Synthesis and optoelectronic properties of some new thiahelicenes

Article abstract of DOI:10.1080/00397911003707220

(Chemical Equation Presented) New symmetrical helically chiral penta- and heptacyclic aromatic systems containing two thiophene rings have been prepared, in good yields, under mild conditions using a photochemical route. Optoelectronic properties of these helically aromatic thia-systems were determined and exhibit interesting behavior. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397911003707220

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Synthesis and Optoelectronic Properties
of Some New Thiahelicenes
Souad Moussa a , Faouzi Aloui a & Béchir Ben Hassine a
a Laboratoire de Synthèse Organique Asymétrique et Catalyse
Homogène, Faculté des Sciences , Monastir , Tunisia
Published online: 03 Mar 2011.
To cite this article: Souad Moussa , Faouzi Aloui & Béchir Ben Hassine (2011) Synthesis and
Optoelectronic Properties of Some New Thiahelicenes, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 41:7, 1006-1016, DOI:
10.1080/00397911003707220
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Synthetic Communications1, 41: 1006–1016, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911003707220
SYNTHESIS AND OPTOELECTRONIC PROPERTIES OF
SOME NEW THIAHELICENES
´
Souad Moussa, Faouzi Aloui, and Bechir Ben Hassine
Laboratoire de Synthese Organique Asymetrique et Catalyse Homogene,
`
´
`
´
Faculte des Sciences, Monastir, Tunisia
GRAPHICAL ABSTRACT
Abstract New symmetrical helically chiral penta- and heptacyclic aromatic systems con-
taining two thiophene rings have been prepared, in good yields, under mild conditions using
a photochemical route. Optoelectronic properties of these helically aromatic thia-systems
were determined and exhibit interesting behavior.
Keywords Helicenes; optoelectronic properties; photodehydrocyclization; thiahelicenes;
Wittig reaction
INTRODUCTION
Helicenes represent a class of helically chiral aromatic molecules in which the
extra ortho-condensed rings give rise to a regular cylindrical helix because of the
repulsive steric overlap of the terminal aromatic nuclei. These shaped molecules have
gained considerable interest thanks to their chiroptical and nonlinear optical proper-
ties.[1,2] They have been considered as new, potentially useful systems in chiral disco-
tic liquid-crystalline materials,[3] as building blocks for helical conjugated
polymers,[4,5] and as rotors.[6,7] Furthermore, enantiomerically enriched helicenes
Received January 30, 2010.
Address correspondence to Bechir Ben Hassine, Laboratoire de Synthese Organique Asymetrique
´
et Catalyse Homogene (01UR1201), Faculte des Sciences, Avenue de l’environnement, 5019 Monastir,
`
´
`
Tunisia. E-mail: bechirbenhassine@yahoo.fr
´
1006

SYNTHESIS OF NEW THIAHELICENES
1007
have been used as helical ligands,[8,9] structures that act as catalysts[10] for enantio-
selective transformations, and asymmetric inducers.[11,12]
Heterohelicenes,[13–15] in particular, are very interesting helical-shaped aro-
matic systems that possess great potential to develop new materials. They are suit-
able building blocks for organic materials with extraordinarily strong chiroptical
and optoelectronic properties.[16] Thiahelicenes, for example, combine the electronic
properties afforded by their extensive p-conjugated system with the chiroptical
properties associated with their helical structure,[17] resulting from the ortho-conden-
sation of benzene and thiophene rings. These helically chiral molecules exhibit a high
electron affinity and a high thermal stability and could serve as promising
electron-transport (n-type) materials for organic light-emitting diodes (OLEDs). In
this context, the development of new hetero-helicenes and the further study of the
underlying structure–property relationships presented an interesting challenge.
In this article, we report the synthesis and characterization of new thiahelicenes
such as 2,11-dithiapentahelicene, 3,10-dithiapentahelicene, 2,15-dithiaheptahelicene,
and 3,14-dithiaheptahelicene. The optoelectronic properties[18] of these compounds
were also investigated.
