Synthesis of triphenylene and dibenzopyrene derivatives: Vanadium oxytrichloride a novel reagent

Article abstract of DOI:10.1055/s-2001-10821

This paper presents an efficient synthetic procedure for the preparation of various triphenylene and dibenzopyrene derivatives using VOC1₃ as a novel reagent. Symmetrically substituted hexaalkoxytriphenylenes are obtained from o-dialkoxybenzenes by oxidative trimerization with VOC1₃ in high yields. The oxidative coupling of a 3,3′,4,4′-tetraalkoxybiphenyl and 1,2-dialkoxybenzenes or 1,2,3-trialkoxybenzenes affords unsymmetrically substituted derivatives of triphenylene. The reagent oxidizes 3,3′,4,4′-tetraalkoxybiphenyl efficiently to 2,5,6,9,12,13-hexaalkoxydibenzo[fg, op]naphthacene-1,8-quinone and its 1,10-quinone isomer. Both the quinones can be converted to liquid crystalline derivatives using well-established chemistry. Effects of solvent, reagent concentration, acid catalyst and temperature have been studied.

Full text of DOI:10.1055/s-2001-10821

PAPER
305
Synthesis of Triphenylene and Dibenzopyrene Derivatives: Vanadium
Oxytrichloride a Novel Reagent
Sandeep Kumar,* Sanjay K. Varshney
Centre for Liquid Crystal Research, P. O. Box 1329, Jalahalli, Bangalore-560013, India
Fax +91(80)8382044; E-mail: uclcr@giasbg01.vsnl.net.in
Received 7 August 2000; revised 7 October 2000
zopyrene derivatives using VOCl3 under various reaction
conditions.
Abstract: This paper presents an efficient synthetic procedure for
the preparation of various triphenylene and dibenzopyrene deriva-
tives using VOCl3 as a novel reagent. Symmetrically substituted
hexaalkoxytriphenylenes are obtained from o-dialkoxybenzenes by
oxidative trimerization with VOCl3 in high yields. The oxidative Synthesis of Hexaalkoxytriphenylenes
coupling of a 3,3’,4,4’-tetraalkoxybiphenyl and 1,2-dialkoxyben-
zenes or 1,2,3-trialkoxybenzenes affords unsymmetrically substi-
The formation of aryl-aryl bonds, particularly by oxida-
tuted derivatives of triphenylene. The reagent oxidizes 3,3’,4,4’-
tetraalkoxybiphenyl efficiently to 2,5,6,9,12,13-hexaalkoxydiben-
zo[fg,op]naphthacene-1,8-quinone and its 1,10-quinone isomer.
Both the quinones can be converted to liquid crystalline derivatives
using well-established chemistry. Effects of solvent, reagent con-
centration, acid catalyst and temperature have been studied.
tive coupling of phenols and phenol ethers is a key step in
biological systems for the synthesis of various complex
molecules. Both, intermolecular and intramolecular C-C
bond formation between aromatic rings is effected under
suitable oxidizing conditions and can be accomplished by
chemical, electrochemical or photochemical means.
When this chemical reaction is carried out under the influ-
ence of Friedel-Crafts reaction conditions, it is common-
ly known as the Scholl reaction.11 Two main types of
mechanism have been suggested; one involves the initial
formation of a very reactive transient cation radical fol-
lowed by dimerization, and the other involves protonation
of the aromatic molecule, followed by electrophilic sub-
stitution and subsequent dehydrogenation.11 Because of
the powerful electron releasing nature of alkoxy groups,
the Scholl reaction has been widely utilized with alkyl
aryl ether substrates.
