Synthesis of new sulfur heteroaromatics isoelectronic with dibenzo[g,p]chrysene by photocyclization of thienyl- and phenyl-substituted ethenes

Article abstract of DOI:10.1021/jo960022x

A series of new sulfur heteroarenes, isoelectronic with dibenzo[g,p]chrysene, have been prepared by double photocyclization of the corresponding tetraaryl substituted ethenes. The first step proceeds efficiently in each case, and the corresponding intermediate sulfur heteroarenes, isoelectronic with phenanthrene, have been isolated. The second ring closure is only efficient when one of the participating aryl substituents is thienyl, which thus manifests a higher electron density on the carbon atom involved in the excited singlet state reaction. Most of the new compounds are of minimal solubility in common solvents and do not display improved electron donor properties otherwise commonly found among heteroaromatics.

Full text of DOI:10.1021/jo960022x

J . Org. Chem. 1996, 61, 6997-7005
6997
Syn th esis of New Su lfu r Heter oa r om a tics Isoelectr on ic w ith
Diben zo[g,p]ch r ysen e by P h otocycliza tion of Th ien yl- a n d
P h en yl-Su bstitu ted Eth en es
Erik Fischer, J an Larsen, J ørn B. Christensen, Marc Fourmigue´,† Hans G. Madsen,‡ and
Niels Harrit*
Department of Chemistry, University of Copenhagen, Symbion, Fruebjergvej 3,
DK-2100 Copenhagen, Denmark
Received J anuary 2, 1996 (Revised Manuscript Received J une 6, 1996X)
A series of new sulfur heteroarenes, isoelectronic with dibenzo[g,p]chrysene, have been prepared
by double photocyclization of the corresponding tetraaryl substituted ethenes. The first step
proceeds efficiently in each case, and the corresponding intermediate sulfur heteroarenes,
isoelectronic with phenanthrene, have been isolated. The second ring closure is only efficient when
one of the participating aryl substituents is thienyl, which thus manifests a higher electron density
on the carbon atom involved in the excited singlet state reaction. Most of the new compounds are
of minimal solubility in common solvents and do not display improved electron donor properties
otherwise commonly found among heteroaromatics.
In tr od u ction
by cyclic voltammetry. For tetrakis(1,4-benzodithiieno)-
[2,3-a:2′,3′-c:2′′,3′′-f:2′′′,3′′′-h]naphthalene4 the electro-
chemical determination of the oxidation potential is
hampered by the low solubility of the compound, an
obstacle which is frequently met with larger, unsubsti-
tuted heteroaromatics.
Two of the requirements to be met for the observation
of electrical conductivity in solid charge transfer salts is
high polarizability of the components and a strong
intermolecular interaction between them.1,2 Both prop-
erties may be achieved by the introduction of heteroat-
oms, and sulfur has been particularly popular for this
purpose.1-13 Introduction of sulfur frequently implies a
reduction of the oxidation potential compared to the all-
carbon analogue.4-6,14 In other cases the effect may be
negligible.3,7
Examples of fused sulfur heteroarenes are 3,4′:4,3′-bis-
(benzo[b]thiophene)7 and 3,3′:4,4′-bis(thieno[2,3-b]thio-
phene),3 which are both isoelectronic with perylene and
contain two and four sulfur atoms, respectively. Also like
perylene, they both form complexes with molecular iodine
with properties very similar to those of the known
perylene-iodine solid. X-ray crystallographic analysis
reveals that 3,3′:4,4′-bis(thieno[2,3-b]thiophene) is planar
in spite of the considerable amount of strain that must
be contained in the structure.3 Dithieno[2,4-d,e:2′,4′-i,j]-
naphthalene5,6 is isoelectronic with pyrene but displays
a lower oxidation potential and is also able to form CT-
salts. The thiophene ring of quinoid structure can serve
as both an acceptor and a donor15 or as an acceptor only.16
Thia analogues of anthracene,8,10 phenanthrene, and
triphenylene9,10 are examples of sulfur aromatics for
which their enhanced donor properties have been verified
For these reasons, the work described herein is aimed
to prepare a series of sulfur aromatics, isoelectronic with
dibenzo[g,p]chrysene (3, Scheme 1),17 containing two and
four sulfur atoms (see below for structures), in order to
relate donor properties with symmetry and substitutional
patterns.
For our purposes, photocyclization of 6π-electron con-
jugated systems, as present in stilbenes and related
compounds, represents a viable synthetic pathway since
it is a major route to heteroaromatic molecules.18 It is
not a universal reaction though, and some 6π-systems
fail to cyclize. For example, it was recognized early on,19
that while photolysis of 1,1,2,2-tetraphenylethene (1)
proceeds smoothly to form 9,10-diphenylphenanthrene (2)
(Scheme 1), this compound resists further ring closure
to the otherwise expected end product dibenzo[g,p]-
chrysene (3).20
(9) Nabeshima, T.; Iwata, S.; Furukawa, N.; Morihashi, K.; Kikuchi,
O. Chem. Lett. 1988, 1988, 1325-1328.
(10) Morihashi, K.; Kikuchi, O.; Nabeshima, T.; Iwata, S.; Furukawa,
N. Chem. Lett. 1989, 1989, 79-82.
(11) Ishii, A.; Nakayama, J .; Kazami, J .; Ida, Y.; Nakamura, T.;
Hoshino, M. J . Org. Chem. 1991, 56, 78-82.
† Present address: Institut des Mate´riaux de Nantes, UMR-CNRS
110, 2 Rue de la Houssinie`re, F-44072 Nantes Cedex 03, France.
‡ Present address: Superfos, Packaging International, DK-4390
Vipperoed, Denmark.
(12) Tsubouchi, A.; Matsumura, N.; Inoue, H. J . Chem. Soc., Chem.
Commun. 1991, 520-521.
(13) Kimura, T.; Ishikawa, Y.; Furukawa, N. Heterocycles 1993, 35,
53-56.
X Abstract published in Advance ACS Abstracts, September 1, 1996.
(1) Saito, G.; Ferraris, J . P. Bull. Chem. Soc. J pn. 1980, 53, 2141-
2145.
(14) Suzuki, T.; Shiohara, H.; Monobe, M.; Sakimura, T.; Tanaka,
S.; Yamashita, Y.; Miyashi, T. Angew. Chem., Int. Ed. Engl. 1992, 31,
455-458.
(2) Williams, J . M. Acc. Chem. Res. 1985, 18, 261-267.
(3) Kono, Y.; Miyamoto, H.; Aso, Y.; Otsubo, T.; Ogura, F.; Tanaka,
T.; Sawada, M. Angew. Chem., Int. Ed. Engl. 1989, 28, 1222-1224.
(4) Bartl, A.; Fro¨hner, J .; Kniess, T.; Domschke, G.; Mayer, R.; Roth,
S. Synth. Met. 1992, 51, 115-119.
(15) Takahashi, K.; Suzuki, T.; Akiyama, K.; Ikegami, Y.; Fukazawa,
Y. J . Am. Chem. Soc. 1991, 113, 4576-4583.
(16) Gu¨nther, E.; Hu¨nig, S.; Peters, K.; Rieder, H.; Schnering, H.
G.; Schu¨tz, J .-U.; So¨derholm, S.; Werner, H.-P.; Wolf, H. C. Angew.
Chem., Int. Ed. Engl. 1990, 29, 204-205.
(5) Moradpour, A. J . Chem. Soc., Perkin Trans. 1 1993, 7-8.
