Synthesis, X-Ray analysis, and evaluation of the optoelectronic properties of a new thia[6]helicene

Article abstract of DOI:10.1080/00397911.2010.534572

The synthesis and structural characterization of a new hexahelicene derivative is reported. This compound features a new type of structure bearing a bromine atom. Suitable crystals of the latter indicate that its conformation closely resembles that of the

Full text of DOI:10.1080/00397911.2010.534572

This article was downloaded by: [University Of Pittsburgh]
On: 11 October 2014, At: 10:22
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, X-Ray Analysis, and Evaluation
of the Optoelectronic Properties of a
New Thia[6]helicene
Souad Moussa a , Faouzi Aloui a , Pascal Retailleau b & Béchir Ben
Hassine a
a Laboratoire de Synthèse Organique Asymétrique et Catalyse
Homogène, Faculté des Sciences , Monastir , Tunisia
b ICSN-CNRS , Gif sur Yvette , France
Accepted author version posted online: 06 Sep 2011.Published
online: 16 Dec 2011.
To cite this article: Souad Moussa , Faouzi Aloui , Pascal Retailleau & Béchir Ben Hassine (2012)
Synthesis, X-Ray Analysis, and Evaluation of the Optoelectronic Properties of a New Thia[6]helicene,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 42:7, 1010-1018, DOI: 10.1080/00397911.2010.534572
To link to this article: http://dx.doi.org/10.1080/00397911.2010.534572
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the
“Content”) contained in the publications on our platform. However, Taylor & Francis,
our agents, and our licensors make no representations or warranties whatsoever as to
the accuracy, completeness, or suitability for any purpose of the Content. Any opinions
and views expressed in this publication are the opinions and views of the authors,
and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content
should not be relied upon and should be independently verified with primary sources
of information. Taylor and Francis shall not be liable for any losses, actions, claims,
proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or
howsoever caused arising directly or indirectly in connection with, in relation to or arising
out of the use of the Content.
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. Terms &
Conditions of access and use can be found at http://www.tandfonline.com/page/terms-
and-conditions

Synthetic Communications1, 42: 1010–1018, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.534572
SYNTHESIS, X-RAY ANALYSIS, AND EVALUATION OF
THE OPTOELECTRONIC PROPERTIES OF A NEW
THIA[6]HELICENE
Souad Moussa,1 Faouzi Aloui,1 Pascal Retailleau,2 and
1
´
Bechir Ben Hassine
Laboratoire de Synthese Organique Asymetrique et Catalyse Homogene,
1
`
´
`
´
Faculte des Sciences, Monastir, Tunisia
2ICSN-CNRS, Gif sur Yvette, France
GRAPHICAL ABSTRACT
Abstract The synthesis and structural characterization of a new hexahelicene derivative is
reported. This compound features a new type of structure bearing a bromine atom. Suitable
crystals of the latter indicate that its conformation closely resembles that of the unsubsti-
tuted [6]helicene, whose idealized symmetry is C2. The optoelectronic properties of this
helical hexacyclic system were determined and exhibit a very interesting behavior.
Keywords Helicenes; optical band gap; photodehydrocyclization; thiahelicenes; Wittig
reaction
Received September 27, 2010.
´
Address correspondence to Bechir Ben Hassine, Laboratoire de Synthese Organique Asymetrique
et Catalyse Homogene (O1UR1201), Faculte des Sciences, Avenue de l’environnement, 5019 Monastir,
`
´
`
´
Tunisia. E-mail: bechirbenhassine@yahoo.fr
1010