Key words: triphenylene, dibenzopyrene, vanadium oxytrichloride,
oxidative coupling, discotic liquid crystals
The supramolecular assemblies of disc-shaped molecules
lead to the formation of discotic liquid crystals.1 These
materials are becoming of increasing interest as self-orga-
nizing molecular wires through which charge or excitons
can migrate rapidly.2 Charge mobility along the molecular
columns was reported to be several orders of magnitude
higher than that observed for the organic polymers.3 Be-
cause of this property, their potential applications in con-
ducting, photoconducting systems, optical data storage,
light emitting diodes, photovoltaic solar cells, gas sensors,
and other devices have been envisaged.4-6
The oxidation of 1,2-dialkoxybenzene to hexaalkoxy-TP
(Scheme 1) is one of the unusual cases of Scholl reaction
where more than one aryl-aryl bonds are formed. Oxida-
tive trimerization of 1,2-dimethoxybenzene (veratrol) in
H2SO4 using chloranil or iron chloride as oxidant results in
the synthesis of hexamethoxytriphenylene (HMTP) in-
volving three consecutive Scholl reactions.11,12 When the
six peripheral alkoxy chains are long enough (of four car-
bon atoms or more), triphenylene derivatives show meso-
morphism. These long alkoxy chain substituted
derivatives were prepared traditionally by demethylating
HMTP and then realkylating the resultant hexaphenol
with the appropriate alkyl halide.7 A few triphenylene de-
rivatives were also prepared in small scale by electro-
chemical methods.13
Triphenylene (TP) and dibenzopyrene (DBP; Chemical
Abstract nomenclature for this molecule is diben-
zo[fg,op]naphthacene) are two very important cores in the
field of discotic liquid crystals. The formation of discotic
liquid crystals by triphenylene molecule was reported7
just after the discovery of discotic liquid crystals in 1977.8
Since then triphenylene remains the focus of attention of
liquid crystal scientists around the world and a variety of
triphenylene derivatives have been synthesized and exten-
sively studied for various physical properties.6 The DBP
core appeared in the LC field very recently9 but has be-
come the focus of attention because of the ferroelectric
switching of columnar mesophases of these derivatives. In
a preliminary communication, we have earlier reported
the use of vanadium oxytrichloride for the oxidative tri-
merization of o-dialkoxybenzenes to hexaalkoxy-TP.10
We have now discovered that vanadium oxytrichloride is
also a novel reagent for the oxidative dimerization of tet-
raalkoxybiphenyl to dibenzopyrene derivatives. Here we
report the preparation of several triphenylene and diben-
The use of FeCl3 as oxidant was further explored by the
Ringsdorf group, who reported the synthesis of hexahex-
yloxytriphenylene by the trimerization of 1,2-dihexyloxy-
benzene in 70% H2SO4 at 80 °C using iron chloride in
20% yield.14 The modified method of the Boden group us-
ing only a catalytic amount of H2SO4 and iron chloride as
oxidant allows the synthesis of triphenylene derivatives in
a much improved scale.15 Recently, we have reported that
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306
S. Kumar, S. K. Varshney
PAPER
Side Products of the Reaction
OR
OR
OR
Currently three reagents, FeCl3, MoCl5, and VOCl3 are in
use for the oxidative trimerization of o-dialkoxybenzenes
to hexaalkoxytriphenylenes. We realized that in all three
cases two main side products are formed. These are mono-
hydroxy-pentaalkoxy-TP 3 and a-chloro-hexaalkoxy-TP
4 (Scheme 2). Under normal reaction conditions about 2-
3% of these products is formed. Both can be separated by
efficient column chromatography and their amounts can
be manipulated, if required, by varying reaction condi-
tions. The a-chlorinated product has recently been pre-
pared by chlorinating hexaalkoxy-TP with iodine
monochloride.18 The monohydroxy-pentaalkoxy-TP is a
very valuable precursor for the synthesis of dimers, oligo-
mers, side-chain polymers and networks. It can be pre-
pared by several different ways19 such as, a non-selective
cleavage of one of the alkoxy chain of hexaalkoxy-TP by
the use of a calculated amount of 9-Br BBN, or B-bro-
mocatecholborane; by the partial alkylation of hexaacet-
oxy-TP to monoacetyl-TP followed by hydrolyses; a se-
lective cleavage of the methyl ether of monomethoxypen-
taalkoxy-TP with lithium diphenylphosphide; or by direct
coupling of a tetraalkoxybiphenyl with alkoxyphenol. By
increasing the amount of H2SO4 (1-10%) in the reaction
mixture, this compound can also be obtained up to 25% as
a side product in the oxidative trimerization of dialkoxy-
benzene using FeCl3, MoCl5 or VOCl3. In the absence of
H2SO4, only traces of monohydroxy-pentaalkoxy-TP are
formed. Dichlorinated-, trichlorinated-hexaalkoxy-TP
and monochloro-dialkoxybenzene are the other side prod-
ucts formed in the reaction
RO
RO
RO
- 6 e-
- 6 H+
RO
CH2Cl2, VOCl3
OR
a: R = C3H7
b: R = C4H9
c: R = C5H11
d: R = C9H19
e: R = C10H21
f: R = C11H23
2
1
g: R = (CH2)2CH(CH3)(CH2)3CH(CH3)2
Scheme 1
in addition to known chloranil and iron chloride, molyb-
denum(V) chloride16 and vanadium oxytrichloride10 can
be utilized for the oxidative trimerization of 1,2-dialkoxy-
benzenes to hexaalkoxytriphenylenes in high yields.
