Twisted polycyclic arenes by intramolecular scholl reactions of C3-symmetric precursors

Article abstract of DOI:10.1021/jo3027752

With the aim of opening an efficient access to large and sterically crowded polycyclic arenes as well as improving insight into the geometrical preferences of the Scholl reaction, a versatile synthesis strategy has been developed to form a family of flexible yet strongly crowded substrates for multiple dehydrocyclizations. Their intramolecular Scholl reactions lead with high selectivity either to considerably twisted species where the initial C3 symmetry is maintained, or to strongly rearranged products where the formation of multiple [6]helicene fragments is avoided by the formation of unusual hexa[7]circulene moieties under loss of the C3 symmetry.

Full text of DOI:10.1021/jo3027752

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pubs.acs.org/joc
Twisted Polycyclic Arenes by Intramolecular Scholl Reactions of C3-
Symmetric Precursors
Anirban Pradhan, Pierre Dechambenoit, Harald Bock, and Fabien Durola*
Centre de Recherche Paul Pascal, CNRS & University Bordeaux, 115 avenue Schweitzer, 33600 Pessac, France
S
* Supporting Information
ABSTRACT: With the aim of opening an efficient access to
large and sterically crowded polycyclic arenes as well as
improving insight into the geometrical preferences of the
Scholl reaction, a versatile synthesis strategy has been
developed to form a family of flexible yet strongly crowded
substrates for multiple dehydrocyclizations. Their intra-
molecular Scholl reactions lead with high selectivity either to
considerably twisted species where the initial C3 symmetry is maintained, or to strongly rearranged products where the
formation of multiple [6]helicene fragments is avoided by the formation of unusual hexa[7]circulene moieties under loss of the
C3 symmetry.
of tribromobenzene 8 with three biphenylic blades (Scheme
2a), has already been described as a proof of the efficiency of
the Scholl reaction to form multiple helicenic compounds.14
We have now developed a systematic and versatile strategy to
synthesize a family of such flexible C3-symmetrical substrates
for subsequent Scholl treatment. This new method involves
more steps than in the case of 10, but it gives access to several
compounds 17a−d from a single common trifunctionalized
precursor 15 by only changing the nature of the arylboronic
acid 16 added in the last step (Scheme 2b).
The formation of the common precursor 15 relies on a
trisubstitution of sym-tribromobenzene 8, by a very efficient
(95% yield) Suzuki cross-coupling reaction in classical
conditions. This time 8 is not reacted with a complete blade
(boronic ester 9) but with the shorter methoxy substituted
arylboronic acid 12, which was synthesized in two steps
following existing procedures.16 The three methoxy groups of
the resulting compound 13 are then deprotected by action of
BBr3, leading quantitatively to the triphenolic intermediate 14,
whose phenol functions are then transformed into triflate
groups in excellent yield to give the common precursor 15.
Because of the important steric hindrance of the reacting sites
on this substrate, optimized catalytic conditions had to be
established for the last trisubstitution step by Suzuki cross-
coupling reaction. A very satisfying catalytic system, developed
by Buchwald’s group,17 is based on Pd(OAc)2, SPhos as ligand
and K3PO4 as base in a mixture of THF and water. Four
commercially available arylboronic acids 16a−d were thus used
to give trisubstituted flexible Scholl substrates 17a−d in
excellent yields (between 92 and 98%).
INTRODUCTION
■
The field of extended polycyclic aromatic hydrocarbons
(PAHs)1 is currently benefitting from the raising interest in
graphenes2 and carbon nanoribbons,3 and their predicted utility
in organic electronics.4 Top-down synthesis techniques quickly
and efficiently lead to giant graphene molecules,5 whereas
longer and more laborious bottom-up synthetic strategies,
pioneered by Mullen’s group 15 years ago,6 have the advantage
̈
of reproducibly forming monodisperse and physically homoge-
neous nanographenes.7 Not all PAHs can be considered as
nanographenes since not all of them may conceptually be cut
out of a flat graphene sheet because of their twisted geometries.
The distortion of such twisted arenes may result from cycle
tensions by inclusion of nonhexagonal rings,8 sometimes
leading to fragments of fullerenes and nanotubes,9 or from
helicenic parts,10 which might only be obtained in graphite by
the introduction of screw disclinations.
Intramolecular Scholl reactions11 (i.e., dehydrocyclization by
acidic oxidants like FeCl3 or DDQ/MeSO3H) have been
established as a powerful tool to form well-designed flat
nanographenes,12 but this well-known yet poorly understood
reaction may show surprising performances and selectivities
(Scheme 1a).13 We have recently reported that the Scholl
reaction is sometimes astonishingly insensitive to steric
hindrance and can favor the formation of congested [5]-
helicenes such as 5 instead of their flat isomers such as 4
(Scheme 1b).14 We and Hilt’s group15 have also observed that
even methoxy groups on protected compounds such as 6 may
be expelled to maintain this regioselectivity and give only
twisted [5]helicenes such as 7 (Scheme 1c).
The triple Suzuki reaction between 9-phenanthracenylbor-
onic acid 16a and tris-triflate 15 affords the flexible but
RESULTS AND DISCUSSION
■
An easy and quick synthesis of highly distorted propeller-
shaped hexa-tert-butyl-hexabenzotriphenylene (t-Bu6-HBTP)
11, from the flexible precursor 10 obtained by trisubstitution
Received: December 21, 2012
© XXXX American Chemical Society
A
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Scheme 1. Examples of the Regioselectivity of Scholl Reaction on o,p,o-Pentaphenylene Substrates
a
Scheme 2. Formation of Trisubstituted Substrates for Intramolecular Scholl Reactions
a
(i) Na2CO3, Pd(PPh3)4 in PhMe/H2O/EtOH, 90 °C, 48 h, 95%. (ii) BBr3 in CH2Cl2, rt, 16 h, 99%. (iii) Tf2O, pyridine in CH2Cl2, rt, 16 h, 96%.
