Controlling the Scholl reaction

Article abstract of DOI:10.1021/jo061515x

Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups (e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly. Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating m-directors (e.g., NO₂) suppress reaction. MoCl₅ and PhI(OOCCF₃)₂/BF ₃·Et₂O are general and effective reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki-Miyaura couplings were used to generate 12 substituted o-terphenyl derivatives.

Full text of DOI:10.1021/jo061515x

Controlling the Scholl Reaction
Benjamin T. King,* Jirˇ´ı Kroul´ık, Charles R. Robertson, Pawel Rempala, Cameron L. Hilton,
Justin D. Korinek, and Lisa M. Gortari
Department of Chemistry, UniVersity of NeVadasReno, Reno, NeVada 89557
king@chem.unr.edu
ReceiVed July 20, 2006
Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate
that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to
oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups
(e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic
aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-
directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly.
Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating
m-directors (e.g., NO2) suppress reaction. MoCl5 and PhI(OOCCF3)2/BF3‚Et2O are general and effective
reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in
alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki-Miyaura couplings were used
to generate 12 substituted o-terphenyl derivatives.
Introduction
aryl boronic acid or ester, which can be difficult to purify and
whose preparation requires an additional step; the Scholl
oxidation requires no functionality. The Suzuki-Miyaura
The Scholl oxidation, which generates a new C-C bond
between two unfunctionalized aryl vertices, has not been a
mainstay of organic synthesis because its outcome has been
somewhat unpredictable. Its use has been essentially limited to
the preparation of hexaalkoxytriphenylenes,1,2 which are widely
studied as discotic liquid crystals, and to the preparation of large
polycyclic aromatic hydrocarbons (PAHs) from branched phe-
nylene precursors,3-5 an area dominated by Mu¨llen and co-
workers. In this work, we aimed to develop a practical set of
guidelines for the rational application of the Scholl reaction.
The Scholl reaction holds much promise, as illustrated by
comparison with the widely used Suzuki-Miyaura coupling.
The Suzuki-Miyaura reaction requires an aryl halide and an
(4) Iyer, V. S.; Yoshimura, K.; Enkelmann, V.; Epsch, R.; Rabe, J. P.;
Mu¨llen, K. Angew. Chem., Int. Ed. 1998, 37, 2696-2699. Mu¨ller, M.; Ku¨bel,
C.; Mu¨llen, K. Chem.-Eur. J. 1998, 4, 2099-2109. Berresheim, A. J.;
Mu¨ller, M.; Mu¨llen, K. Chem. ReV. 1999, 99, 1747-1785. Do¨tz, F.; Brand,
J. D.; Ito, S.; Gherghel, L.; Mu¨llen, K. J. Am. Chem. Soc. 2000, 122, 7707-
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Eur. J. 2000, 6, 1834-1839. Ito, S.; Herwig, P. T.; Bo¨hme, T.; Rabe, J. P.;
Rettig, W.; Mu¨llen, K. J. Am. Chem. Soc. 2000, 122, 7698-7706. Ito, S.;
Wehmeier, M.; Brand, J. D.; Ku¨bel, C.; Epsch, R.; Rabe, J. P.; Mu¨llen, K.
Chem.-Eur. J. 2000, 6, 4327-4342. Rathore, R.; Burns, C. L. J. Org. Chem.
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Mu¨llen, K. Angew. Chem., Int. Ed. 2004, 43, 755-758. Wang, Z.; Tomovic´,
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Mu¨llen, K. J. Org. Chem. 2004, 69, 5179-5186. Wu, J.; Watson, M. D.;
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2005, 44, 1247-1250. Wu, J.; Grimsdale, A. C.; Mu¨llen, K. J. Mater. Chem.
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* Corresponding author.
(1) Kumar, S. Liq. Cryst. 2005, 32, 1089-1013.
(2) Kumar, S.; Manickam, M. Chem. Commun. 1997, 17, 1615-1616.
(3) Simpson, C. D.; Mattersteig, G.; Martin, K.; Gherghel, L.; Bauer,
R. E.; Ra¨der, H. J.; Mu¨llen, K. J. Am. Chem. Soc. 2004, 126, 3139-3147.
10.1021/jo061515x CCC: $37.00 © 2007 American Chemical Society
Published on Web 02/28/2007
J. Org. Chem. 2007, 72, 2279-2288
2279

King et al.
SCHEME 1. Products of the Scholl Reaction of
o-Terphenyl
coupling requires expensive palladium catalysts, whereas the
Scholl reaction can use inexpensive reagents, even iron salts.
The Suzuki-Miyaura coupling is rarely used in cascade
sequences (although it is effective for polymerizations6), but in
contrast the Scholl reaction has been used to make 126 bonds
in a single step.3
A strong acid, often a Lewis acid, and an oxidant are
necessary;7 a single reagent often serves both roles. Brønsted
acids, which are usually present as impurities in Lewis acids
and are necessarily formed as a byproduct of the Scholl reaction,
accelerate the reaction.8 The following cocktails have all been
reported in the literature: FeCl3 in CH2Cl2,9 CuCl2 , or
5
Cu(OSO2CF3)23 with AlCl3 in CS2, MoCl5 with or without TiCl4
in CH2Cl2,10-12 (CF3COO)2IIIIC6H5 (PIFA)13 with BF3‚Et2O in
CH2Cl2, Pb(OAc)4/BF3‚Et2O MeCN,14,15 Tl(O2CCF3)3 in CF3-
CO2H,15 and Tl(O2CCF3)3/BF3‚Et2O in organic solvents.15
Radical cation based7,16 and arenium cation based mechanisms
have been proposed7,17 for the Scholl reaction. In an excellent
paper, Kochi discusses the difficulties of distinguishing acid
vs electron-transfer catalysis.18 Feng, Wu, Enkelmann, and
Mu¨llen recently reported that topology and substituents (iodine,
t-butyl) influence the cyclization of hexa-peri-hexabenzocoro-
nene precursors.19 They attribute this effect to substituents
perturbing the spin density of putative radical cation intermedi-
ates. Recent computational mechanistic studies20,21 suggest that
the arenium cation mechanism has lower key transition state
barriers than the radical cation mechanism in polyphenyl
benzenes. The energetically favored arenium cation mechanism
involves the formation of an arenium cation, its electrophilic
attack on an arene, deprotonation (or possibly decomplexation
of a Lewis acid), and oxidative dehydrogenation to restore
aromaticity.
Results
We first evaluated common Scholl conditions using a simple
reaction, the conversion of unfunctionalized o-terphenyl 1 to
triphenylene 2 (Scheme 1). When using FeCl3, the optimized
yield was ∼20%. Chlorinated solvents (CH2Cl2, CHCl3, CCl4,
CH2ClCH2Cl) gave faster reactions than CH3NO2 or hexane.
When using MoCl5 in CH2Cl2,2,10,11 the optimized yield was
also ∼20%. Aside from triphenylene, unreacted o-terphenyl and
insoluble oligomeric products were present. In a typical
optimized reaction, about 25% of the reaction mixture was
triphenylene and unreacted o-terphenyl. The remaining 75% was
yellow insoluble powder. Vacuum sublimation of this powder
afforded clean 2,2′-bistriphenylene 3. The MALDI-MS of the
residue showed two compounds having a mass 2 or 4 Da less
that of 3, indicating that annulation had occurred. These
compounds likely correspond to 4 and 5, based on the propensity
of the Scholl reaction to give fully fused products.20,21 Higher
oliomers were also evident. Reactions using C6H5I(O2CCF3)2/
BF3‚Et2O (PIFA/BF3) instead of MoCl5 gave similar results.
High dilution conditions (0.5 mg/mL) did not improve the
performance of this reaction. Less oligomeric product (10%)
was formed, but the conversion of 1 to 2 was lower (10%).
The Scholl oxidation of terphenyl homologues also failed to
produce products in good yield. o-Quaterphenyl 6, 1,2,3-
triphenylbenzene 7, and o-quinquephenyl 8 afforded only trace
amounts of their annulated PAH counterparts 9, 9, or 10
respectively, using either MoCl5 or PIFA/BF3‚Et2O. These
experiments are summarized in Scheme 2.