VOCl3 is the only liquid oxidizing reagent so far reported
for the synthesis of TP derivatives. It can be easily han-
dled under anhydrous conditions using standard syringe
technique or by using an addition funnel for large-scale
preparation. The use of VOCl3 in intramolecular oxidative
phenolic couplings is well-documented17 but its use in in-
termolecular couplings is not explored much.
When various 1,2-dialkoxybenzenes (1a-g) were treated
with VOCl3, hexaalkoxytriphenylenes (2a-g) were
formed in high yields (Table 1). The reaction occurs under
very mild conditions with or without any additional acid
catalyst and in a very short time at room temperature
(Scheme 1). VOCl3 is miscible in various organic solvents
and this could be a reason for the almost spontaneous tri-
merization of dialkoxybenzenes into hexaalkoxytriphe-
nylenes. All the products were characterized from their
spectral data, thermal behavior, and by direct comparison
with authentic samples. Unlike the FeCl3 method where
catalytic amount of H2SO4 increases the product yield,15
the VOCl3 method does not require H2SO4. In fact its pres-
ence decreases the yield in many cases.
OH
OR
OR
Cl
OR
OR
RO
RO
RO
+
1
+
2
RO
OR
3
4
OR
OR
Scheme 2
Table 1 Preparation of Triphenylene Derivatives using 2.5 equiv
VOCl3 in CH2Cl2 Solution at r.t.
Effect of Reagent Concentration
Starting Material
Product
Yield %
To determine the optimum amount of VOCl3 for the oxi-
dative trimerization of dialkoxybenzenes to hexaalkoxy-
TPs, we performed the reaction with 1,2-dibutyloxyben-
zene using variable amounts of VOCl3 in CH2Cl2 (it was
found to be the best solvent, see effect of solvent). The re-
sults are summarized in Table 2. Although only 2 equiva-
lents of VOCl3 are required to generate diradical cation
species, the best yield of hexabutyloxy-TP was realized
using 2.5 equivalents of VOCl3. This could be due to the
impurities present in the commercial reagent or non-per-
1a
1b
1b
1c
1c
1d
1e
1f
2a
2b
2b
2c
2c
2d
2e
2f
53
86
79a
85
83a
56
70
70
65
1g
2g
a In the presence of 0.4% H2SO4.
Synthesis 2001, No. 2, 305–311 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Triphenylene and Dibenzopyrene Derivatives
307
Table 2 Oxidative Coupling of 1,2-Dibutyloxybenzene in CH2Cl2
using Different Concentrations of VOCl3 at r.t.
Effect of Temperature
When the reaction is carried out at 0 ∞C in CH2Cl2 using
2.5 equivalents of VOCl3, hexabutyloxy-TP is formed in
about 23% yield. About 50% of unreacted starting materi-
al and traces of monochloro-dibutyloxybenzene were iso-
lated from this reaction. From the above results, it is clear
that the use of 2.5 equivalents of VOCl3 in dry CH2Cl2 at
room temperature are the best reaction conditions for the
trimerization of o-dialkoxybenzene to hexaalkoxy-TP.
The presence of concentrated H2SO4 resulted in the cleav-
Substrate
VOCl3 (mol equiv)
Product (yield, %)
1b
1b
1b
1b
1b
0.5
1.0
2.0
2.5
3.0
2b (28)
2b (50)
2b (76)
2b (86)
2b (45)
fect anhydrous reaction conditions. As expected, reducing age of one or more alkoxy chains, while excess of the re-
the amount of the reagent decreases the product yield, but agent yielded chlorinated side products.
increasing the reagent concentration also decreases the
yield of hexabutyloxy-TP. This could be because of the
formation of side products. It should be noted that all the Synthesis of Unsymmetrical Triphenylene Derivtives
reactions were carried out under identical reaction condi-
tions. Efforts have not been made to optimize various pa- To examine the effect of dissymmetry on the mesophase,
rameters associated with each reaction.
