Efficient Oxidative Coupling of Arenes via Electrochemical Regeneration of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) under Mild Reaction Conditions

Article abstract of DOI:10.1002/adsc.201601331

The intramolecular dehydrogenative carbon-carbon bond formation of aromatic rings in the presence of catalytic amounts of an oxidising agent is herein described. The oxidative coupling is realised under indirect anodic conditions, utilising 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an efficient redox mediator under acidic conditions. In comparison, for the stoichiometric oxidative coupling reaction of hexakis(4-tert-butylphenyl)benzene on a 1.0 gram scale, 1.56 g of DDQ were applied, whereas in the present indirect electrochemical version, only 15 mg of DDQ were needed, resulting in significantly easier purifications of the products. The reaction proceeds smoothly using a variety of polyaromatics including terphenyl, quaterphenyl and heptaphenyl derivatives to give polyphenylenes in excellent yields and current efficiencies. A detailed optimisation study, investigations on the electrochemical behaviour of the redox mediator and synthetic applications of the method are discussed. (Figure presented.).

Full text of DOI:10.1002/adsc.201601331

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DOI: 10.1002/adsc.201601331
Very Important Publication
Efficient Oxidative Coupling of Arenes via Electrochemical
Regeneration of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) under Mild Reaction Conditions
Philipp Rçse,a Steffen Emge,a Christoph Alexander Kçnig,a and Gerhard Hilta,*
a
Fachbereich Chemie, Philipps-Universitꢀt Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany
Fax : (+49)-6421-282-5677; phone: (+49)-6421-282-5601; e-mail: Hilt@chemie.uni-marburg.de
Received: December 2, 2016; Revised: January 23, 2017; Published online: && &&, 0000
Supporting information for this article can be found under http://dx.doi.org/10.1002/adsc.201601331.
Abstract: The intramolecular dehydrogenative reaction proceeds smoothly using a variety of poly-
carbon-carbon bond formation of aromatic rings in aromatics including terphenyl, quaterphenyl and
the presence of catalytic amounts of an oxidising heptaphenyl derivatives to give polyphenylenes in
agent is herein described. The oxidative coupling is excellent yields and current efficiencies. A detailed
realised under indirect anodic conditions, utilising optimisation study, investigations on the electro-
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as chemical behaviour of the redox mediator and syn-
an efficient redox mediator under acidic conditions. thetic applications of the method are discussed.
In comparison, for the stoichiometric oxidative cou-
pling reaction of hexakis(4-tert-butylphenyl)benzene
on a 1.0 gram scale, 1.56 g of DDQ were applied, Keywords: C–C coupling; 2,3-dichloro-5,6-dicyano-
whereas in the present indirect electrochemical ver- 1,4-benzoquinone (DDQ); electrochemistry; oxida-
sion, only 15 mg of DDQ were needed, resulting in tion; oxidative coupling; polycyclic aromatic hydro-
significantly easier purifications of the products. The carbons
Introduction
2, also dimers of 2 either connected via a carbon-
carbon single bond (3) or condensed products (4/5)
The direct dehydrogenative coupling of two arenes, were identified.[3c] The number of side products can
the so-called Scholl reaction, has been accomplished be efficiently reduced by the introduction of directing
by various methods for the preparation of polycyclic groups, such as alkoxy groups, or by the introduction
aromatic hydrocarbons (PAHs).[1] The advantage of
this method is that no pre-functionalisation is re-
quired and it serves as a straightforward, atom and re-
action step economical method, in contrast to cross-
coupling methodologies (Suzuki–Miyaura, Stille,
Kumada, Negishi) using transition metal catalysts.[2]
Two reaction mechanisms of the Scholl reaction
have been proposed and the dispute whether arenium
cations or radical cations are the reactive intermedi-
ates has been thoroughly discussed.[3]
Generally, the carbon-carbon bond formations are
most efficient when electron-rich arene derivatives
are used and a pre-orientation of the aromatic rings,
such as in ortho-terphenyls, allows the access to larger
aromatic ring systems.[3d] In a seminal work, King and
co-workers described the oxidative coupling reaction
of a simple ortho-terphenyl 1 (Scheme 1) and the
problems associated with this seemingly simple trans-
formation. Besides the desired triphenylene product and identified side products reported by King.
Scheme 1. Oxidative coupling reaction of ortho-terphenyl
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of bulky substituents, such as tert-butyl groups to However, examples in which DDQ has been used as
block positions on the arene rings.
electrochemical redox mediator are rare.[15]
In addition, the electronic nature of the arene is an
For a long time, our group has been interested in
important factor since electron-deficient arenes do the efficient synthesis of functionalised poly-aromatic
not undergo this carbon-carbon bond formation hydrocarbons using transition metal catalysts[16] as
either because of their higher redox potentials or well as their use for surface applications.[17] Also, we
their lower nucleophilicities.[4] Moreover, if mixtures have reported the Scholl reaction for the synthesis of
of different substrates are used homo-dehydrodimers oligoarenes some time ago.[18] In this respect, we de-
have been found in significant amounts. This reveals cided to investigate an electrochemical intramolecular
the complex relationship between the redox potential arene-arene coupling using DDQ as mediator under
and the nucleophilicity of each substrate.[5]
oxidative electrochemical reaction conditions, which
Originally, the Scholl reaction was performed we report herein.
using strong Lewis and Brønsted acids and high
reaction temperatures resulting in many side prod-
ucts.[6]
Results and Discussion
Moreover, the intramolecular coupling of electron-
rich polyaromatic systems under direct electrochemi- To explore the reaction, we selected tetramethoxy-
cal oxidation was investigated by Hammerich and ortho-terphenyl 6a and dimethoxy-ortho-terphenyl 6b
Parker yielding a large variety of Scholl products.[7] as model substrates (Scheme 2).
Another approach has been reported by Waldvogel
on the electrochemical phenol-arene cross-coupling
using boron-doped diamond electrodes (BDD) where
the selective generation of a phenoxyl radical inter-
mediate plays a crucial role.[8] An intermolecular
arene-arene cross-coupling reaction has been reported
by Yoshida relying on a selective electrochemical oxi-
dation and accumulation of one reaction partner at
low temperature (“radical-cation-pool method”)
which can react then with a second non-activated
arene.[9]
Furthermore, a large number of strong oxidising
Scheme 2. Oxidative coupling of ortho-terphenylenes 6a/
b under electrochemical conditions.
agents has been reported to accomplish these oxida-
tive coupling reactions, such as CuCl2 or Cu(OTf)2
and AlCl3,[10a,b] Tl(O2CCF3)3 in CF3CO2H,[10c]
Pb(OAc)4/BF3·OEt,[10d] Hg(II) salts,[10e] VOF3,[10f]
At first, cyclic voltammetry was performed to un-
SbCl5,[10g] Meerweinꢂs reagent,[10h] FeCl3
and derstand the electrochemical behaviour of DDQ
[10i]
MoCl5.[1c,10j] Although good results could be achieved, under the original reaction conditions reported for
a significant drawback is that many of those oxidants the oxidative coupling.[12] The cyclic voltammogram
have to be used in over-stoichiometric amounts. (CV) of DDQ/DDQH2 (Figure 1, curve a) exhibits
Thereby, large amounts of toxic chemical waste and two reversible redox potentials for the semiquinone
often chlorinated side products are encountered and the quinone at ꢀ0.21 V and 0.64 V vs. Ag/AgCl
giving rise to ecological problems. Metal-free oxidants when 0.1M Bu4NBF4/CH2Cl2 was used as supporting
such as hypervalent iodine compounds[11] or quinones electrolyte. When methanesulfonic acid was added
seem to be less problematic. Therefore, Rathore re- (curve b) the potentials for the oxidation were shifted
ported the use of stoichiometric amounts of DDQ towards more positive oxidation values of 0.76 V and
(2,3-dichloro-4,5-dicyano-para-benzoquinone)
in 1.10 V (determined via differential pulse voltammetry
acidic solution for the synthesis of polymethoxylated measurements, see the Supporting Information).
triphenylenes.[3d,10h,12] Although DDQ was reported to
For the reductive process, the semiquinone reduc-
be recyclable after isolation,[12,13] we are unaware of tion potential shifted towards more positive potentials
an in situ recycling process utilising DDQ in only cat- and merged into one wave (0.80 V). A similar behav-
alytic amounts in oxidative coupling reactions.
iour is well established for quinoid redox systems.[19]
Many examples for the reversible redox behaviour As shown in Figure 1, the anodic peak current for
of quinones have been reported in the literature and DDQ increases compared to curve b when an excess
many chemical co-oxidants are known for the regen- of 6a is present. Since substrate 6a is not oxidised at
eration of DDQ in organic reactions.[14] Electrolysis those potentials (curve d), the increase in anodic cur-
represents hereby
a
promising environmentally rent results from its re-entering the catalytic oxidation
benign method for the in situ oxidation of DDQH2. cycle. This observation is clear evidence that DDQ
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At first, we conducted the synthesis of 7b under
standard conditions of the oxidative coupling reported
for DDQ, but under electrochemical regeneration of
the redox agent. The desired product could be ob-
tained in a moderate yield of 69% with a good cur-
rent efficiency of 60% (entry 1). When using 2,6-di-
chloro-p-benzoquinone or p-chloranil as redox media-
tor the product was obtained in lower yield and cur-
rent efficiency (entries 2 and 3). In the absence of
a redox mediator, the product was also formed but
the yield was much lower and the reaction time was
twice as long (entry 4).
A strong influence on yield and current efficiency
was found by varying the acid additive. While the use
of trifluoromethanesulfonic acid, p-toluenesulfonic
acid and acetic acid resulted in a lower yield com-
pared to methanesulfonic acid, the use of trifluoroace-
tic acid gave product 7b in an excellent yield of 92%
and 91% current efficiency (entries 5–8). Aqueous
acetic acid as well as sulfuric acid gave no product,
presumably due to their poor solubility in dichloro-
methane (entries 9 and 10). It is noteworthy that
under non-electrochemical reaction conditions no de-
pendency between the acid additive and the product
Figure 1. Cyclic voltammogram of DDQ (2.2 mm): a) in
CH2Cl2/Bu4NBF4 (10 mL, 0.1M); b) with H3CSO3H as addi-
tive (CH2Cl2:H3CSO3H=9:1); c) with H3CSO3H as additive
(CH2Cl2:H3CSO3H=9:1) and 6a (15 mg, 51.7 mmol); d) only
6a (15 mg, 51.7 mmol) in CH2Cl2/Bu4NBF4 (10 mL, 0.1M).
