Synthesis and Characterization of Azine-[5]Helicene Hybrids

Article abstract of DOI:10.1002/ejoc.201900818

Novel azine-helicene hybrids (pyridine-, pyrazine- and quinoxaline-fused along the central ring [5]helicenes) have been prepared in good overall yields through a five-step synthetic sequence. Commercially available 2,3-dihaloazines were used as starting materials. To discern the effect of merging an azine moiety within a helical skeleton, the X-ray structures, UV/Vis absorption spectra, cathodic and anodic electrochemistry of the helicene hybrids were investigated and compared to that of the parent [5]helicene.

Full text of DOI:10.1002/ejoc.201900818

A Journal of
Accepted Article
Title: Synthesis and Characterization of Azine-[5]Helicene Hybrids
Authors: Anna V. Gulevskaya, Daria I. Tonkoglazova, Andrey S.
Guchunov, and Alexander D. Misharev
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201900818
Link to VoR: http://dx.doi.org/10.1002/ejoc.201900818
Supported by

10.1002/ejoc.201900818
European Journal of Organic Chemistry
1
Helicenes
Synthesis and Characterization of Azine-[5]Helicene Hybrids
Anna V. Gulevskaya,*[a] Daria I. Tonkoglazova,[a] Andrey S. Guchunov[a] and Alexander D.
Misharev[b]
Abstract: Novel azine-helicene hybrids (pyridine-, pyrazine- and quinoxaline-fused along the
central ring [5]helicenes) have been prepared in a good overall yields through a five-step synthetic
sequence. Commercially available 2,3-dihaloazines were used as starting materials. To discern the
effect of merging an azine moiety within a helical skeleton, the X-ray structures, UV-vis absorption
spectra, cathodic and anodic electrochemistry of the helicene hybrids were investigated and
compared to that of the parent [5]helicene.
Introduction
[n]Helicenes are polycyclic aromatic molecules in which n ortho-condensed benzene or other
aromatic rings give rise to helical chiral and highly conjugated structures. Unique screw shape,
helically extended -system and intriguing electronic and chirooptical properties of these molecules,
such as exceptionally high values of optical rotation and large circular dichroism, have attracted
scientific interest for decades.[1] The applications of helicenes have now expanded into several fields
including material science, nanoscience, biochemistry, supramolecular and polymer chemistry.
Helicenes have also been studied with respect to conductivity,[2] nonlinear optics,[3] circularly
[a] Prof. Dr. A.V. Gulevskaya, D.I. Tonkoglazova, A.S. Guchinov, Department of Chemistry, Southern Federal University
Zorge str., 7 Rostov-on-Don 344090
Russian Federation
E-mail: agulevskaya@sfedu.ru
http://www.sfedu.ru
[b] Dr. A.D. Misharev, Center for X-ray Diffraction Studies and Chemical Analysis
and Materials Research Centre, Institute of Chemistry,
St. Petersburg State University,
Universitetskii pr. 26, St. Petersburg, Petergof 198504
Russian Federation
http://chem.spbu.ru
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
2
polarized luminescence,[4] organocatalysis,[5] conformational analysis,[6] chirality sensing,[7]
chemical sensors,[8] DNA-intercalators,[9] ets.
The most common structural modifications of helicenes are the preparation of higher helicenes
and incorporation of heteroatoms within the carbon skeleton.[1] Synthesis and investigation of
helicene derivatives with extended -systems resulting from fusion of aromatic or heteroaromatic
rings without lengthening of the helix are not numerous.[1] Though these helicene hybrids exhibit
even more intriguing physical properties relative to simple helicenes,[1,10] synthetic methods
available for their construction are still limited.
The classical synthetic approach for carbohelicenes is oxidative photocyclization of the
stilbene derivatives.[1] The latter are generally available by the Wittig reaction or Heck-type cross-
coupling between aryl halides and aryl ethenes. Due to this method, even the highest carbohelicenes,
including [16]helicene,[1j] were obtained. It is also a helpful way to synthesize heterohelicenes.
Unfortunately, this method is not applicable to the synthesis of [5]helicenes because the [5]helicene
product, initially formed from 1,2-di(naphthyl)ethene or 1,4-distyrylbenzene, is itself photoreactive
and undergoes overannulation to form benzo[g,h,i]perylene.[11] To overcome this difficulty,
alternative synthetic pathways for [5]helicenes have been developed. Among them are the Diels–
Alder reactions of 1,4-divinylbenzenes and benzoquinones[12a-c], [2+2+2]-cycloaddition of arynes
and alkynes,[12d] transition-metal catalyzed cycloisomerizations of 2-ethynyl-1,1'-binaphthyl[11e], 3-
ethynyl-4-phenylphenanthrenes[12f] and 1,2-bis(2-((Z)-but-1-en-3-ynyl)phenyl)ethyne[12g], double
Stille cross-coupling of 2,2'-bis(trimethylstannyl)-1,1'-binaphthyl and 1,2-diiodobenzene[12h], double
Suzuki–Miyaura
bis(pinacolatoboryl)alkene[12i], Heck-type double intramolecular C-H arylation of 1,4-bis(2-
bromostyryl)benzenes[12j], ring-closing metathesis of 2,2'-divinyl-1,1'-binaphthyl[12k]
Rh(II)-
cross-coupling
between
2,2′-dibromo-1,1′-binaphthyl
and
vic-
,
catalyzed cyclization of 1,1'-binaphthyl-2,2'-dicarbaldehyde bis(N-tosylhydrazone)[12l] and some
others. Each method is not without drawbacks such as hardly available starting materials, rather
expensive catalysts, harsh reaction conditions or low product yields.
Transition metal-catalyzed, electrophile-induced and oxidative radical cyclizations of ortho-
alkynylated biaryls are widely used for synthesis of polynuclear aromatics.[13] Alkynes are carbon-
rich and form aromatic rings via cycloisomerization, which is atom-economic process. In addition,
alkyne reactions are highly favorable thermodynamically.[14]
We now report an efficient strategy for the synthesis of azine-[5]helicene hybrids ([5]helicenes
heteroannelated along the central nucleus) starting from commercially available ortho-dihaloazines
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
3
(2,3-dibromopyridine, 2,3-dichloropyrazine and 2,3-dichloroquinoxaline). The method includes two
Sonogashira reactions, Suzuki-Miyaura arylation and two electrophile-induced cyclizations of the
intermediate ortho-alkynylated biaryls (Scheme 1).
Scheme 1. Synthetic strategy for azine-fused [5]helicenes.
It should be noted that [5]helicenes heteroannelated along the central nucleus are rather rare.
Most publications are related to [5]helicenes and tetrahydro[5]helicenes condensed with furan-2,5-
dione[15a-d] or pyrrole-2,5-dione rings[15d-k]. There are single reports on [5]helicenes fused with
pyranone,[15l]
indole,[15m]
phthalocyanine,[15n,o]
triazatruxene,[15p]
dihydroimidazole,[15q]
pyrrolobenzimidazole,[15r] naphthopyrazine,[15s] phenanthropyrazine,[15s] hexahydroquinoxaline[15q]
and pyridine[13i] core.
Results and discussions
In accordance with the above strategy, we first synthesized ortho-halogen alkynylazines 1a-d via the
Sonogashira reaction of commercially available 2,3-dihaloazines (2,3-dichloroquinoxaline and 2,3-
dichloropyrazine) with phenylacetylene and 4-methoxyphenylacetylene using known[13o] procedure.
Coupling of compounds 1a−d with naphthalen-2-ylboronic acid in the Pd(PPh3)4/K3PO4/THF
catalytic system for 24 h under reflux (method A) afforded the desired 3-alkynyl-2-naphthylazines
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
4
2a−d in 72−85 % yields (Table 1). Another catalytic system with a cheaper catalyst, e.g. 5 %
Pd/C/PPh3/K2CO3/toluene (method B), was just as effective.
Table 1. Suzuki coupling of compounds 1 with naphthalen-2-ylboronic acid.
Yield [%]
Entry
R1, R1
R2
H
Product
(method)
72 (A)
85 (B)
85 (A)
82 (A)
80 (B)
85 (A)
1
2
3
4
-(CH=CH)2-
2a
2b
2c
2d
-(CH=CH)2- OMe
H, H
H, H
H
OMe
3-Alkynyl-2-naphthylazines can also be prepared using an alternative synthetic sequence, i.e.
Suzuki-Miyaura arylation – Sonogashira reaction. For example, coupling of 2,3-dichloroquinoxaline
3a and 2,3-dibromopyridine 3b with naphthalen-2-ylboronic acid (1.2 equiv.) in the 5 %
o
Pd/C/PPh3/K2CO3/toluene catalytic system at 100 C for 24 h gave a mixture of the corresponding
mono- and dinaphthyl derivatives 4 (79−80 %) and 5 (9−10 %) (Table 2). The products were easily
separated by column chromatography. ortho-Halogen naphthylazines 4a,b were then introduced into
Sonogashira reaction with phenylacetylene using the Pd(PPh3)2Cl2/CuI/iPr2NH/DMSO catalytic
system giving rise to 3-alkynyl-2-naphthylazines 2a,e in high yields (Table 3).
Table 2. Suzuki coupling of 2,3-dihaloazines with naphthalen-2-ylboronic acid.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
5
Entry
1
X
N
R1, R1
Hal Product Yield [%]
4a
5a
4b
5b
80
9
79
10
-(CH=CH)2-
Cl
Br
2
CH
H, H
Table 3. Sonogashira coupling of compounds 4 with phenylacetylene.
Entry
X
N
CH
R1, R1
-(CH=CH)2-
H, H
Hal Product Yield [%]
1
2
Cl
Br
2a
2e
83
95
Electrophilic cyclizations of 3-alkynyl-2-naphthylazines 2a−e into phenanthroazines 7a−e
were carried out with a 1.5-fold excess of ICl in dry acetonitrile at room temperature in the dark
(Table 4). In all cases, the product yield exceeded 84 %. It should be noted that compounds 7 are
derivatives of the little-known heterocyclic systems naphtho[1,2-h]quinoline,[16a] naphtho[2,1-
f]quinoxaline,[13o,16b,c] naphtho[2,1-a]phenazine[13n,16d-g]. After reviewing these publications, the
synthetic sequence described above seems to be the best method for constructing these
heterosystems.
Table 4. ICl-Induced cyclyzation of compounds 2.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
6
Yield [%]
Entry
X
R1, R1
R2
H
Product
1
2
3
4
5
N
N
N
N
CH
-(CH=CH)2-
-(CH=CH)2- OMe
7a
7b
7c
7d
7e
84
90
85
89
95
H, H
H, H
H, H
H
OMe
H
Performing the next stage of the synthesis, namely, Sonogahira coupling of iodides 7 with p-
tolylacetylene, we encountered some difficulties. In the reaction of 7b, the
Pd(PPh3)2Cl2/CuI/iPr2NH/DMSO catalytic system, which proved to be effective in the synthesis of
compounds 2a,e, made it possible to obtain alkyne 8b in 76 % yield (Table 5, Entry 2). In case of
7a, the reaction was less effective producing alkyne 8a in 51 % yield only (Entry 1). Pyrazine-based
substrate 7c showed even lower reactivity giving rise to the corresponding alkynyl derivative 8c in
21 % yield (Entry 3). The use of the Pd(PPh3)2Cl2/CuI/Et3N/THF catalytic system has led to a
significant increase in the yields of products 8a-d. In the reaction of iodide 7e with p-tolylacetylene,
this catalytic system showed the greatest efficiency, allowing to obtain alkyne 8e in 91 % yield
o
(Entry 5). In case of substrate 7c, the Pd(PPh3)4/CuI/Et3N catalytic system at 85 C gave the best
result (65−74 %).