(6) Watanabe, K.; Aso, Y.; Otsubo, T.; Ogura, F. Chemistry Lett.
1992, 1233-1236.
(17) Heeres, G. J .; Wynberg, H. Synth. Commun. 1972, 2, 335-344.
(18) Mallory, F. B.; Mallory, C. W. In Organic Reactions; Wiley &
Sons: New York, 1984; Vol. 30, p 1.
(7) Wudl, F.; Haddon, R. C.; Zellers, E. T.; Bramwell, F. B. J . Org.
Chem. 1979, 44, 2491-2493.
(19) Mallory, F. B.; Wood, C. S.; Gordon, J . T. J . Am. Chem. Soc.
1964, 86, 3094-3402.
(20) Olsen, R. J .; Buckles, R. E. J . Photochem. 1979, 10, 215-220.
(8) Nabeshima, T.; Furukawa, N.; Ishizawa, T.; Morihashi, K.;
Kikuchi, O. Heterocycles 1990, 31, 1575-1576.
S0022-3263(96)00022-9 CCC: $12.00 © 1996 American Chemical Society

6998 J . Org. Chem., Vol. 61, No. 20, 1996
Fischer et al.
Sch em e 1
Sch em e 3
Sch em e 4
Sch em e 2
P r ep a r a tion of Dia r ylk eton es 4. Bis(thiophene-2-
yl) ketone (4a ) and 2-benzoylthiophene (4d ) were pre-
pared by published procedures.23,24 All other ketones
were prepared by lithiation of the corresponding thiophene
using n-butyllithium followed by reaction with carbon
dioxide25 (Scheme 3).
In the same manner, bis(benzo[b]thiophene-2-yl) ke-
tone (4e) was prepared from benzo[b]thiophene and
carbon dioxide.
McMu r r y Cou p lin g of Dia r yl Keton es. The reduc-
tive McMurry coupling takes place at the surface of
freshly prepared Ti(0),22 but preliminary experiments
showed that the reactivity of the elemental titanium is
crucial when thiophene units are present. We have
experienced that reduction of TiCl3 with alkali metals
or magnesium caused polymerization or degradation in
the subsequent reaction with thienyl ketones. TiCl4
reduced with zinc was better, but still the yields were
unacceptably low. Suzuki et al.14 reported, however, that
the yield is considerably improved when pyridine is added
as mediator in an amount equivalent with titanium. In
the standard procedure for implementation of the Mc-
Murry coupling,21,22 the product is isolated after quench-
ing the reaction by adding aqueous potassiun carbonate
followed by extraction with dichloromethane. At this
point an emulsion is usually formed, which makes the
workup tedious and time consuming. We have therefore
developed a very easy and straightforward workup
procedure as described in the Experimental Section.
Thus, the symmetrically substituted ethenes 5a -e
were prepared from the corresponding ketones 4a -e as
illustrated in Scheme 4.
Therefore, in addition to preparing series of sulfur
aromatics isoelectronic with dibenzo[g,p]chrysene as
mentioned above, an additional objective of this work was
to compare the reactivity of the photoinduced two-step
ring closure of these various thienyl- and phenyl-
substituted ethenes with those of compounds 1 and 2.
Resu lts
Heteroaromatic compounds isoelectronic with dibenzo-
[g,p]chrysene have been synthesized by means of oxida-
tive photocyclization from the corresponding tetraaryl-
substituted ethenes. In most cases, the synthetic
procedures follow the generalized (and simplified) path-
way outlined in Scheme 2.
Phenyl- and thienyl-substituted ketones (4) were pre-
pared by standard methods (see Experimental Section).
When ethene (5) was symmetrically substituted, its
preparation was most conveniently accomplished by a
McMurry coupling.21,22 Irradiation of 5 under oxidative
conditions could, in most cases, be controlled by proper
selection of wavelength to produce first the single-
cyclization product 6, and subsequently the double-
cyclization product 7.
HPLC analysis (with UV-vis detection of the products)
of 1,2-diphenyl-1,2-bis(thiophene-2-yl)ethene (5d ) re-
vealed two peaks, indicating the production of E/ Z-
isomers. The absorption spectrum of the first fraction
was red shifted (λmax ) 262 and 332 nm) from that of
(Z)-1,2-bis(thiophene-2-yl)ethene (λmax ) 305 nm)26 but
otherwise showed the same profile and number of transi-
In additional cases, not included in Scheme 2, the
thiophene group carries an alkyl substituent or is fused
to a benzene ring as a benzothiophene unit.
(23) Acheson, R. M.; MacPhee, K. E.; Philpot, P. G.; Barltrop, J . A.
J . Chem. Soc. 1956, 698-705.
(24) Minnis, W. Organic Syntheses; Wiley: New York, 1943; Coll.
Vol. II, p 520.
(21) Lenoir, D. Synthesis 1977, 553.
(22) Lai, Y.-H. Org. Prep. Proc. Int. 1980, 12, 363-390.
(25) J orgenson, M. J . In Organic Reactions; Dauben, W. G., Ed.;
Wiley and Sons: New York, 1970; pp 1-98.

Sulfur Heteroaromatics Isoelectronic with Dibenzo[g,p]chrysene
J . Org. Chem., Vol. 61, No. 20, 1996 6999
Sch em e 5
Sch em e 6
F igu r e 1. UV-vis spectra recorded at time intervals 0, 25,
40, 55, and 90 min, respectively, during photolysis (λ > 380
nm) of 5a (7.1 × 10-5 M) in aerated cyclohexane with catalytic,
nonabsorbing amounts of iodine.
Sch em e 7
tions with no vibrational structure. Accordingly, the
absorption spectrum of the second fraction (λmax ) 253
and 343 nm) resembled that of (E)-1,2-bis(thiophene-2-
yl)ethene (λmax ) 345 nm)26 with vibrational fine structure
of long wavelength band. When the HPLC analysis was
performed at 304 nm, where the two E/Z-isomers have
identical absorption coefficients (vide infra), integration
of the peaks revealed that the two isomers were formed
in equimolar amounts (50:50). This implies that there
is no preference for either configuration in the coupling
of the two ketyl anion radicals in the product-forming
step,22 and that steric repulsion between the thienyl and
phenyl substituents is the same as that between two
thienyl and two phenyl groups, respectively.
P r ep a r a tion of 1,1-Bis(th iop h en e-2-yl)-2,2-d ip h e-
n yleth en e. The unsymmetrical 1,1-bis(thiophene-2-yl)-
2,2-diphenylethene (5f) was prepared by the reaction
between the ylide of diphenylmethane and bis(thiophene-
2-yl) ketone, followed by acid-catalyzed elimination of
water (Scheme 5).
P r ep a r a tion of 9,10-Bis(th iop h en e-2-yl)p h en a n -
th r en e. Since this compound could not be obtained by
photolysis of 1,2-bis(thiophene-2-yl)-1,2-diphenylethene
(5d ) (vide supra), a thermal synthetic pathway was
developed. 9,10-Phenanthroquinone was reacted with
thiophene-2-yllithium, and the intermediate diol was
reduced with elemental titanium (from TiCl3 + K)
(Scheme 6).