The reactions in Schemes 1 and 2 produced much oligomeric
material. To determine if dimeric products arise from terphenyl
coupling, triphenylene coupling, or cross-coupling, the oxidation
of a 1:1 mixture of 13C-labeled o-terphenyl (C6H5-C6H4-
13C6H5) and unlabeled triphenylene was performed using
substoichiometric oxidant (10 mol % with respect to both
reactants). MALDI-MS revealed that the dimeric products are
unlabeled.
Blocking groups are commonly used to direct electrophilic
aromatic substitution. We exploited this effect to suppress
dimerization. Oxidation of 4,3′,4′′-tri(t-butyl)-o-terphenyl 11 by
PIFA/BF3‚Et2O gave 2,7,10-tri(t-butyl)triphenylene 12 in good
yield (86%) (Scheme 3), but use of MoCl5 gave an intractable
reaction mixture. The oxidation of 4,4′′-di-t-butylterphenyl 13
by PIFA/BF3‚Et2O gave 3,7-di(t-butyl)triphenylene 14 and its
dimer 15, which was crystallographically characterized.
Methoxy groups are effective o,p-directors. We find that
methoxy groups influence the Scholl reaction, and oxidation of
(5) Ku¨bel, C.; Eckhardt, K.; Enkelmann, V.; Wegner, G.; Mu¨llen, K.
J. Mater. Chem. 2000, 10, 879-886.
(6) Schlu¨ter, A. D. In Catalysis from A to Z: a Concise Encyclopedia;
Cornils, B., Herrmann, W. A., Schlo¨gl, R., Wong, C.-H., Eds.; Wiley-
VCH: New York, Weinheim, 2000; p 565.
(7) Balaban, A. T.; Nenitzescu, C. D. In Friedel-Crafts and Related
Reactions; Olah, G. A., Ed.; Wiley: New York, 1964; Vol. 2, Part 2, p
979-1047.
(8) Baddeley, G. J. Chem. Soc. 1950, 994-997. Balaban, A. T.;
Nenitzescu, C. D. Stud. Cercet. Chim., Acad. Repub. Pop. Rom. 1959, 7,
521-529.
(9) Boden, N.; Bushby, R. J.; Headdock, G.; Lozman, O. R.; Wood, A.
Liq. Cryst. 2001, 28, 139-144. Boden, N.; Bushby, R. J.; Cammidge,
A. N.; Duckworth, S.; Headdock, G. J. Mater. Chem. 1997, 7, 601-605.
(10) Kramer, B.; Fro¨hlich, R.; Waldvogel, S. R. Eur. J. Org. Chem. 2003,
3549-3554.
(11) Waldvogel, S. R.; Aits, E.; Holst, C.; Fro¨hlich, R. Chem. Commun.
2002, 1278-1279.
(12) Kovacic, P.; Lange, R. M. J. Org. Chem. 1963, 28, 968-972.
Kovacic, P.; Jones, M. B. Chem. ReV. 1987, 87, 357-379.
(13) Takada, T.; Arisawa, M.; Gyoten, M.; Hamada, R.; Tohma, H.; Kita,
Y. J. Org. Chem. 1998, 63, 7698-7706. Churruca, F.; SanMartin, R.; Carril,
M.; Urtiaga, M. K.; Solans, X.; Tellitu, I.; Dom´ınguez, E. J. Org. Chem.
2005, 70, 3178-3187.
(14) Aylward, J. B. J. Chem. Soc. B 1967, 1268-1270.
(15) McKillop, A.; Turrell, A. G.; Young, D. W.; Taylor, E. C. J. Am.
Chem. Soc. 1980, 102, 6504-6512.
(16) Di Stefano, M.; Negri, F.; Carbone, P.; Mu¨llen, K. Chem. Phys.
2005, 314, 85-99.
(17) Kovacic, P.; Lange, R. M. J. Org. Chem. 1965, 30, 4251-4254.
(18) Rathore, R.; Kochi, J. K. Acta Chem. Scan. 1998, 52, 114-130.
(19) Feng, X.; Wu, J.; Enkelmann, V.; Mu¨llen, K. Org. Lett. 2006, 8,
1145-1148.
(20) Rempala, P.; Kroul´ık, J.; King, B. T. J. Am. Chem. Soc. 2004, 126,
15002-15003.
(21) Rempala, P.; Kroulik, J.; King, B. T. J. Org. Chem. 2006, 71, 5067-
5081.
2280 J. Org. Chem., Vol. 72, No. 7, 2007

Controlling the Scholl Reaction
SCHEME 2. Small, Unsubstituted Oligophenyl Arenes that
Do Not Fuse Cleanly
SCHEME 4. Oxidation of Methoxylated Terphenyl
Derivatives
SCHEME 3. Oxidation of tert-Butylated Terphenyls
3,3′′-dimethoxy-o-terphenyl 16 with MoCl5 in CH2Cl2 gave 2,7-
dimethoxytriphenylene 17 in 53% isolated yield (Scheme 4).
The oxidation of the tetramethoxy derivative 18 using the same
conditions gave the 1,3,10,12-tetramethoxytriphenylene 19 in
30% isolated yield. The best results were obtained with 3 equiv
of MoCl5 and a 45 min reaction time. PIFA/BF3‚Et2O gave
lower conversion and more oligomeric material.
The Scholl oxidation of 3-methoxy-o-terphenyl 20 using
MoCl5/CH2Cl2 gave an intractable mixture in which neither of
the possible corresponding products, 1- or 2-methoxytri-
phenylene, was observed. The use of PIFA/BF3‚Et2O at
-78 °C gave the terphenyl/triphenylene dimer 21. Single-crystal
X-ray diffraction analysis established connectivity.
dibromo-o-terphenyl 25 using MoCl5 did not produce detect-
able quantities of 1,8-dibromotriphenylene under any con-
ditionssonly insoluble oligomers and starting material were
recovered. The oxidation of 3,3′′-dibromo-o-terphenyl 26
using MoCl5/CH2Cl2 gave a mixture of the starting compound
and 2,7-dibromotriphenylene 27 with conversion of about
20% (GC-MS) in an isolated yield of 9% (Scheme 5). Reac-
tion optimization was unsuccessful. Nitro groups, which are
strongly deactivating, m-directing substituents, inhibit the
Scholl reaction. Both 2,2′′-(28) and 3,3′′-dinitroterphenyl (29)
failed to react (28 PIFA/BF3‚Et2O; 29, PIFA/BF3‚Et2O and
MoCl5).
The Suzuki-Miyaura coupling provided a general route to
prepare the substituted terphenyls. Symmetrically substituted
terphenyls were prepared from o-diiodobenzene and a substituted
phenylboronic acid. Unsymmetrical terphenyls were prepared
from 2-iodobiphenyl and a substituted phenylboronic acid or
from 2-biphenylboronic acid and an aryl halide. The syntheses
are compiled in Table 1.
The oxidation of 2,2′′-dimethoxy-o-terphenyl 22 failed to
produce 1,8-dimethoxytriphenylene. From the complex reaction
mixture, we isolated the dimer of the starting compound,
tetramethoxysexiphenyl 23, as the major product in 26% yield,
the structure of which was determined by X-ray diffraction
analysis. Attempts to oxidize 4,4′′-dimethoxy-o-terphenyl 24
gave only intractable reaction mixtures.
The influence of deactivating substituents was examined.
Bromine atoms, which are weakly deactivating, o,p-directing
substituents, are similar to methoxy groups. Oxidation of 2,2′′-
Three substituted o-terphenyls were prepared by alternative
methods (Scheme 6). Suzuki-Miyara coupling was ineffective
for the preparation of 26. ipso-Bromination of 30 afforded 26.
J. Org. Chem, Vol. 72, No. 7, 2007 2281

King et al.
TABLE 1. Suzuki-Miyaura Routes to Terphenyls
SCHEME 5. Deactivated Substrates
SCHEME 6. Other Methods Used for the Synthesis of
Substituted Terphenyls
Friedel-Crafts alkylation of o-terphenyl introduced three t-butyl
groups. o-Quaterphenyl was prepared according to literature
methods.22
Discussion
In previous computational and experimental work,20,21 we
addressed the question, why does the Scholl reaction work well
in large phenylene dendrimers? Here, we address the comple-
mentary question: Why does the Scholl reaction not work well
in small phenylene oligomers, such as o-terphenyl? The answer
is that oligomerization of products is faster than cyclization of
reactants.
This is demonstrated by the labeling experiment shown in
Scheme 7. This experiment relies on observations from the
oxidation of unlabeled parent o-terphenylsthe oligomeric
products do not contain terphenyl units, only triphenylene units.