NEW THIA[6]HELICENE
1011
INTRODUCTION
Heterohelicenes are formed by ortho-condensed aromatic or heteroaromatic
rings. The steric interactions arising in this type of compound do not allow planarity
for molecules with sequences of five or more rings and cause the p-conjugated
systems to get distorted into helices, which are intrinsically chiral structures.[1] Fur-
thermore, enantiomerically enriched helicenes have been used as building blocks for
helical conjugated polymers,[2] helical ligands,[3] structures that act as catalysts[4] for
enantioselective transformations, and asymmetric inducers.[5] The incorporation of
thiophene rings into polycyclic aromatic frameworks has led to considerable success
in the design and synthesis of unique organic semiconductors[6] for organic field
effect transistors and high conductivity.[7] [n]-Helicenes constructed through such
modification have precisely ordered structures as a result of both the helical conju-
gation and the stiff structure.[8] These structures, in particular heterohelicenes,
exhibit interesting opto- and photo-electronic properties.[9]
The present work describes a four-step synthesis of a new helically chiral
hexacyclic system, containing one thiophene ring, over a photochemical route. The
crystallization of this helically chiral compound by slow evaporation of a methylene
chloride=hexane solution afforded single crystals suitable for x-ray diffraction studies.
RESULTS AND DISCUSSION
The synthetic route to thia[6]helicene 1 began with the Wittig condensation of
the benzothiophene-2-carboxaldehyde 2 with phosphonium salt 3,[10] using sodium
methoxide as the base and methanol as the solvent. The mixture was stirred and
gently heated for 3 h at 50 ꢀC to give the desired styryl derivatives 4a and b in 88%
yield as a mixture of cis and trans isomers (cis=trans ¼ 4:6). The resulting diary-
lethenes 4a and b were subjected to photocyclization in toluene for about 3 h in
the presence of iodine, using a 500-W high-pressure mercury immersion lamp, and
provided the expected benzo[c]phenanthrene system 5 in 76% yield after purification
by column chromatography (Scheme 1).
The benzo[c]phenanthrene system 5 and 4-bromostyrene (1.5 equiv) underwent
a Mizoroki–Heck coupling using 1% of Hermann’s catalyst, sodium acetate as the
base, and N,N-dimethylacetamide (DMA) as the solvent, according to Scheme 1.
The mixture was heated at 140 ꢀC for about 48 h to afford the desired diarylethelene
6 in 79% yield. The coupled product is assumed to have an (E)-stereochemestry at the
1
double bond, based on the mechanism of the Heck reaction and confirmed by H
NMR study. The (Z)-isomer was neither isolated nor unambiguously identified as
a minor product in the reaction mixture. The resulting diarylethene 6 was then sub-
jected to photocyclization in toluene for about 3 h, in the presence of a stoichiometric
amount of iodine as an oxidising agent and an excess of propylene oxide,[11] on a 150-
mg scale to give the expected 2-bromothia[6]helicene 1 in 65% yield (Scheme 1).
Suitable crystals of compound 1 were obtained as pale yellow plates by the slow
evaporation of a methylene chloride=hexane solution. The substance crystallizes in
the form of a racemate. It is stable in air and light. The x-ray analysis of the thia[6]-
helicene 1 was carried out on a single crystal obtained from the racemic mixture as
˚
shown in Fig. 1. The bond lengths are in the range of 0.93–1.46 A. The torsion angles

1012
S. MOUSSA ET AL.
Scheme 1. Synthetic strategy for the synthesis of the bromothiahexahelicene 1.
along the inner helical rim (C2– C3– C7– C11, C3– C7– C11– C15, C7– C11– C15– C19,
and C11– C15– C19– C24), which vary from 6.9ꢀ to 33.4ꢀ, are also a convenient mea-
sure of the helicity and are in accordance with those observed in other hexahelicenes.
The intensity data were collected at room temperature on a Bruker Smart CCD
˚
diffractometer (using a graphite monochromated CuKa radiation, k ¼ 1.54180 A),
and crystallographic and experimental details are summarized in Table 1. The struc-
ture was solved by direct methods and refined by full matrix least-squares procedures
(SHELX-97)[12] first with isotropic thermal parameters and then with anisotropic
Figure 1. Crystal structure of (ꢁ)-1: ORTEP drawing, selected dihedral angles (ꢀ), and bonding distances
˚
(A) of 1. (Figure is provided in color online.)

NEW THIA[6]HELICENE
1013
Table 1. Crystal data and structure refinement
for compound 1
Parameter
Value
Formula
FW
C24H13BrS
413.31
Crystal system
Space group
monoclinique
P21=n
˚
a (A)
13.3335(4)
7.2326(2)
18.2038(13)
90
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
94.147(7)
90
3
˚
V (A )
1750.90(14)
4
1.568
Z
Dx (mg ꢄ mꢃ3
)
F(0000)
Crystal size (mm)
m (mmꢃ1
832
0.10 ꢅ 0.10 ꢅ 0.10
4.33
)
thermal parameters in the last cycles of refinement for all the nonhydrogen atoms.
The hydrogen atoms were introduced into the geometrically calculated positions
and refined riding on the corresponding parent atoms. All six fused rings show
distortion from planar arrangement.
OPTICAL PROPERTIES
The optical properties of the synthesized 2-bromo-11-thiahexahelicene were
investigated using ultraviolet (UV)–visible absorption in dilute CHCl3 solution as
shown in Fig. 2. The UV–visible spectrum of the compound exhibit a strong absorp-
tion in the region of 300–410 nm due to the p–pꢂ and nꢃpꢂ electronic transitions.[13]
However, the band corresponds to the highest occupied molecular orbital (HOMO)=
lowest unoccupied molecular orbital (LUMO) energy gap, which depends on the
nature and efficiency of the conjugated p system. The optical band gap (EgOpt
was estimated using the following equation[14]
)
:
EgOpt ¼ hn
The optical band gap of the helical compound established from the onset of its
absorption was 2.9 eV. The band gap can be determined by fitting the absorption
data to the direct transition equation by extrapolation of the linear portions of the
curves to the absorption equal to zero (Fig. 2).[15]
In this article, we have reported the synthesis and characterization of a new
racemic unsymmetrical thiahexahelicene starting from readily available and inexpen-
sive materials. We completed the synthesis of the target helicene in four steps and with
an overall yield of 34%. This heterohelicene derivative shows an optical band gap of
about 2.90 eV. It may also serve as a model system to investigate the structure–property

