Synthesis and characterization of a new chiral pentacyclic phosphine

Article abstract of DOI:10.1080/00397911.2011.596986

A new helically chiral pentacyclic phosphine, containing one thiophene ring, was prepared in good yield and purity via a five-step sequence involving a Wittig reaction, a palladium-catalyzed Mizoroki-Heck coupling, and classical oxidative photocyclization reactions. The investigation using ultraviolet-visible spectroscopy shows that the helicene precursor of the target helical phosphine as well as its phosphine oxide have interesting behaviors.

Full text of DOI:10.1080/00397911.2011.596986

This article was downloaded by: [University of Tennessee, Knoxville]
On: 21 March 2013, At: 05:42
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Synthesis and Characterization of a New
Chiral Pentacyclic Phosphine
Souad Moussa a , Faouzi Aloui a & Béchir Ben Hassine a
a Laboratoire de Synthèse Organique Asymétrique et Catalyse
Homogène (O1UR1201), Faculté des Sciences, Monastir, Tunisia
Accepted author version posted online: 09 Feb 2012.Version of
record first published: 18 Oct 2012.
To cite this article: Souad Moussa , Faouzi Aloui & Béchir Ben Hassine (2013): Synthesis and
Characterization of a New Chiral Pentacyclic Phosphine, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 43:2, 268-276
To link to this article: http://dx.doi.org/10.1080/00397911.2011.596986
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 43: 268–276, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.596986
SYNTHESIS AND CHARACTERIZATION OF A NEW
CHIRAL PENTACYCLIC PHOSPHINE
´
Souad Moussa, Faouzi Aloui, and Bechir Ben Hassine
Laboratoire de Synthese Organique Asymetrique et Catalyse Homogene
`
´
`
´
(O1UR1201), Faculte des Sciences, Monastir, Tunisia
GRAPHICAL ABSTRACT
Abstract A new helically chiral pentacyclic phosphine, containing one thiophene ring, was
prepared in good yield and purity via a five-step sequence involving a Wittig reaction, a
palladium-catalyzed Mizoroki–Heck coupling, and classical oxidative photocyclization
reactions. The investigation using ultraviolet–visible spectroscopy shows that the helicene
precursor of the target helical phosphine as well as its phosphine oxide have interesting
behaviors.
Keywords Heck reaction; helicene; phosphine; photocyclization; Wittig reaction
INTRODUCTION
Helicenes are an extremely attractive class of conjugated molecules consisting of
ortho-fused aromatic rings.[1–5] They combine the electronic properties afforded
by their extensive conjugated p system with the chiroptical properties[6,7] afforded
by their peculiar helixlike structure. However, interest in heterohelicenes has been
not merely speculative but also applicative because these molecules have a nicely
delocalized p-electron system and exhibit interesting opto- and photoelectronic
Received May 23, 2011.
Address correspondence to Bechir Ben Hassine, Laboratoire de Synthese Organique Asymetrique
´
et Catalyse Homogene (O1UR1201), Faculte des Sciences, Avenue de l’environnement, Monastir 5019,
`
´
`
Tunisia. E-mail: bechirbenhassine@yahoo.fr
´
268

NEW CHIRAL PENTACYCLIC PHOSPHINE
269
properties.[8,10] Recently, some potential applications of these helical compounds
have been discovered.[11] The preparation of helicenes has become an increasingly
important subject. Helicenes, especially heterohelicenes, are promising candidates
as chiral auxiliaries and ligands for various asymmetric reactions because of their
stable polyconjugated helical framework and the presence of heteroatoms, such as
sulfur, nitrogen, and oxygen. The heteropentahelicenes are the smallest group in
the helical family and exhibit intriguing electrical and optical properties.[12,13] Beside
carbohelicenes, many heterohelicenes have been investigated for various properties
and applications such as circularly polarized luminescence[14] and nonlinear optics.
Not only the main skeleton frameworks but also the substituted groups can determine
the properties of these compounds. In recent years, the preparation of heterohelicenes
has been studied extensively to exploit the unique properties of these molecules. How-
ever, thiahelicenes bearing phosphoryl groups were not sufficiently elaborated despite
their possible applications in various branches of chemistry.