(iv) Pd(OAc)2, SPhos, K3PO4 in THF/H2O, 67 °C, 48 h, respectively 95, 92, 96, and 98%.
sterically very congested compound 17a (Scheme 3). This
molecule, if represented in 2D, shows several overlaps of
carbons and has two stable conformers at room temperature, as
indicated by a variable temperature 1H NMR study with
coalescence reached around 125 °C in DMSO-d6.18 The Scholl
reaction on this substrate was predicted to form 3 new C−C
bonds, between the central benzene ring and position 10 of
each phenanthrene part, and give a symmetrical triple
B
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Scheme 3. Scholl Reactions on Precursors 17a and 17b Leading to Rearranged Compounds 18 and 19
[6]helicene. Nevertheless, we were surprised to reproducibly
obtain, after purification, an asymmetrical major product 18
whose formula, unambiguously confirmed by mass spectrom-
etry, indicates that 8 hydrogen atoms had been removed,
implying the creation of four instead of three C−C bonds.
Fortunately, we were able to crystallize this compound by slow
diffusion of diisopropyl ether in CCl4, and the analysis by X-ray
diffraction on monocrystal revealed the very unexpected
structure of oligoarene 18 (Figure 1). The latter is highly
phenanthrene (blue) to form the 7-membered ring, and a
fourth cyclization finally occurs between two phenanthrene
parts (red and blue). This reproducible and very efficient, yet
absolutely unpredicted, outcome tells us that a highly twisted
[5]helicenic fragment (between blue and green blades) bearing
2 tert-butyl groups on hindered positions is apparently very
favored by the Scholl reaction since not only does it benefit
from regioselectivity (Scheme 1b) but also rearrangements
might have occurred to prevent its formation. The 7-membered
ring formation by Scholl reaction is also noteworthy since
known examples of such heptagonal structures are exceedingly
rare, either with only sp2-hybridized carbons19 or even
including one tetrahedral apex.20
When 2-naphthylboronic acid 16b is used to form another
flexible substrate 17b, two adjacent carbons are free on the 2-
naphthyl group. Therefore each blade can theoretically cyclize
on the central benzene ring in two different ways. Nevertheless
a unique compound 19 is isolated (90% yield) after Scholl
treatment. This product has the same greenish color as
1
compound 18 and a very similar H NMR spectrum with
several identical peaks, and the mass spectrum also indicates
that 4 C−C bonds were formed. For these reasons, we tend to
think that the structure of 19 is comparable to the one of 18,
but unfortunately, we were not able to crystallize 19 and thus
cannot give any clear evidence of its structure. Intramolecular
rearrangements when trying to form [7]helicenes by Scholl
reaction have already been reported,21 and our results confirm
that this reaction may not be suitable to make helicenes with
more than five benzene rings in the helix.
Given the surprising rearrangements observed during the
Scholl reaction of 17a and probably 17b, we wondered whether
such reactions also occurred, but with no visible consequences,
when cyclizing the fully symmetrical propeller-shaped t-Bu6-
HBTP 11. In order to dissymmetrize its flexible precursor 10
without changing the global shape of the molecule, we coupled
4-(trimethylsilyl)phenylboronic acid 16c on tris-triflate com-
pound 15 to obtain the flexible substrate 17c, which differs
Figure 1. Two different views of the crystal structure of the strongly
distorted [5]helicene- and hexa[7]circulene-based compound 18.
distorted because of two different structural ingredients: (a)
one [5]helicene, whereas [6]helicenes were expected; and (b)
one 7-membered ring that is part of a hexa[7]circulene
fragment. This final structure can be explained by two
successive rearrangements during the Scholl process. One
blade (blue on Scheme 3) cyclized correctly on the central
benzene ring, then a second one (green on Scheme 3) migrated
to an adjacent yet hindered carbon and also cyclized on the
central benzene ring to form a [5]helicene, then the
phenanthrene part of the third blade (red on Scheme 3)
migrated to an adjacent carbon on the benzene part of the
blade to allow its previous position to cyclize onto another
C
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Scheme 4. Scholl Reaction on Compound 17c Leading to TMS-Substituted Hexabenzotriphenylene 20
from 10 only by the replacement of three carbons by three
silicon atoms. The Scholl reaction of this TMS-substituted
compound 17c leads as expected, and with a comparable yield,
to another propeller-shaped HBTP 20, still bearing six
tetrahedral substituents (Scheme 4).
This new oligoarene has been crystallized as a racemic
mixture and analyzed by X-ray diffraction. The propeller shape
of the molecule has thus been confirmed (Figure 2), but the
molecule, i.e., a C3 symmetrical product, showing that no
rearrangement occurred during the Scholl reaction.
The compatibility with TMS groups of this Scholl reaction is
also noteworthy; we did not find a single other example in the
literature. To further investigate this compatibility, and to check
if TMS-substituted substrates obey the same reactivity rules as
their tert-butylated counterparts, we synthesized pentapheny-
lene 26 (Scheme 5) following a similar strategy as for
trisubstituted substrates 17. But contrary to pentaphenylene
3, which mainly leads to [5]helicene 5 by Scholl reaction
(Scheme 1b), the silylated version 26, under the same
conditions, very quickly loses its two TMS groups and fully
cyclizes to give the flat oligoarene 27, whose structure was
perfectly determined by NMR, mass spectrometry and even X-
ray crystallography (Figure 3). So the compatibility of TMS
groups with the Scholl reaction cannot be generalized since
they may also be expelled to favor some bond formations.
