Directed electrophilic cyclizations: Efficient methodology for the synthesis of fused polycyclic aromatics

Article abstract of DOI:10.1021/ja9642673

A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and Negishi type cross-coupling chemistries allow for the preparation of nonfused skeletal ring systems in yields consistently >80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes 4-alkoxyphenylethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended polycyclic aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic insights and problematic side reactions are described.

Full text of DOI:10.1021/ja9642673

4578
J. Am. Chem. Soc. 1997, 119, 4578-4593
Directed Electrophilic Cyclizations: Efficient Methodology for
the Synthesis of Fused Polycyclic Aromatics
Marc B. Goldfinger,† Khushrav B. Crawford,‡ and Timothy M. Swager*,‡
Contribution from the Department of Chemistry, Massachusetts Institute of Technology,
77 Massachuestts AVenue, Cambridge, Massachusetts 02139, and Department of Chemistry,
UniVersity of PennsylVania, Philadelphia, PennsylVania 19104
ReceiVed December 10, 1996X
Abstract: A versatile method for the synthesis of complex, fused polycyclic aromatic systems in high chemical
yield is described. Construction is achieved using a general two-step synthetic sequence. Pd-catalyzed Suzuki and
Negishi type cross-coupling chemistries allow for the preparation of nonfused skeletal ring systems in yields consistently
>80%. The critical ring-forming step, which generally proceeds in very high to quantitative yield, utilizes
4-alkoxyphenylethynyl groups and is induced by strong electrophiles such as trifluoroacetic acid and iodonium
tetrafluoroborate. The reaction in essence produces phenanthrene moieties which are integrated into extended
polycyclic aromatic structures. Fused polycyclic benzenoids as well as benzenoid/thiophene systems may be prepared
utilizing this methodology. The scope of the described cross-coupling/cyclization chemistry including mechanistic
insights and problematic side reactions are described.
Introduction
photo- and electroluminescent,17-20 and molecule-based sensory
devices.21-27 These materials function as a result of their highly
conjugated π electron systems, which can transform an applied
bias or optical input to a desired response. Examples of these
advanced materials include substituted polyphenylenes, poly-
thiophenes, and push-pull NLO materials which are inherently
rigid as a result of their highly unsaturated frameworks. It is
commonly believed that the degree of conjugation and hence
properties in such systems can be enhanced if they can be
rigidified to eliminate conformational disorder which lowers
conjugation.28 Fused polycyclic aromatics are an obvious
chemical structural class which would meet this requirement
while maintaining conjugation.
The availability of rigid molecular platforms is critical to
advances in a number of areas of chemical research. Examples
include host-guest chemistry where rigid molecules often serve
as substrate-specific receptors,1-6 liquid crystal chemistry
wherein molecules posessing a rigid core are required to achieve
mesomorphic behavior,7-10 and even biochemical studies of
synthetic peptides wherein carefully designed rigid segments
serve as â-turn mimics.11-13 The utility of such rigid molecular
structures can be altered and even enhanced if, in addition to
being highly rigid, the molecules are extensively conjugated.
Rigid conjugated materials are the key components in a number
of advanced technologies utilizing nonlinear optical (NLO),14-16
While a number of methodologies are presently available for
the direct preparation of fused polycyclic aromatic systems, most
are plagued by some type of limitation. The most widely
employed and direct method is the Mallory photochemical
cyclization.29 This method is the most versatile route as the
cyclization can be performed on a variety of frameworks
† Taken from the thesis of M.B.G. completed at the University of
Pennsylvania. Present address: DuPont Central Research and Development,
Experimental Station, Wilmington, DE 19880.
‡ Present address: Department of Chemistry, Massachusetts Institute of
Technology, Cambridge, MA 02139.
X Abstract published in AdVance ACS Abstracts, May 1, 1997.
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S0002-7863(96)04267-9 CCC: $14.00 © 1997 American Chemical Society

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4579
Scheme 1
Scheme 2
including cis-substituted stilbenes to give phenanthrene type
subunits, o-terphenyl systems to give triphenylene type struc-
tures, and 2-olefinic biphenyls to produce substituted phenan-
threne systems (Scheme 1). The primary limitation of the
photochemical route is the necessarily dilute conditions (∼10-3
M) under which the reaction must be run, limiting it to the
preparation of only analytical quantities of material.
highly functionalized materials, the lower yields and multistep
syntheses necessary for the preparation of precursor compounds
make these methodologies more amenable to complex molecule
synthesis than to the synthesis of topologically interesting
molecules in useful quantities.
With the goal of ultimately preparing polymeric fused
polycyclic aromatic systems,48 we first endeavored to develop
versatile, high-yielding synthetic routes to their corresponding
molecular analogues. Of interest was a report wherein Barlu-
enga used iodonium tetrafluoroborate (IBF4), a highly electro-
philic source of iodonium ion, to cyclize 1,4-diphenylbut-1-
yne to the corresponding iododihydronapthalene (Scheme 2,
top).49 We desired to modify this system such that cyclization
would produce a fused polycyclic aromatic. In order to
exclusively form 6-membered rings, it was necessary to
convince the majority of positive chargesresulting from initial
electrophilic attacksto reside on the carbon atom labeled as â
(Scheme 2, bottom). Hence, it was necessary to chose a group
R which could provide more favorable positive charge stabiliza-
tion than the phenyl group attached to carbon atom labeled R.
To accomplish this, R was chosen to be an electron-rich
p-alkoxyphenyl group, which provides resonance stabilization
of the positive charge at the â carbon.
This electrophile-direction strategy proved successful, and in
this paper, we describe our studies of this novel cyclization
reaction including synthetic and mechanistic implications. In
addition, we describe the preparation of the cyclization precursor
systems utilizing Pd-catalyzed cross-coupling chemistry. This
tandem cross-coupling/cyclization approach is highly effective
and hence constitutes a new high-yielding, versatile methodolgy
for the synthesis of fused polycyclic aromatic systems.50
Another direct route to fused polycyclic aromatics is the [2
+ 2] cyclization of thioketones which is followed by sulfur
elimination to give the aromatic product.30 This method, while
proceeding in very high yield is limited in its versatility as it
requires structurally specific and synthetically challenging
precursor structures. Another well-explored approach to the
construction of polycyclic aromatics is the utilization of Diels-
Alder chemistry to provide access to precusor ring systems
which may be aromatized upon further chemical treatment.
Miller has oxidatively converted partially saturated precursor
ring systems to linear polyacenequinoids,31 while Schlu¨ter has
used oxidation32,33 and dehydration33,34 protocols to prepare
fused aromatic ladder polymers. In another case, Katz has
prepared [5]- and [6]helicenes by Diels-Alder reaction of
R-substituted divinylnapthalenes with p-benzoquinone.35 Com-
plete aromatization is achieved by reductive trapping of the
quinoidal product.36 Longitudinally twisted polycyclic aromatics
have been prepared by Pascal using a thermally induced Diels-
Alder/elimination protocol.37 Additional routes to fused poly-
cyclic aromatic systems include annulation strategies which
often employ metal carbene38-43 and/or vinyl ketene44-47
intermediates. While these methodologies allow access to
(30) Steliou, K.; Salama, P.; Xu, X. J. Am. Chem. Soc. 1992, 114, 1456.
(31) Thomas, A. D.; Miller, L. L. J. Am. Chem. Soc. 1986, 51, 4160-
4169.
(32) Schlu¨ter, A.; Loffler, M.; Enkelmann, V. Nature 1994, 368, 831.
(33) Schlicke, B.; Schirmer, H.; Schlu¨ter, A. AdV. Mater. 1995, 7, 544.
(34) Loffler, M.; Schlu¨ter, A.; Gessler, K.; Saenger, W.; Toussaint, J.;
Bre´das, J. Angew. Chem., Int. Ed. Engl. 1994, 33, 2209.
(35) Willmore, N. D.; Liu, L.; Katz, T. J. Angew. Chem., Int. Ed. Engl.
1992, 31, 1093-1095.
(36) Nuckolls, C.; Katz, T. J.; Castellanos, L. J. Am. Chem. Soc. 1996,
118, 3767.
(37) Pascal, R. A.; McMillan, W. D.; Engen, D. V.; Eason, R. G. J. Am.
Chem. Soc. 1987, 109, 4660-4665.
(38) Dotz, K. H. Angew. Chem., Int. Ed. Engl. 1984, 23, 587-608.
(39) Katz, T. J.; Sivavec, T. M. J. Am. Chem. Soc. 1985, 107, 737-
738.
Results and Discussion
The general structural requirement for the precursor systems,
in addition to the carbocation directing group, is that the alkynyl
group and the aromatic ring undergoing electrophilic substitution
(Ar′) must be ortho-substituted. All systems reported contain
a central ring to which two (p-alkoxyphenyl)ethynyl-Ar′ pairs
are attached. We have studied symmetric systems in which the
two Ar′ partners are configured para, meta, and ortho to each
other (Figure 1).
(40) Merlic, C. A.; Burns, E. E.; Xu, D.; Chen, S. Y. J. Am. Chem. Soc.
1992, 114, 8722-8724.
(41) Merlic, C. A.; Pauley, M. E. J. Am. Chem. Soc. 1996, 118, 11319.
(42) Semmelhack, M. F.; Ho, S.; Cohen, D.; Steigerwald, M.; Lee, M.
C.; Lee, G.; Gilbert, A. M.; Wulff, W. D.; Ball, R. G. J. Am. Chem. Soc.
1994, 116, 7108-7122.
(46) Xu, S. L.; Moore, H. W. J. Org. Chem. 1992, 57, 326.
(47) Sun, L.; Liebeskind, L. S. J. Org. Chem. 1995, 60, 8194-8203.
(48) Goldfinger, M. B.; Crawford, K. B.; Swager, T. M. Unpublished
results.
(49) Barluenga, J.; Gonzalez, J. M.; Campos, P. J.; Asensio, G. Angew.
Chem., Int. Ed. Engl. 1988, 27, 1546.
(43) Sivavec, T. M.; Katz, T. J.; Chiang, M. Y.; Yang, G. X. Organo-
metallics 1989, 8, 1620-1625.
(44) Koo, S.; Liebeskind, L. S. J. Am. Chem. Soc. 1995, 117, 3389.
(45) Danheiser, R. L.; Casebier, D. S.; Firooznia, F. J. Org. Chem. 1995,
60, 8341-8350.
(50) Goldfinger, M. B.; Swager, T. M. J. Am. Chem. Soc. 1994, 116,
7895.

4580 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
Scheme 3
compounds are obtained as colorless solids and may be
crystallized from a variety of common organic solvents. The
highly soluble nature of these materials is attributed to the
presence of the dodecyloxy groups which provide an entropic
driving force for solubilization. In our optimization of these
coupling reactions, we found several parameters to be critical.
In agreement with the work of Kim and Webster,55 we found
nitrobenzene to be a more effective solvent than toluene and
dimethoxyethane (DME), which are more commonly used. In
addition, employing smaller amounts of catalyst (0.3%) was
generally more effective than larger amounts (2-5%). This
result may be attributable to unwanted Heck type reactions with
the dibenzylideneacetone (dba) ligands and a reduction in the
tendency of the catalyst to deactivate prematurely by forming
Pd black.56,57 We cannot attribute the improved yields with
low catalyst ratios to the inhibition or reduction of aryl exchange
reactions which have been previously observed,58-63 since higher
ligand to metal ratios (>15:1) had virtually no effect on the
reaction. Lower ligand to metal ratios (4:1) were detrimental,
as the catalyst rapidly precipitated out of solution as inactive
Pd black.
Figure 1. General topology of precyclized structures investigated.
Para-Substituted Systems. With a general design concept
in mind, we have prepared precursor systems with the general
structures 2-5. This was accomplished in short order starting
with 1,4-dibromobenzene. Utilizing a modified version of an
iodination procedure developed by Mattern,51 1,4-dibromo-2,5-
diiodobenzene was produced in 50% yield (Scheme 3). Al-
though the yield is modest, starting materials are relatively
inexpensive and quantities on the order of 2-300 g can be easily
prepared. This intermediate is a versatile building block since
coupling at the iodide positions can be effected with complete
chemoselectivity using Pd-catalyzed cross-coupling reactions,
leaving the bromide positions available for further cross-
coupling under more aggressive conditions. The tetrahalide was
reacted with 2 equiv of 4-(dodecyloxy)phenylacetylene, prepared
in three steps from 4-iodophenol (87% overall), using standard
Pd(0)/Cu(1) cocatalysis to produce the dibromide 1 (73%).52,53
Treatment of the dibromide 1 with a variety of substituted
phenylboronic acids under modified Suzuki cross-coupling
conditions54 produced the substituted terphenyls 2-5. These
Initial cyclization attempts were conducted on compound 2
using the protocol reported by Barluenga.49,64,65 Treatment of
I(pyr)2BF4 with 2 equiv of triflic acid (TfOH) precipitates
(55) Kim, Y. H.; Webster, O. W. Macromolecules 1992, 25, 5561.
(56) Ukai, T.; Kawazura, H.; Ishii, Y.; Bonnet, J. J.; Ibers, J. A. J.
Organomet. Chem. 1974, 65, 253-266.
(57) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic:
New York, 1985.
(58) Kong, K.-C.; Cheng, C. J. Am. Chem. Soc. 1991, 113, 6313.
(59) O’Keefe, D. F.; Dannock, M. C.; Maruccio, S. M. Tetrahedron Lett.
1992, 33, 6679.
(60) Wallow, T. I.; Novak, B. M. J. Org. Chem. 1994, 59, 5034.
(61) Segelstein, B. E.; Butler, T. W.; Chenard, B. L. J. Org. Chem. 1995,
60, 12.
(51) Mattern, D. L. J. Org. Chem. 1983, 48, 4772-4773.
(52) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975,
4467.
(62) Hunt, A. R.; Stewart, S. K.; Whiting, A. Tetrahedron Lett. 1993,
34, 3599.
(63) Morita, D. K.; Stille, J. K.; Norton, J. R. J. Am. Chem. Soc. 1995,
117, 8576-8581.
(53) Dieck, H. A.; Heck, R. F. J. Organomet. Chem. 1975, 93, 259-
263.
(54) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-2483.