The present work reports the synthesis of a new helically chiral pentacyclic system
1, containing one thiophene unit and bearing a bromine atom. The synthetic route
involves a Wittig reaction and Mizoroki–Heck coupling followed by oxidative photo-
cyclizations. The resulting bromothiahelicene was then converted into the correspond-
ing helical phosphine 2 through lithiation–phosphination. The new helicene derivatives
have been characterized by the usual 1H, 13C, and 31P NMR spectroscopic techniques.
Their optical properties have also been investigated and show interesting behaviors.
RESULTS AND DISCUSSION
The synthetic route to pentahelicene derivative 1 started from the synthesis
of the substituted alkenes 5 [(E, Z) isomers], which are obtained through Wittig
reaction between the phosphonium salt 3 and 2-thiophene carbaldehyde 4. The
photocyclization of diarylethenes 5 affords the phenanthrene-like system 6 in 85%
yield (Scheme 1).
This last one was reacted with an excess amount of 4-bromostyrene according to
the following conditions:[15] 1% of Hermann’s palladacycle [trans-di(m-acetato)-bis[o-
(di-o-tolylphosphino)benzyl]dipalladium] as the catalyst, sodium acetate as the base,
and N,N-dimethylacetamide (DMA) as the solvent. The mixture was heated at 140ꢀC
for about 48 h to give the desired diarylethene 7 in 76% yield (Scheme 2). The resulting
alkene 7 was subjected to photocyclization in toluene, on a 200-mg scale per run, for
about 3 h. The photolysis was carried out in the presence of a stoichiometric amount
Scheme 1. Synthetic route toward the phenanthrene-like derivative 6.

270
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
Scheme 2. Synthetic strategy for the synthesis of the helically chiral phosphine 2.
of iodine as an oxidizing agent and an excess of propylene oxide[16] to give the expected
bromothiapentahelicene 1 in 64% yield, after purification by column chromatography.
Good analytical data were obtained for the helically chiral compound 1, which
is a white solid. Characteristic spectroscopic data of this compound consisted of a
1
doublet H NMR resonance at 8.85 ppm for H-13 (J ¼ 1.5 Hz) in CDCl3 at room
temperature (Fig. 1).
No other isomer was isolated from the reaction mixture, indicating that the
ring closure of alkene 7 had occurred from the opposite side of the tricyclic system.
Especially, the anthracene-like derivative 8 (Fig. 2) has not been formed through the
cyclization step, because this kind of regioisomer should display characteristic singles
1
in H NMR for both H-6 and H-13 at low field.[17,18]
Figure 1. 1H NMR spectra of the thiapentahelicene 1, recorded in CDCl3.

NEW CHIRAL PENTACYCLIC PHOSPHINE
271
Figure 2. Chemical structure of the anthracene-like derivative 8.
The last step of the synthetic sequence is formation of the phosphine, which can
be achieved through lithiation–phosphinylation of the bromohelicene 1. Thus, the
metallation of 1 proceeded well via metal–halogen exchange using n-butyllithium at
ꢁ78 ꢀC. Subsequent treatment of the resulting lithiated species with chlorodiphenyl-
phosphine yielded the desired phosphinohelicene 2 in 78% yield and in 25% overall
yield over five steps, starting from the readily available 2-thiophene carbaldehyde 4
(Scheme 2). This resulting helically chiral trivalent phosphine was a slightly air-
sensitive solid. It is better handled and stored under an inert atmosphere or treated
with a 35% hydrogen peroxide solution to give the corresponding phosphine oxide
9 in excellent yield. Compound 9 is more stable than phosphine 2 and could be
resolved, by high-performance liquid chromatography (HPLC), using a column
packed with cellulose-tris(3,5-dimethylphenyl-carbamate) and n-heptane=2-propanol
(80:20) mixture as the mobile phase.[19]
Optical Properties
The optical properties of the pentahelicene derivatives 1 and 9 were investigated
using the UV-vis absorption for dilute chloroform solutions (Fig. 3).[20]
Figure 3. Absorption spectrum of compounds 1 and 9 obtained for CHCl3 solutions. (Figure is provided
in color online.)

272
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
Table 1. Physical proprieties of the helically chiral
pentahelicenes 1 and 9
EOpt (eV)
Abs
max
Compound
k
(nm)
1
9
257
288
3.43
3.32
The results summarized in Table 1 show an absorption maxima at 257 nm for 1
and 288 nm for 9, respectively.