P h otolytic Rea ction s Mon itor ed by UV-vis Sp ec-
tr oscop y. The photolytic reactions of the ethenes 5 were
all investigated in dilute solutions by means of absorption
spectroscopy before implementation of the preparative
photolysis. In all cases it was possible, by proper
selection of excitation wavelengths, to effectuate the
individual steps sequentially and record the spectra of
the singly cyclized structures 6. The photolysis of the
parent tetrakis(thiophene-2-yl)ethene (5a ), according to
Scheme 7, will serve as an illustration. The superim-
posed spectra of the transformation of 5a displays an
isosbestic point at 336 nm (Figure 1). This observation
makes the final spectrum (curve 6a) assignable to 4,5-
bis(thiophene-2-yl)thieno[3,2-e]benzo[b]thiophene (6a ).
Likewise, the subsequent course of photolysis (Figure 2)
displayed isosbestic points at 233, 280, 311, 333, 339, and
357 nm making the final spectrum assignable to tetra-
thieno[2,3-a:3′,2′-c:2′′,3′′-f:3′′′,2′′′-h]naphthalene (7a ).
Even though light intensities are not directly compa-
rable in the two experiments shown in Figures 1 and 2,
the much shorter irradiation times cited in the legend of
Figure 2 undoubtedly reflect a greater relative quantum
yield of the second photolytic step. Thus, when the
solution of 5a was exposed to the lamp equipped with
an acetone filter (λ > 330 nm), an isosbestic point was
observed (323 nm) for the direct conversion to 7a , i.e.
there was no trace of the intermediate 6a . This implies
that 6a reacts much more efficiently than 5a , a difference
that might be due to competing processes from the
exciting singlet state of 5a , e.g. twisting around the
double bond.
The photolytic transformation (λ > 380 nm) of 5f into
5-phenyl-4-(thiophene-2-yl)thieno[3,2-a]naphthalene (6f)
(Scheme 8) also proceeded smoothly and displayed an
isosbestic point at 327 nm. Irradiation with λ > 330 nm
(26) Zimmerman, A. A.; Orlando, C. M.; Gianni, M. H. J . Org. Chem.
1969, 34, 73-77.

7000 J . Org. Chem., Vol. 61, No. 20, 1996
Fischer et al.
Sch em e 9
F igu r e 2. UV-vis spectra recorded at time intervals 0, 1, 2,
3, and 6 min, respectively, during photolysis (λ > 330 nm) of
6a (2.0 × 10-5 M) in aerated cyclohexane with catalytic
amounts of iodine.
Sch em e 8
Sch em e 10
produced the absorption spectrum of dibenzo[a;h]dithieno-
[3,2-c:2′,3′-f]naphthalene (7f), and isosbestic points were
observed at 264 and 234 nm.
Contrary to all other reactions investigated, the spectra
recorded during the photolytic transformation (λ > 450
nm) of tetrakis(benzo[b]thiophene-2-yl)ethene (5e) into
6,7-bis(benzo[b]thiophene-2-yl)bis(benzo[b]thiopheno)-
[2,3-a:3′,2′-c]benzene (6e) (Scheme 9) failed to produce
sharp isosbestic points. This is believed to be due to the
ability of 5e to exist as different rotamers, with high
interconversional barriers by analogy to 9,10-bis(1-naph-
thyl)phenanthrene.27 The second step from 6e to tetra-
(benzo[b]thiopheno)[2,3-a:3′,2′-c:2′′,3′′-f:3′′′,2′′′-h]naph-
thalene (7e) proceeded smoothly by means of the low-
intensity light from a 60 W incandescent lamp. Isosbestic
points were observed at 304, 368, 377, and 406 nm.
The photolysis of 1,2 -bis(thiophene-2-yl)-1,2-diphen-
ylethene (5d ) (Scheme 10) represents a special case, since
this starting material was a 50:50 mixture of E/Z-isomers
obtained from the McMurry coupling (vide supra). When
this was dissolved in cyclohexane and nitrogen bubbled
through the solution during light exposure (λ > 380 nm),
the stationary state shifted while an isosbestic point
became observable at 304 nm, which consequently served
as the wavelength of detection in the HPLC evaluation
of the preparation (vide supra). Once the photostationary
state was established, air was admitted into the cell and
a photolytic transformation (isosbestic point 321 nm) into
an absorption spectrum without any vibrational fine
structure was observed. As was revealed by the prepara-
tive experiments, the corresponding product was 4,5-
diphenylthieno[3,2-e]benzo[b]thiophene (6d 2) (Scheme
10). Removing the filter and exposing 6d 2 to the full
spectrum of the lamp did not create a change, i.e. the
photolytic transformation into 7d could not be effectu-
ated.
Small-scale photolysis (λ > 330 nm) of 9,10-bis-
(thiophene-2-yl)phenanthrene (6d 1) (Scheme 10) pro-
ceeded smoothly in the UV-cell under observation of an
isosbestic point at 270 nm and appearance of the highly
structured spectrum of 7d .
(27) Gundermann, K.-D.; Romahn, E.; Zander, M. Z. Naturforsch.
1992, 47b, 1764-1774.

Sulfur Heteroaromatics Isoelectronic with Dibenzo[g,p]chrysene
J . Org. Chem., Vol. 61, No. 20, 1996 7001
P r ep a r a tive P h otolysis. In a typical run, the ethene
5 (ca. 1.2 g) was dissolved in toluene (1.2 l) and irradiated
through Pyrex in an immersion well equipped with a 700
W medium pressure Hg-lamp. Although oxygen acted
cleanly as an oxidant in the diluted solutions (vide supra),
it resulted in low yields of impure products, when used
in more concentrated solutions. This problem may stem
from unwanted reactions of the accumulated hydrogen
peroxide or the higher concentration of singlet molecular
oxygen. A better yield was obtained by flushing the
solution with nitrogen during irradiation and adding an
equimolar amount of iodine. The reactions were moni-
tored by means of thin layer chromatography and stopped
when all the starting material had been consumed.
During the subsequent workup, advantage was often
taken of the fact that the double cyclized product 7 is
generally less soluble than the singly cyclized 6. By
fractional crystallization and chromatography, substan-
tial amounts of 6 could be obtained. This achievement
appears less surprising, when one considers the spectral
shifts accompanying the steps 5 to 6 and 6 to 7 described
in the previous section. The starting materials and the
end products have absorption maxima in the spectral
range of maximum intensity delivered from the medium
pressure Hg-arc (366 nm). The intermediate 6 has a
weaker absorption in the same range and is therefore
screened and protected throughout the photolysis.
Compound 7e represents a special case since its
resistance to dissolve in any solvent (not even in bro-
mobenzene-d5 at 130 °C) prevented spectral characteri-
sation by means of NMR spectroscopy. A weak mass
spectrum was obtained (inlet temperature 400 °C) show-
ing the correct molecular mass. However, since 6e can
undergo alternative electrocyclic ring closure analogous
to the formation of benzo[g,h,i]perylene from dibenzo[c,g]-
phenanthrene (pentahelicene),28 an X-ray structural
analysis was required. This confirmed that the consecu-
tive photoreactions did indeed lead to the symmetrical
structure 7e as shown in Scheme 9. Details of the crystal
structure of 7e and all coordinates will be reported
elsewhere.29
Don or P r op er ties. The oxidation potentials of the
prepared heterocyclic donors were measured by cyclic
voltammetry. The anodic processes were irreversible,
probably due to chemical reactions at the free 2- and
3-positions in the thiophene moieties of the radical
cations. The measurements were further complicated by
adsorbtion phenomena on the electrode. The following
peak values (Ep, V vs SCE, Pt-bottom electrode, 400 mV/
s, CH2Cl2, (n-Bu)4NPF6 (0.1 M)) were obtained: 6d 1 1,40,
6f 1,05, 6d 2 1,20, 7a 1,10, 7b 1,00, 7c 1,08, 7d 1,10, 7e
1,08, 7f 1,05. Electrochemical data on dibenzo[g,p]-
chrysene were not obtainable when investigated under
the same conditions. The first potential notwithstanding,
the oxidation potentials are all within the range 1.0 to
1.2 V, indicating that the new sulfur heterocycles are not
particularly strong donors. Similar values have been
found for other large thiophene-annelated compounds
such as the heterohelicenes.36
F igu r e 3. ORTEP view of the unit cell of 7a -TCNQ. Thermal
ellipsoids are drawn at the 50% probability level. The sulfur
atoms have been darkened.