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4581
pyridine as its triflate salt and liberates free IBF4. However,
use of this procedure resulted in mixtures of cyclization products.
We reasoned that H+ from unreacted TfOH or from the acid
produced during the cyclization was competing with I+.
Consistent with this reasoning, treatment of 2 with TfOH alone
produces the substituted dibenz[a,h]anthracene product 6 ex-
clusively, in quantitative yield. We have found that the same
transformation can be effected under much milder conditions
employing trifluoroacetic acid (TFA) in place of TfOH. Reduc-
tion of the TfOH/I(pyr)2BF4 ratio from 2:1 to 1:1 resulted in
the exclusive formation of 7 (96%), since 1 equiv of pyridine
(pyr) was still available to react with the acid produced during
the reaction. The versatility of the cyclization reaction is
apparent as substrates with a variety of substitution patterns (6-
10) were prepared.
Scheme 4
The conversion of substituted p-terphenyls (2-5) to dibenz-
[a,h]anthracene systems (6-10) was accompanied by consistent
and diagnostic spectral changes. All substituted p-terphenyls
were obtained as colorless materials and were converted to
yellow to bright yellow materials on cyclization. The UV-vis
spectra of these materials, on cyclization, exhibit a characteristic
bathochromic shift for the onset of absorption and a hypso-
chromic shift for λmax. Compound 2, for example, displays an
absorption maximum (λmax) at 342 nm (ꢀ ) 59 900) with a
shoulder at 364 nm (ꢀ ) 51 000). On conversion to 6, λmax
shifts to 318 nm (ꢀ ) 55 600) and lower intensity absorptions
appear at 280 (ꢀ ) 37 500), 356 (ꢀ ) 24 600), 374 (ꢀ ) 24 000),
406 (ꢀ ) 12 100), and 430 (ꢀ ) 14 400) nm. These optical
properties, particularly the observation of low-intensity absorp-
tions (relative to λmax) on the low-energy side of λmax, are similar
to those observed for similar polycyclic aromatic hydrocar-
trends observed for the conversions of compounds 3-5 to 8-10
were consistent with those described for the conversion of 2 to
6 and 7 and are in complete agreement with the reported
structures.
To further investigate the scope of the reaction, we prepared
11-13 (Scheme 4), which lack the p-alkoxy directing groups
present in 2-5. Compound 11 contains simple alkyl directing
groups in place of p-alkoxyphenyl groups. Treatment of these
systems with TFA resulted in the complete recovery of starting
material. Exposure to I(pyr)2BF4 produced complex mixtures
of products, most likely due to competitive aryl ring iodination.
These results indicate that the p-alkoxy group on the phenyl-
ethynyl moiety is indeed critical to the success of the reaction.
In addition, the presence of the electron-activating methoxy
groups as in 2 and 12 is not necessary as evidenced by the
quantitative formation of 8. Regarding solvent, the reaction has
proven successful only in halogenated (polar, non-nucleophilic)
solvents such as methylene chloride, 1,2-dichloroethane, and
1,2,3-trichloropropane. The reaction fails in hydrocarbon
solvents (hexane and pentane) and ethereal solvents (THF and
diethyl ether). These results support our assertion that the
reaction proceeds through a carbocationic intermediate species,
as is shown in Scheme 5. Selective electrophilic attack at the
acetylenic carbon attached to the central ring of the terphenyl
moiety is driven by resonance stabilization provided by the
p-alkoxy directing group. Ring closure may then occur by
electrophilic attack on the outer rings of the terphenyl moiety
in a Friedel-Crafts type manner. This ring closure is ac-
companied by loss of a proton, making the reaction catalytic.
However, for kinetic purposes a large excess of acid was usually
employed. In addition, we believe that ring protonation occurs,
necessitating the use of excess acid. This claim is based on
the deep green color which was observed during the cyclization
of more electron-rich systems. In fact, treatment of compound
9 with TFA-d overnight resulted in extensive substitution of
deuterium for hydrogen on the aromatic ring system.
1
bons.66 The H NMR spectra of these materials also display
characteristic changes. The singlet assigned to the 3′ and 6′
protons of compound 2 appears at 7.59 ppm and shifts downfield
to 10.10 ppm on conversion to 6 where they are located at the
7 and 14 positions. Such downfield signals are characteristic
of bay region protons. The new singlet present for 6 at 7.78
ppm corresponds to the protons at the 6 and 13 positions. Four
additional aromatic resonances are present in the 1H NMR
spectrum of 6, all doublets. Two of these doublets (6.94 and
7.34 ppm) correspond to the protons on the p-alkoxyphenyl
moieties, while the other two doublets (7.03 and 7.18 ppm),
with an integrated area 50% of the first two doublets, correspond
to the protons on the terminal rings of the dibenz[a,h]anthracene
ring system. In the 13C NMR spectra, the conversion from 2
to 6 is accompanied by the disappearance of acetylenic
resonances (88.11 and 93.31 ppm) for 2 and an increase from
13 to 15 for the number of aromatic resonances. This change
is attributable to the conversion of the acetylene carbons to
aromatic carbons. Compounds 2-10 all display high-resolution
mass spectra (HRMS) in agreement with the proposed structures,
and the low-resolution mass spectrum (LRMS) of the diiodide
7 (M+ ) m/z 1170.4) displays signals at m/z 1044 and 918,
corresponding to the loss of the two iodides. As additional
structure proof, the diiodide 7 was treated with s-BuLi and the
reaction was quenched with 2-propanol. The 1H NMR spectrum
of the compound obtained (>99% by NMR) is identical to the
spectrum obtained following the direct treatment of 2 with TFA,
providing additional support for the structure 6. The spectral
(64) Barluenga, J.; Gonzalez, J. M.; Campos, P. J.; Asensio, G. Angew.
Chem., Int. Ed. Engl. 1985, 24, 319.
(65) Barluenga, J.; Rodriguez, M. A.; Gonzalez, J. M.; Campos, P. J.
Tetrahedron Lett. 1990, 31, 4207.
(66) Karcher, W.; Fordham, R. J.; Dubois, J. J.; Glaude, P. G. J. M.;
Ligthart, J. A. M. Spectral Atlas of Polycyclic Aromatic Compounds; D.
Reidel: Dordrecht, The Netherlands, 1985.
As is evident from the structure of 13, we were interested in
preparing fused polycyclic aromatic heterocycles as well as
aromatic hydrocarbons. As a first example we investigated Ar′

4582 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
Scheme 5
We have found that the cyclization may also be performed
directly onto a thiophene moiety. The cyclization precursor 16
was prepared (Scheme 7) in quantitative yield using a Negishi
type coupling,67,68 utilizing the dibromide 1 with 2 equiv of
2-(chlorozincio)-5-methylthiophene. Cyclization of the precur-
sor 16 becomes problematic, however, as a 5/6 mixture of
products 17 and 18 was obtained. While the two structural
1
isomers have proven inseparable, their H NMR (500 MHz,
CDCl3) resonances are easily discernible due to the asymmetric
nature of 18. Changes in chemical shifts due to shielding/
deshielding effects of the migrated phenyl proved critical in
identifying structure 18. The methyl resonance of 17 appears
at 2.64 ppm, and on conversion to 18, the methyl in the relatively
unchanged environment appears at 2.65 ppm while the methyl
on the side of the migrated phenyl, now deshielded, moves
downfield to 2.70 ppm. More diagnostic is the effect on the
thienyl proton which appears at 7.19 ppm for 17. On conversion
to 18, the thienyl proton in the nearly unchanged environment
appears at 7.20 ppm while the deshielded thienyl proton appears
at 7.83 ppm. The thienyl protons are easily identifiable as they
appear as apparent doublets due to a weak coupling (J ) 0.8-
1.2 Hz) with the adjacent methyl groups. The 1H NMR
spectrum of 17 displays four aromatic resonances in addition
to the thienyl resonance just discussed. Two of these resonances
appear as doublets and correspond to the protons on the
p-alkoxyphenyl groups. The remaining two resonances appear
as singlets and correspond to the pseudo bay protons (8.55 ppm)
and the 5/11 protons (7.75 ppm). There are no resonances
detected which display the distinctive coupling constant (J )
3.6 Hz) attributed to a 3,4-thienyl spin system,69 as was evident
in 16. Compound 18, in addition to the two thienyl resonances,
displays four singlets and three doublets in the aromatic region.
Two of the singlets correspond to the pseudo bay region protons
(8.57 and 8.76 ppm) while the remaining two singlets correspond
to the 5 and 10 protons (7.77 and 7.78 ppm). One doublet
(broad) appears at 7.04 ppm and corresponds to four hydrogens
of the p-alkoxyphenyl groups, while the remaining two doublets
(7.59 and 7.74 ppm) correspond to two protons each. Additional
support that the two compounds exist as structural isomers
comes from mass spectral and combustion data. In the low-
resolution mass spectrum, the only signals present are for the
molecular ion (m/z 838) and for the loss a dodecyl side chain
(m/z 670), while the HRMS data obtained are accurate to 1 ppm.
As shown in Scheme 7, product 18 forms by phenyl migration
of the “correct” cyclization product 17, presumably through a
phenonium ion.70 The occurrence of this event is not surprising
as it has been previously reported that biphenyl, 13C-enriched
at the ipso (1) position, undergoes rearrangement at 50 °C with
AlCl3/H2O in C6H6 to give biphenyl which is 13C-enriched at
the 2, 3, and 4 positions.71 The observation that migration is
occurring in our system under much milder conditions is not
surprising as it has been reported that p-methoxyphenyl
undergoes migration approximately 500-880 times faster than
phenyl in the pinacol rearrangement.72,73 Treatment of 16 with
an iodonium source should prevent aryl migration, as I+ addition
groups (Figure 1) incorporating fused heterocyclic linkages.
4-Dibenzothiopheneboronic acid was prepared by metalation of
dibenzothiophene with n-BuLi in THF followed by a B(OMe)3
quench and acidic (5% HCl) hydrolysis.2 Two equivalents of
the boronic acid were coupled with 1 equiv of 1 to produce
cyclization precursor 14 in 86% yield (Scheme 6). The colorless
compound 14 was treated with TFA in CH2Cl2 at room
temperature (rt), and after approximately 10 min, a bright yellow
crystalline compound precipitated from the solution. The
product was exclusively the biscyclized compound 15, indicating
the monocyclized product displays much greater solubility.
On conversion of the colorless 14 to the bright yellow 15,
an approximately 60 nm bathochromic shift is observed for the
onset of absorption (λonset (14) ≈ 390 nm, λonset (15) ≈ 450
nm) in the UV-vis spectrum. Consistent with the observations
made for compounds 2-10, a hypsochromic shift is observed
for λmax following cyclization (λmax (14) ) 346 nm, λmax (15)
) 340 nm), while lower intensity absorptions appear on the
low-energy side of λmax (372, 392, 404, and 430 nm). In the
1H NMR spectrum of 14, the protons assigned to the 3 and 6
positions of the central ring appear as a singlet at 7.98 ppm
and shift downfield to 9.88 ppm on conversion to 15, where
they are now bay region protons (10 and 20). The chemical
shifts of the two doublets attributed to the p-alkoxyphenyl
moiety appear at 6.66 and 6.99 ppm for compound 14, as they
are shielded by the dibenzothiophenyl moiety, which is permitted
to freely rotate. On cyclization to 15, rotation is eliminated;
hence, shielding is reduced and the two doublets are shifted
downfield to 7.12 and 7.60 ppm. These aromatic shielding
effects are not as dramatic in systems 2-10, as the terminal
aryl groups (substituted phenyls), physically much smaller than
the dibenzothiophenyl groups, are not able to shield as ef-
fectively. Two additional doublets appear at 8.12 and 8.31 ppm
1
in the H NMR spectrum of 15 and correspond to the pro-
(67) Negishi, E.; King, A. O.; Okukado, N. J. Org. Chem. 1977, 42,
1821.
(68) Negishi, E. Acc. Chem. Res. 1982, 15, 340.
(69) Silverstein, R. M.; Bassler, G. C.; Morrill, T. C. Spectrometric
Identification of Organic Compounds, 4th ed.; John Wiley & Sons: New
York, 1981; p 236.
(70) Lowery, T. H.; Richardson, K. S. Mechanism and Theory in Organic
Chemistry, 3rd ed.; Harper & Row: New York, 1987; pp 434-446.
(71) Necula, A.; Racoveanu-Schiketanz, A.; Gheorghiu, M. D.; Scott,
L. T. J. Org. Chem. 1995, 60, 3448-3451.
(72) Bachmann, W. E.; Ferguson, J. W. J. Am. Chem. Soc. 1934, 56,
2081.
tons at the 6/16 and 7/17 positions (not assigned). The presence
of these doublets confirms the conversion of the ABC spin
systems present on the dibenzothiophenyl moieties of 14 to
AB spin systems on cyclization to 15. The 13C NMR spec-
trum of compound 14 displays two acetylenic resonances (87.25
and 95.05 ppm) and 17 aromatic resonances (19 expected),
while no acetylene resonances and 21 aromatic resonances
(21 expected) are observed for 15. Accurate HRMS data
and satisfactory combustion analyses were obtained for both
14 and 15.
(73) Depovere, P.; Devis, R. Bull. Soc. Chim. Fr. 1969, 479.

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4583
Scheme 6
Scheme 7
at the phenyl juncture should be energetically unfavorable.
However, this approach was precluded by the rapid oxidation
of 16 on exposure to iodonium.
of slight shielding from the migrated p-butoxyphenyl groups:
the one methyl is shielded by the 13 p-butoxyphenyl and the 8
methyl is shielded by the 6 p-butoxyphenyl. The low-resolution
mass spectrum of 19 displays a lone signal corresponding to
the molecular ion (m/z 630.4) while the HRMS reading is
accurate to 1 ppm. The exclusive formation of the bismigrated
product 19 under thermodynamic conditions is not surprising
as it relieves the strain caused by the two peri interactions
present in 10-C4. In fact, AM1 calculations74 show a 10.9 kJ/
mol higher ∆Hf for 10-C4 (∆Hf ) 69.4 kJ/mol) than for 19
(∆Hf ) 58.5 kJ/mol).
Meta-Substituted Systems. Systems in which the Ar′
(Figure 1) substituents are oriented meta to each other were
prepared following the general synthetic methodology used to
prepare the para-substituted systems reported above. Iodination
of 1,3-dibromobenzene (Scheme 9) produced 1,5-dibromo-2,4-
diiodobenzene in 68% yield. The preparation of this tetrahalide
was operationally simpler than the preparation of its “para”
structural isomer as the reaction is not plagued by overiodinated
side products and can therefore be run between 0 and 25 °C
(<30 min reaction time). Compound 20, the “meta” structual
isomer of 1, was prepared in an analogous fashion in 88% yield
utilizing standard Pd(0)/Cu(1) cocatalysis. Reaction of 20 with
To examine the phenyl migratory event more closely, one of
the original model systems was reexamined. Compound 5-C4
(butoxy replaces dodecyloxy) when treated under standard
cyclization conditions (TFA, CH2Cl2, rt) produced the expected
product 10-C4 (Scheme 8). However, when heated to 135 °C
overnight using difluoroacetic acid in 1,2,3-trichloropropane
(1,2,3-TCP), the bismigrated product 19 was obtained exclu-
sively (74%). Alternately, 19 can be prepared from the
intermediate 10-C4 using the identical conditions. While
compounds 10-C4 and 19 show identical coupling patterns, their
structural assignments are supported by their diagnostic chemical
shifts, particularly those of the methyl groups. In the precyclized
system 5-C4, the two methyl resonances appear at 2.24 and
2.36 ppm. On cyclization to 10-C4, the 4/11 methyl resonances
shift upfield to 2.04 ppm as a result of shielding from the
p-butoxyphenyl groups located at the 5 and 12 positions. The
1/8 methyl protons, deshielded by the dibenz[a,h]anthracene ring
system move downfield to 3.18 ppm. Following rearrangement
to 19, the two methyl resonances appear at 2.70 and 2.79 ppm.
The 4/11 methyls, no longer shielded by the p-butoxyphenyl
groups which have migrated to the 6 and 13 positions, move
downfield while the 1/8 methyls now move upfield as a result
(74) Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P. J.
Am. Chem. Soc. 1985, 107, 3902-3909.

