,5 mmol) in AcOH (10 ml) was stirred at 60°С for
4 h until the full conversion of the starting material 6c
(TLC control, petroleum ether – EtOAc, 4:1). The reaction
mixture was poured into H2O (50 ml), neutralized with
NaHCO3 solution, extracted with EtOAc (3×20 ml).
Combined organic fractions were dried over Na2SO4 and
evaporated to dryness. The product was isolated by column
chromatography, eluent petroleum ether – EtOAc, 4:1.
1,1'-[(4-Chlorophenyl)methylene]bis[6,9-dimethoxy-3-
methyl-10-(5-methylfuran-2-yl)pyrrolo[1,2-b]cinnoline] (8a).
7,8-Dimethoxy-3-methylpyrrolo[1,2-b]cinnoline (6h).
Yield 0.44 g (61%), orange solid, sublimates over 180°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.89 (1H, s,
H Ar); 6.86 (1H, d, J = 4.4, H pyrrol); 6.84 (1H, s, H Ar);
6.59 (1H, s, H Ar); 6.57 (1H, d, J = 4.4, H pyrrol); 3.92
(3H, s, OCH3); 3.87 (3H, s, OCH3); 2.63 (3H, s, CH3).
13C NMR spectrum (CDCl3), δ, ppm: 153.9; 147.8; 144.1;
1039

Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
1
Yield 1.02 g (89%), violet solid, mp 230–231°C. H NMR
μ(CuKα) 0.740 mm–1; F(000) 680.0; 8.728° ≤ 2Θ ≤ 148.342°;
–11 ≤ h ≤ 11, –5 ≤ k ≤ 10, –25 ≤ l ≤ 19. Total of 5711
reflection intensities were measured, including 3092
independent reflections (Rint 0.0295, Rσ 0.0322); final
probability factors: R1 0.0476 (I > 2σ(I)) and wR2 was
0.1412 (all data). The X-ray diffraction data for compound
6b were deposited to the Cambridge Crystallographic Data
Center (deposit CCDC 1955393).
Single crystals of compound 8a were obtained in the
form of dark-violet blocks by slow evaporation of CH2Cl2
from DMSO/CH2Cl2 solution. The single crystals of com-
pound 8а grown by slow evaporation of CH2Cl2 from
DMSO/CH2Cl2 solution at room temperature. Crystal data for
C45H39ClN4O6 (M 767.25): monoclinic, space group P21/n;
a 16.6668(2), b 24.1507(2), c 20.8315(2) Å; β 93.2160(10)°;
V 8371.78(15) Å3; Z 8. The crystal was kept at 100.00(10) K
during data collection, μ(CuKα) 1.226 mm–1; dcalc 1.217 g/cm3;
105174 reflections measured (6.986° ≤ 2Θ ≤ 152.92°),
17466 unique (Rint 0.0403, Rσ 0.0264) which were used in
all calculations. The final R1 was 0.0472 (I > 2σ(I)) and
wR2 was 0.1270 (all data). The collection of reflections,
determination and refinement of unit cell parameters were
performed by using the specialized CrysAlisPro
1.171.38.41 software suite.39 The structures were solved by
using the ShelXT program,37 structure refinement was also
performed with ShelXL program.38 The complete X-ray
diffraction dataset was deposited at the Cambridge
Crystallographic Data Center (deposit CCDC 1978825).
spectrum (CDCl3), δ, ppm (J, Hz): 7.02 (2H, d, J = 8.4,
H-3,5 C6H4Cl); 6.60–6.47 (4H, m, H-3 furan); 6.24 (2H, s,
H-1 Ar); 6.12 (2H, d, J = 8.4, H-2,6 C6H4Cl); 5.98 (2H, br. s,
H-2 Ar); 5.86 (2H, d, J = 2.1, H-4 furan); 5.79 (1H, s, CH);
4.04 (6H, s, OCH3); 3.50 (6H, s, OCH3); 2.70 (6H, s, CH3);
1.98 (6H, s, CH3). 13C NMR spectrum (CDCl3), δ, ppm:
151.4 (2C); 150.3 (2C); 146.4 (2C); 145.3 (2C); 144.0
(2C); 139.4; 130.4; 130.1 (2C); 127.4 (4C); 126.3 (2C);
123.5 (2C); 122.6 (2C); 120.9 (2C); 118.6 (2C); 110.9
(2C); 106.6 (2C); 105.1 (2C); 99.4 (2C); 56.6 (2C); 56.3
(2C); 42.8; 13.2 (2C); 11.9 (2C). Found, m/z: 789.2457
[M+Na]+. C45H39ClN4NаO6. Calculated, m/z: 789.2450.