Reference electrode: Ag/AgCl (KClsat), scan rate=
100 mVsꢀ1.
acts as mediator and that DDQH2 is regenerated yield was determined.
after oxidation of substrate 6a.
Changing the solvent to acetonitrile or methanol
In a series of experiments, we screened various re- did neither improve the chemical yield nor the cur-
action conditions, such as different commercially rent efficiency. However, the fact that both solvents
available para-quinones (Table 1, entries 1–4), we are also suitable may be important for substrates that
modified the acid additive (entries 5–10) and varied are insoluble in dichloromethane (entries 11 and 12).
the solvent (entries 11–13).
In contrast, the use of DMSO as solvent resulted in
The indirect anodic oxidation was conducted in a di- no conversion, neither the DDQ-mediated reaction
vided cell equipped with carbon fibre electrodes (see nor the direct oxidation of 6b took place (entry 13).
the Supporting Information) at room temperature ap- A considerable advantage of the present protocol is
plying a current of 10 mA.
that the transformation can be conducted without
Table 1. The effects of redox mediator, acid additive and solvent on the electrochemical synthesis of 7b.[a]
Entry
Mediator
Acid
Solvent
Yield[b]/(ce)[e]
1
2
3
4
5
6
7
8
DDQ
H3CSO3H
H3CSO3H
H3CSO3H
H3CSO3H
F3CSO3H
p-TsOH
H3CCO2H
F3CCO2H
H3CCO2H/H2O[d]
H2SO4
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH3CN
MeOH
DMSO
69% (60%)
65% (55%)
62% (52%)
54% (25%)
84% (77%)
67% (56%)
75% (41%)
92%[c] (91%)
–
2,6-dichloro-p-benzoquinone
p-chloranil
none
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
DDQ
9
10
11
12
13
–
F3CCO2H
F3CCO2H
F3CCO2H
84% (67%)
88% (65%)
–
[a]
Reaction conditions: terphenyl 6b (58 mg, 165 mmol, 1.0 equiv.), mediator (5 mol%), Bu4NBF4 (1.00 g/chamber, 0.3M),
solvent/acid (10 mL/chamber, 9:1 v/v), carbon fibre electrodes, H-type cell, 10 mA, room temperature.
Yields were determined by H NMR analysis using mesitylene as internal standard.
Isolated yield.
Solvent ratio: 5.5:4.5 (v/v).
ce: current efficiency.
[b]
[c]
[d]
[e]
1
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Table 3. Effects of the applied current and mediator loading
on the electrochemical synthesis of 6a.[a]
strict exclusion of water and air and without encoun-
tering any loss in yield or current efficiency.
Next, we focused upon parameters such as the elec-
trode material, the cell type, the current density and
the amount of redox mediator (Table 2 and Table 3).
No
Mediator loading
Current
Yield[b]/(ce)[d]
1
2
3
4
5
6
none
10 mA
10 mA
20 mA
40 mA
10 mA
10 mA
–
5 mol%
5 mol%
5 mol%
2.5 mol%
1 mol%
85%[c] (82%)
57% (41%)
n.d.
Table 2. Effects of the electrode material and cell type on
the formation of 6b.[a]
79% (72%)
66% (55%)
No Mediator loading Cell type
Yield[b]/(ce)[c]
[a]
Reaction conditions: terphenyl 6a (52 mg, 180 mmol,
1.0 equiv.), DDQ (1–5 mol%), Bu4NBF4 (1.00 g/chamber,
0.3 M), CH2Cl2/H3CCO2H (10 mL/chamber, 9:1 v/v),
carbon fibre electrodes, H-type cell, various currents,
room temperature.
1
2
3
4
5
6
Pt plate
glassy carbon
BDD
H-type
H-type
H-type
H-type
H-type
89% (91%)
89% (75%)
91% (89%)
(decomp. of anode)
55% (37%)
graphite
[b]
1
graphite felt
Yields were determined by H NMR analysis using mesi-
Pt plate[e]
undivided cell 66% (28%)
tylene as internal standard.
Isolated yield on a 2.0 g scale reaction.
ce: current efficiency.
[c]
[d]
[a]
Reaction conditions: terphenyl 6b (58 mg, 165 mmol,
1.0 equiv.), DDQ (5 mol%), Bu4NBF4 (1.00 g/chamber,
0.3M), CH2Cl2/H3CCO2H (10 mL/chamber, 9:1 v/v), elec-
trodes, cell type, 10 mA, room temperature.
Yields were determined by H NMR analysis using mesi-
tylene as internal standard.
ce: current efficiency.
It also is mentionable that in all oxidative coupling
reactions for product 7a and 7b an over-oxidation
toward the radical cations was observed by an instan-
taneous appearance of a dark green colouration of
the reaction mixture when electrolysis was continued
after complete conversion of the starting material.
[b]
[c]
1
As shown in Table 2, excellent yields of 7b were ob- Also precipitation, which might prevent the products
tained when carbon fibre, platinum, glassy carbon and from over-oxidation did not take place in all cases for
BDD (boron-doped diamond) electrodes were used triphenylene and quaterphenylene products 7 and 9
as anode material (entries 1–3). Merely graphite and prepared in this work (see Table 4 and Table 5). Only
graphite felt led to low yields and low current effi- in the cases where hexabenzocoronenes 13 and 16
ciencies and, in addition, decomposition of the elec- were obtained precipitation was observed (see
trode material was observed during the reaction (en- Scheme 5 and Scheme 6). The reduction of the over-
tries 4 and 5). Using an undivided cell type, equipped oxidised products is carried out during the aqueous
with platinum plate electrodes (25ꢃ10 mm) resulted work-up. Such a behaviour has been intensively dis-
in a lower yield (several not identified side products cussed in the past for oxidative coupling reactions of
were observed) and increased reaction times, presum- arenes, for example, triphenylenes.[23]
ably due to a competing reductive processes (entry 6).
Summarising the results described above, we con-
Next, investigations concerning different applied clude that the optimised conditions for the electrolysis
currents and redox mediator loadings were conducted are as follows: DDQ (5 mol%) as redox mediator,
with 2,7-dimethoxytriphenylene (6a) as substrate. This Bu4NBF4 as supporting electrolyte, dichloromethane
change in substrate was undertaken because the start- as solvent, trifluoroacetic acid as additive, in an divid-
ing material has a higher redox potential and there- ed cell equipped with carbon fibre electrodes under
fore undergoes no direct oxidation (Table 3, entry 1). constant current conditions applying 10 mA at room
Noteworthy, the reaction could also be performed on temperature without special precautions for the exclu-
a two gram scale without any loss of yield. The yield sion of air or moisture.
is hereby much higher in comparison with those of
With these optimised conditions in hand, we fo-
classical oxidative coupling reactions using over-stoi- cused our efforts toward the electrochemical oxida-
chiometric amounts of DDQ/MeSO3H (58%),[20] tion of various terphenyl derivatives. The results of
FeCl3 (64%)[21] or MoCl5 (53%).[3c] Merely a modified these electrochemical transformations are summarised
MoCl5/HFIP system reported by Waldvogel gave in Table 4.
a similar good yield (89%).[22]
In accordance with the results of the optimisation
Applying higher currents resulted in lower yields of the tetramethoxytriphenylene derivative 7b, the ox-
and longer reaction times (Table 3, entries 2 and 3). idative coupling of 6c to generate 2,3,7,10-tetrame-
The same loss in yield was observed by reducing the thoxytriphenylene (7c) was achieved in very good
redox mediator loading and the formation of new un- yield and current efficiency (entry 1). In this context,
identified side products was observed (entries 4–6).
it is worthy of mention that if there are no directing
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Table 4. Electrochemical oxidative coupling reaction of ter-
phenyl derivatives under optimised reaction conditions.
groups in the 6- and 11-positions such as in 6a/6b the
2- and 3-positions of the terphenyl have to be blocked
by other substituents to achieve product formation.
Otherwise, a complex mixture of several intramolecu-
lar coupling products will be observed. In contrast to
6b by changing the veratryl fragments with ben-
zo[1,3]dioxole moieties the oxidative coupling result-
ed in the formation of 7d in a slightly decreased yield
presumably due to a slow decomposition of the ben-
zo[1,3]dioxole fragment of 6d under acidic conditions
(entry 2). This could also be proved by stirring 6d in
a mixture of dichloromethane and trifluoroacetic acid
over 3 h followed by GC and GC-MS analysis.
Next, we turned our attention towards thioethers
and alkyl-substituted substrates. The oxidative cou-
pling of the methylthio-substituted terphenyl deriva-
tives 6e/f gave the desired products 7e/f in 61% and
67% yield which are considerably lower than its me-
thoxylated counterparts 7a/c (entries 3 and 4). During
these reactions, the formation of several unidentified
side products was observed. However, the alkylated
terphenyl derivatives 6g–i gave the product in very
good yields and current efficiencies (entries 5–7). In
those cases, side products were not encountered, so
that the terphenylene products could be obtained by
simple filtration over a small pad of silica in pure
form. Last, the oxidative coupling of 6j provided the
chlorinated triphenylene derivative 7j in good yield
but lower current efficiency (entry 8).
In a second set of experiments, we were interested
to investigate the limits of this reaction. Therefore,
we extended the aromatic system towards quater-
phenyl derivatives 9 and hexaphenylbenzenes (HPB)
10/14. Only few examples for oxidative coupling of
quaterphenyls 9 have been reported thus far and
a complex relationship between the substitution pat-
tern and the applied oxidising agent was found.[24] In
this context, we generated a number of 1,2,4-triphe-
nylbenzene derivatives 8 by a cobalt-catalysed cyclo-
trimerisation of aryl-substituted alkynes to access the
desired
intermediates
for
further
oxidation
(Scheme 3).
The anodic oxidation of these derivatives was then
investigated under the optimised conditions to afford
[a]
Reaction conditions: terphenyl 6 (0.50 mmol, 1.0 equiv.),
DDQ (5 mol%), Bu4NBF4 (0.3 M, 1.00 g/chamber),
CH2Cl2/F3CCO2H (10 mL/chamber, 9:1 v/v), carbon fibre
electrodes, 10 mA, room temperature, H-type cell.
Scheme 3. Cobalt-catalysed synthesis of quaterphenyl and
DDQ-catalysed anodic oxidation.
[b]
ce: current efficiency.