1014
S. MOUSSA ET AL.
Figure 2. The absorption spectrum of the bromohelicene derivative in a dilute CHCl3 solution. (Figure is
provided in color online.)
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 monitored by
thin-layer chromatographic (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 temperatures were deter-
mined 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, and N,N-dimethy-
lacetamide was distilled over CaH2. Photocyclizations were carried out in a 1.5-L
water-cooled quartz photoreactor equipped with a high-pressure mercury immersion
lamp (Heraeus TQ 500). Electron-impact (EI) mass spectra were determined at an
ionizing voltage of 70 eV.
Diarylethenes (4a–b)
Sodium methoxide (1 M in methanol) was added over 0.5 h under Ar to a
solution of triphenylphosphonium salt (2 g, 3.90 mmol) and benzothiophene-2-
carbaldehyde 2 (0.57 g, 3.55 mmol) in dry methanol (25 mL). The mixture was
heated at 50 ꢀC for 3 h. The reaction mixture was cooled to room temperature and

NEW THIA[6]HELICENE
1015
concentrated under vaccum to half its volume. Water was added, and the solution
was extracted many times with a large volume of CH2Cl2. After drying and solvent
evacuation, the residue was chromatographed on silica gel using cyclohexane=ethyl
acetate (99:01) to give 0.393 g of the (Z)-isomer 4a (35%) and 0.589 g of the
(E)-isomer 4b (53%).
1
(Z)-Isomer (4a). Mp ¼ 56–58 ꢀC; H NMR (300 MHz, CDCl3): d ¼ 6.62 (d,
J ¼ 12 Hz, 1H), 7.35 (d, J ¼ 12 Hz, 1H), 7.22 (s, 1H), 7.24–7.33 (m, 4H), 7.50 (d,
J ¼ 8.4 Hz, 2H), 7.67 (dd, J ¼ 7.2 Hz, J ¼ 1.8 Hz, 2H) ppm; 13C NMR (75 MHz
CDCl3): d ¼ 121.94, 122.12, 123.43, 124.40, 124.56, 124.81, 125.49, 125.52, 129.85,
130.80, 131.69, 135.67, 139.02, 139.53, 140.10 ppm.
(E)-Isomer 4b. Mp ¼ 139–141 ꢀC;1H NMR (300 MHz, CDCl3): d ¼ 7.248–
7.512 (m, 4H), 7.52–7.58 (m, 3H); 7.63–7.71 (m, 4H) ppm; 13C NMR (75 MHz
CDCl3): d ¼ 128.82, 128.98, 132.20, 132.33, 132.36, 132.42, 132.55, 133.01 ppm.
General Procedure for the Photocyclodehydroganation Reaction
A solution of the respective diarylethene (1 equiv), iodine (1.1 equiv), and
propylene oxide (100 equiv) in toluene (1.5 L) was irradiated for 3 h, under Ar, in
a photoreactor fitted with a water-cooled immersion well and a high-pressure Hg
lamp (500 W, Heraeus). Evaporation of the solvent and column chromatography
(SiO2) yielded the pure compound. Experimental details and specific data for individ-
ual compounds are given.
Compound 5
350 mg (1.11 mmol) of compounds 4a and b were irradiated for about 3 h,
according to procedure A. After evaporation of the solvent, the final product was
purified by chromatography using cyclohexane as the eluent (Rf ¼ 0.72). The desired
1
product was obtained as a white solid in 76% yield. Mp ¼ 139–141 ꢀC; H NMR
(300 MHz, CDCl3): d ¼ 7.53 (t, J ¼ 4.5 Hz, 1H), 7.17–7.66 (m, 2H), 7.81 (d,
J ¼ 5.1 Hz, 1H), 7.86 (d, J ¼ 5.1 Hz, 1H), 7.90 (d, J ¼ 5.1 Hz, 1H), 7.98 (d, J ¼ 4.8 Hz,
1H), 8.73 (d, J ¼ 8.4 Hz, 1H), 9.10 (s, 1H) ppm; 13C NMR (75 MHz CDCl3):
d ¼ 121.46, 121.55, 123.23, 124.39, 125.03, 125.53, 125.70, 127.35, 127.99, 128.15,
130.28, 130.79, 131.44, 136.09, 139.55, 139.68 ppm.
Diarylethene (6)
A solution of compound 5 (1.0 g, 3.19 mmol), 4-bromostyrene (0.82 g,
4.46 mmol), and dry sodium acetate (0.28 g, 3.50 mmol) in N,N-dimethylacetamide
(5 mL) was placed in a Schlenk tube under an argon atmosphere. The mixture was
heated to 100 ꢀC before addition of a solution of the Herrmann catalyst (29.9 mg,
1%) in N,N-dimethylacetamide (2 mL). The mixture was heated then to 140 ꢀC,
and heating was maintained for about 48 h. The workup procedure involves hydroly-
sis, extraction with CH2Cl2, and drying over MgSO4. After column chromatography
using cyclohexane–ethyl acetate (98:2) as the eluent (Rf ¼ 0.39), the final product 6
was obtained in 79% yield as a pale yellow solid. Mp ¼ 158–160 ꢀC; 1H NMR