1,1'-[(4-Nitrophenyl)methylene]bis[6,9-dimethoxy-
3-methyl-10-(5-methylfuran-2-yl)pyrrolo[1,2-b]cinnoline]
(8b). Yield 1.01 g (87%), violet solid, mp 248–250°C.
1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 7.91 (2H, d,
J = 8.4, H-3,5 C6H4NO2); 6.75 (2H, d, J = 7.2, H-2,6
C6H4NO); 6.57 (2H, d, J = 8.0, H-8 Ar); 6.25 (2H, s, H-2
Ar); 6.13 (2H, d, J = 8.0, H-7 Ar); 5.99 (2H. br. s, H-3
furan); 5.89 (3H, d, J = 10.6, H-4 furan, CH); 4.04 (6H, s,
OCH3); 3.50 (6H, s, OCH3); 2.71 (6H, s, CH3); 1.94 (6H, s,
CH3). 13C NMR spectrum (CDCl3), δ, ppm: 153.1 (2C);
151.4 (2C); 150.1 (2C); 146.5; 145.5; 145.2 (2C); 139.5
(2C); 129.6 (2C); 129.1 (2C); 126.0 (2C); 123.7 (2C);
122.7 (2C); 122.4 (2C); 120.7 (2C); 117.1 (2C); 111.2
(2C); 106.8 (2C); 105.2 (2C); 99.6 (2C); 56.5 (2C); 56.3
(2C); 43.3; 13.2 (2C); 11.6 (2C). Found, m/z: 800.2691
[M+Na]+. C45H39N5NаO8. Calculated, m/z: 800.2695.
Optical properties studies. The absorption spectra of
the studied solutions were recorded using an SF-2000
spectrophotometer with a step of 0.1 nm in the spectral
range 200–1100 nm. UNICO Q-104 quartz cuvettes, trans-
parent in the UV spectral region were used. The graphs
were built on several (1–15) series of measurements to
average values. As the number of accumulations increases,
the error decreases to the square root of the number of
registrations, which in our case can be 4 times. The
processing of the results of spectral measurements was
carried out after exporting the data array to the Origin and
Mathlab programs.
Cyclic voltammetry was performed with a three-
electrode cell in an MeCN solution of 0.1 M tetrabutyl-
ammonium perchlorate (Bu4NClO4) at a scan rate (v) of
200 mV/s. A Pt wire was used as counter electrode, glassy
carbon disk was used as working electrode, and an Ag wire
was used as reference electrode.
X-ray structural study of compounds 6b, 8a. X-ray
analysis of a single crystal of compound 6b (C19H18N2O3)
was performed on an Agilent SuperNova automated four-
circle diffractometer (Dual, Cu at zero, Atlas S2 CCD
detector) at 301.4(6) K. The structure was solved by the
direct method implemented in Olex236 and ShelXS37 and
was refined against F2 by the full-matrix least-squares
method in anisotropic approximation for non-hydrogen
atoms using the SHELXL program set.38 Monoclinic
crystal system, space group P21/n, M 322.35; unit cell
parameters: a 9.1839(6), b 8.6480(4), c 20.5307(10) Å;
β 99.246(6)°; V 1609.40(16) Å3; Z 4; dcalc 1.330 g/cm3;
Supplementary information file containing 1H and
13C NMR spectra of the synthesized compounds and X-ray
data of compounds 6b and 8a is available at the journal
website at http://link.springer.com/journal/10593.
This work received financial support from the Russian
Foundation for Basic Research (grant 18-33-01250).
We are grateful to Dr. I. Profatilova for the fruitful
discussions on results of the electrochemical studies.
References
1. Popovici, L.; Amarandi, R.-M.; Mangalagiu, I. I.;
Mangalagiu, V.; Danac, R. J. Enzyme Inhib. Med. Chem.
2019, 34, 230.