and containing an equimolar amount of TCNQ. The CT-
complex precipitated as small, black crystals. X-ray
crystal structure determination confirms the molecular
structure of 7a 47 and reveals a one-dimensional structure
with columns of alternating donor (D) and acceptor (A)
moieties (Figure 3). The flat molecules stack on top of
each other with a plane-to-plane D-A distance of 3.32(2)
Å. As a consequence of this structure, the material is
fully insulating as confirmed by a compressed pellet
conductivity measurement.
The molecule 7a is located on an inversion center and
appears to be essentially planar, the dihedral angle
between the two independant thiophene rings amounting
to 2.5(5)°. One interesting feature is the short intramo-
lecular S(1)-S(2) distance (3.066(5)Å) when compared
with the Van der Waals distance (S-S 3.7 Å), indicating
a degree of delocalization between the two sulfur atoms,
as already postulated in various molecules with the same
1,5-sulfur-sulfur interaction where S-S distances around
3 Å were observed.30-32 The TCNQ molecule also lies on
an inversion center. From the bond lengths, we can
estimate the degree of charge transfer33-35 which is found
to be zero, i.e. we have a neutral D-A complex, as
recently reported for a thiahelicene/TCNQ complex.36
Discu ssion
The lack of reactivity of 9,10-diphenylphenanthrene (2)
(Scheme 1) and other systems has been attributed to both
electronic and steric factors. Thus, Mallory et al.19
recognized that the absorption spectrum of 2 resembles
that of unsubstituted phenanthrene to such an extent
that the phenyl groups are considered not to play a role
in the electronic excitation. Consequently, the “electron
(30) Wudl, F.; Srdanov, G.; Rosenau, B.; Wellman, D.; Williams, K.;
Cox, S. D. J . Am. Chem. Soc. 1988, 110, 1316.
(31) Bryce, M. R.; Coffin, M. A.; Hursthouse, M. B.; Mazid, M.
Angew. Chem., Int. Ed. Engl. 1991, 30, 871.
(32) Salle´, M.; J ubault, M.; Gorgues, A.; Boubekeur, K.; Fourmugue´,
M.; Batail, P.; Canadell, E. Chem. Mat. 1993, 5, 1196.
(33) Flandrois, S.; Chasseau, D. Acta Crystallogr. B 1977, 33B, 2744.
(34) Kistenmacher, T. J .; Emge, T. J .; Bloch, A. N.; Cowan, D. O.
Acta Crystallogr. B 1982, 38B, 1193.
Compound 7a forms a 1:1 complex with tetracyano-p-
quinodimethane (TCNQ), which was obtained by slow
cooling of a boiling o-xylene solution, saturated with 7a
(28) Laarhoven, W. H. In Organic Photochemistry; Padwa, A., Ed.;
Marcel Dekker: New York, 1989; Vol. 10, pp 163-287.
(29) Larsen, S.; Pu¨schl, A.; Binau, K.; J ansen, K. K.; Lolck, R.;
Fischer, E.; Harrit, N. In preparation.
(35) Umland, T. C.; Allie, S.; Kuhlman, T.; Coppens, P. J . Phys.
Chem. 1988, 92, 6456.
(36) Larsen, J .; Dolbecq, A.; Bechgaard, K. Acta Chem. Scand. 1996,
50, 83-89.

7002 J . Org. Chem., Vol. 61, No. 20, 1996
Fischer et al.
availability” in the excited state on the two ortho carbons
between which the new bond is expected to be formed,
cannot be much different from the ground state. A more
quantitative measure for the reactivity in electrocyclic
reactions is the so-called sum of Free Valence Numbers,
ΣFr*, which have been calculated for a series of sys-
tems.28,37-40 Also, the reactivity can be related to the
electronic overlap population of the pair of atoms between
which the new bond is formed in the excited state.41
In the case of 2, Laarhoven28 has also pointed toward
steric conditions as the “obvious” reason for the lack of
reactivity; the two phenyl rings cannot acquire the proper
conformation prerequisite for cyclization, due to interac-
tion between the hydrogen atoms on C1 and C8 of the
phenanthrene moiety. Recent investigations of the pho-
toreactivity of 9,10-bis(1-naphthyl)phenanthrene show,
however, that steric factors are not the consideration.27
This compound exists as two rotational E/Z-isomers with
the naphthalene molecular planes perpendicular to the
phenanthrene plane as revealed by NMR spectroscopy.
The two isomers are not interconvertible but can be
separated and recrystallized. This result is supported
by calculations revealing an insurmountable barrier to
rotation. However, in contrast to the photostability of
2, 9,10-bis(1-naphthyl)phenanthrene closes efficiently
upon irradiation to form benzo[e]phenanthro[1,2,3,4-ghi]-
perylene.27 This result illustrates that photoinduced
cyclization is possible from an almost perpendicular
configuration, and planarity is reached in the course of
the process, concomitantly with the rehybridization of the
carbon atoms involved in bond formation.
4,5-Diphenylthieno[3,2-e]benzo[b]thiophene (6d 2) re-
sisted all attemps to implement 6π-electrocyclic ring
closure, by analogy with 9,10-diphenylphenanthrene (2).
In case of 6d 2, there are no hydrogen atoms preventing
the phenyl groups from obtaining the proper configura-
tion. Neither is this a general phenomenon characteristic
for any two phenyl groups sitting adjacent to one another
on an aromatic ring, since ortho-terphenyl undergoes
photocyclization to triphenylene.42 The origin of this
inertness must be linked to the resemblance of the
electronic structures of the phenanthrene and thieno[3,2-
e]benzo[b]thiophene moieties of 2 and 6d 2, respectively.
The 3-position of the thienyl substituent still seems to
be more inclined to participate in electrocyclic reactions
than the 2-position of phenyl. This is revealed when one
of the phenyl groups of 6d 2 is exchanged with thienyl as
in 6f, in which case cyclization proceeds smoothly (Scheme
8). If two thienyl substituents participate, the process
is very efficient (6a to 7a (Scheme 7) and 6d 1 to 7d
(Scheme 10)). When a competition between thienyl and
phenyl occurs, as in the parallel reactions of (Z)-5d and
(E)-5d , a thienyl-group is clearly preferred over a phenyl-
group as partner in a cyclization reaction (Scheme 10).