Tinh et al. prepared several dissymmetrical hexasubstitut-
ed triphenylenes by putting different alkyl chains in the
periphery and found that an introduction of non-symmet-
ric side-chains does not affect the nature of Colh phase, but
results in the reduction of the mesophase stability.20 Tra-
Effect of Solvent
Choice of reaction solvent has significant effects on the ditionally, these materials have been prepared by statisti-
course of reaction. Oxidative coupling of phenols and cal approach involving either oxidative trimerization of
phenol ethers has been reported in various solvents such a mixture of two different 1,2-dialkoxybenzene deriva-
as CH2Cl2, Et2O, CH3CN, CCl4, etc. In order to find the tives20 or by partial alkylation of hexaacetoxytriphenylene
best solvent for the preparation of triphenylene deriva- followed by alkylation.21 Unsymmetrical TP derivatives
tives, we performed the trimerization of 1,2-dibutyloxy- prepared by the introduction of a single ester side chain
benzene using VOCl3 in various solvents under identical (monoalkanoyloxy-pentaalkoxy-TPs) show significant
reaction conditions. Typically, to a solution of 1.0 g of enhancement in the mesophase stability.21b A plastic co-
1,2-dibutyloxybenzene in 5 mL of the appropriate solvent, lumnar discotic phase is reported in these types of unsym-
was added slowly 2.5 equivalents of VOCl3 and the mix- metric triphenylene derivatives.22 A well defined but
ture was stirred at room temperature for 5-10 min. After, lengthy synthesis of unsymmetrically substituted TP de-
it was quenched with methanol and extracted with H2O/ rivatives was described by Wenz in 1985.23 The incorpo-
CH2Cl2. The crude product was purified by column chro- ration of tetramethoxybiphenyl with veratrol to prepare
matography. The results are summarized in Table 3. As HMTP was reported in 1965 by Musgrave.24 Recent
indicated in Table 3, the best yield was realized using developments of this rational synthesis involving oxida-
CH2Cl2 as a solvent. Reactions carried out in hexane and tive coupling of a tetraalkoxybiphenyl with dialkoxy-
CCl4 resulted in relatively low yield of hexabutyloxy-TP benzene derivatives allowed production of these un-
and produced a significant amount of monochloro-TP (4, symmetrical derivatives in large amounts with high puri-
about 39%). There was no hexabutyloxy-TP formation ty. A variety of unsymmetrical triphenylene discotics
observed in THF, CH3CN and HOAc. It is difficult to ra- have recently been prepared following this process.10,16,25-
tionalize why other solvents result in poor yields of 28 Organometallic chemistry has also been applied for the
hexabutyloxy-TP.
synthesis of unsymmetrical substituted triphenylenes.29
Unsymmetrically substituted TP derivatives 7a-c were
obtained from the oxidation of a mixture of 5a or 5b and
3,3¢,4,4¢-tetrabutyloxybiphenyl 6a or tetrapentyloxybi-
phenyl 6b with VOCl3 in about 50% yield (Scheme 3).
Cross coupling reaction leading to unsymmetrical TPs
dominates over the oxidative dimerization of tetraalkoxy-
biphenyl or trimerization of dialkoxybenzene. In view of
this efficient cross coupling, it has been suggested11b,24
that tetraalkoxybiphenyl is probably the intermediate
product during the oxidative trimerization of 1,2-dialkox-
ybenzene to hexaalkoxy-TP. However, we could not iso-
late any tetraalkoxybiphenyl in the oxidative trimerization
of 1,2-dialkoxybenzene even when only 0.5 equivalent or
Table 3 Oxidative Coupling of 1,2-Dibutyloxybenzene using
2.5 equiv VOCl3 in Different Solvents
Substrate
Solvent
Product (yield, %)
1b
1b
1b
1b
1b
1b
1b
Hexane
CH2Cl2
CH2Cl2
THF
CH3CN
AcOH
CCl4
2b (14)
2b (86)
2b (23)a
2b (0)
2b (0)
2b (0)
2b (22)
a Performed at 0°C.
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308
S. Kumar, S. K. Varshney
PAPER
Table 4 Preparation of Heptaalkoxy-TP Derivatives using VOCl3 in
CH2Cl2 Solution at r.t.
lesser amount of the reagent was used, which resulted in
lower yields of 2 along with appreciable amount of unre-
acted starting material. This indicates that the coupling
occurs concomitant with a concerted two-electron transfer
in the oxidative trimerization of 1,2-dialkoxybenzene to
hexaalkoxy-TP.
