New [4]helicene derivatives: Synthesis, characterization and photophysical properties

Article abstract of DOI:10.1016/j.molliq.2018.04.083

The design and synthesis of new [4]helicene derivatives were carried out by incorporating well-defined electron donor and acceptor groups at selected positions of the aromatic nuclei, aiming to use them in optical applications. Helicenes have been obtained in good overall yields through a five-step sequence involving mild experimental conditions and easy purification. Photophysical properties of these tetracyclic systems have been evaluated by UV–visible absorption and fluorescence spectroscopies and an emission in the visible region was observed.

Full text of DOI:10.1016/j.molliq.2018.04.083

Accepted Manuscript
New [4]helicene derivatives: Synthesis, characterization and
photophysical properties
Nesrine Hafedh, Faouzi Aloui, Sondes Raouafi, Vincent Dorcet,
Béchir Ben Hassine
PII:
S0167-7322(17)35905-6
doi:10.1016/j.molliq.2018.04.083
MOLLIQ 8986
DOI:
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
9 December 2017
13 April 2018
16 April 2018
Please cite this article as: Nesrine Hafedh, Faouzi Aloui, Sondes Raouafi, Vincent Dorcet,
Béchir Ben Hassine , New [4]helicene derivatives: Synthesis, characterization and
photophysical properties. The address for the corresponding author was captured as
affiliation for all authors. Please check if appropriate. Molliq(2017), doi:10.1016/
j.molliq.2018.04.083
This is a PDF file of an unedited manuscript that has been accepted for publication. As
a service to our customers we are providing this early version of the manuscript. The
manuscript will undergo copyediting, typesetting, and review of the resulting proof before
it is published in its final form. Please note that during the production process errors may
be discovered which could affect the content, and all legal disclaimers that apply to the
journal pertain.

ACCEPTED MANUSCRIPT
New [4]helicene derivatives : Synthesis, characterization and photophysical
properties
a
a,
a
b
a
Nesrine Hafedh , Faouzi Aloui *, Sondes Raouafi , Vincent Dorcet , Béchir Ben Hassine
aUniversity of Monastir, Laboratory of Asymmetric Organic Synthesis and Homogenous Catalysis
(
UR11ES56), Faculty of Sciences, Avenue of Environment, 5019 Monastir, Tunisia.
b
Institut des Sciences Chimiques de Rennes, UMR 6226, Campus de Beaulieu 263, CNRS-Université de
Rennes 1, 35042 Rennes Cedex, France.
*
Corresponding author: Tel.: 0021673500279, fax: 0021673500278,
e-mail address: aloui.faouzi@laposte.net
ABSTRACT
The design and synthesis of new [4]helicene derivatives were carried out by incorporating
well-defined electron donor and acceptor groups at selected positions of the aromatic nuclei,
aiming to use them in optical applications. Helicenes have been obtained in good overall
yields through a five-step sequence involving mild experimental conditions and easy
purification. Photophysical properties of these tetracyclic systems have been evaluated by
UV-visible absorption and fluorescence spectroscopies and an emission in the visible region
was observed.
Keywords: Helicenes; Photolysis; Cyclization; Photooxidation; Optical properties.
1
. Introduction
Polycyclic aromatic hydrocarbons (PAHs) represent an important class of organic
compounds which have two or more fused benzene rings. These compounds have received
considerable attention due to their fascinating chemistry [1] and unique physical properties [2-
3
].
Owing to their specific structure and photoelectric properties, polycyclic aromatic
hydrocarbons (PAHs) have led also to applications in electronic devices. They have proven to
be one of the most important semiconductors [4-7]. Acenes, for example, represent highly
attractive compounds with good performance as semiconductors and good emission
properties, and they have been widely used in various fields, such as inorganic field-effect
transistors [8-9], organic light-emitting diodes (OLEDs) [10] and organic photovoltaics [11-
1
2].
1

ACCEPTED MANUSCRIPT
Pyrene molecules, such as pyrene-cored [4]helicene derivatives 1 and 2 (Fig. 1) have
excellent fluorescence features [13-14], which make them promising candidates for several
important applications in modern electronic and optoelectronic devices.
OH
OH
OH
OH
1
2
Figure 1. Chemical structures of pyrene-cored [4]helicenes 1 and 2.
[
4]helicene 3 is the smallest PAH that has showed biological activities such as
carcinogenic [15], mutagenic [16] and antiproliferative activity [17]. 3,4-dihydrodiol 4 and the
corresponding diolepoxide 5 (Fig. 2) are highly potent carcinogenic metabolites [18-20].
Their photophysical and chiroptical properties have been also investigated [21-25].
O
OH
OH
OH
OH
3
4
5
Figure 2. Representative examples of [4]helicene metabolites.
The [4]helicene skeleton demonstrate various applications such as molecular motor,
building blocks for highly conjugated structures as well as larger [n]helicenes that have
proved successful as chiral catalysts and ligands in asymmetric synthesis [26-33] and as blue
emitters in OLEDs [34-35].
Numerous approaches to the synthesis of [4]helicene and its analogs have been developed
in order to explore the particular properties of these molecules. A convenient synthetic
strategy based on a cross-coupling reaction, 3-methoxy[4]helicene has been prepared [36].
Lakshman and co-workers have demonstrated the applicability of Pt-catalyzed
cycloisomerization reactions of 1-(2-ethynylphenyl)naphthalenes to yield benzo[c]-
phenanthrene analogues that are otherwise not easy to access [37]. B. Zajc have described a
photochemical procedure to yield regiospecifically substituted monofluoro PAHs from 1,2-
diarylfluoroethenes, which were synthesized via Julia-Kocienski olefination [38]. More
2

ACCEPTED MANUSCRIPT
recently, Schindler and co-workers developed a synthetic strategy based on iron(III)-catalyzed
carbonyl-olefin metathesis reactions toward benzo[c]phenanthrenes [39].
In this work, we report the synthesis and characterization of new [4]helicene derivatives
bearing different reactive functional groups. Our synthetic approach is based the use of
suitable α,β-unsaturated nitriles which undergo oxidative photocyclization to achieve the
target helicenes.
2
. Results and discussion
2
-naphthylacetonitrile (7) was available in three steps as shown in scheme 1. In the first
step, we have prepared 2-naphthylmethanol (6) in 98% yield by reduction of 2-
naphthaldehyde using sodium borohydride (NaBH ) in anhydrous methanol. Reaction of
alcohol 6 with thionyl chloride then treatment with an aqueous solution of potassium cyanide
6M) under heating at 50 °C in ethanol provided 2-naphthylacetonitrile (7), as a white solid,
in 76% yield.
4
(
O
1
) SOCl , 50 °C
H
NaBH4/MeOH
°C- r.t
OH
2
N
0
2) KCN(6M)
98%
EtOH, 50 °C
6
7
76%
Scheme 1. Synthetic pathway for the synthetis of 2-naphthylacetonitrile (7).
Knovenagel reaction between 2-naphthylacetonitrile (7) and various aromatic aldehydes 8
in the presence of sodium methoxide in methanol gave the corresponding α,β-unsaturated
nitriles 9a-g in 76%-92% yield (Scheme 2, Table 1).
N
R1
R1
MeONa/MeOH
R2
N
+
r.t
HCO
R2
7
6%-92%
9a-g
7
8
Scheme 2. Synthetic strategy to obtain α,β-unsaturated nitriles 9a-g.
Table 1. Chemical yields of α,β-unsaturated nitriles 9a-g.
α,β-unsaturated nitrile R
1
R
2
yield (%)a
9
9
9
9
a
b
c
F
H
H
H
H
85
76
91
92
CF
CO
OCH
3
2
CH
3
3
d
3