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Table 5. Electrochemical oxidative coupling reaction of qua-
terphenyl derivatives for the synthesis of products of type 9.
strates with the terphenyl derivatives 6. Nevertheless,
the DDQ-mediated electrochemical oxidation could
be performed successfully.
Next, we decided to enlarge the scope of oligophe-
nylenes towards unsymmetrical starting materials,
such as the trisbiphenylbenzene derivatives of type 11
(Scheme 4). These materials were obtained by palladi-
um-catalysed cross-coupling of R1-substituted arene-
boronic acids with R2-substituted bromobenzalde-
hydes followed by a Corey–Fuchs reaction to convert
the aldehyde into the terminal alkyne (see below for
experimental details).
Scheme 4. Cobalt-catalysed cyclotrimerization for the syn-
thesis of heptaphenylenes of type 11 or 12.
[a]
Reaction conditions: quaterphenyl
8
(0.50 mmol,
As shown above, the cobalt-catalysed cyclotrimeri-
sation of terminal alkynes led predominantly to 1,2,4-
trisubstituted benzene derivatives. Similar results
were obtained for the application of internal alkyl-
aryl-substituted alkynes where the corresponding re-
gioisomer was isolated. Accordingly, we expected that
alkynyl-substituted biphenyl starting materials of type
1.0 equiv.), DDQ (5 mol%), Bu4NBF4 (0.3 M, 1.00 g/
chamber), CH2Cl2/F3CCO2H (10 mL/chamber, 9:1 v/v),
carbon fibre electrodes, 10 mA, room temperature, H-
type cell.
[b]
ce: current efficiency.
aryl-substituted triphenylenes of type 9. The results 10 would generate the corresponding 1,2,4-substituted
are summarised in Table 5. products 11 (Scheme 4). From there unsymmetrical
Methoxylated quaterphenyl derivatives 9a–c under- coronene derivatives were envisaged after indirect
went the transformation to aryl-substituted tripheny- electrochemical oxidation.
lenes in very good yields and current efficiencies
However, we were surprised to identify the prod-
(Table 5, entries 1–3). Also, no intermolecular carbon- ucts derived from the cobalt-catalysed cyclotrimerisa-
carbon bond formation with the additional phenyl tion reaction as the symmetrical 1,3,5-trisubstituted
ring was observed. Merely derivative 9d was formed isomers of type 12 exclusively. Most likely, the steric
in moderate yield and rather long reaction time, pre- bulkiness of the biaryl moieties forced the cyclotri-
sumably due to a steric hindrance of the methoxy merisation to form the symmetrical product 12. Ac-
groups at the triphenylene core (entry 4). Unfortu- cordingly, with the results of our previous work,[25] we
nately, it was not possible to couple alkylated sub- have identified solvent, ligand as well as substrate ef-
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fects, described herein, of the cobalt-catalysed cyclo-
trimerisation reaction.
Even though the symmetrical product was formed,
still two possible isomers could be formed upon an
electrochemical DDQ-mediated oxidative coupling
reaction (Scheme 5). For once, the planar coronene
derivative 13 could be formed, but also the very inter-
esting non-planar derivative 14 represents a possible
isomer.[26] Therefore, we were very interested to see if
a preference for one or the other product would be
detectable under electrochemical conditions.
Scheme 6. Oxidative coupling of hexaphenyl benzenes 15
under electrochemical conditions.
excellent yields and good to excellent current efficien-
cies of 57% and 92%, respectively. It is noteworthy
that only starting material and product could be ob-
served by TLC analysis when less than 12 F/mol elec-
tricity was applied during the electrolysis of 15b. This
indicates that the first C–C bond being formed is the
slowest. Surprising is the formation of 16a under the
reaction conditions, which has been reported to be
impossible by using a stoichiometric DDQ/H3CSO3H
system. It is conceivable that a combined direct and
indirect electrochemical oxidation took place, where
the first bond was formed by direct oxidative coupling
enabling a further indirect oxidation process.
Scheme 5. Oxidative coupling of trisbiphenylbenzenes 12
under electrochemical conditions.
Although the advantages of an indirect electro-
chemical carbon-carbon bond formation should be
obvious, we would like to illustrate the positive effects
When the trisbiphenylbenzene derivatives of type by a simple comparison: For the formation of 16b, the
12 were subjected to the optimised conditions of the chemical DDQ oxidation on a one gram scale utilised
electrochemical DDQ-mediated oxidative coupling, 1.56 gram of DDQ, resulting in a corresponding
only the coronene products 13 were isolated in ac- amount of spent as well as unreacted DDQ which
ceptable chemical yields and current efficiencies had to be separated from the desired product. In con-
(Scheme 5). Unfortunately, under the indirect electro- trast, the indirect electrochemical DDQ-mediated ox-
chemical conditions no traces of products of type 14 idation utilised 13 milligrams of DDQ. The criticism
were detected but also no other side products could of the need for a supporting electrolyte is absolutely
be isolated. At this point we cannot exclude that understandable in this context. However, the separa-
those products 14 might be formed and lost during re- tion from the supporting electrolyte is rather easy.
crystallisation as well as column chromatography.
Finally, we turned our attention towards the appli-
cation of hexaphenylbenzenes 15a and 15b as starting Conclusions
materials. Since these substrates have been reported
numerous times in the literature, we only selected two In conclusion, we have developed an electrochemical
derivatives for our study (Scheme 6). In these cases intramolecular coupling reaction of arenes applying
the two coronenes 16a and 16b could be isolated in indirect anodic oxidation. The electrochemical synthe-
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ence electrode. The solution was purged with nitrogen
before each measurement. Electrochemical reactions were
carried out in undivided cells with external cooling/heating
circuit or H-type cells. Electrolysis was performed using
a Temna digital-control and programmable DC power
supply (model: 72-10480, 0–30 V, 0–3 A). Carbon fibre elec-
trode material was purchased from R&G Faserverbund-
werkstoffe GmbH Germany (item description: Carbon
roving PyrofilTM TR50S 6k/400 tex). Before use, the
carbon fibres were bound together (850 mg material) and
contacted with a platinum wire.
sis was performed under constant current conditions
in a divided cell using a catalytic amount of DDQ as
redox mediator and a mixture of CH2Cl2 as solvent
and trifluoroacetic acid as additive. Following a de-
tailed optimisation of the reaction conditions, several
terphenyl and quaterphenyl derivatives derived from
simple Suzuki cross-coupling reactions or cobalt-cata-
lysed alkyne trimerizations have been applied in the
reaction and the resulting triphenylene derivatives
were obtained in good to very good yields and excel-
lent current efficiencies. A great advantage of the de-
scribed procedure is in the avoidance of using stoi-
chiometric amounts or large excesses of oxidants,
which simplifies the work-up and minimises side-reac-
tions. This could be demonstrated by the synthesis of
several hexabenzocoronenes from heptaphenylenes
General Procedure for the Suzuki-Type Coupling for
the Preparation of Terphenyl Derivatives 6
The aryl halide (1.0 equiv.) and the boronic acid (1.0–
1.5 equiv./halide) were dissolved in degassed toluene and
and hexaphenylbenzenes where six carbon-carbon aqueous sodium carbonate solution (2.5M, 1:1 v/v, 15–
30 mLmmolꢀ1). Then Pd(PPh3)2Cl2 (5 mol%) was added and
bonds were formed efficiently using just a catalytic
the reaction mixture was refluxed until complete conversion
amount of DDQ instead of over-stoichiometric
was determined by GC-MS analysis (14–20 h). After com-
amounts. Consequently, the electrochemical DDQ-
plete conversion, the mixture was cooled to room tempera-
mediated oxidative coupling of polyaromatic com-
ture, the organic phase was separated and the aqueous
pounds broadens the scope of the Scholl reaction and
phase was extracted with diethyl ether (3ꢃ15 mL). The
serves as a novel efficient straightforward and atom
economical method for such transformations.
combined organic phases were dried over MgSO4, filtered
and the solvent was removed under reduced pressure. The
crude product was purified by flash chromatography (n-pen-
tane/Et2O) or by recrystallisation.
3,3’’-Dimethoxy-1,1’:2’,1’’-terphenyl (6a):[3c] Recrystallisa-
Experimental Section
tion from ethanol (13 mL); white solid; yield: 2.22 g
(7.65 mmol, 77%); 1H NMR (300 MHz, CDCl3): d=7.51–
General Methods
7.40 (m, 4H), 7.16 (t, J=7.9 Hz, 2H), 6.83–6.74 (m, 4H),
All reactions requiring water- or air-sensitive compounds
were carried out in vacuum- and flame-dried flasks utilizing
Schlenk techniques under an argon atmosphere. DCM was
dried over P4O10, while CH3CN was dried over molecular
sieve (3ꢄ) and distilled under a nitrogen atmosphere. ZnI2
was dried under vacuum at 1508C prior to use. 1H NMR
and 13C NMR spectra were recorded at 300 MHz and
75 MHz, respectively, at room temperature utilizing pre-set
pulse programs. The chemical shifts are given relative to tet-
ramethylsilane as an internal standard. The solvent signal
was used for calibration [1H NMR d (CHCl3)=7.26 ppm,
13C NMR d (CHCl3)=77.16 ppm]. Infrared spectra (IR)
were recorded on a FT-IR spectrometer. The absorption
bands are given in wave numbers (cmꢀ1). High resolution
mass spectra (HR-MS) were recorded as electron ionisation
spectra (EI/HR-MS) utilizing a quadrupole mass analyser at
an energy of 70 eV or as electron spray ionisation (ESI/HR-
MS) using an LTQ-FT system. HR-FD mass spectra were
acquired with an AccuTOF GCv 4G (JEOL) Time of Flight
(TOF) mass spectrometer. An internal or external standard
was used for drift time correction. The LIFDI ion source
and FD-emitters were purchased from Linden ChroMasSpec
GmbH. The detected ion masses (m/z) are reported in u cor-
responding to the intensity of the signals as a percentage of
the most intense signal. Cyclic voltammetry measurements
were carried out on a BAS C3 Cell Strand and a BAS 100
Electrochemical Analyser using glassy carbon disk working
electrodes (2.0 mm diameter) and platinum wire counter
electrodes (0.5 mm diameter). Potentials were referred to
a saturated Ag/AgCl (0.3M NaCl or saturated KCl) refer-
6.70 (dd, J=2.6, 1.6 Hz, 2H), 3.63 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=159.3, 143.1, 140.6, 130.5, 129.0, 127.7,
122.4, 115.3, 112.8, 55.3.