Substrate
Product
Yield %
8a + 9a
8b + 9b
8c + 9c
8d + 9d
8e + 9e
8f + 9f
10a
10b
10c
10d
10e
10f
40
25
51
49
48
20
OR
OR
OR
OR
OR
R1O
R2O
R1O
R2O
CH2Cl2
VOCl3
OR
+
(Table 4). Thus, heptaalkoxy-TPs having all the seven
peripheral alkoxy chains identical or three different in size
can be prepared efficiently.
OR
OR
5
7
6
Oxidative Dimerization of Tetraalkoxybiphenyl
a: R = C4H9, R1 = CH3, R2 = C5H11
b: R = R2 = C5H11, R1 = CH3
c: R = C5H11, R1 = R2 = (CH2)2CH(CH3)(CH2)3CH(CH3)2
Discotic liquid crystals based on dibenzopyrene (DBP)
have been the subject of many recent publications. Bock
and Helfrich have demonstrated for the first time the ex-
istence of ferroelectricity in the columnar liquid crystals
of 1,2.5,6,8,9,12,13-octakis-(S)-2-heptyloxypropanoyl-
oxy)dibenzopyrene.9,31 Synthesis of various octaalkoxy-
substituted DBPs and their photophysical properties have
been reported by the Ringsdorf and Markovitsi
groups.27b,32 Mesomorphic properties of five homologues
of the 1,2,5,6,8,9,12,13-octaalkoxy-DBP and their charge
transfer complexes with 2,4,7-trinitro-9-fluorenone are
reported by S. Zamir et al.33 The electro-optical and elec-
tromechanical effects in these materials were also report-
ed very recently.34,35
Scheme 3
Synthesis of Heptaalkoxytriphenylenes
Heptaalkoxy-TP discotic LCs are important as they pos-
sess lower clearing temperatures and broad mesophase
ranges. We have recently reported the synthesis of hep-
taalkoxy-TPs by two different ways, one starting from
monohydroxy-pentaalkoxytriphenylenes, and the other
via biphenyl route using either MoCl5 or FeCl3 as oxi-
dant.30 We have found that the coupling of a tetraalkoxy-
biphenyl with a trialkoxybenzene works well using
VOCl3 as an oxidant (Scheme 4).
All the DBP derivatives were prepared following the
method of Musgrave and Webster36 which involves the
oxidation of 3,3¢,4,4¢-tetramethoxybiphenyl by chloranil
in 70% sulfuric acid to 2,5,6,9,12,13-hexamethoxydiben-
zo[fg,op]naphthacene-1,8-quinone and its 1,10-quinone
isomer. Reductive acetylation followed by alkylation re-
sulted in the synthesis of 1,2,5,6,8,9,12,13-octasubstitut-
ed-DBP liquid crystals. Direct oxidation of
tetrapentyloxybiphenyl by chloranil to hexapentyloxy-
dibenzo[fg,op]naphthacene-1,8-quinone and its conver-
sion to octapentyloxy-DBP by the above mentioned
procedure has also been reported by the Ringsdorf
group.27b We have found that VOCl3 can be efficiently
utilized under very mild reaction conditions for the prep-
aration of two quinones. When 3,3¢,4,4¢-tetrapentyloxybi-
phenyl 6b was treated with VOCl3 in CH2Cl2 containing
0.5% concentrated H2SO4, 2,5,6,9,12,13-hexapentyloxy-
dibenzo-1,8-quinone 11 and 2,5,6,9,12,13-hexapentylox-
ydibenzo-1,10-quinone 12 are formed in 24% and 50%
yield, respectively (Scheme 5). Presence of concentrated
H2SO4 is essential for the dimerization. In its absence, no
product formation was observed. Although the purifica-
tion of these quinones is extremely difficult, they can be
separated by repeated column chromatography. The puri-
ty of the quinones can be monitored by 1H NMR where the
OR
OR
OR
CH2Cl2
VOCl3
OR
OR
OR
R1O
R1O
R1O
R1O
+
OR1
OR1
OR
OR
10
8
9
a: R = R1 = C4H9
b: R = CH3, R1 = C5H11
c: R = C4H9, R1 = C2H5
d: R = C5H11, R1 = C2H5
e: R = C5H11, R1 = C4H9
f: R = C5H11, R1 = C12H25
Scheme 4
When tetraalkoxybiphenyls 9 were reacted with tri-
alkoxybenzenes 8, heptaalkoxy-TPs 10 were formed
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Synthesis of Triphenylene and Dibenzopyrene Derivatives
309
OR
OR
OR
O
O
RO
RO
RO
RO
OR
OR
RO
RO
OR
OR
CH2Cl2, H2SO4
VOCl3
+
O
O
R = C5H11
OR
OR
OR
11
12
6
Scheme 5
three singlets for aromatic protons appear relatively down 4b:
1H NMR: d = 9.06 (s, 1H), 7.79 (2 ¥ s, 4H), 4.25 (m, 10H), 4.12 (t,
2H, J = 6.5 Hz), 1.92 (m, 12H), 1.60 (m, 12H), 1.0 (m, 18H).