Scholl cyclizations of 1,3,5-tris(2-biphenyl)ylbenzene species
have already been studied by Mullen’s group22 but were only
̈
successful in the case of unsubstituted flexible precursors, or
with iodides on nonhindering positions. When these
deactivating iodides are located on hindering positions, the
reaction remains incomplete. The triple Suzuki cross-coupling
reaction of tris-triflate 15 with simple phenylboronic acid 16d
gives the flexible precursor 17d, with only three tert-butyl
substituents located on hindered positions. Submitted to Scholl
reacting conditions, this molecule fully cyclizes, by forming six
C−C bonds, in a good yield (72%) to give 1,7,13-tri-tert-
butylhexabenzocoronene 28 (Scheme 6). This hexabenzocor-
Figure 2. Two different views of the crystal structure of triply helicenic
TMS-bearing hexabenzotriphenylene 20.
TMS and t-Bu groups are indistinguishable in the crystal
structure because of orientational disorder of the molecules in
the unit cell (quaternary C from t-Bu and quaternary Si from
TMS show 50/50 occupancy).18 Nevertheless, the extreme
simplicity of the 1H NMR spectrum of 20 (only 6 aromatic and
2 aliphatic signals) can only stand for a highly symmetrical
a
Scheme 5. Synthesis and Reactivity in Scholl Conditions of TMS-Bearing Pentaphenylene 26
a
(i) Na2CO3, Pd(PPh3)4 in PhMe/H2O/EtOH, 90 °C, 48 h, 90%. (ii) BBr3 in CH2Cl2, rt, 16 h, 99%. (iii) Tf2O, pyridine in CH2Cl2, rt, 16 h, 95%.
(iv) Pd(OAc)2, SPhos, K3PO4 in THF/H2O, 67 °C, 48 h, 90%. (v) FeCl3 in MeNO2/ CH2Cl2, rt, 1.5 h, 91%.
D
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EXPERIMENTAL SECTION
■
1,4-Bis(4,4′-di-tert-butylbiphenyl-2-yl)-2,5-dimethoxyben-
zene (6). Commercially available 1,4-dibromo-2,5-dimethoxybenzene
(296 mg, 1.0 mmol), 2-(4,4′-di-tert-butylbiphenyl-2-yl)-4,4,5,5-tetra-
methyl-1,3,2-dioxaborolane 914 (823 mg, 2.1 mmol) and Na2CO3
(1.06 g, 10 mmol) were dissolved in toluene (24 mL), water (8 mL)
and ethanol (4 mL). The solution was degassed, Pd(PPh3)4 (115 mg,
0.1 mmol) was added under an Ar stream, and the mixture was
degassed again. The solution was heated at 90 °C overnight. The
organic layer was separated, and the aqueous layer was extracted with
CH2Cl2. The combined organic layer was washed with water and
evaporated. The crude product was purified by chromatography on
silica gel by using petroleum ether/CH2Cl2 (20%) as the eluent to give
the title compound 6 (Scheme 8; white solid, 547 mg, 82%): mp 172−
Figure 3. Crystal structure of flat oligoarene 27.
1
173 °C; H NMR (400 MHz, CD2Cl2) δ 7.41 (dd, 2H, J = 2.2, 8.2
Hz), 7.34 (d, 2H, J = 7.2 Hz), 7.33 (d, 2H, J = 2.4 Hz), 7.30 (d, 4H, J
= 8.4 Hz), 7.07 (d, 4H, J = 8.4 Hz), 6.55 (s, 2H), 3.07 (s, 6H), 1.34 (s,
18H), 1.27 (s, 18H); 13C NMR (100 MHz, CD2Cl2) δ 150.2, 150.0,
149.3, 139.0, 138.6, 136.8, 130.6, 129.2, 128.6, 127.9, 124.7, 124.3,
115.2, 55.5, 34.5, 34.3, 31.1; HRMS (FD-TOF) m/z [M]+ Calcd for
C48H58O2 666.44368, found 666.44045.
onene, triply substituted by very bulky groups in bay regions,
has been unambiguously characterized by mass spectrometry,
1H and 13C NMR, but unfortunately, we were not able to
crystallize it to determine its structure. This undoubtedly
distorted oligoarene23 shows unusually high solubilities in many
organic solvents compared to other flat hexabenzocoronenes.
When attempting to crystallize hexabenzocoronene 28, we
could obtain a few monocrystals from a crystallization tube
containing an impure fraction of 28 (about 10% impurities).
Disappointingly, X-ray analysis revealed that these crystals were
only composed of unexpected rearranged products 30 and 31,
cocrystallizing together (in a 3:2 ratio). In this case, again, one
blade migrates onto an adjacent carbon of the central benzene
ring to form the usual [5]helicene, but in addition the t-Bu
group, on the fully cyclized third blade, is removed and replaced
by a chlorine (31) or two opposite hydroxyl groups (30). Such
a loss of a t-Bu group on the symmetrical main product 28,
giving compound 29, and the presence of 30 and 31 has also
been observed by mass spectrometry (Scheme 7).
2,7,10,15-Tetra-tert-butyl-17-methoxydibenzo[f,j]picene (7).