The UV absorption results show that the optical band gap of these new
helicene derivatives was lower than 3.5 eV. This result can be originated from the
formation of aggregation to p ꢁ pꢂ stacking or intermolecular interaction caused
by their nonplanar structures. Moreover, the incorporation of a (POPh2) group
instead of the bromine atom in helicene 1 resulted in decreasing the gap energy of
the corresponding derivative. The thiapentahelicenes 1 and 9 show greater optical
band gap than the functionalized thiaheptahelicene derivatives, which have been
developed by Bossi et al., indicating that the optical properties are not significantly
affected by the electron delocalization but are affected by the functional groups
linked to the helicene backbone.[21]
CONCLUSION
In this work, we have developed a straightforward method for the preparation
of a new helical chiral phosphine starting from readily available and inexpensive
materials. We completed the synthesis of the framework of 2 in five steps, with an
overall yield of 25%, under mild conditions following an easy purification. The
new chiral phosphine could serve as a metal-chelating agent leading to helical metal-
lated complexes capable of catalyzing asymmetric reactions.
EXPERIMENTAL
All reactions were performed under an argon atmosphere and were moni-
tored by thin-layer chromatography (TLC) Merck 60 F-254 silica-gel plates (layer
thickness 0.25 mm). Column chromatography was performed on silica gel (70–230
mesh) using ethyl acetate and cyclohexane mixture as eluents. Melting tempera-
tures 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), 121.5 MHz (31P), and 75 MHz (13C). All chemical shifts were
reported as d values (ppm) relative to internal tetramethylsilane. Toluene, meth-
anol, tetrahydrofuran, and dichloromethane were distilled prior to use. Photocycli-
zations 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.

NEW CHIRAL PENTACYCLIC PHOSPHINE
273
Diarylethenes (5)
A sodium methoxide solution (120 mL, 1 M in methanol) was added over 0.5 h
under Ar to a solution of the triphenylphosphonium salt 3 (1 g, 1.95 mmol) and
2-thiophene carbaldehyde (0.14 mL, 1.5 mmol) in dry methanol (25 mL). Stirring
was continued for 3 h. The reaction mixture was concentrated under vaccum to half
its volume. Water was added, and the solution was extracted three times with a large
volume of CH2Cl2. After drying and solvent evacuation, the residue was chromato-
graphed on silica gel using cyclohexane = ethyl acetate (98: 02) as the eluent to yield
1
290 mg (80%) of compounds 5 [(E, Z) isomers]; H NMR (300 MHz, CDCl3): d
(ppm): 6.60 (d, J ¼ 12 Hz, 2H), 6.91 (m, 1H), 6.94 (d, J ¼ 16 Hz, 2H), 7.01–7.12 (m,
2H), 7.20–7.48 (m, 4H); 13C NMR (75 MHz, CDCl3): d (ppm): 121.31, 121.55,
122.53, 124.04, 124.81, 125.84, 126.59, 126.67, 127.02, 127.57, 127.76, 127.80,
128.48, 130.63, 131.76. 131.86, 135.97, 136.25, 139.39, 142.53.
Procedure a for the Photocyclization Reactions A
Iodine (1.1 equiv.) was added to a solution of the olefin in toluene. The solution
was degassed for 15–30 min, and propylene oxide (50 equiv.) was added. Irradiation
was performed using a falling-film photoreactor and a high-pressure Hg-vapor lamp
(500 W, Heraeus). The argon flow was maintained throughout the irradiation. The
reaction was monitored by TLC. Then the reaction mixture was concentrated in
vacuum, and the crude product was purified by column chromatography on silica gel.
Phenanthrene-Like System (6)
Compound 6 was obtained from alkenes 5, in 85% yield, according to the
procedure A. It was purified by column chromatography using cyclohexane as the
eluent and resulted as a white solid; mp ¼ 142–144 ꢀC; 1H NMR (300 MHz, CDCl3):
d (ppm): 7.61 (m, 2H), 7.7 (d, J ¼ 9 Hz, 1H), 7.8 (d, J ¼ 8.7 Hz, 1H), 7.9 (d, J ¼8.4 Hz,
1H), 7.92 (d, J ¼ 5.1 Hz, 1H), 8.46 (d, J ¼ 1.5 Hz, 1H); 13C NMR (75 MHz, CDCl3): d
(ppm): 124.62, 124.79, 126.19, 126.44, 127.77, 128.61, 129.44, 130.18, 130.47, 131.85,
134.97, 138.25; ESI-MS: m=z ¼ 263.1 [Mþ].