ACCEPTED MANUSCRIPT
9
9
9
e
f
g
CN
SCH
OCH
H
H
OCH
84
87
90
3
3
3
a
Isolated yields.
Finally, the desired benzo[c]phenanthrenes were obtained through oxidative
photocyclization of 1,2-diarylethenes 9a-g using a 500 W high-pressure mercury immersion
lamp. In fact, each resulting diarylethylene has been subjected to photocyclization on a 500
mg scale per 1 liter of toluene, in the presence of stoichiometric amount of iodine as oxidizing
agent and an excess of propylene oxide as hydrogen iodide scavenger, to produce the
corresponding benzo[c]phenanthrene derivative. This allowed us to obtain
benzo[c]phenanthrenes 10a-g in 63%-92% yield (Scheme 3, Table 2).
N
R1
hI -propylene oxide
2
R2
R1
R2
toluene
3%-92%
6
9a-g
N
10a-g
Scheme 3. Photocyclization of α,β-insaturated nitriles 9a-g into [4]helicenes 10a-g.
Table 2. Chemical yields of benzo[c]phenanthrene derivatives 10a-g.
Compound
R
F
CF
CO
OCH
CN
SCH
OCH
1
R
H
H
H
H
H
H
OCH
2
Yield (%)a
1
1
1
1
1
1
1
0a
0b
0c
0d
0
0f
92
75
86
78
63
77
80
3
2
Me
3
e
3
0g
3
3
a
Isolated yields.
In order to extend the scope of these reactions, we have also prepared the
benzo[c]phenathrene like system 10h, containing a thiophene ring, according to the same
synthetic approach. Our procedure uses 2-naphtylacetonitrile (7) and thiophene-2-
carbaldehyde as key building blocks for the synthesis of olefin 9h, which is then converted
into phenanthro[2,1-b]thiophene-5-carbonitrile (10h) by photolysis in 60% yield and 42%
overall yield (Scheme 4).
4

ACCEPTED MANUSCRIPT
S
CHO
N
+
7
MeONa/MeOH
r.t
0%
7
N
h/I -propylene oxide
2
S
toluene
60%
S
N
9h
10h
Scheme 4. Synthetic route to phenanthro[2,1-b]thiophene-5-carbonitrile (10h).
X-ray analysis confirmed the structure of compound 10h. Suitable crystals of this
compound were obtained as orange plates by slow evaporation of a dichloromethane solution.
The product was highly stable in air and to light. The X-ray analysis was carried out on a
single crystal obtained from 10h (Fig. 3). The torsion angles at the inner helical rim
represented by C2-C3-C4-C5 and C3-C4-C5-C6, showed unequal and relatively small angles
of -11° and -10°, respectively.
Figure 3. X-ray crystal structure of the tetracyclic system 10h: ORTEP drawing.
1
Selected H NMR data for the tetracyclic compounds 10a-h are gathered respectively in
tables 3 and 4. Protons H and H12 in compounds 10a-g are the most deshielded compared to
1
the other aromatic protons owing to the magnetic anisotropic effect in the vivinity of the
terminal benzene rings. This series of compound was examined to investigate the deshielding
effect produced by the close approach of cyano group. Proton H
5
in each of the compounds
and
1
0a-g is more deshielded than the rest of the aromatic protons with the exception of H
1
5

ACCEPTED MANUSCRIPT
H12 which are inside the crown. This deshilding is mainly attributed to the electron-
withdrawing effect of the nitrile group. This deshielding appears to be more important in
compounds 10a-c,e which are still substituted with electron-withdrawing groups at position 2
of the tetracyclic skeleton.
Chemical shift of proton H
fact, this proton is more deshielded under the effect of electron-withdrawing groups (CF
CO Me, and CN) and is decreased under the effect of electron-donating groups (SCH and
OCH ). In the case of 2-fluorobenzo[c]phenanthrene-6-carbonitrile 10a, the signal for proton
appears as a doublet of doublet (JH-H = 2.4 Hz, JH-F = 12 Hz) and not a singlet which
proves that it couples with fluorine and proton H
For compound 10h, signals of protons H and H11 appear with characteristic downfield
shifts at  = 8.61 ppm (J = 5.4 Hz) and  = 9.03 ppm (J = 8.1 Hz), respectively. The singlet
1
changes according to the substitutions at positions 2 and 3. In
3
,
2
3
3
H
1
3
.
1
assigned to proton H
4
is more deshielded than that of H in compounds 10a-g ( = 8.44 ppm).
5
1
Table 3. Selected characteristic H NMR (300 MHz) data ( in ppm) for compounds 10a-g.
Compound
Structure
 (H1)
 (H5)
 (H12)
12
1
1
1
0a
0b
F
8.70 (dd)
8.33 (s)
8.93 (d)
5
N
N
N
1
2
1
CF3 9.36 (s)
8.41 (s)
8.89 (d)
5
1
2
O
C
1
1
0c
9.77 (s)
8.36 (s)
8.96 (d)
O
5
6

ACCEPTED MANUSCRIPT
12
1
1
1
0d
O
8.51 (s)
8.27 (s)
9.07 (d)
5
N
12
N
1
0e
9.43 (s)
8.40 (s)
8.89 (d)
5
N
12
1
1
1
0f
S
8.83 (s)
8.47 (s)
8.27 (s)
8.21 (s)
8.98-9.01 (m)
9.02-9.05 (m)
5
N
N
12
1
0g
O
O
5
s: singlet, d: doublet, dd: doublet of doublet, m: multiplet
1
Table 4. Selected characteristic H NMR (300 MHz) data ( in ppm) for compound 10h.
Compound
 (H
1
)
 (H11
)
 (H )
4
11
1
8
.61 (d)
9.03 (d)
8.44 (s)
S
4
N
UV-Vis and fluorescence spectra of 10a-h were measured in dilute chloroform solutions
-5
(
ca = 1.5 × 10 M) at room temperature, and the results are summarized in Table 5. As shown
in Fig.4, all compounds exhibited similar main absorbance bands in the range of 275-450 nm
7