Compound 6 (100 mg, 0.15 mmol) was dissolved in 30 mL of
unstabilized dichloromethane and degassed with an Ar stream for 15
min. A solution of FeCl3 (145 mg, 0.89 mmol) in 5 mL of
nitromethane was added dropwise while continuously degassing with
an Ar stream. After 30 min the reaction was stopped by adding 100 mL
of methanol. The organic phase was then washed twice with water and
dried over anhydrous Na2SO4. The solvent was removed in vacuo, and
the crude product was purified by chromatography on silica gel by
using petroleum ether/CH2Cl2 (8%) as the eluent to give the title
compound 7 (Scheme 8; yellow solid, 84 mg, 89%): mp 314−315 °C;
1H NMR (400 MHz, CD2Cl2) δ 9.56 (d, 1H, J = 2.0 Hz), 8.60 (d, 1H,
J = 8.8 Hz), 8.58 (s, 1H), 8.57 (d, 1H, J = 9.2 Hz), 8.44 (d, 1H, J = 8.4
Hz), 8.41 (d, 1H, J = 8.8 Hz), 8.09 (s, 1H), 8.03 (d, 1H, J = 2.4 Hz),
8.00 (d, 1H, J = 2.0 Hz), 7.79 (dd, 1H, J = 2.0, 8.8 Hz), 7.75 (dd, 1H, J
= 2.2, 8.8 Hz), 7.52 (dd, 1H, J = 1.6, 8.8 Hz), 7.47 (dd, 1H, J = 2.2, 8.6
Hz), 4.31 (s, 3H), 1.54 (s, 9H), 1.50 (s, 9H), 1.02 (s, 18H); 13C NMR
(100 MHz, CD2Cl2) δ 157.0, 149.6, 149.1, 147.3,147.2,131.9, 130.7,
130.6,130.2,128.7, 128.4, 128.3, 128.1, 127.7, 127.4, 126.9, 126.3,
125.2, 124.9, 124.8, 124.5, 123.7, 122.9, 122.8, 122.2, 122.0, 119.2,
102.4, 56.3, 35.0, 34.9, 34.2, 31.3,31.2, 30.6; HRMS (FD-TOF) m/z
[M]+ Calcd for C47H52O 632.40181, found 632.40384.
1,3,5-Tris(5-tert-butyl-2-methoxyphenyl)benzene (13). 1,3,5-
Tribromobenzene 8 (1.0 g, 3.2 mmol), 5-tert-butyl-2-methoxyphe-
nylboronic acid 12 (2.4 g, 11.5 mmol) and Na2CO3 (3.4 g, 32 mmol)
were dissolved in toluene (30 mL), water (10 mL) and ethanol (5
mL). The solution was degassed, Pd(PPh3)4 (369 mg, 0.32 mmol) was
added under an Ar stream, and the mixture was degassed again and
then heated at 90 °C for 48 h. The organic layer was decanted, and the
aqueous layer was extracted twice with CH2Cl2. The combined organic
layer was washed with water and evaporated. The crude product was
purified by chromatography on silica gel by using petroleum ether/
CH2Cl2 (20%) as the eluent to give the title compound 13 (white
solid, 1.67 g, 95%): mp 119−120 °C; 1H NMR (400 MHz, CD2Cl2) δ
CONCLUSION
■
We developed a versatile synthesis technique for the formation
of a family of flexible yet strongly crowded C3-symmetrical
polyaromatic chains as substrates for graphitization by intra-
molecular Scholl reaction and found that the formation of
[6]helicenes appears precluded with this approach because of
surprising rearrangements leading to hexa[7]circulene species.
Nevertheless, under the same conditions, strongly congested
[5]helicenes, with bulky groups on hindered positions, seem to
be highly favored even when a labile TMS group replaces one
of the two t-Bu substituents. Finally, a distorted and soluble
bay-substituted hexabenzocoronene can efficiently be synthe-
sized by Scholl reaction on a tris(biphenyl)ylbenzene precursor
bearing three activating t-Bu groups on congesting positions.
Scheme 6. Scholl Reaction on Precursor 17d Leads to Distorted Hexabenzocoronene 28
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Scheme 7. Scholl Reaction on 17d Also Gives Traces of Rearranged Compounds
Scheme 8. Synthesis Scheme of Compounds 6 and 7
7.55 (s, 3H), 7.39 (d, 3H, J = 2.8 Hz), 7.33 (dd, 3H, J = 2.8, 8.8 Hz),
6.93 (d, 3H, J = 8.4 Hz), 3.79 (s, 9H), 1.30 (s, 27H); 13C NMR (100
MHz, CD2Cl2) δ 154.4, 143.5, 138.5, 130.0, 129.4, 128.3, 125.3, 110.6,
55.5, 34.1, 31.3; HRMS (FD-TOF) m/z [M]+ Calcd for C39H48O3
564.36034, found 564.35856.
degassed again. The solution was heated at 70 °C for 72 h. The
organic layer was then decanted, and the aqueous layer extracted twice
with CH2Cl2. The combined organic layer was washed with water and
evaporated. The crude product was purified by chromatography on
silica gel by using petroleum ether/CH2Cl2 (12%) as the eluent to give
the title compound 17a (white solid, 414 mg, 95%): mp 214−215 °C;
1H NMR (400 MHz, DMSO,150 °C) δ 8.67−8.63 (m, 6H), 7.58−
7.43 (m, 9H), 7.42 (d, 3H, J = 8.0 Hz), 7.31 (d, 3H, J = 8.0 Hz), 7.25−
7.21 (m, 6H), 7.01 (d, 3H, J = 8.4 Hz), 6.96 (s, 3H), 6.68 (s, 3H), 6.49
(s, 3H), 1.05 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ 150.5,150.4,
140.8, 140.3, 138.1, 137.9, 135.4, 131.9, 131.4, 130.2, 129.5, 128.7,
128.6, 128.2, 127.1, 126.6, 126.4, 126.1, 126.0, 123.4, 122.8, 122.5,
34.2, 34.1, 31.0, 30.9; HRMS (FD-TOF) m/z [M]+ Calcd for C78H66
1002.51645, found 1002.52118.