Table 5. Sonogashira coupling of compounds 7 with p-tolylacetylene.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
7
Yield
[%]
51
63
76
Entry
X
R1, R1
R2
H
Base, solvent
Product
iPr2NH, DMSO
1
2
N
N
-(CH=CH)2-
8a
8b
Et3N, THF
-(CH=CH)2- OMe iPr2NH, DMSO
21
iPr2NH, DMSO
3
N
H, H
H
Et3N, THF
Et3Na
Et3N, THF
Et3N, THF
8c
48−52
65−74
62
4
5
N
CH
H, H
H, H
OMe
H
8d
8e
91
a Pd(PPh3)4 was used instead of Pd(PPh3)2Cl2. The reaction was carried out at 85 oC.
In contrast to the above reaction, the interaction of iodides 7a,c with trimethylsilylacetylene
under the same conditions resulted in the formation of exclusively enynes 9a,b (Scheme 2). When
using a 2-fold excess of alkyne, compound 9a was obtained in 10 % yield only. The starting iodide
7a has been recovered by 75 %. The reaction of 7a with a 7-fold excess of trimethylsilylacetylene
gave 9a in 84 % yield. Similarly, iodide 7c was transformed into enyne 9b (64 %). Usually enynes
are formed in the Sonogashira reaction as a minor product.[17] Most recently, a mechanism for their
formation has been proposed and argued.[17c] It is believed that the intermediate of type 10, formed
at the trans-metallation step, coordinates the second trimethylsilylacetylene molecule giving rise to
complex 11 (Scheme 3). Then, migratory insertion of the alkyne ligand into the C–X bond affords
alkenyl palladium cis-complex 12. Subsequent reductive elimination affords enyne 9. Only one
question remains: why is enyne 9 the only product of the above reaction? Probably, the peri-aza
group makes reductive elimination of Pdo from complex 10 difficult and contributes to the
coordination of alkyne in complex 11. This assumption is supported by the fact that the interaction
of the pyridine substrate 7e with a 7-fold excess of trimethylsilylacetylene gave a mixture of the
“normal” Sonogashira product and the corresponding enyne in a 1.5: 1 ratio.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
8
Scheme 2. Sonogashira coupling of compounds 7 with trimethylsilylacetylene.
Scheme 3. A reasonable mechanism for the formation of products 9.
Heating of alkynyl derivatives 8a-e in trifluoroacetic acid led to their isomerization into the
desired [5]helicene hybrids 14a-e (Table 6). Helicenes 14a,b,e were obtained in almost quantitative
yields (Entries 1,2,5), while pyrazine-fused helicenes 14c,d were isolated in 31−35 % yield (Entries
3,4). Apparently, the reason for the low yield of these products is the high basicity of the aza group
adjacent to the triple bond in compounds 8c,d. Its protonation makes the formation of intermediate
13 difficult. Fortunately, the treatment of alkynes 8c,d with triflic acid in СH2Cl2 solution at room
temperature allowed us to obtain the desired helicenes 14c,d in quantitative yield.
Table 6. TFA-Induced cyclyzation of compounds 8.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
9
Yield
[%]
92
Entry
X
R1, R1
R2
H
Product
1
2
N
N
-(CH=CH)2-
-(CH=CH)2- OMe
14a
14b
98
31a
98b
35a
94b
95a
3
N
H, H
H
14c
4
5
N
H, H
H, H
OMe
H
14d
14e
CH
a Reaction was carried out at 85 oC for 24 h.
b Reaction was carried out with TfOH in CH2Cl2 at r.t. for 24 h.
We performed single-crystal diffraction studies of helicenes 14b and 14c (Figure 1) and
compared the solid-state structure of [5]helicene and its benzene- and azine-fused on the central ring
hybrids 14 to see the effect of annelation (Table 7). Compound 14c possesses pronounced
polymorphism: orange prisms and pale yellow plates are simultaneously formed under conditions of
isothermic crystallization from chloroform - acetonitrile solution. X-ray diffraction studies were
carried out for both forms. The orange polymorph seems to be more stable with one independent
molecule in the unit cell (Figure 1, c and Table 7). Its crystal structure is characterized by a compact
arrangement of alternating enantiomeric helicene molecules (Figure 1, d). By contrast, there are five
independent molecules (40 in total) in the unit cell of the pale yellow polymorph (see Supporting
Information, S54). The packing of molecules in a crystal reminds fancy lace (S55).
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
10
Torsion and interplanar angles are usually used to describe the extent of distortion of the helical
skeleton. The former is dihedral angle between the four adjacent inner helix carbon atoms, the latter
is the angle between the two terminal aromatic rings. It is easy to see that benzo[5]helicene[18] is
more twisted than [5]helicene itself. The interplanar angle between the two terminal rings A and D
of [5]helicene is equal to 48.3o,[10d] whereas the same value for benzo[5]helicene is 53.9o. Evidently,
this extra twisting is the result of the repulsive interaction of the H(9) and H(f) atoms of this
molecule. Pyrazine-fused [5]helicene 14c (orange polymorph) demonstrates intermediate helicity
(51.0o). In the case of pale-yellow polymorph, the interplanar angles for five independent molecules
range from 49.1 to 53.1o. Quinoxaline-helicene hybrid 14b depicts a similar twisted helical shape,
but the distortion angle of 41.1o was significantly smaller than in the parent [5]helicene and its
benzo- and pyrazine-fused analogs. On the one hand, this flattening may originate from the
attractive interaction of the aza groups N(f) and N(e) with the H(9) and H(6) atoms, respectively.
The short intramolecular contact H(9)….N(f) (2.459 Å) and H(6)….N(e) (2.449 Å) as well as
smaller angles in the bay region of molecule 14b supports this opinion. But the question arises: why
is this effect not so noticeable in the case of helicene 14c ? Thus, it can be assumed that the
flattening of helicene 14b may be a result of packing forces. In accordance with the foregoing, the
sum of the inner helix torsion angles in the most twisted benzo[5]helicene is the largest, while in the
more planar quinoxaline-helicene this sum is the smallest.
Because of torsion strain, the bond lengths in the helicenes skeletons are different, with different
C-C bonds having features of a single bond or a double bond. In comparison with the bond length of
benzene (1.393 Å), the bond lengths of the C-C bonds in the inner helix of [5]helicene itself are
lengthened to 1.411−1.460 Å, while the outer helix C-C bonds are shortened to 1.342−1.372 Å.
Benzo[5]helicene has the shortest inner helix bonds, while quinoxaline-fused [5]helicene has the
longest both inner and outer helix bonds. The lengths of the C-C bonds of the central C ring are the
most deviated from the standard length. This is especially noticeable in the case of quinoxaline-
[5]helicene hybrid 14b, in which the C(b)-C(c) bond length is 1.475 Å, which is very close to the
value of the standard single C(sp2)-C(sp2) bond (ca. 1.48 Å).
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
11
a
b
c
d
Figure 1. Molecular structure and packing of quinoxaline-fused [5]helicene 14b (a, b) and pyrazine-
fused [5]helicene 14c (c, d) (X-ray data).
Table 7. Comparison of X-ray data of [5]helicene and condensed analogs.
Helicene
Space
group
Bond length [Å]
Inner
helix
Torsion
angle [o]
1-d-c-b
d-c-b-a
Interplanar
angle [o]
A/E
Inner
helix
1-d
d-c
c-b
Outer
helix
3-4
Ring C
b-c
angle [o]
1-d-c
c-6a
6a-7
7-8
8-8a
8a-b
1.447
1.414
1.407
d-c-b
c-b-a
b-a-14
c-b-a-14
5-6
7-8
b-a
9-10
11-12
1.372
1.354
1.359
a-14
1.412
1.449
1.447
[5]Helicene
P21/c
123.50
124.80
124.46
20.20
29.84
16.41
48.29*
50.17
51.30
[10d]
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
12
1.460
1.411
(7.179
1.342
1.360
(6.787
1.359
1.417
1.417
(8.461
in total)
1.454
1.393
1.456
1.414
1.452
1.398
(8.567
in total)
1.462
1.402
1.449
1.404
1.450
1.410
(8.527
in total)
1.475
1.400
1.457
1.431
1.458
1.401
(8.622
in total)
123.21
(495.97
in total)
(66.45
in total)
in total) in total)
Benzo[5]helicene P 21/n
1.407
1.455
1.454
1.447
1.410
(7.173
1.347
1.350
1.414
1.344
1.348
(6.803
123.40
123.11
122.87
123.42
(492.80
in total)
19.64
32.72
20.52
(72.88
in total)
53.91
[18]
in total) in total)
Pyrazine-fused
[5]helicene 14c
(orange
P bca
1.420
1.457
1.462
1.452
1.421
(7.212
1.370
1.363
1.404
1.354
1.367
(6.858
121.77
124.79
124.12
123.47
(494.15
in total)
21.39
30.09
15.88
(67.36
in total)
51.00
polymorph)
in total) in total)
Quinoxaline-fused P 21/c
1.422
1.451
1.475
1.448
1.424
(7.220
1.375
1.377
1.431
1.359
1.371
(6.913
122.19
124.48
124.01
123.16
(493.84
in total)
17.76
28.86
17.49
(64.11
in total)
41.09
[5]helicene 14b
in total) in total)
* There are three independent molecules in the unit cell. All data are of this molecule.
In the crystal packing of 14b, a pair of enantiomeric helicene molecules are aggregated on the
manner of embrace (Figure 1, a). The solid structure of azine-helicene hybrids 14b and 14c
displayed layers of the aromatic molecules. An intermolecular distance of 3.77 Å was found
between the centroids of the central benzene ring C of one molecule of 14b and ring D of another
making  overlap possible. In the case of 14c, the distance between the centroids of the C rings of
two adjacent molecules as measured to be 3.75 Å. The layered structures of both hybrids 14b
(Figure 1, b) and 14c (Figure 1, d) show increased  overlap (with participation of four aromatic
rings of each helicene molecule) when compared to [5]helicene itself (only two aromatic rings of
each helicene molecule participate in overlapping).[10d] Co-planar or stacked-like arrangements
shown in the solid-state structures of 14c and 14b are typically important when developing organic
electronic materials.[19]
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
13
[5]Helicene is an off-white compound with max 350 nm.[10d] Annelation of pyridine or pyrazine
ring to the [5]helicene skeleton changed the wavelength of the absorption maximum (Table 8, S56).
Pyridine- and pyrazine-fused [5]helicenes 14e and 14c,d are off-white (max 357 nm, CHCl3) and
pale yellow (max 396−402 nm), respectively. The absorption of quinoxaline-based [5]helicenes
14a,b was red-shifted (max 415−421 nm). Both compounds are bright yellow. It should be noted
that UV-vis spectrum of [7]helicene,[20] which contains as many aromatic rings as compounds
14a,b, only tails to about 400 nm, whereas these helicene hybrids have a significant absorption
band at 415−421 nm and tails up to 500−508 nm. All azine-fused [5]helicenes 14 were nearly non-
fluorescent in chloroform solution and showed weak fluorescence in the acetonitrile solution (Figure
2). The optical band gaps (Egopt), estimated from the onset point of the absorption spectra, were 2.44
eV (14a), 2.66 eV (14c) and 2.96 eV (14e) (Table 8). The Egopt value of [5]helicene itself estimated
from the intersection between the absorption and emission bands was equal to 3.59 eV.[10d] These
spectral differences are most likely a result of the extended -conjugation in the hybrid helicenes 14,
suggesting a higher HOMO and lower oxidation potential, which are typically desired characteristics
when designing organic materials. As can also be seen, an increase in the -deficiency of heteroring
fused to [5]helicene leads to a decrease in the optical band gap.