In terms of electron density and free valence number,
the enhanced reactivity of the thienyl substituent over
that of phenyl can be viewed, rather naively, as a
reflection of the fact that only five atoms are sharing the
π-electrons of the aromatic sextet.43 Accordingly, the
thiophene ring is an efficient partaker in other 6π-
electrocyclic ring closures,18 and quantitative yields of
reaction are often observed, as in the case of the trans-
formation of 1,2-bis(thiophene-2-yl)ethene into thieno[3,2-
e]benzo[b]thiophene.44
The absence of vibrational fine stucture in the absorp-
tion spectrum can be due to several circumstances, e.g.
conformational broadning and predissociation. The first
phenomenon is found in the spectra of the semiclosed
structures 6 compared to the fully closed structures 7,
as illustrated by 6a and 7a in Figures 1 and 2. Even
though they have the same number of π-electrons, the
spectrum of 7a is shifted to the red and displays a rich
fine structure of electronic and/or vibronic bands, while
that of 6a is diffuse. This is due to the aromaticity and
rigidity of the 7a molecule while the exocyclic thienyl
groups in 6a display a continuum of diedral angles with
respect to the thieno[3,2-e]benzo[b]thiophene core, caus-
ing a blur of the vibrational structure. The same trends
are observed when comparing the spectra of 2 and 3.19,45
By analogy, the absorption spectrum of thieno[3,2-e]-
benzo[b]thiophene44 is structured but otherwise qualita-
tively identical to that of 6a .
Since steric repulsion between the phenyl and thio-
phene-2-yl substituents of 5d is the same, there is no
basis for explaining the difference in observable vibra-
tional structure of the E/Z-pair as being due to confor-
mational effects. Neither is there reason to believe that
the quantum yield for photoisomerization Z f E is
different from the E f Z value. Therefore, the absence
of vibrational fine structure in the absorption spectrum
of (Z)-5d could be due to coupling of the Frank-Condon
excited state to a “dissociative” mode, representing a 6π-
electrocyclic ring closure in accordance with the observa-
tion that (Z)-5d reacts far more efficiently than (E)-5d .
In the CT-complex formed between 7a and TCNQ, the
donor is found to be completely planar. Since the charge
transfer is found to be negligible in the ground state, the
isolated molecule of 7a must also be planar and conse-
quently belongs to the D2h point group. This result
illustrates a characteristic feature of thiaheterocycles
compared to their isoelectronic all-carbon analogues. A
recent study45 of dibenzo[g,p]chrysene (3), which relates
to 7a in this manner, has revealed that it is nonplanar
and possesses D2 symmetry. The distortion from planar-
ity is due to hydrogen crowding in the bay areas of 3
which is obviously not occurring in 7a . Sterically, a
sulfur atom represents a more compact means of intro-
ducing two π-electrons in an aromatic sextet compared
to 1,2-vinylidene. However, the potential of 7a for
enhanced intermolecular interactions does not translate
over to the electrical conductivity of the CT-complex with
TCNQ, since very little conductivity was detectable from
a compressed pellet conducting measurements of the
crystals.
Exp er im en ta l Section
(37) Sato, T.; Morita, T. Bull. Chem. Soc. J ap. 1972, 45, 1548.
(38) Laarhoven, W. H.; Cuppen, T. J . H. M.; Niverd, R. J . F. Recl.
Trav. Chim., Pays-Bas 1968, 687.
(39) Orchin, M.; J affe, H. H. In Symmetry, Orbitals, and Spectra;
Wiley-Interscience: New York, 1971; pp 279-281.
(40) Laarhoven, W. H.; Cuppen, J . H. M.; Nivard, R. J . F. Tetrahe-
dron 1970, 26, 1069-1083.
(41) Muszkat, K. A.; Sharafi-Ozeri, S. Chem. Phys. Lett. 1973, 20,
397-399.
(42) Kharasch, N.; Alston, T. G.; Lewis, H. B.; Wolf, W. J . Chem.
Soc., Chem. Commun. 1965, 242-243.
Gen er a l Meth od s. Melting points are uncorrected and
were determined using a hot plate. HPLC measurements were
performed using an RP-8 column and methanol as solvent (1
(43) Solony, N.; Birss, F. W. Can. J . Chem. 1965, 43, 1569-1576.
(44) Kellogg, R. M.; Groen, M. B.; Wynberg, H. J . Org. Chem. 1967,
32, 3093-3100.
(45) Thulstrup, E. W.; Spanget-Larsen, J .; Waluk, J . Theor. Chim.
Acta 1994, 89, 301-309.

Sulfur Heteroaromatics Isoelectronic with Dibenzo[g,p]chrysene
J . Org. Chem., Vol. 61, No. 20, 1996 7003
mL/min, rt). Mass spectra were obtained at 70 eV ionizing
energy. THF was distilled from sodium benzophenone ketyl
radical. Zinc dust was used without further purification.
Column chromatographic purifications were performed with
activated basic aluminum oxide. All reagents were purchased
from commercial sources and used without further purification
except where reported. Small scale photolysis was carried out
in standard absorption cells (quartz) at room temperature
using a high pressure mercury source (200 W), fitted with a
filter cutting all wavelengths below 380 nm (glass filter) or
330 nm (1 cm acetone). Preparative photolysis was carried
out in an immersion well as outlined below.
Tet r a k is(5-b u t ylt h iop h en e-2-yl)et h en e (5c). Yellow
needles from petroleum ether (35%): mp 93.5-94 °C; 1H-NMR
(90 MHz, CDCl3) δ 6.7 (d, J ) 3.5 Hz, 4H), 6.5 (d, J ) 3.5 Hz,
4H), 2.8-0.8 (m, 36H); MS (70 eV): 580 (M+, 100), 290 (M2+
,
12). UV-vis λmax (nm) (log ꢀ) (hexane): 239 (4.50), 295 (4.58),
363 (4.55), 381 (4.59). Anal. Calcd for C34H44S4: C, 70.29; H,
7.63; S, 22.07. Found: C, 70.39; H, 7.68; S, 22.15.
1,2-Bis(th iop h en e-2-yl)-1,2-d ip h en yleth en e (5d ). Or-
ange needles from CH2Cl2 (40%): mp 219-221 °C; HPLC
indicated a 50/50 mixture of E and Z (see results section). 1H-
NMR (250 MHz, CDCl3) δ 7.4 (s, 10H), 7.0 (dd, 2H), 6.7 (dd,
2H), 6.3 (dd, 2H); MS (70 eV): 344 (M+, 100), 266 (13). Anal.
Calcd for C22H16S2: C, 76.73; H, 4.65; S, 18.62. Found: C,
76.25; H, 4.63; S 18.39.
Bis(th iop h en e-2-yl) k eton e (4a ) was prepared by a pub-
lished procedure.23
Bis(5-m et h ylt h iop h en e-2-yl) Ket on e (4b ). A three-
necked 500 mL flask equipped with a reflux condenser and a
thermometer was charged under dry nitrogen with 9.8 g (100
Tetr akis(ben zo[b]th ioph en e-2-yl)eth en e (5e). The crude
product was not suitable for column chromatography since it
has low solubility in toluene. The crude product was therefore
recrystallized twice from o-xylene (activated charcoal). Yellow
needles (40%): mp 218 °C dec. 1H-NMR (90 MHz, CDCl3) δ
mmol) of 2-methylthiophene and 300 mL of dry THF.
A
solution of butyllithium (40 mL, 2.5 M in hexane, 100 mmol)
was added at -78 °C. The reaction mixture was allowed to
reach room temperature, whereupon carbon dioxide gas was
introduced over a short period of time. This was repeated over
a 30 min period until the temperature of the reaction mixture
remained constant upon further addition of carbon dioxide.