ACCEPTED MANUSCRIPT

with maxima at 289-320 nm that could be assigned to  and n electronic
transitions. The optical band gap values of theses systems appear to be lower than optical gap
of 2-methyl-8,9-diaza[4]helicene (Eg-op = 3.25 eV) [40] and comparable to that of pyrene-
cored [4]helicenes which might be promising candidates in organic light-emitting devices
(OLEDs) [14]. Methyl-6-cyanobenzo[c]phenanthrene-2-carboxylate (10c) shows an optical
band gap of 2.91 eV which was found to be much lower than that of 2-
acetylbenzo[c]phenanthrene (3.05 eV) [41].
The tetracyclic systems 10a-h show a typical emission of organic π-conjugated
molecules. Photoluminescence (PL) of each dilute solution of compounds 10a-g in
chloroform, at room temperature, exhibits two main emissions in the range of 394-450 nm
with shoulder peaks (Fig. 4). The phenanthro[2,1-b]thiophene-5-carbonitrile 10h exhibits four
emissions at 381 nm, 388 nm, 400 nm and 408 with a shoulder peak at 424 nm.
(a)
10a
(b)
1
1
1
1
1
1
1
0b
0c
0d
0e
0f
10a
10b
10c
10d
10e
10f
1
.0
1
1
0
0
.5
.0
.5
.0
0.8
0.6
0g
0h
10g
10h
0
0
.4
.2
0.0
3
00
350
400
450

500
(nm)
550
600
3
50
400
450
500
(nm)
550
600

Figure 4. (a) UV-Vis and (b) normalized emission spectra of 10a-h in dilute chloroform
-5
solutions (c = 1.5 × 10 M) at room temperature.
Table 5. Photophysical properties of [4]helicenes 10a-h.
Compound Absorption
Photoluminescence
b
ems
c
FWHMd
(nm)
abs
max
a

onset
E
(eV)
g-op

(
(ex)

max
(
nm)
nm)
(
nm)
1
1
1
1
1
1
1
1
0a
0b
0c
0d
0e
0f
291
290
292
300
298
309
300
291
406
408
425
400
419
408
404
389
3.05
3.03
2.91
3.10
2.95
3.03
3.06
3.17
394 (340)
408 (360)
422 (350)
415 (350)
420 (360)
403 (340)
399 (350)
382 (330)
42
47
56
54
53
42
54
53
0g
0h
8

ACCEPTED MANUSCRIPT
a
b
c
d
-5
-1
Absorption maxima, measured in chloroform solutions (1.5 x 10 mol.L ) at room temperature.
The optical gap (Eg-op) was estimated from the onset point of the absorption spectra: Eg-op= 1240/onest
Emission maxima, measured in chloroform solutions (1.5 x 10 mol.L ) at room temperature.
Spectrum full width at half maximum.
.
-5
-1
3
. Conclusion
In summary, we have developed a facile and moderately functional-group-tolerant
method witch allow the synthesis of a wide range of new tetracyclic π-conjugated systems
with 39%-58% overall yields. The procedure offers several advantages, such as a simple
synthetic procedure with an easy work-up and ready access to highly functionalized
compounds in a low number of steps. In addition, the obtained compounds allow further
modification reactions. These compounds could be used as building blocks for
multifunctional larger [n]helicenes and supramolecular architectures as they could serve as
convenient materials for optoelectronic applications.
Acknowledgements
The authors are grateful to the DGRS (Direction Generale de la Recherche Scientifique) of
the Tunisian Ministry of Higher Education and Scientific Research.
4
. Experimental section
4
.1. General
All reactions that were carried out under anhydrous conditions were performed under an
inert nitrogen atmosphere. All reagents and solvents used in this work were purchased from
Sigma-Aldrich unless other wise noted. Isolated yields reflect the mass obtained through
filtration or following flash column silica gel chromatography. Organic compounds were
purified using silica gel obtained from Silicycle Chemical division (40-63 nm; 230-240
mesh). The reactions were monitored by thin-layer chromatography using commercial silica-
gel plate 60 coated with a fluorescence indicator (Silicycle Chemical division, 0.25 mm,
F254.). Visualization of TLC plate was performed by UV (254 nm). All mixed solvent eluents
are reported as v/v solutions. Melting points were measured on a Bibby Scientific Stuart
Digital, Advanced, SMP30. All reported compounds were homogeneous by thin layer
1
chromatography (TLC) and by H NMR. NMR spectra were taken in CDCl
3
as solvent with
tetramethylsilane as the internal reference using Bruker AC-300 instruments unless otherwise
1
noted. Signals due to the solvent served as the internal standard (CHCl
3
: δ 7.26 for H, δ
9

ACCEPTED MANUSCRIPT
1
3
1
7
7.16 for C). The acquisition parameters are shown on all spectra. The H NMR chemical
shifts and coupling constants were determined assuming first-order behaviour. Multiplicity is
indicated by one or more of the following: s (singlet), d (doublet), t (triplet), q (quartet), m
(multiplet), br (broad); the list of coupling constants (J) corresponds to the order of the
multiplicity assignment. UV-Vis spectra were recorded on a spectrophotometer UV-1600PC.
4
2
.2. Experimental procedure and spectroscopic data for 2-naphthylmethanol (6)
Sodium borohydride (500 mg, 13.1 mmol) was added in small portions to a stirred solution of
-naphthaldehyde (1 g, 6.4 mmol) in dry methanol (25 mL) at 0 °C. The resulting mixture was
allowed to come to room temperature and then stirred for 1h. The solvent was removed under
vacuum and the resulting solid was washed with water and dried to give 950 mg of pure 2-
1
naphthylmethanol (6) as a white solid in 98% yield. m.p = 79-81 °C; H NMR (300 MHz,
1
3
CDCl
3
): δ (ppm): 1.81 (s, 1H, OH); 4.85 (s, 2H, CH
): δ (ppm): 64.94 (CH ); 124.61 (CH); 124.91 (CH); 125.34 (CH); 125.63 (CH);
27.18 (CH); 127.36 (CH); 127.79 (CH); 132.53 (C); 132.97 (C); 137.90 (C).
2
); 7.48 (m, 3H); 7.82 (m, 4H); C NMR (75
MHz, CDCl
3
2
1
4
.3. Experimental procedure and spectroscopic data for 2-naphthylacetonitrile (8)
A mixture of 2-naphthylmethanol 6 (1 g, 6.3 mmol) and SOCl
2
(15 mL) was stirred
overnight at 50 °C. After removing the excess of SOCl under vacuum, 10 mL of ethanol
2
were added and the mixture was stirred for 15 min at room temperature. Then, 6 mL of a
potassium cyanide solution (6 M) were added and the mixture was stirred vigorously at 50 °C
for 3h and then poured into 50 mL of water and stirred for 30 min. The precipitate formed
was recovered by filtration on fritted glass to give 0.8 g (76%) of the desired product 8 as a
1
white solid. m.p = 82-84 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 3.91 (s, 2H, CH ); 7.38
2
1
3
(
dd, J
1
= 1.5 Hz, J
): δ (ppm): 23.26 (CH
26.36 (C-H); 126.79 (C-H); 127.19 (C); 127.22 (CH); 128.54 (C-H); 132.31 (C); 132.93 (C).
2
= 8.4 Hz, 1H); 7.53-7.55 (m, 2H); 7.84-7.89 (m, 4H); C NMR (75 MHz,
CDCl
3
2
); 117.14 (CN); 124.90 (C-H); 125.97 (C-H); 126.25 (C-H);
1
4
.4. General procedure for the preparation of unsaturated α,β-nitriles (9a-h)
A mixture of 1 molar equivalent of 2-naphthylacetonitrile (7) and 1 molar equivalent of
aldehyde in dry methanol (30 mL) was stirred at 0 °C for 10 min. Then, sodium methoxide (2
1
0