14a
14b
14d
14c
14e
Figure 2. Acetonitrile solutions of [5]helicenes 14 under UV irradiation (365 nm).
The cathodic and anodic electrochemistry of azine-fused [5]helicenes 14a, 14c and 14e was
evaluated by cyclic voltammetry (CV) in dichloromethane solution containing 0.1 M n-Bu4NPF6 vs.
Ag/AgNO3 in the standard three-electrode electrochemical cell (Table 8, S57-S59). All helicenes
displayed three irreversible oxidation waves (in cases of 14a and 14c, two of them are overlapped),
with the little variation of the potentials induced by the fused heteroring. Scanning cathodically,
quinoxaline-fused helicene 14a showed reversible and quasi-reversible reduction waves at E1/2red = -
1.57 V (1) and -1.88 V (2) vs. the ferrocenium/ferrocene couple, respectively. The first of them
corresponds to the anion-radical specie as confirmed by the EPR spectroscopy data (S57). The
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
14
reductions of 14c were very close to one another. In the case of 14e, reduction wave was not
expressed on CV.
From the first oxidation potentials and E1/2(Fc+/Fc) = -4.80 eV, highest occupied molecular
orbital energies EHOMO of -5.58 (14a), -5.67 (14c) and -5.69 eV (14e) were obtained (Table 8). From
the first reduction potential, lowest unoccupied molecular orbital energy and electrochemical band
el
gap of 14a were calculated as -3.23 eV (ELUMO) and 2.35 eV (Eg ), respectively. LUMO energy
opt
levels of 14c and 14e were deduced from the corresponding EHOMO and optical band gaps Eg
Table 8. Photophysical properties of azine-fused [5]helicenes 14.
.
opt
el
Com-
pound
14a
14c
14e
Eg
E1/2ox(1) E1/2red(1)
EHOMO
/
Eg
max onset
[eV]b
2.44
2.66
2.96
[V]c
[V]c
ELUMO [eV] [eV]f
-5.58/-3.23d 2.35
[nm]a [nm]
415
396
357
508
466
419
+0.78
+0.87
+0.89
-1.57
-
-
-5.67/-2.97e
-5.69d/-2.71e
-
-
a Absorption maxima measured in CHCl3 solution10-5 M. b The optical gap was estimated from
the onset point of the absorption spectra: Egopt = 1240/onset. c CV data (vs. Fc+/Fc).
d Estimated from the first oxidation and reduction potential and E1/2(Fc+/Fc) = -4.80 eV.
e Deduced from EHOMO and Egopt. Electrochemical band gap.
f
Conclusions
In summary, novel pyridine-, pyrazine- and quinoxaline-[5]helicene hybrids have been prepared
from commercially available 2,3-dihaloazines via a five-step synthetic sequence. Two key steps of
the method are electrophile-induced 6-endo-dig cyclizations of ortho-alkynylated biaryls. The
overall yields of helicenes in five stages of the synthesis exceed 30 %. It seems that the proposed
method is more efficient than other currently existing synthetic routes for [5]helicenes.
In addition, the azine-fused helicenes represent novel helicene structures with an increased 
surface. Their physical properties were compared to the parent [5]helicene. Spectrophotometric
analysis displayed significant absorption red-shifts (7−65 nm) and reduced optical band gaps (by
0.6−1.2 eV) for the azine-helicene hybrids. The obtained compounds showed amphoteric multiredox
behavior, which is characteristic for -expanded molecules. Extending the  surface of the
[5]helicene molecule by annelating an azine ring (without lengthening of the helix) led to an
increase in the HOMO level and a decrease in the LUMO level resulting in significantly reduced
electrochemical band gap. X-Ray crystal structure analysis of pyrazine- and quinoxaline-helicene
hybrids revealed greater  overlap and, in the case of quinoxaline-fused helicene, a smaller
distortion angle in the “twist” as compared to [5]helicene itself.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
15
Experimental Section
General Information: Reactions were monitored by thin layer chromatography (silica gel 60 F254)
and visualized using UV. Flash column chromatography was performed using silica gel (230−400
mesh, grade 60). Commercial alkynes, naphthalene-2-boronic acid, catalysts, ICl, 2,3-dihaloazines,
diisopropylamine, triethylamine, PPh3, TFA, triflic acid, anhydrous DMSO, THF were used as
1
13
received. H, C NMR spectra were recorded on 250, 400 and 600 MHz spectrometers. Chemical
shifts were reported in ppm relative to Me4Si. The IR spectra were recorded on a FT-IR
spectrometer. The UV-vis spectra were recorded on Varian Cary 50 Probe spectrophotometer in
CHCl3. The HR-ESI mass-spectra were obtained on a BRUKER maXis spectrometer equipped with
an electrospray ionization (ESI) source.
Crystal Structure Determination: X-Ray measurements were conducted with Bruker APEX II
CCD diffractometer and four-circle diffractometer SuperNova, Single source at offset/far,
HyPix3000. Atomic coordinates, bond lengths, bond angles and thermal parameters have been
deposited at the Cambridge Crystallographic Data Centre (CCDC) and allocated the deposition
numbers CCDC 1920988 (14b), CCDC 1920968 (14c, orange polymorph) and CCDC 1920967
(14c, pale yellow polymorph). These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
2-(Naphthalen-2-yl)-3-(phenylethynyl)quinoxaline
(2a):
Method
A.
2-Chloro-3-
(phenylethynyl)quinoxaline 1a[13o] (264 mg, 1.0 mmol), naphthalen-2-ylboronic acid (258 mg, 1.5
mmol), Pd(PPh3)4 (69 mg, 0.06 mmol), K3PO4 (424 mg, 2.0 mmol) and dry THF (15 mL) were
stirred and refluxed under argon for 24 h. The reaction mixture was then evaporated to dryness. The
residue was treated with water (50 mL) and extracted with CH2Cl2 (3  20 mL). The extract was
dried over Na2SO4 and purified by flash column chromatography on silica gel (3.5  50 cm) with
CH2Cl2 as the eluent. The fraction with Rf 0.7 was the recovered starting compound (5−7 %). The
next yellowish fraction with Rf 0.5 gave 258 mg (72 %) of compound 2a.
Method B. 2-Chloro-3-(phenylethynyl)quinoxaline 1a (264 mg, 1.0 mmol), naphthalen-2-
ylboronic acid (189 mg, 1.1 mmol), 5 % Pd/C (16 mg, 0.015 mmol Pd), PPh3 (16 mg, 0.6 mmol),
toluene (1 mL) and a solution of K2CO3 (552 mg, 4 mmol) in water (3 mL) were stirred at 100 oC for
24 h under argon. The reaction mixture was then diluted with water (50 mL) and extracted with
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
16
CH2Cl2 (3  15 mL). The extract was dried over Na2SO4 and purified by flash column
chromatography on silica gel (3.5  40 cm) with CH2Cl2 as the eluent. The yellowish fraction with Rf
0.5 gave 302 mg (85 %) of compound 2a.
Method C. Compound 2a was obtained similarly to 2e starting from 2-chloro-3-(naphthalen-2-
yl)quinoxaline 4a (145 mg, 0.5 mmol). Yield 148 mg (83%).
2-(Naphthalen-2-yl)-3-(phenylethynyl)quinoxaline 2a was obtained as white needles with m.p.
o
1
134−136 C (EtOH). H NMR (400 MHz, CDCl3): δ [ppm] = 7.28−7.40 (m, 3 Н), 7.50 (d, J = 7.0
Hz, 2 H), 7.56−7.62 (m, 2 H), 7.79−7.82 (m, 2 H), 7.97 (d, J = 7.4 Hz, 1 H), 8.02 (d, J = 7.4 Hz, 1
13
H), 8.05 (d, J = 8.6 Hz, 1 H), 8.18−8.21 (m, 2 H), 8.27 (d, J = 8.5, 1.1 Hz, 1 H), 8.73 (s, 1 Н). C
NMR (100 MHz, CDCl3): δ [ppm] = 88.6, 95.2, 121.7, 126.5, 126.9, 127.1, 127.81, 127.82, 128.5,
128.80, 128.82, 129.4, 129.6, 129.9, 130.3, 130.7, 132.2, 133.0, 133.9, 135.0, 138.2, 140.9, 141.1,
+
154.8. HRMS (ESI): m/z calcd. for C26H17N2 [M+H+]: 357.1386, found 357.1387.
2-((4-Methoxyphenyl)ethynyl)-3-(naphthalen-2-yl)quinoxaline (2b) was obtained similarly to 2a
(Method A) starting from 2-chloro-3-((4-methoxyphenyl)ethynyl)quinoxaline 1b (294 mg, 1.0
o
1
mmol). Rf 0.5. Yield 328 mg (85 %). Yellowish needles with m.p. 153−155 C (EtOH). H NMR
(400 MHz, CDCl3): δ [ppm] = 3.80 (s, 3 H), 6.83 (d, J = 8.5 Hz, 2 H), 7.42 (d, J = 8.5 Hz, 2 H),
7.56−7.62 (m, 2 H), 7.77−7.80 (m, 2 H), 7.96−8.05 (m, 3 H), 8.17 (dd, J = 8.6, 4.4 Hz, 2 H), 8.27 (d,
J = 8.5 Hz, 1 H), 8.73 (br s, 1 Н). 13C NMR (100 MHz, CDCl3): δ [ppm] = 55.3, 87.9, 95.9, 113.7,
114.2, 126.5, 126.9, 127.1, 127.7, 127.8, 128.7, 128.8, 129.3 (2C), 129.9, 130.2, 130.4, 132.9, 133.9,
135.1, 138.5, 140.7, 141.1, 154.7, 160.7. HRMS (ESI): m/z calcd. for C27H19N2O+ [M+H+]:
387.1492, found 387.1499.