The reaction mixture was then cooled to -78 °C, and chloro-
trimethylsilane (12.6 mL 10.8 g, 100 mmol) was added. The
reaction mixture was taken to room temperature and poured
into 500 mL of 0.5 M hydrochloric acid. The organic phase
was separated and the water phase extracted twice with 100
mL of ether. The combined organic phases were washed with
saturated sodium carbonate solution and dried (MgSO4), and
the solvent was evaporated in vacuo. Distillation of the crude
product (145 °C/0.6 mbar) afforded 13.3 g (60%) of 4b as light
yellow flakes: mp 53-55 °C; 1H-NMR (90 MHz, CDCl3) δ 7.7
(d, J ) 3.5 Hz, 2H), 6.8 (d, J ) 3.5 Hz, 2H), 2.6 (s, 6H). Anal.
Calcd for C11H10OS2: C, 59.43; H, 4.53; S, 28.84. Found: C,
59.67; H, 4.46; S, 28.70.
Bis(5-bu tylth iop h en e-2-yl) k eton e (4c) was prepared in
64% yield by a procedure analogous to the synthesis of 4b.
Pale yellow flakes from petroleum ether: mp 36-37.5 °C; 1H-
NMR (90 MHz, CDCl3) δ 7.7 (d, J ) 3.5 Hz, 2H), 6.8 (d, J )
3.5 Hz, 2H), 3-0.8 (m, 18H). Anal. Calcd for C17H22O S2: C,
66.62; H, 7.24; S, 20.92. Found: C, 66.74; H, 7.28; S, 21.20.
2-Ben zoylth iop h en e (4d ) was prepared according to a
published procedure.24
7.7 (m, 2H), 7.4 (m, 3H). MS (70 eV): 556 (M+, 100), 278 (M2+
,
13). UV-vis λmax (nm) (log ꢀ) (CH2Cl2): 397 (4.35), 377 (4.35),
306 (4.44). Anal. Calcd for C34H20S4: C, 73.35; H, 3.62.
Found: C, 72.42; H, 3.70.
1,1-Bis(th iop h en e-2-yl)-2,2-d ip h en yleth a n ol. To 100
mL of dry liquid ammonia was added sodium (0.6 g, 26 mmol),
and the suspension was left until it became grey (20 min).
Diphenylmethane (5.04 g, 30 mmol) in 15 mL of dry ether was
then added and the color changed to deep red. After 15 min,
bis(thiophene-2-yl) ketone (5.0 g, 26 mmol) in 25 mL of dry
THF was added to the suspension, and the reaction was left
for another 15 min. The reaction was quenched by pouring it
into 50 mL of liquid ammonia containing NH4Cl (2.67 g, 50
mmol). The ammonia was allowed to evaporate, and the ether
phase was poured into 100 mL of water. The organic phase
was isolated and dried (MgSO4) and the solvent evaporated
in vacuo leaving 7.5 g of a yellow oil. Triturating with 100
mL of hexane resulted in 4.0 g of crystals which were
recrystallized from ethanol leaving 2.5 g 1,1-bis(thiophene-2-
yl)-2,2-diphenylethanol (34%) as colorless crystals: mp 179-
1
181 °C; H-NMR (250 MHz, CDCl3) δ 7.3 (dd, J ) 2 Hz, 4H),
7.1 (8H, m), 6.8 (m, 4H), 4.9 (s, 1H), 3.2 (s, 1H). MS (70 eV):
344 (M+ - H2O, 65), 195 (100), 111(60). Anal. Calcd for
C
22H18OS2: C, 72.89; H, 5.00; S, 17.69. Found: C, 73.16; H,
5.03; S, 17.65.
1,1-Bis(th iop h en e-2-yl)-2,2-d ip h en yleth en e (5f). 1,1-
Bis(thiophene-2-yl)-2,2-diphenylethanol (2.0 g, 70 mmol) dis-
solved in 100 mL of dry benzene was refluxed with a catalytic
amount of p-toluenesulfonic acid using a Dean-Stark water
separator. When the expected amount of water was trapped
the solvent was evaporated in vacuo whereafter the residue
was passed through a short column (basic aluminum oxide,
toluene). The first fraction was evaporated in vacuo, and the
solid recrystallized from acetone giving 1.5 g of 1,1-bis-
(thiophene-2-yl)-2,2-diphenylethene (75%) as colorless crys-
Bis(ben zo[b]th iop h en e-2-yl) k eton e (4e) was prepared
in 60% yield by a procedure analogous to the synthesis of 4b.
Yellow needles from toluene: mp 172-174 °C; H-NMR (250
MHz, CDCl3) δ 8.2 (s, 2H), 7.9 (m, 4H), 7,4 (m, 4H). Anal.
Calcd for C17H10O S2: C, 69.36; H, 3.42. Found: C, 69.81; H,
3.64.
1
Tetr a k is(th iop h en e-2-yl)eth en e (5a ). All tetrasubsti-
tuted ethenes except 1,1-bis(thiophene-2-yl)-2,2-diphenylethene
were prepared by a McMurry coupling, using the procedure
by Lenoir21 as a guideline. Since the workup procedure
described in that article is rather tedious, we have applied the
following modification. After completion of the reaction be-
tween the ketone, pyridine, and low valent titanium, the
solvent (THF) was evaporated in vacuo leaving a black viscous
oil. Addition of 0.5 M hydrochloric acid to this oil resulted in
removal of the titanium (oxide), zinc chloride, and zinc, leaving
the crude product as either crystals or an oil. After decanta-
tion of the water phase, the organic residue was dissolved in
toluene and dried (MgSO4). The solution was passed through
a short column (basic aluminum oxide) which was eluted with
hot toluene. Removal of the solvent and recrystallization
afforded the pure compound. Thus, 5a was obtained in 40%
yield as red flakes from ethanol: mp 196-198 °C, lit.: 196-
198 °C.14
1
tals: mp 165-167 °C; H-NMR (250 MHz, CDCl3) δ 7.1 (m,
12H), 6.8 (m, 4H); MS (70 eV): 344 (M+, 100), 278 (10), 172
(M2+, 4). Anal. Calcd for C22H16S2: C, 76.71; H, 4.68; S, 18.61.
Found: C, 76.86; H, 4.64; S, 18.65. UV-vis λmax (nm) (log ꢀ)
(CH2Cl2): 337 (4.08), 237 (4.27).
(er yth r o/th r eo)-9,10-Bis(th ioph en e-2-yl)-9,10-dih ydr oxy-
9,10-d ih yd r op h en a n th r en e. To a stirred solution of thio-
phene (12.63 g, 0.15 mol) in 200 mL of dry THF was added
butyllithium (60 mL 2.5 M in hexane, 0.15 mol) at -78 °C.
The mixture was allowed to warm up to room temperature,
and 9,10-phenanthroquinone (13.0 g, 0.0625 mol) was added
in small portions during 30 min. The reaction mixture was
left overnight and poured into 400 mL of water. The resulting
suspension was filtered, leaving the crude product. Recrys-
tallization from ethanol gave 4.5 g (19%) of the title compound
as yellow crystals with mp 213-218 °C. Further recrystalli-
zation from toluene did not diminish the melting point range,
and the rather chaotic NMR spectrum indicated an erythro/
threo mixture: 1H-NMR (90 MHz, CDCl3) δ 7.7 (m, 4H), 7.4
(m, 5H), 7.1 (q, J ) 5 Hz, J ) 1 Hz, 2H), 6.6 (m, 4H). MS (70
eV): 376 (M+, 90), 263 (90), 247 (85), 181 (50), 111 (100). Anal.