This could stem either from exclusive oligomerization of
triphenylene or from oligomerization of reactants to give putative
sexiphenyl or terphenyl-triphenylene intermediates, which
rapidly cyclize. To distinguish these scenarios, a 1:1 mixture
of 13C-labeled terphenyl 1* and unlabeled triphenylene 2 was
oxidized. The use of a substoichiometric oxidant (10 mol %
with respect to both reactants) was necessary to minimize the
formation of labeled triphenylene, which would complicate the
analysis, from terphenyl. Each dimerization scenario will give
isotopically unique products: (a) terphenyl-terphenyl coupling
will give two labeled rings; (b) terphenyl-triphenylene coupling
will give a single labeled ring; and (c) triphenylene-triphenylene
coupling will give no labeled rings. The MALDI-MS of the
insoluble products shows a dominant (>95%) peak at 450.
Within the uncertainty of the approximation that only unlabeled
triphenylene is present, triphenylene-triphenylene dimerization
occurs exclusively. The Scholl oxidation of o-terphenyl fails
because the product oligomerizes.
The vast majority of successful Scholl oxidations on unsub-
stituted phenylenes produces insoluble products. This is because
the products precipitate from solution, minimizing their pro-
pensity to oligomerize. This observation supports the conclusion
that oligomerization occurs through the products, not the
reactants. If the reactants did oligomerize rapidly, these suc-
cessful reactions would also be plagued by the production of
oligomers, but they are not. It logically follows that reactants
do not oligomerize rapidly.
Precipitation, however, does not completely prevent the
formation of oligomers. In the oxidation of hexaphenylbenzene
(22) Inoue, A.; Kitagawa, K.; Shinokubo, H.; Oshima, K. Tetrahedron
2000, 56, 9601-9605.
2282 J. Org. Chem., Vol. 72, No. 7, 2007

Controlling the Scholl Reaction
SCHEME 7. Possible Outcomes of the Labeling
Experimenta
FIGURE 1. Thermal ellipsoid plots of the X-ray structure of 19 from
two perspectives. Hydrogen atoms are omitted for clarity.
FIGURE 2. Relative proton affinities (kcal/mol) in 16.
a Only a single isotopomer is shown.
should be manifest. This effect has been used, perhaps fortu-
itously, to control the Scholl reaction, e.g. the oxidation of
veratrole is commonly used to make hexaalkoxytriphe-
nylenes.12,24 Permethoxylated hexa-peri-hexabenzocorone has
been prepared by Scholl oxidation of hexakis(3,4,5-trimethoxy-
phenyl)benzene.25 The methoxy group and probably other
activating o,p-directors that are compatible with acidic oxidants
can control the outcome of the Scholl reaction. As evidenced
by the clean formation of 17 (53%) and the formation of
tetramethoxy triphenylene 19 (30%) and dimers 21 (29%) and
23 (26%) (Scheme 4), aryl-aryl bonds form readily in two
situations: para to two methoxy groups or para to one methoxy
and ortho to another methoxy. We see no evidence for the
expected formation of bonds ortho to two methoxy groups, but
it is difficult to design test substrates that cannot react through
rotamers to give isomeric products. Bonds are not formed meta
to a methoxy group. In substrates with suitably located directing
groups, intramolecular cyclization competes effectively with
oligomerization.
to hexa-peri-hexabenzocoronene, MALDI-MS reveals the for-
mation of oligomers.21 This could be the result of slow
oligomerization of reactants, of the dilute products, or of any
of the numerous intermediates.
It is interesting that in the oxidation of o-terphenyl 1 (Scheme
1), 1,2′- or 1,1′-bistriphenylene was not observedsonly 2,2′-
bistriphenylene 3 could be identified. The prosaic explanation
is that the 2,2′-isomer 3 is formed faster that the 1,2′- or the
1,1′-isomer. However, a more appealing hypothesis exists. The
2,2′-isomer 3 cannot undergo intramolecular Scholl oxidation.
In contrast, the 1,2′- and 1,1′-isomers can undergo intramolecular
Scholl oxidation, to form 4 and 5, respectively. This intramo-
lecular fusion may occur faster than dimerization. Such behavior,
a slippery slope effect, has been noted previously.20,21 The failure
to observe 1,2′- or 1,1′-bistriphenylene may be because they
cyclize rapidly to form 4 and 5.
t-Butyl groups can inhibit vicinal reactions, and this effect
has been used to direct aryl halogenation.23 In the Scholl
oxidation, t-butyl groups inhibit oligomerization (Scheme 3).
Oxidation of tri(t-butyl)terphenyl 11 gave triphenylene 12 in
high yield (85%) without formation of dimeric products. This
contrasts with oxidation of di(t-butyl)terphenyl 13, which gave
only modest yields (23%) of triphenylene 14, along with
significant amounts (28%) of dimer 15, with coupling occurring
at the open ring. For both reactions, the electronic effect of the
t-butyl groups on the formation of the new bond is negligible
because the mildly o,p-directing t-butyl groups are meta to the
new bonds.
The Scholl reaction can introduce significant molecular strain.
Tetramethoxytriphenylene 19 (Figure 1, Scheme 4) possesses
19 kcal/mol of strain, considering 2 and 17 to be unstrained
(B3LYP/6-31G*).
(23) Harvey, R. G.; Pataki, J.; Cortez, C.; Raddo, P. D.; Yang, C. X.
J. Org. Chem. 1991, 56, 1210-1217.
(24) Simoni, D.; Giannini, G.; Baraldi, P. G.; Romagnoli, R.; Roberti,
M.; Rondanin, R.; Baruchello, R.; Grisolia, G.; Rossi, M.; Mirizzi, D.;
Invidiata, F. P.; Grimaudo, S.; Tolomeo, M. Tetrahedron Lett. 2003, 44,
3005-3008.
If the Scholl reaction proceeds by electrophilic aromatic
substitution, as calculations suggest, directing group effects
(25) Wang, Z.; Do¨tz, F.; Enkelmann, V.; Mu¨llen, K. Angew. Chem., Int.
Ed. 2005, 44, 1247-1250.
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King et al.
SCHEME 8. Arenium Cation (Left) and Radical Cation
(Right) Mechanisms for the Conversion of 16 to 17
FIGURE 3. Comparison of arenium cation and radical cation reaction
coordinate diagrams for the conversion of 16 to 17.
The arenium cation pathway is preferred over a radical cation
pathway in the conversion of unsubstituted o-terphenyl to
triphenylene.20,21 However, a radical cation pathway is the
accepted mechanism for Scholl oxidation of aryl ethers.26 Does
the presence of ether functionalities change the nature of the
mechanism? We addressed this point as we have done before,
by calculating the reaction pathways (B3LYP/6-31(d), some
transition-state energies are based on literature values).20,21 To
enable the direct comparison, we make the thermodynamic
assumptions that the initial steps are thermoneutral and that the
net energetic outcomes are equal (see ref 21 for discussion).
The reaction coordinate diagrams are shown in Figure 3. The
arenium cation pathway gives lower C-C bond forming
activation barriers by 7 kcal/mol. The penultimate intermediates,
dihydroterphenyl 36 or radical 43, define the energies of the
rate-determining transition state. The arenium cation pathway
is favored by 22 kcal/mol.
The nature of the C-C bond forming transition state for
radical cation 40 is complex and involves a change in electronic
symmetry. The details of this elementary step will be reported
separately.27
Surprisingly, the oxygen atoms are not the most basic sites
in 16 (Figure 2), carbon 5 is. These results are similar to proton
affinity calculations (B3LYP/6-311++G(d,p)) on anisole,28
where the para carbon is the most basic. Protonation of carbon
6, however, does not place positive charge at position 6, which
is required for the intramolecular electrophilic attack. We have
previously reported21 that protonation ortho to the new bond,
which does put positive charge at the electrophilic position,
provides the lowest-energy transition-state barrier in the conver-
sion of 1 to 2. The same consideration applies to the conversion
of 16 to 17. Because the tautomers are in rapid equilibrium,
the Curtin-Hammett principle applies and reaction will occur
through the lowest-energy transition state. These findings are
summarized in Figure 3 and Scheme 8. The arenium ion
mechanism is energetically preferred for the conversion of 16
to 17.
Deactivating groups were also considered (Scheme 5).