3,3’’,4,4’’-Tetramethoxy-1,1’:2’,1’’-terphenyl (6b):[3d] Recrys-
tallisation from ethanol (74 mL); white solid; yield: 6.24 g
(17.8 mmol, 89%); 1H NMR (300 MHz, CDCl3): d=7.49–
7.35 (m, 4H), 6.78 (d, J=1.1 Hz, 4H), 6.62 (t, J=1.2 Hz,
2H), 3.86 (s, 6H), 3.61 (s, 6H); 13C NMR (75 MHz, CDCl3):
d=148.5, 148.0, 140.4, 134.6, 130.5, 127.4, 122.0, 113.8, 111.1,
56.1, 55.9.
4,4’,4’’,5’-Tetramethoxy-1,1’:2’,1’’-terphenyl (6c): Recrystal-
lisation from ethanol (25 mL); white solid; yield: 915 mg
(2.61 mmol, 87%); mp 140–1418C; 1H NMR (300 MHz,
CDCl3): d=7.12–7.02 (m, 4H), 6.90 (s, 2H), 6.83–6.72 (m,
4H), 3.93 (s, 6H), 3.79 (s, 6H); 13C NMR (75 MHz, CDCl3):
d=158.3, 148.2, 134.2, 132.7, 131.1, 113.9, 113.6, 56.2, 55.3;
IR (ATR): n=3000, 2956, 2836, 1604, 1495, 1461, 1440,
1234, 1170, 1110, 1024, 915, 871, 830, 808, 781, 617, 537; MS
(EI+): m/z=350 (100, [M]+), 335 (10), 307 (25), 292 (3), 261
(5), 233 (3), 189 (5), 152 (4), 132 (7), 89 (2); HR-MS (EI+):
m/z=350.1510, calculated for C22H22O4 ([M]+): 350.1518.
1,2-Bis(benzo[d][1,3]dioxol-5-yl)benzene (6d): Recrystal-
lisation from ethanol (25 mL); white solid; yield: 688 mg
(2.16 mmol, 72%); mp 125–1278C; 1H NMR (300 MHz,
CDCl3): d=7.36 (s, 4H), 6.71 (d, J=8.4 Hz, 2H), 6.67–6.58
(m, 4H), 5.93 (s, 4H); 13C NMR (75 MHz, CDCl3): d=
147.4, 146.4, 140.3, 135.7, 130.7, 127.4, 123.4, 110.4, 108.1,
101.0; IR (ATR): n=2956, 2904, 2868, 1602, 1497, 1459,
1384, 1353, 1262, 1235, 1201, 1160, 1114, 1028, 918, 869, 832,
795, 738, 654, 568; MS (EI+): m/z=318 (100, [M]+), 287 (8),
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259 (15), 231 (6), 202 (23), 189 (4), 158 (7), 129 (4), 101 (15),
75 (2); HR-MS (EI+): m/z=318.0891, calculated for
C20H14O4 ([M]+): 318.0892.
186 (11), 158 (9), 115 (3), 59 (23); HR-MS (EI+): m/z=
402.2555, calculated for C28H34O2 ([M]+): 402.2559.
4,4’’-Dichloro-4’,5’-dimethoxy-1,1’:2’,1’’-terphenyl
(6j):
Flash chromatography (eluent: n-pentane/diethyl ether 5:1);
3,3’’-Bis(methylthio)-1,1’:2’,1’’-terphenyl (6e): Flash chro-
matography (eluent: n-pentane/diethyl ether 50:1); white
solid; yield: 1.38 g (4.29 mmol, 81%); mp 69–718C;
1H NMR (300 MHz, CDCl3): d=7.48–7.41 (m, 4H), 7.20–
7.09 (m, 4H), 7.04–6.91 (m, 4H), 2.26 (s, 6H); 13C NMR
(75 MHz, CDCl3): d=142.2, 140.2, 138.2, 130.5, 128.5, 128.4,
127.9, 126.8, 125.4, 16.0; IR (ATR): n=3054, 2976, 2917,
2863, 1585, 1562, 1462, 1433, 1396, 1262, 1165, 1093, 1026,
960, 878, 788, 754, 695; MS (EI+): m/z=322 (100, [M]+), 274
(24), 260 (17), 259 (24), 228 (46); HR-MS (EI+): m/z=
322.0850, calculated for C20H18S2 ([M]+): 322.0850.
white solid; yield: 677 mg (1.86 mmol, 93%); mp 150–
1
1528C; H NMR (300 MHz, CDCl3): d=7.24–7.16 (m, 4H),
7.09–7.00 (m, 4H), 6.88 (s, 2H), 3.94 (s, 6H); 13C NMR
(75 MHz, CDCl3): d=148.8, 139.8, 132.7, 132.0, 131.3, 128.4,
113.8, 56.3; IR (ATR): n=2991, 2959, 2931, 2904, 2835,
1599, 1519, 1483, 1459, 1347, 1246, 1203, 1163, 1086, 1029,
869, 827, 731, 700; MS (EI+): m/z=358 (100, [M]+), 343
(10), 315 (22), 265 (13), 215 (6), 202 (24), 189 (2), 162 (4),
136 (16), 125 (3), 100 (7), 75 (4); HR-MS (EI+): m/z=
358.0521, calculated for C20H16Cl2O2 ([M]+): 358.0527.
(4’,5’-Dimethoxy-[1,1’:2’,1’’-terphenyl]-4,4’’-diyl)bis(me-
thylsulfane) (6f): Recrystallisation from ethanol (21 mL);
white solid; yield: 681 mg (1.78 mmol, 89%); mp 135–
General Procedure for the Suzuki-Type Coupling for
the Synthesis of 1,1’-Biphenyl-2-carbaldehydes
1
1378C; H NMR (300 MHz, CDCl3): d=7.09 (q, J=8.5 Hz,
8H), 6.90 (s, 2H), 3.93 (s, 6H), 2.47 (s, 6H); 13C NMR
(75 MHz, CDCl3): d=148.5, 138.4, 136.6, 132.5, 130.5, 126.3,
113.9, 56.2, 15.9; IR (ATR): n=2963, 2920, 2839, 1598, 1546,
1516, 1483, 1441, 1384, 1347, 1259, 1232, 1204, 1160, 1095,
961, 862, 824, 793, 735, 638; MS (EI+): m/z=382 (100,
[M]+), 367 (6), 339 (17), 320 (3), 292 (13), 245 (7), 202 (9),
148 (10), 105 (11), 77 (9); HR-MS (EI+): m/z=382.1062, cal-
culated for C22H22O2S2 ([M]+): 382.1061.
Pd(PPh3)2Cl2 (5 mol%) and sodium carbonate (2.0 equiv.)
were dissolved in a degassed mixture of toluene/water/etha-
nol (6:3:1 v/v/v). The 2-bromobenzaldehyde (1.0 equiv.) and
the boronic acid (1.2 equiv.) were added and the reaction
mixture was refluxed for until complete conversion was de-
termined by GC-MS and TLC analysis (5–6 h). The mixture
was cooled to room temperature, diethyl ether (10 mL) was
added, the organic phase was separated and the aqueous
phase was extracted with diethyl ether (3x 15 mL). The com-
bined organic phases were dried over MgSO4, filtered and
the solvent was removed under reduced pressure. The crude
product was purified by flash chromatography.
4’,5’-Dimethoxy-3,3’’,4,4’’-tetramethyl-1,1’:2’,1’’-terphenyl
(6g): Recrystallisation from ethanol (16 mL); white solid;
1
yield: 631 mg (1.82 mmol, 91%); mp 105–1088C; H NMR
(300 MHz, CDCl3): d=7.01 (d, J=2.0 Hz, 2H), 6.98–6.90
(m, 4H), 6.82 (dd, J=7.8, 2.0 Hz, 2H), 3.94 (s, 6H), 2.23 (s,
6H), 2.20 (s, 6H); 13C NMR (75 MHz, CDCl3): d=147.9,
139.1, 135.9, 134.3, 133.0, 130.9, 129.0, 127.4, 113.8, 56.0,
19.7, 19.3; IR (ATR): n=3003, 2913, 2837, 1601, 1493, 1445,
1867, 1338, 1237, 1203, 1177, 1146, 1031, 859, 813, 774, 583;
MS (EI+): m/z=346 (100, [M]+), 331 (5), 303 (19), 288 (2),
273 (12), 259 (4), 245 (7), 230 (8), 215 (5), 197 (2), 173 (2),
158 (4), 115 (3); HR-MS (EI+): m/z=346.1921, calculated
for C24H26O2 ([M]+): 346.1933.
3’-Methoxy-[1,1’-biphenyl]-2-carbaldehyde:[27] Flash chro-
matography (eluent: n-pentane/diethyl ether 10:1); colour-
1
less oil; yield: 2.06 g (9.70 mmol, 97%); H NMR (300 MHz,
CDCl3): d=10.00 (s, 1H), 8.02 (dd, J=7.8, 1.5 Hz, 1H), 7.63
(td, J=7.5, 1.5 Hz, 1H), 7.55–7.42 (m, 2H), 7.38 (t, J=
7.9 Hz, 1H), 7.03–6.89 (m, 3H), 3.85 (s, 3H); 13C NMR
(75 MHz, CDCl3): d=192.5, 159.7, 146.0, 139.3, 134.0, 133.6,
130.7, 129.6, 128.0, 127.6, 122.9, 115.8, 113.8, 55.5.
3’-Methoxy-5-methyl-[1,1’-biphenyl]-2-carbaldehyde:
3,3’’-Di-tert-butyl-4’,5’-dimethoxy-1,1’:2’,1’’-terphenyl (6h):
Recrystallisation from ethanol (15 mL); white solid; yield:
773 mg (1.92 mmol, 96%); mp 82–858C; 1H NMR
(300 MHz, CDCl3): d=7.26–7.08 (m, 6H), 7.03–6.96 (m,
4H), 3.96 (s, 6H), 1.09 (s, 18H); 13C NMR (75 MHz,
CDCl3): d=150.6, 148.3, 141.2, 134.0, 128.3, 127.9, 126.6,
123.1, 113.8, 56.3, 34.5, 31.3; IR (ATR): n=3056, 2956, 2905,
2868, 2838, 1601, 1515, 1475, 1457, 1414, 1386, 1350, 1321,
1252, 1234, 1206, 1165, 1030, 860, 795, 754, 708, 602; MS
(EI+): m/z=402 (100, [M]+), 387 (4), 359 (4), 331 (7), 319
(22), 301 (4), 270 (10), 241 (3), 207 (5), 165 (2), 128 (2), 91
(7), 67 (2), 57 (29); HR-MS (EI+): m/z=402.2559, calculated
for C28H34O2 ([M]+): 402.2559.