Diarylethene (7)
A solution of the thiophene-like system 6 (1 g, 3.80 mmol) and dry sodium
acetate (342 mg, 4.18 mmol) in N,N-dimethylacetamide (8 mL) was placed in a
double-necked flask fitted with a septum, repeatedly degassed, and purged with
argon. To this was then added 0.7 mL of 4-bromostyrene (5.32 mmol), and the
mixture was heated to 100 ꢀC. When this temperature was reached, a solution of
the Herrmann’s catalyst (35 mg, 1%) in N,N-dimethylacetamide (3 mL) was added,
and the reaction mixture was heated to 140 ꢀC. Heating was maintained for about
48 h. The reaction was quenched by an addition of 5% HCl solution, stirred for 30
min at room temperature, and then extracted with CH2Cl2. The combined layers were
dried over MgSO4 and evaporated to dryness. After column chromatography with
cyclohexane = ethyl acetate 90:10 as the eluent, the final product 7 was obtained in

274
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
1
76% yield (1.05 g) as a light yellow solid; mp ¼ 177–149 ꢀC; H NMR (300 MHz,
CDCl3): d (ppm): 7.22 (d, J ¼ 16.5 Hz, 1H, Hvinyl), 7.35 (d, J ¼ 16.5 Hz, 1H, Hvinyl),
7.44–7.55 (m, 4H), 7.63 (d, J ¼ 5.4 Hz, 1H), 7.73 (d, J ¼ 8.7 Hz, 1H), 7.77 (dd,
J ¼ 8.4 Hz, and J ¼ 1.8 Hz, 1H), 7.89 (d, J ¼ 8.7 Hz, 1H), 7.93 (d, J ¼ 8.7 Hz, 1H),
8.04 (d, J ¼ 5.4 Hz, 1H), 8.35 (s, 1H); 13C NMR (75 MHz, CDCl3): d (ppm):
121.21, 121.84, 122.31, 123.04, 123.14, 125.15, 126.48, 128.31, 128.43, 129.38,
129.92, 129.98, 131,02, 132.25, 135,37, 136.30, 136.66, 138.27.
Bromohelicene (1)
The photocyclization of 200 mg (0.41 mmol) of compound 7 in 1 L of toluene
yielded 127 mg of compound 1 (64%) as a white solid, after column chromatography
on silica gel (eluent: cyclohexane = ethyl acetate 98:02); 1H NMR (300 MHz, CDCl3):
d (ppm): 7.5 (d, J ¼ 5.4 Hz, 1H), 7.67 (dd, J ¼ 8.7 Hz and J ¼ 1.5 Hz, 1H), 7.78 (d,
J ¼ 8.4 Hz, 1H), 7.90–7.82 (m, 5H), 7.96 (d, J ¼ 8.4 Hz, 1H), 8.11 (d, J ¼ 8.4 Hz,
1H), 8.85 (s, 1H); 13C NMR (75 MHz, CDCl3): d (ppm): 119.15, 122.15, 124.56,
125.37, 125.97, 126.01, 126.28, 126.85, 127.26, 127.48, 128.79, 129.66, 129.69,
131.52, 131.66, 131.78, 131.88, 132.59, 136.11, 140.00. Anal. calcd. for C20H11BrS:
C, 66.13; H, 3.05. Found: C, 66.07; H, 3.03.