Bromides, which are deactivating but o,p-directing, work like
methoxy but in lower yields. The nitro group is a strongly
deactivating m-director. Not surprisingly, no reaction was
observed when 2,2′- or 3,3′-dinitro-o-terphenyl (28 or 29) was
treated with MoCl5 or PIFA/BF3‚Et2O. The electron-withdraw-
ing nitro group could inhibit either the generation of the arenium
cation or its intramolecular attack with the adjacent phenyl ring,
both of which are necessary for reaction.
(26) Musgrave, O. C. Chem. ReV. 1969, 69, 499-531.
(27) Rempala, P.; King, B. T. to be submitted for publication.
(28) Nam, P.-C.; Nguyen, M. T.; Chandra, A. K. J. Phys. Chem. A 2006,
110, 4509-4515.
A few points of the terphenyl syntheses merit discussion.
Diglyme, which is not widely used in Suzuki reactions, was
notably effective (Table 1). Pd(dppf)2 worked well for the
2284 J. Org. Chem., Vol. 72, No. 7, 2007

Controlling the Scholl Reaction
o-Terphenyl-13C6 (1*). In DMF-H2O (3:1, 40 mL), 2-biphenyl
boronic acid (220 mg, 1.1 mmol) was added to Ba(OH)2‚8H2O (630
mg, 2.0 mmol) and bromobenzene-13C6 (163 mg, 1.0 mmol). After
addition of PdCl2dppf (60 mg, 0.1 mmol), the solution was heated
to 80 °C for 2 h. The solution was filtered through a pad of SiO2,
and the filtrate was extracted with hexane and H2O. The organic
layer was dried over MgSO4, and solvent removal gave pure 1*
(181 mg, 77%).
preparation of both unsubstituted 13C-labeled terphenyl 1* and
nitrated terphenyls29 28 and 29.
Conclusions
The Scholl reaction fails in small, unfunctionalized arenes
because the products oligomerize. This can be suppressed by
blocking groups. Oligomerization is less severe in large dendritic
polyphenylenes because the insoluble products precipitate from
solution. Suitably placed t-butyl groups suppress oligomeriza-
tion. Electronic directing groups can be used to control the
Scholl reaction. o,p-Directing, activating functionality should
be present on both aryl moieties, arranged o,p or, preferably,
p,p to the nascent bond. The Scholl reaction does not form bonds
meta to an o,p-activating group. m-Directing, deactivating
functionality suppresses the Scholl reaction. In alkoxyarenes,
as in unsubstituted arenes, the Scholl reaction proceeds by an
arenium cation pathway.
[2,2′]Bitriphenylenyl (3).30 See general oxidation procedure. A
mixture of o-terphenyl (1.5 g, 6.51 mmol) and MoCl5 (3.79 g, 13.8
mmol) in CH2Cl2 (100 mL) was stirred for 2 h. Sublimation of the
insoluble material at 150 °C/160 mTorr gave 3 as a yellow powder
(1.137 g, 75%): 1H NMR 500 MHz (DMSO-d6) δ 7.76 (m, 4H),
8.33 (dd, J ) 8.5, 2.0 Hz, 1H), 8.86 (m, 2H), 8.90 (m, 1H), 8.97
(d, J ) 9.0 Hz, 1H,), 9.18 (m, 1H), 9.33 (dd, J ) 8.5, 2.0 Hz, 1H);
13C NMR 125 MHz (DMSO-d6) δ 121.9, 123.6, 123.6, 123.7, 124.4,
124.4, 126.8, 127.6, 127.6, 127.7, 127.8, 128.6, 129.0, 129.3, 129.3,
129.4, 129.8, 138.9; MALDI for C36H22 calcd 454.17, found 454.18.
o-Quaterphenyl (6). Analogous to the reported procedure.22 Mg
turnings (0.017 g, 0.687 mmol) in THF (2 mL) were stirred with
2-bromobiphenyl (0.152 g, 0.654 mmol) overnight at room tem-
perature under N2. Additional THF (4 mL) was added, and the
solution was cooled to -78 °C. To the reaction was added TiCl4
(140 mg, 0.654 mmol) dropwise, and the mixture was stirred at
0 °C for 0.5 h. The mixture was poured into a saturated NH4Cl
solution, extracted with EtOAc (3 × 10 mL), and dried over Na2-
SO4. The solvent was removed, and the residue was chromato-
graphed (SiO2/hexane) to give 6 as a white solid (77 mg, 65%):
mp 115-116 °C (lit.31 mp 117.8 °C); GC/MS (EI) 306.
Experimental
General Methods. All reactions were performed under N2 using
conventional vacuum-line techniques. Catalysts were dispensed in
a glove box under Ar. Anhydrous (<50 ppm) THF and Et2O were
dispensed in a glove box from commercially available kegs using
a custom delivery system. CH2Cl2 was distilled from CaH2 and
stored over 4 Å molecular sieves. All other reagents were
commercially available and used without further purification.
Analytical HPLC was performed using MeOH/H2O on a C18
column, a photodiode array, and evaporative light scattering
detectors.
o-Quinquephenyl (8).32 See general Suzuki reaction method.
A mixture of 2-biphenylboronic acid (0.180 g, 0.910 mmol),
o-diiodobenzene (0.154 g, 0.455 mmol), and Pd(PPh3)4 (0.064 g,
0.055 mmol) was stirred in a mixture of NaOH, water, and diglyme
(7 mL of 2.5 M NaOH, 30 mL of diglyme) at 50 °C for 3 h.
Conventional workup with toluene/water, silica gel chromatography
(4:1 hexane/CH2Cl2), and recrystallization (hexane) afforded 8 (156
mg, 87%) as a white solid: mp 162-164 °C (lit.32 mp 152.4 °C);
GC/MS (EI) 383.
4,4′,4′′-Tri-t-butyl-o-terphenyl (11). o-Terphenyl (10.0 g, 43.5
mmol) and t-BuCl (56.0 g, 605 mmol) were stirred in CH2Cl2 (150
mL). A solution of FeCl3 (5 mg) in nitromethane (0.5 mL) was
added dropwise, and the solution was stirred for 1 h. The green
mixture was quenched with H2O, and the organics were extracted.
Chromatography (SiO2, hexane/benzene 1:1) and recrystallization
from (CH3)2CO afforded 11 (10.52 g, 61%) as colorless crystals:
mp 131-132 °C; 1H NMR 500 MHz (CDCl3) δ 1.26 (s, 9H, CMe3),
1.27 (s, 9H, CMe3), 1.36 (s, 9H, CMe3), 7.04 (m, 4H), 7.18 (m,
4H), 7.33 (m, 1H), 7.39 (m, 2H); 13C NMR 125 MHz (CDCl3) δ
31.3, 31.4, 31.5, 34.4, 34.4, 34.6, 124.2, 124.6, 124.6, 127.7, 129.5,
129.6, 130.2, 137.7, 138.5, 139.2, 140.1, 148.9, 149.1, 149.5; IR
(NaCl plates) 2963, 2903, 2868, 2744, 2712, 2404, 1907, 1790,
1668, 1604, 1516, 1509, 1487, 1461, 1393, 1362, 1269, 1253, 1217,
1202, 1118, 1046, 1025, 1015, 1004, 946, 923, 897, 870, 834, 824,
759 cm-1. Anal. calcd for C30H38: C, 90.39; H, 9.61. Found: C,
90.58; H, 9.46.
General Suzuki Reaction Method. o-Diiodobenzene (1 equiv)
is stirred with the corresponding boronic acid (2-3 equiv) and Pd-
(PPh3)4 (10-12 mol %) in a mixture of equal volumes of diethylene
glycol dimethyl ether (diglyme) or DME and 2.5 M NaOH (referred
to as solvent/base). Solutions were degassed by freeze-pump-
thaw cycles or by a dynamic vacuum before the addition of catalyst.
General Oxidation Procedure with MoCl5. To a solution of
o-terphenyl (100 mg, 0.43 mmol) in 10 mL of CH2Cl2 was added
MoCl5 (1-2 equiv, assuming 2e- oxidation). The reaction was
stirred under N2 at room temperature for 2 h. The reaction was
quenched with MeOH (10 mL) and stirred for an additional hour.