RESULTS AND DISCUSSION
The synthetic route followed to obtain the thiahelicenes started from the syn-
thesis of 1,2-disubstituted alkenes, which are obtained through the Wittig reaction
from the appropriate thiophene carbaldehyde and the suitable bisphosphonium salt.
The resulting alkene is then converted into the corresponding helically chiral
thia-system by photolysis.
Scheme 1 shows our general synthetic strategy to prepare the helical pentacyc-
lic thia-system 1a, which is based on a three-step reaction sequence. The synthesis
started from the bisphosphonium salt 2, which was easily prepared on a large scale
from a,a0-dichloro-p-xylene and triphenylphosphine in refluxing dimethylformanide
(DMF). The bis(triphenylphosnium) salt 2 was smoothly produced by a double
nucleophilic reaction. The latter compound and 3-thiophene carbaldehyde were
Scheme 1. Synthetic strategy for the synthesis of helically chiral pentacyclic systems 1a and 1b.

1008
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
subjected to a double Wittig olefination procedure leading to the bis(stilbene)-type
derivative 3a in 74% yield. The mixture gave rise to a violet fluorescent aspect in sol-
ution. To complete the synthesis of the helicene skeleton, alkenes 3a underwent a
double photocyclization, in dilute solution, in the presence of a stoichiometric
amount of iodine and an excess of propylene oxide.[19] The photolysis was performed
on a 200-mg scale per run in a 1-L reactor for about 5 h, to afford the expected
2,11-dithiapentahelicene 1a in 44% yield after purification by column chromato-
graphy. The relatively moderate yield of 44% for 1a is perhaps a consequence of
the unfavorable solubility properties of alkenes 3a in toluene, necessitating their
use as suspensions. No other isomer was isolated from the reaction mixture, indicat-
ing that the ring closure of 3a had occurred from the opposite side of the benzene
ring (Scheme 1).
Utilizing similar conditions to those described for the preparation of 1a, the
synthesis of compound 1b was attempted by the reaction of bisphosphonium salt
2
with 2-thiophene carbaldehyde followed by a photocylization reaction
(Scheme 1). However, 1b was isolated in 60% yield after column chromatography
and fully characterized by NMR and mass spectrometry. This result can be
explained by the higher solubility of alkenes 3b compared to alkenes 3a.
Following this synthetic approach, it was possible to prepare two thiahelicene
derivatives, namely 2,15- and 3,14-dithiaheptahelicenes. The second synthetic
approach may appear longer, because it was necessary to prepare the starting
bisphosphonium salt 4 (Scheme 2) on a gram scale in a four-step sequence involving
a Wittig reaction between p-methylbenzaldehyde and the phosphonium salt derived
from p-methylbenzyl chloride, leading to 4,40-dimethylstilbene 5 in 94% yield.
Alkenes 5 were then irradiated using a 500-W high-pressure mercury immersion
lamp on a 800-mg scale to afford 3,6-dimethylphenanthrene 6 in 90% yield. The
phenanthrene derivative was converted into its dibromide 7 through a double
benzylic bromination with N-bromosuccinimide (NBS) followed by a treatment with
triphenylphosphine in refluxing acetonitrile, which provided the bisphosphonium
salt 4, as a white solid, in 96% yield and an overall 64% yield.
Scheme 2. Synthetic pathway of bisphosphonium salt 4.

SYNTHESIS OF NEW THIAHELICENES
1009
Scheme 3. Synthetic strategy for the synthesis of helically chiral heptacyclic systems 9a and 9b.
The salt 4 was subjected to a double Wittig reaction with either 3- or 2-
thiophene carbaldehyde leading to the corresponding bis(stilbene)-type derivatives
8a and 8b in 75% and 65% yields, respectively (Scheme 3). The last step of the whole
synthetic strategy is the formation of the chiral heptacyclic systems. Thus, the pho-
tolysis of 8a carried out in toluene for about 7 h, on a 200-mg scale, afforded the
expected 2,15-dithiaheptahelicene 9a in 60% yield and an overall 26% yield over
Figure 1. (a) 1H NMR and (b) 13C NMR spectra of 9b in CDCl3.