Diphenylphosphinohelicene (2)
To a solution of the bromothiapentahelicene 1 (0.2 g, 0.55 mmol) in anhydrous
THF (5 mL) was added 300 mL of n-BuLi (2 M in hexane), under argon. The mixture
was stirred at ꢁ78 ꢀC for 1 h. Then a solution of chlorodiphenylphosphine (110 mL,
0.60 mmol) in THF (3 mL) was added dropwise at ꢁ78 ꢀC. The resulting mixture
was stirred overnight at room temperature. The solution was then cooled at 0 ꢀC,
and a 30% aqueous NaOH solution was added dropwise. The organic phase was
extracted with ether under argon, dried over MgSO4, and filtered through a short
silica-gel column with cyclohexane = ethyl acetate (90:10) as the eluent to afford 2
1
as a white solid in 78% yield; H NMR (300 MHz, CDCl3): d (ppm): 7.08–7.15 (m,
1H), 7.19–7.31 (m, 8H), 7.36–7.41 (m, 2H), 7.67–79 (m, 9H), 8.52 (d, J ¼ 8.4 Hz
1H); 13C NMR (75 MHz, CDCl3): d (ppm): 120.03, 123.65, 124.50, 124.59, 124.94,
125.13, 125.31, 125.72, 126.54 (d, Jcp ¼ 2.4 Hz, CH), 126.69, 126.93, 127.33, 127.42,
127.45, 127.492, 127.51, 127.54, 128.01 (d, Jcp ¼ 1.95 Hz, CH), 128.93, 130.29,
130.80, 131.72, 132.09, 132.12, 132.37 (d, Jcp ¼ 2.32 Hz, CH), 134.49, 134.82,
135,80 (d, Jcp ¼ 7.57 Hz, C), 135.92, 135.96, 136.04 (d, Jcp ¼ 8.6 Hz, C),136.18 (d,
Jcp ¼ 12.6 Hz, C), 142.32; 31P NMR (121.5 MHz, CDCl3): d (ppm): ꢁ16.22 (s);
ESI-MS: m=z ¼ 468.1 [Mþ].
Diphnenylphosphine Oxide 9
A 35% hydrogen peroxide solution (15 mL) was added at room temperature to a
solution of phosphine 2 (50 mg, 0.106 mmol) in 15 mL of dichloromethane. The result-
ant mixture was stirred vigorously at room temperature until the reaction was completed
(30 min, monitored by TLC). The organic layer was separated, and the aqueous phase
was extracted three times with dichloromethane. The organic layers were combined and
dried over MgSO4, and the solvent was evaporated to give 84 mg (94%) of pure

NEW CHIRAL PENTACYCLIC PHOSPHINE
275
diphenylphosphine oxide 9; 1H NMR (300MHz, CDCl3): d (ppm): 7.10–7.90 (m, 1H),
7.34–7.42 (m, 6H), 7.36–7.41 (m, 2H), 7.47 (dd, J¼ 7.8 Hz, J ¼ 1.2 Hz, 1H), 7.52–7.59
(m, 2H), 7.65–7.75 (m, 4H), 7.79–7.98 (m, 6H), 8.43 (d, J¼ 8.7Hz, 1H); 13C NMR
(75MHz, CDCl3): d (ppm): 121.56, 125.24, 126.58, 126.79, 126.85, 127.72, 127.95,
128.14, 128.37, 128.78 (d, Jcp ¼ 3.37 Hz), 129.07, 130.17, 131.89, (d, Jcp ¼ 3.22 Hz),
132.09, 132.14, 132.25 (d, Jcp¼ 3.30Hz, C), 132.27, 132.63, 133.16, 136.68, 136.83;
31P NMR (121MHz, CDCl3): d (ppm): 24.50 (s), ESI-MS: m=z ¼ 484.1 [Mþ]. HRMS
(MALDI-TOF) calcd. for C32H21OPS [Mþ]: 484.10486. Found: 848.10507.
ACKNOWLEDGMENT
´ ´
The authors are grateful to Direction Generale de la Recherche Scientifique of the
Tunisian Ministry of Higher Education and Scientific Research for financial support.
REFERENCES
1. Baldoli, C.; Bossi, A.; Giannini, C.; Licandro, E.; Maiorana, S.; Perdicchia, D.; Schiavo,
A. Novel and efficient approach to (Z)-1,2-bis(benzodithienyl)ethane precursors of
tetrathia[7]helicenes. Synlett 2005, 1137–1141.
2. Maiorana, S.; Papagni, A.; Licandro, E.; Annunziata, R.; Parravidino, P.; Perdicchia,
D.; Giannini, C.; Bencini, M.; Clays, K.; Persoons, A. A convenient procedure for the
synthesis of tetrathia[7]helicene and the selective a-functionalisation of terminal thiophene
ring. Tetrahedron 2003, 59, 6481–6488.
