Discotic liquid crystalline hexabenzocoronenes carrying chiral and racemic branched alkyl chains: Supramolecular engineering and improved synthetic methods

Article abstract of DOI:10.1016/S0040-4020(01)00252-6

In this paper we present the synthesis and characterization of three different thermotropic liquid crystalline derivatives of hexabenzocoronene (HBC), substituted at the periphery by six chiral or racemic branched (3,7-dimethyloctanyl) chains, namely the chiral 5a, racemic 5b, and mono-bromo functionalized 18 carrying five alkyl chains. Improved methods for synthesis of HBC precursors, largely relying on transition-metal catalyzed coupling reactions, are also described. Solubility and processability are increased while the thermal K→D_H transitions are shifted to lower temperatures, relative to analogous HBCs carrying n-alkyl chains. In case of substitution with a chiral branched alkyl chain, 5a, strong signals have been recorded by means of circular dichroism spectroscopy. All new compounds were characterized by ¹H, ¹³C NMR, and UV-Vis spectroscopy, and FD-MS. Preliminary mesophase characterization is carried out by differential scanning calorimetry (DSC) and polarized light microscopy. In the course of the DSC experiments, optically pure and racemic HBC derivatives were compared.

Full text of DOI:10.1016/S0040-4020(01)00252-6

TETRAHEDRON
Pergamon
Tetrahedron 57 +2001) 3769±3783
Discotic liquid crystalline hexabenzocoronenes carrying chiral
and racemic branched alkyl chains: supramolecular engineering
and improved synthetic methods
p
È
È
Andreas Fechtenkotter, Natalia Tchebotareva, Mark Watson and Klaus Mullen
È
Max-Planck-Institut fur Polymerforschung, Ackermannweg 10, D-55128Mainz, Germany
Received 3 November 2000; accepted 22 January 2001
AbstractÐIn this paper we present the synthesis and characterization of three different thermotropic liquid crystalline derivatives of
hexabenzocoronene +HBC), substituted at the periphery by six chiral or racemic branched +3,7-dimethyloctanyl) chains, namely the chiral
5a, racemic 5b, and mono-bromo functionalized 18 carrying ®ve alkyl chains. Improved methods for synthesis of HBC precursors, largely
relying on transition-metal catalyzed coupling reactions, are also described. Solubility and processability are increased while the thermal
K!DH transitions are shifted to lower temperatures, relative to analogous HBCs carrying n-alkyl chains. In case of substitution with a chiral
branched alkyl chain, 5a, strong signals have been recorded by means of circular dichroism spectroscopy. All new compounds were
characterized by 1H, 13C NMR, and UV±Vis spectroscopy, and FD-MS. Preliminary mesophase characterization is carried out by differential
scanning calorimetry +DSC) and polarized light microscopy. In the course of the DSC experiments, optically pure and racemic HBC
derivatives were compared. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
crystallinity over temperature ranges of up to 2008C.18
These materials combine several target properties: +a) stable
mesophases over large temperature ranges, +b) high thermal
and photochemical stability, and +c) intense absorption at
long wavelengths.18
Once a chemical substance crosses the border from being
simply a new compound to the stage were its materials
properties become most dominant and relevant for its appli-
cation in devices, one has to think of designing the synthesis
to be as easy, inexpensive and ef®cient as possible. For one
class of compound this border has been crossed some time
ago. Discotic liquid crystals1±3 are being recognized for
their potential applications in photovoltaic devices,4,5 ®eld
effect transistors +FETs)6 and molecular electronics.7 Since
Chandrasekhar in 1977 discovered the ®rst discotic liquid
crystalline material,8 immense research efforts have lead to
a variety of novel discotic mesogens such as phthalo-
cyanines,9,10 porphyrines,9 triphenylenes,11±15 dibenzopyr-
enes,13,16,17 perylenes18,19 and hexabenzocoronenes +HBCs,
Fig. 1).20±29
Among the above-mentioned liquid-crystalline PAHs,
triphenylenes are the ones that have been studied most
extensively in view of their mechanism of charge trans-
port,31±33 one-dimensional energy transport,34,35 photocon-
ductivity,4,5,36±39 ordering of multilayers +investigated by
using Langmuir±Blodgett techniques),40 orientation of
two-dimensional crystals41,42 +investigated using scanning
tunneling microscopy +STM)) and their alignment under
the in¯uence of a magnetic ®eld.43 Further, liquid crystalline
polymers with triphenylenes both in the main and in the
side chain have been prepared and analyzed.13,44±47 Photo-
physical properties of several different alkoxy substituted
dibenzopyrene derivatives have been determined to study
the phase transitions with the help of absorption and ¯uor-
escence spectroscopy.17 Two switchable ferroelectric
phases of a columnar dibenzopyrene derivative have been
reported by Bock et al.16 Here, the co-existence of different
columnar phases depends on the strength of an applied
electric ®eld, thus opening possible applications for elec-
tro-optical displays.
The latter four belong to the class of large polyaromatic
hydrocarbons +PAHs).30 Perylene is a well-known chromo-
phore, which displays high extinction coef®cients and
nearly quantitative ¯uorescence quantum yields with
outstanding photochemical and thermal stability.18,19
However, it suffers from its low processability. This was
overcome with the introduction of solubilizing side groups,
also yielding perylene derivatives that exhibit discotic liquid
Alkyl-, or phenyl-alkyl substituted hexabenzocoronenes
+Fig. 1) and their functionalized derivatives20±29 are discotic
liquid crystalline materials with one of the largest PAH
cores +approximately three times the size of triphenylene).
Keywords: polyaromatic hydrocarbons +PAH); hexabenzocoronenes; disco-
tic liquid crystals; chiral mesophase.
Corresponding author. Tel.: 149-6131-379151; fax: 149-6131-379100;
e-mail: muellen@mpip-mainz.mpg.de
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020+01)00252-6

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3770
R
X
R
R
R
R
R
R
R
R
R
R
1b
1a
"mono"
X
X
R
R
X
R
R
R
R
R
R
X
1c
"ortho"
1d
"para"
R = alkyl
Figure 1. Hexabenzocoronene derivatives with differing substitution patterns.
This class of mesogen is being well recognized for its
extremely large phase widths +up to 2508C)21 and its record
charge carrier mobilities along the columnar axis
+1.13 cm2 V21 s21).23,27
overlap, thus giving rise to larger phase widths and more
stable mesophases. Vast differences for the mesoscopic
properties are also seen by changing the periphery, e.g. a
hexahexylthiotriphenylene5 exhibits a helical columnar
phase and was the previous record holder for charge carrier
mobilities of organic materials other than in single crystals.5
Simmerer et al. showed that by changing the substituents on
the perimeter of the triphenylene disc from pentyloxy to
butyloxy, one does not only proceed from a columnar
From the examples given above, it can be seen that by
varying the size and geometry of the aromatic core of dis-
cotic liquid crystals, the properties change dramatically.
Increasing the size of the core results in enhanced p±p
R
Br
R
R
R
R
R
R
R
R
R
R
5a R =
5b R =
18 R =
Figure 2. All-alkyl and mono-bromo-functionalized hexabenzocoronenes 5a, 5b and 18.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3771
a:
b:
BrMg
BrMg
Br
Br
R
R
[PdCl2(dppf)], THF, reflux
2
3a R =
3b R =
[Co2(CO)8],
dioxane,
reflux
R
R
R
R
R
R
R
R
R
FeCl3, CH3NO2
CH2Cl2
R
R
R
5a R =
4a R =
4b R =
5b R =
Scheme 1. Synthesis of chiral and racemic hexaalkyl substituted hexabenzocoronenes 5a and 5b.
hexagonal packing to the formation of a so-called plastic
discotic phase, but one also increases the mobilities by an
order of magnitude.36 Two different alignments in a
magnetic ®eld were observed when the triphenylene core
is substituted with six 4-n-octyloxybenzoate groups.43 And
®nally Langmuir±Blodgett ®lms were obtained and investi-
gated for an asymmetrically substituted triphenylene
derivative carrying hydrophobic and hydrophilic side
chains.40
It was later shown that various hexaalkoxy derivatives could
be prepared directly from dialkoxy benzenes using
suspended FeCl3 as an oxidizing agent, followed by reduc-
50
tive workupwith methanol.