13C NMR: d = 151.6, 150.3, 149.3, 148.8, 147.6, 146.1, 127.9,
126.1, 125.2, 125.1, 123.4, 123.3, 122.1, 112.3, 108.7, 107.6, 107.1,
105.7, 73.6, 70.1, 69.8, 69.6, 69.3, 69.2, 32.8, 31.9, 31.8, 19.8,14.3.
field for the 1,10-quinone isomer (see experimental). Both
the quinones can be converted to liquid crystalline deriv-
atives using well-established chemistry.27b It should be
noted that derivatives of only the 1,8-isomer, i.e.,
1,2,5,6,8,9,12,13-octasubstituted-DBP have been report-
ed in the literature. Derivatives of the 1,10-isomer, which
has a different symmetry, have so far not been prepared.
MS: m/z = 695.2.
Anal. Calcd for C42H59ClO6: C, 72.54; H, 8.55; Cl, 5.10. Found: C,
We are currently working on the synthesis of these deriv- 72.49; H, 8.58; Cl, 5.13.
atives.
Thermal Behaviour: On first heating the compound melts at 55 ∞C
to a highly ordered columnar mesophase that changes to colh phase
at 96 ∞C and finally clears at 112.2 ∞C. Upon cooling, colh phase ap-
pears at 109.3 ∞C and converted to an unidentified colx phase at 93
∞C. The compound does not show any textural change down to r.t.
However, on second heating, the compound shows all the three
transitions at 55.9 ∞C, 96.3 ∞C and 112.3 ∞C. The low temperature
mesophase in hexabutyloxy-TP derivatives has recently been re-
ported to be more ordered and referred to as colp phase.38 The low
temperature mesophase, which appeared at 93 ∞C on cooling this
compound is probably the colp phase, but x-ray studies have to be
done to confirm this.
Chemicals and solvents (AR quality) were obtained locally and
used as such without any purification. Column chromatographic
separations were performed on silica gel (70-230 and 200-400
mesh). TLC was performed on aluminum sheets precoated with sil-
ica gel (Merck, Kieselgel 60, F254). MS were recorded on a JEOL
JMS-600H spectrometer in FAB+mode using m-NBA matrix. Ele-
mental analysis was provided by Atlantic Microlab, Inc., U.S.A.
1H NMR spectra were recorded on a 200 MHz and 13C NMR spectra
on a 500 MHz Bruker NMR spectrometer in CDCl3. All chemical
shifts (d) are reported in ppm downfield from TMS, and J values are
given in Hz. Transition temperatures were measured using a Mettler
FP82HT hot stage and central processor in conjunction with Leitz
DMRXP polarizing microscope as well as by differential scanning
calorimetry (DSC7 Perkin-Elmer). Peak temperatures observed in
the heating and cooling runs of DSC have been reported.
Synthesis of Unsymmetrical and Heptaalkoxy-TPs; General
Procedure
A mixture of the appropriate tetraalkoxybiphenyl 6 or 9 (1 mmol)
and 1,2-dialkoxybenzene 5 (2 mmol) or 1,2,3-trialkoxybenzene 8 (2
mmol) was dissolved in anhyd CH2Cl2. VOCl3 (3.0 mmol) was add-
ed and the reaction was subjected to the procedure described above.