ACCEPTED MANUSCRIPT
equiv.) was added in small portions and the mixture was stirred for 30 min at 0 °C, and then
for 6 hours at room temperature. The resulting precipitate was collected by filtration on a
fritted glass, washed with water and dried.
4
.4.1. (Z)-3-(p-Fluorophenyl)-2-(naphthalen-2-yl)acrylonitrile (9a)
1
White powder, 85%, m.p = 143-145 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.54-7.58
(m, 2H); 7.64 (s, 1H); 7.70-7.78 (m, 3H); 7.86-7.89 (m, 1H), 7.91 (d, J = 8.1 Hz, 2H); 8.00 (d,
1
3
J = 8.4 Hz, 2H); 8.21 (s, 1H, Hvinyl); C NMR (75 MHz, CDCl
3
): δ(ppm): 114.02 (C); 116.96
(CN); 121.78 (CH); 125.41 (CH); 125.46 (CH); 126.34 (CH); 126.68 (CH); 126.95 (CH);
1
1
27.25 (CH); 128.11 (CH); 128.62 (CH); 128.94 (2CH); 130.45 (C); 131.12 (C); 132.71 (C);
1
9
33.17 (C); 136.61 (C); 139.46 (CH); F NMR (282 MHz, CDCl ): δ(ppm): -109.84.
3
4
.4.2. (Z)-3-(p-Trifluoromethylphenyl)-2-(naphthalen-2-yl)acrylonitrile (9b)
1
White powder, 76%, m.p = 170-172 °C; H NMR (300 MHz, CDCl3): δ (ppm): 7,15 (t, J
=
8.4 Hz, 2H); 7.53-7.56 (m, 2H); 7.63 (s, 1H); 7.75 (dd, J
1
= 8.7 Hz, J
): δ (ppm): 110.51 (C); 111.08 (C);
15.56 (CH); 115.85 (CH); 117.48 (CN); 121.90 (CH); 125.78 (CH); 126.53 (CH); 126.62
2
= 1.5 Hz); 7.85-7.97
1
3
(m, 5H); 8.16 (s, 1H, Hvinyl); C NMR (75 MHz, CDCl
3
1
(
CH); 127.21 (CH); 127.99 (C); 128.47 (C); 129.57 (CH); 129.64 (CH); 130.87 (CH); 130.98
CH); 132.78 (C); 132.92 (C); 140.26 (CH); 143.37 (C).
(
4
.4.3. (Z)-1-Methyl-p-[2-cyano-2-(naphthalen-2-yl)]vinylbenzoate (9c)
1
Yellow solid, 91%, m.p = 144-146 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 3.96 (s, 3H,
OCH
3
); 7.54-7.57 (m, 2H); 7.70 (s, 1H); 7.75 (d, J = 8.7 Hz, 1H); 7.85-7.93 (m, 3H); 7.97 (d,
1
3
J= 8.1 Hz , 2H); 8.13 (d, J = 8.1 Hz, 2H); 8.20 (s, 1H, Hvinyl); C NMR (75 MHz, CDCl
3
): δ
); 113.56 (C); 117.10 (CN); 121.84 (CH); 126.27 (CH); 126.63 (CH);
26.87 (CH); 127.24 (CH); 128.11 (CH); 128.58 (CH); 128.68 (2CH); 129.64 (2CH); 130.67
(
ppm): 51.87 (CH
3
1
(C); 130.94 (C); 132.73 (C); 133.12 (C); 137.37 (C); 140.02 (CH); 165.82 (C=O).
4
.4.4. (Z)-3-(p-Methoxyphenyl)-2-(naphthalen-2-yl)acrylonitrile (9d)
1
1