Recently, Kumar and co-
workers reported that VOCl3 performs the same oxidation
in high yield in very short reaction times +10 min), which
was attributed to the high solubility of the oxidizing agent.51
Further, unsymmetrically substituted triphenylenes were
desired and a number of routes have been developed for
the synthesis of such.9
This ample variety of functions, properties and applications
also provided impetus for the development of new and
improved syntheses of triphenylenes. Since Bachmann
synthesized the ®rst triphenylene48 and Destrade et al. the
®rst liquid crystalline derivative49 in 1979, numerous
improvements in the synthesis and processing of triphenyl-
enes have been reported.
Likewise, the very promising properties of alkyl-substituted
HBCs prompted us to begin systematic investigations of
various functionalized derivatives. The geometry of HBC
suggests the name `superbenzene' and we therefore use
similar nomenclature for HBCs and for compounds built-
up from HBC, such as the `supernaphthalene' and the
`supertriphenylene', consisting of two and three `super-
benzenes', respectively.52 Benzene-analogous nomen-
clature is also used to denote substitution patterns, e.g.
HBC's functionalized in the positions `ortho' and `para'
as depicted in Fig. 1.22 We have yet to implement
alternative procedures to synthesize any `meta' derivatives.
Initially, hexaalkyloxy triphenylenes with groups larger
than methyl had to be prepared by a three-step route
comprised of oxidative trimerization of veratrole with
chloranil, demethylation of the hexamethoxy triphenylene,
and then alkylation of the resulting hexahydroxy compound.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3772
By benzene-analogous transition-metal catalyzed chem-
istry, HBC derivatives with cyano, ether, ester, amino, etc.
functionality were prepared22 from the bromo-functional-
ized HBCs +Fig. 1, XˆBr). Their mesoscopic behavior as
well as their packing in two and three dimensions was
studied. The direct visualization of two-dimensional crys-
tals and liquid crystals of hexabenzocoronene derivatives on
surfaces such as HOPG +highly oriented pyrolytic graphite)
and molybdenum disul®de was achieved by STM tech-
niques.20,22,53,54 From a mono bromo-substituted HBC +1b,
Rˆn-C12H25, XˆBr), a particularly interesting lattice struc-
ture was observed22 with two types of arrangements:
molecules associated in trimers +bromine atoms located in
the center) and single molecules. The supramolecular
arrangement reveals a hexagonal lattice in which single
molecules ®ll positions in the center of an ensemble of six
trimers.22 Further, scanning tunneling spectroscopy
revealed diode-like current±voltage curves for the cores
of single molecules of a hexaalkyl HBC.20
number of triphenylene derivatives emphasize the wide
horizon facing the ®eld of discotic liquid crystalline PAHs.
More thorough understanding of the potential of HBCs as
materials will require a library of derivatives, and improved
synthetic routes to facilitate their preparation is desired.
Recently published routes to prepare substituted hexa-
benzocoronenes relied on multistepsyntheses and long
term planning of the substitution pattern in cases with
reduced symmetry and/or functionalized derivatives. Here,
we discuss improved procedures for preparing the building
blocks needed for HBC synthesis with symmetric six-fold
alkyl substitution, namely the hexa-chiral HBC 5a +HBC-
p
C8 ) and the racemic HBC 5b +HBC-C8) as well as bromo-
functionalized compound 17 +Fig. 2). Dramatic increases in
solubility and processability are noted compared to previous
HBCs substituted with n-alkyl chains, and the effect of
chirality in the side chains was preliminarily investigated.
The mono bromo-substituted HBC was also used as a start-
ing material for a surface active HBC with a tethered
carboxylic acid group+ 1b, Rˆn-C12H25, Xˆ
+CH2)11CO2H).55 This derivative was then complexed with
amino functionalized polysiloxane and polyethyleneimine
resulting in remarkably long columns essentially free of
defects.25,56 The surface activity of this HBC was exploited
to prepare LB ®lms at the air±water interface.57 These few
examples taken together with the already existing vast
2. Results
2.1. Syntheses
2.1.1. HBCs with C6 symmetry. As reported by Herwig and
co-workers in 1996, a four-stepsynthetic sequence was
utilized to prepare alkyl substituted 4,40-diphenylacetylenes,21
the crucial building block for the hexafold-substituted HBC
derivatives. Two disadvantages of this synthesis come
O
O
O
a)
Ts-OH
H2C CH2
OHOH
Br
Br
Br
Br
7
6
O
O
O
H2SO4
BrMg
[PdCl2(dppf)], THF, reflux
7
R
R
R
R
8
9 R =
O
b)
O
BrZn
[PdCl2(dppf)], THF, reflux
Br
Br
R
R
6
9 R =
Scheme 2. +a) Protection, reaction, and deprotection sequence of compound 9; +b) improved synthesis of 9 using a zinc metalated alkyl chain.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3773
easily to mind: +a) two of the four steps are catalyzed by
expensive palladium catalysts, and +b) the introduction of a
different substituent cannot be accomplished on the level of
the 4,40-diphenylacetylene, but must be introduced right at
the beginning of the reaction sequence. Here, we present a
much faster, cheaper and higher yielding one-step synthesis
for the desired diphenylacetylene starting from 4,40-di-
bromodiphenylacetylene +2), which can be prepared accord-
ing to a literature procedure58 on several hundred gram
using the [PdCl2+dppf)] catalyst.29 The extension of this
method to the coupling of alkylmagnesiumbromide species
is outlined in Scheme 1. +S)-3,7-Dimethyloctylmagnesium-
bromide is coupled with 2 under Kumada coupling con-
ditions using [PdCl2+dppf)]59 as the catalyst in THF, to
yield the enantiomerically pure alkyl substituted diphenyl-
acetylene 3a in 85% yield. In a similar fashion the racemic
version of 3a, i.e. 3b was prepared in equally high yields.
This procedure is highly attractive, especially when the
groupto be attached, `R', is either expensive, or must be
prepared by multistep synthesis. In a cyclotrimerization
scale. Previous attempts22 to functionalize
2 under
common Grignard coupling conditions using NiCl2+dppe),
NiCl2+dppp), or Pd+PPh3)4 were unsatisfactory. It was just
recently that we reported the aryl±aryl coupling of 2 with
two equivalents 4-n-dodecylphenyl-magnesiumbromide
60
reaction under catalytic action of Co2+CO)8 3a and 3b
were both transferred to the hexaphenylbenzene derivatives
4a and 4b, respectively. These reactions have yields of
O
O
I2,
DMSO
R
R
155 °C
R
R
3b
10
O
R
R
O
R
R
9
KOH
EtOH
O
O
reflux
R
R
R
R
10
11 R =
Scheme 3. Synthesis of substituted tetraarylcyclopentadienone 11.