Hexa[7]circulene- and [5]Helicene-Based Rearranged Com-
pound (18). Compound 17a (300 mg, 0.3 mmol) was dissolved in 50
mL of unstabilized dichloromethane and degassed with an Ar stream
for 15 min. Then a solution of FeCl3 (970 mg, 6.0 mmol) in 10 mL of
nitromethane was added dropwise while continuously degassing with
an Ar stream. After 1 h the reaction was stopped by adding 100 mL of
ethanol. The organic phase was then washed twice with water and
dried over anhydrous Na2SO4. The solvent was removed in vacuo, and
the crude product was purified by chromatography on silica gel by
using petroleum ether/CH2Cl2 (4%) as the eluent to give the title
compound 18 (greenish yellow solid, 218 mg, 73%): mp > 400 °C; 1H
NMR (400 MHz, CD2Cl2) δ 9.10−9.07 (m, 1H), 8.95−8.91 (m, 1H),
8.76−8.72 (m, 1H), 8.67−8.63 (m, 2H), 8.54 (d, 1H, J = 8.4 Hz), 8.52
(d, 1H, J = 8.4 Hz), 8.43 (d, 1H, J = 8.0 Hz), 8.15 (dd, 2H, J = 2.2, 7.8
Hz), 7.87 (d, 1H, J = 8.0 Hz), 7.75 (d, 1H, J = 8.0 Hz), 7.72−7.68 (m,
5H), 7.59 (dd, 1H, J = 2.0, 8.4 Hz), 7.50 (t, 1H, J = 8.4 Hz), 7.45−7.42
(m, 2H), 7.31 (t, 1H, J = 7.6 Hz), 7.17 (t, 1H, J = 7.2 Hz), 7.14−7.7.05
(m, 4H), 6.98 (d, 1H, J = 7.6 Hz), 6.71 (t, 1H, J = 7.0 Hz), 6.44 (d,
1H, J = 7.6 Hz), 6.43 (d, 1H, J = 7.6 Hz), 1.18 (s, 9H), 1.02 (s, 9H),
0.63 (s, 9H); 13C NMR (100 MHz, CD2Cl2) δ 148.1, 147.7, 147.4,
142.3, 138.2, 136.8, 136.2, 136.1, 134.9, 134.8, 133.5, 133.0, 132.4,
131.6, 131.4, 131.3, 131.1, 130.7, 130.6, 129.8, 129.7, 129.6, 129.5,
129.4, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 128.2, 128.1, 128.0,
127.8, 127.7, 127.4, 127.3, 127.2, 126.8, 126.7, 126.6, 126.0, 125.8,
125.6, 125.5, 125.2, 125.1, 124.9, 124.7, 124.5, 124.4, 124.3, 123.9,
123.6, 123.5, 122.5, 122.2, 121.3, 121.1, 35.9, 34.7, 34.4, 32.3, 30.9,
30.5; HRMS (FD-TOF) m/z [M]+ Calcd for C78H58 994.45385,
found 994.45604.
1,3,5-Tris(5-tert-butyl-2-hydroxyphenyl)benzene (14). Com-
pound 13 (1.72 g, 3.05 mmol) was dissolved in 50 mL of dry CH2Cl2
under Ar and brought to −20 °C. BBr3 (1 M in CH2Cl2, 12.2 mmol,
12.2 mL) was added dropwise with vigorous stirring, and the reaction
mixture was stirred overnight and finally warmed to room temperature.
The reaction mixture was then poured on crushed ice, the organic
layer was decanted, and the aqueous layer was extracted twice with
CH2Cl2. The combined organic layer was washed with water and dried
over anhydrous Na2SO4. The solvent was removed under a vacuum,
yielding 14 without further purification (1.57 g, 99%) as a white solid:
1
mp 247−248 °C; H NMR (400 MHz, CD2Cl2) δ 7.63 (s, 3H), 7.34
(d, 3H, J = 2.4 Hz), 7.28 (dd, 3H, J = 2.6, 8.2 Hz), 6.88 (d, 3H, J = 8.8
Hz), 5.24 (s, 3H), 1.29 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ
150.3, 143.9, 139.4, 128.9, 127.5, 126.9, 126.3, 115.5, 34.1, 31.3;
HRMS (FD-TOF) m/z [M]+ Calcd for C36H42O3 522.31339, found
522.31410.
1,3,5-Tris(5-tert-butyl-2-trifluoromethylsulfonyloxyphenyl)-
benzene (15). To compound 14 (1.50 g, 2.87 mmol) dissolved in
100 mL of anhydrous CH2Cl2 were added 5 mL of pyridine, and the
solution was cooled to 0 °C. Trifluoromethanesulfonic anhydride (1.9
mL, 11 mmol) was added dropwise, and the mixture was warmed to
room temperature and stirred overnight. The solvent was removed
under a vacuum. The crude product was purified by chromatography
on silica gel by using petroleum ether/CH2Cl2 (15%) as the eluent to
give the title compound 15 (white solid, 2.53 g, 96%): mp 173−174
°C; 1H NMR (400 MHz, CD2Cl2) δ 7.65(s, 3H), 7.64 (d, 3H, J = 2.8
Hz), 7.48 (dd, 3H, J = 2.6, 9.0 Hz), 7.31 (d, 3H, J = 8.8 Hz), 1.36 (s,
27 Hz); 19F NMR (400 MHz, CD2Cl2) δ −74.21; 13C NMR (100
MHz, CD2Cl2) δ 152.3, 144.7, 136.9, 133.8, 130.1, 129.4, 126.7, 121.4,
34.8, 30.9; HRMS (FD-TOF) m/z [M]+ Calcd for C39H39O9F9S3
918.16125, found 918.16261.