Tetr a k is(5-m eth ylth iop h en e-2-yl)eth en e (5b). Yellow
needles from ethanol (53%): mp 130-131 °C; 1H-NMR (90
MHz, CDCl3) δ 6.6 (m, 8H), 2.4 (d, J ) 1 Hz, 12H); MS (70
eV): 512 (M+, 100), 364 (15), 206 (M2+, 13). UV-vis λmax (nm)
(log ꢀ) (CH2Cl2): 382 (4.32), 296 (4.27). Anal. Calcd for
C22H20S4: C, 64.04; H, 4.89; S, 31.08. Found: C, 64.20; H,
4.95; S, 30.55.

7004 J . Org. Chem., Vol. 61, No. 20, 1996
Fischer et al.
Calcd for C22H16O2S2: C, 70.19; H, 4.28; S, 17.03. Found: C,
70.28; H, 4.48; S, 16.83.
only compound that could be isolated was the double ring
closed compound 7b in 42% yield as yellow needles fromo-
1
xylene: mp > 230 °C; H-NMR (250 MHz, bromobenzene-d5,
9,10-Bis(th iop h en e-2-yl)p h en a n th r en e (6d ). TiCl3 (1.08
g, 7 mmol) was slowly added to 75 mL of dry THF under dry
nitrogen at room temperature. Thereafter potassium (0.79 g,
25 mmol) was added in small pieces under reflux. After
refluxing for a further 2 h, (erythro/threo)-9,10-bis(thiophene-
2-yl)-9,10-dihydroxy-9,10-dihydrophenanthrene (2.0 g, 5.3 mmol)
in 15 mL of dry THF was added, and the suspension was
refluxed for additional 20 h. The reaction mixture was
quenched with ethanol and then poured into 200 mL of water.
The phases were separated, and the water phase was extracted
twice with 50 mL of CHCl3. The combined organic phases were
washed with water and dried (MgSO4), and the solvent was
evaporated in vacuo. The crude product was redissolved in
boiling toluene and purified by column chromatography (basic
aluminum oxide, hot toluene). The first fraction was collected,
the solvent was evaporated in vacuo, and the residue was
recrystallized from acetone leaving 0.298 g (16%) as yellow
crystals: mp > 230 °C; 1H-NMR (250 MHz, CDCl3) δ 8.8 (d, J
) 8 Hz, 2H), 7.8 (dd, J ) 8 Hz, J ) 1 Hz, 2H), 7.7 (dt, J ) 8,
J ) 1, 2H), 7.5 (dt, J ) 8 Hz, J ) 1 Hz, 2H), 7.35 (dd, J ) 5
Hz, J ) 1 Hz, 2H), 7.0 (dd, J ) 5 Hz, J ) 5 Hz, 2H), 7.95 (dd,
J ) 5 Hz, J ) 1 Hz, 2H). MS (70 eV): 342 (M+, 100), 308
(40), 296 (20), 171 (M2+, 2). Anal. Calcd for C22H14S2: C, 77.16;
H, 4.12; S, 18.72. Found: C, 76.74; H, 4.18; S, 18.00.
130 °C) 7.4 (q, J ) 1.0 Hz, 1H), 2.7 (d, J ) 1 Hz, 3H). MS (70
eV): 408 (M+, 100), 204 (M2+, 8). Anal. Calcd for C22H16S4:
C, 64.69; H, 3.92; S, 31.39. Found: C, 64.75; H, 3.99; S, 31.14.
1,4,7,10-Tetr abu tyltetr ath ien o[2,3-a :3′,2′-c:2′′,3′′-f:3′′′,2′′′-
h ]n a p h th a len e (7c). Tetrakis(5-butylthiophene-2-yl)ethene
(5c) was photolyzed according to the standard procedure and
7c isolated in 34% yield as yellow needles from hexane (active
1
carbon): mp 160-162 °C; H-NMR (90 MHz, CDCl3) δ 7.5 (s,
4H), 1-3 (m, 36H). Anal. Calcd for C34H40S4: C, 70.82; H,
6.94; S, 22.24. Found: C, 70.63; H, 6.95; S, 22.07.
Dith ien o[2,3-a :3′,2′-c]tr ip h en ylen e (7d ). 9,10-Bis(thio-
phene-2-yl)phenanthrene (6d ) was photolyzed according to the
standard procedure to give 7c in 69% yield as yellow needles
from toluene (active carbon): mp > 230 °C; 1H-NMR (250 MHz,
bromobenzene-d5) δ 9.2 (dd, J ) 1 Hz, J ) 8 Hz, 2H), 8.4 (dd,
J ) 8 Hz, J ) 1 Hz, 2H), 7.5 (d, J ) 5 Hz, 2H), 7.4 (m, 2H), 7.3
(d, J ) 5 Hz, 2H). MS (70 eV): 340 (M+, 100), 295 (15), 170
(M2+, 9). Anal. Calcd for C22H12S2: C, 77.61; H, 3.55; S, 18.83.
Found: C, 77.53; H, 3.59; S, 18.68. UV-vis λmax (nm) (log ꢀ)
(CH2Cl2): 289 (4.72), 299 (4.75), 328 (4.30), 342 (4.25).
Tet r a k is(b en zo[b]t h iop h en e-2-yl)[2,3-a :3′,2′-c:2′′,3′′-f:
3′′′,2′′′-h ]n a p h th a len e (7e). Tetra(benzo[b]thiophene-2-yl)-
ethene (5e) was photolyzed according to the standard proce-
dure. Compound 7e is extremely insoluble in toluene and
precipitated during photolysis. Occasional cleaning of the
cooling jacket was necessary. Compound 7e was isolated by
filtration and recrystallized from o-dichlorobenzene as yellow
needles (81%): mp > 320 °C. The low solubility of 7e
prevented the use of NMR as a means of characterization. The
X-ray structure was obtained (vide supra).
P r ep a r a tive P h otolysis. In a typical run, 1.2 g of ethene
(5) and 2 equiv of iodine was dissolved in 1.4 L of toluene.
This solution was irradiated through Pyrex in an immersion
well equipped with either a 700 W or 400 W medium pressure
Hg-lamp. During photolysis the solution was flushed with
nitrogen. Irradiation was stopped when the starting material
was no longer detectable by means of either TLC or absorption
spectrometry. In some cases, the product precipitated during
photolysis, and the solution was filtered before further workup.
Intermediate cleaning of the surface of the cooling mantle was
sometimes necessary during preparative photolysis. The
filtered solution was shaken with a solution of sodium dithion-
ite in water in order to remove excess iodine. The phases were
separated, and the organic phase was washed with water and
the solvent evaporated in vacuo leaving the crude product.
Recrystallization (or fractional recrystallization if two products
arose from the photolysis) of the crude product and the filtrate
afforded the pure compound(s).
5-P h e n yl-4-(t h iop h e n e -2-yl)-t h ie n o[3,2-a ]n a p h t h a -
len e (6f) a n d Diben zo[a ,h ]d ith ien o[3,2-c:2′,3′-f]n a p h th a -
len e (7f). 1,1-Dithienyl-2,2-diphenylethene (1.0 g, 2.9 mmol)
was irradiated according to the standard procedure. Com-
pound 7f is rather soluble in toluene and did not precipitate.