1010
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
six steps. On the other hand, the photocyclization of alkenes 8b conducted in the
same conditions gave only 40% yield of 3,14-dithiaheptahelicene 9b.
3,14-Dithiaheptahelicene 9b is a light yellow solid. It shows a violet fluores-
cence when dissolved. It is characterized by 1H and 13C NMR spectroscopy.
Figure 1 shows the two NMR spectra.
Optical Properties
The ultraviolet (UV)–visible absorption spectra of the four dithia-helically
chiral systems 1a, 1b, 9a, and 9b have been recorded with a Hach-Lang-DR50000
spectrometer, in chloroform (10ꢀ5 M). The lowest energy absorption bands belong
to the p–pꢁ transitions.
Dithiapentaheicenes 1a and 1b have different absorption maxima (kAmbaxs ) at 246
and 263 nm, respectively. However, in the case of 2,15-dithiaheptahelicene 9a and
Abs
max
3,14-dithiaheptahelicene 9b, the absorption k
corresponds to 267 and 271 nm,
respectively.
Optical band gaps (EOpt) determined from the absorption edge of the solution
spectra are given in Table 1. The optical band gap varies from 3.05 eV (compound
9b) to 3.40 eV (compound 1a, Table 1). The gap energy was evaluated by the extra-
polation of the tangent to the first inflexion point in the UV curve.[20]
The UV-visible absorption spectrum of 3,14-dithiaheptahelicene 9b is shown in
Fig. 2. The sample shows a strong absorption below 400 nm (3.05 eV) with a
well-defined absorbance peak at around 271 nm (4.67 eV). The band gap can be
determined by fitting the absorption data to the direct transition equation by an
extrapolation of the linear portions of the curves to absorption equal to zero (Fig. 2):
Eg ¼ hn
where hn is the photon energy and Eg is the direct band gap determined by
UV-visible spectroscopy. The estimated band gap of compound 9b is found to be
3.05 eV.
It can be seen that the increase in conjugation length and the increased elec-
tronic density in hepta systems leads to a large bathochromic shift of an absorption
maximum, compared to pentacyclic systems.
In summary, four new symmetrical helically chiral aromatic compounds having
benzothiophene units were synthesized in good overall yields starting from readily
available and inexpensive materials. Among these new thiahelicenes, 3,14-dithiahep-
tahelicene showed the lowest band gap (3.05 eV) and the largest wavelength
Table 1. Physical properties of helically chiral dithia-helicenes 1a, 1b, 9a, and 9b
EOpt (eV)
Abs
max
Compound
k
(nm)
1a
1b
9a
9b
246
3.40
3.35
3.20
3.05
263
267
271

SYNTHESIS OF NEW THIAHELICENES
1011
Figure 2. Room-temperature optical absorbance spectrum of 3,14-dithiaheptahelicene 9b.
(271 nm). These new dithiahelicenes may also serve as model systems to investigate
the structure–property relationships with respect to the electronic, electrochemical,
photoconductive, and nonlinear optical properties of p-conjugated polymers.
EXPERIMENTAL
All reactions were performed under an argon atmosphere and were monitored
by thin-layer chromatography (TLC) Merck 60 F-254 silica-gel plates (layer thick-
ness 0.25 mm). Column chromatography was performed on silica gel (70–230 mesh)
using ethyl acetate and cyclohexane mixture as eluents. Melting temperatures were
determined on an Electrothermal 9002 apparatus and were reported uncorrected.
NMR spectra were recorded on a Bruker AC-300 spectrometer at 300 MHz (1H)
and 75 MHz (13C). All chemical shifts were reported as d values (ppm) relative to
internal tetramethylsilane. Toluene was distilled from sodium prior to use. Photocy-
clizations were carried out in a 1.5-L water-cooled quartz photoreactor equipped
with a high-pressure mercury immersion lamp [Heraeus TQ 500]. Mass spectra
(MS) were recorded on a Hewlett-Packard HP 5989 instrument. High-resolution
mass spectra (HRMS) were recorded on a matrix-assisted laser desorption=
ionization time-of-flight (MALDI-TOF) Perspective Biosystems Voyager DE-STR
instrument.