The resulting mixture was diluted with CH2Cl2 and MeOH, and
insoluble materials were removed by filtration. The solids were
thoroughly washed with CH2Cl2, air-dried (24 h), and massed. This
material was analyzed using MALDI-TOF. The organics were
washed with H2O and dried over MgSO4, and the solvent was
removed. The composition of the resulting reaction mixture was
1
analyzed by HPLC, GC/MS, and H NMR. The products were
isolated by SiO2 chromatography.
General Oxidation Procedure with PIFA and BF3‚Et2O. To
a solution of o-terphenyl (100 mg, 0.43 mmol) in CH2Cl2 (8 mL)
was added dropwise a solution of the equimolar mixture of PIFA
and BF3‚Et2O (1.5-2.5 equiv/bond) in CH2Cl2 (2 mL) under N2 at
-40 °C. The reaction mixture was stirred for 2 h and then warmed
to -10 °C over 1.5 h. The reaction was quenched by MeOH and
an aqueous solution of Na2SO3. The resulting mixture was diluted
with CH2Cl2 and MeOH, and insoluble materials were removed
by filtration. The solids were thoroughly washed with CH2Cl2, air-
dried (24 h), and massed. This material was analyzed using MALDI-
TOF. The organics were washed with H2O and dried over MgSO4,
and the solvent was removed. The composition of the resulting
2,6,11-Tri-t-butyl-triphenylene (12). See general oxidation
procedure. A solution of 21 (1.00 g, 2.51 mmol) in CH2Cl2 (10
mL) was stirred, and a solution of PIFA (2.70 g, 6.28 mmol) and
BF3‚Et2O (1.07 g, 7.54 mmol) in CH2Cl2 (5 mL) was added
dropwise at -78 °C under nitrogen. The reaction mixture was stirred
for 2 h and allowed to warm to -7 °C over 1 h. Workup and
chromatography (SiO2, petroleum ether/benzene 10:1) and subse-
1
(30) Shih, H.-T.; Shih, H.-H.; Cheng, C.-H. Org. Lett. 2001, 3, 811-
814.
(31) Ozasa, S.; Fujioka, Y.; Hashino, H.; Kimura, N.; Ibuki, E. Chem.
Pharm. Bull. 1983, 31, 2313-2320.
(32) Ibuki, E.; Ozasa, S.; Fujioka, Y.; Okada, M.; Yanagihara, Y. Chem.
Pharm. Bull. 1982, 30, 2369-2379.
reaction mixture was analyzed by HPLC, GC/MS, and H NMR.
The products were isolated by SiO2 chromatography.
(29) Franc, C.; Denonne, F.; Cuisinier, C.; Ghosez, L. Tetrahedron Lett.
1999, 40, 4555-4558.
J. Org. Chem, Vol. 72, No. 7, 2007 2285

King et al.
quent removal of iodobenzene under a high vacuum afforded 0.858
g (86%) of 12 as a yellow oil, which crystallized from petroleum
ether at -30 °C. An analytical sample was obtained by sublimation
of DME and aqueous base. After degassing, Pd(PPh3)4 (1.16 g,
1.00 mmol) was added and the reaction was heated to 85 °C for 4
h. The mixture was separated by Et2O extraction. After removal of
solvent, the residue was chromatographed (SiO2, hexane/CH2Cl2
3:1). Recrystallization from hexane gave 2.39 g (80% yield) of 16
1
at 150 °C/60 mTorr (63 mg, 6.3%): mp 114-118 °C; H NMR
500 MHz (CDCl3) δ 1.49 (s, 9H, CMe3), 1.50 (s, 9H, CMe3), 1.51
(s, 9H, CMe3), 7.68 (m, 3H), 8.52 (d, J ) 8.5 Hz, 1H), 8.53 (d, J
) 8.5 Hz, 1H), 8.60 (m, 2H), 8.64 (d, J ) 2.0 Hz, 1H), 8.65 (d, J
) 1.5 Hz, 1H); 13C APT NMR 125 MHz (CDCl3) δ 31.4 (CH3),
31.46 (CH3), 31.50 (CH3), 35.00 (CMe3), 35.01 (CMe3), 118.85
(CH), 118.95 (CH), 119.03 (CH), 122.85 (CH), 122.98 (CH), 122.99
(CH), 124.7 (CH), 124.86 (CH), 124.94 (CH), 127.2 (C), 127.6
(C), 127.9 (C), 129.1 (C), 129.3 (C), 129.7 (C), 149.2 (C), 149.3
(C), 149.4 (C); IR (NaCl plates) 2963, 2903, 2868, 2360, 2342,
1762, 1614, 1510, 1490, 1479, 1459, 1413, 1400, 1362, 1268, 1238,
1216, 1202, 1141, 1119, 1044, 1031, 1004, 909, 880, 836, 815,
759 cm-1; GC/MS (EI) 297, 282. Anal. calcd for C30H36: C, 90.85;
H, 9.15. Found: C, 90.91; H, 9.19.
1
as a white solid: mp 89-91 °C; H NMR 500 MHz ((CD3)2CO)
δ 3.59 (s, 3H, OMe), 6.66 (m, 1H), 6.73 (m, 2H), 7.13 (t, J ) 8.0
Hz, 1H), 7.40 (s, 2H); 13C NMR 125 MHz ((CD3)2CO) δ 55.4,
113.4, 116.1, 122.9, 128.5, 129.9, 131.3, 141.4, 144.0, 160.3; IR
(NaCl plates) 3058, 3001, 2956, 2938, 2834, 2493, 2044, 1931,
1841, 1745, 1603, 1579, 1468, 1424, 1318, 1288, 1250, 1217, 1179,
1116, 1087, 1047, 1022, 995, 951, 874, 857, 789, 760, 734, 704
cm-1; UV-vis (hexane) λmax (log ꢀ) 221 (3.73), 279 (3.69); GC/
MS (EI) 290. Anal. calcd for C20H18O2: C, 82.72; H, 6.26. Found:
C, 82.62; H, 6.51.
2,7-Dimethoxytriphenylene (17). See general oxidation proce-
dure. A solution of 16 (201 mg, 0.694 mmol) and MoCl5 (189 mg,
0.694 mmol) in CH2Cl2 (15 mL) was stirred for 22 h. A second
portion of MoCl5 (189 mg) was added, and the reaction was stirred
for an additional 6.5 h. After workup, the yellow crude product
was purified by sublimation at 150 °C/160 mTorr to give 17 as a
white solid (106 mg, 53%): mp 153-155 °C; 1H NMR 500 MHz
(DMSO-d6) δ 4.04 (s, 3H, OMe), 7.30 (dd, J ) 9.0, 2.5 Hz, 1H),
7.69 (m, 1H), 8.19 (d, J ) 2.5 Hz, 1H), 8.61 (d, J ) 9.5 Hz, 1H),
8.77 (m, 1H); 13C NMR 125 MHz (DMSO-d6) δ 55.8, 106.4, 117.3,
124.5, 124.7, 125.4, 128.2, 130.8, 131.0, 159.5; IR (NaCl plates)
2963, 2836, 2433, 2366, 2343, 1613, 1498, 1452, 1427, 1282, 1250,
1218, 1180, 1048, 1018, 842, 812, 761 cm-1; UV-vis (hexane)
λmax (log ꢀ) 264 (5.02), 288 (4.33), 299 (4.23); GC/MS (EI) 288.
Anal. calcd for C20H16O2: C, 83.31; H, 5.59. Found: C, 83.27; H,
5.62.
4,4′′-Di(t-butyl)-o-terphenyl (13). See general Suzuki reaction
method. To o-diiodobenzene (4.95 g, 15.0 mmol) in 450 mL of
DME and aqueous base was added 4-t-butylphenylboronic acid
(8.00 g, 44.9 mmol). The solution was degassed, and Pd(PPh3)4
(2.13 g, 1.85 mmol) was added. The reaction was stirred at 80 °C
for 18 h. The reaction mixture was filtered and extracted with
petroleum ether, and the organics were washed with H2O several
times. After solvent removal, the residue was recrystallized from
MeCN to give 13 as colorless prisms (3.72 g, 72%): mp 76-79
1
°C; H NMR 500 MHz (CDCl3) δ 1.25 (s, 9H, CMe3), 7.03 (m,
2H), 7.17 (m, 2H), 7.33 (m, 1H), 7.38 (m, 1H); 13C APT NMR
125 MHz (CDCl3) δ 31.3 (CH3), 34.4 (C(CH3)3), 124.6 (CH), 127.2
(CH), 129.5 (CH), 130.5 (CH), 138.6 (C), 140.5 (C), 149.2 (C);
IR (NaCl plates) 3057, 3026, 2903, 2867, 2711, 2360, 1907, 1791,
1665, 1612, 1598, 1512, 1478, 1462, 1442, 1398, 1363, 1269, 1241,
1217, 1202, 1161, 1113, 1105, 1059, 1025, 1006, 944, 922, 875,
835, 762, 743 cm-1. Anal. calcd for C26H30: C, 91.17; H, 8.83.