4584 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
Scheme 8
the conversion of 21 to 22 are not as great as those observed in
the para-oriented systems. Changes in the onset and maximum
of absorption are shifted by no more than 10 nm in either
direction on cyclization, while the overall spectral shapes are,
qualitatively, very similar. Both 21 and 22 display accurate
HRMS data and give satisfactory combustion analyses.
The cyclization of such meta-substituted systems provides
fused ring systems with an different overall shape than their
para analogues. For example, compound 22 is “U shaped”.
To generate analogs with a cavity, we prepared the extended
bis(dibenzothiophenyl) compound 23 (Scheme 10). On treat-
ment with TFA, an inseparable mixture of cyclized products
was obtained. Keeping in mind our previous experience with
phenyl migration, we sought to circumvent the problem with
the use of iodonium, which should block the adjacent position
and prevent migration. This strategy proved successful as a
single compound 24 was isolated as a bright yellow solid in
92% yield. The reaction was conducted using iodonium
generated in situ by reaction of Hg(TFA)2 with I2 in the presence
of 2,6-lutidine. This procedure proved to be operationally
simpler than using the bis(pyridine)iodonium tetrafluoroborate
reagent, since the addition of 2,6-lutidine may be carefully
controlled, precluding the addition of small quantities of TfOH.
The reaction using this procedure was rapid and usually
complete after only 10-20 min. The bay region proton (20)
now appears at 11.12 ppm, while the proton (10) sandwiched
between the two iodides appears at 9.67 ppm. These protons
appeared as singlets at 7.95 and 8.01 ppm prior to cyclization,
i.e., for compound 23. Similar shielding effects were observed
for the two doublets attributed to the p-alkoxyphenyl rings as
were observed for their counterparts in the conversion of 14 to
15. These doublets appear at 6.69 and 7.03 ppm for 23 and
shift downfield to 7.10 and 7.27 ppm after cyclization to 24.
This effect is not as dramatic as in the para case as a result of
shielding provided by the iodides. Compound 24 displays two
additional doublets (7.66 and 8.23 ppm) which result from the
conversion of the ABC spin systems on the dibenzothiophenyl
moieties of 23 to AB systems on cyclization, consistent with
Scheme 9
the observations made for the conversion of 14 to 15. The 13
C
NMR of 23 displays two acetylenic resonances and 19 aromatic
resonances (20 expected), while for 24, no acetylene resonances
are present and 22 aromatic resonances (22 expected) are
observed. The most upfield aromatic carbon resonance, present
at 107.14 ppm, most likely corresponds to the aryl carbons
bearing the iodides, which are known to dramatically shield the
carbons to which they are attached. Compound 24 gave a
HRMS accurate to 2.5 ppm and satisfactory combustion
analysis.
The iodides of 24 may be easily replaced by protons using
s-BuLi-mediated lithium-halogen exchange followed by a
2-propanol quench. The reduced product 25 was again isolated
1
as a bright yellow solid (97%). The H NMR spectrum of 25
2 equiv of phenylboronic acid produced the m-terphenyl 21 in
81% yield as an off-white solid. TFA-induced cyclization
provided the substituted dibenz[a,j]anthracene 22 (96%) as a
displays an additional resonance not observed for 24, a singlet
at 7.75 ppm attributed to the replacement of iodides with
protons. Interestingly, the two doublets assigned to the p-
alkoxyphenyl group now appear at 7.02 and 7.45 ppm. While
the downfield shift of one doublet due to removal of the
shielding iodides is expected, the reason for the slight upfield
shift of the other doublet is not apparent. The 13C NMR
spectrum of 25 displays 22 aromatic carbons (22 expected), and
the resonance which appeared at 107.12 ppm for 24 and was
assigned to the iodide bearing carbons is no longer observed,
with the most upfield aromatic resonance appearing at 114.37
ppm. The loss of the iodides is also reflected in the HRMS
which is accurate to within 1 ppm and in the combustion
1
light yellow solid. The H NMR spectrum of this compound
displays two downfield resonances corresponding to the three
bay region protons of 22: a doublet at 9.08 (2H) and a singlet
at 10.06 (1H) ppm. In the 13C NMR spectra, cyclization from
21 to 22 is accompanied by loss of the acetylenic resonances at
87.26 and 93.11 ppm and an increase in the number of aromatic
resonances from 12 to 16. The increase of four aromatic carbons
can be accounted for by the conversion of acetylenes to
components of the aromatic ring structure and desymmetrization
of the first and third rings of the o-terphenyl moiety on
cyclization. The effects on the optical properties observed for

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4585
Scheme 10
Scheme 11
analysis. In the UV-vis spectra, the wavelength of maximum
absorption λmax is shifted hypsochromically on cyclization, from
318 nm for 23 to 286 and 280 nm for 24 and 25, respectively.
Again the onset of absorption is shifted bathochromically from
ca. 380 nm for 23 to ca. 440 nm for both 24 and 25. It should
be noted that comparison of the 1H NMR spectrum of 25 with
spectra of materials obtained by the direct reaction of 23 with
TFA showed no overlap, thereby indicating that extensive acid-
promoted rearrangements/migrations were occurring.
As demonstrated earlier, we were interested in performing
cyclizations directly onto heterocyclic rings. The meta-
substituted bisthienyl compound 26 was prepared (Scheme 11)
in an analogous fashion to its para analogue 16. TFA promoted
cyclization now proceeds more cleanly, providing a 6:1 mixture
of the correct cyclization product 27 to its inseparable phenyl-
migrated isomer 28. In accord with the proposed structure 27,
three singlets were observed in the aromatic region at 8.65 (1H),
8.43 (1H), and 7.70 (2H) ppm, corresponding to the 12, 6, and
5/7 protons, respectively. Again, the thienyl proton of 27 is
observed as an apparent doublet at 7.20 ppm due to weak
coupling (J ) 0.9 Hz) with the adjacent methyl group. This
proton appeared at 6.80 ppm as a doublet of doublets (J ) 3.6,
0.9 Hz) prior to cyclization, i.e., for 26. Note also that the
doublet at 7.58 ppm (J ) 3.6 Hz) for 26 is no longer present in
the spectrum of 27 as this resonance corresponds to the proton
which is eliminated after the initial cyclization. The shielding
effects on the p-alkoxyphenyl are less dramatic than in the
conversion of 23 to 24 as the methylthienyl group is physically

4586 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
smaller than the dibenzothiophenyl group and not able to shield
as well. These p-alkoxyphenyl doublets appear at 6.88 and 7.47
ppm for 26 and shift to 7.03 and 7.57 ppm on conversion to
27. The cyclization is again accompanied by loss of the
acetylene resonances (13C NMR, appearing at 87.62 and 94.61
ppm for 26) and an increase in the number of aromatic
resonances from 12 (12 expected) for 26 to 14 (14 expected)
for 27. Due to the small amount present and the overlap of
resonances with 27, the structure 28 may only be tentatiVely
assigned; however, strong evidence exists in support of this
assignment. Minor resonances present in the 1H NMR spectrum
occur at 8.86 (s), 8.44 (s), and 7.92 (s) ppm and most likely
correspond to the 12, 6, and 9 protons of 28, respectively. The
7.92 ppm resonance qualitatively displays very similar line shape
to the resonance at 7.20 assigned to the 3 and 9 thienyl protons
and may correspond to the thienyl resonance on the “side” of
the molecule which has undergone phenyl migration. This
dramatic downfield shift from 7.20 to 7.92 ppm is consistent
with the analogous shift observed in the 17/18 system (7.19 to
7.83 ppm) and is again attributed to deshielding of the thienyl
proton. Additional signals appear at 7.71 and 7.73 and may
correspond to the 5/8 protons of 28, recalling that the 5/7 protons
of 27 appear at 7.70 ppm. The remaining resonances, i.e., those
of the p-alkoxyphenyl groups and the thienyl resonance in the
nearly unchanged environment are obscured by the resonances
attributed to 27. Interestingly, heating the mixture 27/28 with
TFA in 1,2-dichloroethane at 75 °C for 2 h improved the product
ratio from 6:1 to 10:1. This observation strongly supports the
assertion that 28 exists as a structural isomer which forms as
the result of an isomerization process from 27. Additional
support that 28 exists as a structural isomer comes from mass
spectral evidence. In the LR mass spectrum only two signals
ppm resonance corresponds to the 5/7 protons and the 7.58 ppm
resonance corresponds to the 3/9 thienyl protons. The conver-
sion of 29 to 31 is accompanied by loss of the acetylene
resonances (87.59 and 95.72 ppm) in the 13C NMR and an
increase in the number of aromatic carbons from 16 (16
expected) for 29 to 18 (18 expected) for 31. Again, due to the
small amount present and the overlap of resonances with 31,
the structure 32 may only be tentatiVely assigned. The positions
of the minor resonances ascribed to 32 relative to the resonances
ascribed to 31 reveal a trend consistent with the relative positions
observed for the 27/28 system. Minor resonances present in
1
the H NMR spectrum occur at 8.95 (s), 8.46 (s), and 8.29 (s)
ppm and correspond to the 12, 6, and 9 protons of 32,
respectively. The 8.29 ppm resonance qualitatively displays
very similar line shape to the resonance at 7.58 assigned to the
3 and 9 thienyl protons and may correspond to the thienyl
resonance on the side of the molecule which has undergone
phenyl migration. This downfield shift from 7.58 to 8.29 ppm
is consistent with the analogous shift observed in the 27/28
system (7.20 to 7.92 ppm) and is again attributed to deshielding
of the thienyl proton. The relative downfield positioning of
the signals is attributed to the deshielding effect of replacing a
methyl group with a thienyl group. Additional weak signals
appear at 7.73 and 7.75 and may correspond to the 5/8 protons
of 32. The remaining resonances are all obscured by the
resonances attributed to 31. The low-resolution mass spectrum
of the 31/32 mixture does display two signals at m/z 798 and
823 at 10% the intensity of the molecular ion (m/z 806, 100);
however, satisfactory combustion analysis was obtained provid-
ing additional support that 32 exists as a structural isomer.
Interestingly, the conversion is accompanied by a narrowing of
features in the UV-vis absorption spectrum of 31/32 relative
to 29. Compound 29 displays a broad absorption from 450 to
290 nm (λmax ) 366 nm). Following cyclization, low-intensity
absorptions appear at 440 and 406 nm, while the absorption
corresponding to λmax (370 nm) begins at 390 and ends at 280
nm with relatively sharp features. This narrowing effect is
attributed to a reduction in the number of accessible conforma-
tions available to the molecule upon rigidification of the ring
system.
Ortho-Substituted Systems. To extend the electrophilic
cyclization strategy beyond the meta and para systems, we
decided to explore the more sterically demanding ortho-
substituted system (where the aryl groups undergoing electro-
philic cyclization are ortho to each other; see Figure 1). If this
methodology were to be successful, it would provide entry to a
host of interesting helical structures.
To determine the efficacy of the cyclization for the ortho-
substituted systems, we targeted the o-terphenyl 35. This proves
an ideal substrate to study since the parent pentahelicene of the
cyclization product 37 is a known compound and its NMR is
available in the literature.76-78 Compound 35 was synthesized,
in a manner similar to that employed for the meta and para
systems, as outlined in Scheme 12.
are observed, corresponding to M+ (m/z 838.5) and (M+
-
C12H25) (m/z 670), while the HRMS agrees to within 1.5 ppm
of the calculated value.
The preparation of more complex structures was easily
accomplished by coupling of bithiophene to the dibromide 20.
In an effort to prepare conjugated polymers with helical
architectures, we were interested in preparing the bromide 30
by reaction of 1 equiv of 5-(chlorozincio)-2,2′-bithiophene with
1 equiv of 20. Homopolymerization of 30 using conditions
developed by McCullough75 would produce the desired poly-
mers. The coupling reaction to produce 30 afforded a statistical
mixture of products as the desired product 30 was obtained in
35% yield, while the disubstituted product 29 was obtained in
17% yield. The attempted cyclization of 29 using standard
conditions (CH2Cl2, 25 °C) resulted in the recovery of only
starting material. Heating the reaction to 65 °C in the higher
boiling solvent 1,2-dichloroethane produced a 6:1 mixture of
the product 31 and its phenyl-migrated structural isomer 32.
In the aromatic region of the 1H NMR spectrum of 31 a 2,3,4-
thienyl spin system is clearly present, as are the doublets
attributed to the p-(hexyloxy)phenyl groups. The remaining four
signals in the aromatic region are all singlets. The singlet at
8.72 (1H) corresponds to the pseudo bay region proton (12)
while the singlet at 8.42 (1H) corresponds to the proton at the
6 position. The remaining singlets at 7.58 and 7.72 ppm (2H
each) correspond to the 5/7 protons and the 3/9 thienyl protons.
The presence of thienyl rather than methyl groups at the 2/10
positions precludes splitting of the 3/9 thienyl protons, however,
the protons analogous to the 5/7 protons in 31 appear at 7.75
and 7.70 ppm in 17 and 27, respectively, implying that the 7.72
The synthesis commenced with the readily available (two
steps from o-xylene) 3,4-dibromo-2,5-diiodo-o-xylene. Chemose-
lective Pd(0)/Cu(I)-catalyzed coupling with 4-(butyloxy)phe-
nylacetylene provided the substituted dibromide 33 in good
yield. Unlike the meta and para systems, Suzuki coupling on
the dibromide 33 was unsuccessful. To increase the reactivity,
(76) Martin, R. H.; Defay, N.; Figeys, H. P.; Flammang-Barbieux, M.;
Cosyn, J. P.; Gelboke, M.; Schurter, J. J. Tetrahedron 1969, 25, 4985.
(77) Matthews, R. S.; Jones, D. W.; Bartle, K. D. Spectrochim. Acta A
1971, 27, 1185.
(75) McCullough, R. D.; Tristram-Nagle, S.; Williams, S. P.; Lowe, R.
D.; Jayaraman, M. J. Am. Chem. Soc. 1993, 115, 4910.
(78) Defay, N.; Zimmerman, D.; Martin, R. H. Tetrahedron Lett. 1971,
1871.