Flash chromatography (eluent: n-pentane/diethyl ether
15:1!10:1!5:1); colourless oil; yield: 1.07 g (4.72 mmol,
1
94%); H NMR (300 MHz, CDCl3): d=9.95 (d, J=0.9 Hz,
1H), 7.94 (d, J=7.9 Hz, 1H), 7.37 (t, J=7.9 Hz, 1H), 7.30
(d, J=9.0 Hz, 1H), 7.25 (d, J=1.6 Hz, 1H), 7.01–6.89 (m,
3H), 3.86 (s, 3H), 2.47 (s, 3H); 13C NMR (75 MHz, CDCl3):
d=192.2, 159.7, 146.1, 144.6, 139.5, 131.7, 131.3, 129.5, 128.9,
127.7, 122.8, 115.8, 113.7, 55.5, 21.9; IR (ATR): n=3002,
2944, 2841, 2753, 1685, 1598, 1481, 1457, 1428, 1397, 1282,
1265, 1220, 1165, 1119, 1033, 874, 824, 785, 700; MS (EI+):
m/z=226 (100, [M]+), 211 (17), 198 (79), 183 (9), 167 (29),
155 (30), 128 (11), 89 (5), 63 (7); HR-MS (EI+): m/z=
226.0990, calculated for C15H14O2 ([M]+): 226.0994.
4,4’’-Di-tert-butyl-4’,5’-dimethoxy-1,1’:2’,1’’-terphenyl (6i):
Recrystallisation from ethanol (15 mL); white solid; yield:
1.14 g (2.81 mmol, 94%);: mp 120–1228C; 1H NMR
(300 MHz, CDCl3): d=7.25–7.18 (m, 4H), 7.11–7.03 (m,
4H), 6.95 (s, 2H), 3.94 (s, 6H), 1.31 (s, 18H); 13C NMR
(75 MHz, CDCl3): d=149.2, 148.2, 138.7, 133.2, 129.7, 124.8,
114.0, 56.2, 34.5, 31.5; IR (ATR): n=2956, 2904, 2868, 1602,
1497, 1459, 1384, 1353, 1262, 1235, 1201, 1160, 1114, 1028,
918, 869, 832, 795, 738, 654, 568; MS (EI+): m/z=402 (100,
[M]+), 387 (56), 359 (1), 316 (12), 274 (2), 241 (2), 215 (3),
3’-(tertButyl)-[1,1’-biphenyl]-2-carbaldehyde: Flash chro-
matography (eluent: n-pentane/diethyl ether 50:1!25:1);
colourless oil; yield: 1.14 g (4.78 mmol, 91%); 1H NMR
(300 MHz, CDCl3): d=9.99 (d, J=0.8 Hz, 1H), 8.10–7.99
(m, 1H), 7.65 (td, J=7.5, 1.5 Hz, 1H), 7.55–7.45 (m, 3H),
7.45–7.34 (m, 2H), 7.21 (dt, J=7.4, 1.5 Hz, 1H), 1.37 (s,
9H); 13C NMR (75 MHz, CDCl3): d=192.7, 151.6, 146.7,
137.6, 134.0, 133.6, 130.9, 128.3, 127.8, 127.6, 127.5, 127.3,
125.2, 34.9, 31.5; IR (ATR): n=3062, 2960, 2905, 2867, 2751,
1690, 1596, 1472, 1393, 1364, 1265, 1245, 1194, 826, 801, 762,
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708, 627; MS (EI+): m/z=238 (66, [M]+), 223 (100), 205
(58), 195 (20), 181 (57), 165 (37), 152 (28), 139 (4), 104 (9),
77 (7), 57 (10); HR-MS (EI+): m/z=238.1358, calculated for
C17H18O ([M]+): 238.1358.
General Procedure for the Cobalt-Catalysed
Cyclotrimerisation of Alkynes
Under an argon atmosphere cobalt(II) bromide (10 mol%),
zinc powder (10 mol%) and anhydrous zinc iodide
(10 mol%) were dissolved in acetonitrile (2 mLmmolꢀ1).
The alkyne (1.0 equiv.) was added and the reaction mixture
was stirred at ambient temperature until complete conver-
sion was determined by TLC analysis (1 h). After complete
reaction n-pentane was added followed by filtration over
a plug of silica (eluent: n-pentane/diethyl ether) and the sol-
vent was removed. The crude product was suspended in eth-
anol (1 mLmmolꢀ1) and heated to reflux. More ethanol was
added until the remaining solid had dissolved completely.
Then, water was added until precipitation was observed and
the mixture was cooled over 16 h. The solid was filtered off
and dried under reduced pressure to give the product.
General Procedure for the Corey–Fuchs Reaction
PPh3 (3.6 equiv.) was dissolved in dichloromethane
(3 mLmmolꢀ1), CBr4 (1.8 equiv.) was added slowly at 08C
and the solution was stirred for 15 min. Then, the [1,1’-bi-
phenyl]-2-carbaldehyde (1.0 equiv.) was added and the mix-
ture was stirred for 2 h at room temperature. The mixture
was concentrated, n-pentane (2 mLmmolꢀ1) was added, the
mixture was filtered over a plug of silica (eluent: n-pentane/
dichloromethane 5:1) and the solvent was removed under
reduced pressure. The resulting dibromo-olefin was dis-
solved in tetrahydrofuran (1 mLmmolꢀ1), the mixture was
cooled to ꢀ358C and n-BuLi (2.5M in hexane, 2.2 equiv.)
was added. The mixture was allowed to warm up to room
temperature and was stirred until completion was deter-
mined by GC-MS and TLC analysis (2 h). It was quenched
with saturated aqueous NH4Cl solution, the organic phase
was separated and washed with brine (3ꢃ15 mL) and the
aqueous phase was extracted with diethyl ether (3ꢃ15 mL).
The combined organic phases were dried over MgSO4 and
the solvent was removed under reduced pressure. The crude
product was purified by flash chromatography.
4,4’’-Dimethoxy-4’-(4-methoxyphenyl)-1,1’:2’,1’’-terphenyl
(8a):[24b] Recrystallisation from ethanol/water (23 mL, 2:1 v/
1
v); yellow solid; yield: 456 mg (1.15 mmol, 87%); H NMR
(300 MHz, CDCl3): d=7.67–7.55 (m, 4H), 7.45 (dd, J=7.8,
0.7 Hz, 1H), 7.20–7.06 (m, 4H), 7.08–6.95 (m, 2H), 6.80 (dq,
J=8.4, 3.0 Hz, 4H), 3.87 (s, 3H), 3.81 (s, 3H), 3.80 (s, 3H);
13C NMR (75 MHz, CDCl3): d=159.4, 158.5, 158.4, 140.6,
139.8, 138.6, 134.3, 133.9, 133.4, 131.15, 131.11, 131.0, 129.1,
128.2, 125.5, 114.4, 113.6, 113.6, 55.5, 55.32, 55.26.
3,3’’-Dimethoxy-4’-(3-methoxyphenyl)-1,1’:2’,1’’-terphenyl
(8b): Flash chromatography (eluent: n-pentane/diethyl ether
5:1); yellow oil; yield: 1.46 g (3.68 mmol, 91%); 1H NMR
(300 MHz, CDCl3): d=7.71–7.63 (m, 2H), 7.53 (d, J=
7.9 Hz, 1H), 7.39 (t, J=7.9 Hz, 1H), 7.32–7.14 (m, 4H), 6.94
(dd, J=8.2, 2.5 Hz, 1H), 6.87–6.72 (m, 6H), 3.89 (s, 3H),
3.65 (s, 3H), 3.64 (s, 3H); 13C NMR (75 MHz, CDCl3): d=
160.2, 159.4, 159.3, 143.0, 142.6, 142.3, 141.0, 140.5, 139.8,
131.0, 130.0, 129.4, 129.10, 129.07, 126.4, 122.5, 122.4, 119.8,
115.4, 115.3, 113.1, 113.0, 112.98, 112.9, 55.5, 55.29, 55.27; IR
(ATR): n=2999, 2939, 2836, 1582, 1518, 1485, 1448, 1243,
1212, 1134, 1020, 867, 809, 761; MS (EI+): m/z=396 (100,
[M]+), 365 (10), 333 (7), 278 (5), 198 (5), 144 (3), 91 (5);
HR-MS (EI+): m/z=396.1727, calculated for C27H24O3
([M]+): 396.1725.
2-Ethynyl-3’-methoxy-1,1’-biphenyl (10a):[28] Flash chro-
matography (eluent: n-pentane/diethyl ether 10:1!7:1); col-
ourless oil; yield: 1.47 g (7.07 mmol, 75%); 1H NMR
(300 MHz, CDCl3): d=7.67 (dt, J=7.6, 1.1 Hz, 1H), 7.49–
7.27 (m, 4H), 7.25–7.18 (m, 2H), 6.97 (ddd, J=8.2, 2.5,
1.1 Hz, 1H), 3.90 (s, 3H), 3.11 (s, 1H); 13C NMR (75 MHz,
CDCl3): d=159.4, 144.4, 141.8, 134.1, 129.7, 129.1, 129.1,
127.2, 121.8, 120.6, 115.0, 113.5, 83.3, 80.4, 55.4.
2-Ethynyl-3’-methoxy-5-methyl-1,1’-biphenyl (10b): Flash
chromatography (eluent: n-pentane/diethyl ether 7:1!5:1);
white solid; yield: 1.28 g (5.76 mmol, 65%); mp 55–588C;
1H NMR (300 MHz, CDCl3): d=7.53 (d, J=7.8 Hz, 1H),
7.35 (t, J=8.1 Hz, 1H), 7.24–7.08 (m, 4H), 6.93 (ddd, J=
8.3, 2.6, 1.1 Hz, 1H), 3.86 (s, 3H), 3.03 (s, 1H), 2.41 (s, 3H);
13C NMR (75 MHz, CDCl3): d=159.3, 144.3, 141.9, 139.2,
134.0, 130.4, 129.1, 128.0, 121.8, 117.6, 114.9, 113.5, 83.4,
79.7, 55.4, 21.6; IR (ATR): n=3272, 3034, 2999, 2966, 2933,
2836, 1603, 1574, 1462, 1431, 1218, 1166, 1031, 870, 828, 783,
696, 656, 622, 543, 508; MS (EI+): m/z=222 (100, [M]+), 207
(40), 179 (78), 152 (12), 111 (3), 89 (3), 63 (2); HR-MS
(EI+): m/z=222.1033, calculated for C16H14O ([M]+):
222.1045.