General Procedure A for Wittig Reaction
Sodium methoxide (1 M in methanol) was added over 0.5 h under Ar to a
refluxing solution of triphenylphosphonium salt and the corresponding aldehyde
in dry methanol (25 mL). Heating at reflux was continued for 3 h. The reaction
mixture was cooled to room temperature and concentrated under vaccum to half
its volume. Water was added, and the solution was extracted many times with a large

1012
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
volume of CH2Cl2. After drying and solvent evacuation, the residue was chromato-
graphed on silica gel. Solvents, yield, melting points, and data for individual
compounds are reported for each case.
General Procedure B for the Photocyclodehydrogenation Reaction
A solution (or a suspension in the cases of 3a and 8b) of the respective bis(stil-
bene) (1 equiv), iodine (1.2 equiv), and propylene oxide (100 equiv) in toluene (1.5 L)
was irradiated for 5–7 h, under Ar, in a photoreactor fitted with a water-cooled
immersion well and a high-pressure Hg lamp. Evaporation of the solvent and col-
umn chromatography (SiO2) yielded the pure racemic helicene. Experimental details
and specific data for individual compounds are given.
Bisphosphonium Salt (2)
Compound 2 was prepared from a,a0-dichloro-p-xylene (2 g, 11.4 mmol) and
triphenylphosphine (6.62 g, 25.21 mmol) in boiling dimethylformamide (DMF,
35 mL). The bisphosphonium salt was precipitated and filtered off at the end of
the reaction. Compound 2 was obtained as a white solid in 95% yield, mp > 300 ꢂC
(decomposed), and was used directly without further purification. 1H NMR
(300 MHz, CDCl3): d ¼ 5.38 (d, JH-P ¼ 13.2 Hz, 4H, 2 CH2-P), 6.94 (s, 4H),
7.66–7.75 (m, 30H) ppm;13C NMR (75 MHz, CDCl3): d ¼ 29.8 (d, JC-P ¼ 46.2 Hz,
2CH2-P), 117.07–134.99 (21C) ppm; 31P NMR (121.5 MHz, CDCl3): d ¼ 24.47
(s) ppm.
Bis-stilbene-Type Derivatives (3a)
Compounds 3a [(E, Z) isomers] were obtained from the bisphosphonium salt 2
(5 g, 6.34 mmol) and 3-thiophene carbaldehyde (1 mL, 11.4 mmol) in 74% yield
(2.45 g) according to procedure A. They were purified by column chromatography
using cyclohexane=ethyl acetate (90:10) as the eluent. 1H NMR (300 MHz, CDCl3):
d ¼ 6.55 (d, J ¼ 16.2 Hz, 2H); 6.94 (d, J ¼ 16.2 Hz, 2H), 7.15 (d, J ¼ 6.6 Hz, 2H), 7.33
(d, J ¼ 6.6 Hz, 2H), 7.34–7.60 (m, 6H) ppm;13C NMR (75 MHz, CDCl3): d ¼ 122.47,
122.88, 124.18, 124.45, 124.94, 125.03, 126.20, 126.29, 128.08, 128.34, 129.20, 129.26,
136.31, 136.95, 138.35, 140.17 ppm; MS (EI, 50 ev): m=z ¼ 294 ([M]þ, 65%).