1016
S. MOUSSA ET AL.
(300 MHz, CDCl3): d ¼ 7.27 (d, J ¼ 16.5 Hz, 1H, Hvinyl), 7.44 (d, J ¼ 16.5 Hz, 1H,
H
vinyl), 7.50–7.56 (m, 5H), 7.66 (t, J ¼ 7.5 Hz, 1H), 7.83 (d, J ¼ 8.5 Hz, 1H), 7.86
(d, J ¼ 9 Hz, 1H), 7.90 (d, J ¼ 8.5 Hz, 1H), 8.00 (d, J ¼ 8 Hz, 1H), 8.03 (d, J ¼ 8 Hz,
Hz, 1H), 8.90 (d, J ¼ 8.5 Hz, 1H), 8.98 (s, 1H) ppm; 13C NMR (75 MHz, CDCl3):
d ¼ 121.18, 121.57, 122.09, 122.71, 123.29, 124.68, 124.88, 125.35, 127.52, 128.12,
128.36, 129.01, 129.86, 129.92, 130.95, 131.59, 131.88, 135.69, 136.25, 136.63,
139.18, 139.85 ppm.
Thiahexahelicene (1)
The photocyclization of 150 mg (0.36 mmol) of compound 6, according to pro-
cedure A, yielded 65% of 2-bromothiahexahelicene as a yellow solid, after 3 h of
irradiation followed by column chromatography on silica gel using cyclohexane=ethyl
acetate (99:01) as the eluent (Rf ¼ 0.50), mp ¼ 198–200 ꢀC. 1H NMR (300 MHz,
CDCl3): d ¼ 6.9 (dd, J ¼ 4.8 Hz, J ¼ 0.9 Hz, 2 H), 7.36 (t, J ¼ 8.1 Hz, 1 H), 7.54 (dd,
J ¼ 8.7 Hz, J ¼ 1.8 Hz, 1 H), 7.85–8.12 (m, 8 H), 8.15 (s, 1 H) ppm; 13C NMR
(75 MHz, CDCl3): d ¼ 120.50, 122.18, 122.73, 122.97, 124.86, 126.02, 126.17, 126.54,
127.06, 127.37, 127.96, 128.62, 129.18, 129.56, 130.27. 131.42, 131.63, 131.72,
132.03, 132.98, 136.06, 138.90, 140.38 ppm; MS (EI, 70 eV): m=z ¼ 413 ([Mþ], 100%).
X-Ray Crystal Structure Determination of Thiahexahelicene 1
Single crystals of 1 were obtained by slow evaporation of a methylene chloride=
hexane solution at ambient temperature. X-ray data were recorded on a a Bruker
Smart CCD diffractometer. Chemical formula C24H13BrS, M ¼ 413.31, crystal
dimensions 0.10 ꢅ 0.10 ꢅ 0.10 mm, monoclinic, space group P21=n. At 20 ꢀC:
3
˚
˚
˚
˚
a ¼ 13.3335(4) A, b ¼ 7.2326(2) A, c ¼ 18.2038(13) A, volume 1750.90(14) A ,
3
˚
Z ¼ 4, qcalcd ¼ 1.568 g=cm , x-ray source Cu Ka, k ¼ 01.54180 A, measured reflections
6591, independent reflections 3100, reflections used 3100, refinement type Fmls,
parameters refined 236, R1 ¼ 0.088, wR2 ¼ 0.306. CCDC 781749 contains the
supplementary crystallographic data for thiahexahelicene. The data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: (þ44) 1223-336-033 or e-mail: deposit@ ccdc.cam.ac.uk).
ACKNOWLEDGMENT
´ ´
The authors are grateful to the DGRS (Direction Generale de la Recherche
Scientifique) of the Tunisian Ministry of Higher Education and Scientific Research
for financial support.
REFERENCES
1. Martin, R. H.; Marchant, M.-J.; Baes, M. Rapid synthesis of hexa- and heptahelicenes.
Helv. Chim. Acta 1971, 54, 358–360.
2. (a) Katz, T. J.; Sudhakar, A.; Teasley, M. F.; Gilbert, A. M.; Geiger, W. E.; Robben, M. P.;
Wuensch, M.; Ward, M. D. Synthesis and properties of optically active helical metallocene