Instead, the solvent was evaporated in vacuo, and the remain-
ing solid was dissolved in 50 mL of hot toluene and subjected
to column chromatography (basic aluminum oxide, hot tolu-
ene). The first fraction was collected and the solvent evapo-
rated in vacuo. Recrystallization from toluene (active carbon)
afforded 423 mg (43%) of 7f as pale yellow flakes: mp 260-
1
262 °C; H-NMR (250 MHz, DMSO-d6) δ 9.1 (dd, J ) 8 Hz, J
) 2 Hz, 2H), δ 8.75 (dd, J ) 8 Hz, J ) 2 Hz, 2H), 8.5 (d, J )
5 Hz, 2 H), 8.2 (d, J ) 5, 2H), 7.8 (m, 4H); MS (70 eV): 340
(M+, 100), 395 (7), 170 (M2+, 8). UV-vis λmax (nm) (log ꢀ)
(CH2Cl2): 237 (4.46), 296 (4.69), 307 (4.81), 341 (4.22), 355
(4.16), 385 (3.54). Anal. Calcd for C22H12S2: C, 77.61; H, 3.55;
S, 18.83. Found: C, 77.83; H, 3.64; S, 18.93.
The filtrate was evaporated in vacuo and recrystallized from
petroleum (bp 60-80 °C)/toluene (10:2) affording 184 mg (19%)
of 6f as colorless flakes: mp 196.5-198.5 °C; 1H-NMR (250
MHz, CDCl3) δ 8.4 (d, J ) 5 Hz, 1H), δ 8.1 (d, J ) 5 Hz, 1H),
7.6 (t, 3H), 7.3 (m. 7H), 7.1 (d, 1H), 7.0 (t, 1H) MS (70 eV):
342 (M+, 100), 308 (30), 171 (M2+, 8). UV-vis λmax (nm) (log ꢀ)
(CH2Cl2): 247 (4.66), 313 (4.16). Anal. Calcd for C22H14S2:
C, 77.15; H, 4.12; S, 18.73. Found: C, 77.19; H, 4.12; S, 18.01.
4,5-B is (t h io p h e n e -2-y l)t h ie n o [3,2-e]b e n zo [b ]t h io -
p h en e (6a ) a n d Tetr a th ien o[2,3-a :3′,2′-c:2′′,3′′-f:3′′′,2′′′-h ]-
n a p h th a len e (7a ). Tetrakis(thiophene-2-yl)ethene (1.75 g,
4.9 mmol) was irradiated as described above and monitored
by means of UV-spectroscopy. When the photolysis was
finished, the solution was filtered and processed as in the
general procedure. The solid from the filtrate (502 mg) and
the precipitate (1.30 g) were combined and extracted with 40
mL of boiling toluene. After evaporation of the toluene in
vacuo and recrystallization of the crude product twice from
toluene/heptane 85/15 (active carbon), 6a could be isolated as
colorless crystals (243 mg, 14%); mp 147-149 °C; 1H-NMR (250
MHz, DMSO-d6) δ 8.1 (dd, J ) 5,5 Hz, 4H), 7.8 (q, J ) 5 Hz,
J ) 1 Hz, 2H), 7.3 (q, J ) 5 Hz, J ) 5 Hz, 2H), 7.2 (q, J ) 5
Hz, J ) 5 Hz, 2H). MS (70 eV): 354 (M+, 100), 309 (20), 277
(M2+, 4). Anal. Calcd for C18H10S4: C, 61.00; H, 2.82; S, 36.18.
Found: C, 61.02; H, 2.82; S, 36.36. UV-vis λmax (nm) (log ꢀ)
(cyclohexane): 256 (4.60), 283 (4.59), 318 (4.59). The residue
from the extraction was recrystallized twice from o-xylene
(active carbon) leaving 503 mg (29%) of 7a as yellow-orange
needles: mp > 330 °C; 1H-NMR (250 MHz, bromobenzene-d5,
130 °C) 8.1 (dd, J ) 5,0 Hz). MS (70 eV): 352 (M+, 100), 307
(9), 276 (M2+, 12). UV-vis λmax (nm) (log ꢀ) (benzene): 289
(4.66), 300 (4.95), 324 (4.39), 338 (4.46), 359 (3.55), 378 (3.62).
Anal. Calcd for C18H8S4: C, 61.34; H, 2.27; S, 36.38. Found:
C, 61.36; H, 2.36; S, 36.58.
4,5-Diph en ylth ien o[3,2-e]ben zo[b]th ioph en e (6d2). 1,2-
Bis(thiophene-2-yl)-1,2-diphenylethene (E/Z) (5d ) (1.02 g, 3.0
mmol) was irradiated according to the standard procedure.
Evaporation of the solvent in vacuo and recrystallization from
heptane afforded 678 mg (68%) of 6d 2 as colorless needles:
1
mp 190-192 °C; H-NMR (250 MHz, CDCl3) δ 7.8 (d, J ) 5
Hz, 2H), δ 7.4 (d, J ) 5 Hz, 2H), 7.3 (m, 10H). MS (70 eV):
342 (M+, 100), 308 (35), 282 (10). UV-vis λmax (nm) (log ꢀ) (CH2-
Cl2): 254 (4.35), 307 (4.27). Anal. Calcd for C22H14S2: C,
77.15; H, 4.12; S, 18.73. Found: C, 77.36; H, 4.11; S, 18.48.
(Z)-1,2-Bis(th iop h en e-2-yl)eth en e was prepared accord-
ing to Kumada et al.46 using (thiophene-2-yl)magnesium
1,4,7,10-Tetr am eth yltetr ath ien o[2,3-a :3′,2′-c:2′′,3′′-f:3′′′,2′′′-
h ]n aph th alen e (7b). Tetrakis(5-methylthiophene-2-yl)ethene
(5b) was photolyzed according to the standard procedure. The
(46) Kumada, M.; Tamao, K.; Sumitani, K. Organic Syntheses;
Wiley: New York, 1963; Coll. Vol. IV, p 407.

Sulfur Heteroaromatics Isoelectronic with Dibenzo[g,p]chrysene
J . Org. Chem., Vol. 61, No. 20, 1996 7005
bromide, (E)-dichloroethene, and dichloro[1,2-bis(diphenylphos-
phino)ethane]nickel(II). Bp 105-109 °C/1.4 mbar. 1H-NMR
(90 MHz, CDCl3) δ 6.6 (s, 2H), 6.95 (dd, J ) 1 Hz, J ) 5 Hz,
2H) 7.15 (dd, J ) 5 Hz, J ) 5 Hz, 2H) 7.25 (dd, J ) 1 Hz, J )
5 Hz, 2H); MS (70 eV): 192 (M+, 100), 147 (39), 115 (10).
Ch a r ge Tr a n sfer Com p lex betw een Tetr a th ien o[2,3-
a :3′,2′-c:2′′,3′′-f:3′′′,2′′′-h ]n a p h th a len e a n d Tetr a cya n o-p-
qu in od im eth a n e (TCNQ). To a hot saturated solution of
7a (50 mL) in o-xylene was added a hot saturated solution of
TCNQ in o-xylene (50 mL). The mixture was left for slow
cooling overnight. The crystals were collected by filtration and
washed with small amounts of xylene and dried. IR (KBr)
-1
2221 cm
(CN). Anal. Calcd for C30H12N4S4: C, 64.74; H,
2.16; N, 10.06; S, 23.04. Found: C, 64.80; H, 2.21; N, 10.04;
S, 22.96.
(47) The authors have deposited atomic coordinates for this struc-
ture with the Cambridge Crystallography Deposition Center. The
coordinates, bond distances and angles, and thermal parameters can
be obtained, on request, from the Director, Cambridge Crystallography
Deposition Center, 12 Union Road, Cambridge CB2 1EZ, UK.
J O960022X