2-(Naphthalen-2-yl)-3-(phenylethynyl)pyrazine (2c) was obtained similarly to 2a (Methods A and
B) starting from 2-chloro-3-(phenylethynyl)pyrazine 1c (214 mg, 1.0 mmol). Rf 0.35. Yield 251
o
mg (82 %, Method A) and 245 mg (80 %, Method B). Colorless needles with m.p. 100−102 C
(EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.32−7.40 (m, 3 Н), 7.49−7.51 (m, 2 Н), 7.55−7.61
(m, 2 Н), 7.94−8.03 (m, 3 Н), 8.22 (dd, J = 8.5, 1.4 Hz, 1 Н), 8.59 (d, J = 2.2 Hz, 1 Н), 8.65 (d, J =
13
2.2 Hz, 1 Н), 8.71 (br s, 1 H). C NMR (100 MHz, CDCl3): δ [ppm] = 87.7, 94.8, 121.8, 126.5,
127.1, 127.77, 127.83, 128.5, 128.8, 129.47 (2C), 129.52, 132.0, 132.9, 133.8, 134.4, 137.6, 142.4,
+
142.5, 155.4. HRMS (ESI): m/z calcd. for C22H15N2 [M+H+]: 307.1230, found 307.1234.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
17
2-((4-Methoxyphenyl)ethynyl)-3-(naphthalen-2-yl)pyrazine (2d) was obtained similarly to 2a
(Method A) starting from 2-chloro-3-((4-methoxyphenyl)ethynyl)pyrazine 1d (245 mg, 1.0 mmol).
o
1
Rf 0.3. Yield 286 mg (85 %). Yellow solid with m.p. 84−85 C (EtOH). H NMR (600 MHz,
CDCl3): δ [ppm] = 3.78 (s, 3H), 6.82 (d, J = 8.8 Hz, 2 Н), 7.39 (d, J = 8.8 Hz, 2 Н), 7.52−7.57 (m, 2
Н), 7.90 (d, J = 7.8 Hz, 1 Н), 7.94 (d, J = 7.8 Hz, 1 Н), 7.97 (d, J = 8.5 Hz, 1 Н), 8.17 (dd, J = 8.5,
1.7 Hz, 1 Н), 8.53 (br s, 1 H), 8.58 (br s, 1 H), 8.66 (br s, 1 H). 13C NMR (150.94 MHz, CDCl3): δ
[ppm] = 55.3, 86.8, 95.3, 113.8, 114.2 (2C), 126.4, 126.5, 127.0, 127.7, 128.7, 129.4, 132.9, 133.6,
133.8, 134.5, 137.9, 142.0, 142.3, 155.0, 160.6. IR (Nujol): 2218 (CC) cm-1. HRMS (ESI): m/z
calcd. for C23H17N2O+ [M+H+]: 337.1335, found 337.1338.
2-(Naphthalen-2-yl)-3-(phenylethynyl)pyridine (2e): A mixture of 3-bromo-2-(naphthalen-2-
yl)pyridine 4b (142 mg, 0.5 mmol), Pd(PPh3)2Cl2 (35 mg, 0.05 mmol), CuI (4 mg, 0.02 mmol),
o
iPr2NH (1 mL) and DMSO (5 mL) was stirred at 80 C for 20 min under argon. Then a solution of
phenylacetylene (153 mg, 0.16 mL, 1.5 mmol) in iPr2NH (2 mL) was added by portions for 1 h. The
reaction mixture was stirred at 80 oC for 24 h, evaporated without heating to remove iPr2NH, treated
with H2O (50 mL) and extracted with CH2Cl2 (3  20 mL). The extract was dried over Na2SO4 and
evaporated to dryness. The residue was purified by flash column chromatography on silica gel (3.5 
35 cm) with CH2Cl2 as the eluent. The fraction with Rf 0.25 and violet fluorescence gave 145 mg (95
%) of 2-(naphthalen-2-yl)-3-(phenylethynyl)pyridine 2e. The viscous oily product was crystallized
by mashing with EtOH (0.5 mL). Yellowish solid with m.p. 79−81 oC. 1H NMR (400 MHz, CDCl3):
δ [ppm] = 7.28−7.34 (m, 4 Н), 7.42−7.45 (m, 2 Н), 7.53−7.59 (m, 2 Н), 7.93−8.06 (m, 4 Н), 8.22
13
(dd, J = 8.6, 1.5 Hz, 1 Н), 8.66 (s, 1 H), 8.74 (dd, J = 4.7, 1.5 Hz, 1 Н). C NMR (100 MHz,
CDCl3): δ [ppm] = 87.7, 94.9, 118.2, 121.5, 122.8, 126.1, 126.6, 127.0, 127.5, 127.7, 128.4, 128.69,
128.71, 129.2, 131.5, 133.1, 134.6, 136.8, 141.0, 148.6, 159.4. HRMS (ESI): m/z calcd. for C23H16N+
[M+H+]: 306.1277, found 306.1266.
3-Bromo-2-(naphthalen-2-yl)pyridine
(4b) and 2,3-di(naphthalen-2-yl)pyridine (5b): A
mixture of 2,3-dibromopyridine 3b (119 mg, 0.5 mmol), naphthalen-2-ylboronic acid (103 mg, 0.6
mmol), 5 % Pd/C (16 mg, 0.015 mmol), PPh3 (16 mg, 0.06 mmol), 2M aqueous solution K2CO3 (2
o
mL) and toluene (0.5 mL) were stirred at 100 C under argon for 24 h. The reaction mixture was
then extracted with CH2Cl2 (3  15 mL). The extract was dried over Na2SO4 and purified by flash
column chromatography on silica gel (3.5  20 cm) with CH2Cl2 as the eluent. The fraction with Rf
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
18
0.3 gave compound 4b 140 mg (98 %). The loadings may be increased 4-fold. In this case,
compound 4b was obtained in 79 % together with 2,3-di(naphthalen-2-yl)pyridine 5b (10 % yield,
Rf 0.2).
3-Bromo-2-(naphthalen-2-yl)pyridine 4b was obtained as an off-white solid with m.p. 63−66 oC.
1H NMR (600 MHz, CDCl3): δ [ppm] = 7.15 (dd, J = 8.1, 4.6 Hz, 1 Н), 7.49−7.54 (m, 2 Н), 7.80
(dd, J = 8.5, 1.7 Hz, 1 Н), 7.88−7.94 (m, 3 Н), 8.02 (dd, J = 8.1, 1.4 Hz, 1 Н), 8.19 (d, J = 1.1 Hz, 1
Н), 8.66 (dd, J = 4.6, 1.4 Hz, 1 Н). 13C NMR (150.94 MHz, CDCl3): δ [ppm] = 120.1, 123.3, 126.2,
126.7, 126.8, 127.6, 127.7, 128.6, 129.0, 132.9, 133.3, 137.0, 141.4, 148.1, 158.1. HRMS (ESI): m/z
calcd. for C15H11BrN+ [M+H+]: 286.0049 (81Br), 284.0069 (79Br); found 286.0056 (81Br), 284.0075
(79Br).
2,3-Di(naphthalen-2-yl)pyridine 5b was obtained as an off-white solid with m.p. 115−118 oC. 1H
NMR (400 MHz, CDCl3): δ [ppm] = 7.22 (dd, J = 8.5, 1.6 Hz, 1 Н), 7.41−7.47 (m, 4 Н), 7.48−7.52
(m, 2 Н), 7.63 (d, J = 8.5 Hz, 1 Н), 7.64 (d, J = 8.5 Hz, 1 Н), 7.75−7.83 (m, 4 Н), 7.88 (s, 1 H), 7.91
13
(dd, J = 7.7, 1.5 Hz, 1 Н), 8.11 (s, 1 H), 8.83 (dd, J = 4.7, 1.5 Hz, 1 Н). C NMR (100 MHz,
CDCl3): δ [ppm] = 122.2, 125.9, 126.2, 126.3, 127.3, 127.5, 127.6, 127.71, 127.78, 127.81 (2C),
128.1, 128.3, 128.6, 129.6, 132.4, 132.9, 133.3, 133.5, 136.2, 137.6, 137.7, 139.1, 148.6, 157.0.
HRMS (ESI): m/z calcd. for C25H19N+ [M+H+ ]: 332.1434, found 332.1439.
2-Chloro-3-(naphthalen-2-yl)quinoxaline (4a) and 2,3-di(naphthalen-2-yl)quinoxaline (5a):
Compounds 4a and 5a were obtained similarly to 4b and 5b starting from 2,3-dichloroquinoxaline
(100 mg, 0.5 mmol). The flash column chromatography was carried out on silica gel (3.5  40 cm)
with CH2Cl2 as the eluent.
2-Chloro-3-(naphthalen-2-yl)quinoxaline 4a was obtained as white needles with m.p. 153−155
1
oC (EtOH). Yield 116 mg (80 %). Rf 0.6. H NMR (600 MHz, CDCl3): δ [ppm] = 7.54−7.59 (m, 2
Н), 7.79−7.82 (m, 2 H), 7.90−8.00 (m, 4 H), 8.07−8.10 (m, 1 H), 8.16−8.19 (m, 1 H), 8.38 (br s, 1
13
Н). C NMR (150.94 MHz, CDCl3): δ [ppm] = 126.6, 127.3, 127.7, 127.9, 128.2, 128.8, 129.3,
129.9, 130.5, 130.8, 132.9, 133.7, 134.1, 141.0, 141.1, 146.3, 152.9. HRMS (ESI): m/z calcd. for
+
C18H12ClN2 [M+H+]: 293.0654 (37Cl), 291.0684 (35Cl); found 293.0669 (37Cl), 291.0693 (35Cl).
o
2,3-Di(naphthalen-2-yl)quinoxaline 5a was obtained as white needles with m.p. 191−193 C
1
(EtOH). Yield 17 mg (9 %). Rf 0.5. H NMR (600 MHz, CDCl3): δ [ppm] = 7.44−7.50 (m, 2 Н),
7.52 (dd, J = 8.5, 1.7 Hz, 1 H), 7.68 (d, J = 8.5 Hz, 1 H), 7.78−7.81 (m, 3 H), 8.22−8.24 (m, 2 H).
13C NMR (150.94 MHz, CDCl3): δ [ppm] = 126.3, 126.8, 127.1, 127.7, 127.8, 128.7, 129.3, 129.8,
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
19
+
130.1, 133.2, 133.3, 136.7, 141.4, 153.4. HRMS (ESI): m/z calcd. for C28H19N2 [M+H+]: 383.1543,
found 383.1550.
6-Iodo-5-phenylnaphtho[2,1-a]phenazine (7a): To a suspension of 2-(naphthalen-2-yl)-3-
(phenylethynyl)quinoxaline 2a (71 mg, 0.2 mmol) in dry CH3CN (10 mL) a solution of ICl (49 mg,
0.3 mmol) in dry CH3CN (5 mL) was added. The reaction mixture was kept at room temperature for
24 h in the dark and evaporated to dryness. The residue was shaken with CHCl3 (10 mL) and
Na2S2O3 solution (5 mL) and extracted with CHCl3 (3  10 mL). The extract was dried over Na2SO4
and purified by flash column chromatography on silica gel (2.5  40 cm) with CHCl3 as the eluent.
The bright yellow fraction with Rf 0.9 gave 81 mg (84 %) of the cyclization product. 6-Iodo-5-
o
phenylnaphtho[2,1-a]phenazine 7a was obtained as bright yellow needles with m.p. 217−219 C
(EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.09−7.13 (m, 1 Н), 7.44−7.47 (m, 4 Н), 7.62−7.66
(m, 3 Н), 7.90−7.92 (m, 3 Н), 8.14 (d, J = 8.8 Hz, 1 H), 8.42−8.45 (m, 2 H), 9.60 (d, J = 8.8 Hz, 1
13
H). C NMR (100 MHz, CDCl3): δ [ppm] = 112.6, 122.6, 125.5, 126.6, 128.33, 128.34, 128.8,
129.1, 129.3, 129.6, 129.97, 130.01, 130.2, 130.50, 130.55, 130.6, 131.1, 135.3, 140.6, 141.4, 142.8,
+
143.9, 148.3, 149.5. HRMS (ESI): m/z calcd. for C26H16IN2 [M+H+]: 483.0353, found 483.0355.