3. (a) Nakano, K.; Hidehira, Y.; Takahashi, K.; Hiyama, T.; Nozaki, K. Stereospecific
synthesis of hetero[7]helicenes via the palladium-catalyzed double N-arylation and
intramolecular O-arylation. Angew. Chem., Int. Ed. 2005, 44, 7136–7138; (b) Rajca, A.;
Miyasaka, M.; Pink, M.; Wang, H.; Rajca, S. Helically annelated and cross-conjugated
oligothiophenes: asymmetric synthesis, resolution, and characterization of a carbonꢁsulfur
[7]helicene. J. Am. Chem. Soc. 2004, 126, 15211–15222.
4. (a) Carreno, M. C.; Gonzalez-Lopez, M.; Urbano, A. Efficient asymmetric synthesis of
[7]helicene bisquinones. Chem. Commun. 2005, 611–613; (b) Ogawa, Y.; Toyama, M.;
Karikomi, M.; Seki, K.; Haga, K.; Uyehara, T. Synthesis of chiral [5]helicenes using
aromatic oxy-Cope rearrangement as a key step. Tetrahedron Lett. 2003, 44, 2167–2170.
5. Tanaka, K.; Kitahara, Y.; Suzuki, H.; Osuga, H.; Kawai, Y. A. Novel route to disubsti-
tuted [7]thiaheterohelicene via biaryl- and carbonyl-coupling reactions. Tetrahedron Lett.
1996, 37, 5925–5928.
6. Larsen, J.; Dolbecq, A.; Bechgaard, K. Synthesis of unsubstituted thia[5]–[9] and [13]
heterohelicenes. Acta Chem. Scand. 1996, 50, 83–89.
7. Collins, S. K.; Vachon, M. P. Unlocking the potential of thiaheterohelicenes: Chemical
synthesis as the key. Org. Biomol. Chem. 2006, 4, 2518–2524.
8. Caronna, T.; Sinisi, R.; Catellani, M.; Luzzati, S.; Abbate, S.; Longhi, G. Chiroptical
properties of some monoazapentahelicenes. Synth. Met. 2001, 119, 79–80.
9. Tian, Y. H.; Park, G.; Kertesz, M. Electronic structure of helicenes, C2S helicenes, and
thiaheterohelicenes. Chem. Mater. 2008, 20, 3266–3277.
10. Rajca, A.; Pink, M.; Xiao, S.; Miyasaka, M.; Rajca, S.; Das, K.; Plessel, K. Functiona-
lized thiophene-based [7]helicene: Chirooptical properties versus electron delocalization.
J. Org. Chem. 2009, 74, 7504–7513.
11. Sahasithiwat, S.; Mophuang, T.; Menbangpung, L.; Kamtonwong, S.; Sooksimuang, T.
3,12-Dimethoxy-7,8-dicyano-[5]helicene as a novel emissive material for organic
light-emitting diode. Synthetic Metals 2010, 160, 1148–1152.

276
S. MOUSSA, F. ALOUI, AND B. BEN HASSINE
12. (a) Champagne, B.; Andre, J. M.; Botek, E.; Licandro, E.; Maiorana, S.; Bossi, A.; Clays,
K.; Persoons, A. Theoretical design of substituted tetrathia-[7]-helicenes with large
second-order nonlinear optical responses. Chem. Phys. Chem. 2004, 5, 1438–1442; (b)
Wigglesworth, T. J.; Sud, D.; Norsten, T. B.; Lekhi, V. S.; Branda, N. R. Chiral discrimi-
nation in photochromic helicenes. J. Am. Chem. Soc. 2005, 127, 7272–7273; (c) Furche, F.;
Ahlrichs, R.; Wachsmann, C.; Weber, E.; Sobanski, A.; Vogtle, F.; Grimme, S. Circular
dichroism of helicenes investigated by time-dependent density functional theory. J. Am.
Chem. Soc. 2000, 122, 1717–1724; (d) Xu, Y.; Zhang, Y. X.; Sugiyama, H.; Umano, T.;
Osuga, H.; Tanaka, K. (P)-Helicene displays chiral selection in binding to Z-DNA. J.