2. Ungureanu, M.; Mangalagiu, I.; Grosu, G.; Petrovanu, M.
Ann. Pharm. Fr. 1997, 55, 69.
3. Nasir, A. I.; Gundersen, L.-L.; Rise, F.; Antonsen, Ø.;
Kristensen, T.; Langhelle, B.; Bast, A.; Custers, I.;
Haenen, G. R. M. M.; Wikström, H. Bioorg. Med. Chem. Lett.
1998, 8, 1829.
4. Østby, O. B.; Dalhus, B.; Gundersen, L.-L.; Rise, F.; Bast, A.;
Haenen, G. R. M. M. Eur. J. Org. Chem. 2000, 3763.
5. Østby, O. B.; Gundersen, L.-L.; Rise, F.; Antonsen, Ø.;
Fosnes, K.; Larsen, V.; Bast, A.; Custers, I.; Haenen, G. R. M. M.
Arch. Pharm. 2001, 334, 21.
6. (a) Ohtani, M.; Fuji, M.; Fukui, Y.; Adachi, M. WO Patent
059999, 1999. (b) Salvati, M. E.; Illig, C. R.; Wilson, K. J.;
Chen, J.; Meegalla, S. K.; Wall, M. J. US Patent 7030112B2,
2006. (c) Fu, J.-M. US Patent 7074791, 2006.
7. Hynes, J., Jr.; Wu, H.; Kempson, J.; Duan, J. J.-W.; Lu, Z.;
Jiang, B.; Stachura, S.; Tokarski, J. S.; Sack, J. S.; Khan, J. A.;
Lippy, J. S.; Zhang, R. F.; Pitt, S.; Shen, G.; Gillooly, K.;
1040

Chemistry of Heterocyclic Compounds 2020, 56(8), 1030–1041
McIntyre, K.; Carter, P. H.; Barrish, J. C.; Nadler, S. G.;
21. Uchuskin, M. G.; Molodtsova, N. V.; Abaev, V. T.;
Trushkov, I. V.; Butin, A. V. Tetrahedron 2012, 68, 4252.
22. Vetelino, M. G.; Coe, J. W. Tetrahedron Lett. 1994, 35,
219.
Salter-Cid, L. M.; Fura, A.; Schieven, G. L.; Pitts, W. J.;
Wrobleski, S. T. Bioorg. Med. Chem. Lett. 2017, 27, 3101.
8. Kempson, J.; Ovalle, D.; Guo, J.; Wrobleski, S. T.; Lin, S.;
Spergel, S. H.; Duan, J. J.-W.; Jiang, B.; Lu, Z.; Das, J.;
Yang, B. V.; Hynes, J., Jr.; Wu, H.; Tokarski, J.; Sack, J. S.;
Khan, J.; Schieven, G.; Blatt, Y.; Chaudhry, C.; Salter-Cid, L. M.;
Fura, A.; Barrish, J. C.; Carter, P. H.; Pitts, W. J. Bioorg.
Med. Chem. Lett. 2017, 27, 4622.
23. Kumar, S.; Wachtel, E. J.; Keinan, E. J. Org. Chem. 1993, 58,
3821.
24. Xiong, X.-D.; Chen, W.-X.; Kuang, Y.-Y.; Chen, F.-E. Org.
Prep. Proced. Int. 2009, 41, 423.
25. Tsiunchik, F. A.; Abaev, V. T.; Butin, A. V. Chem.
Heterocycl. Compd. 2005, 41, 1476. [Khim. Geterotsikl.
Soedin. 2005, 1796.]
9. Duan, J. J.-W.; Lu, Z.; Jiang, B.; Yang, B. V.; Doweyko, L. M.;
Nirschl, D. S.; Haque, L. E.; Lin, S.; Brown, G.; Hynes, J., Jr.;
Tokarski, J. S.; Sack, J. S.; Khan, J.; Lippy, J. S.; Zhang, R. F.;
Pitt, S.; Shen, G.; Pitts, W. J.; Carter, P. H.; Barrish, J. C.;
Nadler, S. G.; Salter-Cid, L. M.; McKinnon, M.; Fura, A.;
Schieven, G. L.; Wrobleski, S. T. Bioorg. Med. Chem. Lett.
2014, 24, 5721.