2,11-Dithiapentahelicene (1a)
Compound 1a was obtained from alkenes 3a, in 44% yield, according to the
procedure B. It was purified by column chromatography using cyclohexane as the
eluent (Rf ¼ 0.41) and resulted as a light yellow solid, mp 50–52 ꢂC. 1H NMR
(300 MHz, CDCl3): d ¼ 7.85 (d, J ¼ 9 Hz, 2H), 7.91 (d, J ¼ 8.7 Hz, 2H), 8.00–8.13
(m, 4H), 8.73 (s, 2H) ppm; 13C NMR (75 MHz, CDCl3): d ¼ 119.79, 122.03,
126.28, 128.40, 129.05, 129.50, 135.53, 136.32, 137.49 ppm; ESI-MS: m=z ¼ 313.0
[M þ Na]þ. HRMS (MALDI-TOF) calcd. for C18H10S2Na [M þ Na]þ: 313.0121.
Found: 313.0135.

SYNTHESIS OF NEW THIAHELICENES
1013
Bis-stilbene-Type Derivatives (3b)
Compound 3b was obtained from 2 (1 g, 1.26 mmol) and 2-thiophene carbalde-
hyde (215 mL, 2.30 mmol) in 78% yield according to the procedure A. It was purified
by column chromatography using cyclohexane=ethyl acetate (98:2) as the eluent.
1
White solid, mp 149–151 ꢂC. H NMR (300 MHz, CDCl3): d ¼ 6.58 (d, J ¼ 11.7 Hz,
Hz, 2H), 6.7 (d, J ¼ 11.7 Hz, 2H), 6.9 (dd, J ¼ 4.8 and 3.9 Hz, 2H), 7.01 (d, J ¼ 3 Hz,
2H), 7.15 (d, J ¼ 4.8 Hz, 2H), 7.36 (s, 4H) ppm;13C NMR (75 MHz, CDCl3):
d ¼ 123.48, 125.52, 126.27, 126.56, 129.26, 129.48, 136.65, 139.84 ppm; MS (EI,
50 ev): m=z ¼ 294 ([M]þ, 70%).
3,10-Dithiapentahelicene (1b)
Compound 1b was obtained from 3b as a light yellow solid, in 60% yield,
according to procedure B. It was purified by column chromatography using cyclo-
hexane as the eluent (Rf ¼ 0.41), mp ¼ 25–27 ꢂC. 1H NMR (300 MHz, CDCl3):
d ¼ 7.71 (d, J ¼ 8.7 Hz, 2H), 7.83 (d, J ¼ 8.4 Hz, 2H), 7.86 (d, J ¼ 5.1 Hz, 2H), 7.98
(d, J ¼ 5.4 Hz, 2H), 8.13 (s, 2H) ppm; 13C NMR (75 MHz, CDCl3) d ¼ 119.79,
125.52, 126.90, 127.33, 129.05, 129.50, 135.53, 136.32, 137.49 ppm; ESI-MS: m=z ¼
313.0 [M þ Na]þ, HRMS (MALDI-TOF) calcd. for C18H10S2Na [M þ Na]þ:
313.0121. Found: 313.0139.
Bisphosphonium Salt (4)
The compound was prepared from 3,6-bis(bromomethyl)phenanthrene 7 (3 g,
8.24 mmol) and triphenylphosphine (4.75 g, 18.10 mmol) in boiling acetonitrile
(60 mL). The bisphosphonium salt precipitated after cooling at room temperature
and was filtered off. Compound 4 was obtained as a white solid in 96% yield, mp
1
300–302 ꢂC. H NMR (300 MHz, CD3OD): d ¼ 5.24 (d, JH-P ¼ 15 Hz, 4H, 2CH2-
P), 7.11–7.14 (m, 2H), 7.64–7.70 (m, 26H), 7.81–7.91 (m, 8H), 8.32 (s, 2H) ppm;
13C NMR (300 MHz, CD3OD): d ¼ 31.87 (d, JC-P ¼ 47.4 Hz, 2CH2-P), 119.01,
120.15, 127.70, 127.80, 127.92, 128.04, 128.87, 130.34, 130.82, 131.48, 131.78,
131.95, 133.74, 135.88, 136.01, 136.88, 136.92, 136.93 ppm;31P NMR (121.5 MHz,
CD3OD): d ¼ 23.70 (s) ppm.