3’-(tertButyl)-2-ethynyl-1,1’-biphenyl (10c): Flash chroma-
tography (eluent: n-pentane/diethyl ether 50:1); red oil;
yield: 906 mg (3.87 mmol, 92%); 1H NMR (300 MHz,
CDCl3): d=7.71 (q, J=1.4 Hz, 1H), 7.63 (d, J=7.5 Hz, 1H),
7.50–7.34 (m, 5H), 7.31 (dq, J=8.7, 4.1 Hz, 1H), 3.04 (s,
1H), 1.37 (s, 9H); 13C NMR (75 MHz, CDCl3): d=150.7,
145.1, 139.9, 134.1, 129.8, 129.1, 127.9, 127.1, 127.0, 126.3,
124.5, 120.6, 83.6, 80.1, 35.0, 31.5; IR (ATR): n=3287, 3061,
2959, 2868, 1598, 1471, 1409, 1363, 1241, 1205, 1098, 965,
798, 757, 705, 635, 611; MS (EI+): m/z=234 (8, [M]+), 219
(30), 202 (15), 189 (7), 179 (41), 165 (5), 150 (3), 109 (2), 101
(5), 95 (5), 82 (7), 57 (33); HR-MS (EI+): m/z=234.1420,
calculated for C18H18 ([M]+): 234.1409.
4’-(3,4-Dimethoxyphenyl)-3,3’’,4,4’’-tetramethoxy-
1,1’:2’,1’’-terphenyl (8c):[24a] Recrystallisation from ethanol
(17 mL); yellow solid; yield: 596 mg (1.23 mmol, 78%);
1H NMR (300 MHz, CDCl3): d=7.61–7.47 (m, 2H), 7.42 (d,
J=7.9 Hz, 1H), 7.17–7.07 (m, 2H), 6.89 (d, J=8.3 Hz, 1H),
6.81–6.67 (m, 4H), 6.58 (dd, J=9.6, 1.7 Hz, 2H), 3.88 (s,
3H), 3.86 (s, 3H), 3.79 (s, 3H), 3.77 (s, 3H), 3.55 (s, 3H),
3.54 (s, 3H); 13C NMR (75 MHz, CDCl3): d=149.5, 149.0,
148.6, 148.5, 148.1, 148.0, 140.7, 140.2, 139.0, 134.6, 134.2,
133.8, 130.9, 128.9, 125.8, 122.0, 122.0, 119.6, 113.8, 113.7,
111.8, 111.12, 111.09, 110.7, 56.2 (2C), 56.1, 56.0, 55.9, 55.8.
4’-(3,5-Dimethoxyphenyl)-3,3’’,5,5’’-tetramethoxy-
1,1’:2’,1’’-terphenyl (8d): Recrystallisation from ethanol
(24 mL); yellow solid; yield: 753 mg (1.55 mmol, 75%); mp
167–1688C; 1H NMR (300 MHz, CDCl3): d=7.67 (d, J=
1.9 Hz, 1H), 7.63 (dd, J=7.9, 2.0 Hz, 1H), 7.52 (d, J=
7.9 Hz, 1H), 6.81 (d, J=2.3 Hz, 2H), 6.50 (t, J=2.2 Hz,
1H), 6.41 (d, J=2.3 Hz, 2H), 6.39 (d, J=2.2 Hz, 2H), 6.35
(dt, J=4.4, 2.3 Hz, 2H), 3.86 (s, 6H), 3.65 (s, 6H), 3.65 (s,
6H); 13C NMR (75 MHz, CDCl3): d=161.3 (2C), 160.50
(2C), 160.45 (2C), 143.6, 143.2, 142.9, 141.0, 140.7, 139.9,
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130.8, 129.1, 126.4, 108.1 (2C), 108.0 (2C), 105.6 (2C), 99.8,
99.52, 99.46, 55.6 (2C), 55.49 (2C), 55.46 (2C); IR (ATR):
n=3009, 2937, 2837, 1591, 1456, 1422, 1332, 1199, 1046,
1031, 935, 860, 830, 699, 568; MS (EI+): m/z=486 (100,
[M]+), 471 (7), 455 (7), 364 (9), 243 (7), 191 (2), 84 (17);
HR-MS (EI+): m/z=486.2045, calculated for C30H30O6
([M]+): 486.2042.
5’’-([3’-Methoxy-1,1’-biphenyl]-2-yl)-1,1’:2’,1’’:3’’,1’’’:2’’’,1’’’’-
quinquephenyl (12a): Recrystallisation from ethanol
(31 mL); dark red solid; yield: 756 mg (1.21 mmol, 75%);
mp 208–2108C; 1H NMR (300 MHz, CDCl3): d=7.33–7.22
(m, 6H), 7.18 (td, J=7.1, 1.8 Hz, 3H), 7.11 (t, J=7.9 Hz,
3H), 6.75 (s, 3H), 6.72 (s, 6H), 6.66 (s, 3H), 6.49 (d, J=
7.6 Hz, 3H), 3.62 (s, 9H); 13C NMR (75 MHz, CDCl3): d=
159.5, 143.2, 140.8, 140.50, 140.45, 130.6, 130.3, 129.8, 129.0,
127.5, 127.4, 123.1, 115.8, 112.3, 55.4; IR (ATR): n=3052,
2937, 2831, 1582, 1470, 1416, 1294, 1263, 1294, 1263, 1209,
1167, 1046, 1017, 881, 858, 755, 697, 617; MS (EI+): m/z=
624 (100, [M]+), 592 (1), 486 (31), 427 (6), 363 (3), 312 (1),
243 (2), 195 (9), 130 (2), 68 (4); HR-MS (EI+): m/z=
624.2668, calculated for C45H36O3 ([M]+): 624.2664.
TLC and GC-MS analysis. After complete conversion the
solution was diluted with dichloromethane (15–30 mL) and
the organic phase was neutralised with aqueous ammonia
solution (20 mL, 5M) (the electrodes should be rinsed thor-
oughly) and the organic phase was separated. The aqueous
phase was extracted (3ꢃ10 mL) and the combined organic
phases were dried over MgSO4, filtered and the solvent was
removed under reduced pressure. The crude product was
purified by column chromatography (n-pentane/diethyl
ether) or by recrystallisation.
2,7-Dimethoxytriphenylene (7a):[22] Flash chromatography
(eluent: n-pentane/diethyl ether 3:1!1:1); white solid;
yield: 97 mg (0.43 mmol, 85%, 2.05 F, 82% ce); 1H NMR
(300 MHz, CDCl3): d=8.61–8.51 (m, 2H), 8.42 (d, J=
9.0 Hz, 2H), 8.01 (d, J=2.7 Hz, 2H), 7.73–7.57 (m, 2H),
7.24 (dd, J=9.0, 2.6 Hz, 2H), 4.01 (s, 6H); 13C NMR
(75 MHz, CDCl3): d=158.4, 130.3, 130.1, 127.2, 124.5, 124.1,
123.5, 116.0, 106.0, 55.6.
2,3,6,7-Tetramethoxytriphenylene (7b):[3d] Flash chroma-
tography (eluent: dichloromethane/methanol 3:1!1:1);
white solid; yield: 160 mg (0.46 mmol, 92%, 2.01 F, 91% ce);
1H NMR (300 MHz, CDCl3): d=8.44 (dt, J=7.4, 3.6 Hz,
2H), 7.91 (s, 2H), 7.67 (s, 2H), 7.59 (ddd, J=6.3, 3.3,
1.0 Hz, 2H), 4.10 (br s, 12H); 13C NMR (75 MHz, CDCl3):
d=149.5, 149.0, 129.0, 126.1, 124.0, 123.6, 122.9, 104.8, 104.4,
56.2, 56.1.
5’’-([3’-Methoxy-4-methyl-1,1’-biphenyl]-2-yl)-
1,1’:2’,1’’:3’’,1’’’:2’’’,1’’’’-quinquephenyl (12b): Recrystallisation
from ethanol (45 mL); dark red solid; yield: 533 mg
(0.80 mmol, 53%); mp 232–2348C; 1H NMR (300 MHz,
CDCl3): d=7.17 (s, 3H), 7.14–7.07 (m, 5H), 6.99 (dd, J=
7.9, 1.8 Hz, 3H), 6.82 (t, J=8.0 Hz, 2H), 6.78–6.68 (m, 4H),
6.68–6.63 (m, 5H), 6.53–6.44 (m, 2H), 3.61 (s, 9H), 2.30 (s,
9H); 13C NMR (75 MHz, CDCl3): d=159.4, 143.2, 140.5,
140.2, 137.7, 136.9, 130.9, 130.4, 129.5, 128.8, 128.1, 122.9,
115.5, 112.1, 55.2, 21.0; IR (ATR): n=2999, 2918, 2832,
1598, 1579, 1475, 1458, 1426, 1312, 1282, 1260, 1221, 1167,
1038, 877, 816, 783, 697; MS (EI+): m/z=666 (34, [M]+), 486
(100), 471 (7), 222 (58), 207 (22), 178 (21), 152 (8), 131 (12),
105 (11), 91 (13), 68 (20); HR-MS (EI+): m/z=666.3121, cal-
culated for C48H42O3 ([M]+): 666.3134.
2,3,7,10-Tetramethoxytriphenylene (7c): Flash chromatog-
raphy (eluent: n-pentane/diethyl ether 1:1); white solid;
yield: 168 mg (0.48 mmol, 96%, 2.11 F, 91% ce); mp 157–
1
1598C; H NMR (300 MHz, CDCl3): d=8.35 (d, J=9.0 Hz,
2H), 7.92 (d, J=2.6 Hz, 2H), 7.82 (s, 2H), 7.25 (dd, J=9.0,
2.5 Hz, 2H), 4.09 (s, 6H), 4.02 (s, 6H); 13C NMR (75 MHz,
CDCl3): d=158.2, 149.0, 130.3, 124.5, 124.2, 123.3, 115.8,
106.2, 104.4, 56.1, 55.6; IR (ATR): n=3097, 2995, 2927,
2833, 2065, 1612, 1505, 1452, 1417, 1346, 1306, 1259, 1205,
1162, 1045, 1021, 924, 831, 796, 574, 537; MS (EI+): m/z=
348 (100, [M]+), 333 (20), 318 (2), 305 (22), 290 (12), 274
(5), 262 (8), 247 (8), 219 (7), 174 (12), 131 (5), 100 (2), 57
(1); HR-MS (EI+): m/z=348.1372, calculated for C22H20O4
([M]+): 348.1362.