6-Iodo-5-(4-methoxyphenyl)naphtho[2,1-a]phenazine (7b) was obtained similarly to 7a starting
from 2-((4-methoxyphenyl)ethynyl)-3-(naphthalen-2-yl)quinoxaline 2b (77 mg, 0.2 mmol). Yield 92
o
1
mg (90 %). Rf 0.9. Bright yellow needles with m.p. 244−246 C (EtOH). H NMR (400 MHz,
CDCl3): δ [ppm] = 4.00 (s, 3 H), 7.14−7.19 (m, 3 Н), 7.34 (d, J = 8.6 Hz, 2 H), 7.47 (t, J = 7.4 Hz, 1
H), 7.55 (d, J = 8.9 Hz, 1 H), 7.89−7.94 (m, 3 Н), 8.14 (d, J = 8.8 Hz, 1 H), 8.42−8.45 (m, 2 H), 9.60
13
(d, J = 8.8 Hz, 1 H). C NMR (100 MHz, CDCl3): δ [ppm] = 55.4, 113.2, 114.4, 122.5, 125.6,
126.6, 128.4, 128.8, 129.3, 129.6, 130.0, 130.2, 130.5, 130.6, 130.9, 131.1, 131.3, 135.4, 140.66,
140.73, 141.5, 142.8, 143.8, 149.3, 159.6. HRMS (ESI): m/z calcd. for C27H18IN2O+ [M+H+]:
513.0458, found 513.0462.
12-Iodo-11-phenylnaphtho[2,1-f]quinoxaline (7c) was obtained similarly to 7a starting from 2-
(naphthalen-2-yl)-3-(phenylethynyl)pyrazine 2c (61 mg, 0.2 mmol). Flash column chromatography
was carried out on silica gel (2.5  30 cm) with CH2Cl2 as the eluent. The yellow fraction with Rf
0.7 gave 73 mg (85 %) of the cyclization product. When using a larger excess of ICl (0.33 mmol),
o
the product 7c was obtained in near quantitative yield. Off-white needles with m.p. 220−222 C
(EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.16 (t, J = 7.8 Hz, 1Н), 7.39−7.41 (m, 2 Н), 7.50−
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
20
7.52 (m, 2 Н), 7.62−7.64 (m, 3 Н), 7.97 (d, J = 7.8 Hz, 1 Н), 8.15 (d, J = 8.9 Hz, 1 Н), 8.99 (br s, 1
Н), 9.07 (br s, 1 Н), 9.44 (d, J = 8.9 Hz, 1 Н). 13C NMR (100 MHz, CDCl3): δ [ppm] = 111.8, 122.0,
125.7, 126.8, 128.4, 128.5, 128.9, 129.3, 129.8, 130.1 (2C), 130.7, 131.2, 135.0, 140.4, 141.2, 144.3,
+
145.7, 148.1, 148.7. HRMS (ESI): m/z calcd. for C22H14IN2 [M+H+]: 433.0196, found 433.0201.
12-Iodo-11-(4-methoxyphenyl)naphtho[2,1-f]quinoxaline (7d) was obtained similarly to 7a
starting from 2-((4-methoxyphenyl)ethynyl)-3-(naphthalen-2-yl)pyrazine 2d (67 mg, 0.2 mmol).
Flash column chromatography was carried out on silica gel (2.5  30 cm) with CH2Cl2 as the eluent.
The yellow fraction with Rf 0.6 gave 82 mg (89 %) of cyclization product. Light yellow solid with
m.p. 196−198 oC (EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 3.98 (s, 3 H), 7.14 (d, J = 8.6 Hz,
2 Н), 7.16−7.22 (m, 1 Н), 7.26 (d, J = 8.6 Hz, 2 Н), 7.49 (t, J = 7.4 Hz, 1 Н), 7.56 (d, J = 8.9 Hz, 1
Н), 7.90 (d, J = 7.8 Hz, 1 Н), 8.04 (d, J = 8.9 Hz, 1 Н), 8.88 (d, J = 1.7 Hz, 1 Н), 8.98 (d, J = 1.7 Hz,
1 Н), 9.31 (d, J = 8.9 Hz, 1 Н). 13C NMR (100 MHz, CDCl3): δ [ppm] = 55.4, 112.6, 114.6, 121.8,
125.6, 126.7, 128.5, 128.8, 129.8, 129.9. 130.9, 131.0, 131.2, 134.9, 140.2, 140.6, 141.1, 144.1,
145.5, 148.3, 159.6. HRMS (ESI): m/z calcd. for C23H16IN2O+ [M+H+]: 463.0302, found 463.0312.
12-Iodo-11-phenylnaphtho[1,2-h]quinoline (7e) was obtained similarly to 7a starting from 2-
(naphthalen-2-yl)-3-(phenylethynyl)pyridine 2e (61 mg, 0.2 mmol). Flash column chromatography
was carried out on silica gel (2.5  30 cm) with CH2Cl2 as the eluent. The fraction with Rf 0.7 gave
57 mg (66 %) of the cyclization product. The use of ICl (65 mg, 0.4 mmol) gave 7e in 95% yield.
Yellowish prisms with m.p. 155−157 oC. 1H NMR (400 MHz, CDCl3): δ [ppm] = 7.12 (ddd, J = 8.7,
6.8, 1.4 Hz, 1 Н), 7.35−7.40 (m, 2 Н), 7.46−7.50 (m, 2 Н), 7.59−7.63 (m, 3 Н), 7.65 (dd, J = 8.4, 4.2
Hz, 1 Н), 7.95 (dd, J = 8.2, 1.1 Hz, 1 Н), 8.12 (d, J = 9.0 Hz, 1 Н), 8.80 (dd, J = 8.4, 1.5 Hz, 1 Н),
13
9.06 (dd, J = 4.2, 1.5 Hz, 1 Н), 9.58 (d, J = 9.0 Hz, 1 Н). C NMR (100 MHz, CDCl3): δ [ppm] =
108.9, 122.6, 123.4, 125.3, 126.4, 128.2, 128.4, 128.5, 128.8, 129.2, 129.5, 130.0, 130.5, 131.6,
134.8, 142.5, 144.8, 145.5, 149.1, 149.8 (2C). HRMS (ESI): m/z calcd. for C23H15NI+ [M+H+]:
432.0244, found 432.0244.
5-Phenyl-6-(p-tolylethynyl)naphtho[2,1-a]phenazine
(8a):
6-Iodo-5-phenylnaphtho[2,1-
a]phenazine 7a (97 mg, 0.2 mmol), Pd(PPh3)2Cl2 (14 mg, 0.02 mmol), CuI (2 mg, 0.01 mmol) and
Et3N (5 mL) was stirred under argon for 20 min at 80−82 oC. Then a solution of p-tolylacetylene (46
mg, 0.4 mmol) in dry THF (5 mL) was added by portions for 3 h. The reaction mixture was stirred
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
21
o
for total 24 h at 80−82 C. Then it was evaporated to dryness, treated with H2O (100 mL) and
extracted with CHCl3 (3  20 mL). The extract was dried over Na2SO4 and evaporated. The residue
was purified by flash column chromatography on silica gel (3.5  45 cm) with CHCl3 as the eluent.
The first and second fractions were 1,4-di-p-tolylbuta-1,3-diyne and traces of the starting compound.
The next yellow orange fraction with Rf 0.5 and yellow fluorescence under UV (356 nm) gave 59
o
1
mg (63 %) of compound 8a. Yellow orange solid with m.p. 234−236 C (EtOH). H NMR (400
MHz, CDCl3): δ [ppm] = 2.39 (s, 3 H), 7.14−7.19 (m, 3 Н), 7.28 (d, J = 8.0 Hz, 2 H), 7.52 (t, J = 7.3
Hz, 1 H), 7.55−7.65 (m, 5 H), 7.70 (d, J = 8.8 Hz, 1 H), 7.91−7.96 (m, 2 H), 7.99 (d, J = 7.7 Hz, 1
13
H), 8.19 (d, J = 8.8 Hz, 1 H), 8.44−8.51 (m, 2 H), 9.69 (d, J = 8.8 Hz, 1 H). C NMR (100 MHz,
CDCl3): δ [ppm] = 21.6, 86.9, 101.3, 120.7, 122.5, 122.6, 125.4, 126.6, 127.9, 128.5, 128.8 (2C),
128.9, 129.7, 129.9, 130.0, 130.12, 130.15, 130.2, 130.3, 130.4, 130.9, 131.7, 135.3, 138.4, 141.0,
141.9, 142.6, 143.1, 143.5, 147.2. UV-vis, max nm (lg ): 264 (4.76), 308 (4.52), 339 (4.47), 353
+
(4.36), 396 (4.06), 417 (4.15), end absorption up to 471 nm. HRMS (ESI): m/z calcd. for C35H23N2
[M+H+]: 471.1856, found 471.1844.
5-(4-Methoxyphenyl)-6-(p-tolylethynyl)naphtho[2,1-a]phenazine
(8b):
6-Iodo-5-(4-
methoxyphenyl)naphtho[2,1-a]phenazine 7b (102 mg, 0.2 mmol), Pd(PPh3)2Cl2 (10 mg, 0.014
mmol), CuI (2 mg, 0.01 mmol), iPr2NH (2 mL) and DMSO (6 mL) was stirred under argon for 20
min at 80 oC. Then a solution of p-tolylacetylene (35 mg, 0.3 mmol) in iPr2NH (2 mL) was added by
o
portions for 30−45 min. The reaction mixture was stirred for 24 h at 80 C. Then it was evaporated
without heating to remove iPr2NH, treated with H2O (100 mL) and extracted with CH2Cl2 (3  20
mL). The extract was dried over Na2SO4 and evaporated. The residue was purified by flash column
chromatography on silica gel (3.5  60 cm) with CH2Cl2 as the eluent. The first and second fractions
were 1,4-di-p-tolylbuta-1,3-diyne and traces of the starting compound. The next bright yellow
fraction with Rf 0.7 and bright yellow fluorescence under UV (356 nm) gave 76 mg (76 %) of
o
1
compound 8b as bright yellow orange solid with m.p. 214−216 C (EtOH). H NMR (400 MHz,
CDCl3): δ [ppm] = 2.40 (s, 3 H), 3.99 (s, 3 H), 7.14−7.23 (m, 5 Н), 7.36 (d, J = 8.0 Hz, 2 H), 7.49−
7.56 (m, 3 Н), 7.77 (d, J = 8.8 Hz, 1 H), 7.90−7.93 (m, 2 Н), 7.97 (d, J = 7.8 Hz, 1 H), 8.15 (d, J =
8.8 Hz, 1 H), 8.41−8.49 (m, 2 H), 9.63 (d, J = 8.8 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ [ppm] =
21.6, 55.5, 87.1, 100.9, 114.2, 120.8, 122.4, 122.6, 125.3, 126.6, 128.5, 128.7, 128.9, 129.7, 129.9,
130.12, 130.17, 130.2 (2C), 130.5, 130.8, 131.4, 131.8, 135.3, 135.4, 138.4, 141.0, 142.0, 142.5,
143.4, 146.8, 159.4. UV-vis, max nm (lg ): 262 (4.71), 268 (4.70), 303 (4.64), 330 (4.73), 389
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
22
(4.05), 411 (4.19), 459 (3.96), end absorption up to 501 nm. HRMS (ESI): m/z calcd. for
C36H25N2O+ [M+H+]: 501.1961, found 501.1952.