4,4’-Dimethylstilbene (5)
4,40-Dimethylstilbene 5 [(E,Z) isomers] was prepared in 94% yield, from
p-methylbenzaldehyde (2 g, 16.65 mmol) and tolylmethyltriphenylphosphonium
chloride (7.37 g, 18.30 mmol), according to procedure A. It was purified by column
chromatography using cyclohexane=ethyl acetate (98:2) as the eluent and resulted
1
as a white solid, mp 165–167 ꢂC. H NMR (300 MHz, CDCl3): d ¼ 2.37 (s, 6H,
2CH3), 7.05 (s, 2H), 7.17 (m, 4H), 7.42 (m, 4H) ppm; 13C NMR (75 MHz, CDCl3):
d ¼ 21.30, 126.36, 127.68, 129.42, 134.78, 137.33 ppm; MS (EI, 70 ev): m=z ¼ 208
([M]þ, 78%).

1014
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
3,6-Dimethylphenanthrene (6)
The photolysis of 4,40-dimethylstilbene 5 according to procedure B gave
1
3,6-dimethylphenanthrene 6 as a white solid in 60% yield. H NMR (300 MHz,
CDCl3): d ¼ 2.63 (s, 6H), 6.97 (d, J ¼ 8.1 Hz, 2H), 7.65 (s, 2H), 7.77 (d, J ¼ 8 Hz,
2H), 8.48 (s, 2H) ppm; 13C NMR (75 MHz, CDCl3): d ¼ 22.17, 122.41, 125.82,
128.20, 128.68, 129.17, 130.12, 136.06 ppm; MS (EI, 70 ev): m=z ¼ 206 ([M]þ, 75%).
3,6-Bis(Bromomethyl)phenanthrene (7)
3,6-Dimethylphenanthrene (5.0 g, 24.27 mmol), N-bromosuccinimide (8.64 g,
48.54 mmol), and benzoylperoxide (0.011 g, 0.48 mmol) were dissolved in 20 mL of
anhydrous carbon tetrachloride under a nitrogen atmosphere. The mixture was
refluxed with a vigorous stirring at 80 ꢂC for 24 h under nitrogen and then cooled
to room temperature. The succinimide produced was filtered out with suction, and
water (25 mL) was added to the filtrate, which was extracted three times with diethyl
ether (60 mL). The organic layer was washed successively with saturated aqueous
sodium bicarbonate (30 mL) and sodium chloride solution (30 mL) and dried with
anhydrous potassium carbonate. After the evaporation of the solvent, the resulting
crude residue was purified by column chromatography with cyclohexane=ethyl acet-
1
ate (98:2) as the eluent to yield 8.45 g (80% yield) of 7; mp ¼ 142–144 ꢂC. H NMR
(300 MHz, CDCl3): d ¼ 4.84 (s, 4H, 2CH2-Br), 7.72 (dd, J ¼ 8.4 and 1.5 Hz, 2H), 7.83
(s, 2H), 7.96 (dd, J ¼ 8.4 and 1.5 Hz, 2H), 8.74 (d, J ¼ 1.2 Hz, 2H) ppm; 13C NMR
(75 MHz, CDCl3): d ¼ 33.87 (2CH2-Br), 113.85–138.12 (14Carom.) ppm; MS (EI,
70 ev): m=z ¼ 364 ([M]þ, 68%).
Bis-stilbene-Type Derivatives (8a)
Bis-stilbene-type derivatives 8a [(E,Z) isomers] were prepared from
bisphosphonium salt 4 (2 g, 2.24 mmol) and 3-thiophene carbaldehyde (360 mL,
1
0.45 mmol), in 75% yield, according to procedure A. H NMR (300 MHz, CDCl3):
d ¼ 6.68–7.56 (m, 5H), 7.61–7.91 (m, 9H), 8.47–8.82 (m, 4H) ppm;13C NMR
(75 MHz, CDCl3): d (ppm): 121.40, 121.52, 122.11, 122.28, 122.46, 122.54, 123.11,
123.24, 123.76, 123.88, 124.08, 124.51, 124.61, 125.70, 125.81, 126.33, 126.33,
126.53, 126.65, 126.87, 126.93, 127.00, 172.26, 127.47, 127.64, 127.78, 128.48,
128.53, 128.74, 128.87, 129.00, 129.26, 130.15, 130.36, 130.57, 131.61, 131.82,
134.96, 135.26 ppm; ESI-MS: m=z ¼ 417.0 [M þ Na]þ.