Triphenyleno[2,3-d:6,7-d’]bis([1,3]dioxole) (7d): Flash
chromatography (eluent: diethyl ether); pale yellow solid;
yield: 115 mg (0.36 mmol, 73%, 2.01 F, 70% ce); mp 162–
1648C. The compound is too poorly soluble in organic sol-
vents for NMR analysis. CHN analysis: (C20H12O4, MW:
316.31 gmolꢀ1); found (calculated): C: 75.89% (75.94%), H:
3.75% (3.82%); IR (ATR): n=2960, 2919, 1725, 1501, 1453,
1377, 1255, 1206, 1092, 1028, 935, 901, 852, 797, 749, 700,
618; MS (EI+): m/z=316 (100, [M]+), 293 (11), 258 (6), 228
(7), 200 (22), 149 (41), 127 (7), 100 (11), 71 (15), 69 (10), 57
(19); HR-MS (EI+): m/z= calculated for C20H12O4 ([M]+):
316.0736; found: 316.0747.
5’’-([3’-(tert-Butyl)-1,1’-biphenyl]-2-yl)-
1,1’:2’,1’’:3’’,1’’’:2’’’,1’’’’-quinquephenyl (12c): Recrystallisation
from ethanol (14 mL); yellow solid; yield: 584 mg
(0.83 mmol, 71%); mp 178–1808C; 1H NMR (300 MHz,
CDCl3): d=7.40 (s, 3H), 7.33 (td, J=6.7, 5.8, 1.5 Hz, 3H),
7.29–7.27 (m, 2H), 7.25 (dd, J=2.2, 1.2 Hz, 2H), 7.23 (d, J=
2.6 Hz, 2H), 7.19 (dq, J=4.4, 1.4 Hz, 4H), 7.17–7.10 (m,
4H), 6.79–6.58 (m, 7H), 1.19 (s, 27H); 13C NMR (75 MHz,
CDCl3): d=150.9, 141.5, 141.1, 140.4, 140.2, 130.2, 130.1,
129.8, 127.5, 127.4, 127.3, 127.1, 127.0, 123.2, 34.6, 31.3; IR
(ATR): n=3057, 2958, 2867, 1595, 1473, 1407, 1362, 1259,
1091, 1021, 895, 866, 797, 753, 706; MS (EI+): m/z=703
(100, [M]+), 645 (57), 568 (19), 493 (21), 473 (11), 305 (5),
209 (15), 133 (19); HR-MS (EI+): m/z=703.4220, calculated
for C54H54 ([M]+): 703.4226.
2,7-Bis(methylthio)triphenylene (7e): Flash chromatogra-
phy (eluent: n-pentane/diethyl ether 50:1!20:1!10:1);
white solid; yield: 97 mg (0.30 mmol, 61%, 2.02 F, 60% ce);
mp 164–1658C; 1H NMR (300 MHz, CDCl3): d=8.58 (dd,
J=6.2, 3.4 Hz, 2H), 8.45 (dd, J=5.4, 3.4 Hz, 4H), 7.65 (dd,
J=6.3, 3.3 Hz, 2H), 7.53 (dd, J=8.5, 1.9 Hz, 2H), 2.67 (s,
6H); 13C NMR (75 MHz, CDCl3): d=137.5, 130.1, 129.6,
127.6, 127.3, 126.4, 123.7, 123.4, 121.1, 16.4; IR (ATR): n=
3054, 2960, 2920, 2854, 1726, 1591, 1432, 1399, 1258, 1091,
1018, 956, 868, 796, 757, 696, 586; MS (EI+): m/z=320 (100,
General Procedure for the Electrochemical DDQ-
Mediated Oxidative Coupling
In an H-type cell the anodic chamber was charged with sub-
strate (1.0 equiv.) and DDQ (5 mol%). In addition, both
chambers were charged with TBABF4 (0.3M, 1.00 g/cham-
ber) and dichloromethane/trifluoroacetic acid (10 mL/cham-
ber, 9:1 v/v). The cell was equipped with carbon fibre elec-
trodes and electrolysed at room temperature under constant
current (10 mA). The reaction progress was monitored by
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[M]+), 305 (56), 274 (19), 258 (54), 246 (17), 231 (20), 226
(23), 149 (15), 97 (5), 71 (10), 57 (16); HR-MS (EI+): m/z=
320.0712, calculated for C20H16S2 ([M]+): 320.0693.
123.3, 123.0, 104.2, 56.1; IR (ATR): n=3578, 3004, 2930,
2840, 1725, 1609, 1497, 1457, 1414, 1297, 1266, 1203, 1166,
1142, 1098, 1024, 865, 838, 798, 734, 548, 485; MS (EI+): m/
z=356 (100, [M]+), 313 (14), 278 (43), 251 (3), 200 (19), 149
(8), 99 (5); HR-MS (EI+): m/z=356.0379, calculated for
C20H14Cl2O2 ([M]+): 356.0371.
(6,7-Dimethoxytriphenylene-2,11-diyl)bis(methylsulfane)
(7f): Flash chromatography (eluent: n-pentane/diethyl ether
5:1!3:1); yellow solid; yield: 128 mg (0.34 mmol, 67%,
2.39 F, 56% ce); mp 172–1758C; 1H NMR (300 MHz,
CDCl3): d=8.31 (d, J=2.0 Hz, 2H), 8.25 (dd, J=8.7, 4.1 Hz,
2H), 7.77 (s, 2H), 7.50–7.32 (m, 2H), 4.03 (d, J=2.2 Hz,
6H), 2.59 (s, 6H); 13C NMR (75 MHz, CDCl3): d=149.6,
136.4, 129.1, 127.6, 126.6, 123.8, 123.5, 121.4, 104.5, 56.2,
16.6; IR (ATR): n=2560, 2917, 2855, 1601, 1533, 1496, 1440,
1402, 1261, 1199, 1159, 1091, 1017, 866, 837, 791, 587; MS
(EI+): m/z=380 (100, [M]+), 365 (16), 322 (6), 290 (23), 275
(6), 232 (4), 190 (10), 147 (6), 116 (3); HR-MS (EI+): m/z=
380.0901, calculated for C22H20O2S2 ([M]+): 380.0905.
2,11-Dimethoxy-6-(4-methoxyphenyl)triphenylene
(9a):[24a] Flash chromatography (eluent: n-pentane/dichloro-
methane 1:1); white solid; yield: 153 mg (0.39 mmol, 79%,
1
2.07 F, 77% ce); H NMR (300 MHz, CDCl3): d=8.53 (t, J=
2.4 Hz, 1H), 8.52–8.39 (m, 1H), 8.36 (dt, J=6.3, 3.8 Hz,
2H), 7.98–7.76 (m, 2H), 7.63 (dq, J=8.8, 2.1 Hz, 3H), 7.22–
7.07 (m, 2H), 7.03–6.93 (m, 2H), 3.92 (s, 6H), 3.82 (s, 3H);
13C NMR (75 MHz, CDCl3): d=159.0, 158.9, 158.8, 138.5,
138.4, 133.9, 131.2, 130.9, 129.1, 128.8, 127.6, 126.3, 125.0,
124.9, 124.3, 124.2, 123.3, 120.6, 115.7, 115.6, 115.5, 114.9,
114.5, 114.5, 55.6, 55.54, 55.49.
2,3-Dimethoxy-6,7,10,11-tetramethyltriphenylene
(7g):
Flash chromatography (eluent: diethyl ether); yellow solid;
6,11-Dimethoxy-2-(3-methoxyphenyl)triphenylene
(9b):
yield: 158 mg (0.46 mmol, 92%, 2.10 F, 88% ce); mp 216–
Flash chromatography (eluent: n-pentane/diethyl ether
5:1!3:1); pale brown solid; yield: 140 mg (0.36 mmol, 72%,
2.06 F, 70% ce); 1H NMR (300 MHz, CDCl3): d=8.71 (d,
J=1.9 Hz, 1H), 8.59 (d, J=8.5 Hz, 1H), 8.44 (dd, J=9.1,
2.9 Hz, 2H), 8.07 (d, J=2.6 Hz, 1H), 8.01 (d, J=2.6 Hz,
1H), 7.85 (dd, J=8.5, 1.9 Hz, 1H), 7.46 (t, J=7.8 Hz, 1H),
7.41–7.30 (m, 2H), 7.28–7.23 (m, 2H), 7.03–6.94 (m, 1H),
4.12–3.97 (m, 6H), 3.94 (s, 3H); 13C NMR (75 MHz,
CDCl3): d=160.1, 158.34, 158.31, 142.8, 139.7, 130.2 (2C),
129.9 (2C), 129.2, 126.3, 124.42, 124.37, 124.3, 124.0, 123.9,
121.9, 120.0, 115.9, 115.8, 113.5, 112.7, 106.1, 105.8, 55.6,
55.5, 55.4; IR (ATR): n=2956, 2841, 1623, 1561, 1449, 1432,
1396, 1295, 1221, 1159, 1147, 1007, 833, 618; MS (EI+): m/
z=394 (100, [M]+), 363 (9), 331 (7), 276 (5), 198 (6), 142
(3), 91 (5); HR-MS (EI+): m/z=394.1564, calculated for
C27H22O3 ([M]+): 394.1569.
1
2178C; H NMR (300 MHz, CDCl3): d=8.34 (s, 2H), 8.17
(s, 2H), 7.93 (s, 2H), 4.12 (s, 6H), 2.51 (s, 12H); 13C NMR
(75 MHz, CDCl3): d=149.1, 135.5, 135.1, 127.5, 127.4, 123.9,
123.8, 123.3, 104.6, 56.1, 20.40, 20.35; IR (ATR): n=2915,
2856, 1736, 1612, 1506, 1443, 1410, 1374, 1257, 1202, 1166,
1143, 1036, 848, 806, 645; MS (EI+): m/z=344 (2, [M]+), 291
(3), 267 (2), 253 (1), 202 (100), 174 (23), 150 (39), 126 (14),
111 (10), 98 (15), 74 (4); HR-MS (EI+): m/z=344.1770, cal-
culated for C24H24O2 ([M]+): 344.1776.