BrMg
TBAF
TMS
Br
TMS
R
H
R
[PdCl2(dppf)], THF, reflux
THF, reflux
12
13
14
Pd(PPh3)4,
toluene, Et3N,
80 °C
Br
Br
I
Br
15
R
R
R
diphenylether, reflux
O
R
R
R
16
R
R
R
R
11
17 R =
Scheme 4. [412] Diels±Alder reaction leading to the bromo-substituted hexaphenylbenzene 17.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3774
around 90% and the products are easily puri®ed using stan-
dard column chromatography. The ®nal step for this reac-
tion sequence is the oxidative planarization of the six
pending phenyl rings in 4a and 4b, with concurrent loss of
twelve hydrogens. The cyclodehydrogenation26 is achieved
by adding a solution of FeCl3 in nitromethane to the hexa-
phenylbenzene precursors 4a and 4b in dichloromethane to
afford the alkyl substituted hexabenzocoronenes 5a and 5b,
respectively. Isolated yields after puri®cation using column
chromatography and slow reprecipitation are of the order of
80%.
The HBCs 5a and 5b, substituted with branched alkyl chains
show solubilities in common organic solvents more than ten
times higher than HBC derivatives, substituted with n-alkyl
chains, synthesized earlier by our group.21,22,24 The above
1
introduced compounds have been characterized by H- and
13C NMR, UV±Vis spectroscopy, and FD-MS. As a typical
example for the hexaalkyl-substituted HBCs, the H NMR
spectrum of 5a is depicted in Fig. 3.
1
2.1.2. HBC with reduced symmetry. After showing that
the introduction of branched alkyl chains greatly increases
Figure 3. 1H NMR spectra of 5a at different concentrations +C2D2Cl4, rt).
Br
Br
R
R
R
R
R
R
R
FeCl3, CH3NO2
CH2Cl2
R
R
R
17
18 R =
Scheme 5. Cyclodehydrogenation reaction of 17 yielding hexabenzocoronene 18.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3775
Figure 4. Circular dichroism spectra of 5a and 5b recorded from spincoated ®lms.
solubility, as demonstrated for compounds 5a and 5b herein,
we set out to prepare the mono-bromo-functionalized HBC
18. The necessary functionalized hexaphenylbenzene
precursor is prepared via the [412] cycloaddition of a
suitably substituted diphenylacetylene, 16, and 2,3,4,5-
tetraarylcyclopenta-2,4-dien-1-one 11. The cyclopenta-
dieneone is synthesized via double Knoevenagel conden-
sation between a 4,40-substituted benzyl and a 1,3-
diarylacetone +Scheme 3). The synthesis of a suitable 1,3-
diarylacetone has until now, been the stepwith the lowest
yields +47%) in the entire reaction sequence. For these
reasons we chose a protection, deprotection route for the
acetone derivative 9 +Scheme 2). At ®rst, we protected
1,3-bis+4-bromophenyl)-2-propanone 622 with ethylene
glycol to give the acetal 7. Next, under Kumada coupling
conditions, the alkyl substituent was introduced in high
yields. Just as in the herein reported synthesis of 3a and
3b, here we bene®t from the advantage that the substituent
`R', which might be expensive monetarily or in terms of
effort, is introduced after the low yielding process of synthe-
sizing the dibromo functionalized acetone derivative 6. The
protected compound 8 proved to be extremely stable:
quantitative deprotection could only be achieved by stirring
8 in concentrated sulfuric acid for several minutes.
chemistry.61 As described in the literature,62 zinc-alkyl
compounds tolerate the ketone functional group and a
wide range of other functionalities. Scheme 2 shows the
direct alkyl functionalization of 6 via Pd-catalyzed coupling
with 3,7-dimethyloctanylzincbromide, whereby 1,3-Bis-
+4-+3,7-dimethyloctanyl)phenyl)-2-propanone +9) was
obtained in good yields as a colorless oil. Oxidation of the
above synthesized diphenylacetylene 3b with iodine in
DMSO at 1558C resulted in the 4,40-alkylated benzil 10.
Twofold Knoevenagel condensation of 9 with 10 in t-buta-
nol at 858C afforded cyclopentadienone 11 in 84% yield
+Scheme 3).
In order to obtain a mono-functionalized HBC derivative, an
asymmetrically substituted diphenylacetylene is required
+Scheme 4). 1-Bromo-4-trimethylsilylethinylbenzene +12)
was alkylated similar to previous approaches with
3,7-dimethyloctanyl-magnesiumbromide and [PdCl2+dppf)].59
After quantitative deprotection of 13 in DMF with potas-
sium ¯uoride, classical Hagihara±Sonogashira coupling63
of the deprotected acetylene 14 with 1-bromo-4-iodo-
benzene +15) resulted in the bromine substituted diphenyl-
acetylene 16. [412] Diels±Alder reaction22 of
cyclopentadienone 11 and diphenylacetylene 16 in re¯uxing
diphenylether afforded mono-bromo substituted hexa-
phenylbenzene 17 +Scheme 4). Planarization of 17 was
carried out in the same manner as for compounds 5a and
5b and hexabenzocoronene 18 was obtained in high isolated
yields +Scheme 5). As for hexabenzocoronenes 5a and 5b,
the solubility and processability of 18 was dramatically
While this procedure is acceptable for Rˆalkyl, the harsh
deprotection will certainly limit the scope of functionalities
which might be incorporated into this sequence. Therefore,
we turned to the area of zinc chemistry, well known and
widely applied in the ®eld of organic- and natural product-

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3776
Table 1. Optical, thermal and thermodynamical data for compounds 5a, 5b
and 18 +Kˆcrystalline phase, Colhoˆordered hexagonal columnar meso-
phase, Iˆisotropisation)
number with decreasing concentration, a conclusion which
®nds support in theoretical calculations67,68 in concert with
solid-state NMR measurements.26,29,69,70 Similar shifts to
lower ®elds are observed with increasing temperature +for
a constant concentration) and when carbon disul®de +a good
solvent for the aromatic core) is added.
Compound
Transition
T +8C)
DH +J g21
)
5a
K!Colp
96
430
26
ho
Colpho!I
5b
18
K!Colho
81
420
31
Structural information for an optically active compound
such as 5a can be obtained from circular dichroism +CD)
spectroscopy which is an important method to study, e.g. the
helical orientation of discotic liquid crystalline aggregates
such as triphenylenes and phthalocyanines.10,71 CD spectra
can either be recorded from solution or ®lms, i.e.
Langmuir±Blodgett or spincoated ®lms. Here, we studied
thin ®lms of the chiral HBC derivative 5a and the racemic
5b, prepared by spincoating concentrated solutions of 5a
and 5b on quartz substrates. These samples were investi-
gated by means of CD spectroscopy at room temperature
and the resulting spectra are given in Fig. 4. As expected,
the racemic HBC derivative 5b did not show any CD effect
at room temperature or after annealing in the mesophase at
908C. Under the same experimental conditions, the all chiral
HBC derivative 5a showed two very strong, characteristic
CD signals. A signal was observed at a wavelength of
lˆ361 nm, with a positive Cotton-effect in the CD spectra
as depicted in Fig. 4. However, the most dominant signal in
the spectra +Fig. 4) is a so-called CD-couplet that traverses
the baseline at lˆ229 nm. A CD-couplet is de®ned as the
direct succession of two intensive Cotton-effects with
reversed signs. Within this CD-couplet, compound 5a
exhibits a positive Cotton-effect at higher wavelength and
a negative one at lower wavelength. In contrast to optically
active phthalocyanine derivatives10 the prepared ®lms of 5a
did not have to be annealed at higher temperatures to
achieve optical activity which is probably an indication of
a very high degree of preorientation of the HBC discs before
Colho!I
K!Colho
Colho!I
32
.350
enhanced with the introduction of the branched alkyl chains
in place of the n-alkyl chains.