Found: C, 91.26; H, 8.99.
3,3′′,5,5′′-Tetramethoxy-o-terphenyl (18). See general Suzuki
reaction method. To o-diiodobenzene (7.98 g, 24.2 mmol) was
added 3,5-dimethoxyphenylboronic acid (11.01 g, 60.5 mmol) in
500 mL of diglyme/base. The solution was degassed before the
addition of Pd(PPh3)4 (1.40 g, 1.20 mmol). The reaction was heated
to 80 °C for 18 h and then extracted with toluene, washed with
water to remove diglyme, and evaporated. The residue was
chromatographed (SiO2, toluene/CH2Cl2 4:1). The product was
recrystallized from ethanol to give 18 as a white solid (7.70 g, 91%
2,11-Di(t-butyl)triphenylene (14) and 7,7′,10,10′-Tetra(t-bu-
tyl)-[2,2′]-bitriphenylenyl (15). See general oxidation procedure.
To a solution of 13 (0.500 g, 1.46 mmol) in CH2Cl2 (40 mL) was
added dropwise a solution of PIFA (0.942 g, 2.19 mmol) and BF3‚
Et2O (0.311 g, 2.19 mmol) in CH2Cl2 (10 mL) at -78 °C under
nitrogen. The reaction mixture was stirred for 3.5 h and allowed to
warm to -40 °C over 1 h. The reaction was quenched with MeOH
(5 g). Chromatography (SiO2, petroleum ether/benzene 9:1) gave
two bands.
1
yield): mp 100-101 °C; H NMR 500 MHz, (C6D6) δ 3.23 (s,
6H, OMe), 6.46 (t, J ) 2.5 Hz, 1H), 6.56 (d, J ) 2.5 Hz, 2H),
7.20 (m, 1H), 7.46 (m, 1H); 13C APT NMR 125 MHz (CDCl3) δ
55.3 (OCH3), 99.2 (CH), 107.9 (CH), 127.6 (CH), 130.2 (CH),
140.5 (C), 143.5 (C), 160.2 (C); IR (NaCl plates) 3000, 2938, 2836,
1591, 1458, 1416, 1349, 1335, 1304, 1269, 1249, 1204, 1154, 1063,
1028, 992, 928, 876, 838, 762 cm-1; UV-vis (hexane) λmax (log
ꢀ) 207 (5.17), 273 (4.64); GC/MS (EI) 350. Anal. Calcd for
C22H22O4: C, 75.41; H, 6.33. Found: C, 75.46; H, 6.58.
Band 1 gave 0.189 g of 14 accompanied by starting material.
Further purification by fractional crystallization from heptane
afforded 14 (0.116 g, 23%) as pure colorless prisms: mp 167-
1
169 °C; H NMR 500 MHz (CDCl3) δ 1.52 (s, 9H, CMe3), 7.61
(m, 1H), 7.72 (dd, J ) 8.5, 2.0 Hz, 1H), 8.58 (d, J ) 8.5 Hz, 1H),
8.61 (m, 1H), 8.67 (d, J ) 2.0 Hz, 1H); 13C NMR 125 MHz (CDCl3)
δ 31.5 (CH3), 35.0 (CMe3), 118.9, 123.1, 123.2, 125.0, 126.7, 127.6,
129.5, 129.6, 149.7; IR (NaCl plates) 2962, 2903, 2868, 2366, 1613,
1512, 1479, 1461, 1401, 136172, 1264, 1201, 1110, 1044, 879,
819, 766 cm-1; HRMS (EI) calcd for C26H28 340.2191, found
340.2188.
1,3,10,12-Tetramethoxytriphenylene (19). See general oxida-
tion procedure. A solution of 18 (250 mg, 0.713 mmol), MoCl5
(585 mg, 2.14 mmol), and TiCl4 (406 mg, 2.14 mmol) in CH2Cl2
(25 mL) was stirred for 45 min. Removal of solvent and chroma-
tography (SiO2, benzene) and crystallization from MeOH gave
colorless crystals of 19 (75 mg, 30%): mp 152-153 °C; 1H NMR
500 MHz (CDCl3) δ 3.98 (s, 3H, OMe), 4.01 (s, 3H, OMe), 6.72
(d, J ) 2.0 Hz, 1H), 7.56 (d, J ) 1.5 Hz, 1H), 7.58 (m, 1H), 8.44
(m, 1H); 13C NMR APT 125 MHz (CDCl3) δ 55.5 (OMe), 55.8
(OMe), 97.0 (CH), 98.4 (CH), 113.1 (C), 123.5 (CH), 127.2 (CH),
130.5 (C), 132.1 (C), 158.7 (C), 158.8 (C); IR (NaCl plates) 1602,
1542, 1466, 1413, 1361, 1279, 1205, 1159, 1117, 1072, 1027, 936,
824, 761 cm-1; HRMS (EI) calcd for C22H20O4 348.1362, found
348.1358.
3-Methoxy-o-terphenyl (20). See general Suzuki reaction
method. To a solution of 2-iodobiphenyl (3.25 g, 11.6 mmol) in
330 mL of diglyme/aqueous base was added 3-methoxyphenylbo-
ronic acid (1.93 g, 12.7 mmol). After degassing, Pd(PPh3)4 (0.686
g, 0.6 mmol) was added and the reaction was heated to 50 °C for
36 h. Additional Pd(PPh3)4 (0.679 g, 0.6 mmol) was added, and
Band 2 gave 0.140 g of 15 (28%) by recrystallization from
MeOH/CHCl as colorless needles: mp 366-371 °C (decomp.);
1H NMR 500 MHz (CDCl3) δ 1.47 (s, 18H, CMe3), 7.68 (m, 2H),
7.95 (dd, J ) 8.5, 1.5 Hz, 1H), 8.55 (d, J ) 8.5 Hz, 1H), 8.65 (m,
4H), 8.91 (d, J ) 1.5 Hz, 1H); 13C APT NMR 125 MHz (CDCl3)
δ 31.4, 31.5, 35.1, 119.0 (CH), 119.1 (CH), 121.8 (CH), 123.3 (CH),
123.8 (CH), 125.1 (CH), 125.2 (CH), 126.1 (CH), 127.5 (C), 127.7
(C), 128.3 (CH), 128.8 (C), 129.7 (C), 129.91 (C), 129.94 (C), 139.5
(C), 149.8 (C), 149.9 (C); IR (NaCl plates) 2360, 1614, 1509, 1479,
1393, 1362, 1264, 878, 809 cm-1; HRMS calcd for C52H54
678.4226, found 678.4236.
3,3′′-Dimethoxy-o-terphenyl (16). See general Suzuki reaction
method. 3-Methoxyphenyl boronic acid (3.04 g, 20 mmol) and
o-diiodobenzene (3.30 g, 10.0 mmol) were combined in 600 mL
2286 J. Org. Chem., Vol. 72, No. 7, 2007

Controlling the Scholl Reaction
the solution was heated to 80 °C for 2 days. Benzene was added,
and the mixture was washed with H2O to remove diglyme. Removal
of solvent and chromatography (SiO2, hexane/CH2Cl2 9:1) gave
pure 20 as a colorless oil (2.03 g, 67%): 1H NMR 500 MHz
(CDCl3) δ 3.61 (s, 3H, OMe), 6.68 (m, 1H), 6.77 (m, 2H), 7.13-
7.26 (m, 6H), 7.42-7.48 (m, 4H); 13C APT NMR 125 MHz
(CDCl3) δ 55.0 (OMe), 112.6 (CH), 115.2 (CH), 122.3 (CH), 126.4
(CH), 127.4 (CH), 127.5 (CH), 127.9 (CH), 128.8 (CH), 129.8 (CH),
130.4 (CH), 130.5 (CH), 140.4 (C), 140.6 (C), 141.6 (C), 142.8
(C), 159.0 (C); IR (NaCl plates) 3058, 2937, 2833, 1601, 1577,
1488, 1471, 1435, 1417, 1319, 1297, 1243, 1209, 1179, 1046, 1021,
1008, 995, 863, 777, 761, 751, 700; UV-vis (hexane) λmax (log ꢀ)
208 (5.05), 279 (4.74); GC/MS (EI) 260. Anal. calcd for C19H16O:
C, 87.66; H, 6.19. Found: C, 87.67; H, 6.57.
and 138.63 observed as a multiplet), 155.5 (C), 156.5 (C); IR (NaCl
plates) 3007, 2935, 2833, 1601, 1492, 1475, 1461, 1432, 1249,
1249, 1180, 1144, 1124, 1064, 1027, 808 cm-1; HRMS (EI) calcd
for C40H34O4 578.2457, found 578.2447.