11-Phenyl-12-(p-tolylethynyl)naphtho[2,1-f]quinoxaline (8c): 12-Iodo-11-phenylnaphtho[2,1-
f]quinoxaline 7c (86 mg, 0.2 mmol), Pd(PPh3)4 (23 mg, 0.02 mmol), CuI (4 mg, 0.02 mmol) and
o
Et3N (5 mL) were stirred under argon for 20 min at 85 C. Then a solution of p-tolylacetylene (46
mg, 0.4 mmol) in Et3N (5 mL) was added by portions for 3 h. The reaction mixture was stirred for
total 24 h at 82−85 oC. Then it was evaporated to dryness, treated with H2O (100 mL) and extracted
with CH2Cl2 (3  20 mL). The extract was dried over Na2SO4 and evaporated. The residue was
purified by flash column chromatography on silica gel (3.5  60 cm) with CHCl3 as the eluent. The
first and second fractions were 1,4-di-p-tolylbuta-1,3-diyne and the starting compound. The next
yellow fraction with Rf 0.35 gave 62 mg (74 %) of compound 8c. Yellow orange solid, decomp. >
o
1
210 C (EtOH). H NMR (400 MHz, CDCl3): δ [ppm] = 2.36 (s, 3 H), 7.11 (d, J = 8.0 Hz, 2 Н),
7.15−7.21 (m, 3 Н), 7.52 (t, J = 7.4 Hz, 1 Н), 7.56−7.64 (m, 5 Н), 7.68 (d, J = 8.8 Hz, 1 Н), 7.97 (d,
J = 7.7 Hz, 1 Н), 8.12 (d, J = 8.9 Hz, 1 Н), 9.06 (d, J = 1.8 Hz, 1 Н), 9.11 (d, J = 1.8 Hz, 1 Н), 9.41
(d, J = 8.9 Hz, 1 Н). 13C NMR (100 MHz, CDCl3): δ [ppm] = 21.6, 86.8, 101.7, 120.2, 121.8 (2C),
122.5, 125.6, 126.8, 127.9, 128.4, 128.8, 128.9, 129.0, 129.8, 130.0, 130.1, 130.7, 131.9, 134.9,
138.6, 140.3, 141.4, 143.0, 144.1, 145.2, 146.5. UV-vis (CHCl3), max nm (lg ): 275 (4.47), 319
+
(4.50), 338 (4.24), 389 (3.93), end absorption up to 466 nm. HRMS (ESI): m/z calcd. for C31H21N2
[M+H+]: 421.1699, found 421.1697.
11-(4-Methoxyphenyl)-12-(p-tolylethynyl)naphtho[2,1-f]quinoxaline (8d) was obtained similarly
to 8a starting from 12-iodo-11-(4-methoxyphenyl)naphtho[2,1-f]quinoxaline 7d (93 mg, 0.2 mmol).
Flash column chromatography was carried out on silica gel (3.5  45 cm) with CH2Cl2 as the eluent.
The first and second fractions were 1,4-di-p-tolylbuta-1,3-diyne and the starting compound. The
next yellow fraction with Rf 0.3 and yellow fluorescence under UV (356 nm) gave 56 mg (62 %) of
o
1
compound 8d. Yellow orange solid with m.p. 191−193 C (EtOH). H NMR (400 MHz, CDCl3): δ
[ppm] = 2.37 (s, 3 H), 3.98 (s, 3 H), 7.12−7.17 (m, 4 H), 7.21−7.23 (m, 1 H), 7.27 (d, J = 8.7 Hz, 2
Н), 7.48−7.55 (m, 3 Н), 7.80 (d, J = 8.8 Hz, 1 Н), 7.97 (d, J = 7.7 Hz, 1 Н), 8.11 (d, J = 8.9 Hz, 1
13
Н), 9.03 (d, J = 1.7 Hz, 1 Н), 9.10 (d, J = 1.7 Hz, 1 Н), 9.40 (d, J = 8.9 Hz, 1 Н). C NMR (100
MHz, CDCl3): δ [ppm] = 21.5, 55.5, 86.7, 100.9, 114.4, 120.5, 121.8, 122.7, 125.5, 126.7, 128.5,
128.7, 128.9, 129.8, 130.1, 130.3, 130.7, 131.3, 131.7, 134.9, 135.3, 138.5, 140.2, 141.5, 143.8,
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
23
145.3, 146.2, 159.4. UV-vis (CHCl3), max nm (lg ): 267 sh (4.45), 286 sh (4.52), 306 (4.59), 323
(4.47), 376 (4.04), 416 sh (3.97), end absorption up to 466 nm. HRMS (ESI): m/z calcd. for
C32H23N2O+ [M+H+]: 451.1805, found 451.1806.
11-Phenyl-12-(p-tolylethynyl)naphtho[1,2-h]quinoline (8e) was obtained similarly to 8a starting
from 12-iodo-11-phenylnaphtho[1,2-h]quinoline 7e (86 mg, 0.2 mmol). Yield 77 mg (91 %). Rf 0.7.
Yellowish solid with m.p. 162−165 oC. 1H NMR (250 MHz, CDCl3): δ [ppm] = 2.38 (s, 3 H), 7.12−
7.20 (m, 5 Н), 7.47−7.63 (m, 6 Н), 7.68−7.76 (m, 2 Н), 7.97 (d, J = 7.9 Hz, 1 Н), 8.11 (d, J = 9.0 Hz,
1 Н), 8.94 (dd, J = 8.3, 1.5 Hz, 1 Н), 9.15 (dd, J = 4.1, 1.5 Hz, 1 Н), 9.56 (d, J = 9.0 Hz, 1 Н). 13C
NMR (62.9 MHz, CDCl3): δ [ppm] = 21.6, 86.7, 100.0, 120.2, 120.7, 122.4, 125.1, 125.7, 126.3,
127.6, 128.5, 128.7, 128.8, 129.1, 129.4, 129.6, 130.3, 130.4, 131.4, 134.7, 134.9 (2C), 138.6 (2C),
142.6, 143.7, 145.3, 149.6. HRMS (ESI): m/z calcd. for C32H22N+ [M+H+]: 419.1747, found
420.1750.
6-(2,4-Bis(trimethylsilyl)but-1-en-3-ynyl)-5-phenylnaphtho[2,1-a]phenazine (9a): 6-Iodo-5-
phenylnaphtho[2,1-a]phenazine 7a (97 mg, 0.2 mmol), Pd(PPh3)2Cl2 (14 mg, 0.02 mmol), CuI (4
mg, 0.02 mmol), Et3N (5 mL) and dry THF (3 mL) was stirred under argon for 20 min at 75−80 oC.
Then a solution of trimethylsilylacetylene (118 mg, 0.17 mL, 1.2 mmol) in Et3N (2 mL) was added
o
by portions for 2 h. The reaction mixture was stirred for total 24 h at 75−80 C. Then it was
evaporated to dryness, treated with H2O (50 mL) and extracted with CHCl3 (3  20 mL). The extract
was dried over Na2SO4 and evaporated. The residue was purified by flash column chromatography
on silica gel (3.5  55 cm) with CHCl3 as the eluent. The yellow fraction with Rf 0.65 gave 92 mg
(84 %) of compound 9a. 6-(2,4-Bis(trimethylsilyl)but-1-en-3-ynyl)-5-phenylnaphtho[2,1-
o
1
a]phenazine 9a was obtained as yellow solid with m.p. 199−201 C (EtOH). H NMR (400 MHz,
CDCl3): δ [ppm] = -0.41 (s, 9 H), 0.15 (s, 9 H), 7.12−7.17 (m, 2 Н), 7.44−7.46 (m, 2 Н), 7.49−7.52
(m, 4 Н), 7.71 (d, J = 8.8 Hz, 1 H), 7.85−7.92 (m, 2 Н), 8.01 (d, J = 7.9 Hz, 1 H), 8.19 (d, J = 8.8 Hz,
1 H), 8.32 (d, J = 7.9 Hz, 1 H), 8.45 (d, J = 8.8 Hz, 1 H), 9.74 (d, J = 8.8 Hz, 1 H). 13C NMR (100
MHz, CDCl3): δ [ppm] = -2.1, -0.5, 103.2, 106.2, 122.7, 125.2, 126.3, 127.5, 128.4, 128.7, 128.9,
129.1, 129.60, 129.61, 129.85, 129.89, 130.2, 130.7, 130.8, 131.2, 135.3, 136.6, 141.0, 141.1, 141.5,
+
142.1, 142.5, 143.0, 145.26, 145.33. HRMS (ESI): m/z calcd. for C36H35N2Si2 [M+H+]: 551.2339,
found 551.2330.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
24
12-(2,4-Bis(trimethylsilyl)but-1-en-3-ynyl)-11-phenylnaphtho[2,1-f]quinoxaline
(9b):
Compound 9b was obtained similarly to 9a starting from 12-iodo-11-phenylnaphtho[2,1-
f]quinoxaline 7c (86 mg, 0.2 mmol). Yield 64 mg (64 %). Rf 0.3. Yellowish needles with m.p.
145−147 oC (EtOH). 1H NMR (250 MHz, CDCl3): δ [ppm] = −0.23 (s, 9 H), 0.10 (s, 9 H), 7.03 (s, 1
H), 7.14 (t, J = 7.5 Hz, 1 Н), 7.32−7.44 (m, 2 Н), 7.45−7.57 (m, 4 Н), 7.70 (d, J = 8.8 Hz, 1 Н), 7.98
(d, J = 7.7 Hz, 1 Н), 8.11 (d, J = 8.9 Hz, 1 Н), 9.01 (s, 2 Н), 9.48 (d, J = 8.9 Hz, 1 Н). 13C NMR (100
MHz, CDCl3): δ [ppm] = −2.1, 0.2, 102.9, 106.0, 122.0, 125.3, 126.4, 127.5, 128.4, 128.8, 128.9,
129.0, 129.5, 129.8, 130.6(1), 130.6(4), 131.1, 134.9, 136.8, 140.0, 140.3, 140.9, 142.5, 143.1,
+
144.4, 145.8. HRMS (ESI): m/z calcd. for C32H33N2Si2 [M+H+]: 501.2182, found 501.2158.
9-p-Tolyldinaphtho[2,1-a:1',2'-c]phenazine (14a): A purple solution of 5-phenyl-6-(p-
tolylethynyl)naphtho[2,1-a]phenazine 8a (47 mg, 0.1 mmol) in CF3COOH (5 mL) was heated at
55−60 oC for 3 h. The reaction mixture was evaporated to dryness, treated with saturated K2CO3 (2
mL) and CHCl3 (10 mL), shaked and separated in a separating funnel. The orange CHCl3 phase was
dried over Na2SO4 and purified by flash column chromatography on silica gel (3.5  40 cm) with
CHCl3 as the eluent. The bright yellow fraction with Rf 0.9 gave the cyclization product (43 mg, 92
%). 9-p-Tolyldinaphtho[2,1-a:1',2'-c]phenazine 14a was obtained as bright yellow plates with m.p.
264−268 oC (EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 2.57 (s, 3 H), 7.32−7.37 (m, 2 Н), 7.47
(d, J = 7.7 Hz, 2 H), 7.53 (t, J = 7.5 Hz, 1 H), 7.60 (t, J = 7.4 Hz, 1 H), 7.72 (d, J = 7.7 Hz, 2 H),
7.83−7.89 (m, 2 H), 8.05 (d, J = 8.0 Hz, 1 H), 8.14 (d, J = 8.3 Hz, 1 H), 8.18−8.23 (m, 3 H), 8.33−
8.40 (m, 2 H), 9.46 (s, 1 H), 9.49 (d, J = 8.7 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ [ppm] = 21.4,
122.2, 122.5, 124.6, 124.8, 126.4, 126.94, 126.96, 128.1 (2C), 128.4, 128.6, 129.0, 129.2, 129.3,
129.51, 129.53, 129.61, 129.7, 129.8, 129.9, 130.2, 130.8, 131.4 (2C), 132.9, 134.3, 137.3, 137.6,
140.6, 142.28, 142.32, 142.36, 142.5. UV-vis, max nm (lg ): 263 (4.72), 289 (4.61), 300 (4.62), 308
(4.63), 336 (4.56), 352 sh (4.47), 393 (4.14), 415 (4.23), 450 sh (3.63), end absorption up to 508 nm.