2.2. Spectroscopic characterization
NMR spectroscopy is an important tool for investigating
aromatic stacking. It has been used to investigate the p±p
aggregation of phenylacetylene macrocycles64,65 and
columnar structures formed by hexabenzocoronene deriva-
tives66 in the solid state. Here, the down®eld signal at, e.g.
dˆ8.2 ppm for the core protons of compound 5a clearly
documents the diatropic character of these PAHs. These
chemical shifts originate from a complex interplay of
aromatic core size, perimeter type28 and aggregation. We
1
have utilized H NMR spectra to qualitatively assess the
strong in¯uence that changes of concentration have on the
aggregation of these aromatic compounds in solution. As
depicted in Fig. 3, decreasing the concentration only from
12.36£1023 to 0.82£1023 mol L21 results in a shift to lower
®eld by Ddˆ0.33 ppm for the signals arising from the core
protons. A less pronounced shift to lower ®eld can be
observed for the a-CH2 protons of the alkyl side chains.
We attribute these shifts to a decrease in aggregation
Figure 5. Differential scanning calorimetry traces of 5a, 5b and 18.

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A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3777
in order to study their thermal behavior as an addition to the
DSC experiments. Drop-cast ®lms were prepared from
chloroform solutions. The ®lms were heated at
10 K min21 under a nitrogen atmosphere upon which the
HBC samples changed from a crystalline to a liquid crystal-
line phase at temperatures reported in Table 1. The
columnar hexagonal mesophases were preserved over
large temperature ranges and ®nally entered the isotropic
phase at above 4008C. Fig. 6 +compound 5a) reveals
textures which are typical for the columnar hexagonal meso-
phase formed from alkyl-substituted HBCs. These textures
were observed after annealing the sample for a few minutes
at the isotropisation temperature followed by cooling the
sample to lower temperatures. These textures did not change
until the sample temperature was decreased to the point of
recrystallisation below 968C.
3. Discussion
Figure 6. Optical textures of the hexagonal discotic mesophase of 5a
observed under polarized light.
The production of materials on large scale becomes more
and more important when the targeted compound is being
tested for possible device applications. The availability of
hexaalkyl-substituted HBCs on a multi gram scale has
become more facile with the incorporation of [PdCl2-
+dppf)]59 for the alkyl functionalization of 4,40dibromo-
diphenylacetylenes. However, the Co2+CO)8 catalyzed
cyclotrimerization of a functionalized diphenylacetylene
only gives access to molecules with C6 symmetry. It has
the advantage of a fast and easy access to soluble alkylated
HBCs, but has the disadvantage of not providing single site
functionalization or break of symmetry in any controlled
manner. Alternately, Ito et al. presented a synthetic strategy
that allows mono-, ortho-di-, and para-di-functionalization
of the hexabenzocoronene discs.22 The sp2 C±Br bond of
bromo-functionalized HBC's served as a reactive site for
coupling reactions leading to a number of new functional-
ized HBC's. These syntheses met with varying levels of
success, which were no doubt limited in some cases by
low solubility. For this reason, we prepared the highly
soluble compound 18, via a similar but simpler route to
that of Ito. Utilization of Pd-catalyzed aryl halide±zincate
coupling reactions not only simpli®ed the synthesis of
compound 18, but also opens the way to prepare an endless
number of other functionalized derivatives by more direct
means. In principle, HBCs with each substitution pattern
shown in Fig. 1, and with a broad range of functionalities,
can now be prepared via coupling reactions starting just
from the dibromo compounds 2, 6 and 10 +RˆBr).
or during the preparation of the ®lms. However, artifacts
due to linear dichroism can be excluded, since the identical
spectrum was obtained from the same sample after rotating
by 908 in the plane normal to the incident light. Further,
temperature dependent CD measurements on thin ®lms
were conducted to probe the stability of the chiral super-
structures. Here, the temperature was increased in steps of
20 K from 2108C upto 70 8C. The recorded CD signals lost
intensity on the order of 20% during the course of heating,
but never faded completely.
2.3. Mesophase characterization
Preliminary differential scanning calorimetry +DSC) and
optical polarization microscopy experiments were
performed to study the phase behaviors of HBCs 5a, 5b
and 18. A summary of the thermal behavior derived from
these measurements is shown in Table 1. At room tempera-
ture all compounds are yellow solids. Upon heating, all
three compounds enter the columnar discotic mesophase
Colho which is of chiral nature in the case of 5a, as deter-
mined by CD spectroscopy, and therefore denoted as Colho
p
.
For the chiral HBC 5a, a sharpendothermic peak at 96 8C
+Fig. 5) with a characteristic enthalpic value of 26 J g21
indicates the transition from the solid phase into the chiral
columnar mesophase. A phase transition 158C lower, i.e.
818C, as depicted in Fig. 5 is observed for the racemic
compound 5b with an enthalpic value of 31 J g21. The
bromo-functionalized derivative 18 enters the mesophase
at 328C, almost 508C lower than its analogue bearing 6
alkyl chains +5b). On heating, an additional reproducible
®rst-order exotherm occurs just before this transition,
which is absent in subsequent heating scans after annealing
at its peak +2188C). In all of the above cases, liquid crystal-
linity is maintained over a very large temperature range and
no additional mesophase transitions were observed for any
of the compounds.
Further, the fact that branching of the introduced alkyl
chains has a positive impact on the processability of the
described compounds has been demonstrated. Not only
has the solubility been increased dramatically compared
to HBCs substituted with n-alkyl chains +e.g. 1a Rˆ
n-C12H25)20,21 but also the phase transition temperature
into the columnar hexagonal mesophase was reduced by
upto 27 8C,23 without compromising the stability of the
mesophase +Tisotrop.4008C).
The fact that compound 5a is substituted with 6 chiral alkyl
chains and is optically active gives hope for increased
one-dimensional charge carrier mobility, as was reported
Optical polarization microscopy studies were conducted for
all the HBC derivatives introduced above, i.e. 5a, 5b and 18,

È
A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3778
for the helical mesophase of a hexa hexylthiotriphenylene
derivative.5,31 Before the introduction of liquid-crystalline
hexabenzocoronenes, this material was the previous record
holder for the mobility of charge carriers in organic liquid
crystals.23,27 The synthesis of the racemic derivative 5b was
important for several reasons. The mesophase formation of
an optically pure material +5a) can be documented properly
only if the racemic version +5b) of this compound is also
subjected to similar characterization. DSC results showed
that 5a enters the columnar hexagonal mesophase at 968C
whereas 5b already shows a phase transition at 818C +Table
1).
relatively stable since the intensity only dropped by a factor
of 20% while the temperature was raised from 210 upto
708C. The loss of intensity is attributed to higher mobility of
the alkyl side-chains leading to the formation of more
mobile, but still chiral, aggregates. Upon entry into the
discotic mesophase at 968C the uni-axial rotation should
drastically increase, and whether the helical orientation of
the molecules is still preserved will be investigated at a
later time. The preliminary characterization presented
here does not permit assignment of the helical arrange-
ment of 5a to one of the three arrangements suggested
by van Nostrum and co-workers.10 More detailed
morphological studies are underway including X-ray
analysis, solid state NMR, and more detailed tempera-
ture-dependant CD measurements. To investigate the
aggregation of the HBC discs in solution and the pos-
sible resulting optical activity of the aggregates, CD
measurements in a range of solvents are planned as
well as temperature dependent CD experiments for
both solution and ®lm samples.