4,4′′-Dimethoxy-o-terphenyl (24).33 See general Suzuki reaction
method. To o-diiodobenzene (237 mg, 0.70 mmol) in 60 mL of
diglyme/aqueous base was added 4-methoxyphenylboronic acid
(213 mg, 1.4 mmol). The solution was degassed, and Pd(PPh3)4
(99 mg, 0.085 mmol) was added. The reaction was stirred and
heated to 80 °C for 1.25 h. Hexane extraction and chromatography
(SiO2, hexane/CH2Cl2 1:1), gave 24 as a white solid (0.160 g,
1
78%): mp 107-108 °C; H NMR 500 MHz (CDCl3) δ 3.77 (s,
3H, OMe), 6.75 (m, 2H), 7.04 (m, 2H), 7.35 (m, 2H); 13C NMR
75 MHz (CDCl3) δ 55.5, 113.8, 127.3, 130.8, 131.2, 134.6, 140.5,
158.7; GC/MS (EI) 290.
2-Methoxy-1-(5-methoxy-o-terphenyl-2-yl)triphenylene (21).
See general oxidation procedure. To a solution of 20 (600 mg, 2.31
mmol) in CH2Cl2 (50 mL) was added dropwise a solution of PIFA
(1.49 g, 3.46 mmol) and BF3‚Et2O (0.492 g, 3.46 mmol) in CH2-
Cl2 (10 mL) at -78 °C. The reaction mixture was stirred for 3 h at
-78 °C and allowed to warm to -40 °C over 1.5 h. Chromatog-
raphy (petroleum ether/benzene 8.5:1.5), crystallization (CH2Cl2-
MeOH), and recrystallization (o-xylene) afforded colorless crystals
of 21 (175 mg, 29%): mp 271-273 °C; 1H NMR 500 MHz (1,2-
dichlorobenzene-d4, 60 °C) δ 3.34 (s, 3H, OMe), 3.47 (s, 3H, OMe),
6.63 (m, 1H), 6.74 (s, 1H), 6.84 (m, 2H), 6.90-7.02 (m, 4H), 7.09-
7.21 (m, 6H), 7.34 (t, J ) 7.5 Hz, 1H), 7.46 (m, 2H), 7.79 (d, J )
9.0 Hz, 1H), 8.37 (m, 4H); 13C NMR APT/DEPT 125 MHz (1,2-
dichlorobenzene-d4, 60 °C) δ 54.89 (OMe), 54.94 (OMe), 111.4
(CH), 114.6 (CH), 118.1 (CH), 122.9 (CH), 123.1 (CH), 123.3 (CH),
123.6 (CH), 125.1(C), 125.4 (CH), 126.0 (CH), 126.2 (CH), 126.31
(C), 126.33 (CH), 126.5 (CH), 126.9 (CH), 127.3 (CH), 127.5 (CH),
127.8 (CH), 129.2 (CH), 129.5 (C), 129.95 (CH), 130.00 (CH),
130.1 (CH), 130.4 (CH), 130.6 (C), 130.9 (C), 131.4 (C), 131.6
(C), 131.8 (C), 133.7 (CH), 139.6 (C), 140.4 (C), 141.5 (C), 141.8
(C), 156.4 (C), 158.7 (C); IR (NaCl plates) 2993, 2936, 2833, 1604,
1589, 1555, 1494, 1461, 1449, 1427, 1406, 1383, 1341, 1300, 1266,
1250, 1206, 1174, 1127, 1087, 1044, 1012, 893, 862, 816, 804,
779, 771, 753, 744, 722, 701 cm-1; HRMS (EI) calcd for C38H28O2
516.2089, found 516.2084.
2,2′′-Dibromo-o-terphenyl (25).34 o-Diiodobenzene (1.75 g, 5.3
mmol), 2-bromophenylboronic acid (10.36 g, 52 mmol), PPh3 (3.42
g, 13 mmol), and Pd(PPh3)4 (485 mg, 0.53 mmol) were combined
with 300 mL of nitrobenzene and 320 mL of 2.5 M NaOH. The
yellow/green solution was heated to 60 °C for 24 h. The mixture
was extracted with H2O, hexane, and brine. The organic layer was
cooled to -20 °C to crystallize out much of the nitrobenzene.
Evaporation of the solid gave a yellow oil, which was washed
through a silica plug using hexanes. Evaporation of the solvent gave
a yellow oil. Residual nitrobenzene was removed by bulb-to-bulb
vacuum distillation at 60 °C with a collection bulb cooled by N2(l)
in liquid nitrogen. Hexane was added to the residue, and the solution
was filtered through silica gel using hexane. Solvent was removed,
giving 25 (1.8 g, 90%) as an oil. The product was contaminated
by <1% of 2-bromo-o-terphenyl. Analytically pure product was
isolated by preparative HPLC (C18, water/MeOH 6:4), yielding 25
(1.19 g, 60% yield) as an opaque oil: 1H NMR 300 MHz (DMSO-
d6) δ 7.53 (m, 2H), 7.46 (dd, J ) 3.0, 3.3 Hz, 2H), 7.33 (m, 1H),
7.28 (dd, J ) 4.5, 6.0 Hz, 1H), 7.11 (m, 6H); EI-MS m/z (rel.
abundance) 388 (M+), 308 (M+ - 1Br), 228 (M+ - 2Br).
3,3′′-Dibromo-o-terphenyl (26).35 A solution of Br2 (3.91 g,
24.4 mmol) in CCl4 (14 mL) was added to 30 (0.852 g, 2.27 mmol)
in CCl4 at 0 °C. The reaction was stirred for 35 min and quenched
by the addition of 14 mL of saturated Na2SO3. The aqueous layer
was extracted with CH2Cl2. The solvent was removed, and the
resulting oily residue was recrystallized from ethanol to give 26 as
a white solid (0.762 g, 86% yield): mp 90-91 °C (lit.35 mp
90.9 °C); 1H NMR 500 MHz (CDCl3) δ 6.95 (m, 1H), 7.05 (t, J )
7.5 Hz, 1H), 7.32-7.36 (m, 2H), 7.39 (m, 1H), 7.42 (m, 1H); 13C
NMR 125 MHz (CDCl3) δ 122.1, 128.1, 128.7, 129.4, 129.8, 130.5,
132.6, 139.0, 143.1; GC/MS (EI) 388, 228 (M+ - 2Br).
2,2′′-Dimethoxy-o-terphenyl (22). A mixture of o-diiodobenzene
(1.14 g, 3.47 mmol) and 2-methoxyphenyl boronic acid (1.05 g,
6.94 mmol) in 600 mL of DME/aqeous base was degassed. Pd-
(PPh3)4 (400 mg, 0.35 mmol) was added, and the reaction was
stirred at 85 °C for 2 h. Extraction (hexane/water), chromatography
(SiO2, hexane/CH2Cl2 2:1), and crystallization (EtOH) gave 22 (621
1
mg, 62%) as a white solid: mp 109-111 °C; H NMR 500 MHz
(CDCl3) δ 3.51 (s, 3H, OMe), 6.74 (d, J ) 8.0 Hz, 1H), 6.86 (t,
J ) 7.5 Hz, 1H), 7.11 (d, J ) 6.5 Hz, 1H), 7.18 (dt, J ) 8.0, 2.0
Hz, 1H), 7.44 (s, 2H); 13C NMR (125 MHz, CDCl3, 25 °C) δ 54.9,
110.1, 119.7, 127.0, 128.0, 130.5, 130.9, 131.4, 138.3, 156.2; IR
(NaCl plates) 3059, 3023, 2935, 2833, 1600, 1581, 1495, 1465,
1432, 1247, 1237, 1181, 1122, 1052, 1030, 1009, 932, 798, 740
cm-1; GC/MS (EI) 290; HRMS (EI) for C20H18O2 calcd 290.1307,
found 290.1303. Anal. calcd for C20H18O2: C, 82.73; H, 6.25.