+
HRMS (ESI): m/z calcd. for C35H23N2 [M+H+]: 471.1856, found 471.1849.
2-Methoxy-18-p-tolyldinaphtho[2,1-a:1',2'-c]phenazine (14b) was obtained similarly to 14a
starting from 5-(4-methoxyphenyl)-6-(p-tolylethynyl)naphtho[2,1-a]phenazine 8b (50 mg, 0.1
o
1
mmol). Yield 49 mg (98 %). Rf 0.7. Yellow solid with m.p. 244−246 C (EtOH). H NMR (400
MHz, CDCl3): δ [ppm] = 2.57 (s, 3 H), 3.93 (s, 3 H), 6.99 (dd, J = 9.3, 2.4 Hz, 1 H), 7.37 (t, J = 7.5
Hz, 1 H), 7.45−7.49 (m, 3 Н), 7.60 (t, J = 7.3 Hz, 1 H), 7.72 (d, J = 7.7 Hz, 2 H), 7.84−7.87 (m, 2
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
25
Н), 8.05 (d, J = 8.0 Hz, 1 H), 8.11 (d, J = 9.3 Hz, 1 H), 8.19 (d, J = 8.7 Hz, 1 H), 8.24 (d, J = 8.6 Hz,
13
1 H), 8.32−8.40 (m, 2 H), 9.43 (s, 1 H), 9.49 (d, J = 8.6 Hz, 1 H). C NMR (100 MHz, CDCl3): δ
[ppm] = 21.4, 55.3, 105.5, 116.1, 122.3, 123.3, 124.9, 126.5 (2C), 126.9, 127.7, 128.1, 128.5, 128.6,
129.1, 129.3 (2C), 129.50, 129.52, 129.7, 130.0 (2C), 130.9, 131.4, 134.3, 134.6, 137.3, 137.8,
139.7, 142.1, 142.3 (2C), 142.6, 158.4. UV-vis, max nm (lg ): 266 (4.87), 292 (4.55), 307 (4.58),
321 (4.61), 343 sh (4.48), 358 (4.36), 400 (4.15), 421 (4.23), end absorption up to 500 nm. HRMS
(ESI): m/z calcd. for C36H25N2O+ [M+H+]: 501.1961, found 501.1947.
1-p-Tolyldinaphtho[2,1-f:1',2'-h]quinoxaline (14c): To a solution of compound 8c (42 mg, 0.1
mmol) in CH2Cl2 (11 mL) CF3SO3H (0.1 mL) was added. The dark red reaction mixture was kept at
room temperature for 24 h in the dark. Then it was evaporated to dryness without heating. The dark
red residue was treated with saturated K2CO3 (50 mL) and CH2Cl2 (10 mL), shaken in a separating
funnel and separated. The yellow CH2Cl2 phase was dried over Na2SO4 and purified by flash column
chromatography on silica gel (2  50 cm) with CH2Cl2 as the eluent. The bright yellow fraction with
o
Rf 0.7 gave the cyclization product (41 mg, 98 %). Yellowish needles with m.p. 181−183 C
(EtOH). 1H NMR (400 MHz, CDCl3): δ [ppm] = 2.55 (s, 3 H), 7.30−7.37 (m, 2 Н), 7.43 (d, J = 7.8
Hz, 2 Н), 7.52 (t, J = 7.6 Hz, 1 Н), 7.61 (t, J = 7.4 Hz, 1 Н), 7.70 (d, J = 7.9 Hz, 2 Н), 8.06 (d, J =
8.0 Hz, 1 Н), 8.14 (d, J = 8.3 Hz, 1 Н), 8.19 (d, J = 8.7 Hz, 1 Н), 8.35 (t, J = 9.4 Hz, 2 Н), 8.96 (d, J
13
= 1.9 Hz, 1 Н), 8.97 (d, J = 1.9 Hz, 1 Н), 9.28 (s, 1 H), 9.32 (d, J = 8.7 Hz, 1 Н). C NMR (100
MHz, CDCl3): δ [ppm] = 21.3, 121.4, 121.6, 124.6, 124.8, 126.4, 126.92, 126.96, 127.5, 128.10,
128.12, 128.5, 128.9, 129.2, 129.42, 129.49, 129.7, 130.1, 130.6, 131.3, 132.4, 133.9, 137.3, 137.5,
140.5, 141.2, 141.4, 143.52, 143.56. UV-vis (CHCl3), max nm (lg ): 305 (4.61), 322 (4.57), 341
+
(4.50), 375 (3.95), 396 (3.84), end absorption up to 466 nm. HRMS (ESI): m/z calcd. for C31H21N2
[M+H+]: 421.1699, found 421.1680; m/z calcd. for C31H20N2Na+ [M+Na+]: 443.1519, found
443.1502.
15-Methoxy-1-p-tolyldinaphtho[2,1-f:1',2'-h]quinoxaline (14d): Compound 14d was obtained
similarly to 14c starting from 11-(4-methoxyphenyl)-12-(p-tolylethynyl)naphtho[2,1-f]quinoxaline
8d (45 mg, 0.1 mmol). Flash column chromatography was carried out on silica gel (2.5  30 cm)
with CH2Cl2 as the eluent. The yellow fraction with Rf 0.5 gave the cyclization product (42 mg, 94
1
%). Yellow solid with m.p. 204−206 oC (EtOH). H NMR (400 MHz, CDCl3): δ [ppm] = 2.54 (s, 3
H), 3.86 (s, 3 H), 6.98 (dd, J = 9.3, 2.5 Hz, 1 Н), 7.36 (t, J = 7.6 Hz, 1 Н), 7.43 (d, J = 7.7 Hz, 2 Н),
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
26
7.49 (d, J = 2.5 Hz, 1 Н), 7.60 (t, J = 7.4 Hz, 1 Н), 7.70 (d, J = 7.7 Hz, 2 Н), 8.05 (d, J = 8.0 Hz, 1
Н), 8.17 (d, J = 8.7 Hz, 1 Н), 8.23 (d, J = 9.3 Hz, 1 Н), 8.37 (d, J = 8.5 Hz, 1 Н), 8.94 (br s, 2 H),
9.25 (s, 1 H), 9.30 (d, J = 8.7 Hz, 1 Н). 13C NMR (100 MHz, CDCl3): δ [ppm] = 21.4, 55.3, 105.6,
115.8, 121.5, 122.3, 124.8, 126.3, 126.9, 127.3, 127.8, 128.0, 128.1, 128.4, 129.2, 129.3, 129.5,
129.9, 130.7, 131.4, 133.8, 134.2, 137.3, 137.6, 139.7, 141.0, 141.4, 143.1, 143.5, 158.4. UV-vis
(CHCl3), max nm (lg ): 267 (4.58), 312 (4.51), 340 sh (4.41), 380 (3.87), 402 sh (3.72), end
absorption up to 486 nm. HRMS (ESI): m/z calcd. for C32H23N2O+ [M+H+] 451.1805, found
451.1798.
8-p-Tolyldinaphtho[2,1-f:1',2'-h]quinoline (14e): Compound 14e was obtained similarly to 14a
starting from 11-phenyl-12-(p-tolylethynyl)naphtho[1,2-h]quinoline 8e (42 mg, 0.1 mmol). Yield 40
o
mg (95 %). Rf 0.7. Off-white needles with m.p. 236−238 C (EtOH). 1H NMR (250 MHz, CDCl3):
δ [ppm] = 2.60 (s, 3 H), 7.31−7.39 (m, 2 Н), 7.48−7.72 (m, 7 Н), 8.10 (d, J = 8.2 Hz, 2 Н), 8.23 (d, J
= 8.8 Hz, 1 Н), 8. 34 (dd, J = 8.5, 1.8 Hz, 2 Н), 8.61 (s, 1 H), 8.98 (dd, J = 8.4, 1.3 Hz, 1 Н), 9.10
(dd, J = 4.3, 1.5 Hz, 1 Н), 9.49 (d, J = 8.8 Hz, 1 Н). 13C NMR (62.9 MHz, CDCl3): δ [ppm] = 21.4,
120.5, 121.9, 122.0, 124.6, 124.7, 124.8, 125.6, 126.2, 126.4, 126.6, 127.3, 127.7, 128.1, 128.2,
129.3, 129.5, 130.0, 130.1, 130.6, 130.8, 131.0, 131.4, 131.7, 133.6, 137.5, 137.7, 140.1, 146.5,
149.0. UV-vis (CHCl3), max nm (lg ): 283 (4.91), 305 sh (4.98), 312 (4.99), 338 sh ( 4.64), 357
(4.59), end absorption up to 419 nm. HRMS (ESI): m/z calcd. for C32H22N+ [M+H+]: 420.1747,
found 420.1728.
1
Supporting Information: Copies of the H and 13C NMR spectra of all compounds, X-ray, UV-vis
and CV data (PDF).
Acknowledgments
The authors gratefully acknowledge the Russian Foundation for Basic Research (project No 18-03-
00006) for financial support of this research. We also thanks Drs. Anna V. Tkachuk and Oleg N.
Burov (Scientific and Educational Laboratory of Resonance Spectroscopy, Department of Natural
and High Molecular Compounds Chemistry, Southern Federal University) for NMR measurements,
Dr. Kyrill Y. Suponitsky (A. N. Nesmeyanov Institute of Organoelement Compounds, Moscow) and
Dr. Olesya V. Khoroshilova (Institute of Chemistry, St. Petersburg State University, St. Petersburg)
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
27
for X-ray studies, Prof. Alexandra G. Berezhnaya and Pavel A. Knyazev (Southern Federal
University) for CV experiments.
Keywords: Synthetic methods − Nitrogen heterocycles − Helical structures − Azine-[5]helicene
hybrids
[1] a) Y. Shen, C.-F. Chen, Chem. Rev. 2012, 112, 1463−1535; b) M. Gingras, Chem. Soc. Rev.
2013, 42, 968−1006; c) M. Gingras, G. Feґlix, R. Peresuttiab, Chem. Soc. Rev. 2013, 42,
1007−1050; d) M. Gingras, Chem. Soc. Rev. 2013, 42, 1051−1095; e) F. Dumitrascu, D. G.
Dumitrescu, I. Aron, Arkivoc 2010, (i), 1−32; f) N. Saleh, C. Shen, J. Crassous, Chem. Sci.
2014, 5, 3680−3694; g) M. Shigeno, Y. Kushida, M. Yamaguchi, Chem. Commun. 2016, 52,
4955−4970; h) H. Isla, J. Crassous, C. R. Chimie 2016, 19, 39−49; i) C.-F. Chen, Y. Shen,
Helicene Chemistry: From Synthesis to Applications. Springer-Verlag Berlin Heidelberg,
2017, 272 p.; j) K. Mori, T. Murase, M. Fujita, Angew. Chem. Int. Ed. 2015, 54, 6847−6851; k)
M. Rickhaus, M. Mayor, M. Juríček, Chem. Soc. Rev. 2016, 45, 1542−1556.
[2] a) L. Rulíšek, O. Exner, L. Cwiklik, P. Jungwirth, I. Starý, L. Pospíšil, Z. Havlas, J. Phys.