Synthesis of Hexaalkoxy-TPs; General Procedure
7a:
To a solution of 1,2-dialkoxybenzene (0.005 mol) in dry CH2Cl2
(10 mL), VOCl3 (0.013 mol) was added dropwise. The reaction
mixture was stirred at r.t. for 5-10 min under N2 atm. The reaction
was quenched with MeOH (5 mL), poured over ice-water (20 mL)
and extracted with CH2Cl2 (4 ¥ 20 mL). The crude product was pu-
rified by repeated column chromatography over silica gel (hexane-
CH2Cl2 mixtures). All the known products were characterized from
1H NMR: d = 7.85, 7.83 (s, 1H each), 7.81 (3 ¥ s, 4H), 4.24 (m,
10H), 4.10 (s, 3H), 1.93 (m, 10H), 1.57 (m, 12H), 1.05 (m, 15H).
13C NMR: d = 149.5, 124.1, 123.8, 107.8, 106.8, 105.5, 69.8, 56.7,
31.9, 29.4, 28.7, 23.0, 19.8, 14.4.
MS: m/z = 633.0.
1
Anal. Calcd for C40H56O6: C, 75.91; H, 8.92. Found: C, 75.89; H,
8.90.
their spectral data and phase behaviour. H NMR data, mass and
thermal behaviour of all the derivatives were found to be in accor-
dance with the structure and literature data.16,30,37 Spectral data and
thermal behaviour of new compounds are given below.
Thermal Behaviour: The compound melts at 86.9 ∞C to colh phase
which clears at 110.4 ∞C. The DSC shows another weak transition
at 68.1 ∞C (enthalpy 2.8 kJ mol-1), which is clearly not the crystal-
lization temperature and, therefore, the compound stays in another
highly ordered columnar phase below this temperature. The DSC
does not show the crystallization peak down to r.t. but the material
is not shearable at r.t. Probably it transforms into a glassy state at
lower temperature but the glass transition is not detected in DSC.
2g:
Mp: 27 ∞C.
1H NMR: d = 7.85 (s, 6H), 4.27 (m, 12H), 2.00-1.20 (m, 60H), 1.03
(d, 18H, J = 6.5 Hz), 0.88 (d, 36H, J = 6.5 Hz).
13C NMR: d = 149.5, 124.1, 107.9, 68.5, 39.8, 37.9, 36.9, 30.5, 28.4,
25.2, 23.1, 23.0, 20.2.
7c:
1H NMR: d = 7.84 (s, 6H), 4.25 (m, 12H), 2.00-1.20 (m, 44H),
1.05-0.90 (m, 30H).
MS: m/z = 1164.2.
Anal. Calcd for C78H132O6: C, 80.35; H, 11.41. Found: C, 80.20; H,
11.48.
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310
S. Kumar, S. K. Varshney
PAPER
13C NMR: d = 149.4, 124.0, 107.7, 70.1, 68.4, 39.7, 37.9, 36.8, 30.5,
13C NMR: d = 152.2, 150.0, 149.3, 148.9, 148.6, 142.4, 126.9,
125.0, 124.4, 124.2, 123.9, 118.6, 112.3, 108.9, 107.6, 102.3, 74.5,
74.4, 70.4, 70.1, 70.0, 69.7, 69.3, 32.3, 31.2, 31.1, 31.0, 30.1, 29.9,
29.8, 29.6, 29.5, 28.8, 26.7, 26.6, 23.1, 22.9, 14.5.
29.6, 28.8, 28.4, 25.2, 23.1, 23.0, 20.2, 14.5.
MS: m/z = 885.7.
Anal. Calcd for C58H92O6: C, 78.68; H, 10.47. Found: C, 78.52; H,
10.56.
MS: m/z = 1125.0.
Anal. Calcd for C74H124O7: C, 78.95; H, 11.10. Found: C, 79.33; H,
11.27.
Thermal Behaviour: The compound is liquid crystalline at r.t. It
clears at 63 ∞C on heating. On cooling, the colh appears at 61 ∞C and
stays down to r.t.
Oxidative Dimerization of Tetraalkoxybiphenyl
10b:
Mp: 138.1 ∞C.