2,16-Dithiahepthahelicene (9a)
The photolysis of the bis-stilbene-type derivatives 8a according to procedure B
gave 2,16-dithiahepthahelicene 9a as a light yellow solid in 60% yield; mp
139–141 ꢂC. 1H NMR (300 MHz, CDCl3): d ¼ 7.15 (s, 2H), 7.20–7.49 (m, 6H),
7.70 (s, 2H), 7.83 (d, J ¼ 8.1 Hz, 2H), 8.53 (s, 2H) ppm; 13C NMR (75 MHz, CDCl3):
d ¼ 122.81, 126.22, 127.28, 128.33, 128.60, 128.81, 129.17, 129.27, 129.60, 130.43,
130.50, 130.57, 136.43 ppm; ESI-MS: m=z ¼ 413.0 [M þ Na]þ. HRMS
(MALDI-TOF) calcd. for C26H14NaS2 [M þ Na]þ: 413.04346. Found 413.04487.

SYNTHESIS OF NEW THIAHELICENES
1015
Bis-stilbene-Type Derivatives (8b)
Bis-stilbene-type derivatives 8b were prepared from bisphosphonium salt 4 (1 g,
1.12 mmol) and 2-thiophene carbaldehyde (200 mL, 1.02 mmol) according to pro-
cedure A. Workup and purification on column chromatography yielded 65% of a
1
yellow solid [(E,Z) isomers of 8b]. H NMR (300 MHz, CDCl3): d ¼ 6.76–7.28 (m,
8H), 7.38–7.88 (m, 8H), 8.39–8.78 (m, 2H) ppm;13C NMR (75 MHz, CDCl3):
d ¼ 121.40, 121.52, 122.11, 122.28, 122.46, 122.54, 123.11, 123.24, 123.76, 123.88,
124.09, 142.51, 124.61, 125.70, 125.81, 126.33, 126,53, 126.65, 126.87, 126.93,
127.00, 127.26, 127.47, 127.64, 127.78, 128.48, 128.53, 128.74, 128.87, 129.00,
129.26, 130.15, 130.36, 130.57, 131.61, 131.82, 134.96, 135.26, 135.58, 136.45 ppm;
ESI-MS: m=z ¼ 417.0 [M þ Na]þ.
3,14-Dithiahepthahelicene (9b)
The photolysis of bis-stilbene-type derivatives 8b according to procedure B
gave 3,14-dithiahepthahelicene 9b as a light yellow solid in 60% yield; mp
229–231 ꢂC. 1H NMR (300 MHz, CDCl3): d ¼ 6.24 (d, J ¼ 5.4 Hz, 2H); 6.60 (d,
J ¼ 5.4 Hz, 2H), 7.85–7.91 (m, 4H), 7.99 (d, J ¼ 8.4 Hz, 2H), 8.06 (s, 2H), 8.08 (d,
J ¼ 8.4 Hz, 2H) ppm; 13C NMR (75 MHz, CDCl3): d ¼ 121.34, 122.93, 124.06,
124.56, 125.03, 125,35, 127.00, 127.75, 127.86, 129.79, 132.15, 135.23, 135.90 ppm;
ESI-MS: m=z ¼ 413.0 [M þ Na]þ. HRMS (MALDI-TOF) calcd. for C26H14NaS2
[M þ Na]þ: 413.04346. Found 413.04479.
ACKNOWLEDGMENT
´ ´
The authors are grateful to DGRSRT (Direction Generale de la Recherche
´
Scientifique et de la Renovation Technologique) of the Tunisian Ministry of Higher
Education, Scientific Research, and Technology for the financial support.
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