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4587
Scheme 12
Scheme 13
Cyclization using I+ as the electrophile prepared from
mercury(II) trifluoroacetate and I2 was successfully employed
for the meta system. This approach resulted in the starting
material 35 being recovered in almost quantitative yield. We
reasoned that perhaps a more reactive form of I+ was required,
and therefore, the earlier protocol was altered by replacing the
mercury(II) trifluoroacetate with silver triflate. There was also
a question in our mind as to the effect of added base, which
may reduce the reactivity of the I+. Compound 35 was
subjected to the iodine/silver triflate mixture in the presence of
only half an equivalent of base (2,6-dimethylpyridine), and the
result was encouraging. One of the distinguishing features of
the 1H NMR of the parent pentahelicene was the downfield shift
1
(8.34 ppm) of the innermost (bay) protons. The H NMR of
the crude reaction mixture indicated a doublet at 8.43 ppm. By
integrating the signals for the methyl peaks on the aromatic
rings, it was observed that the crude mixture contained ap-
proximately equal amounts of 35 and what we believed was
the expected cyclized helicene 37 along with some decomposi-
tion products. This seemed to suggest that the base was indeed
interfering with the reaction. In all subsequent runs, the base
was omitted. It was observed that the order of mixing had a
very pronounced effect on the reaction. The addition of 35 to
a mixture of silver triflate and iodine gave a complex mixture
of products, whereas addition of iodine to a mixture of 35 and
silver triflate gave a much cleaner reaction.
the bromines were replaced by iodine by prolonged treatment
of 33 with large excesses of both CuI and KI in hot (ca. 145
°C) DMF. The diiodide 34 could be converted in very high
yield to the target terphenyl 35 under the modified Suzuki
coupling conditions (used for the meta and para systems), so
long as a large excess (about 10 equiv) of the phenylboronic
acid was used.
Optimized conditions gave 37 in 20% yield. Pure samples
of 37 were isolated, and to our surprise, characterization by mass
spectroscopy, 1H NMR, and 13C NMR indicated that the product
did not contain any iodine! We were able to confirm, on the
1
basis of COSY, H NMR, and 13C NMR, along with careful
With the target terphenyl 35 in hand, attempts were made to
induce the cyclization which would lead to a pentahelicene.
Initial attempts focused on the acid-catalyzed cyclization. The
protocol employed in the previous cases (meta and para) failed
to work in this instance. 1H NMR and TLC indicated a complex
and nearly inseparable mixture of products had been formed.
A careful analysis of the 1H NMR of the crude reaction mixture
indicated that in most cases one of the major products was most
likely the monocyclized compound 36 (see Scheme 13). There
also appeared to be a somewhat smaller amount of the expected
product 37. Since the cyclization appeared to have gone at least
partway, we decided to use more aggressive reaction conditions.
The solvent and reagents were switched to the higher boiling
1,2,3-trichloropropane and trichloroacetic acid. Refluxing at
higher temperatures or using a stronger acid (triflic acid, -78
°C to room temperature) proved unsuccessful, and in most cases,
we obtained complex mixtures wherein the major identifiable
component was usually the monocyclized product 36.
1
comparison of the H NMR reported for the parent penta-
helicene,76-78 that the iodine/silver triflate protocol actually
provided us with 37 (E ) H). To further confirm the identity
of 37 it was subjected to the Mallory photocyclization reaction29
to form the corresponding benzo[ghi]perylene 38 (see Scheme
1
13) whose H NMR agreed quite well with that of the parent
benzo[ghi]perylene.79
We have considered that the iodine actually played no role
in the reaction. To test this hypothesis, a sample of 35 was
treated with silver triflate and then divided into two parts; one
part was treated with iodine, while the other was allowed to
stir for the appropriate amount of time and subjected to the usual
workup conditions. It was observed that the aliquot which had
not been treated with iodine gave a complex mixture of products,
(79) The Aldrich Library of 13C and 1H FT NMR Spectra, 1st ed.;
Pouchert, C. J., Behnke, J., Eds.; Aldrich Chemical Co.: Milwaukee, WI,
1994; Vol. 2, p 58C.

4588 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
lit.80 161-163 °C). 1H NMR (250 MHz, CDCl3): δ 8.02 (s, 2H). 13
NMR (62.9 MHz, CDCl3): δ 101.5, 129.2, 142.3. HRMS (CI CH4,
positive ion): found m/z 485.6646 (M+); calcd for C6H2Br2I2 m/z
485.6613 (M+). Anal. Calcd for C6H2Br2I2: C, 14.78; H, 0.41.
Found: C, 14.58; H, 0.43.
C
whereas that which had been treated with iodine gave 37 (E )
H). Furthermore, the substitution of sliver trifluoroacetate or
mercury trifluoroacetate for silver triflate led to complex
mixtures.
1,4-Dibromo-2,5-bis((4-(dodecyloxy)phenyl)ethynyl)benzene (1).
To a 500 mL flask charged with 1,4-dibromo-2,5-diiodobenzene (16.0
g, 0.0328 mol), (Ph3P)2PdCl2 (0.461 g, 0.657 mmol), CuI (0.656 g,
3.44 mmol), and (C4H9)4NBr (0.634 g, 1.97 mmol) were added 75 mL
of toluene, 75 mL of DIPA, and 50 mL of THF. 4-(Dodecyloxy)-
phenylacetylene (19.74 g, 0.0689 mol) dissolved in 25 mL of THF
was added dropwise at 25 °C generating a noticeable amount of heat.
After 2 h of stirring without any external source of heat, the mixture
was diluted with 200 mL of CHCl3 and washed with 5% HCl (3 × 50
mL), H2O (50 mL), 5% NH4OH (2 × 50 mL), and H2O (2 × 50 mL).
MeOH was added to precipitate the compound as a yellow solid. After
crystallization from THF/MeOH, 1 (19.17 g, 73%) was obtained as
small colorless plates (mp 108-110 °C). 1H NMR (250 MHz,
CDCl3): δ 0.86 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.77 (m, 4H),
3.95 (t, 4H, J ) 6.5 Hz), 6.86 (d, 4H, J ) 8.9 Hz), 7.47 (d, 4H, J )
8.7 Hz), 7.71 (s, 2H). 13C NMR (62.9 MHz, CDCl3): δ 14.1, 22.7,
26.0, 29.2, 29.4, 29.6, 31.9, 68.1, 85.8, 96.9, 114.1, 114.6, 123.4, 126.3,
133.3, 135.7, 159.9. Anal. Calcd for C46H60O2Br2: C, 68.65; H, 7.51.
Found: C, 68.28; H, 7.46.
Conclusion
We have described a versatile method for the synthesis of
complex, fused polycyclic aromatic systems in high chemical
yield. Construction is achieved using a general two-step
synthetic sequence. Pd-catalyzed Suzuki and Negishi type
cross-coupling chemistries allow for the preparation of nonfused
skeletal ring systems in yields consistently >80%. The critical
ring-forming step, which generally proceeds in very high to
quantitative yield in the meta and para cases (but not in the
ortho case), utilizes 4-alkoxyphenylethynyl groups and is
induced by strong electrophiles such as trifluoroacetic acid
(TFA) and iodonium tetrafluoroborate. Fused polycyclic ben-
zenoids as well as benzenoid/thiophene systems have been
prepared utilizing this methodology. We have studied sym-
metric systems which contain two ethynyl-Ar′ partners. When
the ethynyl groups and the aryl groups undergoing electrophilic
substitution (Ar′) are situated para to each other, the resulting
cyclization products are substituted bisaryl[a,h]anthracenes. In
the case where the ethynyl-Ar′ partners are situated meta to
each other, cyclization provides substituted bisaryl[a,j]an-
thracenes. When the ethynyl-Ar′ partners are situated para
to each other and the aryl groups undergoing electrophilic
cyclization are ortho to each other, the product is a helicene.
Unfortunately, the ortho system does not work as well as the
meta and para cases. The forcing conditions and low yields of
this method render it of limited synthetic utility for the
preparation of helicenes. Our ongoing studies will focus on
applying this methodology to the design and construction of
graphite ribbons (rigid aromatic polymeric systems) and other
electronic polymers.48
General Coupling Procedure for Preparation of p-Terphenyls
2-5. 2′,5′-Bis((4-(dodecyloxy)phenyl)ethynyl)-2,2′′,5,5′′-tetramethoxy-
[1,1′:4′,1′′]terphenyl (2). A 25 mL Schlenk tube was charged with 1
(0.089 g, 0.111 mmol), 2,5-(dimethoxy)phenylboronic acid (0.043 g,
0.234 mmol), Pd(dba)
2 (0.0004 g, 6.66 × 10-4 mmol), triphenylphos-
phine (0.0026 g, 9.99 × 10-3 mmol), and KOH (0.131 g, 2.34 mmol).
To the mixture was added H2O (1 mL) followed by PhNO2 (4 mL).
The heterogeneous mixture was purged with a rapid stream of argon
for 20 min before being placed in an oil bath (85 °C). After 16 h of
heating at the stated temperature, the solution was allowed to cool,
diluted with CHCl3 (4 mL), washed with 5% NaOH (2 × 4 mL), H2O,
5% HCl (3 × 4 mL) and H2O, and dried (Na2SO4). The solvent was
removed at 85 °C under high vacuum (0.01 Torr), and the solid residue
was chromatographed on silica gel (1:1 hexanes/toluene) to afford 3
(0.089 g, 86.9%) as a colorless solid (mp 158-159 °C). 1H NMR
(250 MHz, CDCl3): δ 0.87 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.74
(m, 4H), 3.75 (s, 6H), 3.78 (s, 6H), 3.90 (t, 4H, J ) 6.5 Hz), 6.75 (d,
4H, J ) 8.6 Hz), 6.92 (s, 4H), 7.00 (s, 2H), 7.13 (d, 4H, J ) 8.7), 7.59
(s, 2H). 13C NMR (125 MHz, CDCl3): δ 14.08, 22.67, 25.99, 29.16,
29.32, 29.35, 29.54, 29.57, 29.61, 29.63, 31.90, 55.80, 56.37, 68.03,
88.11, 93.31, 112.27, 114.39, 114.42, 115.44, 116.83, 122.76, 129.97,
132.81, 133.34, 139.51, 151.38, 153.21, 159.07. UV-vis (CHCl3) λmax
(ꢀ, cm-1 M-1): 364 (sh, 51 000), 342 (59 800), 258 (27 300) nm.
Luminescence spectrum (CHCl3) λmax (rel intensity): 376 (1), 392 (0.96)
nm. HRMS (FAB): found m/z 918.5783 (M+); calcd for C62H78O6
m/z 918.5798 (M+). Anal. Calcd for C62H78O6: C, 81.01; H, 8.55.
Found: C, 80.64; H, 8.48.
Experimental Section
General Methods. NMR spectra (1H and 13C) were obtained on
Bruker AC-100, AC-250, and AMX-500 spectrometers. Chemical
shifts are reported in ppm relative to residual protio solvent (chloroform
7.24 ppm (1H), 77.0 ppm (13C); DMSO 2.49 ppm (1H)). Microanalyses
and mass spectra were obtained at the University of Pennsylvania
instrumentation center. UV-vis spectra were recorded in CHCl3 on a
Hewlett Packard 8452A diode array spectrophotometer. Luminescence
spectra were recorded in CHCl3.
All solvents were distilled by vacuum transfer. THF was stored
over CaH2 before being distilled from sodium benzophenone ketyl.
Toluene was distilled from sodium metal. Nitrobenzene and methylene
chloride were distilled from P2O5. Nitrobenzene was stored in the dark.
Diisopropylamine (DIPA) was distilled from solid KOH pellets.
Synthetic manipulations were performed under an argon atmosphere
in oven-dried glassware using standard Schlenk techniques.
1,4-Dibromo-2,5-diiodobenzene. To a 3000 mL three-neck round
bottom flask equipped for mechanical stirring was added concentrated
H2SO4 (1500 mL) and periodic acid (66.6 g, 0.292 mol). After
dissolution of the periodic acid, KI (145.6 g, 0.880 mol) was added in
small portions over 40 min to produce a deep purple solution. The
temperature was then lowered to -30 °C and 1,4-dibromobenzene (138
g, 0.585 mol) was added over approximately 5 min. An additional
600 mL portion of H2SO4 was added to facilitate stirring. The mixture
was stirred for 24 h while maintaining the temperature between -30
and -20 °C. The entire mixture was then poured over approximately
9000 g of ice and filtered on a glass frit. The solid was taken up in
CHCl3, washed with 5% NaOH (2×) and H2O, and dried (MgSO4),
and the solvent was removed in vacuo. Following recrystallization
from THF (1×) and CHCl3 (2×), 1,4-dibromo-2,5-diiodobenzene (142.1
g, 49.8%) was obtained as a white crystalline solid (mp 159-161 °C,
2′,5′-Bis((4-(dodecyloxy)phenyl)ethynyl)[1,1′:4′,1′′]terphenyl (3).
Compound 3 was prepared as described for compound 2, substituting
phenylboronic acid for 2,5-(dimethoxy)phenylboronic acid. Compound
3 was obtained as a colorless solid in 91.3% yield (mp 102-104 °C).
1H NMR (250 MHz, CDCl3): δ 0.87 (t, 6H, J ) 6.8 Hz), 1.1-1.5
(36H), 1.83 (m, 4H), 3.92 (t, 4H, 6.6 Hz), 6.79 (d, 4H, J ) 8.8 Hz),
7.25 (d, 4H, J ) 8.8 Hz), 7.45 (m, 6H), 7.68 (s, 2H), 7.74 (d, 4H, J )
7.5 Hz). 13C NMR (62.9 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3,
29.6, 31.9, 68.0, 87.9, 93.9, 114.5, 115.1, 121.6, 127.6, 127.9, 129.3,
132.8, 133.5, 139.6, 142.0, 159.2. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1):
366 (sh, 53 400), 348 (57 200), 286 (43 700) nm. Luminescence
spectrum (CHCl3) λmax (rel intensity): 382(1), 398 (0.81) nm. HRMS
(FAB): found m/z 799.5463 (M + H+); calcd for C58H71O2 m/z
799.5454.
2′,5′-Bis((4-(dodecyloxy)phenyl)ethynyl)-4,4′′-dimethoxy[1,1′:
4′,1′′]terphenyl (4). Compound 4 was prepared as described for
compound 2, substituting 4-(methoxy)phenylboronic acid for 2,5-
(dimethoxy)phenylboronic acid. Compound 4 was obtained as a
colorless solid in 82.2% yield. 1H NMR (250 MHz, CDCl3): δ 0.87
(80) Hart, H.; Harada, K.; Chi-Jen, F. D. J. Org. Chem. 1985, 50, 3104.