These results are in contrast to those which van Nostrum and
co-workers reported for chiral and racemic derivatives of
phthalocyanines.10 They determined a higher phase tran-
sition temperature for the racemic than for the optically
pure material, which lacks a crystalline phase, and only
shows amorphous behavior at low temperatures. This was
not expected and could also not be explained in the course of
their experiments. As depicted in Fig. 4 spincoated ®lms of
5a give very strong signals during CD measurements even
without annealing whereas spincoated ®lms of 5b do not
show any signal +as expected). In a similar experiment,
®lms of chiral phthalocyanines had to be annealed before
CD signals could be recorded.10 While in that case, the
identical alkyl chains were utilized, they were separated
from the core by an oxygen +ether linkage) spacer. This
not only increases the distance between the core and the
stereogenic center, but also the added rotational freedom
associated with an ether linkage may serve to further
diminish the effect of the optically active center on the
packing behavior of the core. In the case of the HBC 5a,
the stereogenic center is very close to the center and there-
fore has a stronger, more direct in¯uence on the packing
behavior. The reported signals in the CD spectra +Fig. 4) can
be assigned as follows: Since compound 5a is per de®nition
chiral, with six alkyl chains, each carrying a stereogenic
center, the signal at lˆ361 nm is resulting from the indi-
vidual discotic molecule 5a. A similar signal is observed by
UV±Vis spectroscopy, also at lˆ361 nm, assigned as the
b-band according to Clar's nomenclature.72 The presence of
a CD-couplet as shown in Fig. 4 is an indication for the co-
existence of two electronic excited states with individual
transition dipole moments. These two dipole moments are
4. Conclusions
Dramatically enhanced solubility and processability are
imparted when branched alkyl chains +3,7-dimethyloctanyl)
are employed in place of n-alkyl chains at the periphery of
hexabenzocoronene. Preliminary characterization by CD
measurements revealed a distinct effect upon introduction
of chiral side groups, which was tentatively assigned to a
helical arrangement within the discotic columnar meso-
phase. An HBC carrying these chains as well as a single
bromo-function attached to the core was also prepared. The
high solubility of this compound in a range of organic
solvents has facilitated further functionalization and the
buildupof oligomers and polymers, all of which will be
the subject of forthcoming publications.
5. Experimental
5.1. General methods
p
1H and 13C NMR spectra were recorded in CDCl3 and
C2D2Cl4 on a Bruker DPX 250, Bruker AMX 300 and
Bruker DRX 500 with use of the solvent proton or carbon
signal as internal standard. Melting points were determined
on a BuÈchi hot stage apparatus and are uncorrected. Infrared
spectra were recorded on a Nicolet FT-IR 320 spectrophoto-
meter as KBr pellets or as ®lm between NaCl discs. Mass
spectra were obtained on a VG Instruments ZAB 2-SE-FPD
by using FD. Elemental analyses were carried out on a Foss
Heraeus Vario EL.
assigned to two HBC-C8 monomers. A splitting of the
energy levels occurs, since the antiparallel orientation of
dipole moments is energetically preferred. This gives rise
to the two absorptions at different wavelengths +lˆ249 and
218 nm) in the CD-spectra. The energy difference is calcu-
lated to be Dlˆ31 nm +249±218 nm). This phenomena is
commonly addressed as exciton-coupling or Davydov-
coupling.73 This coupling is occurring at a wave length
where the UV±Vis sp ectra shows a p resumed aggre-
gation band, suggesting that the columnar superstructure
formed by the individual HBC-C8
p
molecules
+compound 5a) might have a helical orientation. These
assumptions were made in analogy to the conclusions
drawn from detailed experiments with triphenylenes71 and
phthalocyanines.10
Differential scanning calorimetry +DSC) was measured on a
Mettler DSC 30 with heating and cooling rates of
10 K min21. First order transition temperatures were
reported as the minima of their endothermic peaks during
heating. A Zeiss Axiophot with a nitrogen ¯ushed Linkam
THM 600 hot stage was used to characterize the optical
textures under cross polars.
From the initial temperature-dependent CD experiments, it
can be concluded that the chiral aggregates formed must be

È
A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3779
5.2. Materials
ether/CH2Cl2 +9/1) as the eluent, yielding 1.8 g 4a as color-
less oil. Yield: 90%. 1H NMR +500 MHz, C2D2Cl4): dˆ6.61
3
3
+S)-1-Bromo-3,7-dimethyloctane was synthesized accord-
ing to standard literature procedure74 using commercially
+d, J+H,H)ˆ7.9 Hz, 12H; CH), 6.56 +d, J+H,H)ˆ7.9 Hz,
12H; CH), 2.29 +m, 12H; a-CH2), 1.47 +m, 6H; CH), 1.35
+m, 6H; CH), 1.20±0.98 +m, 48H; CH2), 0.82 +d,
3J+H,H)ˆ6.7 Hz, 36H; CH3), 0.75 +d, 3J+H,H)ˆ6.1 Hz,
18H; CH3); 13C NMR +125 MHz, C2D2Cl4): 136.58,
135.52, 134.91, 130.0, 122.84, 35.92, 35.24, 33.68, 29.46,
28.52, 24.49, 21.26, 19.36, 19.29, 16.22; MS +FD, 8 kV):
m/z +%)ˆ1377.0 +100) [M1] +calcd for C102H150ˆ1376.31).
available
+3S)-+1)-3,7-dimethyl-6-octene-1-ylbromide
from Aldrich. 4,40-Dibromodiphenylacetylene +2)58 and
1,3-bis+4-bromophenyl)-2-propanone +6)22 were synthe-
sized as previously described in the literature.
[PdCl2+dppf)], Pd+PPh3)4 were used as received from
Strem. THF +A.C.S. reagent, Riedel-de Haen) was re¯uxed
over potassium and distilled freshly before use. All other
materials were used as received.
5.3.4. Hexa-4-23,7-dimethyloctanyl)hexaphenylbenzene
24b). Prepared as described above for compound 4a. Color-
less oil, yield: 88%. 1H NMR +500 MHz, C2D2Cl4): dˆ6.58
5.3. Syntheses
3
3
+d, J+H,H)ˆ7.6 Hz, 12H; CH), 6.53 +d, J+H,H)ˆ7.9 Hz,
12H; CH), 2.26 +m, 12H; a-CH2), 1.45 +m, 6H; CH), 1.32
+m, 6H; CH), 1.19±1.10 +m, 36H; CH2), 1.05±0.97 +m, 12H;
CH2), 0.80 +d, 3J+H,H)ˆ6.7 Hz, 36H; CH3); 0.73 +d,
3J+H,H)ˆ5.5 Hz, 18H; CH3); 13C NMR +125 MHz,
C2D2Cl4): 139.45, 138.41, 137.78, 130.87, 125.71, 38.79,
38.15, 36.56, 32.34, 31.34, 27.37, 24.14, 22.23, 22.16,
19.09; MS +FD, 8 kV): m/z +%)ˆ1375.9 +100) [M1]
+calcd for C102H150ˆ1376.31).