Am. Chem. Soc. 2004, 126, 6566–6567; (e) Nuckolls, C.; Shao, R.; Jang, W.-G.; Clark,
N. A.; Walba, D. M.; Katz, T. Electro-optic switching by helicene liquid crystals. J. Chem.
Mater. 2002, 14, 773–776; (f) Sugiura, H.; Takahira, Y.; Yamaguchi, M. Functionalized
[3þ3] cycloalkanes: Substituent effect on self-aggregation by nonplanar p–p interactions.
J. Org. Chem. 2005, 70, 5698–5708; (g) Verbiest, T.; Van Elshocht, S.; Kauranen, M.;
Hellemans, L.; Snauwaert, J.; Nuckolls, C.; Katz, T. J.; Persoons, A. Second-order
nonlinear optical properties of highly symmetric chiral thin films. Science 1998, 282, 913–915.
13. Gorner, H.; Stammel, C.; Mattay, J.; Mattay, J. Excited state behaviour of pentahelicene
dinitriles. J. Photochem. Photobiol. A: Chem. 1999, 120, 171–179.
14. Field, J. E.; Muller, G.; Riehl, J. P.; Venkataraman, D. Efficient thia-bridged triarylamine
heterohelicenes: Synthesis, resolution, and absolute configuration. J. Am. Chem. Soc.
2003, 125, 11808–11809.
15. (a) Aloui, F.; El Abed, R.; Guerfel, T.; Ben Hassine, B. Synthesis and x-ray analysis of a
new [6]helicene. Synth. Commun. 2006, 11, 1557–1567; (b) Aloui, F.; El Abed, R.;
Marinetti, A.; Ben Hassine, B. Synthesis and characterization of new hexahelicene
derivatives. Tetrahedron Lett. 2007, 48, 2017–2020; (c) El Abed, R.; Aloui, F.; Genet, J.
P.; Ben Hassine, B.; Marinetti, A. Synthesis and resolution of 2-(diphenylphosphino)-
heptahelicene. J. Organomet. Chem. 2007, 692, 1156–1160.
16. Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. Improved methodology for photocyliza-
tion reactions. J. Org. Chem. 1991, 56, 3769–3775.
17. (a) Harrowven, D. C.; Nunn, M. I. T.; Fenwick, D. R. [5]Helicenes by tandem radical cycli-
sation. Tetrahedron Lett. 2002, 43, 7345–7347; (b) Martin, R. H.; Marchant, M.-J.; Baes,
M. Rapid synthesis of hexa- and heptahelicenes. Helv. Chim. Acta 1971, 54, 358–360; (c)
Soudhakar, A.; Katz, T. J. Directive effect of bromine on stilbene photocyclizations: An
improved synthesis of [7]helicene. Tetrahedron Lett. 1986, 27, 2231–2234.
18. Murguly, E.; McDonald, R.; Branda, N. R. Chiral discrimination in hydrogen-bonded
[7]helicenes. Org. Lett. 2000, 2, 3169–3172.
19. (a) Aloui, F.; El Abed, R.; Marinetti, A.; Ben Hassine, B. Synthesis and resolution of a new
helically chiral azahelicene. Tetrahedron Lett. 2008, 49, 4092–4095; (b) Aloui, F.; El Abed,
R.; Marinetti, A.; Ben Hassine, B. A new approach to 3,14-dihydroxyhexahelicene: Resol-
ution and attribution of the absolute configuration. C. R. Chim. 2009, 12, 284–290.
20. (a) Rabinowitz, R.; Marcus, R. Direct synthesis of p-sytyryldiphenylphosphine. J. Org.
Chem. 1961, 26, 4157–4158; (b) Kima, C.; Marks, T. J.; Facchetti, A.; Schiavo, M.; Bossi,
A.; Maiorana, S.; Licandro, E.; Todescato, F.; Toffanin, S.; Muccini, M.; Graiff, C.;
Tiripicchio, A. Synthesis, characterization, and transistor response of tetrathia-[7]-helicene
precursors and derivatives. Organic Electronics 2009, 10, 1511–1520.
21. Bossi, A.; Licandro, E.; Maiorana, S.; Rigamonti, C.; Righetto, S.; Stephenson, G. R.;
Spassova, M.; Botek, E.; Champagne, B. Theoretical and experimental investigation of
electric field induced second harmonic generation in tetrathia[7]helicenes. J. Phys. Chem.
C 2008, 112, 7900–7907.