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4589
(t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.75 (m, 4H), 3.87 (s, 6H), 3.93
(t, 4H, J ) 6.70 Hz), 6.80 (d, 4H, J ) 8.66 Hz), 7.00 (d, 4H, J ) 8.66
Hz), 7.28 (d, 4H, J ) 8.66 Hz), 7.63 (s, 2H), 7.67 (d, 4H, J ) 8.63
Hz). 13C NMR (125 MHz, CDCl3): δ 14.12, 22.68, 26.00, 29.18, 29.37,
29.58, 29.62, 31.91, 55.35, 68.10, 88.19, 93.73, 113.38, 114.54, 115.25,
121.51, 130.47, 132.21, 132.85, 133.44, 141.24, 159.26, 159.27. UV-
vis (CHCl3) λmax (ꢀ, cm-1 M-1): 368 (sh, 40 100), 344 (44 600), 298
(50 000) nm. Luminescence spectrum (CHCl3) λmax (rel intensity): 382
(1), 398 (0.83) nm. HRMS (FAB): found m/z 858.5549 (M+); calcd
for C60H74O2 m/z 858.5587.
2′,5′-Bis((4-(dodecyloxy)phenyl)ethynyl)-2,5,2′′,5′′-tetramethyl-
[1,1′:4′,1′′]terphenyl (5). Compound 5 was prepared as described for
compound 2, substituting 2,5-(dimethyl)phenylboronic acid for 2,5-
(dimethoxy)phenylboronic acid. Compound 5 was obtained as a white
solid in 85.4% yield (mp 164-167 °C). 1H NMR (250 MHz, CDCl3):
δ 0.88 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.75 (m, 4H), 2.26 (s, 6H),
2.37 (s, 6H), 3.90 (t, 4H, J ) 6.53 Hz), 6.75 (d, 4H, J ) 8.80 Hz),
7.07 (d, 4H, J ) 8.75), 7.11-7.21 (m, 6H), 7.49 (s, 2H). 13C NMR
(62.9 MHz, CDCl3): δ 14.12, 19.57, 20.97, 22.68, 25.98, 29.14, 29.35,
29.58, 31.91, 68.00, 87.73, 93.83, 114.40, 115.12, 112.57, 128.28,
129.57, 130.59, 132.32, 132.81, 133.34, 134.56, 139.81, 143.02, 159.14.
UV-vis (5-C4 (butoxy replaces dodecyloxy), CHCl3) λmax (ꢀ, cm-1
M-1) 364 (sh, 61 200), 342 (63 900) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 372 (1), 390 (0.77) nm. HRMS (FAB):
found m/z 854.6008 (M+); calcd for C62H78O2 m/z 854.6002.
sity): 374 (0.58), 442 (1) nm (very low intensity). HRMS (FAB):
found m/z 1170.3802 (M+); calcd for C62H76O6I2 m/z 1170.3731. Anal.
Calcd for C62H76O6I2: C, 63.59; H, 6.54. Found: C, 63.51; H, 6.59.
Preparation of 5,12-Bis(4-(dodecyloxy)phenyl)-1,4,8,11-tet-
ramethoxydibenz[a,h]anthracene (6) from 5,12-Bis(4-(dodecyloxy)-
phenyl)-6,13-diiodo-1,4,8,11-tetramethoxydibenz[a,h]anthracene (7).
A solution of 7 (0.005 g, 0.004 mmol) in 3 mL of THF was cooled to
-78 °C, and s-BuLi (0.10 mL, 1.53 M, 0.153 mmol) was added. After
5 min of stirring, the golden yellow solution was quench by the rapid
addition of 1 mL of MeOH. The mixture was diluted with CHCl3 (30
mL), washed with 5% HCl (2 × 10 mL) and H2O (10 mL), and dried
(Na2SO4) before removing the solvent in vacuo. The product 6 (>95%
by NMR) exhibited a 1H NMR spectrum identical to material prepared
via TFA-induced cyclization of the terphenyl 2.
5,12-Bis(4-(dodecyloxy)phenyl)dibenz[a,h]anthracene (8). Com-
pound 8 was prepared as described for compound 6, using 3 as the
starting material. Species 8 was isolated as a pale yellow solid in 99.4%
yield (mp 146-149 °C). 1H NMR (250 MHz, CDCl3): δ 0.87 (t, 6H,
J ) 6.8 Hz), 1.1-1.5 (36H), 1.83 (m, 4H), 4.06 (t, 4H, J ) 6.5 Hz),
7.06 (d, 4H, J ) 8.6 Hz), 7.52 (d, 4H, J ) 8.6 Hz), 7.56 (t, 2H, J )
7.9 Hz), 7.70 (t, 2H, J ) 7.9 Hz), 7.88 (s, 2H), 7.97 (d, 2H, 8.1 Hz),
8.91 (d, 2H, J ) 8.3 Hz), 9.14 (s, 2H). 13C NMR (62.9 MHz, CDCl3):
δ 14.1, 22.7, 26.2, 29.4, 29.7, 31.9, 68.2, 114.4, 122.0, 123.1, 126.6,
126.8, 127.1, 127.9, 129.0, 130.4, 130.6, 131.1, 131.7, 132.9, 138.5,
158.7. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1): 408 (1390), 366 (16 500),
350 (16 600), 314 (55 400), 304 (51 100) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 412 (1), 436 (0.61) nm. HRMS (FAB):
found m/z 799.5452 (M + H+); calcd for C58H71O2 m/z 799.5454.
5,12-Bis(4-(dodecyloxy)phenyl)-3,10-dimethoxydibenz[a,h]an-
thracene (9). Compound 9 was prepared as described for compound
6, using compound 4 as the starting material. Species 9 was isolated
as a yellow solid in 98.7% yield (mp 151-154 °C). 1H NMR (250
MHz, CDCl3): δ 0.89 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.85 (m,
4H), 3.81 (s, 6H), 4.04 (t, 4H, J ) 6.40 Hz), 7.04 (d, 4H, 8.72 Hz),
7.30 (dd, 2H, J ) 8.94, 2.62 Hz), 7.37 (d, 2H, J ) 2.55 Hz), 7.50 (d,
4H, J ) 8.67 Hz), 7.81 (s, 2H), 8.77 (d, 2H, J ) 9.06), 8.95 (s, 2H).
13C NMR (62.9 MHz, CDCl3): δ 14.13, 22.70, 26.13, 29.38, 29.48,
29.65, 31.92, 55.32, 68.12, 108.70, 114.39, 115.78, 121.19, 124.59,
124.70, 128.35, 128.52, 129.82, 130.90, 132.93, 132.98, 138.05, 158.37,
158.61. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1): 410 (2800), 370
(18 100), 322 (98 100), 286 (46 600) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 414 (1), 438 (0.55) nm. HRMS (FAB):
found m/z 858.5596 (M+); calcd for C60H74O2 m/z 858.5587.
5,12-Bis(4-(dodecyloxy)phenyl)-1,4,8,11-tetramethyldibenz[a,h]-
anthracene (10). Compound 10 was prepared as described for 6, using
compound 5 as the starting material. Species 10 was isolated as a bright
yellow solid in 98.2% yield (mp 180-184 °C). 1H NMR (250 MHz,
CDCl3): δ 0.89 (t, 6H, J ) 6.83 Hz), 1.1-1.6 (36H), 1.82 (m, 4H),
2.04 (s, 6H), 3.18 (s, 6H), 4.03 (t, 4H, J ) 6.52 Hz), 6.96 (d, 4H, J )
8.67 Hz), 7.25 (d, 2H, J ) 7.50 Hz), 7.33 (d, 4H, J ) 8.56 Hz), 7.42
(d, 2H, J ) 7.50 Hz), 7.69 (s, 2H), 9.06 (s, 2H). 13C NMR (62.9 MHz,
CDCl3): δ 14.15, 22.72, 25.16, 26.14, 26.70, 29.39, 29.48, 29.66, 30.33,
31.95, 68.14, 114.05, 125.53, 127.03, 129.42, 129.57, 130.07, 130.32,
130.89, 131.98, 132.12, 133.22, 133.87, 137.71, 138.43, 158.19. UV-
vis (10-C4 (butoxy replaces docecyloxy), CHCl3) λmax (ꢀ, cm-1 M-1):
418 (2500), 378 (28 800), 364 (27 300), 310 (71 200) nm. Lumines-
cence spectrum (10-C4 (butoxy replaces docecyloxy), CHCl3) λmax (rel
intensity): 426 (1), 448 (0.64) nm. HRMS (FAB): found m/z 854.6031
(M+); calcd for C62H78O2 m/z 854.6002.
1,4-Bis(dibenzo[b,d]thiophen-4-yl)-2,5-bis((4-(dodecyloxy)-
phenyl)ethynyl)benzene (14). Compound 14 was prepared as de-
scribed for compound 2, substituting 4-dibenzothiopheneboronic acid
for 2,5-(dimethoxy)phenylboronic acid. The crude product was crystal-
lized from CHCl3/EtOH. Compound 14 was obtained as a colorless
solid in 86.3% yield (mp 168-169 °C). 1H NMR (500 MHz, CDCl3):
δ 0.86 (t, 6H, J ) 6.8 Hz), 1.2-1.42 (36H), 1.70 (m, 4H), 3.85 (t, 4H,
J ) 6.60 Hz), 6.66 (d, 4H, J ) 8.79 Hz), 6.99 (d, 4H, J ) 8.81 Hz),
7.47 (m, 4H), 7.61 (t, 2H, J ) 7.66 Hz), 7.73 (dd, 2H, J ) 7.37, 1.03
Hz), 7.84 (m, 2H), 7.98 (s, 2H), 8.23 (m, 4H). 13C NMR (125 MHz,
CDCl3, partial): δ 14.10, 22.67, 25.95, 29.12, 29.33, 29.53, 29.56,
29.61, 31.90, 68.00, 87.25, 95.05, 114.37, 114.84, 120.93, 121.69,
122.63, 122.75, 124.29, 126.73, 128.32, 132.85, 133.06, 134.82, 135.84,
General Acid-Induced Cyclization Procedure. 5,12-Bis(4-(dode-
cyloxy)phenyl)-1,4,8,11-tetramethoxydibenz[a,h]anthracene (6). In
a 100 mL Schlenk flask, 2 (0.500 g, 0.544 mmol) was dissolved in 50
mL of CH2Cl2. To the solution was added trifluoroacetic acid (1.5
mL, 19.5 mmol) in one portion at room temperature. The solution
turned in color first to a light red, then to a yellow brown, and finally
1
to a deep green. After 45 min, H NMR indicated the reaction was
complete. The solution was washed with 10% NaHCO3 solution (3 ×
10 mL) and H2O (2 × 15 mL) and dried (Na2SO4). After removal of
the solvent under reduced pressure, the crude product was recrystallized
from benzene. Compound 6 was obtained (0.498 g, 99.6%) as bright
yellow needles (mp 209-211 °C). 1H NMR (250 MHz, CDCl3): δ
0.87 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.83 (m, 4H), 3.43 (s, 6H),
4.03 (t, 4H, J ) 6.5 Hz), 4.13 (s, 6H), 6.94 (d, 4H, J ) 8.6 Hz), 7.03
(d, 2H, J ) 8.8 Hz), 7.18 (d, 2H, J ) 9.0 Hz), 7.34 (d, 4H, J ) 8.5
Hz), 7.78 (s, 2H), 10.10 (s, 2H). 13C NMR (25 MHz, CDCl3): δ 14.0,
22.7, 26.2, 29.3, 29.5, 29.6, 31.9, 56.5, 57.0, 68.4, 110.0, 111.1, 113.3,
122.8, 124.7, 128.0, 128.1, 129.1, 131.1, 132.7, 135.7, 138.9, 151.8,
154.1, 157.5. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1): 430 (14 400), 406
(12 100), 374 (24 000), 356 (24 600), 318 (55 600), 280 (37 500) nm.
Luminescence spectrum (CHCl3) λmax (rel intensity): 438 (1), 462 (0.53)
nm. HRMS (FAB): found m/z 918.5841 (M+); calcd for C62H78O6
m/z 918.5798 (M+). Anal. Calcd for C62H78O6: C, 81.01; H, 8.55.
Found: C, 80.66; H, 8.65.
5,12-Bis(4-(dodecyloxy)phenyl)-6,13-diiodo-1,4,8,11-tetramethox-
ydibenz[a,h]anthracene (7). To a 50 mL Schlenk tube wrapped with
aluminum foil to omit light and containing I(pyr)2BF4 (0.250 g, 0.672
mmol) was added CH2Cl2 (25 mL), followed by CF3SO3H (60 µL, 6.78
× 10-4 mmol). The solution was allowed to stir at room temperature
for 15 min before being cooled to -40 °C. After this time, 2 (0.300
g, 0.326 mmol) dissolved in CH2Cl2 (10 mL) was added in one portion.
The solution was allowed to warm from -40 to -30 °C over 30 min
and then from -30 to 10 °C over 1.5 h. To the solution were added
50 mL saturated aqueous thiosulfate solution and 50 mL of CHCl3.
The organic layer was washed with an additional portion of thiosulfate
(50 mL) and H2O (2 × 50 mL) and dried (MgSO4). After removal of
solvent under reduced pressure, the crude solid was recrystallized from
THF/MeOH to afford 7 (0.368 g, 96.3%) as a yellow solid (mp 232-
233 °C). 1H NMR (250 MHz, CDCl3): δ 0.88 (t, 6H, J ) 6.7 Hz),
1.1-1.5 (36 H), 1.84 (m, 4H), 3.29 (s, 6H), 4.04 (t, 4H, J ) 6.6 Hz),
4.19 (s, 6H), 6.97 (d, 4H, J ) 8.5 Hz), 6.99 (d, 2H, J ) 8.7), 7.12 (d,
4H, J ) 8.5 Hz), 7.21 (d, 2H, J ) 8.7 Hz), 10.13 (s, 2H). 13C NMR
(25 MHz, CDCl3): δ 14.0, 22.7, 26.2, 29.7, 31.9, 57.3, 57.5, 68.3,
111.4, 111.8, 113.4, 113.5, 122.5, 125.7, 128.7, 129.9, 132.2, 134.9,
142.6, 143.9, 151.1, 153.1, 157.8. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1):
436 (14 100), 410 (11 000), 380 (16 900), 362 (20 100), 328 (58 800),
284 (42 600) nm. Luminescence spectrum (CHCl3) λmax (rel inten-