3,3¢,4,4¢-Tetrapentyloxybiphenyl 6 (1 mmol) was dissolved in an-
hyd CH2Cl2 (10 mL) containing 0.5% concd H2SO4. VOCl3 (2.5
mmol) was added and the reaction was stirred at r.t. for 15 min. It
was then poured over ice-water (20 mL) and extracted with CH2Cl2
(4 ¥ 20 mL). The black crude product was purified by repeated col-
umn chromatography over silica gel (hexane: CH2Cl2, 6:4) to afford
2,5,6,9,12,13-hexapentylkoxydibenzo[fg,op]naphthacene-1,8-
quinone (11, 24%)27b and 2,5,6,9,12,13-hexapentylkoxydiben-
zo[fg,op]naphthacene-1,10-quinone (12, 50%).
1H NMR: d = 9.25 (s, 1H), 7.81 (s, 3H), 7.69 (s, 1H), 4.12 (m, 18H),
1.93 (m, 6H), 1.50 (m, 12H), 0.91 (m, 9H).
13C NMR: d = 152.3, 152.1, 149.7, 149.2, 148.5, 142.5, 126.8,
124.6, 124.2, 123.9, 123.7, 118.6, 110.0, 105.5, 104.7, 104.3, 102.1,
74.5, 69.2, 56.6, 56.5, 56.4, 56.3, 30.7, 30.6, 29.6, 28.9, 28.8, 28.6,
23.1, 23.0, 14.5.
MS: m/z = 606.4.
11:
1H NMR: d = 9.36 (s, 2H), 7.32 (s, 2H), 7.13 (s, 2H), 4.20 (m, 12H),
Anal. Calcd for C37H50O7: C, 73.24; H, 8.31. Found: C, 72.88; H,
8.70.
1.98 (m, 12H), 1.50 (m, 24H), 1.00 (m, 18H).
13C NMR: d = 181.4, 155.5, 153.3, 150.3, 131.6, 131.1, 128.4,
10c:
Mp: 89.9 ∞C.
119.3, 106.2, 105.3, 102.2, 68.8, 68.6, 28.8, 28.4, 22.6, 14.1.
1H NMR: d = 9.24 (s, 1H), 7.83 (s, 2H), 7.81 (s, 1H), 7.69 (s, 1H),
4.25 (m, 14H), 1.93 (m, 8H), 1.56 (m, 17H), 1.04 (m, 12H).
13C NMR: d = 151.9, 150.0, 149.2, 148.9, 148.5, 142.3, 126.9,
125.0, 124.4, 124.1, 123.8, 118.7, 112.0, 108.6, 107.4, 102.6, 69.97,
69.81, 69.75, 69.66, 69.53, 69.25, 64.97, 31.9, 19.8, 16.4, 15.4,
14.4.
MS: m/z = 848.9.
12:
1H NMR: d = 9.47 (s, 2H), 7.39 (s, 2H), 7.20 (s, 2H), 4.20 (m, 12H),
1.98 (m, 12H), 1.50 (m, 24H), 1.00 (m, 18H).
13C NMR: d = 181.5, 155.6, 153.4, 150.4, 131.8, 131.3, 128.5,
119.2, 106.3, 105.4, 102.3, 68.9, 68.7, 28.8, 28.3, 22.6, 14.1.
MS: m/z = 648.5.
MS: m/z = 848.9.
Anal. Calcd for C40H56O7: C, 74.04; H, 8.70. Found: C, 73.58; H,
8.66.
Anal. Calcd for C54H72O8: C, 76.38; H, 8.55. Found: C, 76.44; H,
8.70.
10d:
Mp: 82.6 ∞C.
Acknowledgement
1H NMR: d = 9.24 (s, 1H), 7.82 (s, 2H), 7.80 (s, 1H), 7.69 (s, 1H),
4.21 (m, 14H), 1.95 (m, 8H), 1.54 (m, 25H), 0.97 (t, 12H).
13C NMR: d = 151.93, 151.87, 149.9, 149.2, 148.8, 148.5, 142.3,
126.9, 125.0, 124.4, 124.1, 123.8, 118.7, 112.0, 108.5, 107.4, 102.6,
70.3, 70.0, 69.9, 69.8, 69.5, 65.0, 29.5, 28.8, 23.0, 16.4, 15.4, 14.5.
We are very grateful to professor S. Chandrasekhar for helpful dis-
cussions.
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MS: m/z = 704.4.
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Synthesis 2001, No. 2, 305–311 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Triphenylene and Dibenzopyrene Derivatives
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Synthesis 2001, No. 2, 305–311 ISSN 0039-7881 © Thieme Stuttgart · New York