5.3.1. 2S)-4,40-Bis23,7-dimethyloctanyl)diphenylacetyl-
ene 23a). +As an example for the synthesis of substituted
diphenyl acetylenes.) In a 250 mL two-necked round
bottom ¯ask, 60 mL of a 1 M solution of +S)-3,7-dimethyl-
octanyl-1-magnesiumbromide +prepared immediately prior
to use from +S)-1-bromo-3,7-dimethyloctane and mag-
nesium) was added dropwise to 5 g +14.9 mmol) 4,40-di-
bromodiphenylacetylene +2) dissolved in 150 mL of dry
THF. Then, 500 mg of [PdCl2+dppf)] catalyst was added
to this solution. The resulting mixture was stirred under
re¯ux in an inert atmosphere overnight. The reaction was
quenched with methanol and the solvent removed under
reduced pressure. Puri®cation using column chroma-
tography on silica gel with petrol ether as the eluent afforded
5.8 g 3a as a colorless oil. Yield: 85%. 1H NMR +500 MHz,
5.3.5. 2S)-Hexa23,7-dimethyloctanyl)hexa-peri-hexabenzo-
coronene 25a). +As an example for the cyclodehydrogen-
ation reaction.) A 250 mL two necked round bottom ¯ask
was charged with 0.50 g +0.36 mmol) of +S)-hexa-4-+3,7-
dimethyloctanyl)hexaphenylbenzene +4a) and 100 mL of
CH2Cl2. Using a glass capillary, a constant stream of
argon was bubbled through the solution. Then, 1.12 g
+6.9 mmol) of FeCl3 dissolved in CH3NO2 +13 mL) was
added dropwise using a syringe. After 30 min, the mixture
was quenched with a large excess of methanol and the pre-
cipitate was ®ltered. The resulting yellow solid was redis-
solved in dichloromethane and ®ltered through a short pad
of silica gel and dried under vacuum to yield 0.39 g 5a as a
yellow powder. Yield: 80%; 1H NMR +500 MHz, C2D2Cl4):
dˆ8.09 +s, 12H; CH), 2.96 +m, 12H; a-CH2), 2.01 +m, 6H;
CH), 1.8 +m, 12H; CH2), 1.64 +m, 12H; CH2), 1.54 +m, 6H;
CH), 1.43 +m, 12H; CH2), 1.33 +m, 12H; CH2), 1.23 +d,
3J+H,H)ˆ6.1 Hz, 18H; CH3), 0.97 +d, 3J+H,H)ˆ6.7 Hz,
36H; CH3); 13C NMR +125 MHz, C2D2Cl4, 1008C): dˆ
140.36, 129.98, 123.41, 121.42, 119.56, 40.01, 39.96,
37.95, 35.12, 33.69, 28.42, 25.32, 23.13, 23.05, 20.36;
mp.3008C MS +FD, 8 kV): m/z +%)ˆ1364.0 +100) [M1]
+calcd for C102H138ˆ1364.21) EA: Anal. Calcd +%) for
C102H138: C 89.80, H 10.20; found: C 89.77, H 10.17.
3
C2D2Cl4): dˆ7.42 +d, J+H,H)ˆ7.9 Hz, 4H; CH), 7.15 +d,
3J+H,H)ˆ7.9 Hz, 4H; CH), 2.63 +m, 4H; a-CH2), 1.63 +m,
4H; b-CH2), 1.55 +m, 2H; CH), 1.47 +m, 4H; CH2), 1.37±
1.24 +m, 6H; CH, CH2), 1.81 +m, 4H; CH2), 0.94 +d,
3J+H,H)ˆ6.1 Hz, 6H; CH3) 0.91 +d, J+H,H)ˆ6.1 Hz, 12H;
3
CH3); 13C NMR +125 MHz, C2D2Cl4): dˆ140.12,
128.11.40, 124.89, 117.35, 85.75, 35.95, 35.06, 33.76,
29.99, 29.13, 24.45, 21.17, 19.16, 19.10, 16.17; MS +FD,
8 kV): m/z +%)ˆ458.1 +100) [M1] +calcd for C34H50ˆ
458.77).
5.3.2.
4,40-Bis23,7-dimethyloctanyl)diphenylacetylene
23b). Prepared as described above for compound 3a. Color-
less oil, yield: 86%. 1H NMR +500 MHz, C2D2Cl4): dˆ7.38
3
3
+d, J+H,H)ˆ7.9 Hz, 4H; CH), 7.11 +d, J+H,H)ˆ7.9 Hz,
4H; CH), 2.54 +m, 4H; a-CH2), 1.55 +m, 2H; CH), 1.47
+m, 2 H; CH), 1.37 +m, 4H; CH2), 1.25 +m, 4H; CH2),
3
1.11±1.05 +m, 8H; CH2), 0.87 +d, J+H,H)ˆ6.1 Hz, 6H;
CH3) 0.82 +d, 3J+H,H)ˆ6.7 Hz, 12H; CH3); 13C NMR
+125 MHz, C2D2Cl4): dˆ143.96, 131.85, 128.75, 120.72,
89.35, 39.62, 38.98, 37.43, 33.73, 32.79, 28.25, 25.01,
23.09, 23.00, 19.94; MS +FD, 8 kV): m/z +%)ˆ458.5 +100)
[M1] +calcd for C34H50ˆ458.77).
5.3.6. Hexa23,7-dimethyloctanyl)hexa-peri-hexabenzo-
coronene 25b). Prepared as described above for compound
5a. Yellow powder, yield: 83%. 1H NMR +500 MHz,
C2D2Cl4): dˆ8.26 +s, 12H; CH), 3.05 +m, 12H; a-CH2),
2.06 +m, 6H; CH), 1.83 +m, 12H; CH2), 1.65 +m, 12H;
CH2), 1.56±1.43 +m, 18H; CH, CH2), 1.35 +m, 12H; CH2),
5.3.3. 2S)-Hexa-4-23,7-dimethyloctanyl)hexaphenylben-
zene 24a). +As an example for the cyclotrimerization reac-
tion.) 230 mg +0.68 mmol) [Co2+CO)8] was added under
argon to a degassed solution of 2 g +4.36 mmol) +S)-4,40-
bis+3,7-dimethyloctanyl)diphenylacetylene +3a) in 100 mL
of dioxane in a 250 mL round bottom ¯ask equipped with a
re¯ux condenser. After re¯uxing for 3 h, the solvent was
evaporated under vacuum, and the residue was puri®ed
using column chromatography on silica gel with petrol
3
3
1.23 +d, J+H,H)ˆ6.3 Hz, 18H; CH3), 0.97 +d, J+H,H)ˆ
6.6 Hz, 36H; CH3); 13C NMR +125 MHz, C2D2Cl4,
1008C): dˆ140.07, 129.68, 123.10, 121.18, 119.25, 39.93,
39.87, 37.81, 35.00, 33.57, 28.31, 25.21, 23.06, 22.97,
20.25; mp .3008C, MS +FD, 8 kV): m/z +%)ˆ1363.5
+100) [M1] +calcd for C102H138ˆ1364.21), EA: Anal.
Calcd +%) for C102H138: C 89.80, H 10.20; found: C 89.83
H 10.11.

È
A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3780
5.3.7. 1,3-Bis24-23,7-dimethyloctanyl)phenyl)-2-propa-
none 29): three step protection, Grignard coupling,
deprotection route: 1,3-bis24-bromophenyl)-2-propa-
none ethylene acetal 27)Ðprotection. A mixture of 1,3-
Bis+4-bromophenyl)-2-propanone +6) +16 g, 43.5 mmol),
ethylene glycol +3.77 g, 60.9 mmol), and p-toluenesulfonic
acid +Ts-OH, 4.35 mg) in 50 mL of dry toluene was re¯uxed
in a round-bottomed ¯ask ®tted with a Dean±Stark for 12 h.
The reaction mixture was cooled to room temperature and
washed with 10% NaHCO3 and water. The organic phase
was dried +MgSO4) and concentrated under reduced
pressure to give a white solid, which was recrystallized
from n-heptane to give pure 6 as white crystals. Yield:
99%. 1H NMR +250 MHz, C2D2Cl4): dˆ7.32 +d,
room temperature. ZnBr2 +3.6 g, 16.3 mmol) was dissolved
in dry THF +8 mL) in a 50 mL three-necked ¯ask with
stirring and under argon. After cooling this solution to
below 08C, the Grignard solution was added dropwise,
accompanied by precipitation and exothermic reaction.