4590 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
135.93, 139.81, 141.70, 159.25. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1):
368 (52 900), 346 (56 500), 290 (37 900) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 388 nm. HRMS (FAB): found m/z
1010.5111 (M+); calcd for C70H74O2S2 m/z 1010.5130. Anal. Calcd
for C70H74O2S2: C, 83.12; H, 7.37. Found: C, 83.22; H, 7.53.
2H, J ) 8.60 Hz), 7.74 (d, 2H, J ) 8.66 Hz), 7.770 (s, 1H), 7.775 (s,
1H), 7.83 (d, 1H, J ) 1.07 Hz), 8.57 (s, 1H), 8.76 (s, 1H). UV-vis
(17/18, CHCl3) λmax (ꢀ, cm-1 M-1): 408 (10 700), 384 (18 700), 362
(24 600), 326 (142 000) nm. Luminescence spectrum (CHCl3) λmax (rel
intensity): 426 nm. HRMS (FAB): found m/z 838.4823 (M+); calcd
for C56H70O2S2 (17/18) m/z 838.4817. LRMS (FAB): 838 (100, M+),
670 (10, M+ - C12H25), 460 (10). Anal. Calcd for C56H70O2S2 (17/
18): C, 80.14; H, 8.41. Found: C, 79.68; H, 8.55.
6,13-Bis(4-butoxyphenyl)-1,4,8,11-tetramethyldibenz[a,h]an-
thracene (19). A 250 mL Schlenk flask was charged with 5 (butyloxy
replaces dodecyloxy) (0.300 g, 0.476 mmol), 1,2,3-trichloropropane
(150 mL), and difluoroacetic acid (15 mL). The mixture was subjected
to three freeze-pump-thaw cycles and was then heated at 130 °C for
12 h. The mixture was allowed to cool and was diluted with 150 mL
of CH2Cl2 before being washed with 5% NaOH (2 × 75 mL) and H2O.
The organic layer was dried (MgSO4), and the solvent was removed
under reduced pressure to provide a crude product which was purified
by silica gel chromatography (1:1 hexanes/toluene). Crystallization
from CHCl3/i-PrOH provided compound 19 as a light yellow solid
(0.222 g, 74.0%).
8,18-Bis(4-(dodecyloxy)phenyl)bis(dibenzo[b,d]thiophene)[4,3-a,h]-
anthracene (15). To a solution of 14 (0.205 g, 0.203 mmol) in 55
mL of CH2Cl2 was added 1 mL of TFA. After 30 min, a bright yellow
product precipitated out of solution. Stirring was allowed to continue
for an additional 20 min. The solution was diluted with 50 mL of
CHCl3, and the organic layer washed with 5% NaOH (2 × 20 mL)
and H2O. The solvent was dried (MgSO4) and removed under reduced
pressure. The solid was crystallized from benzene to afford the product
15 as bright yellow needles (0.202 g, 98.5%) (mp > 290 °C). 1H NMR
(500 MHz, CDCl3): δ 0.88 (t, 6H, J ) 6.8 Hz), 1.2-1.4 (m, 32H),
1.55 (quint, 4H, J ) 7.73 Hz), 1.89 (quint, 4H, J ) 7.15 Hz), 4.11 (t,
4H, J ) 6.45 Hz), 7.12 (d, 4H, J ) 8.55 Hz), 7.54 (m, 4H), 7.60 (d,
4H, J ) 8.54 Hz), 8.05 (m, 2H), 8.14 (d, 2H, J ) 8.62 Hz), 8.19 (s,
2H), 8.28 (m, 2H), 8.35 (d, 2H, J ) 8.66 Hz), 9.88 (s, 2H). 13C NMR
(125 MHz, CD2Cl4, 100 °C): δ 13.74, 22.38, 25.98, 29.06, 29.23, 29.33,
29.39, 31.67, 68.51, 114.88, 120.00, 121.43, 122.10, 124.61, 124.67,
126.07, 126.40, 126.60, 128.08, 128.76, 131.06, 131.30, 132.29, 133.36,
134.76, 134.91, 135.81, 139.32, 139.51, 158.92. UV-vis (CHCl3) λmax
(ꢀ, cm-1 M-1): 430 (18 000), 404 (21 400), 392 (28 000), 372 (24 400),
340 (89 900), 324 (77 100), 260 (63 100) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 438 (1), 462 (0.50) nm. HRMS (FAB):
found m/z 1010.5116 (M+); calcd for C70H74O2S2 m/z 1010.5130. Anal.
Calcd for C70H74O2S2: C, 83.12; H, 7.37. Found: C, 83.41; H, 7.38.
2,5-Bis((4-(dodecyloxy)phenyl)ethynyl)-1,4-bis(5-methylthiophen-
2-yl)benzene (16). To a cooled (0 °C) solution of 2-methylthiophene
(140 µL, 1.45 mmol) dissolved in 10 mL of THF was added n-BuLi
(0.67 mL, 1.75 M, 1.17 mmol). After 25 min, a solution of ZnCl2
(0.507 g, 3.72 mmol) dissolved in 8 mL of THF was added to the
2-methyl-5-lithiothiophene solution. The mixture was allowed to stir
for 20 min and then was cannulated into a separate flask containing 1
(0.25 g, 0.311 mmol) and (Ph3P)2PdCl2 (0.0087 g, 0.012 mmol). The
reaction was refluxed for 4 h and, after cooling to room temperature
(rt), carefully quenched with MeOH. The mixture was diluted with
diethyl ether (CHCl3 for shorter side chain derivatives), washed with
5% HCl and H2O, and dried (MgSO4). The solvent was removed under
reduced pressure, and the product was purified by silica gel chroma-
tography (15:1 hexanes/THF eluent) to afford 16 as a yellow/orange
solid (0.254 g, 97.4%) (mp 160-162 °C). Species 16-C4 was purified
by recrystallization from CHCl3/i-PrOH. Compound 16. 1H NMR (500
MHz, CDCl3): δ 0.88 (t, 6H, J ) 7.04 Hz), 1.24-1.47 (36H), 1.78
(m, 4H), 2.54 (app s, 6H), 3.96 (t, 4H, J ) 6.59 Hz), 6.77 (app dd, 2H,
J ) 3.60, 0.97 Hz), 6.87 (d, 4H, J ) 8.71 Hz), 7.45 (d, 4H, J ) 8.70
Hz), 7.52 (d, 2H, J ) 3.58 Hz), 7.75 (s, 2H). 13C NMR (125 MHz,
CDCl3): δ 14.10, 15.40, 22.68, 26.02, 29.19, 29.34, 29.38, 29.57, 29.59,
29.63, 31.92, 68.13, 88.17, 95.25, 114.63, 115.18, 120.15, 125.61,
126.85, 132.91, 133.14, 133.90, 138.80, 140.64, 159.47. UV-vis (16-
C4 (butoxy replaces dodecyloxy), CHCl3) λmax (ꢀ, cm-1 M-1): 358
(41 900), 326 (78 200) nm. Luminescence spectrum (16-C4 (butoxy
replaces dodecyloxy), CHCl3) λmax (rel intensity): 422 nm. HRMS
(FAB): found m/z 838.4802 (M+); calcd for C56H70O2S2 m/z 838.4817.
Anal. Calcd for C40H38O2S2 (16-C4, butoxy replaces dodecyloxy): C,
78.14; H, 6.23. Found: C, 78.51; H, 6.32.
Alternately, the cyclized compound 10 (butoxy replaces dodecyloxy)
may be exposed to identical conditions to provide 19 (>70% by NMR).
1H NMR (500 MHz, CDCl3): δ 1.07 (t, 6H, J ) 7.40 Hz), 1.60 (m,
4H), 1.89 (quint, 4H), 2.71 (s, 6H), 2.81 (s, 6H), 4.11 (t, 4H, J ) 6.50),
7.11 (d, 4H, J ) 8.55 Hz), 7.33 (d, 2H, J ) 7.48 Hz), 7.35 (d, 2H, J
) 7.65 Hz), 7.57 (d, 4H, J ) 8.51 Hz), 7.85 (s, 2H), 9.31 (s, 2H). 13
C
NMR (125 MHz, CDCl3): δ 13.92, 19.33, 20.15, 26.51, 26.83, 31.43,
67.93, 114.52, 124.02, 126.42, 127.86, 129.69, 129.88, 129.93, 130.39,
131.17, 131.62, 132.57, 133.18, 133.69, 138.42, 158.69. UV-vis
(CHCl3) λmax (ꢀ, cm-1 M-1): 410 (2230), 374 (20 600), 358 (20 600),
340 (17 300), 318 (72 200), 304 (77 300) nm. Luminescence spectrum
(CHCl3) λmax (rel intensity): 412 (1), 436 (0.60) nm. HRMS (FAB):
found m/z 630.3494 (M+); calcd for C46H46O2 m/z 630.3498.
1,5-Dibromo-2,4-diiodobenzene. Periodic acid (36.95 g, 0.162mol)
was allowed to dissolve in 150 mL of concentrated H2SO4. To the
colorless solution was slowly added KI (80.75 g, 0.487 mol), and the
mixture was cooled to 0 °C. 1,3-Dibromobenzene (75 g, 0.318 mol)
was quickly added in one portion, and the reaction mixture was allowed
to stir for 30 min. The entire reaction was poured onto ice and filtered
(glass frit), and the crude product was crystallized two times from THF/
MeOH. 1,3-Dibromo-4,6-diiodobenzene was obtained as a colorless
crystalline solid (155.04 g, 68.1%) (mp 164-165 °C, lit.80 166-167
°C). 1H NMR (250 MHz, CDCl3): δ 7.81 (s, 1H), 8.26 (s, 1H). 13C
NMR (62.9 MHz, CDCl3): δ 100.40, 130.47, 135.30, 149.46. HRMS
(CH4 CI, positive ion): found m/z 485.6635 (M+); calcd for C6H2Br2I2
m/z 485.6613. Anal. Calcd for C6H2Br2I2: C, 14.78; H, 0.41.
Found: C, 15.16; H, 0.53.
1,5-Dibromo-2,4-bis((4-(dodecyloxy)phenyl)ethynyl)benzene (20).
Compound 20 was prepared in an analogous fashion to compound 1
only replacing 1,4 dibromo-2,5-diiodobenzene with 1,5-dibromo-2,4-
diiodobenzene. The compound was isolated by removing ca. three-
fourths of the reaction solvent under reduced pressure and diluting the
remaining solvent with benzene. The organics were washed with 5%
HCl, H2O, 5% NH4OH, and H2O before being dried (MgSO4). The
solvent was reduced to ca. one-third volume, and the crude product
was precipitated by the addition of MeOH/acetone. The solid was
filtered and recrystallized two times from n-hexane. Compound 20
was obtained as an off-white amorphous solid (88.3%) (mp 111-112
°C). 1H NMR (250 MHz, CDCl3): δ 0.89 (t, 6H, J ) 6.8 Hz), 1.1-
1.5 (36H), 1.78 (m, 4H), 3.94 (t, 4H, J ) 6.25 Hz), 6.86 (d, 4H, J )
8.45 Hz), 7.48 (d, 4H), J ) 8.37 Hz), 7.65 (s, 1H), 7.83 (s, 1H). 13C
NMR (62.9 MHz, CDCl3): δ 14.14, 22.71, 26.01, 29.08, 29.39, 29.65,
31.93, 68.06, 85.53, 95.60, 114.23, 114.55, 124.50, 125.07, 133.20,
135.49, 135.93, 159.75. HRMS (CH4 CI, positive ion): found m/z
634.1090 (M+); calcd for C34H36O2Br2 (side chains ) -OC6H13) m/z
634.1082.
4,10-Bis(4-(dodecyloxy)phenyl)-2,8-dimethylbisthien[2,3-a,h]an-
thracene (17) and 4,11-Bis(4-(dodecyloxy)phenyl)-2,8-dimethyl-
bisthien[2,3-a,h]anthracene (18). Compounds 17 and 18 were
prepared using the standard TFA-induced cyclization conditions.
Chromatography on silica gel (4:3:1 hexanes/toluene/CHCl3) provided
a 6:5 mixture of the inseparable structural isomers 17/18 (82.5%). As
compound 18 is asymmetric, its proton resonances are easily discernible
from those of 17. Compound 17. 1H NMR (500 MHz, CDCl3): δ
0.88 (t, 6H, J ) 7.07 Hz), 1.24-1.47 (36H), 1.84 (quint, 4H), 2.64 (d,
6H, J ) 0.93 Hz), 4.04 (t, 4H, J ) 6.56 Hz), 7.036 (d, 4H, J ) 8.76
Hz), 7.192 (d, 2H, J ) 1.14 Hz), 7.58 (d, 4H, J ) 8.62 Hz), 7.75 (s,
2H), 8.55 (s, 2H). Compound 18. 1H NMR (500 MHz, CDCl3): δ
0.88 (t, 6H, J ) 7.07 Hz), 1.24-1.47 (36H), 1.84 (quint, 4H), 2.65 (d,
3H, 1.02 Hz), 2.70 (d, 3H, J ) 0.89 Hz), 4.04 (t, 4H, J ) 6.56 Hz),
7.042 (br d, 4H, J ) 8.64 Hz), 7.199 (d, 1H, J ) 1.25 Hz), 7.59 (d,
4′,6′-Bis((4-(dodecyloxy)phenyl)ethynyl)[1,1′:3′,1′′]terphenyl (21).
Compound 21 was prepared in an analogous fashion to compound 3
only replacing 2,5-dibromo-1,4-bis((4-(dodecyloxy)phenyl)ethynyl)-
benzene (1) with 1,5-dibromo-2,4-bis((4-(dodecyloxy)phenyl)ethynyl)-
benzene (20). Purification by silica gel chromatography (15:1 hexanes/
THF) provided 21 as an off-white solid in 80.9% yield (mp 65-68