ACCEPTED MANUSCRIPT
1
Yellow solid, 92%, m.p = 129-131 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 3.91 (s, 3H,
OCH
3
); 7.01 (d, J = 8.4 Hz
,
2H); 7.52-7.55 (m, 2H ), 7.62 (s, 1H); 7.75 (d, J = 7,8 Hz, 1H);
1
3
7
1
1
.86-7.97 (m, 5H); 8.16 (s, 1H , Hvinyl); C NMR (75 MHz, CDCl
3
): δ (ppm): 54.90 (OCH );
3
08.43 (C); 113.97 (2CH and CN); 122.08 (CH); 125.26 (CH); 126.19 (C); 126.26 (CH);
26.33 (CH); 127.13 (CH); 127.86 (CH); 128.27 (CH); 130.70 (2CH); 131.66 (C); 132.76
(C); 132.91 (C); 141.32 (CH); 161.03 (C).
4
.4.5. (Z)-3-(p-Cyanophenyl)-2-(naphthalen-2-yl)acrylonitrile (9e)
1
Yellow solid, 84%, m.p = 205-207 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.57-7.60
(m, 2H); 7.67 (s, 1H); 7.76-7.79 (m, 3H); 7.88-7.89 (m ,1H); 7.94 (d, J = 9 Hz, 2H); 8.01 (d, J
1
3
=
6 Hz, 2H); 8.22 (s ,1H, Hvinyl); C NMR (75 MHz, CDCl ): δ (ppm): 113.11 (C); 115.06
3
(
C); 116.62 (CN); 117.60 (CN); 121.73 (CH); 126.5 (CH); 126.71 (CH); 127.40 (CH); 127.24
CH); 128.12 (CH); 128.68 (CH); 129.08 (2CH); 130.32 (CH); 132.09 (2CH); 132.74 (C);
(
1
33.33 (C); 137.45 (C); 138.64 (C).
4
.4.6. (Z)-3-(p-(Methylthio)phenyl)-2-(naphthalen-2-yl)acrylonitrile (9f)
1
Yellow solid, 87%, m.p = 142-144 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 2.54 (s, 3H,
CH
3
); 7.32 (d, J = 8.4 Hz, 2H); 7.51-7.59 (m, 2H ); 7.60 (s, 1H); 7.73 (d, J = 8.4 Hz,
): δ (ppm): 14.52
); 109.81 (C); 117.81 (CN); 121.96 (CH); 125.31 (2CH); 125.57 (CH); 126.46 (CH);
1
H); 7.83-7.92 (m, 4H); 8.15 (s, 1H, Hvinyl); 13C NMR (75 MHz, CDCl
CH
3
(
3
1
1
27.20 (CH); 127.96 (CH); 128.38 (CH); 129.18 (2CH); 129.69 (C); 131.29 (C); 132.82 (2C);
40.98 (2CH); 142.16 (C).
4
.4.7. (Z)-3-(3’,4’-Dimethoxyphenyl)-2-(naphthalen-2-yl)acrylonitrile (9g)
1
Yellow solid, 90%, m.p = 119-121 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 3.97 (s, 3H,
= 8.4 Hz , J = 2.1 Hz, 1H
; 7.53-7.56 (m, 2H); 7.61 (s, 1H); 7.75-7.78 (m, 2H ); 7.85-7.94 (m, 3H); 8.31 (s, 1H, Hvinyl);
13C NMR (75 MHz, CDCl
): δ (ppm): 55.53 (2OCH ); 108.23 (C); 110.89 (CH); 110.98
CH); 118.24 (CN); 122.53 (CH); 124.47 (CH); 125.79 (CH); 126.85 (CH); 126.91 (CH);
OCH
3
); 4.02 (s, 3H, OCH
3
); 6.95 (d, J = 8.4 Hz, 1H) ; 7.41 (dd, J
1
2
)
3
3
(
1
1
27.68 (CH); 128.40 (CH); 128.83 (CH); 131.92 (C); 132.70 (2C); 132.85 (C); 142.09 (CH);
48.59 (C-O); 150.70 (C-O).
1
2

ACCEPTED MANUSCRIPT
4
.4.8. (Z)-2-(Naphthalen-2-yl)-3-(thiophen-2-yl)acrylonitrile (9h)
1
Yellow solid, 70%, m.p = 121-123 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.18-7.21 (m,
1
H); 7.51-7.59 (m, 3H ); 7.73-7.76 (m, 2H); 7.82 (s, 1H); 7.85-7.93 (3H); 8.15 (s, 1H, Hvinyl);
13C NMR (75 MHz, CDCl
): δ (ppm): 107.85 (C); 117.74 (CN); 121.68 (CH); 125.46 (CH);
3
1
26.50 (2CH); 127.20 (CH); 127.42 (CH); 127.92 (2CH); 128.45 (CH); 129.61 (CH); 130.62
(C); 132.76 (C); 132.84 (C); 133.61 (CH); 137.57 (C).
4
.5. General procedure for the photocyclization of α,β-unsaturated nitriles into [4]helicenes
To a solution of olefin 9 (2 mmol) in toluene (1 L) was added iodine (56 mg, 1.1 equiv).
The solution was degassed for 15-20 min, and then propylene oxide (50 equiv) was added.
Irradiation was performed using a falling-film photoreactor and a high-pressure Hg-vapor
lamp (500 W, Hanovia). A flow of argon was maintained throughout the irradiation. The
reaction was monitored by thin-layer chromatography (TLC). After completion, the solvent
was removed under reduced pressure and the crude residue was purified by flash silica gel
column chromatography (cylohexane/EtOAc: 90/10) to yield the pure compound 10.
Spectroscopic data of the benzo[c]phenanthrene derivatives are given subsequently.
4
.5.1. 2-Fluorobenzo[c]phenanthrene-6-carbonitrile (10a)
1
Brown powder, 92%, m.p = 218-220 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.47
(
ddd, J
1
= 9 Hz, J
2
= 8.7 Hz, J
3
= 2.4 Hz, 1H); 7.69-7.77 (m, 2H); 8.02-8.08 (m, 3H); 8.19 (d,
); 8.70 (dd, JH-F = 12 Hz, JH-H = 2.4 Hz, 1H, H ); 8.93 (d, J = 9
Hz, 1H, H12); C NMR (75 MHz, CDCl ): δ (ppm): 108.63 (d, JF-C = 2.62 Hz, C); 112.94 (d,
F-C = 23.85 Hz, CH); 116.45 (d, JF-C = 24.45 Hz, CH); 117.99 (CN); 123.03 (CH); 127.10
J = 9 Hz, 1H); 8.33 (s, 1H, H
5
1
13
3
J
(
CH); 127.18 (CH); 127.24 (C); 127.31 (CH); 128.25 (C); 128.84 (C); 128.95 (CH); 129.65
C); 129.93 (CH); 131.62 (d, JF-C = 9.52 Hz, CH); 133.11 (d, JF-C = 9.37 Hz, C); 133.57 (C);
(
1
1
34.59 (CH); 161.48 (d, JF-C = 284.4 Hz, C-F); 19F NMR (282 MHz, CDCl
3
) : δ (ppm) : -
08.29 (s).
4
.5.2. 2-(Trifluoromethyl)benzo[c]phenanthrene-6-carbonitrile (10b)
1
3