NEW THIA[6]HELICENE
1017
oligomers. J. Am. Chem. Soc. 1993, 115, 3182–3198; (b) Dai, Y.; Katz, T. J. Synthesis of
helical conjugated ladder polymers. J. Org. Chem. 1997, 62, 1274–1285; (c) Fox, J. M.;
Lin, D.; Itagaki, Y.; Fujita, T. Synthesis of conjugated helical acetylene-bridged polymers
and cyclophanes. J. Org. Chem. 1998, 63, 2031–2038.
3. Fox, J. M.; Katz, T. J. Conversion of a [6]helicene into an [8]helicene and a helica. J. Org.
Chem. 1999, 64, 302–305.
4. (a) Tsuneomi, K.; Kenta, K.; Emanuela, L.; Alberto, B.; Stefano, M.; Kenso, S. Enantio-
selective synthesis induced by tetrathia-[7]-helicenes in conjunction with asymmetric auto-
catalysis. Tetrahedron: Asymmetry 2006, 17, 2050–2053; (b) Reetz, M. T.; Sostmann, S.
2,15-Dihydroxy-hexahelicene (HELIXOL): Synthesis and use as an enantioselective fluor-
escent sensor. J. Organomet. Chem. 2000, 603, 105–109; (c) Dreher, S. D.; Katz, T. J.;
Lam, K. C.; Rheingold, A. L. Application of the russig laatsch reaction to synthesize a
bis[5]helicene chiral pocket for asymmetric catalysis. J. Org. Chem. 2000, 65, 815–822;
(d) Okubo, H.; Yamaguchi, M.; Kabuto, C. Macrocyclic amides consisting of helical
chiral1,12-dimethylbenzo[c]phenanthrene-5,8-dicarboxylate. J. Org. Chem. 1998, 63,
9500–9509; (e) Reetz, M. T.; Beuttenmuller, E. W.; Goddart, R. First enantioselective
catalysis using a helical diphosphane. Tetrahedron Lett. 1997, 38, 3211–3214.
5. (a) Ben Hassine, B.; Gorsane, M.; Geerts-Evrard, F.; Pecher, J.; Martin, R. H.; Castelet,
`
`
D. Syntheses et syntheses ennthioselectives d’epoxydes derivant du (E)-stilbene et de l’a-
methylstilbene par la methode de payne. Bull. Soc. Chim. Belg. 1986, 95, 547–556; (b) Ben
Hassine, B.; Gorsane, M.; Pecher, J.; Martin, R. H. Diastereoselective NaBH4 reductions
of (dl) a-ketoesters. Bull. Soc. Chim. Belg. 1985, 94, 597–603.
6. (a) Tovar, J. D.; Rose, A.; Swager, T. M. Functionalizable polycyclic aromatics through
oxidative cyclization of pendant thiophenes. J. Am. Chem. Soc. 2002, 124, 7762–7769; (b)
Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. Synthesis, morphology, and field-effect
mobility of anthradithiophenes. J. Am. Chem. Soc. 1998, 120, 664–672.
7. (a) Boorum, M. M.; Vasilev, Y. V.; Drewello, T.; Scott, L. T. Groundwork for a rational
synthesis of C60: Cyclodehydrogenation of a C60H30 polyarene. Science 2001, 294, 828–
831; (b) Scott, L. T.; Boorum, M. M.; McMahon, B. J.; Hagen, S.; Mack, J.; Blank, J.;
Wegner, H.; de Meijere, A. A rational chemical synthesis of C60. Science 2002, 295,
1500–1503; (c) Rabideau, P. W.; Abdourazak, A. H.; Marcinow, Z.; Sygula, R.; Sygula,
A. Buckybowls, 2:Toward the total synthesis of buckminsterfullerene (C60): Benz[5,6]-as-
indaceno-[3,2,1,8,7-mnopqr]indeno[4,3,2,1-cdef]chrysene. J. Am. Chem. Soc. 1995, 117,
6410–6411; (d) Sygula, A.; Rabideau, P. W. A practical, large scale synthesis of the cor-
annulene system. J. Am. Chem. Soc. 2000, 122, 6323–6324.
8. (a) Wynberg, H. Some observations on the chemical, photochemical, and spectral properties
of thiophenes. Acc. Chem. Res. 1971, 4, 65–67; (b) Phillips, K. E. S.; Katz, T. J.; Jockusch, S.;
Lovinger, A. J.; Turro, N. J. Synthesis and properties of an aggregating heterocyclic helicene.
J. Am. Chem. Soc. 2001, 123, 11899–11907; (c) Kitahara, Y.; Tanaka, K. Synthesis, crystal
structure and properties of thiaheterohelicenes containing phenolic hydroxy functions. Chem.
Commun. 2002, 932–933; (d) Miyasaka, M.; Rajca, A.; Pink, M.; Rajca, S. Chiral molecular
glass: Synthesis and characterization of enantiomerically pure thiophene-based [7]-helicene.
Chem. Eur. J. 2004, 10, 6531–6539; (e) Maiorana, S.; Papagni, A.; Licandro, E.; Annunziata,
R.; Paravidino, P.; Perdicchia, D.; Giannini, C.; Bencini, M.; Clays, K.; Persoons, A. A con-
venient procedure for the synthesis of tetrathia-[7]-helicene. Tetrahedron 2003, 59, 6481–6488.
9. Caronna, T.; Sinisi, R.; Catellani, M.; Luzzati, S.; Abbate, S.; Longhi, G. Chiroptical
properties of some monoazapentahelicenes. Synth. Met. 2001, 119, 79–80.
10. (a) Tanaka, K.; Osuga, H.; Suzuki H. Diastereocontrolled synthesis of optically pure func-
tionalized heterohelicenes. Tetrahedron: Asymmetry 1993, 4, 1843–1856; (b) Murguly, E.;
McDonald, R.; Branda, N. R. Chiral discrimination in hydrogen-bonded [7]helicenes.
Org. Lett. 2000, 2, 3169–3172; (c) Stammel, C.; Frohlich, R.; Wolff, C.; Wenck, H.;
¨