10. Lim, J.; Altman, M. D.; Baker, J.; Brubaker, J. D.; Chen, H.;
Chen, Y.; Kleinschek, M. A.; Li, C.; Liu, D.; Maclean, J. K. F.;
Mulrooney, E. F.; Presland, J.; Rakhilina, L.; Smith, G. F.;
Yang, R. Bioorg. Med. Chem. Lett. 2015, 25, 5384.
11. Cheng, Y.; Ma, B.; Wudl, F. J. Mater. Chem. 1999, 9, 2183.
12. Mitsumori, T.; Bendikov, M.; Sedó, J.; Wudl, F. Chem.
Mater. 2003, 15, 3759.
13. Mitsumori, T.; Craig, I. M.; Martini, I. B.; Schwartz, B. J.;
Wudl, F. Macromolecules 2005, 38, 4698.
14. Swamy, K. M. K.; Park, M. S.; Han, S. J.; Kim, S. K.; Kim, J. H.;
Lee, C.; Bang, H.; Kim, Y.; Kim, S.-J.; Yoon, J. Tetrahedron
2005, 61, 10227.
15. Zbancioc, G. N.; Mangalagiu, I. I. Synlett 2006, 804.
16. Dumitraşcu, F.; Dumitrescu, D. G. ARKIVOC 2008, (i), 232.
17. Plieva, A. T. Chem. Heterocycl. Compd. 2019, 55, 199.
[Khim. Geterotsikl. Soedin. 2019, 55, 199.]
26. Butin, A. V.; Smirnov, S. K.; Stroganova, T. A.; Bender, W.;
Krapivin, G. D. Tetrahedron 2007, 63, 474.
27. Abaev, V. T.; Plieva, A. T.; Chalikidi, P. N.; Uchuskin, M. G.;
Trushkov, I. V.; Butin, A. V. Org. Lett. 2014, 16, 4150.
28. Butin, A. V.; Stroganova, T. A.; Abaev, V. T.; Zavodnik V. E.
Chem. Heterocycl. Compd. 1997, 33, 1393. [Khim.
Geterotsikl. Soedin. 1997, 1614.]
29. Abaev, V. T.; Gutnov, A. V.; Butin, A. V.; Zavodnik, V. E.
Tetrahedron 2000, 56, 8933.
30. Butin, A. V.; Smirnov, S. K.; Tsiunchik, F. A.; Uchuskin, M. G.;
Trushkov, I. V. Synthesis 2008, 2943.
31. Posch, P.; Thelakkat, M.; Schmidt, H.-W. Synth. Met. 1999,
102, 1110.
32. Kim, J.-Y.; Kim, E.-S.; Choi, J.-H. J. Appl. Phys. 2002, 91, 1944.
33. Lee, S. T.; Hou, X. Y.; Mason, M. G.; Tang, C. W. Appl.
Phys. Lett. 1998, 72, 1593.
34. Barth, S.; Müller, P.; Riel, H.; Seidler, P. F.; Rieß, W.;
Vestweber, H.; Bässler, H. J. Appl. Phys. 2001, 89, 3711.
35. Zweig, A.; Hodgson, W. G.; Jura, W. H. J. Am. Chem. Soc.
1964, 86, 4124.
36. Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.;
Puschmann, H. J. Appl. Crystallogr. 2009, 42, 339.
37. Sheldrick, G. M. Acta Crystallogr. A: Found. Crystallogr.
2008, A64, 112.
38. Sheldrick, G. M. Acta Crystallogr. C: Struct. Chem. 2015,
C71, 3.
39. CrysAlisPro, version 1.171.38.41; Rigaku Oxford Diffraction,
2015. https://www.rigaku.com/en/products/smc/crysalis
18. Ames, D. E.; Chandrasekhar, S.; Simpson, R. J. Chem. Soc.,
Perkin. Trans. 1 1975, 2035.
19. Hamer, R. R. L.; Sekerak, D.; Effland, R. C.; Klein, J. T.
J. Heterocycl. Chem. 1988, 25, 991.
20. Flitsch, W.; Lauterwein, J.; Leimkühler, M.; Leaver, D.;
Lewinski, U.; Mattes, R.; Temme, R.; Wibbeling, B. Liebigs
Ann. Chem. 1990, 627.
1041