ACCEPTED MANUSCRIPT
1
White solid, 75%, m.p = 144-146 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.25-7.83
(m, 2H); 7.90 (d, J = 8.7 Hz, 1H); 8.10-8.13 (m, 2H); 8.17 (d, J = 8.4 Hz, 1H); 8.25 (d, J = 9
13
Hz, 1H); 8.41 (s, 1H, H
5
); 8.89 (d, J = 8.1 Hz, 1H, H12); 9.36 (s, 1H, H ); C NMR (75 MHz,
1
CDCl
3
): δ(ppm): 111.56 (C); 117.50 (CN); 122.33 (C); 122.83 (CH); 122.89 (CH); 125.50
CH); 127.39 (CH); 127.60 (CH); 127.68 (CH); 128.16 (C); 128.82 (C); 129.03 (CH); 130.09
CH); 130.21 (CH); 130.41 (C); 130.84 (C); 130.90 (C); 132.71 (C); 133.86 (C); 134.09
(
(
(
1
9
CH); F NMR (282 MHz, CDCl ) : δ (ppm) : - 62.22 (s)
3
4
.5.3. Methyl-6-cyanobenzo[c]phenanthrene-2-carboxylate (10c)
1
Yellow solid, 86%, m.p = 218-220 °C; H NMR (300 MHz, CDCl
); 7.71-7.78 (m, 2H); 8.06-8.09 (m, 3H); 8.22-8.29 (m, 2H); 8.36 (s, 1H, H
); 13C NMR (75 MHz, CDCl
): δ(ppm): 52.66 (OCH
11.46 (C); 117.71 (CN); 122.90 (CH); 126.65 (CH); 127.44 (CH); 127.54 (CH); 127.87
3
): δ (ppm): 4.04 (s, 3H,
); 8.96 (d, J =
);
CH
3
5
8
1
.1 Hz, 1H, H12); 9.77 (s, 1H, H
1
3
3
(
CH); 128.23 (C); 128.58 (C); 128.88 (CH); 129.33 (CH); 129.46 (C); 129.90 (CH); 130.20
C); 130.54 (CH); 131 (C); 133.55 (C); 133.86 (C); 134.22 (CH); 166.81 (C=O).
(
4
.5.4. 2-Methoxybenzo[c]phenanthrene-6-carbonitrile (10d)
1
Yellow solid, 78%, m.p = 162-164 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 4.02 (s, 3H,
CH
3
); 7.32 (dd, J
.99-8.06 (m, 2H); 8.19 (d, J = 8.7 Hz); 8.27 (s, 1H, H
H, H12); 13C NMR (75 MHz, CDCl
): δ(ppm): 55.64 (OCH
17.56 (CH); 118.48 (CN); 123.26 (CH); 126.45 (C); 126.72 (2CH); 127.02 (CH); 127.11
1
= 9 Hz, J
2
= 2.4 Hz, 1H, H
3
); 7.67-7.70 (m, 2H); 7.92 (d, J = 8.7 Hz, 1H);
); 8.51 (s, 1H, H ); 9.07 (d, J = 9.3 Hz,
); 106.55 (C); 109.49 (CH);
7
1
1
5
1
3
3
(
C); 128.89 (CH); 129.02 (C); 129.25 (CH); 130.01 (C); 130.81 (CH); 133.48 (C); 133.55
C); 134.77 (CH); 160.64 (C-O).
(
4
.5.5. 2-Cyanobenzo[c]phenanthrene-6-carbonitrile (10e)
1
Yellow solid, 63%, m.p = 259-261 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.77-7.89
(m, 3H); 8.12-8.18 (m, 3H); 8.28 (d, J = 8.7 Hz, 1H); 8.40 (s, 1H, H
5
); 8.89 (d, J = 8.1 Hz, 1H,
H12); 9.43 (s, 1H, H
1
); 13C NMR (75 MHz, CDCl
3
): δ(ppm): 112.59 (2C); 117.19 (CN);
1
18.74 (CN); 122.85 (CH); 127.45 (CH); 127.67 (C); 127.90 (CH); 128 (CH); 129.06 (C);
1
4

ACCEPTED MANUSCRIPT
1
1
29.13 (CH); 130.19 (CH); 130.64 (CH); 131.01 (C); 132.94 (C); 133.48 (CH); 133.86 (CH);
34 (C).
4
.5.6 2-(Methylthio)benzo[c]phenanthrene-6-carbonitrile (10f)
1
White solid, 77%, m.p = 143-145 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 2.68 (s, 3H,
CH
3
); 7.54 (dd, J
1
= 8.4 Hz, J
2
= 1.5 Hz, 1H, H
3
); 7.68-7.75 (m, 2H); 8.22-8.29 (m, 2H); 7.90
(d, J = 8.4 Hz, 1H); 8.02 (d, J = 8.7 Hz, 1H); 8.05-8.09 (m, 1H); 8.19 (d, J = 8.7 Hz, 1H); 8.27
1
3
(
s, 1H, H
5
); 8.83 (s, 1H, H
1
); 8.98-9.01 (m, 1H, H12); C NMR (75 MHz, CDCl ): δ(ppm):
3
1
4.96 (CH
3
); 107.47 (C); 117.78 (CN); 122.62 (CH); 123.13 (CH); 124.97 (CH); 126.35
(
CH); 126.44 (CH); 126.40 (C); 126.84 (CH); 128.35 (C); 128.39 (CH); 128,50 (C); 128.75
CH); 128.91 (CH); 129.21 (C); 131.59 (C); 133.13 (C); 134.16 (CH); 140.83 (C).
(
4
.5.7. 2,3-Dimethoxbenzo[c]phenanthrene-6-carbonitrile (10g)
1
Beige powder, 80%, m.p = 209-211 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 4.09 (s,
= 6 Hz,
); 9.02-9.05 (m,
); 55.67 (OCH ); 106.42 (C);
07.53 (CH); 107.91 (CH); 118.11 (CN); 122.85 (CH); 126.01 (CH); 126.25 (CH); 126.40
6
H, 2OCH
3
); 7.31 (s,1H, H
4
); 7.66-7.69 (m, 2H); 7.93 (d, J = 8.7 Hz, 1H); 8.03 (dd, J
); 8.47 (s, 1H, H
): δ(ppm): 55.60 (OCH
1
J
2
= 2.4 Hz, 1H); 8.16 (d, J = 8.7 Hz, 1H); 8.21 (s, 1H, H
5
1
13
1
1
H, H12); C NMR (75 MHz, CDCl
3
3
3
(
CH); 126.67 (C); 126.76 (C); 127.01 (C); 127.48 (C); 127.77 (CH); 128.43 (CH); 129.22
C); 132.98 (CH); 133.10 (C); 149.10 (C-O); 151.07 (C-O).
(
4
.5.8. Phenanthro[2,1-b]thiophene-5-carbonitrile (10h)
1
Brown solid, 60%, m.p = 150-152 °C; H NMR (300 MHz, CDCl
3
): δ (ppm): 7.70-7.80
); 8.61
): δ(ppm):
07.15 (C); 118.48 (CN); 123.57 (CH); 125.93 (CH); 126.35 (CH); 126.85 (C); 127.22
2CH); 127.74 (CH); 128.78 (CH); 129.01 (CH); 129.33 (C); 129.85 (C); 131.11 (CH);
(
m, 2H); 7.95-7.99 (m, 2H); 8.02-8.09 (m, 1H); 8.25 (d, J = 9Hz, 1H); 8.47 (s, 1H, H
4
13
(
d, J = 5.4 Hz, 1H, H
1
); 9.03 (d, J = 8.1 Hz, 1H, H11); C NMR (75 MHz, CDCl
3
1
(
1
33.01 (C); 138.19 (C); 138.30 (C).
Crystal data for compound 10h (C17
9
H NS) were recorded on a D8 VENTURE Bruker
AXS diffractometer, M = 259.31, monoclinic, space group P 21. a = 3.8867(14) Å, b =
3
-3
1
7.900(6)Å, c = 16.609(6)Å, V = 1153.8(7)Å , Z = 4, ρcalcd = 1.493 g.cm , X-ray source Mo-
1
5