1018
S. MOUSSA ET AL.
Mattay, J. Efficient phenanthrene, helicene, and azahelicene syntheses. Eur. J. Org. Chem.
1999, 1709–1718.
11. Aloui, F.; El Abed, R.; Ben Hassine, B.; Marinetti, A. A new approach to 3,14-dihydrox-
yhexahelicene: Resolution and attribution of the absolute configuration. C. R. Chimie
2009, 12, 284–290.
12. Sheldrick, M. Program for Crystal Structure Refinement, University of Go¨ttingen;
Germany, 1997. SHELXL-97:
13. Liu, L.; Yang, B.; Katz, T. J.; Poindexter, M. K. Improved methodology for photocycliza-
tion reactions. J. Org. Chem. 1991, 56, 3769–3775.
14. Ku, C.-H.; Kuo, C.-H.; Leung, M.-K.; Hsieh, K.-H. Carbazole–oxadiazole containing
polyurethanes as phosphorescent host for organic light emitting diodes. Eur. Polym. J.
2009, 45, 1545–1553.
15. Phokaa, S.; Laokul, P.; Swatsitang, E.; Promarak, V.; Seraphinc, S.; Maensiri, S. Syn-
thesis, structural and optical properties of CeO2 nanoparticles synthesized by a simple
polyvinyl pyrrolidone (PVP) solution route. Mater. Chem. Phys. A 2009, 115, 423–428.