Found: C, 82.73; H, 6.25.
2,7-Dibromotriphenylene (27). See general oxidation procedure.
A solution of 26 (150 mg, 0.387 mmol) and MoCl5 (212 mg, 0.776
mmol) in CH2Cl2 (15 mL) was stirred for 12 h. The crude product
was chromatographed (SiO2, petroleum ether) to afford 0.090 g
(30% mass recover). Fractional crystallization from MeCN gave
1
27 (14 mg, 9%) as colorless crystals: mp 220-223 °C; H NMR
500 MHz (CDCl3) δ 7.68 (m, 1H), 7.71 (dd, J ) 8.5, 2.0 Hz, 1H),
8.37 (d, J ) 9.5 Hz, 1H), 8.50 (m, 1H), 8.70 (d, J ) 2.0 Hz, 1H);
13C NMR 125 MHz (CDCl3) δ 122.1, 123.4, 124.9, 126.3, 127.9,
128.1, 128.9, 130.4, 131.4; IR (NaCl plates) 2918, 1594, 1571,
1486, 1435, 1413, 1087, 998, 858, 799, 757 cm-1; HRMS (EI)
calcd for C18H10Br2 385.9129, found 385.9126.
2,2′′′′′′,4′′′,4′′′′-Tetramethoxy-[1,1′;2′,1′′;3′′,1′′′;2′′′,1′′′′;2′′′,1′′′′′]-
sexiphenyl (23). See general oxidation procedure. To a solution
of 22 (500 mg, 1.72 mmol) in CH2Cl2 (125 mL) was added MoCl5
(475 mg, 1.74 mmol), and the reaction mixture was stirred for 40
min at 0 °C. Workup and chromatography (petroleum ether/CH2-
Cl2 1:1) gave recovered 22 (69 mg, 14%) and 23 (29 mg, 26%) as
2,2′′-Dinitro-o-terphenyl (28). o-Diiodobezene (500 mg, 1.5
mmol), 2-nitrophenyl boronic acid (501 mg, 3.0 mmol), Ba(OH)2‚
8H2O (950 mg, 3.0 mmol), and 60 mL of DMF-H2O (4:1) were
combined. After degassing, PdCl2dppf (100 mg, 0.1 mmol) was
1
colorless crystals (hexane): mp 204-206 °C; H NMR 500 MHz
(CDCl3) δ 3.39 (br s, 3H, OMe), 3.49 (br s, 3H, OMe), 6.68 (m,
2H), 6.80 (m, 1H), 7.12 (br m, 4H), 7.41 (m, 4H); 13C APT NMR
125 MHz (CDCl3, 60 °C) δ 55.0 (CH3), 55.2 (CH3), 110.6 (CH),
110.8 (CH), 120.0 (CH), 125.86 (CH), 126.90 (CH), 127.0 (CH),
128.10 (CH), 130.2 (CH), 130.57 (CH), 130.59 (CH) (at 25 °C
signals 130.57 and 130.59 observed as a singlet), 131.3 (C), 131.4,
131.6, 132.7 (C), 138.5 (C), 138.6 (C) (at 25 °C signals 138.47
(33) Van der Vlugt, J. I.; Van Duren, R.; Batema, G. D.; den Heeten,
R.; Meetsma, A.; Fraanje, J.; Goubitz, K.; Kamer, P. C. J.; van Leeuwen,
P. W. N. M.; Vogt, D. Organometallics 2005, 24, 5377-5382.
(34) Wittig, G.; Hahn, E.; Tochtermann, W. Chem. Ber. 1962, 95, 431-
442.
(35) Fujioka, Y. Bull. Chem. Soc. Jpn. 1984, 57, 3494-506.
J. Org. Chem, Vol. 72, No. 7, 2007 2287

King et al.
added and the solution was stirred at 60 °C for 8 h. Filtration,
thorough extraction (EtOAc/H2O), chromatography (SiO2, hexane/
EtOAc 85:15), and evaporation gave yellow crystals. Recrystalli-
zation from EtOAc gave 28 (100 mg, 26% yield): 1H NMR 500
MHz ((CD3)2CO) δ 7.20 (m, 3H), 7.35 (m, 7H), 7.72 (m, 1H),
7.93 (m, 1H); 13C NMR 125 MHz ((CD3)2CO) δ 123.3, 124.2,
128.6, 129.0, 129.3, 129.7, 130.9, 133.0, 133.4; IR (NaCl plates)
2360, 2342, 1596, 1571, 1521, 1433, 1348, 1312, 1104, 1007, 855,
786, 769, 747, 706, 669 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 231
(5.40); GC/MS (EI) 320. Anal. calcd for C18H12N2O4: C, 67.50;
H, 3.78. Found: C, 67.66; H, 3.79.
1H), 7.22 (m, 1H), 7.25-7.29 (m, 2H), 7.31 (m, 1H), 7.43 (m,
1H); 13C NMR 125 MHz (C6D6) δ -1.2, 127.8, 127.9, 130.5, 130.8,
131.6, 136.0, 139.7, 141.4, 141.6; IR (NaCl plates) 3021, 2955,
1463, 1384, 1261, 1248, 1121, 1023, 857, 837, 796, 750 cm-1
;
GC/MS (EI) 375; UV-vis (hexane) λmax (log ꢀ) 216 nm (4.71).
Anal. calcd for C24H30Si2: C, 76.94; H, 8.07. Found: C, 76.87; H,
8.08.
Acknowledgment. This work was supported by the National
Science Foundation (CHE-0449740, diffractometer CHE-
0226402, NMR spectrometers CHE-0521191, mass spectrometer
CHE-0443647). Acknowledgment is made to the Donors of the
American Chemical Society Petroleum Research Fund for partial
support of this research. An award from the Research Corpora-
tion also supported this research.
3,3′′-Dinitro-o-terphenyl (29).35 Prepared similarly as above
using 3-nitrophenyl boronic acid (501 mg, 3.0 mmol) and heating
to 80 °C for 8 h. After chromatography, crystallization gave 29 as
yellow crystals (195 mg, 40% yield): 1H NMR 500 MHz ((CD3)2-
CO) δ 7.56 (m, 2H), 7.62 (m, 6H), 8.06 (m, 2H), 8.13 (m, 2H);
13C NMR 125 MHz ((CD3)2CO) δ 122.0, 124.6, 129.2, 129.8, 130.9,
136.5, 138.6, 142.7, 148.4; UV-vis (CH2Cl2) λmax (log ꢀ) 232
(5.26); GC/MS (EI) 320.
Note added in proof. After revision of this manuscript, a
lower energy (∆G, by 5 kcal/mol) rotamer of the radical cation
of 3,3′′-dimethoxy-o-terphenyl (39) was located. This does not
affect conclusions about the preference for the arenium ion
mechanism.
3,3′′-Bis(trimethylsilyl)-o-terphenyl (30). See general Suzuki
reaction method. To o-diiodobenzene (1.70 g, 5.2 mmol) in 100
mL of diglyme/base were added 3-trimethylsilylphenylboronic acid
(3.00 g, 15.5 mmol) and Pd(PPh3)4 (586 mg, 0.5 mmol). After 16
h at 60 °C, additional Pd(PPh3)4 (0.290 g, 0.25 mmol) was added.
After 1 day at 80 °C, the solution was extracted with toluene and
the organics were washed with water (8 × 80 mL). Removal of
solvent, chromatography (SiO2/hexane), and recrystallization from
MeOH gave 30 as a colorless solid (0.781 g, 40%): mp 83-84
Supporting Information Available: Crystallographic informa-
tion files for 13-15, 17-19, 21, 23, 28, and 29, 1H and 13C spectra
of all synthesized compounds, coordinates of calculated structures
16, 17, and 31-44, and computational methods. This material is
available free of charge via the Internet at http://pubs.acs.org.
1
°C; H NMR 500 MHz (C6D6) δ 0.09 (s, 9H, SiMe3), 7.13 (m,
JO061515X
2288 J. Org. Chem., Vol. 72, No. 7, 2007