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4591
°C). 1H NMR (500 MHz, CDCl3): δ 0.91 (t, 6H, J ) 7.12 Hz), 1.26-
1.47 (m, 36H), 1.78 (m, 4H), 3.95 (t, 4H, J ) 6.54 Hz), 6.83 (d, 4H,
J ) 8.74 Hz), 7.30 (d, 4H, J ) 8.74 Hz), 7.41 (t, 2H, J ) 7.47 Hz),
7.48 (t, 4H, J ) 7.72 Hz), 7.51 (s, 1H), 7.75 (d, 4H, J ) 7.18 Hz),
7.91 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 14.12, 22.68, 26.00,
29.17, 29.35, 29.37, 29.57, 29.60, 29.63, 31.92, 68.06, 87.26, 93.11,
114.51, 115.20, 120.96, 127.66, 127.90, 129.30, 130.54, 132.82, 136.72,
140.01, 142.88, 159.26. UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1): 314
(74 400) nm. Luminescence spectrum (CHCl3) λmax (rel intensity): 388
nm. HRMS (FAB): found m/z 798.5395 (M+); calcd for C58H70O2
m/z 798.5376. Anal. Calcd for C58H70O2: C, 87.17; H, 8.83. Found:
C, 87.45; H, 8.97.
5,9-Bis(4-(dodecyloxy)phenyl)dibenz[a,j]anthracene (22). Com-
pound 22 was prepared in an analogous fashion to compound 6, using
compound 21 as the starting material. Purification by silica gel
chromatography (20:1 hexanes/THF) provided 22 as a yellow solid in
95.7% yield. 1H NMR (500 MHz, CDCl3): δ 0.90 (t, 6H, J ) 7.05
Hz), 1.23-1.42 (32H), 1.48-1.54 (m, 4H), 1.82-1.88 (m, 4H), 4.05
(t, 4H, J ) 6.56 Hz), 7.05 (d, 4H, J ) 8.60 Hz), 7.50 (d, 4H, J )
8.58), 7.58 (td, 2H, J ) 7.60, 1.05 Hz), 7.75 (td, 2H, J ) 7.60, 1.05
Hz), 7.77 (s, 2H), 7.98 (dd, 2H, J ) 8.20, 1.00 Hz), 8.29 (s, 1H), 9.08
(d, 2H, J ) 8.07 Hz), 10.06 (s, 1H). 13C NMR (125 MHz, CDCl3): δ
14.11, 22.70, 26.14, 29.38, 29.46, 29.64, 29.69, 31.94, 68.16, 114.38,
116.08, 123.05, 126.62, 126.70, 127.21, 127.26, 127.30, 128.40, 130.78,
131.05, 131.13, 131.70, 132.87, 138.76, 158.71. UV-vis (CHCl3) λmax
(ꢀ, cm-1 M-1): 400 (1270), 380 (2820), 350 (23 700), 318 (85 200),
266 (44 300) nm. Luminescence spectrum (CHCl3) λmax (rel inten-
sity): 410 (1), 432 (0.69) nm. HRMS (FAB): found m/z 798.5360
(M+); calcd for C58H70O2 m/z 798.5376. Anal. Calcd for C58H70O2:
C, 87.17; H, 8.83. Found: C, 87.18; H, 8.88.
1,5-Bis(dibenzo[b,d]thiophen-4-yl)-2,4-bis((4-(dodecyloxy)-
phenyl)ethynyl)benzene (23). Compound 23 was prepared as de-
scribed for compound 2, substituting 4-dibenzothiopheneboronic acid
for 2,5-(dimethoxy)phenylboronic acid and 20 for 1. The crude product
was crystallized once from THF/MeOH and once from acetone/CHCl3.
Compound 23 was obtained as a colorless solid in 78.4% yield (mp
165-169 °C). 1H NMR (500 MHz, CDCl3): δ 0.87 (t, 6H, J ) 7.01
Hz), 1.24-1.42 (m, 40H), 1.72 (quint, 4H, J ) 7.75 Hz), 3.87 (t, 4H,
J ) 6.56 Hz), 6.70 (d, 4H, J ) 8.81 Hz), 7.03 (d, 4H, J ) 8.80 Hz),
7.43 (m, 4H), 7.58 (t, 2H, J ) 7.61 Hz), 7.73 (dd, 2H, J ) 7.40, 0.92
Hz), 7.80 (dd, 2H, J ) 6.80, 2.32 Hz), 7.95 (s, 1H), 8.01, (s, 1H), 8.18
(m, 4H). 13C NMR (125 MHz, CDCl3, partial): δ 13.98, 22.68, 25.97,
29.13, 29.34, 29.57, 29.64, 31.91, 68.04, 86.66, 94.08, 114.42, 114.88,
120.91, 121.64, 122.73, 122.96, 124.23, 126.68, 128.35, 130.02, 132.88,
135.00, 135.78, 135.92, 136.32, 139.75, 139.79, 141.53, 159.27. UV-
vis (CHCl3) λmax (ꢀ, cm-1 M-1): 318 (73 800), 298 (58 400) nm.
Luminescence spectrum (CHCl3) λmax (rel intensity): 394 nm. HRMS
(FAB): found m/z 842.3267 (M+); calcd for C58H50O2S2 (23-C6) m/z
842.3252. Anal. Calcd for C58H50O2S2 (23-C6): C, 82.62; H, 5.98.
Found: C, 82.24; H, 6.04. Anal. Calcd for C70H74O2S2: C, 83.12; H,
7.37. Found: C, 83.30; H, 7.37.
124.79, 126.45, 126.54, 126.91, 128.98, 131.14, 132.69, 133.15, 134.98,
135.05, 135.34, 138.02, 140.01, 141.33, 146.55, 158.96. UV-vis
(CHCl3) λmax (ꢀ, cm-1 M-1): 432 (5070), 402 (18 400), 384 (26 400),
356 (57 600), 338 (48 900), 286 (106 000), 258 (72 000) nm. Lumi-
nescence spectrum (CHCl3) λmax (rel intensity): 436 (1), 462 (0.63)
nm (very low intensity). HRMS (FAB): found m/z 1094.1161 (M+);
calcd for C58H48I2O2S2 (24-C6) m/z 1094.1184. Anal. Calcd for
C58H48I2O2S2 (24-C6): C, 63.62; H, 4.42. Found: C, 63.84; H, 4.96.
8,12-Bis(4-(dodecyloxy)phenyl)bis(dibenzo[b,d]thiophene)[4,3-a:
3′,4′-j]anthracene (25). Compound 24 (0.110 g, 0.100 mmol) was
dissolved in 35 mL of THF and cooled to -78 °C. To the solution
was added s-BuLi (1.5 mL, 1.53 M, 0.98 mmol) resulting in the
formation of a deep green solution. After 4 min of stirring, the reaction
was quenched by the rapid addition of 3 mL of MeOH. The mixture
was diluted with 100 mL of CHCl3, and the organic layer was washed
with 5% HCl (2 × 30 mL) and H2O and dried (Na2SO4) before removal
of the solvent in vacuo. The residue was purified by silica gel
chromatography (7:7:1 hexanes/toluene/CHCl3) to afford 25 as a bright
yellow solid (0.082 g, 96.8%) (mp 194-195 °C). 1H NMR (500 MHz,
CDCl3): δ 0.91 (t, 6H, J ) 7.05 Hz), 1.37-1.44 (m, 36H), 1.52 (quint,
4H, J ) 6.75 Hz), 1.85 (quint, 4H, J ) 8.02 Hz), 4.03 (t, 4H, J ) 6.56
Hz), 7.02 (d, 4H, J ) 8.57 Hz), 7.45 (d, 4H, J ) 8.53 Hz), 7.52 (m,
4H), 7.75 (s, 2H), 8.03 (m, 2H) overlapped with 8.04 (d, 2H, J ) 8.58
Hz), 8.25 (m, 2H), 8.285 (d, 2H, J ) 8.67 Hz), 8.290 (s, 1H), 11.01 (s,
1H). 13C NMR (125 MHz, CDCl3): δ 14.12, 22.71, 26.17, 29.39,
29.41, 29.50, 29.67, 29.72, 31.95, 68.16, 114.37, 119.94, 121.55, 121.88,
122.36, 124.57, 124.61, 126.59, 127.22, 127.45, 127.67, 127.84, 130.99,
131.14, 132.05, 133.23, 134.49, 135.09, 135.47, 139.58, 139.85, 158.72.
UV-vis (CHCl3) λmax (ꢀ, cm-1 M-1): 430 (4440), 380 (28 200), 350
(71 200), 334 (51 100), 296 (63 800), 280 (85 300), 266 (67 200) nm.
Luminescence spectrum (CHCl3) λmax (rel intensity): 434 nm. HRMS
(FAB): found m/z 1010.5088 (M+); calcd for C70H74O2S2 m/z 1010.5130.
Anal. Calcd for C70H74O2S2: C, 83.12; H, 7.37. Found: C, 83.24; H,
7.45.
2,4-Bis((4-(dodecyloxy)phenyl)ethynyl)-1,5-bis(5-methylthiophen-
2-yl)benzene (26). Compound 26 was prepared as described for 16,
substituting the dibromide 20 for 1. The crude product was purified
by silica gel chromatography (6:1 hexanes/ethyl acetate) to afford 26
as a yellow solid in 98.4% yield. 1H NMR (250 MHz, CDCl3): δ
0.86 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.77 (m, 4H), 2.55 (app s,
6H), 3.96 (t, 4H, J ) 6.53 Hz), 6.80 (dd, 2H, J ) 3.60, 0.89 Hz), 6.88
(d, 4H, 8.77 Hz), 7.47 (d, 4H, J ) 8.76 Hz), 7.58 (d, 2H, J ) 3.59
Hz), 7.74 (s, 1H), 7.82 (s, 1H). 13C NMR (62.9 MHz, CDCl3): δ 14.12,
15.39, 22.68, 26.00, 29.17, 29.37, 29.62, 31.91, 68.02, 87.62, 94.61,
114.52, 115.18, 118.59, 125.69, 127.05, 127.85, 132.79, 135.08, 138.50,
139.20, 140.88, 159.31. HRMS (FAB): found m/z 838.4839 (M+);
calcd for C56H70O2S2 m/z 838.4817.
4,8-Bis(4-(dodecyloxy)phenyl)-2,10-dimethylbisthien[2,3-a:3′,2′-
j]anthracene (27) and 4,7-Bis(4-(dodecyloxy)phenyl)-2,10-dimeth-
ylbisthien[2,3-a:3′,2′-j]anthracene (28). Compounds 27 and 28 were
prepared using standard acid cyclization conditions. Silica gel chro-
matography (3:2 hexanes/toluene) provided a 6:1 mixture (69%) of the
inseparable structural isomers 27/28. Due to the small amount present
and the apparent overlap of several resonances with 27, the structure
28 can only be tentatiVely assigned. Compound 27. 1H NMR (250
MHz, CDCl3): δ 0.86 (t, 6H, J ) 6.8 Hz), 1.1-1.5 (36H), 1.83 (m,
4H), 2.67 (app s, 6H), 4.03 (t, 4H, J ) 6.55 Hz), 7.03 (d, 4H, J ) 8.60
Hz), 7.20 (d, 2H, J ) 0.87 Hz), 7.57 (d, 4H, J ) 8.57), 7.70 (s, 2H),
8.43 (s, 1H), 8.65 (s, 1H). 13C NMR (125 MHz, CDCl3): δ 16.18,
22.67, 26.09, 29.33, 29.41, 29.60, 31.90, 68.14, 114.50, 115.63, 123.29,
124.62, 126.87, 128.23, 129.43, 130.13, 133.27, 135.19, 136.38, 137.18,
139.57, 158.74. UV-vis (27/28, CHCl3) λmax (ꢀ, cm-1 M-1): 416
(6130), 392 (8800), 370 (8680), 328 (103 000). Luminescence spectrum
(27/28, CHCl3) λmax (rel intensity): 426 (1), 452 (0.65) nm. HRMS
(FAB): found m/z 838.4826 (M+); calcd for C56H70O2S2 (27/28) m/z
838.4817.
8,12-Bis(4-(dodecyloxy)phenyl)-9,11-diiodobis(dibenzo[b,d]-
thiophene)[4,3-a:3′,4′-j]anthracene (24). To a 50 mL Schlenk tube
containing I2 (0.40 g, 1.57 mmol) was added 14.56 mL of a Hg(TFA)2/
CH2Cl2 solution (0.03 M, 0.437 mmol) followed by 2,6-lutidine (50
µL, 0.429 mmol). The mixture was cooled to 0 °C and allowed to stir
for 15 min before a solution of 23 (0.16 g, 0.190 mmol) dissolved in
5 mL of CH2Cl2 was added. After 20 min of stirring, maintaining the
temperature at 0 °C, the reaction was quenched with 5% NaOH (15
mL). The mixture was diluted with CHCl3, washed with additional
5% NaOH (2 × 30 mL), H2O, 5% HCl (2 × 30 mL), and H2O, and
dried (Na2SO4), and the solvent was removed in vacuo. The crude
product was chromatographed on silica gel (1:1 hexanes/toluene) to
provide 24 as a bright yellow solid (0.192 g, 92.3%) (mp 202-204
°C). 1H NMR (500 MHz, CDCl3): δ 0.89 (t, 6H, J ) 7.10 Hz), 1.24-
1.44 (m, 36H), 1.54 (quint, 4H, J ) 7.72 Hz), 1.88 (quint, 4H, J )
7.93 Hz), 4.10 (t, 4H, J ) 6.53 Hz), 7.11 (d, 4H, J ) 8.64 Hz), 7.27
(d, 4H, J ) 8.59 Hz), 7.50 (m, 4H), 7.66 (d, 2H, J ) 8.55 Hz), 7.94
(ddd, 2H, J ) 7.35, 1.99, 0.94 Hz), 8.23 (d, 2H, 8.68 Hz) overlapping
2,4-Bis((4-(hexyloxy)phenyl)ethynyl)-1,5-bis(2,2′-bithiophene-5-
yl)benzene (29) and 1-Bromo-2,4-bis((4-(hexyloxy)phenyl)ethynyl)-
5-(2,2′-bithiophene-5-yl)benzene (30). To a cooled (-50 °C) solution
of 2,2′-bithiophene (0.330 g, 1.98 mmol) dissolved in 10 mL of THF
was added n-BuLi (1.28 mL, 1.55 M, 1.98 mmol). After 20 min of
stirring, a solution of ZnCl2 (0.338 g, 2.48 mmol) in 10 mL of THF
with 8.23 (dd, 2H, J ) 7.38, 2.05 Hz), 9.67 (s, 1H), 11.12 (s, 1H). 13
C
NMR (125 MHz, CDCl3): δ 14.12, 22.71, 26.21, 29.38, 29.45, 29.51,
29.66, 31.94, 68.15, 107.14, 114.45, 120.73, 121.71, 122.16, 122.45,