6,11-Di-tert-butyl-2,3-dimethoxytriphenylene (7h): Flash
chromatography (eluent: diethyl ether); yellow solid; yield:
185 mg (0.46 mmol, 93%, 2.16 F, 82% ce); mp 157–1608C;
1H NMR (300 MHz, CDCl3): d=8.57 (d, J=8.6 Hz, 2H),
8.48 (d, J=2.0 Hz, 2H), 8.06 (s, 2H), 7.69 (dd, J=8.7,
1.9 Hz, 2H), 4.17 (s, 6H), 1.51 (s, 18H); 13C NMR (75 MHz,
CDCl3): d=149.4, 128.9, 127.1, 124.9, 124.5, 123.2, 118.6,
105.0, 56.2, 35.2, 31.7; IR (ATR): n=2956, 2904, 2866, 1612,
1516, 1458, 1411, 1359, 1250, 1204, 1164, 1116, 1033, 868,
838, 813, 769, 720, 642, 614; MS (EI+): m/z=400 (100,
[M]+), 385 (67), 355 (3), 329 (3), 314 (5), 283 (3), 239 (4),
185 (5), 157 (8), 126 (2); HR-MS (EI+): m/z=400.2400, cal-
culated for C28H32O2 ([M]+): 400.2402.
7,10-Di-tert-butyl-2,3-dimethoxytriphenylene (7i): Flash
chromatography (eluent: diethyl ether); yellow solid; yield:
169 mg (0.42 mmol, 85%, 2.20 F, 77% ce); mp 165–1678C;
1H NMR (300 MHz, CDCl3): d=8.70 (d, J=2.0 Hz, 2H),
8.45 (d, J=8.7 Hz, 2H), 7.99 (s, 2H), 7.72 (dd, J=8.6,
2.0 Hz, 2H), 4.13 (s, 6H), 1.61–1.49 (m, 18H); 13C NMR
(75 MHz, CDCl3): d=149.3, 148.9, 129.1, 127.5, 125.0, 124.1,
122.8, 119.1, 104.7, 56.1, 35.1, 31.6; IR (ATR): n=3100,
3002, 2954, 2903, 2866, 1613, 1538, 1501, 1458, 1363, 1307,
1264, 1228, 1201, 1021, 912, 878, 843, 813, 813, 738, 658, 599,
550; MS (EI+): m/z=400 (100, [M]+), 385 (74), 355 (3), 314
(5), 283 (3), 239 (3), 200 (2), 157 (12), 126 (2, 57 (17); HR-
MS (EI+): m/z=400.2415, calculated for C28H32O2 ([M]+):
400.2402.
10-(3,4-Dimethoxyphenyl)-2,3,6,7-tetramethoxytripheny-
lene (9c):[24a] Flash chromatography (eluent: n-pentane/ethyl
acetate 3:2!1:1); white solid; yield: 217 mg (0.45 mmol,
1
90%, 2.11 F, 86% ce); H NMR (300 MHz, CDCl3): d=8.51
(d, J=1.8 Hz, 1H), 8.45 (d, J=8.6 Hz, 1H), 7.93 (d, J=
10.1 Hz, 2H), 7.74 (dd, J=8.5, 1.8 Hz, 1H), 7.69 (s, 2H),
7.42–7.27 (m, 2H), 7.04 (d, J=8.2 Hz, 1H), 4.09 (d, J=
2.7 Hz, 12H), 4.02 (s, 3H), 3.97 (s, 3H); 13C NMR (75 MHz,
CDCl3): d=149.61, 149.55, 149.5, 149.1 (2C), 149.0, 138.8,
134.8, 129.1, 127.8, 125.2, 124.3, 123.9, 123.6, 123.5, 123.4,
121.0, 120.0, 112.0, 111.2, 104.9, 104.7, 104.4 (2C), 56.3,
56.24, 56.20 (2C), 56.17, 56.1.
6-(3,5-Dimethoxyphenyl)-1,3,10,12-tetramethoxytripheny-
lene (9d): Flash chromatography (eluent: n-pentane/ethyl
acetate 5:1); yellow solid; yield: 121 mg (0.25 mmol, 50%,
4.71 F, 21% ce); mp 180–1828C; 1H NMR (300 MHz,
CDCl3): d=8.58 (d, J=1.9 Hz, 1H), 8.48 (d, J=8.5 Hz, 1H),
7.78 (dd, J=8.4, 1.8 Hz, 1H), 7.59 (dd, J=13.7, 2.3 Hz, 2H),
6.90 (d, J=2.3 Hz, 2H), 6.73 (t, J=2.6 Hz, 2H), 6.54 (t, J=
2.3 Hz, 1H), 4.02 (d, J=1.9 Hz, 6H), 3.99 (s, 6H), 3.91 (s,
6H); 13C NMR (75 MHz, CDCl3): d=161.4 (2C), 159.1
(2C), 158.9, 158.8, 143.7, 140.1, 132.3, 132.1, 130.9, 130.0,
128.0, 126.5, 124.1, 122.2, 113.6, 113.3, 106.1, 99.5, 98.7, 98.7,
97.5, 97.3, 56.0 (2C), 55.8, 55.6, 55.5 (2C); IR (ATR): n=
2927, 2839, 1595, 1540, 1457, 1417, 1388, 1272, 1198, 1151,
4447, 1027, 933, 818; MS (EI+): m/z=484 (100, [M]+), 441
(15), 397 (22), 364 (26), 293 (7), 249 (5), 242 (12), 213 (10),
7,10-Dichloro-2,3-dimethoxytriphenylene (7j): Flash chro-
matography (eluent: n-pentane/diethyl ether 5:1!3:1!
1:1); brown solid; yield: 146 mg (0.41 mmol, 82%, 2.52 F,
1
65% ce); mp 180–1828C; H NMR (300 MHz, CDCl3): d=
8.18 (d, J=2.2 Hz, 2H), 8.10 (d, J=8.9 Hz, 2H), 7.59 (s,
2H), 7.45 (dd, J=8.8, 2.1 Hz, 2H), 4.05 (s, 6H); 13C NMR
(75 MHz, CDCl3): d=149.7, 132.4, 129.2, 128.1, 127.7, 124.2,
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149 (31), 119 (6), 91 (4), 85 (10); HR-MS (EI+): m/z=
484.1886, calculated for C30H26O6 ([M]+): 484.1886.
d) N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–
2483; e) A. de Meijere, S. Brꢀse, M. Oestreich, in:
Metal-Catalysed Cross-Coupling Reactions and More,
1st edn., Vol. 1, Wiley-VCH, Weinheim, 2014; f) W.
Carruthers, I. Coldham, in: Modern Methods of Organ-
ic Synthesis, 4th edn., Cambridge University Press, Cam-
bridge, 2004, pp 89–100.
2,8,14-Trimethoxyhexabenzo[bc,ef,hi,kl,no,qr]coronene
(13a): Recrystallisation from ethanol (43 mL); orange solid;
yield: 37 mg (60.3 mmol, 63%, 14.3 F, 53% ce); mp >2708C;
IR (ATR): n=3051, 2960, 2834, 1606, 1491, 1454, 1412,
1362, 1258, 1209, 1168, 1086, 1017, 795, 758; CHN analysis
(C45H24O3, MW: 612.68 gmolꢀ1): found (calculated)
C
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88.19% (88.22%), H 3.99% (3.95%); HR-MS (FD): m/z=
612.2044, calculated for C45H24O3 ([M]+): 612.1725.
2,8,14-Trimethoxy-5,11,17-trimethylhexabenzo[bc,ef,-
hi,kl,no,qr]coronene (13b): Recrystallisation from ethanol
(57 mL); orange solid; yield: 30 mg (45.9 mmol, 51%, 16.2 F,
38% ce); mp >2708C; CHN analysis (C45H24O3, MW:
612.68 gmolꢀ1): found (calculated) C 87.85% (88.05%), H
4.41% (4.62%); IR (ATR): n=2924, 2850, 1712, 1603, 1493,
1456, 1227, 1175, 1071, 1033, 858, 807; HR-MS (FD): m/z=
654.1399, calculated for C48H31O3 ([M]+): 654.2195.
2,8,14-Tri-tert-butylhexabenzo[bc,ef,hi,kl,no,qr]coronene
(13c): Purification was performed by dissolving the crude
product in dichloromethane (15 mL) followed by precipita-
tion with methanol (100 mL); yellow solid; yield: 54 mg
(78.7 mmol, 69%, 13.9 F, 60% ce); mp >2708C; CHN analy-
sis (C45H24O3, MW: 612.68 gmolꢀ1): found (calculated) C
93.99% (93.87%), H 6.35% (6.13%); IR (ATR): n=2955,
2863, 1604, 1467, 1361, 1254, 1205, 1094, 1019, 942, 903, 869,
800, 729, 664, 605; HR-MS (FD): m/z=690.3295, calculated
for C54H43 ([M]+): 690.3295.
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Hexabenzo[bc,ef,hi,kl,no,qr]coronene (16a):[29] Recrystal-
lisation from chloroform/ethanol (1:1, 100 mL); yellow
solid; yield: 254 mg (485 mmol, 95%, 20.1 F, 57% ce); mp
>2708C. IR (ATR): n=3013, 1893, 1688, 1607, 1304, 1128,
1128, 952, 840, 762, 538; HR-MS (FD): m/z=522.1413, cal-
culated for C42H18 ([M+H]+): 522.1409.
2,5,8,11,14,17-Hexa-tert-butylhexabenzo[bc,ef,hi,kl,no,qr]-
coronene (16b):[3d] Purification was performed by dissolving
the crude product in dichloromethane (10 mL) followed by
precipitation with methanol (100 mL); orange solid; yield:
425 mg (495 mmol, 99%, 12.9 F, 92% ce); 1H NMR
(300 MHz, CHCl3): d=9.33 (s, 12H), 1.85 (s, 54H);
13C NMR (75 MHz, CHCl3): d=149.2, 130.7, 124.2, 120.6,
119.0, 35.9, 32.2.
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Efficient Oxidative Coupling of Arenes via Electrochemical
Regeneration of 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) under Mild Reaction Conditions
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Adv. Synth. Catal. 2017, 359, 1 – 15
Philipp Rçse, Steffen Emge, Christoph Alexander Kçnig,
Gerhard Hilt*
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