1,3,5-Tris(5-tert-butyl-2-phenanthren-9-ylphenyl)benzene
(17a). Compound 15 (400 mg, 0.435 mmol) and phenanthrene-9-
boronic acid 16a (386 mg, 1.74 mmol) and K3PO4 (1.11 g, 5.22
mmol) were dissolved in a mixture of THF (10 mL) and water (2
mL). The solution was degassed, Pd(OAc)2 (14.6 mg, 0.065 mmol)
and 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl SPhos (32 mg,
0.078 mmol) were added under an Ar stream, and the mixture was
F
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1,3,5-Tris(5-tert-butyl-2-naphthalen-2-ylphenyl)benzene
(17b). Compound 15 (600 mg, 0.65 mmol), naphthalene-2-boronic
acid 16b (448 mg, 2.6 mmol) and K3PO4 (1.67 g, 7.82 mmol) were
dissolved in a mixture of THF (10 mL) and water (2 mL). The
solution was degassed, Pd(OAc)2 (22 mg, 0.1 mmol) and 2-
dicyclohexylphosphino-2′,6′-dimethoxybiphenyl SPhos (48 mg, 0.12
mmol) were added under an Ar stream, and the mixture was degassed
again. The solution was heated at 70 °C for 48 h. The organic layer
was then decanted, and the aqueous layer was extracted twice with
CH2Cl2. The combined organic layer was washed with water and
evaporated. The crude product was purified by chromatography on
silica gel by using petroleum ether/CH2Cl2 (10%) as the eluent to give
the title compound 17b (white solid, 511 mg, 92%): mp 186−187 °C;
1H NMR (400 MHz, CD2Cl2) δ 7.81−7.77 (m, 6H), 7.76 (s, 3H),
7.64 (d, 3H, J = 8.8 Hz), 7.47−7.40 (m, 6H), 7.31 (d, 3H, J = 8.0 Hz),
7.29 (d, 3H, J = 8.4 Hz), 6.89 (s, 3H), 6.84 (dd, 3H, J = 2.0, 8.8 Hz),
6.69 (s, 3H),1.01 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ 150.6,
141.6, 139.8, 139.3, 137.3, 133.6, 132.0, 130.6, 129.8, 128.9, 128.1,
128.0, 127.8, 126.6, 126.1, 125.9, 124.4, 34.1, 30.8; HRMS (FD-TOF)
m/z [M]+ Calcd for C66H60 852.46950, found 852.47021.
Unidentified Rearranged Compound (19). Compound 17b
(200 mg, 0.24 mmol) was dissolved in 50 mL of unstabilized
dichloromethane and degassed with an Ar stream for 15 min. Then a
solution of FeCl3 (760 mg, 4.7 mmol) in 10 mL of nitromethane was
added dropwise while continuously degassing with an Ar stream. After
1.5 h the reaction was stopped by adding 100 mL of ethanol. The
organic phase was then washed twice with water and dried over
anhydrous Na2SO4. The solvent was removed in vacuo, and the crude
product was purified by chromatography on silica gel by using
petroleum ether/CH2Cl2 (4%) as the eluent to give the title
compound 19 (greenish yellow solid, 178 mg, 90%): mp > 400 °C;
1H NMR (400 MHz, CD2Cl2) δ 9.17 (s, 1H), 9.13 (d, 1H, J = 8.4 Hz),
9.03(d, 1H, J = 8.4 Hz), 8.78 (d, 1H, J = 9.2 Hz), 8.66 (d, 1H, J = 8.0
Hz), 8.59 (d, 1H, J = 8.8 Hz), 8.49 (d, 1H, J = 8.4 Hz), 8.45 (d, 1H, J
= 8.4 Hz), 8.30 (d, 1H, J = 8.4 Hz), 8.17 (d, 1H, J = 8.4 Hz), 8.14 (d,
1H, J = 8.8 Hz), 7.87 (d, 1H, J = 8.4 Hz), 7.83 (d, 1H, J = 7.6 Hz),
7.68−7.57 (m, 6H), 7.43−7.40 (m, 2H), 7.23 (t, 1H, J = 7.4 Hz), 7.17
(t, 1H, J = 7.2 Hz), 6.80 (t, 1H, J = 7.6 Hz), 6.62 (t, 1H, J = 8.2 Hz),
1.04 (s, 9H), 0.79 (s, 9H), 0.76 (s, 9H); 13C NMR (100 MHz,
CD2Cl2) δ 149.3, 149.0, 148.8, 132.9, 132.8, 132.7, 132.0, 132.6, 131.0,
130.8, 130.7, 130.4, 129.4, 128.8, 128.7, 128.4, 128.2, 128.0, 127.9,
127.8, 127.7, 127.5, 127.4, 127.2, 126.9, 126.8, 126.2, 125.9, 125.8,
125.6, 125.5, 125.3, 125.2, 125.0, 124.6, 124.5, 124.4, 124.2, 124.0,
123.7, 122.9, 122.4, 121.4, 121.0, 120.8, 120.0, 118.3, 39.3, 34.1, 34.0,
32.6, 30.5, 30.4; HRMS (FD-TOF) m/z [M]+ Calcd for C66H52
844.40690, found 844.40311.
1,3,5-Tris(5-tert-butyl-2-(4-trimethylsilylphenyl)phenyl)-
benzene (17c). Compound 15 (400 mg, 0.44 mmol), 4-
(trimethylsilyl)phenylboronic acid 16c (338 mg, 1.7 mmol) and
K3PO4 (1.1 g, 5.2 mmol) were dissolved in a mixture of THF (10 mL)
and water (2 mL). The solution was degassed, Pd(OAc)2 (14.7 mg,
0.065 mmol) and 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl
SPhos (32 mg, 0.078 mmol) were added under an Ar stream, and the
mixture was degassed again. The solution was heated at 70 °C for 48 h.