4592 J. Am. Chem. Soc., Vol. 119, No. 20, 1997
Goldfinger et al.
was added via cannula. The solution was allowed to warm to room
temperature and stir for an additional 10 min before being transferred
to another flask containing 1,5-dibromo-2,4-bis((4-(hexyloxy)phenyl)-
ethynyl)benzene (C6 side chain version of 20) (1.25 g, 1.97 mmol) and
(Ph3P)2PdCl2 (0.028 g, 0.040 mmol) predissolved in 10 mL of THF.
The reaction was allowed to stir at rt for 14 h before being carefully
quenched with MeOH. The mixture was diluted with diethyl ether,
washed with H2O, and dried (MgSO4), and the solvent was concentrated
under reduced pressure. The crude mixture was separated by column
chromatography using alumina as the stationary phase (12:1 hexanes/
EtOAc) to provide two major fractions. The first fraction was further
purified by performing a second column using the same conditions to
afford compound 30 as a yellow solid (0.49 g, 34.7%) (mp 97-100
°C). The second fraction from the first column was further purified
by performing a second column using alumina as the stationary phase
(8:1 hexanes/EtOAc eluent). Compound 29 was isolated as a yellow
solid (0.276 g, 17.4%) (mp 108-111 °C). Compound 29. 1H NMR
(250 MHz, CDCl3): δ 0.89 (t, 6H, J ) 6.30 Hz), 1.1-1.5 (12H), 1.75
(m, 4H), 3.91 (t, 4H, J ) 6.55 Hz), 6.84 (d, 4H, J ) 8.82 Hz), 6.99
(dd, 2H, J ) 5.03, 3.66 Hz), 7.17 (m, 6H), 7.44 (d, 4H, J ) 8.72 Hz),
7.62 (d, 2H, J ) 3.87 Hz), 7.76 (s, 1H), 7.77 (s, 1H). 13C NMR (62.9
MHz, CDCl3): δ 14.04, 22.59, 25.68, 29.15, 31.57, 68.05, 87.59, 95.72,
114.58, 115.00, 119.08, 123.71, 123.82, 124.50, 127.40, 127.76, 127.90,
132.87, 134.32, 137.37, 138.04, 138.54, 140.14, 159.44. UV-vis
(CHCl3) λmax (ꢀ, cm-1 M-1): 366 (60 300), 258 (31 500) nm.
Luminescence spectrum (CHCl3) λmax (rel intensity): 446 nm. HRMS
(FAB): found m/z 806.2367 (M+); calcd for C50H46O2S4 m/z 806.2381.
Anal. Calcd for C50H46O2S4: C, 74.40; H, 5.74. Found: C, 74.30; H,
5.82. Compound 30. 1H NMR (250 MHz, CDCl3): δ 0.88 (t, 6H, J
) 6.8 Hz), 1.1-1.5 (12H), 1.72 (m, 4H), 3.87 (t, 4H, J ) 6.50 Hz),
6.81 (br d, 4H, J ) 8.69 Hz), 6.96 (t, 1H, J ) 3.75 Hz), 7.13 (m, 3H),
7.42 (d, 2H, J ) 8.38 Hz), 7.45 (d, 2H, J ) 8.28 Hz), 7.54 (d, 1H, J
) 3.94 Hz), 7.65 (s, 1H), 7.76 (s, 1H). 13C NMR (125 MHz, CDCl3):
δ 14.00, 22.58, 25.68, 29.15, 31.56, 68.12, 86.20, 86.97, 95.42, 95.93,
114.58, 114.61, 114.70, 114.78, 119.54, 123.84, 123.89, 124.32, 124.70,
124.75, 127.94, 128.08, 131.41, 132.91, 133.23, 133.27, 135.30, 137.21,
137.39, 138.63, 139.00, 159.65, 159.69. UV-vis (CHCl3) λmax (ꢀ, cm-1
M-1): 380 (35 200), 328 (60 300), 262 (30 100) nm. Luminescence
spectrum (CHCl3) λmax (rel intensity): 436 nm. HRMS (FAB): found
m/z 720.1748 (M+); calcd for C42H41O2BrS2 m/z 720.1731.
3.4 mol %) in a 200 mL Schlenk flask was evacuated and back-filled
with argon. Toluene (100 mL) was added with vigorous stirring
followed by diisopropylamine (4.5 mL, 32 mmol, 3.2 equiv). The
mixture was allowed to stir for about 5 min during which time it became
progressively more red. 4-(Butyloxy)phenylacetylene (4.20 g, 24 mmol,
2.4 equiv) was added dropwise over a period of about 10 min. The
reaction was heated at 70 °C for 24 h, cooled, and filtered through
silica gel using chloroform (300 mL). The solvent was removed under
reduced pressure, and the resulting black sludge was stirred with ether
(125 mL), filtered, and washed with ether to give 34 (4.879 g, 80%)
as a pale yellow powder which was essentially pure. An analytically
pure sample was obtained by recrystallization from THF/MeOH (mp
136-137 °C). 1HNMR (250 MHz, CDCl3): δ 0.99 (t, 6H, J ) 7.32
Hz), 1.50 (m, 4H), 1.79 (m, 4H), 2.51 (s, 6H), 3.99 (t, 4H, J ) 6.50
Hz), 6.90 (d, 4H, J ) 8.77 Hz), 7.51 (d, 4H, J ) 8.77 Hz). 13C NMR
(125 MHz, CDCl3): δ 13.82, 19.21, 19.28, 31.23, 67.84, 87.44, 99.50,
114.66, 114.78, 125.38, 126.54, 133.10, 138.59, 159.74. HRMS
(FAB): found m/z 606.0777 (M+); calcd for C32H32O2Br2 m/z 606.0768.
1,2-Diiodo-3,6-bis((4-butoxyphenyl)ethynyl)-4,5-dimethylben-
zene (34). A mixture of cuprous iodide (22.3 g, 117 mmol, 23 equiv),
potassium iodide (45 g, 270 mmol, 54 equiv), and 34 (3.03 g, 5 mmol)
in a 500 mL Schlenk flask was evacuated and back-filled with argon.
DMF (200 mL) was added with vigorous stirring, and the mixture was
heated to 145-150 °C for 90 h. After cooling, a significant portion
(150-170 mL) of the DMF was removed under reduced pressure, and
the mixture was diluted with chloroform (500 mL) and filtered through
silica gel, which was washed with more chloroform (500 mL). The
combined filtrate and washings were washed with concentrated
ammonium hydroxide (4 × 800 mL), and the solvent was removed
under reduced pressure. The yellow black sludge was stirred with ether
(125 mL), filtered, and washed successively with ether, water, and cold
acetone to give 35 (2.96 g, 84%) as a pale yellow solid which was
essentially pure. A single recrystallization from THF/MeOH provided
analytically pure compound (mp 174-176 °C). 1H NMR (250 MHz,
CDCl3): δ 0.98 (t, 6H, J ) 7.39 Hz), 1.50 (m, 4H), 1.79 (m, 4H), 2.53
(s, 6H), 3.99 (t, 4H, J ) 6.53 Hz), 6.89 (d, 4H, J ) 8.79 Hz), 7.51 (d,
4H, J ) 8.71 Hz). 13C NMR (125 MHz, CDCl3): δ 13.82, 19.21,
20.00, 31.23, 67.84, 92.95, 98.06, 112.19, 114.66, 114.77, 130.62,
132.96, 138.71, 159.75. HRMS (FAB): found m/z 702.0403 (M+);
calcd for C32H32I2O2 m/z 702.0410.
4,8-Bis(4-(hexyloxy)phenyl)-2,10-bis(thiophen-2-yl)bisthien[2,3-
a:3′,2′-j]anthracene (31) and 4,7-Bis(4-(hexyloxy)phenyl)-2,10-bis-
(thiophen-2-yl)bisthien[2,3-a:3′,2′-j]anthracene (32). A 200 mL
Schlenk flask was charged with 29 (0.100 g, 0.124 equiv) and 110 mL
of 1,2-dichloroethane. The solution was subjected to two freeze-
pump-thaw cycles before TFA (1.5 mL) was added and the solution
was heated to 65 °C. After 4 h, the reaction was allowed to cool to rt
and was diluted with 50 mL of CHCl3. The organics were washed
with 5% NaOH (2 × 40 mL) and H2O (40 mL), dried (Na2SO4), and
concentrated in vacuo. Silica gel chromatography (1:1 hexanes/CHCl3)
afforded a 6:1 mixture of the inseparable structural isomers 31/32 as a
bright yellow solid (0.055 g, 55.0%). Due to the small amount present
and the apparent overlap of resonances with 31, the structure 32 can
only be tentatiVely assigned. Compound 31. 1H NMR (500 MHz,
CDCl3): δ 0.93 (t, 6H, J ) 7.08 Hz), 1.37 (m, 8H), 1.51 (m, 4H), 1.85
(quint, 4H), 4.06 (t, 4H, J ) 6.54 Hz), 7.06 (d, 4H, J ) 8.67 Hz), 7.08
(dd, 2H, J ) 5.03, 3.66 Hz), 7.29 (dd, 2H, J ) 5.09, 1.10 Hz), 7.35
(dd, 2H, J ) 3.55, 1.07 Hz), 7.58 (s, 2H), 7.59 (d, 4H, J ) 8.61), 7.72
(s, 2H), 8.42 (s, 1H), 8.72 (s, 1H). 13C NMR (62.9 MHz, CDCl3): δ
14.10, 22.66, 25.81, 29.34, 31.66, 68.08, 114.49, 115.66, 120.97, 124.55,
125.00, 126.29, 127.91, 128.17, 129.35, 129.67, 130.11, 132.76, 135.08,
136.11, 136.30, 137.14, 137.60, 158.74. UV-vis (31/32, CHCl3) λmax
(ꢀ, cm-1 M-1): 440 (8120), 406 (28 200), 370 (93 000), 358 (92 800),
340 (75 400), 322 (67 100) nm. Luminescence spectrum (CHCl3) λmax
(rel intensity): 452 (1), 480 (0.70) nm. HRMS (FAB): found m/z
806.2350 (M+); calcd for C50H46O2S4 (31/32) m/z 806.2381. LRMS
(FAB): 823 (10), 806 (100, M+), 798 (10), 460. Anal. Calcd for
C50H46O2S4 (31/32): C, 74.40; H, 5.74. Found: C, 74.12; H, 5.94.
3′,6′-Bis((4-butoxyphenyl)ethynyl)-4′,5′-dimethyl[1,1′:2′,1′′]ter-
phenyl (35). A mixture of diiodide 34 (545 mg, 0.78 mmol),
phenylboronic acid (1.03 g, 8.4 mmol, 11 equiv), palladium bis-
(dibenzylideneacetone) (28 mg, 0.05 mmol, 6 mol %), potassium
hydroxide powder (2.15 g, 38 mmol, 49 equiv), and triphenylphosphine
(0.29 g, 1.1 mmol, 1.4 equiv) in a 200 mL Schlenk flask was evacuated
and back-filled with argon. Nitrobenzene (40 mL) was added with
vigorous stirring followed by water (12 mL). The reaction mixture
was purged with argon for about 30 min and then heated to 100 °C for
16 h. After cooling, the reaction was diluted with ether (250 mL).
The organic layer was washed with 2 M potassium hydroxide (2 ×
100 mL) and 10% hydrochloric acid (2 × 100 mL) and filtered through
silica gel which was washed with ether (150 mL). The solvents were
removed under reduced pressure, and the brown sludge was dissolved
in chloroform (10 mL) and filtered to remove insolubles. The filtrate
was diluted with methanol (300 mL), and the product precipitated. This
was filtered and washed with methanol. The filtrate and washings were
evaporated under reduced pressure. The brown solid was coated onto
silica gel from methylene chloride, loaded onto a silica gel column,
and eluted with 60% hexane/40% toluene mixture. The solid was then
dissolved in chloroform (1 mL), diluted with methanol (30 mL), filtered,
and washed with methanol. This gave 35 (441 mg, 94%) as a pale
yellow solid which was essentially pure (mp 149-151 °C). 1H NMR
(250 MHz, CDCl3): δ 0.95 (t, 6H, J ) 7.42 Hz), 1.46 (m, 4H), 1.74
(m, 4H), 2.62 (s, 6H), 3.92 (t, 4H, J ) 6.57 Hz), 6.73 (d, 4H, J ) 8.75
Hz), 7.00 (d, 4H, J ) 8.78 Hz), 7.16 (s, 10H). 13C NMR (125 MHz,
CDCl3): δ 13.82, 18.61, 19.19, 31.21, 67.72, 87.80, 98.40, 114.38,
115.55, 123.25, 126.20, 127.04, 130.81, 132.62, 137.09, 140.48, 141.23,
159.04. HRMS (FAB): found m/z 602.3193 (M+); calcd for C44H42O2
m/z 602.3185.
1,2-Dibromo-3,6-bis((4-butoxyphenyl)ethynyl)-4,5-dimethylben-
zene (33). A mixture of 3,4-dibromo-2,6-diiodo-o-xylene (5.171 g,
10.0 mmol, 1 equiv), bis(triphenylphosphino)palladium(II) chloride (130
mg, 0.19 mmol, 19 mol %), and cuprous iodide (65 mg, 0.34 mmol,
1,6-Bis(4-butoxyphenyl)-3,4-dimethyldibenzo[c,g]phenanthrene
(37). To a solution of 120 mg of 35 (0.2 mmol) in 50 mL of CH2Cl2

Synthesis of Fused Polycyclic Aromatics
J. Am. Chem. Soc., Vol. 119, No. 20, 1997 4593
contained in a flask wrapped in aluminium foil was added 140 mg of
silver triflate (0.54 mmol). After 4 h, 0.6 g of iodine (2.4 mmol) was
added, and the reaction was allowed to stir for a further 8 h. The
reaction was quenched by addition of 10 mL each of 2 M KOH and
saturated NH4Cl solutions. The organic layer was dried (MgSO4), and
the solvent was removed in vacuo yielding 130 mg of a black solid.
Silica gel chromatography (65:35 hexanes/toluene) gave 37 as a bright
yellow solid (24 mg, 20%) (mp 186-189 °C). 1H NMR (CDCl3, 500
MHz): δ 8.43 (d, 2H, J ) 8.5 Hz, H(1)), 8.08 (s, 2H, H(6)), 7.96 (dd,
2H, J ) 7.7, 0.5 Hz, H(4)), 7.62 (d, 4H, J ) 8.5 Hz, OCdCHCH),
7.38 (dd, J ) 7.1, 7.1 Hz, H(3)), 7.20 (dd, 2H, J ) 7.1, 7.1 Hz, H(2)),
7.10 (d, 4H, J ) 8.5 Hz, OCdCH), 4.08 (t, 4H, J ) 6.5 Hz, OCH2),
2.78 (s, 6H, CdCCH3), 1.88-1.82 (m, 4H, OCH2CH2), 1.59-1.51 (m,
4H, CH3CH2), 1.03 (t, 6H, J ) 7.4 Hz, CH2CH3). 13C NMR (CDCl3,
125 MHz): δ 158.72, 138.52, 133.28, 131.61, 131.20, 130.99, 130.61,
130.55, 130.07, 125.92, 125.69, 124.90, 124.25, 122.6, 114.47, 67.86,
31.44, 19.33, 15.97, 13.89. HRMS (FAB): found m/z 602.3178 (M+);
calcd for C44H42O2 m/z 602.3185.
toluene/hexane solution. Careful chromatography on silica gel with
3:1 hexane/toluene gave 38 (5 mg, 40%) as a yellow solid (mp 207-
209 °C). 1H NMR (CDCl3, 500 MHz): δ 9.06 (d, 2H, J ) 8.1 Hz),
8.33 (s, 2H), 8.25 (d, 2H, J ) 7.8 Hz), 7.94 (dd, 2H, J ) 8, 8 Hz),
7.65 (d, 4H, J ) 9 Hz), 7.13 (d, 4H, J ) 8.7 Hz), 4.12 (t, 4H, J ) 6.3
Hz), 3.05 (s, 6H), 1.90-1.83 (m, 4H), 1.62-1.50 (m, 4H), 0.86 (t,
6H, J ) 7.7 Hz). HRMS (EI): found m/z 600.3024 (M+); calcd for
C44H40O2 m/z 600.3028.
Acknowledgment. The authors are grateful to Dr. Bing Xu
for performing AM1 calculations on 10 and 19. This work was
supported by a DuPont Young Professor Grant, an Alfred P.
Sloan Fellowship, a Camille Dreyfus Teacher-Scholar award,
and the Office of Naval Research.
Supporting Information Available: Synthetic procedures
and spectral data for the synthesis of 4-(dodecyloxy)pheny-
1
lacetylene including UV, emission, H NMR, and 13C NMR
4,11-Bis(4-butoxyphenyl)-1,2-dimethylbenzo[ghi]perylene (38).
To a solution of 37 (12.5 mg, 0.02 mmol, 1 equiv) in benzene (500
mL) were added iodine (94 mg, 0.37 mmol, 18.5 equiv) and propylene
oxide (2 mL, 28 mmol, 1400 equiv). The solution was irradiated
through pyrex for 2 h and then evaporated under reduced pressure.
The crude material was filtered through a plug of silica gel using a 1:1
spectra of most of the compounds reported (105 pages). See
any current masthead page for ordering and Internet access
instructions.
JA9642673