After stirring for an additional 15 min at 08C, the reaction
mixture was cooled to 2788C, and PdCl2+dppf) +20 mg,
0.027 mmol) and 1,3-bis+4-bromophenyl)-2-propanone +6)
+solution in 8 mL of THF) were added consecutively. The
cooling bath was removed, and the reaction mixture was
stirred overnight. After the reaction was quenched with
10% HCl, extracted with CH2Cl2, dried with MgSO4 and
evaporated. The residue was puri®ed by column chroma-
tography, eluent PE/CH2Cl2+50:50), to give 9 as a colorless
oil. Yield: 75%.
3
3J+H,H)ˆ8.3 Hz, 4H; CH), 7.06 +d, J+H,H)ˆ8.39 Hz, 4H;
CH), 3.37 +s, 4H, CH2), 2,78 +s, 4H, CH2). 13C NMR
+125 MHz, C2D2Cl4): 135.79, 132.82, 131.25, 120.71,
110.51, 65.76, 44.19. MS +FD, 8 kV): m/z +%)ˆ412.2
+100) [M1] +calcd for C17H16´Br2O2ˆ412.12).
5.3.11. 4,40-23,7-Dimethyloctanyl)benzil 210). 15.2 g
+32.7 mmol) of 4,40-bis+3,7-dimethyloctanyl)diphenyl-
acetylene +3b) and 4.15 g +16.35 mmol) iodine were
dissolved in 130 mL of DMSO and stirred overnight at
1558C under an Ar atmosphere. After cooling, the reaction
mixture was poured into 150 mL of 4% solution of NaSO3
and stirred 30 min. The product was extracted with PE,
concentrated and puri®ed by column chromatography with
5.3.8. 1,3-Bis24-23,7-dimethyloctanyl)-phenyl)-2-propa-
none ethylene acetal 28)ÐGrignard coupling. Compound
8 was prepared utilizing a procedure identical to that used
for preparation of 3a, starting from dibromo compound 7.
The reaction was quenched with methanol and the solvent
removed under reduced pressure. Puri®cation using column
chromatography on silica with petrolether as the eluent,
afforded 5.9 g of 8 as a colorless oil. Yield: 75%. 1H
1
PE as eluent. Yield: 71%. H NMR +250 MHz, C2D2Cl4):
3
3
dˆ7.79 +d, J+H,H)ˆ8.01 Hz, 4H; CH), 7.25 +d, J+H,H)ˆ
8.39 Hz, 4H; CH), 2.61 +m, 4H; a-CH2), 1.54±1.06 +m,
20H), 0.84 +d, 3J+H,H)ˆ6.11 Hz, 6H; CH3) 0.78 +d,
3J+H,H)ˆ6.87 Hz, 12H; CH3); 13C NMR +125 MHz,
C2D2Cl4): 194.90, 151.91, 130.93, 130.38, 129.39, 39.56,
38.67, 37.33, 34.10, 32.81, 28.22, 24.95, 23.06, 22.97,
19.87.
3
NMR +250 MHz, C2D2Cl4): dˆ7.09 +d, J+H,H)ˆ8.01 Hz,
3
4H; CH), 7.02+d, J+H,H)ˆ8.01 Hz, 4H; CH), 3.41+s, 4H,
CH2), 2,80 +s, 4H, CH2), 2.50 +m, 4H; a-CH2), 1.55±1.07
3
+m, 20H), 0.82 +d, J+H,H)ˆ6.11 Hz, 6H; CH3) 0.79 +d,
3J+H,H)ˆ6.49 Hz, 12H; CH3); 13C NMR +125 MHz,
C2D2Cl4): 141.44, 133.92, 130.92, 128.15, 111.21, 65.61,
44.30, 39.59, 39.19, 37.44, 33.38, 32.84, 28.22, 24.99,
23.07, 22.98, 19.98. MS +FD, 8 kV): m/z +%)ˆ537.9
+55%) [M1] +calcd for C37H58O2ˆ534.84); m/zˆ305.0
+100%) [M12CH2±C6H4±C10H21]; m/zˆ232.7 +65%)
[CH2±C6H4±C10H21].
5.3.12. 2,3,4,5-Tetrakis24-23,7-dimethyloctanyl)phenyl)-
cyclopentadienone 211). 5.2 g +10.7 mmol) of 1,3-bis-
+4-+3,7-dimethyloctanyl)-phelyl)-2-propanone +9) and
5.2 g +10.7 mmol) of 4,40-+3,7-dimethyloctanyl)benzil +10)
were dissolved in 13 mL of t-butanol under Ar atmosphere
and stirred at 858C. A solution prepared from 7.4 mL of
0.8 M tetrabutylammoniumhydroxide in methanol and
3.3 mL of t-butanol was added. After 10 min, the reaction
mixture was quenched by addition of 50 mL H2O. The
product was extracted with CH2Cl2, concentrated, and
puri®ed by column chromatography, eluent PE/CH2Cl2
5.3.9. 1,3-Bis24-23,7-dimethyloctanyl)phenyl)-2-propa-
none 29)Ðdeprotection. To 5 g +10 mmol) of 8, 10 mL
of concentrated sulfuric acid was added. The reaction
mixture was stirred for 5 min, then poured into water. The
product was extracted with toluene, washed with 10% of
NaHCO3, H2O, dried with MgSO4 and ®ltered through silica
gel to give 3.9 g of 9 as a colorless oil. Yield: 80%. 1H NMR
1
+4:1). Yield: 8.6 g, +84%). H NMR +250 MHz, C2D2Cl4):
dˆ7.07+d, 3J+H,H)ˆ8.01, 4H, CH), 7.00 +d, 3J+H,H)ˆ8.39,
4H, CH), 6.91 +d, 3J+H,H)ˆ8.01, 4H, CH), 6.72+d,
3J+H,H)ˆ8.39, 4H, CH), 2.49 +m, 8H, a-CH2), 1.51±1.07
+m, 40H, CH2), 0.84 +d, 3J+H,H)ˆ6.48 Hz, 12H, CH3), 0.79
+d, 3J+H,H)ˆ6.87 Hz, 24H, CH3). 13C NMR +125 MHz,
C2D2Cl4): 154.74, 143.83, 142.64, 130.56, 130.25, 129.65,
128.56, 128.31, 128.04, 124.77, 39.60, 38.94, 38.71, 37.44,
33.57, 32.91, 32.64, 28.22, 25.04, 24.99, 23.07, 22.99,
19.95. MS +FD, 8 kV): m/z +%)ˆ945.5 +100%) [M1]
+calcd for C69H100Oˆ945.57).
3
+250 MHz, C2D2Cl4): dˆ7.35 +d, J+H,H)ˆ8.01 Hz, 4H;
CH), 6.96 +d, 3J+H,H)ˆ8.01 Hz, 4H; CH), 3.61+s, 4H,
CH2), 2.51 +m, 4H; a-CH2), 1.57±1.05 +m, 20H), 0.84 +d,
3J+H,H)ˆ6.49 Hz, 6H; CH3) 0.79 +d, 3J+H,H)ˆ6.48 Hz,
12H; CH3); 13C NMR +125 MHz, C2D2Cl4): 142.34,
131.27, 129.75, 128.94, 49.01, 39.6, 39.12, 37.42, 33.36,
32.86, 28.23, 24.98, 23.07, 22.98, 19.95. MS +FD, 8 kV):
m/z +%)ˆ490.8 +100%) [M1] +calcd for C35H54Oˆ490.82)
5.3.10. 1,3-Bis24-23,7-dimethyloctanyl)-phenyl)-2-propa-
none 29)Ðdirect route. A 50 mL, three-necked ¯ask was
charged with Mg +0.396 g, 16.3 mmol) and THF +16 mL).