The organic layer was then decanted, and the aqueous layer was
extracted twice with CH2Cl2. The combined organic layer was washed
with water and evaporated. The crude product was purified by
chromatography on silica gel by using petroleum ether/CH2Cl2 (12%)
as the eluent to give the title compound 17c (white solid, 384 mg,
96%): mp 254−255 °C; 1H NMR (400 MHz, CD2Cl2) δ 7.53 (d, 6H,
J = 7.6 Hz), 7.39 (dd, 3H, J = 2.0, 8.4 Hz), 7.28 (d, 3H, J = 8.4 Hz),
7.14 (d, 3H, J = 1.6 Hz), 6.98 (d, 6H, J = 7.6 Hz), 6.82 (s, 3H), 1.28
(s, 27H), 0.20 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ 150.5, 142.5,
141.5, 139.9, 138.1, 137.4, 132.9, 130.4, 129.6, 128.0, 124.8, 34.5, 31.1,
−1.2; HRMS (FD-TOF) m/z [M]+ Calcd for C63H78Si3 918.54113,
found 918.54367.
in 10 mL of nitromethane was added dropwise while continuously
degassing with an Ar stream. After 1.5 h the reaction was stopped by
adding 100 mL of ethanol. The organic phase was then washed twice
with water and dried over anhydrous Na2SO4. The solvent was
removed in vacuo, and the crude product was purified by
chromatography on silica gel by using petroleum ether/CH2Cl2
(2%) as the eluent to give the title compound 20 (yellow solid, 129
1
mg, 65%): mp > 300 °C (decomposes at 300 °C); H NMR (400
MHz, CD2Cl2) δ 8.55 (d, 3H, J = 8.4 Hz), 8.53 (d, 3H, J = 8.4 Hz),
8.29 (s, 3H), 8.14 (d, 3H, J = 2.0 Hz), 7.65 (dd, 3H, J = 1.8, 8.4 Hz),
7.60 (dd, 3H, J = 1.8, 8.4 Hz), 1.05 (s, 27H), −0.02 (s, 27H); 13C
NMR (100 MHz, CD2Cl2) δ 148.1, 136.6, 136.5, 131.7, 130.9, 130.6,
130.2, 128.5, 128.4, 127.6, 124.5, 122.9, 122.2, 34.5, 30.8, −1.7; HRMS
(FD-TOF) m/z [M]+ Calcd for C63H72Si3 912.49418, found
912.49536.
1,3,5-Tris(4-tert-butylbiphenyl-2-yl)benzene (17d). Com-
pound 15 (430 mg, 0.47 mmol), phenylboronic acid 16d (230 mg,
1.9 mmol) and K3PO4 (1.2 g, 5.7 mmol) were dissolved in a mixture of
THF (10 mL) and water (2 mL). The solution was degassed,
Pd(OAc)2 (15.8 mg, 0.070 mmol) and 2-dicyclohexylphosphino-2′,6′-
dimethoxybiphenyl SPhos (35 mg, 0.084 mmol) were added under an
Ar stream, and the mixture was degassed again. The solution was
heated at 70 °C for 48 h. The organic layer was then decanted, and the
aqueous layer was extracted 2 times with CH2Cl2. The combined
organic layer was washed with water and evaporated. The crude
product was purified by chromatography on silica gel by using
petroleum ether/CH2Cl2 (10%) as the eluent to give the title
1
compound 17d (white solid, 322 mg, 98%): mp 263−264 °C; H
NMR (400 MHz, CD2Cl2) δ 7.36 (dd, 3H, J = 2.0, 8.0 Hz), 7.31−7.21
(m, 12H), 7.00 (d, 6H, J = 7.2 Hz), 6.91 (d, 3H, J = 2.0 Hz), 6.77 (s,
3H), 1.28 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ 150.4, 141.6,
141.5, 139.9, 137.7, 130.2, 130.1, 129.7, 127.8, 127.7, 126.5, 124.4,
34.5, 31.2; HRMS (FD-TOF) m/z [M]+ Calcd for C54H54 702.42255,
found 702.42535.
1,7,13-Tri-tert-butyl-hexa-peri-hexabenzocoronene (28).
Compound 17d (150 mg, 0.21 mmol) was dissolved in 50 mL of
unstabilized dichloromethane and degassed with an Ar stream for 15
min. Then a solution of FeCl3 (690 mg, 4.3 mmol) in 10 mL of
nitromethane was added dropwise while continuously degassing with
an Ar stream. After 1 h the reaction was stopped by adding 100 mL of
ethanol. The organic phase was then washed twice with water and
dried over anhydrous Na2SO4. The solvent was removed in vacuo, and
the crude product was purified by chromatography on silica gel by
using petroleum ether/CH2Cl2 (5%) as the eluent to give the title
1
compound 28 (yellow solid, 106 mg, 72%): mp > 400 °C; H NMR
(400 MHz, CD2Cl2) δ 8.94 (d, 3H, J = 8.8 Hz), 8.92 (d, 3H, J = 8.8
Hz), 8.46 (d, 3H, J = 7.6 Hz), 8.39 (d, 3H, J = 8.8 Hz), 7.92 (t, 3H, J =
7.6 Hz), 1.61 (s, 27H); 13C NMR (100 MHz, CD2Cl2) δ 147.2, 131.7,
130.5, 130.3, 129.5, 128.3, 123.8, 121.6, 120.7, 120.3, 120.0, 38.5, 34.4;
HRMS (FD-TOF) m/z [M]+ Calcd for C54H42 690.32865, found
690.32689.
Traces of 29, 30 and 31. MS (FD-TOF) m/z [M]+ Calcd for
C50H34 (29) 634.3, found 634.2; [M]+ Calcd for C50H36O2 (30)
668.3, found 668.2; [M]+ Calcd for C50H35Cl (31) 670.2, found 670.2.
1,4-Bis(5-tert-butyl-2-methoxyphenyl)benzene (23). 1,4-Phe-
nylenediboronic acid 22 (1.0 g, 6.0 mmol), 5-tert-butyl-2-methox-
yphenylbromide 21 (3.2 g, 13.1 mmol) and Na2CO3 (6.30 g, 59.5
mmol) were dissolved in toluene (48 mL), water (16 mL) and ethanol
(8 mL). The solution was degassed, Pd(PPh3)4 (690 mg, 0.60 mmol)
was added under an Ar stream, and the mixture was degassed again.