ACCEPTED MANUSCRIPT
Kα, λ = 0.71073 Å, T = 150(2) K; observed reflections 2098; refinement method Full-matrix
2
2
Least-squares on F ; parameters refined 140; R(F) = 0.1305, wR(F ) = 0.3105.
Crystallographic data for the structure in this Letter have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication number CCDC 1588231. These
data can be obtained free of charge from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 (0) 1223 336033; e-
mail:deposit@ccdc.cam.ac.uk or via www.ccdc.cam.ac.uk/data_request/cif.
References
[
1] G. Trinquier, J.-P. Malrieu, Predicting the Open-Shell Character of Polycyclic
Hydrocarbons in Terms of Clar Sextets. J. Phys. Chem. A 122 (2018) 1088-1103.
2] L. Gang, Z. Yongbiao, L. Junbo, C. Jun, Z. Jia, W.S. Xiao, Z. Qichun, Synthesis,
[
Characterization, Physical Properties, and OLED Application of Single BN-Fused Perylene
Diimide. J. Org. Chem. 80 (2015) 196-203
[
3] G.R. Kiel, S.C. Patel, P.W. Smith, D.S. Levine, T.D. Tilley, Expanded Helicenes: A
General Synthetic Strategy and Remarkable Supramolecular and Solid-State Behavior. J. Am.
Chem. Soc. 139 (2017) 18456-18459
[
4] T. Takahashi, T. Takenobu, J. Takeya, Y. Iwasa, Ambipolar Light-Emitting Transistors of
a Tetracene Single Crystal. Adv. Funct. Mater. 17 (2007) 1623-1628.
5] Y. Zhang, E. Galoppini, Organic Polyaromatic Hydrocarbons as Sensitizing Model Dyes
for Semiconductor Nanoparticles. ChemSusChem 3 (2010) 410-428.
6] D. Stassen, N. Demitri, D. Bonifazi, Extended O-Doped Polycyclic Aromatic
Hydrocarbons. Angew. Chem., Int. Ed. 55 (2016) 5947-5951.
7] X. Cui, C. Xiao, L. Zhang, Y. Li, Z. Wang, Polycyclic aromatic hydrocarbons with
orthogonal tetraimides as n-type semiconductors. Chem. Commun. 52 (2016) 13209-13212.
8] T. Lei, Y. Zhou, C.Y. Cheng, Y. Cao, Y. Peng, J. Bian, J. Pei, Aceno[2,1,3]thiadiazoles
for Field-Effect Transistors: Synthesis and Crystal Packing. Org. Lett. 13 (2011) 2642-2645.
9] W.F. Zhang, Y.Q. Liu and G. Yu, Heteroatom Substituted Organic/Polymeric
Semiconductors and their Applications in Field-Effect Transistors. Adv. Mater. 26 (2014)
898-6904.
[
[
[
[
[
6
1
6

ACCEPTED MANUSCRIPT
[
10] B.-B. Jang, S.H. Lee, Z.H. Kafafi, Asymmetric Pentacene Derivatives for Organic Light-
Emitting Diodes. Chem. Mater. 18 (2006) 449-457.
11] Y. Shao, S. Sista, C.W. Chu, D. Sievers, Y. Yang, Enhancement of tetracene
photovoltaic devices with heat treatment. Appl. Phys. Lett. 90 (2007) 103501-103503.
12] Y.Z. Lin, Y.F. Li, X.W. Zhan, Small molecule semiconductors for high-efficiency
organic photovoltaics. Chem. Soc. Rev. 41 (2012) 4245-4272.
13] A. Paudel, J.-Y. Hu, T. Yamato, Synthesis and structural properties of novel polycyclic
[
[
[
aromatic compounds using photo-induced cyclisation of 2,7-di-tert-butyl-4-(phenylethenyl)-
pyrenes. J. Chem. Res. (2008) 457-460.
[
14] J.-Y. Hu, A. Paudel, N. Seto, X. Feng, M. Era, T. Matsumoto, J. Tanaka, M.R.J.
Elsegood, C. Redshaw, T. Yamato, Pyrene-cored bleue-light emitting [4]helicenes: Synthesis,
crystal structures, and photophysical properties. Org. Biomol. Chem. 11 (2013) 2186-2197.
[
15] W. Levin, A.W. Wood, R.L. Chang, Y. Ittah, M. Croisy-Delcey, H. Yagi, D.M. Jerina,
A.H. Conney, Exceptionally High Tumor-initiating Activity of Benzo[c]phenanthrene Bay-
Region Diol-Epoxides on Mouse Skin. Cancer Res. 40 (1980) 3910-3914.
[
16] A. W. Wood, R.L. Chang, W. Levin, D. . Ryan, P.E. Thomas, M. Croisy-Delcey, Y.
Ittah, H. Yagi, D.M. Jerina, A.H. Conney, Mutagenicity of the Dihydrodiols and Bay-Region
Diol-Epoxides of Benzo[c]phenanthrene in Bacterial and Mammalian Cells. Cancer Res. 40
(1980) 2876-2883.
[
17] N. Perin, I. Martin-Kleiner, R. Nhili, W. Laine, M.H. David-Cordonnier, O. Vugrek, G.
Karminski-Zamola, M. Kralj, M. Hranjec, Biological activity and DNA binding studies of 2-
substituted benzimidazo[1,2-a]quinolines bearing different amino side chains. Med. Chem.
Commun. 4 (2013) 1537-1550.
[
18] M.S. Newman, H.V. Anderson, K.H. Takemura, The Synthesis of Polynuclear Aromatic
Hydrocarbons. II. Methylbenzo[c]phenanthrenes. J. Am. Chem. Soc. 75 (1953) 347-349.
19] C. Djerassi, T.T. Grossnickle, The Dienone-Phenol Rearrangement in the
[
Benzo[c]phenanthrene Series. A Case of Concurrent Methyl and Methylene Migration. J. Am.
Chem. Soc. 76 (1954) 1741-1746.
1
7