Under an Ar atmosphere, the Grignard reaction was started
5.3.13.
4-23,7-Dimethyloctanyl)-trimethylsilylethinyl-
benzene 213). In round bottom ¯ask, 60 mL of a 1 M solu-
tion of +S)-3,7-dimethyloctanyl-1-magnesiumbromide was
added dropwise to 3 g +12 mmol) 1-bromo-4-trimethylsilyl-
ethinylbenzene +12) dissolved in 30 mL of dry THF. Then
350 mg of [PdCl2+dppf)] catalyst was added to this solution.
The resulting mixture was re¯uxed under argon over night.
by adding
16.3 mmol) and a one dropof CH Br2 with stirring and
a
3,7-dimethyloctanyl-1-bromide +3.6 g,
2
gentle heating. The reaction mixture was stirred for 1 h at

È
A. Fechtenkotter et al. / Tetrahedron 57 *2001) 3769±3783
3781
The reaction was quenched with methanol and the solvent
removed under reduced pressure. Puri®cation using column
chromatography on silica gel with petrolether as the eluent,
as eluent to afford 6.2 g of 17, as a yellow oil. Yield: 53%.
1H NMR +250 MHz, C2D2Cl4): dˆ6.85 +d, 3J+H,H)ˆ
8.39 Hz, 2H, Ar-H), 6.57 +m, 22H, Ar-H), 2.3±2.24 +m,
10H, a-CH2), 1.49±1.04 +m, 50H), 0.78 +d, 3J+H,H)ˆ
6.87 Hz, 30H, CH3), 0.71 +m, 15H, CH3). 13C NMR
+125 MHz, C2D2Cl4): 140.12, 139.71, 139.41, 138.74,
138.27, 138.12, 133.59, 131.59, 129.64, 126.89, 126.61,
39.63, 38.98, 38.85, 37.38, 34.45, 33.17, 32.26, 32.18,
28.21, 24.97, 23.07, 23.01, 19.92. MS +FD, 8 kV): m/z
+%)ˆ1315.2 +100%) [M1] +calcd for C92H129Brˆ1314.96).
1
afforded 3.2 g 13 as a colorless oil. Yield: 85%. H NMR
+250 MHz, C2D2Cl4): dˆ7.3 +d, 3J+H,H)ˆ8.01 Hz, 2H,
CH), 7.04 +d, 3J+H,H)ˆ8.01, 2H, CH), 2.52 +m, 2H,
a-CH2), 1.47 +m, 3H, b-CH2,CH), 1.34±1.1 +m, 7H, CH2),
3
3
0.83 +d, J+H,H)ˆ6.11 Hz, 3H, CH3), 0.79 +d, J+H,H)ˆ
6.4 Hz, 6H, CH3), 0.17 +s, 9H, CH3). 13C NMR +125 MHz,
C2D2Cl4): 144.40, 132.38, 128.62, 120.47, 105.58, 93.98,
39.61, 38.94, 37.41, 33.71, 32.73, 28.24, 24.99, 23.08,
22.99, 19.91, 0.44. MS +FD, 8 kV): m/z +%)ˆ314.7
+100%) [M1] +calcd for C21H34Siˆ314.59).
5.3.17. 2-Bromo-5,8,11,14,17-penta 23,7-dimethylocta-
nyl)-hexa-peri-hexabenzo-coronene 218). Compound 18
was prepared from 17 as described for 5a to give an orange
1
solid. Yield: 80%. H NMR +250 MHz, C2D2Cl4): dˆ7.85
5.3.14. 4-23,7-Dimethyloctanyl)-phenylacetylene 214). 3 g
+9.5 mmol) of 4-+3,7-dimethyloctanyl)-trimethylsilylethinyl-
benzene +13) was dissolved in 20 mL of DMF, together with
1.1 g +19 mmol) KF. The reaction mixture was stirred for
4 h at rt, then quenched with water and extracted with tolu-
ene. The solvent was removed under reduced pressure. Puri-
®cation using column chromatography on silica gel with
petrol ether as the eluent, afforded 2 g 14 as a white solid,
yield 90%. 1H NMR +250 MHz, CDCl3): dˆ7.38 +d,
+bs, 2H, Ar-H), 7.74 +bs, 2H, Ar-H), 7.57 +bs, 4H, Ar-H),
7.46 +bs, 2H, Ar-H), 7.28 +bs, 2H, Ar-H), 2.83±2.62 +m,
10H, a-CH2), 2.61±1.14 +m, 65H), 0.99±0.93 +m, 30H,
CH3). 13C NMR +125 MHz, C2D2Cl4): 139.18, 130.24,
129.01, 128.77, 128.55, 128.39, 127.26, 122.76, 121.97,
121.93, 121.82, 121.74, 121.18, 120.75, 120.58, 120.50,
120.10, 118.39, 118.02, 117.83, 117.02, 40.44, 40.25,
39.89, 39.87, 39.73, 37.82, 35.12, 34.99, 33.80, 33.72,
28.39, 25.35, 25.33, 23.19, 23.08, 20.35, 20.30, 20.24. MS
+FD, 8 kV): m/z +%)ˆ1302.9 +100%) [M1] +calcd for
C92H117Brˆ1302.86)
3
3J+H,H)ˆ8.39 Hz, 2H, CH), 7.11 +d, J+H,H)ˆ8.01, 2H,
CH), 2.55 +m, 2H, a-CH2), 1.61±1.12 +m, 10H, CH2), 0.9
+d, 3J+H,H)ˆ6.49 Hz, 3H, CH3), 0.85 +d, 3J+H,H)ˆ6.87 Hz,
6H, CH3). 13C NMR +125 MHz, CDCl3): 144.67, 132.48,
128.77, 119.63, 84.30, 76.79, 39.72, 39.06, 37.52, 33.85,
32.87, 28.37, 25.07, 23.08, 23.00, 19.97. MS +FD, 8 kV):
m/z +%)ˆ242.4 +100%) [M1] +calcd for C18H26ˆ242.41).
Acknowledgements
This research was supported by the TMR European
Research Program through the SISITOMAS project and
5.3.15. 4-Brom-40-23,7-dimethyloctanyl)diphenylacetyl-
ene 216). To the solution of 6.5 g +27 mmol) 4-+3,7-
dimethyloctanyl)-phenylacetylene +14), 12 g +54 mmol)
4-bromiodobenzene, 0.51 g +2.7 mmol) CuI and 0.7 g
+2.7 mmol) triphenylphosphine in 100 mL dry THF,
35 mL triethylamine and 0.94 g +1.35 mmol) bis+triphenyl-
phosphine)palladium+II)chloride were added consecutively
under argon. The reaction mixture was stirred overnight at
room temperature, quenched with 2 M HCl, and extracted
with CH2Cl2. The extract was concentrated under reduced
pressure and puri®ed by column chromatography with
petrol ether as eluent to afford 8.8 g of 16 as a white
solid. Yield: 82%. 1H NMR +250 MHz, C2D2Cl4): dˆ
È
the Volkswagen-Stiftung. We thank Petra Rader for
conducting `last-minute' DSC and TGA experiments. The
helpand advice from Professor Dr E. W. Meijer and his
group, especially from Luc Brunsveld, during the CD
experiments is gratefully acknowledged.
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