The solution was heated at 90 °C for 48 h. The organic layer was then
decanted, and the aqueous layer was extracted twice with CH2Cl2. The
combined organic layer was washed with water and evaporated. The
crude product was purified by chromatography on silica gel by using
petroleum ether/CH2Cl2 (20%) as the eluent to give the title
1
compound 23 (white solid, 2.15 g, 90%): mp 165−166 °C; H NMR
3,11,19-Tri-tert-butyl-6,14,22-tris(trimethylsilyl)hexabenzo-
triphenylene (20). Compound 17c (200 mg, 0.22 mmol) was
dissolved in 50 mL of unstabilized dichloromethane and degassed with
an Ar stream for 15 min. Then a solution of FeCl3 (700 mg, 4.3 mmol)
(400 MHz, CD2Cl2) δ 7.50 (s, 4H), 7.35 (d, 2H, J = 2.8 Hz), 7.32 (dd,
2H, J = 2.6, 8.6 Hz), 6.93 (d, 2H, J = 8.4 Hz), 3.79 (s, 6H), 1.31 (s,
18H); 13C NMR (100 MHz, CD2Cl2) δ 154.4, 143.5, 137.7, 129.8,
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129.1, 128.0, 125.3, 110.7, 55.5, 34.0, 31.3; HRMS (FD-TOF) m/z
[M]+ Calcd for C28H34O2 402.25588, found 402.25699.
35.2, 31.3; HRMS (FD-TOF) m/z [M]+ Calcd for C38H32 488.25040,
found 488.25075.
1,4-Bis(5-tert-butyl-2-hydroxyphenyl)benzene (24). Com-
pound 23 (1.86 g, 4.6 mmol) was dissolved in 50 mL of dry
CH2Cl2 under Ar and brought to −20 °C. BBr3 (1 M in CH2Cl2, 11.6
mmol, 11.6 mL) was added dropwise with vigorous stirring, the
reaction mixture was stirred overnight and finally warmed to room
temperature. The reaction mixture was then poured onto crushed ice,
the organic layer was then decanted, and the aqueous layer was
extracted twice with CH2Cl2. The combined organic layer was washed
with water and dried over anhydrous Na2SO4. The solvent was
removed under a vacuum, yielding 24 (1.71 g, 99%) as a white solid:
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic characterization for 18, 20, 27, and 30+31
1
(CIF). H NMR, 13C NMR, and 19F NMR (if applicable)
spectra for new isolated compounds: 6, 7, 13−15, 17a−d to 20,
23−28. This material is available free of charge via the Internet
at http://pubs.acs.org.
1
mp 161−162 °C; H NMR (400 MHz, CD2Cl2) δ 7.59 (s, 4H), 7.29
AUTHOR INFORMATION
Corresponding Author
*E-mail: durola@crpp-bordeaux.cnrs.fr.
Notes
■
(d, 2H, J = 2.8 Hz), 7.27 (dd, 2H, J = 2.6, 7.8 Hz), 6.87 (d, 2H, J = 8.4
Hz), 5.10 (s, 2H), 1.31 (s, 18H); 13C NMR (100 MHz, CD2Cl2) δ
150.3, 143.8, 137.2, 129.8, 127.3, 127.1, 126.1, 115.4, 34.1, 31.3;
HRMS (FD-TOF) m/z [M]+ Calcd for C26H30O2 374.22458, found
374.22408.
The authors declare no competing financial interest.
1,4-Bis(5-tert-butyl-2-trifluoromethylsulfonyloxyphenyl)-
benzene (25). To compound 24 (1.50 g, 4.0 mmol) in 100 mL of
anhydrous CH2Cl2 were added 3.5 mL of pyridine, and the solution
was cooled to 0 °C. Trifluoromethanesulfonic anhydride (1.7 mL, 10
mmol) was added dropwise, and the mixture was warmed to room
temperature and stirred overnight. The solvent was removed under a
vacuum. The crude product was purified by chromatography on silica
gel by using petroleum ether/CH2Cl2 (15%) as the eluent to give the
ACKNOWLEDGMENTS
■
We are grateful to the Reg
buy laboratory equipment.
́
ion Aquitaine for financial support to
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■
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title compound 25 (white solid, 2.43 g, 95%): mp 180−181 °C; H
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7.47 (dd, 2H, J = 2.0, 8.8 Hz), 7.32 (d, 2H, J = 8.4 Hz), 1.35 (s, 18H);
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K3PO4 (1.6 g, 7.5 mmol) were dissolved in a mixture of THF (10 mL)
and water (2 mL). The solution was degassed, Pd(OAc)2 (21 mg, 0.09
mmol) and 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl SPhos
(46 mg, 0.11 mmol) were added under an Ar stream, and the mixture
was degassed again. The solution was heated at 70 °C for 48 h. The
organic layer was then decanted, and the aqueous layer was extracted
twice with CH2Cl2. The combined organic layer was washed with
water and evaporated. The crude product was purified by
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(10%) as the eluent to give the title compound 26 (white solid, 540
mg, 90%): mp 305−306 °C; 1H NMR (400 MHz, CD2Cl2) δ 7.58 (d,
1H, J = 2.4 Hz), 7.41 (d, 1H, J = 2.0 Hz), 7.39 (d, 2H, J = 1.6 Hz),
7.38 (d, 4H, J = 7.6 Hz), 7.32 (d, 2H, J = 8.4 Hz), 7.10 (d, 4H, J = 8.0
Hz), 6.99 (s, 4H), 1.35 (s, 18H), 0.22 (s, 18H); 13C NMR (100 MHz,
CD2Cl2) δ 150.6, 141.9, 140.2, 139.9, 138.2, 137.6, 132.8, 130.3, 129.5,
129.2, 127.6, 124.6, 34.5, 31.1, −1.4; HRMS (FD-TOF) m/z [M]+
Calcd for C44H54Si2 638.37640, found 638.37464.
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Hz), 8.95 (t, 2H, J = 8.0 Hz), 7.82 (dd, 2H, J = 1.6, 8.8 Hz), 1.60 (s,
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