ACCEPTED MANUSCRIPT
[
20] S. M. Mukhergi, V.S. Gaind, P.N. Rao, Friedel-Crafts reaction involving unsaturated
ketones and esters.III. A new route to benzo[C]phenanthrene derivatives. J. Org. Chem. 19
(1957) 328-332.
[
21] J. Seixas de Melo, J. Pina, L.M. Rodrigues, R.S. Becker, A comprehensive study of the
spectral and photophysical properties of arylthiophenes. Journal of Photochemistry and
Photobiology A: Chemistry 194 (2008) 67-75.
[
22] J. Elm, J. Lykkebo, T.J. Sorensen, B.W. Laursen, K.V. Mikkelsen, Obtaining Enhanced
Circular Dichroism in [4]Heterohelicenium Analogues. J. Phys. Chem. A 116 (2012) 8744-
752.
23] D. Sakamaki, D. Kumano, E. Yashima, S. Seki, A double hetero[4]helicene composed of
two phenothiazines: synthesis, structural properties, and cationic states. Chem. Commun. 51
8
[
(2015) 17237-17240.
[
24] S. Pascal, C. Besnard, F. Zinna, L.D. Bari, B.L. Guennic, D. Jacquemin, J. Lacour,
Zwitterionic [4]helicene: a water-soluble and reversible pH-triggered ECD/CPL chiroptical
switch in the UV and red spectral regions. Org. Biomol. Chem. 14 (2016) 4590-4594.
[
25] X. Zhang, L.E. Clennan, T. Petek, J. Weber, Synthesis, computational, and photophysical
characterization of diaza-embedded [4]helicenes and pseudo[4]helicenes and their pyridinium
and viologen homologues. Tetrahedron 73 (2017) 508.
[
26] F. Aloui, S. Moussa, B. Ben Hassine, Synthesis and characterization of a new hexacyclic
helicene. Tetrahedron Lett. 53 (2012) 3216-3219.
27] Q. Lefebvre, M. Jentsch, M. Rueping Continuous flow photocyclization of stilbenes-
scalable synthesis of functionalized phenanthrenes and helicenes. Beilstein J. Org. Chem. 9
[
(2013) 1883-1890.
[
28] S.D. Dreher, T.J. Katz, K.C. Lam, A.L. Rheingold, Application of the Russig-Laatsch
Reaction to Synthesize a Bis[5]helicene Chiral Pocket for Asymmetric Catalysis. J. Org.
Chem. 65 (2000) 815-822.
[
29] J. Chen, N. Takenaka, Helical Chiral Pyridine N-Oxides: A New Family of Asymmetric
Catalysts. Chem. Eur. J. (2009) 7268-7276.
[
(
30] D. Nečas, R.P. Kaiser, J. Ulč, Selective borylation of [4]helicene. Eur. J. Org. Chem. 34
2016) 5647-5652.
1
8

ACCEPTED MANUSCRIPT
[
31] T. Kawasaki, K. Suzuki, E. Licandro, A. Bossi, S. Maiorana, K. Soai, Enantioselective
synthesis induced by tetrathia-[7]-helicenes in conjunction with asymmetric autocatalysis.
Tetrahedron: Asymmetry 17 (2006) 2050-2053.
[
32] C.S. Demmer, A. Voituriez, A. Marinetti, Catalytic uses of helicenes displaying
phosphorus functions. C. R. Chimie 20 (2017) 860-879.
33] T. Tsujihara, N. Inada-Nozaki, T. Takehara, D.-Y. Zhou, T. Suzuki, T. Kawano, Nickel-
Catalyzed Construction of Chiral 1-[6]Helicenols and Application in the Synthesis of
[
[
[
6]Helicene-Based Phosphinite Ligands. Eur. J. Org. Chem. 29 (2016) 4948-4952.
34] S. Sahasithiwat, T. Mophuang, L. Menbangpung, S. Kamtonwong, T. Sooksimuang,
3
,12-Dimethoxy-7,8-dicyano-[5]helicene as a novel emissive material for organic light-
emitting diode. Synth. Met. 160 (2010) 1148-1152.
35] L. Shi, Z. Liu, G. Dong, L. Duan, Y. Qiu, J. Jia, W. Guo, D. Zhao, D. Cui, X. Tao,
[
Synthesis, Structure, Properties, and Application of a Carbazole-Based Diaza[7]helicene in a
Deep-Blue-Emitting OLED. Chem, Eur. J. 18 (2012) 8092-8099.
[
36] S. Kumar, A New and Concise Synthesis of 3-Hydroxybenzo[c]phenanthrene and 12-
Hydroxybenzo[g]chrysene, Useful Intermediates for the Synthesis of Fjord-Region Diol
Epoxides of Benzo[c]phenanthrene and Benzo[g]chrysene. J. Org. Chem. 62 (1997) 8535-
8
539.
[
37] P.F. Thomson, D. Parrish, P. Pradhan, M.K. Lakshman, Modular, Metal-Catalyzed
Cycloisomerization Approach to Angularly Fused Polycyclic Aromatic Hydrocarbons and
Their Oxidized Derivatives. J. Org. Chem. 80 (2015) 7435-7446.
[
38] S. Banerjee, S. Sinha, P. Pradhan, A. Caruso, D. Liebowitz, D. Parrish, M. Rossi, B.
Zajc, Regiospecifically Fluorinated Polycyclic Aromatic Hydrocarbons via Julia-Kocienski
Olefination and Oxidative Photocyclization. Effect of Fluorine Atom Substitution on
Molecular Shape. J. Org. Chem. 81 (2016) 3983-3993.
[
39] C.C. McAtee, P.S. Riehl, C.S. Schindler, Polycyclic Aromatic Hydrocarbons via
Iron(III)-Catalyzed Carbonyl-Olefin Metathesis. J. Am. Chem. Soc. 139 (2017) 2960-2963.
40] X. Zhang, E.L. Clennan, T. Petek, J. Weber, Synthesis, computational, and photophysical
[
characterization of diaza-embedded [4]helicenes and pseudo[4]helicenes and their pyridinium
and viologen homologues. Tetrahedron 73 (2017) 508-518.
[
41] H. Guédouar, F. Aloui, B. Ben Hassine, Benzo[c]phenanthrene derivatives: Synthesis,
optical properties and cytotoxic activity. J. Advances Chem. 22 (2016) 4404-40412.
1
9

ACCEPTED MANUSCRIPT
Graphical abstract
R1
S
R2
N
N
R = F, CF , CO Me, OMe, CN, SMe
1
3
2
R2 = H, OMe
2
0

ACCEPTED MANUSCRIPT
Highlights
Facile method was developed for [4]helicenes preparation from 2-naphthaldehyde.
Photophysical properties of [4]helicenes were studied in solutions.
Optical gap values of [4]helicenes were found to be less than 3.2 eV.
2
1