Chem. C 2007, 111, 14948–14955; b) J. Hrbac, J. Storch, V. Halouzka, V. Cirkva, P. Matejka,
J. Vacek, RSC Adv. 2014, 4, 46102–46105; c) J. Vacek, J. Vacek Chocholoušová, I. G. Stará, I.
Starý, Y. Dubi, Nanoscale 2015, 7, 8793–8802; d) T. Fujikawa, N. Mitoma, A. Wakamiya, A.
Saeki, Y. Segawa, K. Itami, Org. Biomol. Chem. 2017, 15, 4697–4703.
[3] a) T. Verbiest, S. van Elshocht, M. Kauranen, L. Hellemans, J. Snauwaert, C. Nuckolls, T. J.
Katz, A. Persoons, Science 1998, 282, 913–915; b) B. J. Coe, D. Rusanova, V. D. Joshi, S.
Sánchez, J. Vávra, D. Khobragade, L. Severa, I. Císařová, D. Šaman, R. Pohl, K. Clays, G.
Depotter, B. S. Brunschwig, F. Teplý, J. Org. Chem. 2016, 81, 1912–1920.
[4] a) K. E. S. Phillips, T. J. Katz, S. Jockusch, A. J. Lovinger, N. J. Turro, J. Am. Chem. Soc. 2001,
123, 11899–11907; b) J. E. Field, G. Muller, J. P. Riehl, D. Venkataraman, J. Am. Chem. Soc.
2003, 125, 11808−11809; c) Y. Sawada, S. Furumi, A. Takai, M. Takeuchi, K. Noguchi, K.
Tanaka, J. Am. Chem. Soc. 2012, 134, 4080−4083; d) M. S. Sundar, H. R. Talele, H. M.
Mande, A. V. Bedekar, R. C. Tovar, G. Muller, Tetrahedron Lett. 2014, 55, 1760−1764; e) K.
Nakamura, S. Furumi, M. Takeuchi, T. Shibuya, K. Tanaka, J. Am. Chem. Soc. 2014, 136,
5555−5558; f) Y. Yamamoto, H. Sakai, J. Yuasa, Y. Araki, T. Wada, T. Sakanoue, T.
Takenobu, T. Kawai, T. Hasobe, Chem. Eur. J. 2016, 22, 4263–4273; h) Y. Yamamoto, H.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
28
Sakai, J. Yuasa, Y. Araki, T. Wada, T. Sakanoue, T. Takenobu, T. Kawai, T. Hasobe, J. Phys.
Chem. C 2016, 120, 7421–7427.
[5] a) B. B. Hassine, M. Gorsane, J. Pecher, R. H. Martin, Bull. Soc. Chim. Belg. 1986, 95,
557−566; b) M. T. Reetz, E. W. Beuttenmüller, R. Goddard, Tetrahedron Lett. 1997, 38,
3211−3214; c) R. Takenaka, S. Sarangthem, B. Captain, Angew. Chem. Int. Ed. 2008, 47,
9708−9710; d) P. Aillard, A. Voituriez, A. Marinetti, Dalton Trans. 2014, 43, 15263−15278; e)
D. Dova, L. Viglianti, P. R. Mussini, S. Prager, A. Dreuw, A. Voituriez, E. Licandro, S.
Cauteruccio, Asian J. Org. Chem. 2016, 5, 537−549.
[6] T. Fujikawa, Y. Segawa, K. Itami, J. Am. Chem. Soc. 2016, 138, 3587−3595.
[7] Q. Huang, L. Jiang, W. Liang, J. Gui, D. Xu, W. Wu, Y. Nakai, M. Nishijima,G. Fukuhara, T.
Mori, Y. Inoue, C. Yang, J. Org. Chem. 2016, 81, 3430−3434.
[8] M. Tounsi, M. B. Braiek, A. Baraket, M. Lee, N. Zine, M. Zabala, J. Bausells, F. Aloui, B. B.
Hassine, A. Maaref, A. Errachid, Electroanalysis 2016, 28, 2892−2899.
[9] a) Y. Xu, Y. X. Zhang, H. Sugiyama, T. Umano, H. Osuga, K. Tanaka, J. Am. Chem. Soc.
2004, 126, 6566−6567; b) R. Passeri, G. G. Aloisi, F. Elisei, L. Latterini, T. Caronna, F.
Fontana, I. N. Sora, Photochem. Photobiol. Sci. 2009, 8, 1574−1582.
[10] For selected examples, see: a) Y. Sawada, S. Furumi, A. Takai, A. Takeuchi, K. Noguchi, K.
Tanaka. J. Am. Chem. Soc. 2012, 134, 4080−4083; b) J. Kelber, M.-F. Achard, F. Durola, H.
Bock. Angew. Chem. Int. Ed. 2012, 51, 5200−5203; c) S. Xiao, S. J. Kang, Y. Wu, S. Ahn,
J. B. Kim, Y.-L. Loo, T. Siegrist, M. L. Steigerwald, H. Li, C. Nuckolls. Chem. Sci. 2013, 4,
2018-2023; d) A.-C. Bédard, A. Vlassova, A. C. Hernandez-Perez, A. Bessette, G. S. Hanan,
M. A. Heuft, S. K. Collins. Chem. Eur. J. 2013, 19, 16295−16302.
[11] a) M. Scholz, M. Mühlstädt, F. Dietz. Tetrahedron Lett. 1967, 8, 665–668; b) D. D. Morgan, S.
W. Horgan, M. Orchin. Tetrahedron Lett. 1972, 13, 1789–1792; c) F. Dietz, M. Scholz.
Tetrahedron 1968, 24, 6845–6849; d) W. H. Laarhoven, Th. J. H. M. Cuppen, R. J. F. Nivard.
Tetrahedron 1970, 26, 1069–1083; e) A. V. Bedekar, A. R. Chaudhary, M. Shyam Sundar, M.
Rajappa. Tetrahedron Lett. 2013, 54, 392–396; f) N. Ito, T. Hirose, K. Matsuda. Org. Lett.
2014, 16, 2502–2505.
[12] a) L. B. Liu, T. J. Katz. Tetrahedron Lett. 1990, 31, 3983–3986; b) T. J. Katz, L. B. Liu, N. D.
Willmore, J. M. Fox, A. L. Rheingold, S. H. Shi, C. Nuckolls, B. H. Rickman. J. Am. Chem.
Soc. 1997, 119, 10054–10063; c) N. D. Willmore, L. B. Liu, T. J. Katz. Angew. Chem. Int. Ed.
Engl. 1992, 31, 1093–1095; d) J. Caeiro, D. Pena, A. Cobas, D. Perez, E. Guitian. Adv. Synth.
Catal. 2006, 348, 2466–2474; e) V. Mamane, P. Hannen, A. Fürstner. Chem. Eur. J. 2004, 10,
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201900818
European Journal of Organic Chemistry
29
4556–4575; f) K. Yamamoto, M. Okazumi, H. Suemune, K. Usui. Org. Lett. 2013, 15, 1806–
1809; g) F. Teply, I. G. Stara, I. Stary, A. Kollarovic, D. Saman, L. Rulisek, P. Fiedler. J. Am.
Chem. Soc. 2002, 124, 9175–9180; h) X. Xue, L. T. Scott. Org. Lett. 2007, 9, 3937–3940; i)
M. Shimizu, I. Nagao, Y. Tomioka, T. Hiyama. Angew. Chem. Int. Ed. 2008, 47, 8096–8099;
j) K. Kamikawa, I. Takemoto, S. Takemoto, H. Matsuzaka. J. Org. Chem. 2007, 72, 7406–
7408; k) S. K. Collins, A. Grandbois, M. P. Vachon, J. Cote. Angew. Chem. Int. Ed. 2006, 45,
2923–2926; l) Y. Xia, Z. Liu, Q. Xiao, P. Qu, R. Ge, Y. Zhang, J. Wang. Angew. Chem. Int.
Ed. 2012, 51, 5714–5717.
[13] a) G. V. Baryshnikov, P. Gawrys, K. Ivaniuk, B. Witulski, R. J. Whitby, A. Al-Muhammad, B.
Minaev, V. Cherpak, P. Stakhira, D. Volyniuk, G. Wiosna-Salyga, B. Luszczynska, A.
Lazauskas, S. Tamuleviciush, J. V. Grazuleviciusf, J. Mater. Chem. C 2016, 4, 5795−5805; b)
M. Weimar, R. Correa da Costa, F.-H. Lee, M. J. Fuchter, Org. Lett. 2013, 15, 1706−1709; c)
J. Carreras, M. Patil, W. Thiel, M. Alcarazo, J. Am. Chem. Soc. 2012, 134, 16753−16758; d)
M. Frigoli, J. Marrot, P. L. Gentili, D. Jacquemin, M. Vagnini, D. Pannacci, F. Ortica,
ChemPhysChem 2015, 16, 2447−2458; e) Y. Li, J. Waser, Angew. Chem. Int. Ed. 2015, 54,
5438−5443; f) H. Oyama, K. Nakano, T. Harada, R. Kuroda, M. Naito, K. Nobusawa, K.
Nozaki, Org. Lett. 2013, 15, 2104-2107; g) K. Hirano, Y. Inaba, K. Takasu, S. Oishi, Y.
Takemoto, N. Fujii, H. Ohno, J. Org. Chem. 2011, 76, 9068−9080; h) T. Yao, M. A. Campo,
R. C. Larock, J. Org. Chem. 2005, 70, 3511−3517; i) R. K. Mohamed, S. Mondal, J. V.
Guerrera, T. M. Eaton, T. E. Albrecht-Schmitt, M. Shatruk, I. V. Alabugin, Angew. Chem. Int.
Ed. 2016, 55, 12054−12058; j) J. Storch, J. Čermák, J. Karban, I. Císařová, J. Sýkora, J. Org.
Chem. 2010, 75, 3137−3140; k) A. K. Mandadapu, M. D. Dathi, R. K. Arigela, B. Kundu,
Tetrahedron 2012, 68, 8207−8215; l) K. S. Kumar, B. Bhaskar, M. S. Ramulu, N. P. Kumar,
M. A. Ashfaq, M. Pal, Org. Biomol. Chem. 2017, 15, 82−87; m) K. Pati, C. Michas, D.
Allenger, I. Piskun, P. S. Coutros, G. dos Passos Gomes, I. V. Alabugin, J. Org. Chem. 2015,
80, 11706–11717; n) A. V. Gulevskaya, Eur. J. Org. Chem. 2016, 4207–4214; o) A.V.
Gulevskaya, E. A. Shvydkova, D. I. Tonkoglazova. Eur. J. Org. Chem. 2018, 5030–5043.
[14] a) I. V. Alabugin, E. Gonzalez-Rodrigues, Acc.Chem. Res. 2018, 51, 1206–1219; b) I. V.
Alabugin, B. Gold, J. Org. Chem. 2013, 78, 7777–7784.
[15] a) H. S. Blair, M. Crawford, J. M. Spence, V. R. Supanekar. J. Chem. Soc. 1960, 3313–3318;
b) M. Crawford, R. A. M. Mackinnon, V. R. Supanekar. J. Chem. Soc. 1959, 2807–2812; c)
M.S. Newman. J. Chem. Soc. 1940, 62, 1683–1687; d) H. A. Weialich. Ber. 1938, 71B, 1203–
This article is protected by copyright. All rights reserved.